Expanded clinical-grade membrane-bound IL-21/4-1BBL NK cell products exhibit activity against acute myeloid leukemia in vivo

Background Adoptive NK cell infusion is a promising immunotherapy for acute myeloid leukemia (AML) patients. The aim of this study was to test the activity of clinical-grade membrane-bound IL-21/4-1BBL-expanded NK cell products against AML in vivo. Methods Fresh peripheral blood mononuclear cells (PBMCs) were incubated with equal numbers of irradiated membrane-bound IL-21/4-1BBL-expressing K562 cells for 2-3 weeks to induce clinical-grade NK cell expansion. Results Expansion for 2 and 3 weeks produced similar to 4 and 8 x 10(9) NK cells from 2 x 10(7) PBMCs. The production of CD107a and TNF-alpha in NK cell products in response to AML cell lines and primary blasts was higher than that observed in resting NK cells. The 2-week expanded NK cell products were xenografted into immunodeficient mice with leukemia and were persistently found in the BM, spleen, liver, lung, and peripheral blood for at least 13 days; furthermore, these expanded products reduced the AML burden in vivo. Compared with matched AML patients with persistent or relapsed minimal residual disease (MRD+) who underwent regular consolidation therapy, MRD+ patients who underwent NK treatment had better overall survival and showed no major adverse events. Conclusions Clinical-grade mbIL-21/4-1BBL-expanded NK cells exhibited antileukemic activity against AML in vitro and in vivo.