A novel feeder cell based on 4-1BBL and membrane-bound IL-21/IL-15 induce highly expansion and anti-tumor effect of natural killer cells.

Background: Natural killer (NK) cell immunotherapy is a promising approach for cancer treatment. However, its extensive clinical application was limited to the large-scale clinical-grade expansion of NK cells. In this study, we expanded NK cells from healthy donor's peripheral blood mononuclear cells (PBMCs) using a newly designed K562 feeder cell line.

Methods: The feeder cells were generated by transducing K562 cells with lentiviral particles carrying 4-1BBL and mbIL-21/-15. NK cells were expanded from PBMCs with these genetically modified, frozen-thawed and irradiated K562 feeder cells in the presence of IL-2. The purity, quantity, and receptors expression of the expanding NK cells were dynamically monitored. Furthermore, their anti-tumor efficacy was evaluated both in vitro and in vivo following a two-week expansion period.

Results: The K562-4-1BBL-mbIL-21/-15 feeder cells induced highly-efficient NK cells expansion from PBMCs (17902-fold) within two weeks. There was a notable upregulation in the expression of activating receptors including NKG2D, NKp30, NKp44, and NKp46 during the expansion process. Moreover, the expanded NK cells displayed enhanced cytotoxicity against a variety of hematological (K562, MOLM-13, OCI-AML-3, THP-1) and solid (Hep-G2, OVCAR3) cancer cell lines in vitro. In the humanized U937 xenograft mouse model, the NK cells extended the median survival time of the AML-bearing mice from 19.40 to 28.25 days.

Conclusions: We have successfully established a highly-efficient, cost-effective and rapid NK cell expansion platform from PBMCs utilizing K562-4-1BBL-mbIL-21/-15 feeder cells, which also significantly improved the cytotoxicity both in vitro and in vivo, presenting a significant advancement in the field of NK cell-based immunotherapy.