B2M and graft versus host disease: A recent study has shown the potential of multiplex editing for the optimization of therapeutic T cell products by simultaneously knocking out four genes (TRAC or CD3E, Beta-2 microglobulin - B2M, Class II Major Histocompatibility Complex Transactivator – CIITA, and Poliovirus receptor) to eliminate the risk of GVHD, as well as rejection by both T lymphocytes and NK cells (147).