Expansion and Activation of Human Natural Killer Cells ex vivo in the Presence of Transgenic Feeder Cells

Preliminary results of clinical trials show that the use of activated and expanded ex vivo natural killer cells is a promising tool for adoptive immunotherapy of acute myeloid leukemia, as well as a number of solid tumors, when used together with targeted monoclonal antibodies. However, the introduction of this approach into clinical practice is limited by the possibility of obtaining a sufficient amount of the NK cell product with required characteristics. To solve this problem, we obtained transgenic feeder cells based on immortalized K562 cells expressing the recombinant membrane-bound variant of human interleukin-21 and 4-1BBL protein. Cocultivation of mononuclear cells obtained from the peripheral blood of ten healthy donors with genetically modified feeder cells resulted in significant expansion of natural killer cells (median expansion fold 21 589 times; minimum, 3150 times; maximum, 304 328 times) with a minimum content of T-cells (median, 0.5%; minimum, 0.06%; maximum, 4.7%) compared with their initial number. NK cells obtained in this way were not contaminated with the BCR–ABL1 oncogene from feeder cells and had a lower expression of c-MYC protooncogene compared to the initial level.