Updated: August 9, 2007
Update on New Adverse Effects
Harvey Runs into a Road-block
Since our hypothetical patient Harvey has developed a modest following of his own, our readers will be interested in some new developments. Harvey’s experience coincides with recently published reports on new adverse effects of Rituxan therapy. While the post-marketing surveillance of Rituxan has so far identified only a small percentage of patients having these serious adverse effects, the danger is high and very real for these patients and therefore worth discussing. Find the details in our next installment of the Harvey Saga, Harvey Runs into a Road-block. (2/14/06)
Rituxan Warning - Rituxan in the News
The Risk of Hepatitis B Virus Reactivation During Rituxan Therapy; New Therapy Combining Rituxan with Fenretinide
The FDA, Genentech and Biogen-Idec Issue Warning
Topics Alert Number 49 identifies another warning issued by the drug industry. This latest one to hit the fan is the warning regarding the risk of hepatitis B virus reactivation during Rituxan therapy. This is not good news, but it is not the end of the world, either – just one more thing to remember and track.
On a positive note, our follow-up article, Rituxan in the News, examines a promising new combination therapy with Rituxan and a new agent for CLL, Fenretinide. This drug is an analog of Vitamin A, with a long track record of low toxicity. (10/14/04)
Rituxan plus Neupogen
Improving Efficacy and Reducing Neutropenia
Neupogen as Booster to Rituxan Monotherapy
In this article, Neupogen as Booster to Rituxan Monotherapy, we discuss one method of getting maximum mileage from Rituxan monotherapy. First we examine the impressive results of a major Phase 3 study from Amgen on the use of G-CSF (Neupogen) in moderately myelosuppressive (breast) cancer therapy, in which the authors conclude their logic would hold for any cancer therapy with the risk of neutropenia. We also cover a wide range of abstracts that point to the important role played by neutrophils in the depth and duration of remissions produced by Rituxan in CLL and in the avoidance of resistance to Rituxan therapy. We also discuss the risks involved and conclude with a plea for the rapid publication of critical results from clinical trials. (7/6/04)
Approaches to Turbocharge Response
Drug Modifications and Biological Response Modifiers
Tweaking the structure of Rituxan, inducing a density of expression of the CD20 antigen and reinforcing the action of the patient's native immune system are all approaches to turbocharge the relatively mild responses obtained in CLL by the use of single agent Rituxan. Our review, Rituxan Enhancements, explores and analyzes some of these approaches. (6/9/03)
Single Agent Rituxan
Kinder and Gentler than Chemo?
Rituxan As Frontline and Maintenance Therapy
With its reputedly low toxicity profile and narrow targeting of B-cells, Rituxan is an attractive candidate for use as a frontline monotherapy in CLL. In our article, Single Agent Rituxan, we review some of the early work in the use of Rituxan monotherapy in CLL (and its sister disease, NHL) and discuss some key questions such as response, toxicity, remission durability, side effects, repeatability, resistance to Rituxan, timing, limitations and suitability to patients. (5/2/03)
The Search for Efficacy
Cytokine Combinations with Rituxan Have Impact
High target specificity makes Rituxan a valuable drug in the treatment arsenal for CLL. However, it produces variable results when used as monotherapy. To get deeper and more durable responses a variety of strategies are being examined, among them the use of immune modulators which augment the immune system's response in various ways. We examine the early results from these approaches in Immunomodulators & Rituxan. (5/12/03)
Results from Phase II Clinical Trials
Rituxan Combos with Purine Analogs, Alkylating Agents and Steroids
In Phase II results presented in the 2001 and 2002 ASH annual meetings, there was considerable encouragement for Rituxan-containing chemoimmunotherapy regimens. Here we review the reports on a few important protocols that represent major improvements in response rates and quality of remissions when compared to straight chemotherapy. While there are many questions still to be answered, there is no doubt that treatment approaches involving Rituxan Combos will be further developed in the years to come. (12/15/02)
Date: July 13, 2003
by Chaya Venkat
This is the title of an article in the New England Journal of Medicine, June 26, 2003. Below is a short "extract" provided kindly by the editors. Notice the patient group had CLL patients as well as NHL patients.
June 26, 2003 Number 26
To the Editor: Rituximab is effective in B-cell lymphomas either as a single agent or combined with chemotherapy. Its toxic effects are generally mild and transient.1,2 We report eight cases of acute and severe neutropenia that occurred 8 to 23 weeks after the administration of Rituximab for non-Hodgkin's lymphoma or chronic lymphocytic leukemia. All patients had a normal polymorphonuclear-cell count before rituximab treatment (Table 1). None of the known causes of neutropenia were found. Previous treatment with rituximab two to four months before the development of neutropenia was a common factor in these eight patients, . . .
There has been a lot of discussion recently on potential risks of neutropenia, as well as its causes. Contrary to our understanding up to this point, there are some indications that Rituxan-only therapy may be implicated in delayed onset of neutropenia in some patients. The jury is very much out on this one, please do not look for easy or unequivocal answers. If this topic is of interest to you, do read prior articles in this thread to get the full picture, as much as there is right now. May I also repeat that individual responses do not prove or disprove the hypothesis, that is the weakness of all anecdotal information. What we need to judge this issue better is good, solid statistical information based on large numbers of patients.
I have reviewed the latest paper published in the New England Journal of Medicine, July 15, 2003.. While it too raises the flag for potential neutropenia after Rituxan therapy in a small sub-set of patients, the sample size is small (8 patients) and the circumstances complex, making the inferences iffy at best.
The study reports 8 cases of severe / acute neutropenia that raised its ugly head as many as 8 to 23 weeks after completion of Rituxan therapy. The patients all had normal neutrophil counts before therapy, and there was no other obvious reason for the onset of neutropenia. The authors comment that the neutropenia is not likely due to direct cell kill of neutrophils by Rituxan, since neutrophils do not exhibit the CD20 marker that is targeted by Rituxan. They suggest that the neutropenia is potentially due to generation of anti-neutrophil antibodies. Rituxan therapy is aimed at depletion of all the B-cells in patients, and the B-cell population is gradually re-established in 3-9 months after therapy. This total depletion of B-cells and their subsequent re-population is hardly a "normal, business as usual" situation. The authors hypothesize that these extraordinary conditions may favor formation of unanticipated but temporary screw-ups, such as antibodies directed against neutrophils and stem cells.
I find insufficient concrete evidence presented in this paper to back up this hypothesis. If it is supported by more definitive data, it is a worrisome finding. I do not like the idea of antibodies developed against neutrophils, and much less so against the all important stem cells, even if such developments are only "transient". There is nothing in the paper either to explain why the authors think the problem is only a "transient" one, seemed more something they tacked on to the sentence to make their comments less scary.
The paper was reviewed by scientists at IDEC (manufacturers of Rituxan). As expected, they suggest that the data is not "clean", and the inferences drawn are ambiguous at best. According to IDEC, "Our calculated post-marketing reporting rate (not incidence) of late-onset neutropenia is currently less than 0.02 percent, with more than 300,000 patients worldwide exposed to rituximab". Notice the careful caveat: the actual incidence of delayed onset of neutropenia may be higher than the 0.02% that have been reported to date.
Its not enough that we have do deal with impenetrable jungles of jargon, scientists are fast learning from lawyers how to use CYA phrases! Bottom-line, there is no smoking gun, yet. But this is one development worth watching, especially if Rituxan monotherapy is of interest to you. You can bet I will be watching.
I had serious problems with this paper, it sample size was too small, the case histories of the patients too complex, the data was less than substantial, and the conclusions drawn "iffy" at best. I hope this is enough to get across my point, in my opinion this paper offers little by way of clarity, we will have to wait for future work with larger sample base and better designed retrospective studies to get a fix on this issue.
Even if this paper and the hypothesis it presents are totally accurate and beyond reproach, it is illogical to apply a potential problem in a very small percentage of patients and then leap to the assumption this must be what is happening in the case of a single individual. Surely we have learnt by now, CLL is a variable and complex disease, with very different patterns exhibited in different patients. Throw in a couple of chemotherapy regimes like Chlorambucil and prednisone, and the permutations and combinations become too complex to come up with easy answers.
Neutropenia is a dangerous complication of CLL. There can be many different causes for it, often more than one cause contributes to it. Rather than looking at very low percentage and relatively unproven risk factors associated with Rituxan, I would think to look more closely at the record of myelosuppression associated with different chemotherapy agents, or even something more fundamental, a bone marrow that is having trouble making the necessary cell lines. Detailed testing and professional evaluation may be able to sort it out, we are not going to be able to do it as laypersons.
As for different protocols suggested for Rituxan therapy, I did review a variety of them. I think I reviewed Hainsworth, O'Brien and Byrd. During the early learning curve of Rituxan use in CLL, researchers tried to see if the response rate can be improved by increasing dose, or frequency of dose. I think most would agree now that over-kill may not be the most cost effective way of doing it. I voiced a similar thought, especially as it related to complement depletion. It is not my job to make recommendations for therapy choices for individuals, I merely present the information, and my best effort at analyzing it. Therapy choice is your responsibility, your call to make.
It is frustrating that there is not more concrete information on this whole subject of possible (not proven) delayed onset of neutropenia after Rituxan therapy. Frankly, the most credible information I have seen on this whole issue is the response I got back from Dr. Hainsworth when I requested his opinion.
Systemic Rituxan Therapy and Neutropenia: An Expert Opinion
Date: June 7, 2003
by Chaya Venkat
Rituxan therapy in one form or another has become a very important aspect of CLL therapy. Its major appeal for many patients is its reputation of excellent toxicity profile. From that perspective, my article yesterday discussing potential for delayed onset of neutropenia caused by Rituxan therapy may be disquieting.
I decided to see if I can get an expert to weigh in on this subject, give us a sense of how "real" this potential risk may be. My letter to Dr. Hainsworth is attached below, as well as his very prompt response back. It is good to hear that based on his experience, and he has done more to establish Rituxan as a viable monotherapy option for CLL than any one else, there is no significant risk of long term neutropenia, even with repeat administration of Rituxan. That is indeed good news.
It is good to know that there are expert research oncologists out there who nevertheless take time out of their busy schedules to communicate with patient groups. As our membership grows, and we maintain our reputation as a serious CLL patient education and advocacy group, I hope we can build a network of mentors and supporters in the research community. This is part of "winning friends and influencing people", this is how we get our voices heard. Dr. Hainsworth's email address is attached to his response. Please, no "spam" email to this generous man, do not waste his time. But if you are so inclined, do write this influential researcher a short & sweet thank you note, as a member of CLL Topics.
From: Chaya Venkat
Sent: Friday, June 06, 2003 4:23 PM
To: John Hainsworth
Subject: Systemic Rituxan therapy and delayed onset of high grade neutropenia
Dear Dr. Hainsworth:
As you may well imagine, the attached abstract in the latest British Journal of Haematology linking Rituxan therapy with delayed onset of grade - 4 neutropenia in some patients is of significant interest to our membership. I am writing to you on behalf of our patient education / support group, CLL Topics. You probably have more experience than any one else with long term use of Rituxan in B-cell malignancies such as NHL and CLL. Have you seen indications of high grade and relatively long-lived neutropenia in repeated use of Rituxan in your work? Do you consider this a significant risk to the CLL population at large, or one that is limited to specific sub-sets of patients? Your comments would be greatly appreciated, and with your permission I would like to share them with our general membership on our group discussion site. Our group is now 450 members strong, and keeps growing!
On a personal note, my husband P.C continues to do very well, all his CBC numbers are solidly in the normal ranges, and he is feeling great! Both of us are extremely pleased with the quality of remission he has obtained with Rituxan frontline therapy. Many thanks for your expert advice!
Founder, CLL Topics
From: Dr. John Hainsworth
Sent: Saturday, June 07, 2003 9:08 AM
To: 'Chaya Venkat'
Subject: RE: Systemic Rituxan therapy and delayed onset of high grade neutropenia
We have not seen any episodes of severe neutropenia in our patients receiving maintenance rituximab. We have now treated a total of 106 patients with either follicular NHL or CLL on first-line/maintenance studies, so these patients had not been previously exposed to any chemotherapy. We have also treated 55 previously treated patients with maintenance rituximab, as part of a separate study, and did not see any neutropenia episodes in this group, either. Most of the patients in whom these rare occurrences have been seen have had extensive previous chemotherapy (often high dose therapy with peripheral stem cell support), or are receiving chemotherapy concurrently with rituximab. The mechanism of this toxicity is not yet understood. At present, there does not seem to be any connection between the amount or duration of rituximab administered and risk for this side effect.
John Hainsworth, MD
Rituxan Therapy: Not Risk Free
Date: June 6, 2003
by Chaya Venkat
This news is hot of the presses, and all I have seen thus far is the abstract attached below, the full article would certainly be worth reading. But if this information is confirmed in other larger retrospective studies, it just goes to show there is no such thing as a free lunch: Rituxan therapy and deep depletion of B-cells may carry the risk of delayed neutropenia (reduced counts of neutrophils).
Nothing about CLL is either simple or without risk. Remember what we have been learning all along, Rituxan targets cells that carry the CD20 marker. Most mature B-cells carry this marker, not just the CLL B-cells. In cases where the patient has a deep response to Rituxan monotherapy, B-cell populations can be taken down to just about zero. (You may wish to check out P.C's Patient Profile, he has shown such a deep depletion of all B-cells; the remaining small amount of lymphocytes are probably T-cells).
That are the implications of near-total depletion of all B-cells as a result of Rituxan therapy? Clearly, our immune systems are designed to have B-cells playing an important role. Long term and deep reduction in B-cells will leave a hole in the immune system. for example, B-cells are responsible for one important aspect, namely the "memory" of the immune system, which remembers prior encounters with antigens, and therefore mounts a quick and efficient response when the same antigen presents itself again. This is the basis of protection obtained by vaccinations, and this memory function may be compromised by long lasting destruction of all B-cells. Please see a prior articles by me on this subject in our archives.
But over and beyond just the specific immune function jobs done by the B-cells, the different aspects of the human immune system are so closely inter-twined, with complex network of cytokines loops and feed-back mechanisms that control many aspects of the functioning of all the other cell lines, I suppose it is naive to think that one can kill off all B-cells in the body for a period of time and not have this impact on other cell lines. In this case, the hit seems to be on a very important group, the neutrophils. Neutropenia is a serious issue, left untreated it could lead to frequent and severe infections that can land you in the hospital. Fortunately, it is relatively easily handled these days with G-CSF drugs (Granulocyte Colony Stimulating Factors) such as Neupogen and Neulasta.
But let us not get too carried away by this report. Therapy decisions in CLL are all a question of smart balancing act between risks and rewards. Rituxan is not quite the 100% "smart" bomb, killing just the CLL infected B-cells; it kills the good B-cells as well. But it sure beats straight chemotherapy, or even another monoclonal antibody like Campath, when it comes to being selective. As we have discussed before, Campath kills not just B-cells, but all T-cells and several other cell lines as well. The disruption of the immune system as a result of Campath therapy is far greater, and in fact it is one of the serious drawbacks of this drug.
For now, Rituxan is still the most selective monoclonal antibody drug there is for B-cell cancers like NHL and CLL. Till we get even more selective drugs, if the choice is between progressive CLL with all the dangers associated with late stage cancer, versus deep depletion of B-cells and the hole this leaves in your immune network, I think the second option is still the preferred one, by far. Refusing to make therapy choices because of the possible side-effects of the drugs when your disease needs to be treated is a clear case of being penny wise but pound foolish. We have all seen case histories where patients got into trouble for leaving therapy till too late, or doing too little when their particular brand of CLL required more emphatic therapy. Be smart, people. If you need therapy now, get it soon, and live to fight another day.
Hoping for miraculous breakthroughs in unrealistic time frames is like running up your credit card debt, because you are sure you are going to win the lottery next month. I took some heat early last year, when I wrote (see Gene Therapy) what I thought was realistic expectation of when technology would be a viable therapy option open to CLL patients.
In that article I suggested "Gene Therapy" is not likely to be available to the general CLL public any time before 2008. We have not yet seen the full details of the Phase -2 trial recently completed at UCSD, but based on what I have seen thus far, I would be willing to bet my prior estimate of 2008 is, if anything, a little too optimistic.
Br J Haematol. 2003 Jun;121(6):913-918.
Delayed-onset neutropenia associated with rituximab therapy.
Chaiwatanatorn K, Lee N, Grigg A, Filshie R, Firkin F.
Department of Haematology, and Department of Clinical Haematology, St Vincent's Hospital, Fitzroy, Department of Haematology, Royal Melbourne Hospital, Melbourne, and University of Melbourne, Department of Medicine, St Vincent's Hospital, Fitzroy, Vic., Australia.
The characteristics of severe neutropenia with a delayed onset following administration of rituximab have been evaluated in 53 consecutively treated patients. All but one patient received rituximab for the treatment of non-Hodgkin's lymphoma. Eight episodes of grade 4 neutropenia were detected between 1 and 5 months after rituximab, when administered alone on five occasions, and on three occasions in combination with chemotherapy, where neutrophil counts had recovered prior to the development of neutropenia. In three episodes, the patients presented with sepsis. Development of neutropenia did not correlate with either the presence of detectable disease or the administration of further treatment. Neutropenia was associated with selective depletion of neutrophil precursors in all but one episode, where it was associated with generalized bone marrow hypoplasia. All episodes developed after a period of either normal or mildly depressed neutrophil counts following treatment with rituximab, and persisted for between several days and several months, before undergoing spontaneous recovery in four instances, and after administration of filgrastim in the remainder. Episodes of neutropenia were associated with disordered immune status manifested by lymphopenia and hypogammaglobulinaemia, raising the possibility that either disturbance of the balance of lymphocyte subsets or an immune dyscrasia induced by rituximab resulted in the development of this type of neutropenia.
Resistance to Rituxan Therapy
Date: April 5, 2003
by Chaya Venkat
There has been a great deal of enthusiasm for Rituxan therapy among CLL patients, both as frontline therapy and as a maintenance regime. The big question then is this: do some patients become refractory to Rituxan, stop responding to it after multiple uses? After all, this type of resistance to chemotherapy drugs after several uses is pretty common, almost inevitable and unavoidable. Is there something about the mechanism by which monoclonals work that makes them exempt from developing this kind of resistance?
The jury is still out on exactly why there is resistance to a second or third round of Rituxan therapy in some patients, after responding to the first round, but there is ample evidence that some people do develop resistance. For example, whether it be in the NHL study reported in the first abstract attached below, or Dr. Hainsworth's work reported on earlier, of the patients who responded to the first round, the percentage responding to the second round of Rituxan was in the region of 50%. A lot of us would like to gloss over this little piece of information, so let me underline it for clarity: statistically speaking, if you responded to the first series of Rituxan infusions, and you went back for a second maintenance series, you have roughly even chances of responding the second time. Roughly half of you will not respond the second time around, even though you responded beautifully the first time around. Obviously, as individuals we can always hope to be the lucky ones that continue to respond each time we go back for additional therapy.
So, given that some of us do not respond the second time, what causes that resistance? There is quite a bit of discussion on this subject, one theory is that after the first series of Rituxan infusion, all or most of the CD20 positive cells are killed, and the remnants left over are CD20 negative. When the B-cell population grows back, there may be a preference for this CD20 negative B-cell population to become the dominant species. This does not happen in all patients, or even in the majority of patients. But Drs. Davis and Levy clearly think this does happen some of the time, that in some patients who have been through Rituxan therapy and subsequently relapse, the B-cell population the second time around may be CD20 negative. The PubMed Citation of their work is below, as also the URL link to the full paper (free of charge), so you can read the detailed analysis if you wish.
Immediately below the PubMed citation for Drs. Davis and Levy is the rebuttal from Genentech. Their response too is available free of charge, and I have included the URL for it. Simply put, they question the methods used for determining whether or not some percentage of patients become CD20 negative after an initial response to Rituxan therapy. Their argument is that traces of Rituxan last in the body for as long as six months after completion of first series of infusions, and this will confound and confuse the normal testing methods for CD20 levels. I have also come across several other reputable reports that suggest that it is only the rare patient that becomes CD20 negative after first successful therapy with Rituxan. The consensus seems to be leaning in that direction.
But the clinical evidence is not in question, a significant percentage of patients who responded the first time to Rituxan the first time do not respond, or respond not as well, the second or third time around. If it is not due to newly acquired CD20 negativity, what else can be causing this resistance to repeat therapy?
The answer may lie in the role played by complement inhibitory proteins such as CD55 and CD59. (See the third abstract below, by Dr. Golay et al). We have discussed this before, there are several mechanisms for cell kill achieved by Rituxan. One of the important mechanisms depends on complement activation. We know that when the B-cell carrying the CD20 markers gets tagged by Rituxan, the presence of this antigen-antibody pair causes complement proteins in the blood plasma to home in on the tagged cell, and the cell gets thoroughly coated with complement fragments. The cell is said to be "opsonized" by complement fragments. In normal circumstances, such an opsonized cell is quickly attacked, killed and devoured by any macrophage or neutrophil that happens to come by. This is the basis of the CDCC (Complement Dependent Cellular Cytotoxicity) that is one of the big mechanisms for cell kill with Rituxan.
You may wish to re-read the article dated January 23, 2003 on this subject to get a cartoon version of this complex process: Beta Glucan, Complement and Rituxan.
Now comes the fly in the ointment: unlike many of the NHL type cancers, the B-cells in CLL cells exhibit higher levels of complement inhibitory markers, such as CD55, CD59. You can see why Rituxan works so much better for follicular lymphoma than it does for CLL. Follicular lymphoma has much higher levels of CD20 markers per cell (that is good, for Rituxan to tag all these CD20 markers on each cell), and this type of cancer cells also has much lower levels of the pesky CD55 and CD59 markers, so once the cell is opsonized by complement, there is little resistance to its getting killed by the surrounding macrophages or neutrophils. The situation exactly backwards with CLL: lower CD20 levels for the Rituxan to target, and higher levels of the CD55 and CD59 markers that inhibit the proper functioning of complement.
One can suggest that during the first Rituxan therapy, the cells that do not have a lot of these complement inhibitory proteins will get killed preferentially. In other words, the ones left behind will be the ones that do have high expressions of CD55, CD59 and the like. If these cells are then the parents for all future generations of CLL cells as they grow back, it makes sense that the second time around in Rituxan therapy, we are facing a more hostile crowd of CLL cells, cells that can defend themselves against complement mediated cell kill. So perhaps in addition to the CD20 levels the researchers need to be looking to see if the CLL cells develop higher levels of CD55 CD59 inhibitory proteins after first treatment with Rituxan.
Once it becomes clear as to why the resistance develops, it might be possible to find ways around this escape route. If it is indeed reduced levels of CD20, we are making headway in finding drugs that will up-regulate the expression of this marker. Our beloved Fludarabine is thought to be one such drug, possibly even at low dosages. Another one that is being investigated for its role in up regulating CD20 is the GM-CSF (granulocyte If on the other hand the development of resistance to Rituxan therapy rests on up-regulation of complement mediated cell kill, there are several interesting approaches to short-circuit this inhibition of complement function, one of which has been discussed in the past, namely beta glucan. As you know, beta-glucan is obtained from yeast (and other grains such as oats). In the next few days I will be discussing another approach to getting around complement inhibition based on a snippet of bacterial DNA. This one is already in clinical trials sponsored by the National Cancer Institute, for NHL, in combination with Rituxan. Don't you wish just once CLL is not the me-too follower of NHL research?
I am sure the story will not be a simple yes or no situation, nothing about cancer is simple. For some people one mechanism of resistance to Rituxan therapy may be the primary cause, for others it may be an entirely different cause, or a mix of a variety of causes. With better testing for these tell-tale markers, and better understanding of what they imply it may soon be possible to custom design some of these immunotherapies to get maximum benefit for the individual patient.
All this said, how does one deal with the local oncologist who refuses to listen and refuses "new fangled ideas"? We have had several members report that their local guy will not consider Rituxan because it is "too toxic". Rubbish! Except for the extremely rare individual who has proven to be allergic to Rituxan, and this is an extremely rare occurrence, this monoclonal has a safety profile that stands tall. I do not know of a single standard chemotherapy drug that does better on that score. Any number of very solid studies have proven this. Frustrating, when we as the lay persons have to educate the oncologists that are supposed to take care of us. Hopefully this represents a very small percent of local oncs, and we are indeed talking about the exceptions, not the general rule.
Article from Clinical Cancer Research (Full-text)
Clin Cancer Res 1999 Mar;5(3):611-5
Therapy of B-cell lymphoma with anti-CD20 antibodies can result in the loss of CD20 antigen expression.
Davis TA, Czerwinski DK, Levy R.
National Cancer Institute, NIH, Rockville, MD.
Rituximab is a chimeric antibody with human gamma-1 and kappa constant regions and murine variable regions. It recognizes the CD20 antigen, a pan B-cell marker. Therapeutic trials in patients with B-cell non-Hodgkin's lymphoma (NHL) have shown significant efficacy with a primary response rate of 50%, and a secondary response rate of 44% after repeat treatments in prior responders. The selection for proliferating tumor cells that no longer express CD20 may compromise repeated treatment. We have identified a patient who developed a transformed NHL that lost CD20 protein expression after two courses of therapy with rituximab. In a pretreatment lymph node biopsy, 83% of B cells (as defined by CD19 and surface immunoglobulin) expressed surface CD20. A biopsy from the recurrent tumor after two courses of rituximab revealed a diffuse large cell NHL where 0% of B cells expressed CD20 with no evidence of bound rituximab. Cytoplasmic staining showed no CD20 protein. Sequencing of immunoglobulin heavy chain cDNA identified identical variable sequences in the initial and recurrent lymphomas, confirming the association between the two tumors. Literature and database review suggests that approximately 98% of diffuse large cell lymphomas express CD20, which suggests that these tumors rarely survive without CD20. This is the first identified case of loss of CD20 expression in a lymphoma that has relapsed after rituximab therapy, although several other cases have since been identified. Considering the significant number of patients treated with anti-CD20 antibodies, this may occur only rarely and is unlikely to preclude recurrent therapy with anti-CD20 antibodies in the majority of patients. However, because many patients have relapsed after anti-CD20 antibody therapy and have not been biopsied to identify clones with down-regulated CD20 antigen, we do not currently know the true frequency of this phenomenon. When possible, patients should undergo evaluation for CD20 expression before repeated courses of anti-CD20 therapy.
Corrrespondence in Clinical Cancer Research titled: re: T. Davis et al., Therapy of B-Cell Lymphoma with Anti-CD20 Antibodies Can Result in Loss of CD20 Antigen Expression. Clin. Cancer Res., 5: 611-615, 1999.
"Although it has been documented that 10% of intermediate-grade NHL patients have B-cell lymphomas that de novo are CD20 negative (3) , there is a paucity of information in the medical literature to specifically address loss of CD20 expression. We have recently completed a 60-patient clinical trial of Rituximab retreatment that showed all patients to be CD20 positive on relapse, including some patients who had received two courses of Rituximab (4) . These two case reports raise questions regarding the incidence and frequency of antigen loss as a result of the natural history of low-grade lymphoma or as a result of therapeutic interventions".
"The mechanism of action of Rituximab results in rapid and specific B-cell depletion (5) , with B-cell recovery beginning from 3-6 months posttreatment. Thus, peripheral blood and bone marrow samples will be CD20 negative by flow cytometric analysis during this period, indicating B-cell depletion rather than any change in CD20 status. We have detected measurable levels of free, circulating Rituximab for as long as 6 months after treatment (6) . The presence of this antibody in the circulation will block CD20 binding sites, again resulting in apparent CD20 negativity. Circulating B cells may be coated with Rituximab and blocked from detection by commonly used flow cytometric diagnostic reagents that only detect surface CD20. Immunoperoxidase staining with L26 antibody, which recognizes the intracellular domain, is necessary to confirm the CD20 antigen status in the presence of circulating Rituximab".
Blood 2001 Dec 1;98(12):3383-9
CD20 levels determine the in vitro susceptibility to rituximab and complement of B-cell chronic lymphocytic leukemia: further regulation by CD55 and CD59.
Golay J, Lazzari M, Facchinetti V, Bernasconi S, Borleri G, Barbui T, Rambaldi A, Introna M.
Laboratory of Molecular Immunohematology, Istituto Ricerche Farmacologiche Mario Negri, Milano, Italy.
Complement-dependent cytotoxicity is thought to be an important mechanism of action of the anti-CD20 monoclonal antibody rituximab. This study investigates the sensitivity of freshly isolated cells obtained from 33 patients with B-cell chronic lymphocytic leukemia (B-CLL), 5 patients with prolymphocytic leukemia (PLL), and 6 patients with mantle cell lymphoma (MCL) to be lysed by rituximab and complement in vitro. The results showed that in B-CLL and PLL, the levels of CD20, measured by standard immunofluorescence or using calibrated beads, correlated linearly with the lytic response (coefficient greater than or equal to 0.9; P <.0001). Furthermore, the correlation remained highly significant when the 6 patients with MCL were included in the analysis (coefficient 0.91; P <.0001), which suggests that CD20 levels primarily determine lysis regardless of diagnostic group. The role of the complement inhibitors CD46, CD55, and CD59 was also investigated. All B-CLL and PLL cells expressed these molecules, but at different levels. CD46 was relatively weak on all samples (mean fluorescence intensity less than 100), whereas CD55 and CD59 showed variability of expression (mean fluorescence intensity 20-1200 and 20-250, respectively). Although CD55 and CD59 levels did not permit prediction of complement susceptibility, the functional block of these inhibitors demonstrated that they play an important role in regulating complement-dependent cytotoxicity. Thus, lysis of poorly responding B-CLL samples was increased 5- to 6-fold after blocking both CD55 and CD59, whereas that of high responders was essentially complete in the presence of a single blocking antibody. These data demonstrate that CD20, CD55, and CD59 are important factors determining the in vitro response to rituximab and complement and indicate potential strategies to improve the clinical response to this biologic therapy.
The Semin Oncol 2002 Feb;29(1 Suppl 2):2-9
Rituximab: mechanism of action and resistance.
Maloney DG, Smith B, Rose A.
Clinical Research Division of the Fred Hutchinson Cancer Research Center, Seattle, WA.
Rituximab (Rituxan; Genentech, Inc, South San Francisco, CA, and IDEC Pharmaceuticals, San Diego, CA)-mediated killing of CD20-positive tumor cells is likely caused by a combination of immune-mediated effects including complement-mediated lysis and antibody-dependent cell-mediated cytotoxicity and direct effects induced by CD20 ligation. In vivo, the clearance of damaged or preapoptotic cells through specific receptors for phosphatidylserine translocated to the outer cell membrane may also be important. Direct effects, including growth inhibition and apoptosis, have been shown in vitro; however, their contribution to the clinical effect is not known. Currently, most data suggest that the predominant effector mechanism is antibody-dependent cell-mediated cytotoxicity, with a minor role of complement. With treatment, resistance to rituximab-mediated killing may emerge. Little is known regarding the molecular pathogenesis of this resistance. In rare cases, the CD20 antigen may be lost. Complement-resistance proteins may also increase, but it is not clear that this is the reason for loss of sensitivity. A better understanding of these mechanisms should allow combination therapy with agents capable of augmenting antibody-based killing. Copyright 2002 by W.B. Saunders Company.
Rituxan Therapy Reduces Humoral Immune Response
Date: February 23, 2003
by Chaya Venkat
There have been a lots of articles on this site on the benefits of Rituxan therapy. One of the major attractions of this type of immunotherapy, as opposed to more conventional chemotherapy is the reduced toxicity, and reduced immune suppression. But.. too bad, there is always a 'but' in these matters.... Rituxan therapy is not without a price tag.
As we have learned, Rituxan therapy works because the monoclonal antibody tags the CD20 marker present to some degree or the other on all B-cells. I repeat, all B-cells, which means good B-cells and CLL B-cells. The good news is that other cells of the immune system, such as T-cells, granulocytes macrophages etc do not exhibit this marker, and neither do the stem cells or precursor cells, which is why all these cell lines are spared. If you are lucky enough to get a deep response, a full CR, it means just about all of your B-cells are wiped out. Their numbers will recover over time, because the stem cells will continue to produce more B-cells as time goes on. Hopefully most if not all of the new B-cells produced are good B- cells, not the CLL type. But even after the B-cell population is back up to its normal counts, something is lost for ever, and that is the "memory B-cells" that are crucial in mounting an immediate and effective humoral response.
When you are a kid, and you got exposed to measles or whooping cough, or get vaccines against these childhood diseases, your body got to see what these pathogens look like. Some B-cells got to recognize the antigens presented by these pathogens, and they became "memory cells" that live for a long time. When they die, they make daughter memory cells to keep the knowledge alive. Next time your body is invaded by the same pathogen, the memory cells kick into action quickly, they become what are called "plasma cells" that are no more than factories for quickly churning out large quantities of the specific antibodies to fight that particular infection. This is why inoculations and vaccinations work. This is how we educate the body to recognize the specific pathogens, and the knowledge is then carried forward by generations of memory B-cells.
When Rituxan therapy wipes out B-cells, it wipes out many of the memory B-cells too; perhaps all memory cells of a particular family are wiped out, say all memory cells that remember what whopping cough looks like. You start with a new slate, more or less, and have much reduced protection from previous vaccinations etc. The new B-cells made by the bone marrow have no memory cells, and your body will have to start all over again, learning the old tricks it used to know before Rituxan therapy. This is not a huge price to pay, not when you compare the risks associated with cancer. But what this does mean is that if you have had Rituxan therapy, or any other chemotherapy for that matter, you might not want to expose yourself to childhood diseases on the assumption that you are protected against them because of long ago vaccinations in your childhood.
Turning the logic on its head, in some types of autoimmune disease, where the body starts attacking perfectly good cells because it thinks they are foreign invaders. Destroying all the memory cells that have this cock-eyed notion as their mission in life may have a significant impact on the autoimmune disease. We are just beginning to see the results of clinical trials of Rituxan used for controlling autoimmune diseases of various sorts, someday this may be a bigger market than CLL and NHL.
Blood 2002 Sep 15;100(6):2257-9
Rituximab treatment results in impaired secondary humoral immune responsiveness.
van der Kolk LE, Baars JW, Prins MH, van Oers MH.
Department of Hematology, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
In lymphoma patients, treatment with chimeric CD20 monoclonal antibodies (rituximab) results in a depletion of normal and malignant B cells, persisting for 6 to 9 months. This B-cell depletion leads neither to a decrease in immunoglobulin levels nor an increase in the number of infectious complications. However, the effect of rituximab treatment on the immune responsiveness is unknown. In 11 patients with relapsed, low-grade lymphoma, we investigated the effect of rituximab treatment on the humoral immune response to 2 primary antigens and 2 recall antigens. After rituximab treatment, the humoral immune response to the recall antigens was significantly decreased when compared with the response before treatment. Already before rituximab treatment, none of these patients was able to mount a response to the primary antigens. These findings are relevant regarding the feasibility of rituximab in maintenance treatment and may also offer a rationale for the treatment of antibody-mediated autoimmune diseases with rituximab.
Complement Dependent Response in Rituxan Therapy
Date: February 15, 2003
by Chaya Venkat
The jury is in: good complement dependent response is essential for good Rituxan response.
I have been trying to assemble the jig-saw pieces of this puzzle for a while. Well, no longer. The jury is in. To quote the abstract below, poor sensitivity to CDC (Complement Dependent Cytotoxicity) makes for poor response to Rituxan. And, based on CD20 expression and expression of complement inhibitory proteins such as CD55 and CD59, it is possible to predict CDC sensitivity, therefore Rituxan efficacy.
We have discussed in previous articles that Rituxan does not do any large percentage of the killing of the b-cells by itself. All it does (mostly) is to "finger" the B-cells, by virtue of locking on to the CD20 marker they exhibit. We also know that the actual killing is done by two functions of the immune system: ADCC, antibody dependent cellular cytotoxicity, is carried out by other cells of the immune system, such as T-cells, NK-cells etc. We have talked in previous articles of ways of boosting the T-cell and NK cell counts, to make this part more efficient.
The second part, CDC, or Complement Dependent Cytotoxicity, is the topic of interest in this article. A little bit of background: We know that once you remove all the red blood cells and white blood cells etc from whole blood, what is left behind is called "plasma". It is a clear, amber colored liquid, that is more than 90% water. It has in it about 6% proteins, some lipids and salts. Some of these proteins form the "Complement" of the immune system. Unlike whole blood, plasma transfusions do not require blood type matching, since there are no live cells in it.
What is Complement? Complement is a set of proteins in the plasma, that form a complex and inter-linked chain that work together in fighting infections. When an "antigen" on the surface of a bacteria is tagged by an antibody (in our case, the CD20 marker on B-cells is the "antigen", and it is tagged by the Rituxan acting as the "antibody"), this combination of antigen-antibody pair triggers a response from the Complement system in the blood plasma. There are more than 20 proteins involved in the complement system. They work together to start the process of destroying and taking apart the antigen-antibody complex, tearing it into pieces and attracting macrophages etc to the site that actually cart away and gobble up the debris. If this bit of biology 101 has you cross-eyed, just remember this sound bite: Complement in your blood is what kills B-cells, once they are tagged by Rituxan. The abstract below describes cell studies, animal studies, etc. But the interesting and telling part deals with a live CLL patient, who was administered Rituxan at the standard dose, once a week for four weeks. His blood was analyzed for Complement proteins before and after each infusion of Rituxan. Prior to the first administration, his Complement level was normal. During infusion, it was clearly seen that Rituxan homed in on the CD20 positive B-cells, and that Complement proteins in turn zeroed in on the **B-cell/Rituxan** pair, as they are supposed to, to begin the process of destroying the whole shebang. At the end of the infusion, much of the available supply of the Complement proteins in the blood had been used up, there was a **five fold decrease** in the concentration of these essential proteins by the end of the first infusion. The level recovered somewhat by the next week, in time for the second infusion, but not all the way. By the time the fourth infusion rolled around, the crucial Complement protein concentrations were down as much as ten-fold. Given time, the body produced more of these proteins. Three weeks after the last dose of Rituxan, the Complement levels were almost back up to normal.
What does this say about how Rituxan should be administered? Well, for starters, treating with mega doses of Rituxan, or standard doses but three or more times a week is not likely to get you much more by way of cell kill, you will specifically and literally be pissing away money. Without giving the body time to recover its complement levels depleted after initial therapy, you will not accomplish much cell kill. I am inclined to think the once a week, four week approach is better for this reason than either the mega doses or much more frequent infusions, or even more prolonged (8 weeks instead of 4 weeks) approaches. Also to think about, is it a good idea to wring out the last bit of complement proteins in your body, by overtaxing the available resources? Seems to me that if you do so, until these proteins levels are replenished by your body, you are vulnerable to opportunistic pathogens.
What are the implications for early stage versus late stage patients? There has been enough evidence now to show that if the tumor burden is high to begin with, Rituxan does not seem to be able to handle it as well as if the number of tumor cells was small to begin with, the remissions are poorer, and more of the cancer cells are left behind. But perhaps we have it backwards, it is not that the Rituxan cannot handle the larger number of tumor cells, but that the Complement proteins are depleted before the job is done, hence the large amount of residual cancer cells left un-killed?? Wow. This has really got me thinking.
Last but not least, can we give mother nature a hand here? Why can't we make sure there is sufficient concentration of Complement before each Rituxan infusion, heck why not make it a little bit better than normal? Plasma transfusions are no big deal, and maybe rather than the whole plasma, it might be possible to transfuse just the complement proteins. I understood both are readily available commercial products. This is not a toxic drug, nor a complex cytokine like Interleukin-2 with potential for unforeseen consequences and complex autocrine loop feedback effects. Unlike whole blood transfusions, there is no need to match blood types, or worry about iron overload type of issues down the road. This seems to be such a simple and yet elegant way of improving the efficacy of this very important drug, I am surprised it is not being done routinely right now. By the way, this is not my idea, the authors of the abstract below from ASH2002 spell it out clearly enough in their concluding remark:
"We suggest that if an anti-tumor monoclonal antibody such as Rituxan requires robust Complement activation for therapeutic efficacy, then insuring an adequate level of Complement activity in a patient, by supplementation with either fresh plasma or a purified Complement component such as C2, may provide an important approach for improving the therapeutic efficacy"
This is not exactly a subject most local oncologists want to discuss. Follow-up research from the scientists in this field will help convince practitioners that this could work.
Complement (C) Activation Is Required for Rituximab (RTX) Mediated Killing of CD20 Positive Cells, and a High Tumor Burden May Decrease Therapeutic Efficacy Due to C Depletion as a Consequence of Therapy. In Vitro and In Vivo Studies.
Ronald Taylor, Adam Kennedy, Michael Solga, Paul Beum, Patricia Foley, Margaret Lindorfer, Charles Hess, John Densmore.
Biochemistry, University of Virginia School of Medicine, Charlottesville, VA, USA; Comparative Medicine, University of Virginia School of Medicine, Charlottesville, VA, USA; Hematology/Oncology, University of Virginia School of Medicine, Charlottesville, VA.
We investigated C activation, C3bi deposition, and cell killing when RTX was bound to Raji or DB cells, in serum (NHS) as a C source. In the presence of RTX and C, large numbers of C3bi molecules deposit per cell, and fluorescence microscopy revealed that C3bi co-localized with bound RTX. Both cell types are killed by RTX in the presence of NHS, and use of mAb 3E7, specific for C3bi, enhanced killing. However, in the absence of NHS, little or no killing was demonstrable. RTX was infused into monkeys and we found that it rapidly bound to circulating B cells and activated C; 2 min after RTX infusion, C3bi was co-localized with RTX bound to the B cells. A similar pattern of co-localization of C3bi and RTX was obtained in vitro in opsonization experiments with blood samples taken from patients with B cell lymphomas.
A patient with CLL was treated with the standard 4 week course of RTX therapy. Analyses of blood samples taken during this time revealed the following: Immediately after the first infusion, flow cytometry measurements and fluorescence microscopy indicated that RTX and deposited C3bi were associated with both B cells and cellular debris, and a high degree of co-localization of C3bi with RTX was evident. After the first infusion, CH50 assays demonstrated that the patient's C titer, normal before treatment, had been substantially reduced (~ 5 fold). Although C levels were partially restored before the second infusion, the same pattern of C depletion occurred after this infusion, and by week three and four the patient's C levels were reduced ~ 10-fold, but returned to baseline 3 weeks later. We found, however, that in vitro supplementation of the C-depleted sera with C component C2 markedly increased C activity, leading to levels that were at least 50% of the pre-therapy baseline. In vitro studies with RTX, B cell lines, and NHS gave rise to similar findings. That is, at high cell concentrations RTX-mediated C3bi deposition and killing is limited by serum C, and both of these activities can be enhanced by supplementation with purified human C2. Our results indicate that the primary mechanism of action of RTX in killing CD20 positive cells is mediated through C, and it is likely that the in vivo form of this mAb bound to target cells has covalently incorporated C3bi. We suggest that if an anti-tumor mAb such as RTX requires robust C activation for therapeutic efficacy, then insuring an adequate level of C activity in a patient, by supplementation with either fresh plasma or a purified C component such as C2, may provide an important approach for improving the therapeutic efficacy of a C-fixing mAb.
Keywords: Rituximab\ Complement\ Immunotherapy
In practical terms, what does this mean? For starters, I think this has implication for the Rituxan scheduling in different protocols. Since complement is so important, I think going 'over the top' in Rituxan infusion (multiple infusions per week, or extra high doses) may not get you good bang for the buck, since complement gets depleted as it works with Rituxan, and it takes some time to recover the original levels of this important immune function. See previous post on this subject in the archives. The more I learn about this, the more I like Dr. Hainsworth's approach, 4 weekly infusions, standard dose, followed by maintenance administration along the same line, six months later. Long enough for the complement etc to have recovered completely, and yet most likely not long enough for the CLL to have re-established its dominance. Hit the enemy, wait till your troops recover, then hit it again before the enemy has a chance to recover and regroup. I like it.
Complement is secreted by specialized cells called Kupffer cells, which are a type of macrophages, that reside in the liver. I do not know if a connection exists, if liver involvement due to CLL also means the Kupffer cells are compromised. One more possible reason why Rituxan therapy may be better initiated in early stage, before these secondary complications set in.
It also means that you should try and stay in good health, no colds, no sniffles, just prior to initiating Rituxan therapy. Complement levels drop as they are used up to combat pathogens, and it takes time for the body to get the levels back up.
It might help to down-regulate the effect of CD55 and CD59, by any means possible. In this context, the report that Fludarabine down regulates these inhibitory proteins is interesting news and makes "RF Lite" an interesting concept.
It might be interesting to investigate complement mediated cytotoxicity that gets around the CD55 and CD59 type of inhibitory proteins via activating the lectin pathway of activating macrophages (see Beta Glucan, Complement and Rituxan) by using appropriate immunomodulatory compounds.
The role of complement mediated cell kill during Rituxan therapy is relatively new, and the role played by inhibitory proteins like CD55 and CD59 is even more recent. It will be a while before the importance of these markers makes it into mainstream thinking and therefore into routine blood analysis. Remember, just a couple of years ago, based on clinical trials with heavily pretreated patients, Rituxan monotherapy for CLL was written off as not effective. Even now, most patients have to be assertive to get quantitative flow cytometry done, to find out what their CD20 expression levels are.
As for the level of CD20 expression and intensity, and what constitutes "good enough", I am not competent to answer that. There is so much detail to this business that predicting how a particular patient responds, accurately, is not yet within our grasp. The best we can do is consider the odds and the probabilities. Maybe someday they will be able to draw a little blood from a patient, do a quick test and say which particular therapy regime is best for that individual. We are not there yet, tests like DISC assay (and it is still a controversial test) do not even consider monoclonals in the list of drugs they test for.
Your oncologist or CLL specialist can request a quantitative flow cytometry, that gives the percentage of B-cells that are CD20 positive. I do not know if there is a cut-off as such, but I personally think CD20 percentage of 80% or higher is good. As for intensity, it is reported as dim, moderate or bright (or 1+, 2+ and 3+ respectively). CLL patients rarely have bright CD20 (i.e., 3+) intensity, moderate intensity is good enough. This does not mean that I would not consider Rituxan-only therapy if the % and intensity is lower, just that it might reduce the chances of getting a good response. Sorry for the caveats, the jury is still out on this to some degree. This is why I think RF Lite is such as intriguing idea, it covers the bets a bit better, without a big price tag in terms of toxicity.
As for who does Rituxan-only frontline therapy, a lot of local oncologists now seem to be willing to go along with this approach, without the hassle of going through the formality of a clinical trial. If you are looking for more discussion on this subject, try "Hainsworth" or "Rituxan" as the keyword on our customized Google search engine — and read our article on Single Agent Rituxan. As for Rituxan plus low dose Fludarabine, I am not sure there are any formal clinical trials addressing this, yet. And I am equally sure many community oncologists are already doing this, it is too logical to miss as a therapy option. It is a question of getting yourself organized, get all your information together and negotiating with your local oncologist. In times of rapid change, patients have to take on extra responsibility for their own healthcare, it is hard for a doctor who sees you for 10-15 minutes in his office to focus on the latest thinking on your particular disease. I hope CLL Topics will play a constructive role in getting you organized for your next meeting with your doctor.
Yes, if one is an early stage patient, with the right profile for Rituxan therapy, I think it is a good idea to discuss Rituxan monotherapy as frontline intervention, not wait till the CLL gets a chance to get entrenched and precipitate other medical conditions. That was the logic we followed in my husband's case, and so far we are very happy with the results.
We live in interesting times. The more I learn about this stuff, the more interesting I find it. I think I will stay tuned in, even if my husband goes into CR after the four standard infusions of Rituxan...
Blood 2003 Feb 1;101(3):949-54
In vitro mechanisms of action of rituximab on primary non-Hodgkin lymphomas.
Manches O, Lui G, Chaperot L, Gressin R, Molens JP, Jacob MC, Sotto JJ, Leroux D, Bensa JC, Plumas J.
Department of Research and Development, EFS Rhone-Alpes, and Research Group on Lymphoma, Albert Bonniot Institute, La Tronche, France; and Clinical Hematological Department, Michallon Hospital, Grenoble, France.
To assess the sensitivity of primary non-Hodgkin lymphoma cells to rituximab-mediated cytotoxicity, we compared the potency of several rituximab-mediated killing mechanisms on fresh lymphoma cells. All lymphoma cells tested were equally sensitive to antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-mediated phagocytosis of tumor cells, and rituximab-induced apoptosis. However, they were differentially lysed by complement-dependent cytotoxicity (CDC). We found that taking into account both CD20 and complement regulatory protein expression on tumor cells could predict CDC sensitivity in vitro. Importantly, the sensitivity of lymphoma cells to CDC was consistent with the reported different clinical response rates of lymphomas: rituximab induced high CDC killing of follicular lymphoma cells, whereas mantle cell lymphoma and diffuse large cell lymphoma cells were moderately sensible to CDC, and small lymphocytic lymphoma cells were almost all resistant. We propose that CDC is a determinant mechanism of rituximab-induced killing in vivo. Poor sensitivity to CDC in vitro might predict a poor clinical response, whereas high sensitivity to CDC would only indicate a likelihood of response to rituximab treatment.
A member observed that the abstract above indicated differential CDC efficacy — with high CDC killing of follicular lymphoma cells, whereas mantle cell lymphoma and diffuse large cell lymphoma cells were moderately sensible to CDC, and small lymphocytic lymphoma cells were almost all resistant. His interpretation was that Rituximab did a good job of killing the FLL cells, a moderate job on MCL cells and a terrible job on SLL cells.
His interpretation is quite correct.
The consensus seems to be emerging that one, repeat one, of the major mechanisms of cell kill during Rituxan therapy is CDC, (complement dependent cytotoxicity), which is poor in SLL/CLL, moderate in MCL, and quite good in FLL. This is attributed to the lower expression of CD20 in CLL cells, as well as the higher expression of complement inhibitory markers CD55, CD59 etc in CLL cells, compared to FLL and MCL. This may explain why the overall response rate is so much better using Rituxan in FLL and even MCL, and significantly poorer for CLL.
There are other mechanisms for cell kill during Rituxan therapy, namely antibody dependent cellular cytotoxicity (ADCC) and direct apoptosis due to the Rituxan all by itself. The former works a lot better when T-cells, NK cells, neutrophils, etc., are in good shape, hence the greater efficacy of Rituxan even in CLL patients, if these are early stage patients.
It seems clear that response rates will increase in CLL as well, to the nice high levels obtained in say FLL, if we can get around the inhibition of the complement dependent cytotoxicity (CDC) mechanisms. This is especially important to previously treated patients, whose ADCC mechanisms may not work as well, whereas CDC mechanisms are more robust, and less likely to be compromised as a result of prior chemotherapy.
It is a complex picture, and I am not sure we have all the pieces of the puzzle yet, but we surely know more now than we did even a couple of years ago. I am willing to bet folks at IDEC, Genentech and other companies are busy trying to find ways around these road blocks, to further increase the efficacy of Rituxan.
How Does Rituxan Work in CLL?
Date: January 3, 2003
by Chaya Venkat
This has been a topic of hot debate for the past few years, ever since this monoclonal antibody showed such dramatic results in the case of some types of non-Hodgkin's lymphoma, especially Follicular Lymphoma. The frustration for us has been that the results seems to be so much poorer for CLL patients, in earlier studies where this drug was used as single therapy. The results are somewhat better now. In this article I will try to summarize some of the more important trials, and also try to make sense of why the results are so different between some of them. We do not know all the answers yet, but the picture is getting clearer.
1. Initial studies with refractory CLL/SLL patients were disappointing. Only about 15% of the patients responded, when treated with the now standard dose of 375 milligrams/meter square (see a previous article about how to calculate body surface area or BSA, to find out what your particular dose would be), once a week for four weeks.
2. The effort was made to see if escalating the dose of the drug would improve the response rate (see first abstract below). The quantity of Rituximab administered was escalated from 375 mg/m2 (standard) all the way to 2,250 mg/m2. Infusion related toxicity was much more severe at the higher doses, as expected. However, even at 500 - 825 mg/m2, only about 22% of the patients responded, and the median duration of the response was only 8 months. Better than the 15% response rate seen before, but not much to write home about.
3. The first breakthrough came when Dr. Hainsworth looked at Rituxan as frontline therapy, i.e., in 'naive' patients that had not been subjected any therapy before. This study included NHL and SLL/CLL patients. The patients were a mixed bag, most of them in later stages. The standard 375 mg/m2 was used, once a week for four weeks, followed by the same amount once every 6 months as "maintenance" therapy, for a total of four sessions. The response rate with this approach was a whopping 70%, and the duration of the responses was also much longer, about 24 months. (see the second abstract below).
4. Now comes the last piece of the puzzle: Early stage CLL patients (stage 0, 1 and 2) were recruited, "naive" patients who had no symptoms, in no obvious need of therapy, with relatively low tumor burden. The only criteria was that they had beta-2-microglobulin higher than 2.0, classifying them as "high risk". (Between you and me, I think this was just a way to get the study going, a way to justify treating these patients in the first place. Labeling them as high risk patients must have made it easier to get around guidelines. Majority of patients have B2M higher than 2.0 at some point in their w&w period, with no obvious deterioration in their status).
In any case, getting back to our mystery, here is this group of very early stage, not at all sick CLL patients, and they received the standard dose, 375 mg/m2, once a week for 8 weeks. No infusion related toxicity to speak off, since the dose was the standard variety. Guess what, the response rate was a tremendous 90%, too early yet to say much about the duration of the response, but it is expected to be long. (See the third abstract below). What's more, recent studies have shown that patients can be re-treated with Rituxan, in fact the second time around the response duration can be even longer than the first time.
OK. Now let us see if we can get this straight. Refractory patients, who have already been through chemo, do not do so well on Rituxan alone. They are better off with one of the combo therapies, such as RFC (Rituxan, Fludarabine, Cyclophosphamide). It doesn't help much to just give them more of the juice, you run into toxicity problems at the higher doses, without really getting a whole lot more bang for the buck.
The key seems to be, using Rituxan as frontline therapy, in previously untreated patients. Hainsworth's study got a respectable response rate for the first time, for CLL patients, because he used only "naive" patients. But the real advantage came when Rituxan was used as frontline and single agent therapy in **early stage** patients, who had never been through therapy, in fact before they looked like they needed any therapy at all.
Now for some of the theories researchers have kicked around to explain the results. It was originally proposed that CLL cells exhibited lower number and concentration of the CD20 marker, compared to Follicular lymphoma cells. Since Rituxan locks on to the CD20 marker, this was proposed to be the reason for the poorer response. More detailed and careful studies showed that there was not a great deal of difference in the response of different patient groups that had different levels of CD20.
The next theory was that the CD20 marker sheds off the cancer cell and into the blood plasma more readily in the case of CLL than NHL. This free floating and junk CD20 was supposed to sop-up the precious Rituxan, tying it up and wasting it, so that in reality only a fraction of the drug actually got to the cancer cells. If this were the case, the dose escalation study should have shown sharp improvement in the response rates, because using this approach we were over whelming the free CD20 in the blood plasma. It was not the case. Another theory in jeopardy of being not quite the case.
Now we are beginning to understand better how Rituxan works, the pieces of the puzzle are coming together. Rituxan is not supposed to do a lot of the killing of the cancer cells by itself. As I wrote before, it is thought to lock on to the CD20 markers of the B-cells, and thereby make them attractive targets for killing. The actual killing is done by the other cells of the immune system, the t-cells, NK cells (natural killer cells), and others. Think of the Rituxan as collaring the b-cells, painting a big red "kill me" sign on them, making them more easy targets for the actual assassins. If you like jargon, the processes are called "antibody dependent cellular cytotoxicity" (ADCC) and "Complement dependent cytotoxicity" (CDC).
Problem is, while CLL patients usually have pretty good t-cell counts, except in special situations, for some reason the t-cells seem to get more and more compromised in their effectiveness as the disease progresses. It is as if the growing cancer cells are able to put out subversive propaganda, putting all the other cells of the immune system off guard. In fact, this is not a bad analogy, the cancer cells do put out chemical messages called cytokines that make the t-cells "anergic" or unable to function. The higher the tumor burden, the worse it gets. And in patients who have been through chemo already and refractory, the CLL cells left behind are even more adept at putting the t-cells to sleep.
OK, now we get it. In order for the Rituxan to work effectively as single agent, the patient must have an immune system that is still capable of functioning well, i.e., before the cancer burden has gotten out of hand, or before it has been traumatized by prior chemo. That is why the early stage, "naive' patients did so well in the last abstract below. And if the re-treatment is done before the CLL gets out of hand, the t-cell and NK cell populations are healthy, and able to do their jobs. Hence the good responses upon re-treatment.
Does this mean Rituxan is only for early stage and "naive" patients? By no means. If a patient has been through chemo, and there is reason to believe that his immune system cannot be counted on to be effective assassins and kill the b-cells tagged by the Rituxan, we can use other methods of killing, such as other chemotherapy drugs. That is why combos like RFC work so well. The Rituxan tags them, and the other two drugs kill them. It does not matter whether or not the rest of the immune system is up to snuff.
Down the road, we might be able to do better than that. Immune system not so good any more at killing Rituxan tagged b-cells? Not to worry, we will be able to grow huge armies of the patients own T- cells outside his body, train them to be efficient killers, and put them back into the body (see several articles in the archives on the subject of CTL therapy). Or we can use immunomodulatory drugs like Interleukin-2, which boosts t-cell production (see previous articles on this subject, combining Rituxan with IL-2, interferon alpha, GM-CSF etc.) Or we may come up with more effective ways of stimulating the immune system in-vivo, by approaches such as the "gene therapy" experiment now being conducted in phase - 2 trials at UCSD. The future looks bright indeed.
Sorry this got so long. But as you can see, it is a complex subject of great importance to us all, especially those in w&w and pondering future therapy choices.
J Clin Oncol 2001 Apr 15;19(8):2165-70
Rituximab dose-escalation trial in chronic lymphocytic leukemia.
O'Brien SM, Kantarjian H, Thomas DA, Giles FJ, Freireich EJ, Cortes J, Lerner S, Keating MJ.
Leukemia Department, The University of Texas M.D. Anderson Cancer Center, Houston, TX .
PURPOSE: To conduct a dose-escalation trial of rituximab in patients with chronic lymphocytic leukemia (CLL) to define the maximum-tolerated dose (MTD), to evaluate first-dose reactions in patients with high circulating lymphocyte counts, and to assess the efficacy at higher versus lower doses.
PATIENTS AND METHODS: Fifty patients with CLL (n = 40) or other mature B-cell lymphoid leukemias (n = 10) were treated with four weekly infusions of rituximab. The first dose was 375 mg/m(2) for all patients; dose- escalation began with dose 2 but was held constant for each patient. Escalated doses were from 500 to 2,250 mg/m(2).
RESULTS: Toxicity with the first dose (375 mg/m(2)) was noted in 94% of patients but was grade 1 or 2 in most, predominantly fever and chills. Six patients (12%) experienced severe toxicity with the first dose, including fever, chills, dyspnea, and hypoxia in all six patients, hypotension in five, and hypertension in one. Toxicity on subsequent doses was minimal until a dose of 2,250 mg/m(2) was achieved. Eight (67%) of 12 patients had grade 2 toxicity, including fever, chills, nausea, and malaise, although no patient had grade 3 or 4 toxicity. Severe toxicity with the first dose was significantly more common in patients with other B-cell leukemias, occurring in five (50%) of 10 patients versus one (2%) of 40 patients with CLL (P <.001). The overall response rate was 40%; all responses in patients with CLL were partial remissions. Response rates were 36% in CLL and 60% in other B-cell lymphoid leukemias. Response was correlated with dose: 22% for patients treated at 500 to 825 mg/m(2), 43% for those treated at 1,000 to 1,500 mg/m(2), and 75% for those treated at the highest dose of 2,250 mg/m(2) (P =.007). The median time to disease progression was 8 months. Myelosuppression and infections were uncommon.
CONCLUSION: Rituximab has significant activity in patients with CLL at the higher dose levels. Severe first-dose reactions were uncommon in patients with CLL, even with high circulating lymphocyte counts, but were frequent in patients with other mature B-cell leukemias in which CD20 surface expression is increased. Efficacy of rituximab was also significant in this group of patients.
J Clin Oncol 2002 Oct 15;20(20):4261-7
Rituximab as first-line and maintenance therapy for patients with indolent non-hodgkin's lymphoma.
Hainsworth JD, Litchy S, Burris HA 3rd, Scullin DC Jr, Corso SW, Yardley DA, Morrissey L, Greco FA.
Sarah Cannon Cancer Center and Tennessee Oncology, Professional Limited Liability Corporation, Nashville, TN.
PURPOSE: To evaluate response to single-agent rituximab in patients with indolent non-Hodgkin's lymphoma (NHL) and no previous systemic therapy, and the feasibility, toxicity, and efficacy of maintenance rituximab, administered at 6-month intervals, in patients with objective response or stable disease after first-line rituximab therapy.
PATIENTS AND METHODS: Patients with indolent NHL (follicular or small lymphocytic subtypes) previously untreated with systemic therapy received rituximab 375 mg/m(2) intravenously weekly for 4 weeks. Patients were restaged at week 6 for response; those with objective response or stable disease received maintenance rituximab courses (identical dose and schedule) at 6-month intervals. Maintenance was continued for a maximum of four rituximab courses or until progression. Between March 1998 and May 1999, 62 patients were entered onto this trial; minimum follow-up was 24 months.
RESULTS: Sixty patients (97%) completed the first 4-week course of rituximab and were assessable for response. All have now completed rituximab therapy; 36 (58%) received four courses at 6-month intervals. The objective response rate at 6 weeks was 47%; 45% of patients had stable disease. With continued maintenance, final response rate increased to 73%, with 37% complete responses. Response was similar in patients with follicular versus small lymphocytic subtypes (76% v 70%, respectively). Median actuarial progression-free survival was 34 months. Two patients experienced grade 3/4 toxicity with the first dose; one patient was removed from treatment. No cumulative or additional toxicities were seen with maintenance courses.
CONCLUSION: Rituximab is highly active and extremely well tolerated as first-line single-agent therapy for indolent NHL. First-line treatment with scheduled maintenance at 6-month intervals produces high overall and complete response rates and a longer progression-free survival (34 months) than has been reported with a standard 4-week treatment.
Single Agent Rituxan in Early Stage Chronic Lymphocytic Leukemia (CLL).
Deborah A. Thomas, Susan O'Brien, Francis J. Giles, Jorge Cortes, Stefan Faderl, Hagop Kantarjian, Susan Lerner, Razelle Kurzrock, Michael Keating.
Department of Leukemia, M. D. Anderson Cancer Center, Houston, TX; Department of Bioimmunotherapy, M. D. Anderson Cancer Center, Houston, TX
Currently, patients with early stage CLL without active disease are observed. However, those patients with elevated beta-2 microglobulin levels appear to have a shorter median survival (6 years versus 10+ years). Strategies designed to impact the eventual progression of disease include use of targeted therapies with minimal long term risk. Single agent Rituxan has activity in previously treated CLL [O'Brien S et al, JCO 19:2165, 2001; Byrd J et al, JCO 19:2153, 2001], and in untreated low grade lymphomas [Hainsworth D, Sem Oncol 27:25, 2000]. We designed this study to investigate the activity of Rituxan in untreated high risk, early stage CLL. Patients were eligible if they had untreated Rai stage 0 to II CLL with beta-2 microglobulin levels 2.0 mg/dL, without indications for therapy according to the NCI Working Group criteria. Rituxan was given 375 mg/m2 weekly for 8 weeks. Baseline cytokine profiles known to be prognostic in CLL, including IL-6, IL-10, and TNF-alpha [Fayad et al, Blood 97:256, 2001], were obtained with serial measurements when feasible. Thirty-one patients have been enrolled to date; characteristics were median age 67 years (range, 50-82), Rai stage II in 32%, and median beta-2 microglobulin 3.6. The overall response rate in 21 evaluable patients [8 under active therapy, 2 not reassessed] was 90% (19% complete response, 19% nodular PR, 48% PR). Significant reductions in fatigue were reported. Two patients did not respond. With a median follow up of 8 months (range, 2-16), one patient with PR progressed. No unexpected toxicities were observed; most were grade I-II fever, chills, and/or hypotension related to the first infusion. Samples were collected for cytokine analysis in 10 patients to date. Although the numbers were small, preliminary observations suggested reductions in TNF-alpha levels correlated with response. In conclusion, Rituxan has significant activity in early stage CLL. Impact on survival and time to progression requires longer follow up. Further investigation of the effect of Rituxan on cytokine profiles and implementation of strategies to modulate CD20 expression is planned.
Does Rituxan Work on Large Nodes?
Date:September 29, 2002
by Chaya Venkat
CLL patients are constantly facing the issue of the limited efficacy of Rituxan in cases with bulky nodes.
This is truly the million dollar question. None of us have a crystal ball to give the perfectly correct answer, we just take semi-educated shots at it.
Actually, Rituxan has a better track record of cleaning out the lymph nodes than clearing the bone marrow. Campath, on the other hand, has a tougher time with Lymph nodes compared to bone marrow. Both monoclonals seem to have a relatively easy job of clearing the peripheral blood.
Part of the rationale for multiple drug combos is to get around this problem, attack the tumor at all the sites where it lives, blood, lymph nodes and bone marrow, spleen etc. It is also the reason why the new thinking is not to wait too long before starting therapy. In the past, when we did not have drugs such as the monoclonals, it was the thing to do was to wait out starting therapy as long as possible, because none of the drugs available then could hope to get really good remissions, and early therapy just meant you had to live with the side effects of therapy that much sooner, and it did not really change your overall survival length, not significantly.
The smart money these days says that if you have a variety of CLL that responds well to therapy, and you are relatively young and in good health otherwise, it might be better to go for an earlier bout of therapy, and try to aim for a complete response, hopefully PCR negative remission. If this is followed by some sort of immunotherapy such as idiotype vaccine, CTL therapy and the like, to clean out any last lingering cells of CLL, dare we hope we are now looking at a "cure", or a remission that is long enough and of high quality as to make no difference? If you have a long and healthy remission, and you can fast forward the available technology another 8-10 years, it is reasonable to hope your choices may be vastly different by then. The name of this game is this: live today, and live to fight another day.
We are all different in how the disease progresses in us, how we react to therapy, and how we personally view the consequences. The risk versus reward is different for all of us. I am just giving you my two cents take on this, not really prescribing a mode of action to anyone else.
Pros and Cons of Rituxan Therapy
Date: July 20, 2002
by Chaya Venkat
The subject of timing Rituxan treatment has come up on several occasions: treat now or wait until the bitter end before initiating Rituxan therapy? Prior conventional wisdom with standard chemotherapy was clear, there was no survival advantage to early treatment, better stay in w&w as long as possible. Now, with the availability of monoclonal antibodies like Rituxan, the answer is not so clear.
One of the points you should be aware of is that Rituxan has the least infusion related problems in patients with a relatively low tumor burden. If the absolute lymphocyte count is too high, the CLL cells are killed so fast and in such vast numbers that "tumor lysis syndrome" can become a problem. That is just a fancy term for saying that if the cells are killed in large numbers and too quickly, the body has trouble disposing off of the remnants, putting a high load especially on the liver and kidneys. Below is a PubMed reference that outlines this point. In many cases, for patients with high blood counts or large lymph nodes etc, the bulk of the disease is first eliminated by conventional chemo, followed by the more elegant Rituxan for mop up of the remaining lot.
So, if you are determined not to use conventional chemo, you may wish to think about this before letting the lymphocyte count get too high.
Optimizing the use of rituximab for treatment of B-cell non-Hodgkin's lymphoma: a benefit-risk update.
Kunkel L, Wong A, Maneatis T, Nickas J, Brown T, Grillo-Lopez A, Benyunes M, Grobman B, Dillman RO.
Genentech, Inc, South San Francisco, CA.
Rituximab (Rituxan; Genentech, Inc, South San Francisco, CA and IDEC Pharmaceutical Corporation, San Diego, CA), the first monoclonal antibody approved in the United States for the treatment of cancer, is indicated for the treatment of patients with relapsed or refractory CD20+ low-grade non-Hodgkin's lymphoma. From November 1997 through May 1999, approximately 36,000 patients have been treated with rituximab. Serious cardiopulmonary infusion reactions culminating in death have been reported to occur in approximately 0.04% to 0.07% of patients. Post-approval tumor lysis syndrome has been reported within 12 to 24 hours after the first antibody infusion and is estimated to occur in 0.04% to 0.05% of patients. The risk of tumor lysis appears to be higher in patients with high numbers of circulating malignant cells. Serious infusion-related adverse drug reactions, most often consisting of cardiopulmonary reactions associated with the rapid lysis of large numbers of circulating malignant cells, have been fatal in approximately 0.5 per 1,000 treated patients. Major risk factors include high numbers of circulating malignant lymphoma cells, pulmonary infiltrates or lymphoma involvement, and prior cardiovascular disease. This report updates the safety experience of rituximab therapy with data from clinical trials and postmarketing safety experience, and examines how this information can be used to optimize therapy.
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