Primary tumor cells show specific susceptibility to KIR-incompatible NK-cell mediated lysis in an ex- vivo single cell cytotoxic assay (SCCA)

Abstract

2569 Background: NK cells recognize target cells through a balance of activating and inhibiting receptors. When NK cell-inhibitory receptors (killer immunoglobulin-like receptors-KIRs) bind to compatible groups of class I MHC molecules, their cytotoxicity function is blocked. Failure to recognize the appropriate KIR ligand on target cells can trigger NK cell cytotoxic activity. Methods: We analyzed the susceptibility of primary tumor cells to NK-mediated killing by a single-cell cytotoxicity assay (SCCA) using flow-cytometry. Nine consecutive samples out of one hundred biopsies were considered suitable for assay in terms of viability and tumor cell content (1 gastric cancer, 4 colon cancer and 4 renal cancer). Effectors cells obtained from healthy donors were purified as CD3-/CD56+ cells and further enriched for the expression of the specific KIRs. Results: NK cells who recognized specific HLA-C allotypes were able to kill both tumor cells and EBV-LCL target cells that lack a matching HLA-C KIR ligand (specific lysis >35% at 20:1 effector-target ratio,). In contrast, target cells bearing KIR ligand matched alleles showed a specific lysis <12% at 20:1 effector-target ratio. Futhermore the larger the number of receptor- ligand mismatch pairs, the higher the susceptibility of tumor cells to NK cell- mediated lysis (72% lysis of tumor cells expressing only one KIR ligand versus 50% lysis of tumor cells expressing two KIR ligand alleles at 40:1 effector- target ratio). Tumor cells were consistently found to express adhesion molecules. Conclusion: We show that the NK-mediated lysis observed against acute myeloid leukemia following KIR-incompatible haploidentical transplantation might also occur against selected solid tumors, thus providing additional insights for designing new cell therapy approaches based on NK alloreactivity in solid tumors. No significant financial relationships to disclose.