CTLA4 and graft versus host disease: Several studies have reported the occurrence of GVHD in murine models of ICIs, specifically in the setting of allogeneic hematopoietic stem cell transplantation.11,12 Blazar et al conducted a study that showed how CTLA-4 blockade led to increased severity of GVHD in a murine model, thereby making it difficult to evaluate anti-tumor responses.13 The aforementioned findings emphasize the necessity of performing carefully planned animal studies that consider the probable confounding impacts of GVHD.