CD8 T cells are strongly induced in response to certain strains of vaccinia virus (VACV) and the generation of this population is tightly regulated by two Tumor Necrosis Factor (TNF)/TNFR superfamily members, OX40 (CD134) and CD27. In this study, we examined the role of another member of the TNFR superfamily, 4-1BB (CD137, TNFRSF9), and its ligand (4-1BBL, CD137L, TNFSF9), that have been described to control the generation of memory CD8 T cell populations elicited by other viruses such as influenza. Expression of 4-1BB and 4-1BBL was observed in wild-type mice during the primary infection, but we found that both 4-1BB and 4-1BBL deficient mice generated normal numbers of VACV-specific effector CD8 T cells that produced IFN-γ and TNF. Additionally, CD8 T cells deficient in 4-1BB were able to expand and persist comparably to wild-type T cells in response to VACV infection. Furthermore, the knockout mice also showed no defect in development of VACV-specific CD8 memory T cell populations. Lastly, showing alternate control mechanisms were not active in the gene-deficient environments that masked any activity, blocking 4-1BB/4-1BBL interactions using neutralizing antibody also had no effect on the number of VACV-specific memory CD8 T cells induced. Thus, our data demonstrate that 4-1BB and 4-1BBL do not play a strong or dominant role in driving the generation of high frequencies of VACV-specific CD8 T cells.
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