B2M and graft versus host disease: A common strategy is to isolate T-cells from healthy non-cancer patient donors and genetically modify them to evade the immune system via genetic modifications, such as knocking-out the T-cell receptor (TCR) via a TRAC knock-out (KO) and/or knocking out class 1 major histocompability complex (MHC) via β2M KO to reduce graft-versus-host disease (GVHD) and decrease potential for rejection of the allogeneic CAR-T product by the patients’ own T-cells.