NK-92 metabolism and comparison of time-resolved cytotoxicity measurement methods

Abstract

NK-92 is a highly cytotoxic natural killer cell line, with favourable properties for application in adoptive cell therapy. Relations between NK-92 metabolism and cytotoxic function are yet to be elucidated and the use of different cytotoxicity assays prevents comparison between experiments. Here NK-92 metabolism-cytotoxicity relationships were investigated, and three commonly used cytotoxicity methods were compared.NK-92 cells were cultured for 21 days in a pseudo-static setup with a daily sampling procedure. Cell clustering was analysed via brightfield microscopy and metabolite concentrations were measured in the culture via amino acid HPLC and enzymatic assays. Cytotoxicity measurement at effector to target ratios (E:T) of 1:1 and 5:1, after 4 h of co-culture with K-562 via LDH release assay, calcein release assay and a flow cytometry-based method were performed and compared.Correlations were found between metabolite concentrations, metabolite rates, aggregate formation, and cell count. Results of the three cytotoxicity methods showed no significant difference at 5:1 E:T. The results of the calcein release assay were significantly higher than those of the other two methods at 1:1 E:T. A correlation between spontaneous LDH release from NK-92 cells and the ratio of necrotic and apoptotic target cells was identified, indicating a potential role of spontaneous LDH release as soft sensor for the mode of killing of NK-92.