Pretreatment of mice with monoclonal antibodies against CD2 and CD48 significantly reduced the severity of CD4+ (but not CD8+) T lymphocyte-induced graft versus host disease (GVHD) and marrow aplasia, supporting a key role of CD48 costimulation in the induction of bone marrow failure by the bm12 allogeneic T cells (108). This evidence concerns the gene CD2 and graft versus host disease.