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Direct activation of antigen-presenting cells is required for CD8+ T-cell priming and tumor vaccination

Kratky, Wolfgang, Reis e Sousa, Caetano, Oxenius, Annette, Spörri, Roman
Proceedings of the National Academy of Sciences of the United States of America 2011 v.108 no.42 pp. 17414-17419
CD4-positive T-lymphocytes, adjuvants, antigen-presenting cells, antigens, cytotoxic T-lymphocytes, immune response, inflammation, mice, neoplasms, receptors, vaccination
Successful priming of adaptive immune responses is crucially dependent on innate activation signals that convert resting antigen-presenting cells (APCs) into immunogenic ones. APCs expressing the relevant innate pattern recognition receptors can be directly activated by pathogen-associated molecular patterns (PAMPs) to become competent to prime T-cell responses. Alternatively, it has been suggested that APCs could be activated indirectly by proinflammatory mediators synthesized by PAMP-exposed cells. However, data obtained with CD4+ T cells suggest that inflammatory signals often cannot substitute for direct pattern recognition in APC activation for the priming of T helper responses. To test whether the same is true for CD8+ T cells, we studied cytotoxic T lymphocyte development in vitro and in mixed chimeric mice in which coexisting APCs can either present a preprocessed model antigen or directly recognize a given PAMP, but not both. We show that indirectly activated APCs promote antigen-specific proliferation of naïve CD8+ T cells but fail to support their survival and cytotoxic T lymphocyte differentiation. Furthermore, CD8+ T cells primed by indirectly activated APCs are unable to reject tumors. Thus, inflammation cannot substitute for direct recognition of single PAMPs in CD8+ T-cell priming. These findings have important practical implications for vaccine design, indicating that adjuvants must be judiciously chosen to trigger the relevant pattern recognition receptors in APCs.