Bispecific antibodies reactive with the multidrug‐resistance‐related glycoprotein and CD3 induce lysis of multidrug‐resistant tumor cells

We describe the lysis of multidrug-resistant (MDR) tumor cells by various lymphocytic effector cells, retargeted with bispecific antibodies (heteroconjugates). The Ab-heteroconjugate used was prepared by chemically cross-linking the OKT3 monoclonal antibody (MAb) reactive with CD3 antigen on T lymphocytes, with the MRK16 MAb, which recognizes the MDR-associated P-glycoprotein. Cloned TCR alpha beta/CD3+ T lymphocytes, OKT3-activated peripheral-blood mononuclear cells and peripheral-blood mononuclear blood lymphocytes, stimulated with allogeneic irradiated cells in a mixed lymphocyte culture, could be induced to lyse MDR ovarian tumor cells in the presence of Ab-heteroconjugate CD3/MRK16, whereas the drug-sensitive parental tumor cells lacking the P-glycoprotein were not lysed by these retargeted effector cells. Cloned TCR gamma delta/CD3+ T lymphocytes showed a high MHC-unrestricted lysis of MDR tumor cells. Addition of Ab-heteroconjugate CD3/MRK16 could therefore not enhance target-cell lysis. Melanoma tumor cells transfected with the mdr-I gene which codes for the P-glycoprotein were also efficiently lysed by Ab-heteroconjugate retargeted cloned TCR alpha beta/CD3+ T cells. Tumor cell lines derived from organs known to express the P-glycoprotein also were lysable by the retargeted effector cells.