CD52 and graft versus host disease: To reduce the risk of graft-versus-host disease (GVHD) and host-versus-graft reactions, knockout (KO) of the genes that encode the T cell receptor alpha (TCR) constant (TRAC) and CD52 by transcription activator-like effector nuclease (TALEN) technology in combination with an anti-CD52 antibody can be used to prevent TCR-mediated recognition of histocompatibility antigens and protect CAR-T cells from lymphodepletion (LD) mediated by an anti-CD52 antibody.