HLA-S and graft versus host disease: To avoid graft versus host disease (GVHD) and host versus graft (HVG) reactions, immunogenicity factors including T cell receptor (TCR) and human leukocyte antigens (HLAs) need to be suppressed in allogeneic CAR-T cells, also known as universal CAR-T (UCAR-T) cells (7–10).