Although immunotherapy has a unique set of toxicities compared to traditional chemotherapy, in general, grade 3 or 4 toxicities are rare—with the exception of grade 3 diarrhea and colitis. The mechanisms by which immune-related diarrhea and colitis occur are not clear. However, T-cell activation leads to high levels of CD4 T-helper cell cytokines and cytolytic CD8 T-cell tissue infiltration. Some research suggests that depleting regulatory T cells also induces autoimmunity.