Augmenting Natural Killer cell antibody binding to enhance ovarian and prostate tumor cell killing via ADCC

Abstract

Ovarian cancer and metastatic castration resistant prostate cancer (mCRPC) are a leading cause of cancer-related deaths worldwide. Natural killer (NK) cells are cytotoxic lymphocytes that rapidly kill tumor cells via antibody-dependent cell-mediated cytotoxicity (ADCC). ADCC is exclusively mediated by the IgG Fcγ receptor (FcγR) CD16A, and many clinically successful therapeutic monoclonal antibodies (mAbs) utilize ADCC as a mechanism of action to eradicate tumor cells. However, CD16A binds IgG with low affinity and is rapidly cleaved by ADAM17 upon activation, limiting therapeutic mAb efficacy. NK adoptive cell transfer has been shown to be effective for treating many cancer types, but strategies that enhance NK cell cytolytic activity have not been thoroughly investigated for the treatment of ovarian cancer or mCRPC. My research focused on developing approaches to boost CD16A function to improve the efficacy of mAbs. To enhance NK cell binding to tumor-targeting mAbs and subsequent ADCC, we generated a novel high-affinity recombinant FcγR, referred to here as CD64/16A. CD64/16A consists of the extracellular region of CD64, the highest affinity IgG FcγR, and the transmembrane and intracellular regions of CD16A. We expressed CD64/16A in human NK-92 cells, a cell line that lacks expression of endogenous FcγRs but mediates ADCC upon expression of CD16A. My studies show that CD64/16A is functional in vitro and can facilitate ADCC of ovarian cancer cell lines. We also expressed wild-type CD64 in the NK cell line NK-92 MI, which can produce its own IL-2 for expansion and persistence. We show that CD64 can signal through CD3ζ to kill metastatic castration resistant prostate cancer cells as well as tumor-associated stromal cells via ADCC. My studies also address the in vivo persistence, variation, and scalability of NK cell lines or primary NK cell sources by generating of iPSC-derived NK cells (iNK) expressing CD64/16A with and without an IL-15 receptor fusion protein. I show that iNK-CD64/16A cells stay bound to a tumor-targeting mAb payload after cryopreservation and that robust ADCC is maintained both in vitro and in vivo in the presence of saturating human IgG. This work has provided new insights into using Fc receptor based adoptive cell therapies and lays the preclinical foundation necessary for developing an “off the shelf” NK cell-based immunotherapy for the treatment of ovarian cancer.