Natural Killer cell immune engagers to induce optimal anti-tumor activity.

Abstract

NK cells are immune cells that recognize tumor transformed cells. However, their lack of tumor antigen specificity led us to design killer engagers that redirect NK cells towards tumor based on tumor antigen. Our group previously developed a Trispecific Killer engager (TriKE) which consists of an anti-CD16 component to engage NK cells, IL-15 for survival and proliferation and anti-CD33 for acute myeloid leukemia targeting. This work focuses on modifications that can enhance engaer functions. Firstly, CD16 is expressed on NK cells, monocytes and neutrophils. Neutrophils are a larger proportion of the peripheral blood cells which can lead to a sink effect when using CD16 as the NK cell engaging component. Secondly, while IL-15 is an important cytokine to NK cells, continuous IL-15 stimulation has been shown to induce exhaustion in NK cells. Changing the cytokine could change NK cell responses that would enhance the anti-tumor response. We hypothesize that changing the NK cell engaging components of the TriKE will enhance the NK cell response to tumor by becoming more NK cell specific and offer a more varied response from the NK cell. Thus we chose to target NKG2C, an activating receptor present on NK cells and a small subset of CD8 T cells, for the engaging portion of the NK cell. NKG2C+ cells are also enriched in adaptive NK cells which produce more cytokine than conventional NK cells. The NKG2C-killer engager (NKG2C-KE) which utilizes an anti-NKG2C component, IL-15, and anti-CD33 was able to target NKG2C+ cells towards CD33+ cells and selectively proliferate NKG2C+ cells. In combination with an induced pluripotent stem cell derived NK cell, the NKG2C-KE was also able to kill primary AML cells. Then to change the cytokine, we replaced IL-15 with IL-12, a potent anti-tumor cytokine. The IL12-KE which consisted of anti-CD16, IL-12 and anti-CD33 components effectively engaged NK cells in the presence of CD33+ cell lines. IL12-KE also induced abundant IFNγ production in NK cells even after exhaustion and induced dendritic cell maturation. These two killer engagers demonstrate enhancements that can make engagers more effective at inducing anti-tumor effects in NK cells.