Discussion

We developed an animal component free medium for the culture and expansion of human NK cells. Addition of vericyte® proliferation factors to basal medium resulted in an induction of NK cell proliferation with an expansion rate of over 50-fold (compared to basal medium).
NK cells were cultured in medium supplemented with 10 % human serum AB and 1000 IU/mL IL 2 at an initial cell number of 105 NK cells per well. Cells were expanded for 4 weeks. For comparison, NK cells were cultured in medium without vericyte® growth factors. After a lag phase of one week NK cells started proliferating in medium containing vericyte® proliferation factors up to a cell number of 6 x 106 per well whereas control cells remained at the initial cell density.
Expanded NK cells retained primary cell characteristics as monitored by expression of NK cell marker (CD3-, CD16+, CD56+, NKp46+) and by determination of killing efficiency. NK cells proliferated in vericyte® NK cell medium showed slightly higher killing efficiency compared to freshly isolated NK cells. Cytotoxicity of NK cells was determined by incubation with K562 target cells in different ratios. Specific target cell lysis by NK cells was determined after 4 hours using the 51Cr-release method.
This study supports the use of Vericyte® NK cell growth medium to produce large NK cell batches with consistent quality.