In HLA-matched or mismatched unrelated donor setting, conditioning regimens will often include serotherapy such as Alemtuzumab (monoclonal anti-CD52 antibody) or thymoglobulin (polyclonal horse or rabbit thymocyte globulin [ATG]) to remove alloreactive T cells in the recipient that can cause acute Graft versus Host Disease (GVHD). The gene discussed is CD52; the disease is graft versus host disease.