Ex vivo-expanded allogeneic natural killer cells for the treatment of cancer

Abstract

Ex vivo-expanded, allogeneic natural killer (NK) cells can be used for the treatment of various types of cancer. In allogeneic NK cell therapy, NK cells from healthy donors must be expanded in order to obtain a sufficient number of highly purified, activated NK cells. In the present study, we established a simplified and efficient method for the large-scale expansion and activation of NK cells from healthy donors under good manufacturing practice (GMP) conditions. After a single step of magnetic depletion of CD3+ T cells, the depleted peripheral blood mononuclear cells (PBMCs) were stimulated and expanded with irradiated autologous PBMCs in the presence of OKT3 and IL-2 for 14 days, resulting in a highly pure population of CD3-CD16+CD56+ NK cells which is desired for allogeneic purpose. Compared with freshly isolated NK cells, these expanded NK cells exhibited activated phenotypes, and showed robust cytokine production and potent cytolytic activity against various cancer cell lines in vitro. In vivo anti-tumor efficacy of expanded NK cells was also verified by various xenograft mouse models. Furthermore, expanded NK cells expressing high levels of CD16 (FcγRIII) efficiently induced tumor regression mediated by antibody-dependent cellular cytotoxicity (ADCC) with extremely low dose of rituximab in Raji human B-cell lymphoma model Of note, cytolytic activity of expanded NK cells was focused on tumor targets while sparing normal cells in coculture assays, supporting the feasibility of clinical application of expanded NK cells for allogeneic NK cell therapy. In fact, no significant side effects have been noted in the phase I clinical study using expanded allogeneic NK cells. Genetic and phenotypic analyses of donor-versus-recipient incompatibility in vitro and in vivo suggested that the percentages of KIR-mismatched NK cells correlated with both in vitro anti-tumor cytotoxicity and clinical outcomes. Allogeneic NK cell therapy from KIR A/B donors seems to impro...