Cross-priming of CD8(+) T cells by viral and tumor antigens is a robust phenomenon

Cross-priming refers to the activation of naive CD8(+) T cells by antigen-presenting cells that have acquired nominal antigens from another cell. The biological relevance of cross-priming of CD8(+)T cells has recently been challenged (Zinkernagel, R. M., Eur J. Immunol. 2002. 32: 2385-2392), on the basis that responses are weak or poorly quantitated, and the determinants recognized are undefined. Here we show that cross-priming is a robust process that elicits vigorous primary responses to multiple pepticles in two well-defined systems. Our findings support the relevance of cross-priming in CD8(+) T cell responses to viruses and tumor cells, and demonstrate that cross-priming elicits CD8(+) T cells to determinants generated by the endogenous processing pathway.