FAP and neoplasm: Bispecific FAP-targeted 4-1BB ligand (RG7826), correctly assembled through CH1-CL domain crossover, knob into hole (KIH) amino acid mutation in the fragment crystallizable (Fc) domain, as well as mutations in CH1 (EE) and CL (RK) (12, 115), led to intensive IFN-γ and granzyme B secretion in human tumor samples while combined with tumor antigen-targeted (CEA) T cell bispecific (TCB) molecules (89, 116).