CTLA4 and colitis: While CD4 T cells are the main driver of colitis in our model and in patients who developed colitis after receiving anti-CTLA-4 treatment (figure 2 and32), CD8 T cells are required for antitumor efficacy in the three syngeneic models that we studied.33–35 Unlike CD8 T cells from colon lamina propria, tumor-infiltrating CD8 T cells express high level of CTLA-4 and PD-136; therefore, we hypothesized that the differential expression or requirement of CTLA-4 in other immune cell subsets such as CD8 T cells or conventional CD4 T cells can explain this observation.