Natural killer (NK) cells are lymphocytes of the innate immune system and are important in controlling tumors and infections without depending on the recognition of specific antigens. The activation of NK cells occur via NK cell receptor interactions, including the CD 16 (Fc-gamma) receptors that bind antibodies (eg. IgG) attached to pathogens and infected cells. The CD16 receptor is involved in antibody-dependent cellular cytotoxicity, a process associated with the effectiveness of antibody-based cancer immunotherapies.
CD16 can induce NK cell activation without additional receptor signals; therefore, it can be used as a strategy to promote NK cell expansion. Various cytokines have been used to expand NK cells but without adequate effectiveness. Cancer cells lines have been used as feeder cells (used to nourish cultured tissue cells) for the large-scale expansion of NK cells. However, this requires methods to limit the growth of the feeder cells so that these do not contaminate the expanded NK cells.
To circumvent this issue, researchers instead used irradiated autologous peripheral blood mononuclear cells for large-scale expansion of purified cytotoxic NK cells activated with anti-CD16 monoclonal antibody. They exposed peripheral blood mononuclear cells to a radiation dose sufficient to inactivate T cells during NK expansion. The irradiated donor cells were then cultured with anti-CD16 antibody. This combination induced a stronger increase in expanded NK cells compared to irradiated cells alone. Further, flow cytometry analysis showed that the anti-CD16 and irradiated cell combination upregulated NK cell-activating receptors.
NK cells expanded via the combination method were found to secrete the cytokine INF-gamma after stimulation with target cancer cells (human cancer cell lines). Further, coculturing of target cancer cells with expanded NK cells led to increased target cell death. Tumor growth was suppressed in immunodeficient mice inoculated with lung and colon cancer cells after injection with NK cells expanded by the combination method. The results of these experiments demonstrate that NK cell expansion using anti-CD16 antibody and irradiated peripheral blood mononuclear cells can provide sufficient expansion of purified cytotoxic human NK cells with strong in vitro and in vivo antitumor activity and applicability to antitumor immunotherapy.
Lee, H., Son, C., Koh, E., Bae, J., Kang, C., Yang, K., & Park, Y. (2017). Expansion of cytotoxic natural killer cells using irradiated autologous peripheral blood mononuclear cells and anti-CD16 antibody. Scientific Reports, 7(1). doi:10.1038/s41598-017-09259-1