CTLA4 and graft versus host disease: Currently, GVHD prophylaxis includes immunosuppressive agents such as calcineurin inhibitors (Cyclosporin-A and Tacrolimus), anti-metabolites (Mycophenolate Mofetil (MMF) and Methotrexate, MTX), post-transplant cyclophosphamide (PTCy), T-cell depleting antibodies (Antithymocyte globulins (ATG), and Abatacept (a recombinant soluble CTLA-4-Ig) [6].