At the June 2004 annual meeting of the American Society of Clinical Oncology, Johann Vieweg, MD, associate professor of urology and immunology at Duke University Medical Center, presented exciting findings on an immunotherapeutic vaccine he is testing against prostate cancer.
Unlike traditional vaccines that when administered protect the recipient from acquiring a disease, immunotherapeutic vaccines facilitate the destruction of an existing disease. Dr. Vieweg’s vaccine provokes an immune attack against cells that overexpress telomerase, a polypeptide that is silent in normal human cells but abundantly expressed in more than 85% of all tumor cells, including those of the prostate, breast, lung, colon, and kidney. Telomerase is known to protect tumor cells from undergoing preprogrammed cell death, yet because of these differences in expression, telomerase can serve as an immunological target, thereby making tumor cells vulnerable while preserving the integrity of normal cells.
Of the 20 men with prostate cancer who are enrolled in Dr. Vieweg’s study, 19 were able to successfully generate their own specific immune T cells with cytotoxic activity against telomerase-associated tumor cells and without appreciable side effects. As a result, the typical 2.9-month doubling time for prostate-specific antigen (PSA) in the blood increased to 100 months. PSA doubling time is a convenient measure of a prostate cancer patient’s response to treatment—the longer the doubling time, the better the response.
Furthermore, 9 of 10 subjects who initially had detectable levels of circulating prostate cancer were found to have a significant reduction or complete absence of these cells following vaccination. In the study’s next phase, the subjects will receive booster vaccinations to prolong their immunity and presumptive protection from prostate cancer.
Unfortunately, while the few men participating in the study have benefited, many other eligible men will not. The telomerase vaccine is in Phase I/II clinical trials as a product in development for Geron Corporation, and it may well be years before this promising vaccine is made available to the public.
—Dean S. Cunningham, MD, PhD