Effector Cell Analysis of Human Multidrug‐resistant Cell Killing by Mouse‐Human Chimeric Antibody against P‐Glycoprotein

A mouse‐human chimeric monoclonal antibody (mAb), MH162, against P‐glycoprotein was previously found to be more effective than an all‐mouse mAb (MRK16) in lysis of multidrug‐resistant (MDR) tumor cells by blood mononuclear cells. The present study was performed to identify the effector cells responsible for the chimeric mAb‐dependent cell‐mediated cytotoxicity (ADCC) against MDR cells. The ADCC reaction was assessed by a 6‐h (51)Cr release assay. Highly purified lymphocytes (>99%), monocytes (>99%) and neutrophils (>96%) were obtained from peripheral blood of the same healthy donors. A comparison of these three effector cell populations showed no difference between MH162 and its all‐murine counterpart MRK16 in MDR cell lysis by monocytes or neutrophils. But MH162 was more effective than MRK16 in lymphocyte‐mediated lysis of the MDR cells. The lymphocytes responsible for this ADCC had CD16+ Fc receptors. Pretreatment of monocytes with colony‐stimulating factors (IL‐3, GM‐CSF and M‐CSF) caused significant increase in their MH162‐mediated lysis of MDR cells. Another anti‐P‐glycoprotein chimeric mAb (MH171) was also more effective than its murine counterpart MRK17 in lymphocyte‐mediated lysis of MDR cells. These findings suggest that mouse‐human chimeric mAbs may be useful therapeutically for in vivo destruction of MDR cancer cells by the ADCC reaction.