hIL-15-gene modified human natural killer cells (NKL-IL15) exhibit anti-human leukemia functions

Natural killer (NK) cells can kill transformed cells and represent anti-tumor activities for improving the immunotherapy of cancer. In previous works, we established human interleukin-15 (hIL-15) gene-modified NKL cells (NKL-IL15) and demonstrated their efficiency against human hepatocarcinoma cells (HCCs) in vitro and in vivo. To further assess the applicability of NKL-IL15 cells in adoptive cellular immunotherapy for human leukemia, here we report their natural cytotoxicity against leukemia in vitro and in vivo.

Flow cytometry, ELISA and MTT methods were performed for molecular expression, cell proliferation and cytotoxicity assays. Leukemia xenograft NOD/SCID mice were established by subcutaneous injection with K562 cells, and then treated with irradiated NKL cells.

We found NKL-IL15 cells displayed a significant high cytolysis activity against both human leukemia cell lines and primary leukemia cells from patients, accompanied with up-regulated expression of molecules related to NK cell cytotoxicity such as perforin, granzyme B and NKp80. Moreover, cytokines secreted by NKL-IL15 cells, including TNF-α and IFN-γ, could induce the expression of NKG2D ligands on target cells, which increased the susceptibility of leukemia cells to NK cell-mediated cytolysis. Encouragingly, NKL-IL15 cells significantly inhibited the growth of leukemia cells in xenografted NOD/SCID mice and prolonged the survival of tumor-bearing mice dramatically. Furthermore, NKL-IL15 cells displayed stimulatory effects on hPBMCs, indicating the immunesuppressive status of leukemia patients could be improved by NKL-IL15 cell treatment.

These results provided evidence that IL-15 gene-modification could augment NK cell-mediated anti-human leukemia function, which would improve primary NK cell-based immunotherapy for leukemia in future.