Measurement of individual tumors clearly shows a slowing of tumor growth in the Avelumab-treated mice. By day 36 post-tumor implantation, there is a significant (P<0.01) reduction in the average tumor volume of the Avelumab-treated mice. Reduction in MB49 tumor growth in the mice treated with Avelumab is durable and leads to a significant (P<0.05) improvement in percent survival. Avelumab treatment of 10 mice with bladder tumors results in complete tumor regression in 8 mice, confirmed by histopathology. However, in mice depleted of either CD4 or CD8 cells, Avelumab treatment is much less effective in controlling bladder tumor burden with tumor breakthrough occurring in a higher frequency in mice depleted of CD4 T cells^[3].