Moreover, we have shown that in vitro activation of 4-1BB-costimulated CAR4 T cells upregulates IL-2 and IL-21, which are cytokines that augment the function of CD8+ T cells during viral infection,77, 78, 79 and thus may have contributed to the sustained CAR8 T cell response that we observed in vivo. This evidence concerns the gene CD8A and viral infectious disease.