To prevent graft-versus-host-disease (GvHD) or rejection of HLA-incompatible cells, the T cell receptor alpha constant (TRAC) and B2M (necessary for HLA class I assembly and presentation) were edited using CRISPR/Cas9 technology in donor-derived allogeneic CAR-T19 cells and named universal CAR-T19 (U-CAR-T19) cells [12]. The gene discussed is B2M; the disease is graft versus host disease.