Phase I Study: Safety and Efficacy of an Ex Vivo-Expanded Allogeneic Natural Killer Cell (MG4101) with Rituximab for Relapsed/Refractory B Cell Non-Hodgkin Lymphoma

Reprogramming natural killer cells for cancer therapy

The last decade has seen rapid development in the field of cellular immunotherapy, particularly in regard to chimeric antigen receptor (CAR)-modified T cells. However, challenges, such as severe treatment-related toxicities and inconsistent quality of autologous products, have hindered the broader use of CAR-T cell therapy, highlighting the need to explore alternative immune cells for cancer targeting. In this regard, natural killer (NK) cells have been extensively studied in cellular immunotherapy and were found to exert cytotoxic effects without being restricted by human leukocyte antigen and have a lower risk of causing graft-versus-host disease; making them favorable for the development of readily available "off-the-shelf" products. Clinical trials utilizing unedited NK cells or reprogrammed NK cells have shown early signs of their effectiveness against tumors. However, limitations, including limited in vivo persistence and expansion potential, remained. To enhance the antitumor function of NK cells, advanced gene-editing technologies and combination approaches have been explored. In this review, we summarize current clinical trials of antitumor NK cell therapy, provide an overview of innovative strategies for reprogramming NK cells, which include improvements in persistence, cytotoxicity, trafficking and the ability to counteract the immunosuppressive tumor microenvironment, and also discuss some potential combination therapies.

Potentiation of natural killer cells to overcome cancer resistance to NK cell-based therapy and to enhance antibody-based immunotherapy

Natural killer (NK) cells are cellular components of the innate immune system that can recognize and suppress the proliferation of cancer cells. NK cells can eliminate cancer cells through direct lysis, by secreting perforin and granzymes, or through antibody-dependent cell-mediated cytotoxicity (ADCC). ADCC involves the binding of the Fc gamma receptor IIIa (CD16), present on NK cells, to the constant region of an antibody already bound to cancer cells. Cancer cells use several mechanisms to evade antitumor activity of NK cells, including the accumulation of inhibitory cytokines, recruitment and expansion of immune suppressor cells such as myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs), modulation of ligands for NK cells receptors. Several strategies have been developed to enhance the antitumor activity of NK cells with the goal of overcoming cancer cells resistance to NK cells. The three main strategies to engineer and boost NK cells cytotoxicity include boosting NK cells with modulatory cytokines, adoptive NK cell therapy, and the employment of engineered NK cells to enhance antibody-based immunotherapy. Although the first two strategies improved the efficacy of NK cell-based therapy, there are still some limitations, including immune-related adverse events, induction of immune-suppressive cells and further cancer resistance to NK cell killing. One strategy to overcome these issues is the combination of monoclonal antibodies (mAbs) that mediate ADCC and engineered NK cells with potentiated anti-cancer activity. The advantage of using mAbs with ADCC activity is that they can activate NK cells, but also favor the accumulation of immune effector cells to the tumor microenvironment (TME). Several clinical trials reported that combining engineered NK cells with mAbs with ADCC activity can result in a superior clinical response compared to mAbs alone. Next generation of clinical trials, employing engineered NK cells with mAbs with higher affinity for CD16 expressed on NK cells, will provide more effective and higher-quality treatments to cancer patients.