Influence of NK cell magnetic bead isolation methods on phenotype and function of murine NK cells

Natural killer (NK) cells are a promising tool for cell therapy due to their capacity to lyse tumor cells without prior activation and their influence on the innate as well as the adaptive immunity. To characterize distinct NK cell populations, it is important to find a reliable isolation method. We investigated separation methods for NK cell isolation by magnetic bead labeling. There are three commonly used different MACS protocols to isolate NK cells from murine spleen: CD49b (DX5) MicroBeads, the NK Cell Isolation Kit and a separation method which is based on a positive selection for NKp46 expressing cells. Interestingly, we found a significant difference of NK cell purities depending on the mouse strains and the purification protocol used. We observed a significantly higher level of purity and yield of NK cells by preparations from Balb/c splenocytes. In this study, we modified the negative selection protocol and adapted it to C57Bl/6 mice to obtain equal purity, viability and yields of NK cells in the different mouse strains. Moreover, we optimized the NKp46 NK cell selection method by addition of a B cell depletion step. To our knowledge, this is the first report that has directly compared and essentially modified the different NK cell purification strategies in parallel, both in C57Bl/6 and Balb/c mouse strains. Altogether, these results are a basic prerequisite for the further development of NK cell therapy protocols in murine in vivo models.