CTLA4 and graft versus host disease: Different regulatory cell populations such as (CD4+CD25+FoxP3+) regulatory T cells (Treg), natural killer T (NKT) cells, anti-inflammatory cytokines (i.e. IL-10, TGF-β), and inhibitory molecules (i.e. CTLA-4 and PD-1) involved in controlling the proliferation and activation of alloreactive T cells have been identified and found to play important roles in GVHD pathophysiology [3], [4], [5], [6], [7], [8], [9], [10], [11], [12].