CTLA4 and graft versus host disease: Administration of antibodies against CTLA-4 immediately after allo-HSCT was shown to increase acute GvHD, while the blocking of CTLA-4 at late phases of allo-HSCT did not increase GvHD but resulted in lethal lympho-splenomegaly, autoimmune hepatitis and increased circulating anti-DNA auto-antibodies [9].