Development of OX40 ligand-expressing feeder cell-based NK cell expansion method

Abstract

Natural killer (NK) cell-based immunotherapy used to treat cancer requires the adoptive transfer of a large number of activated NK cells. To increase NK cells in numbers and improve their antitumor activity for clinical applications, ex vivo cultivation is a effective method. Recently, a remarkable activation and expansion of NK cells was achieved using K562 cells genetically engineered to express cytokines and co-stimulatory factors and additional novel co-stimulatory factors for NK cell activation and expansion are continuously being sought. In addition, the mechanism of NK cell expansion through the interaction between genetically engineered feeder cells expressing co-stimulatory factors and NK cells has not been elucidated. To address this problem, we developed genetically engineered K562 feeder cells expressing OX40 ligand (K562-OX40L). Using this new feeder cells, we systematically studied the roles of OX40 ligand for NK cell expansion. First, we demonstrated that NK cell purity, expansion rate were significantly augmented cultured with K562-OX40L compared to conventional K562. Second, we identified transient exposure to IL-21 had a synergistic effect with OX40 signaling for NK cell expansion. Finally, we demonstrated that homotypic interaction between NK cells through the OX40-OX40L axis is necessary for NK cell expansion.