Project Summary Ovarian cancer continues to represent an unmet clinical need, as two-thirds of diagnosed patients eventually die of the disease and new therapeutics have made little impact over the past decade. In this proposal, we will utilize a novel panel of anti-MUC16 antibodies and our extensive knowledge of how Fc?-receptor (Fc?R) pathways contribute to the anti-tumor activities of therapeutic antibodies to perform a preclinical study for the optimization of anti-MUC16 antibodies for the treatment of ovarian cancer. MUC16 is an attractive target for antibody-based immune therapies for ovarian cancer because of its tissue-specific overexpression in most of the ovarian cancers. We have obtained a novel panel of monoclonal Abs (mAbs) against the extracellular portion of MUC16, and will characterize the in vivo mechanisms by which these mAbs mediate anti-tumor activities in novel syngeneic and spontaneous tumor models that express human MUC16. In Aim 1, we will determine the specific Fc?R interactions required by anti-MUC16 antibodies for their optimal in vivo anti-tumor activities by using Fc mutants and strains specifically lacking Fc?Rs. We will exploit these results and utilize our unique strain of Fc?R- humanized mice as a preclinical platform to develop humanized Fc-engineered anti-human MUC16 antibodies optimized for augmented in vivo anti-tumor activity. In Aim 2, we will exploit our recent finding that passive administration of cytotoxic anti-tumor antibodies stimulates and anti-tumor cellular immune reponses to determine whether combining anti-MUC16 mAb with immunomodulatory antibodies that also stimulate cellular anti-tumor immune responses synergistically enhances anti-tumor immunity. For these studies, we will focus on agonistic anti-CD40 and antagonist anti-CTLA-4 antibodies that have been Fc engineered for optimal engagement of the appropriate Fc?R pathways that mediate their effects in vivo. By testing humanized anti- MUC16 antibodies in a preclinical in vivo models expressing the human Fc?R pathways and human MUC16 as a target, the proposed research is highly translatable to human patients, and if successful, may lead to the development of specific clinical candidate antibodies for trials.