A Novel Natural Killer Cell Expansion Technology for the Development of Cellular Immunotherapies

Abstract Adoptive cell therapy based on Natural Killer (NK) cells holds great promise for the treatment of cancer. For all approaches aiming at utilizing NK cells in immunotherapy, efficient ex vivo expansion technologies for the generation on of cytotoxic NK cells are a prerequisite for clinical translation. In this study, a novel multifunctional fusion protein consisting of a CD20-directed Fab-fragment, an agonistic anti-4-1BB single-chain Fragment variable (scFv), the Sushi domain of the interleukin (IL)-15 receptor and human IL-15 was generated. This molecule triggered strong NK cell expansion when bound to co-cultivated autologous B cells, due to trans-presentation of IL-15 and binding to 4-1BB/CD137. Expansion rates of up to 7,500-fold were achieved and the NK cells showed high cytotoxic capacity against a panel of tumor cell lines representing various tumor entities. Importantly, the activated NK cells did not show cytolytic activity against non-malignant B cells indicating that NK cells amplified by our novel approach were still physiologically regulated. The cytotoxic activity of the expanded NK cells was further enhanced by combination with therapeutic antibodies. Our molecule was additionally able to trigger efficient proliferation of NK cells from cord blood as well as multiple myeloma (MM) and acute myeloid leukemia (AML) patients. In conclusion, our novel platform technology provides ex vivo expansion of NK cells by using a single multifunctional fusion protein and may be well-suited for the development of NK cell-based immunotherapies. Key points A novel fusion protein that enables NK cell expansion from different sources including peripheral blood, bone marrow and cord blood Competing Interest Statement The authors have declared no competing interest.