Other immune checkpoints, such as cytotoxic T-lymphocyte associated protein 4 (CTLA4), lymphocyte activating 3 (LAG3) and indoleamine 2,3-dioxygenase 1 (IDO1) have been also studied in immunosuppressive viral diseases such as PMWS and CSF (15, 18). Here, CTLA4 is linked to viral infectious disease.