Tumor-specific T cells (red) infiltrate a tumor after vaccination.

Tumor-specific T cells can be detected in the blood and the tumors of many melanoma patients, and yet these cells are unable to kill the tumor. What causes the impotence of these T cells is a mystery. Equally mysterious is why vaccination against tumor-specific antigens sometimes causes regression without expanding large numbers of vaccine-specific killer T cells.Pierre Coulie's group studied the specificity of antitumor T cell responses in patients vaccinated with a tumor antigen called MAGE-3. In one patient whose tumors regressed after vaccination, the authors found that T cells specific for nonvaccine tumor antigens became detectable or expanded from their prevaccine frequencies. Vaccine-specific T cells became detectable but remained at low frequency. Thus, reinvigoration of existing tumor-specific T cells and activation of new T cells after vaccination does not require large numbers of vaccine-specific T cells.

Although the mechanism underlying this phenomenon remains unknown, Coulie thinks that the few T cells stimulated by the vaccine may change the local environment of the tumor such that existing T cells can be reactivated and new T cells can be recruited.

High frequency of antitumor T cells in the blood of melanoma patients before and after vaccination with tumor antigens

Catherine Germeau, Wenbin Ma, Francesca Schiavetti, Christophe Lurquin, Emmanuelle Henry, Nathalie Vigneron, Francis Brasseur, Bernard Lethé, Etienne De Plaen, Thierry Velu, Thierry Boon, and Pierre G. Coulie
J. Exp. Med. 2005 201: 241-248. [Abstract] [Full Text] [PDF]