Augmentation by Bispecific F(ab′)(2) Reactive with P‐Glycoprotein and CD3 of Cytotoxicity of Human Effector Cells on P‐Glycoprotein Positive Human Renal Cancer Cells

A bispecific F(ba′)(2) was constructed that was composed of two Fab fragments, one derived from anti‐CD3 monoclonal antibody (mAb) (OKT3) and the other from anti P‐glycoprotein mAb (MRK 16). This bispecific F(ab′)(2) enhanced the binding and cytotoxicity of human peripheral blood mononuclear cells (PBMCs) on P‐glycoprotein‐positive human kidney cancer cells (ADMHK/E). It had no effect on the cytotoxicity of PBMCs on P‐glycoprotein‐negative HK/E cells [long‐term cultured HK/E (LCHK/E)]. Control F(ab′)(2) composed of OKT3 or MRK16 alone did not influence the cytotoxicity of PBMCs on ADMHK/E cells. These findings suggest that the MRK16‐OKT3 bispecific F(ab′)(2) may be therapeutically beneficial in treatment of human multidrug‐resistant cancers.