Umbilical cord blood as a promising source of NK cells for immunotherapy

Currently, a large number of studies on genetic modification of cord blood NK cells (UCB-NK) are carried out at both clinical and preclinical levels. Immunotherapy based on UCB-NK cells has great potential for antitumor therapy. However, despite having known several advantages over peripheral blood NK cells (PB- NK), including a high concentration in cord blood and low virulence rate, UCB-NK cells are predominantly characterized in the scientific literature as immature and low-functioning NK cells. In this work, we studied the phenotypic characteristics of UCB-NK cells and the possibility of stimulatory compensation of the decreased functional activity of UCB-NK cells. Our studies revealed UCB-NK cells can be characterized as poorly differentiated and weakly activated cells with high level of inhibitory receptor NKG2A and low level of activating receptor NKG2C and HLA-DR, accordingly with the literature data. Two types of stimuli were chosen to stimulate freshly isolated UCB-NK cells: 1) 100 units of IL-2; 2) combinations of 100 units IL-2 and K-562 feeder cells expressing membrane-bound IL-21 (K562-mbIL21). It was shown the degranulation (LAMP-1) and proliferative activity was higher than for parallel cultured ex vivo PB-NK cells under the same conditions for UCB-NK cells stimulated for 7 days with IL-2 + K562-mbIL21. Moreover, stimulation in the way of IL-2 + K562-mbIL21 seemed to be a more perspective way to obtain a large number of proliferatively active UCB-NK cells compared to stimulation with IL-2 only. Since genetic modification of NK cells is a promising way to improve the antitumor properties of NK cells, retroviral transduction procedure was performed to study of the stimulated UCB-NK cells. UCB-NK cells stimulated with IL-2 + K562-mbIL21 were transduced on day 8 of cultivation. In this study, we used targeted overexpression of the adaptor molecule DAP12, which is involved in the signaling of activating NK cell receptors. PB-NK cells and UCB-NK cells were transduced under the equal experimental conditions in same volume of viral particles. As a result, the transduction efficiency was found to be more than 4-fold higher for UCB-NK cells compared to PB-NK cells. Thus, UCB-NK cells appear to be a promising tool for further research in cancer immunotherapy.