ERBB2 and neoplasm: Because human NK cells cannot be reconstructed in the PBMC-“humanized” tumor xenograft model, the question of whether the antitumor efficacy and potency of HER2/PD-L1 in IgG1 are superior to that of HER2/PD-1 BsAb in IgG4, which is currently under intense testing at our laboratory, is yet to be answered.