B2M and neoplasm: UCAR T cells, which could not cause graft‐versus‐host‐disease (GvHD) and host‐versus‐graft (HvG) through knocking out endogenous TCR and MHC class I molecules, express mutant B2M‐HLA‐E (mBE) and B2M‐HLA‐G (mBG) fusion proteins protecting against allogeneic NK‐mediated lysis and enhancing their survival persistence and anti‐tumor ability in vivo (Image created with BioRender.com).