Date: July 28, 2003
by Chaya Venkat
We started tracking this story, thanks to a member who sent me the conference material from the "Leukemia 2002" conference in Miami last year. That conference had an article by Kipps, et. al. that describes their T- cell clinical trial strategy. They are working in collaboration with a start-up bio-technology firm called "Xcyte Therapies", which is a Seattle based corporation. The company's website is no longer accessible, but I am sure you can you can follow the brief overview I have put together.
Editor's Note: Xcyte Therapies is out of business, apparently having merged its operations with Cyclacel Pharmaceuticals, Inc. of Short Hills, NJ. Cyclael have a number of programs they list in their product pipeline but the technology pioneered by Xcyte does not appear to be in that list. There is also an obscure note that Xcyte sold its assets, including intellectual property and data from its clinical trials to Invitrogen in December 2005. Invitrogen appears to be in the biotech research tools and supplies business and is not listed as conducting any clinical trials at the moment.
If we are to have any hope of the body's own immune system recognizing and attacking the tumor cells, the T-cells of the body must be involved in the process. This is how the process is supposed to work, in healthy people: Antigens from the tumor (or virus) are presented by dendritic cells (these are so-called professional antigen presenting cells, or APCs) by displaying the antigens on their major histocompatibility sites (MHC sites). Now all that is required is for the dendritic cell to produce, at the same time as the antigen is presented, a co-stimulatory signal, before the T-cell will be properly activated.
Think of the dendritic cell as the traditional English butler, and the MHC site as his silver platter. The antigen is the extra dry martini on the silver platter. The butler has to present the martini on a silver platter, and announce "your drink is served, my lord", at the same time. The butler, the silver platter, the martini and the announcement are all necessary pieces of the puzzle.
The antigen displayed on the MHC site of the dendritic cell triggers a specific site on T-cells, called TCR/CD3 complex. The co-stimulatory signal sent out by the dendritic cell is received by another site on the T-cell, called the CD28. Both the CD3 site and the CD28 site on the T-cell must be simultaneously stimulated for the T-cell to be activated.
Part of the problem in CLL is that both the quality and quantity of T-cells is less than optimum in patients, which is probably why the disease got a foothold in the first place. There are also some concerns that as the cancer grows, proper functioning of dendritic cells and T-cells is further compromised. This is the reason why a lot of researchers are looking at growing billions of a patient's T-cells in the laboratory, away from tumor cells and under constant and simultaneous stimulation of their CD3 and CD28 sites.
Xcyte Therapies utilizes super-paramagnetic microbeads that approximate the size and shape of dendritic cells, to artificially mimic the process of T-cell activation. By attaching anti-CD3 and anti-CD28 monoclonal antibodies to these microbeads, artificial APCs are created that can be used to activate T cells. Monocytes from the patient's blood are incubated with these coated microbeads and in a matter of 11-14 days, there is a 100-1000 fold expansion of the T-cells, and even more important, these T-cells are now fully functional, motivated and ready to kill. When their job is done, the microbeads are easily removed, since they are paramagnetic and can be separated from the rest of the potion by applying a magnetic field.
If you recall the article I did a few days ago about bispecific monoclonal antibodies, these microbeads with anti-CD3 and anti-CD28 can be thought of as one type of bispecific monoclonal antibody. Instead of needing the English butler, silver platter and announcement, we now have a tiny microbead that does the job of simultaneously tickling the CD3 and CD28 centers of the T-cell, all by itself. Notice, though, the martini (specific antigen) is missing from this picture. More on this pesky detail later on. In so far as it goes, this approach seems to do the job of activating T-cells remarkably well. These "Xcyted" T-cells are like a billion Arnold Schwartezneggers on testosterone.
Kipps et al believe that in the presence of the activated T-cells, malignant b-CLL cells are attacked and are also readily induced into cell death pathways, suggesting that "non-antigen specific mechanisms, in addition to antigen-specific mechanisms are playing a role in leukemic B cell death".
I am truly impressed by the technology of ex-vivo activation of T- cells. If there is a concern here, and I may be missing the boat someplace in my understanding and interpretation of the technical stuff, the problem has to do with the missing martini in my analogy above. It is all well and good to get these billions of motivated T- cells ready and willing to kill, but if they have not been trained to kill cells exhibiting one specific antigen or set of antigens (namely the antigen(s) expressed by the cancer cells), how do they know what to attack, and equally important, when to quit? There is always the issue of auto-immunity complications in vaccine type approaches. As you goose the immune system, there have to be checks and balances that prevent the T-cells from running amuck and start attacking the body itself. The distinction between "self" and "non-self" is a very fine one, and the two ends of that spectrum are immune deficiency versus auto-immune problems. As I said above, I may be missing something here, wish we can get a clarification on this point.
Kipps, et al. state that they will be starting Phase-I/II dose escalation trials of CD3/CD28 based microbead technology from Xcyte Therapies. Patients will have mononuclear cells collected by leukapheresis, have the cells undergo CD3/CD28 activation in the lab, followed by expansion of the size of the population of these activated T-cells, which will then be injected into patients. The researchers will be looking for reduction in lymphocyte counts and changes in lymph node size as end points, similar to the end points in the Phase-I gene therapy trial. I am also intrigued that the end- points are not more ambitious, looking for potential complete remissions and/or PCR negativity.
An article from researchers in University of Chicago covers much of the same ground. You may want to read it by clicking on the following URL:
UC Hospitals news item – "New approach supercharges immunotherapy: Co-stimulation activates T cells against resistant lymphomas."
Xcyte Therapies announces Issuance Of Patent Providing Broad Rights For Its Core T Cell Therapy Technology
SEATTLE, March 13 /PRNewswire/ -- Xcyte Therapies, Inc. today announced that the U.S. Patent and Trademark Office (PTO) has issued U.S. patent #6,352,694 covering the Company's core technology used in its products currently in clinical trials in cancer patients. Xcyte Therapies uses this proprietary technology, known as the Xcellerate (TM) Technology, to mimic the body's natural mechanisms to stimulate T cells, which are key components of the immune system, to fight disease. A variety of medical conditions including cancer, HIV, congenital immunodeficiencies as well as treatments for cancer are associated with deficiencies in T cells. Patients with T cell deficiencies are at increased risk of developing serious and often life-threatening infectious diseases, including viral, bacterial and fungal infections. Patients with T cell deficiencies are also at high risk of developing certain types of cancer. Conversely, the presence of healthy T cells is associated with improved therapeutic outcome in patients with cancer, HIV and possibly other diseases. Xcellerate(TM) is designed to rapidly activate a patient's own T cells outside of the body by simulating natural events of the immune system to generate activated T cells, known as Xcellerated T Cells(TM). Xcellerate(TM) is believed to increase T cell quantity, improve T cell quality and broaden T cell diversity, all of which are necessary for generating effective immune responses to fight disease.
For those of you interested in the "T-cell" therapy clinical trial at UCSD, here is a link to the description of the trial, exclusion criteria, contact information and the like.
Link: Description of Clinical Trial at UCSD - Phase I/II Study of Xcellerated T cells in Patients with CLL.
As part of my advocacy efforts on behalf of CLL Topics members, I often write to executives in the companies that are developing technology of interest to us. I have become quite shameless in my solicitation of their help, in trying to make sure they hear our patient perspective. Once in a while, I get a response back that tells me it is not all useless busy-work. Here is a response back from Xcyte Therapies, they of the Xcyted T-cell fame.
Hello Dr. Venkat,
I'm the medical director at Xcyte. Lew Chapman passed on your e-mail. Dr. Kipps at UCSD had previously forwarded me some of your postings.
I apologize for the delay in getting back to you. I just finished a large grant and am now out of town until next week.
I'm impressed with your sophisticated understanding of the CLL biology and available therapies!
Rather than respond to your questions with a lengthy e-mail, perhaps it would be more efficient to chat on the phone next week. I can also forward you some literature when I'm not limited by modem. There are several publications using the 3x28 technology by the group of Carl June, one of our scientific founders. These are in both the HIV (Levine et al., Nature Medicine 2002) and Non-Hodgkin's Lymphoma (LaPort et al. Blood 2003) settings. Xcyte has a paper in press in Clinical Cancer Research (Thompson et al.) describing the results of a trial of Xcellerated T Cells in renal cell carcinoma patients. We are currently writing up our laboratory investigations of Xcellerated T Cells in CLL, and will be submitting that shortly. We also have trials ongoing in prostate cancer and multiple myeloma.
I will try to call you next week, or feel free to try me at the number below.
Mark W. Frohlich, MD
VP & Medical Director
Xcyte Therapies, Inc.
I tracked down the two references that Mr. Frohlich of Xcyte mentioned in his letter. The abstracts are attached below. The third reference is not yet published.
Nat Med. 2002 Jan;8(1):47-53.
Adoptive transfer of co-stimulated CD4+ T cells induces expansion of peripheral T cells and decreased CCR5 expression in HIV infection.
Levine BL, Bernstein WB, Aronson NE, Schlienger K, Cotte J, Perfetto S, Humphries MJ, Ratto-Kim S, Birx DL, Steffens C, Landay A, Carroll RG, June CH.
Abramson Family Cancer Research Institute, University of Pennsylvania Cancer Center, Philadelphia, Pennsylvania, USA.
To study the safety and feasibility of T-cell reconstitution in HIV-infected individuals, we adoptively transferred activated autologous CD4+ T cells. Polyclonal peripheral blood CD4+ cells were costimulated ex vivo and subjects were given infusions of up to 3 x 1010 activated CD4+ cells. Dose-dependent increases in CD4+ cell counts and in the CD4:CD8 ratio were observed. Sustained increases in the fraction of cytokine-secreting T cells and decreases in the percentage of CD4+CCR5+ cells were noted in vivo, suggesting enhanced function and resistance to HIV infection. The frequency of CD4+Ki-67+ cells increased whereas CD4+ T cells containing T cell-receptor rearrangement excision circles (TRECs) decreased. These findings indicate that expansion of the peripheral T-cell pool mediated the increase in CD4 counts and suggest that approaches to reconstitute CD4 helper cell activity and decrease CCR5 expression may augment natural immunity to HIV infection.
Blood. 2003 May 22 [Epub ahead of print]
Adoptive transfer of co-stimulated T cells induces lymphocytosis in patients with relapsed/refractory non-Hodgkin's lymphoma following CD34-selected hematopoietic cell transplantation.
Laport GG, Levine BL, Stadtmauer EA, Schuster SJ, Luger SM, Grupp S, Bunin N, Strobl FJ, Cotte J, Zheng Z, Gregson B, Rivers P, Vonderheide RH, Liebowitz DN, Porter DL, June CH.
Abramson Family Cancer Research Institute, University of Pennsylvania Cancer Center, Philadelphia, PA
We explored the feasibility and toxicity of administering escalating doses of anti-CD3/CD28 ex vivo costimulated T cells as a therapeutic adjunct for patients with relapsed, refractory or chemotherapy-resistant, aggressive non-Hodgkin lymphoma (NHL) following high dose chemotherapy and CD34(+)-selected hematopoietic cell transplantation (HCT). Sixteen patients had infusions on day 14 after HCT of autologous T cells that had been stimulated using beads coated with anti-CD3 and anti-CD28 monoclonal antibodies. At baseline, the subjects had severe quantitative and functional T cell impairments. The culture procedure partially reversed impaired cytokine responsiveness in T cells in vitro and in vivo. Transient dose-dependent infusion toxicities were observed. There was a rapid reconstitution of lymphocytes, however there were persistent defects in CD4 cells. Most interestingly, 5 patients had a delayed lymphocytosis between day 30 and day 120 after HCT. Maximal clinical responses included 5 patients with a CR, 7 pts with a PR and 4 patients with stable disease. At a median follow-up of 33 months (range=26-60), 5 pts are alive with stable or relapsed disease and 3 pts remain in CR. In conclusion, this Phase I trial demonstrates that adoptive transfers of autologous costimulated T cells 1) is feasible in heavily pretreated patients with advanced NHL, 2) is associated with a rapid recovery of lymphocyte counts, 3) reverses cytokine activation deficits in vitro and 4) is associated with delayed lymphocytosis in a subset of patients.
Editor's Note: As previously noted, Xcyte Therapies and its technology are no longer with us. The science, however, could and probably does provide clues for other, perhaps more effective, approaches — if only we could get at the results!
"Arabella Gets Xcyted" is the personal story of one of our intrepid volunteers who participated in the Xcyte trial. There is of course no expectation that early phase clinical trials like this one will results in positive results. However, a detailed resport of the results would be of great value. We are disappointed that the sacrifice of Arabella and her fellow volunteers in this trial has not been rewarded by at least a bare-bones reporting of the results — at least so far.
Interestingly enough, the clinicaltrials.gov site shows a currently active trial, NCT00081783, still "currently recruiting" at 18 recruitment centers across the United States! Clearly someone just forgot to tell the NCI about the fate of this effort. The most recent update to this trial listing was June 23, 2005. The principal investigator listed for the study was none other than Mark W. Frohlich, MD, Study Chair, Xcyte Therapies Inc., author of the letter above.
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Topic: CTL Therapy