Acute graft-versus-host-disease (aGVHD) is mediated by donor T-cells. The preventative and therapeutic strategies described above have therefore focused on quantitative reduction in T cells or reduction of their function through immune-modulation. The role of B-lymphocytes in the pathogenesis of GHVD is unclear. Recent reports of successful use of rituximab in cGVHD support the hypothesis that a coordinated B and T cell response is instrumental in cGVHD. The significance of B-cells in pathogenesis of aGVHD is unknown.