Enhancement of NK cell proliferation by activation pre-processing of autologous feeder cell before irradiation

Abstract Background Natural killer (NK) cells play a crucial role in early immune defenses against transformed cells and are used in therapeutic strategies for cancer. However, it is hard to sufficiently obtain high-purity activated NK cells for clinical application. The function of NK cells depends on the balance of activation and inhibitory signals. It is more powerful and diverse stimuli are required to increase the function of NK cells. Radiotherapy modulates the expression of various immunomodulatory molecules that recruit and activate NK cells. NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) is one of the most potent cytotoxic effects of NK cells against target cancer cells. Methods To generate activated and irradiated autologous PBMCs, cytokine and monoclonal antibody stimulation followed by ionizing radiation. Expanded NK cells were cultured for 21 days using activated/irradiated autologous PBMCs. Two colon cancer cells, SW480 and HT-29 cells were used to analyze the expression of NKG2D ligands and EGFR by radiation. The surface expression ratio was analyzed using flow cytometry. The cytotoxicity of radiation plus NK cell-based targeted therapy against colorectal cancer cell lines was analyzed using flow cytometry. Results Activated and irradiated PBMCs significantly increased the expression of various activating ligands that stimulate NK cells. This method finally obtained more than 10,000-fold high-purity activated NK cells, with negligible T-cell contamination. To confirm the antitumor activity of NK cells expanded by this method, we treated expanded NK cells with radiotherapy or a combination of radiotherapy and cetuximab using human colon cancer cells. Expanded NK cells were effective at targeting human colon cancer cells, especially when combined with radiotherapy and cetuximab. Conclusions We developed a novel method to robustly expand NK cells using activated and irradiated peripheral blood mononuclear cells (PBMCs) without cancer cells or virus-derived feeder cells. In addition, the combined radiotherapy and antibody-based immunotherapy with expanded NK cells may be an effective way to enhance the treatment efficiency of colon cancer.