Feb. 6, 2008 What if we could prevent cancer recurrence for years after surgery by giving simple recall injections every two or three years? This concept may no longer be a fantasy. In a clinical study a team headed by the international Ludwig Institute for Cancer Research (LICR) has shown that a vaccine against a protein found in cancer cells produces an immune response that can be boosted and strengthened with additional vaccine shots. Patients with resected non-small cell lung cancer (NSCLC) were treated with this investigational agent, also known as an Antigen-Specific Cancer Immunotherapeutic (ASCI), in another clinical study conducted by GlaxoSmithKline. The results showed a reduction in risk of cancer recurrence in these patients, a finding that prompted GlaxoSmithKline to initiate the largest ever clinical trial in lung cancer (MAGRIT study).
According to LICR's Dr. Sacha Gnjatic, the senior author of this LICR-sponsored study, the long 'immunological memory' is exactly what cancer immunologists are hoping to see. "Vaccines against infectious diseases induce immunological responses that typically last for years, and ideally we want a cancer vaccine that does the same thing. We previously learned that our vaccine could stimulate an immune response recognizing a protein found in lung cancer cells but we did not know how long the response lasted. We now know that this vaccine induces strong and persistent immunity over several years, which can be further 'boosted' with additional vaccination."
Dr. Gnjatic said that the booster shots, given two years after the first cycle of vaccinations, not only reactivated the initial immune response in patients who received the priming vaccination, it also diversified the types of immune cells specific for the cancer protein. "We've not only kept the immune system interested, we've also got it to more broadly recognize the protein that marks the cell as being a cancer cell."
LICR and the Cancer Research Institute, both head-quartered in New York, supported the study under the auspices of the Cancer Vaccine Collaborative, with the clinical component conducted by Dr. Nasser Altorki at New York Presbyterian Hospital / Weill Medical College of Cornell University.
Cancer vaccines have two principal components. One component, the 'adjuvant,' stimulates the immune system in a general way, and the other component, the 'tumor antigen' -- in this case, the MAGE-A3 antigen -- directs the immune response specifically against the cancer cell. Last month, another LICR-sponsored clinical trial within the Cancer Vaccine Collaborative showed that a cancer vaccine based on the tumor antigen NY-ESO-1 stimulated an immune response in women with ovarian cancer. The results from that trial were suggestive that a similar boost strategy could be beneficial for long-term immunological memory in that disease also.
A completely unexpected finding from the present study was that the inital formulation and delivery of the tumor antigen to the immune system is critical and suggests that the combination of the antigen with an immunological adjuvant is key. The original, small clinical study, conducted three years ago by the Cancer Vaccine Collaborative, showed that the adjuvant was necessary for activation of the immune system; patients who received antigen alone failed to mount specific immune responses. Surprisingly, these same patients also failed to mount immune responses even when they received the full vaccine -- adjuvant plus antigen -- as a booster shot.
"This is such a surprising result," says LICR's Dr. Lloyd Old, another author on the study and Director of the Cancer Vaccine Collaborative. "In the vaccine field, boosters are given to convert negative or weak reactions to positive ones, and we really thought we would see the same thing. One intriguing possibility is that regulatory mechanisms were activated following the original weak response induced by the vaccine without adjuvant. These findings will certainly have ramifications for the whole field to determine the formulation and delivery of future cancer vaccines."
This research was published online the week of February 4 by the Proceedings of the National Academy of Sciences USA.
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