Sensitivity of Multidrug-Resistant Tumor Cell Lines to Immunologic Effector Cells

The ability of malignant cells to survive exposure to cytotoxic agents is a major obstacle to cure in patients with cancer. Multidrug resistance and the expression of P-glycoprotein are emerging as a cause of chemotherapy failure. Immunologic effector cells such as lymphokine-activated killer (LAK) cells or cytokine-induced killer (CIK) cells are capable of killing a broad range of tumor cell lines or freshly isolated tumor cells. As demonstrated here, LAK and CIK cells possess a high level of cytotoxic activity against tumor cell lines both resistant and sensitive to chemotherapeutic agents such as doxorubicin or vinblastine. CIK cells possessed a higher level of cytotoxic activity than LAK cells as determined by51Cr release and a tumor colony assay. Monoclonal antibodies against P-glycoprotein did not block the lysis of tumor cells resistant to chemotherapy by CIK cells. In contrast, antibodies to LFA-1 and ICAM-1 blocked CIK cell-mediated tumor cell lysis. These data demonstrate that immunological approaches to cancer therapy may be useful in overcoming disease caused by drug resistance.