Ascorbic acid promotes proliferation of natural killer cell populations in culture systems applicable for natural killer cell therapy

Background aims Natural killer (NK) cell–based immunotherapy is a promising treatment for a variety of malignancies. However, generating sufficient cell numbers for therapy remains a challenge. To achieve this, optimization of protocols is required. Methods Mature NK cells were expanded from peripheral blood mononuclear cells PBMCs in the presence of anti-CD3 monoclonal antibody and interleukin-2. Additionally, NK-cell progenitors were generated from CD34+ hematopoietic stem cells or different T/NK-cell progenitor populations. Generated NK cells were extensively phenotyped, and functionality was determined by means of cytotoxicity assay. Results Addition of ascorbic acid (AA) resulted in more proliferation of NK cells without influencing NK-cell functionality. In more detail, PBMC-derived NK cells expanded 2362-fold (median, range: 90–31,351) in the presence of AA and were capable of killing tumor cells under normoxia and hypoxia. Moreover, hematopoietic stem cell–derived progenitors appeared to mature faster in the presence of AA, which was also observed in the NK-cell differentiation from early T/NK-cell progenitors. Conclusions Mature NK cells proliferate faster in the presence of phospho-L-AA, resulting in higher cell numbers with accurate functional capacity, which is required for adoptive immunotherapy.