Dissecting the immunomodulatory effects of NK cells on immune responses to cancer

PROJECT SUMMARY Current immunotherapies, such as anti-PD-1 immunotherapy, have low objective responses in patients, necessitating the development of novel therapies that boost immune responses to cancer and responses to these treatments. Further, most immunotherapies in the clinic, anti-PD-1 immunotherapy included, predominantly act on T cells. While combinations of T cell-directed therapies can lead to excellent outcomes for some, most patients still have no objective responses to combinations of these immunotherapies. Thus, it is imperative to identify novel therapeutic targets that work synergistically with anti-PD-1 immunotherapy and other T cell-directed therapies. Natural killer (NK) cells are innate lymphocytes that can control tumors through direct cytotoxicity or their immunomodulatory production of cytokines and chemokines. NK cell abundance in the tumor correlates with increased patient survival and patient responses to immunotherapies. We previously found that a key immunomodulatory function of NK cells is their production of the cytokine FLT3LG which regulates type 1 conventional dendritic cell (cDC1) abundance in the tumor microenvironment (TME). cDC1s are an important antigen presenting cell that shapes anti-tumor T cell responses. We found that NK cell production of FLT3LG regulates cDC1 abundance in the TME which leads to increased patient survival and responses to anti-PD-1 immunotherapy. We hypothesize that targeting the immunomodulatory effects of NK cells in the tumor microenvironment will lead to more protective cDC1s, better tumor-directed T cell responses, and increased efficacy of immunotherapies. Thus, it is critically important that we define how NK cells are regulated in the tumor microenvironment. In particular, the cellular and molecular mechanisms regulating NK cell phenotype and function in the tumor are unknown, and the molecular mechanisms controlling NK cell production of the cytokine FLT3LG are unknown. In Aim 1 of this project, we will determine tumor-intrinsic features that regulate NK cell phenotype and function in the tumor. In Aim 2, we will define the mechanisms that regulate NK cell production of Flt3L. In Aim 3, we will elucidate the mechanisms regulating NK cell phenotype and function in human metastatic melanoma. To address these aims we have developed ectopic tumor models and in vitro NK cell stimulation assays that allow us to define the molecular mechanisms regulating NK cell production of Flt3L. We have also developed complimentary human immunology studies of metastatic melanoma samples that allow for the study of NK cells and their immunomodulatory effects in a translational setting. The studies outlined in this proposal will provide answers to longstanding questions about how NK cell phenotypes and functions are regulated in the TME and will be foundational to the development of novel immunotherapies that target the immunomodulatory effects of NK cells to increase a patient’s immune response to cancer.