Tumor antigen presentation: changing the rules

 Cell-based tumor vaccines have been developed on the basis of the hypothesis that tumor cells can be genetically modified to present antigen to T lymphocytes directly. Contrary to expectations, cross-priming is the predominant pathway for activation of tumor-specific CD8⁺ T cells, while direct presentation of antigen dominates activation of tumor-specific CD4⁺ T cells. These results pose interesting paradoxes for the generation of immune responses, and have definite implications for the development of anti-cancer vaccines. Received: 10 October 1997 / Accepted 10 January 1998