CD34 and graft versus host disease: Following the observation that T cell depletion prevented GVHD in mice (18), clinical studies confirmed that GVHD also failed to develop following rigorous donor T cell depletion with CD34 positive selection of the donor inoculum and the administration of anti-thymocyte globulin (ATG); none developed GVHD even without posttransplant immunosuppression (21, 22).