TNFR2-Deficient Memory CD8 T Cells Provide Superior Protection against Tumor Cell Growth

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Abstract
TNF receptor-2 (TNFR2) plays a critical role in promoting the activation and survival of naive T cells during the primary response. Interestingly, anti-CD3 plus IL-2 activated TNFR2−/− CD8 T cells are highly resistant to activation-induced cell death (AICD), which correlates with high expression levels of prosurvival molecules such as Bcl-2, survivin, and CD127 (IL-7Rα). We determined whether the resistance of activated TNFR2−/− CD8 T cells to AICD contributes to more effective protection against tumor cell growth. We found that during a primary tumor challenge, despite initial inferiority in controlling tumor cell growth, TNFR2−/− mice were able to more effectively control tumor burden over time compared with wild-type (WT) mice. Furthermore, vaccination of TNFR2−/− mice with recombinant Listeria monocytogenes that express OVA confers better protection against the growth of OVA-expressing E.G7 tumor cells relative to similarly vaccinated WT mice. The enhanced protection against tumor cell growth was not due to more effective activation of OVA-specific memory CD8 T cells in vaccinated TNFR2−/− mice. In vitro studies indicate that optimally activated OVA-specific TNFR2−/− CD8 T cells proliferated to the same extent and possess similar cytotoxicity against E.G7 tumor cells as WT CD8 T cells. However, relative to WT cells, activated OVA-specific TNFR2−/− CD8 T cells were highly resistant to AICD. Thus, the enhanced protection against E.G7 in TNFR2−/− mice is likely due to the recruitment and activation of OVA-specific memory TNFR2−/− CD8 T cells and their prolonged survival at the tumor site.

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