CD4 and graft versus host disease: identified germline loss‐of‐function mutations in the SOCS1 gene related to early onset autoimmune manifestations.[34] SOCS1 was also identified as a checkpoint for antigen‐experienced CD4+ T cell expansion.[35] However, the role of SOCS1 in another immune‐related disorder, GVHD, has not been elucidated.