Expansion of CD16+ CD56+ NK cells in vericyte® NK cell growth medium

Natural Killer (NK) cells play a key role in host resistance to virus and tumour. These cells are potent killers of virus infected and tumour cells via a direct recognition of the target by activation receptor such as NKG2D or by inducing Fcγ receptor (FcγRIII, CD16) mediated antibody dependent cellular cytotoxicity (ADCC). Current NK cell-based cancer immunotherapy aims to produce large amounts of functional NK cells, unfortunately most culture media used for NK cell expansion induced the downregulation of CD16 on NK cells. Here, we tested the impact of a new NK cell growth medium (Vericyte® from Medicyte) on CD16 expression.
Sorted NK cells and peripheral blood mononuclear cells (PBMC) were cultivated in vericyte® NK cell growth medium and cells issued from these cultures were characterized in term of expansion and phenotype at several time points.
After 5 days of culture, an expansion of both NK cells and PBMC was observed and maintained at least until day 20 of culture. In PBMC cultures, we observe only a small preferential NK cell growth since NK cells were around 5-10% at beginning of the culture and this percentage increased to 15% at the end of the culture. However, these cells showed a high proliferative potential when we started the culture with sorted NK cells (the proportion of contaminant cells remain low, under 5%). NK cells expressed CD56 and NKp46 and interestingly after a decreased expression of CD16 on the cell surface at day 3, this receptor was up regulated and most of the cells are CD56bright CD16bright from day 7 to day 12. According FACS FCS/SSC dot plot, NK cells acquired morphology of large activated lymphocytes and some of them expressed activation markers such CD25. Finally, these cells were able to kill efficiently tumour cell line K562.
Thus our data show that vericyte® NK cell growth medium allows the expansion of functional CD16+CD56+ NK cells. Cytokine production and ADCC function are under investigation.