Our long-term goal is to improve the efficacy of EGFR family-directed monoclonal antibody therapy with the overarching hypothesis that antibodies can be combined with other anti-tumor agents to promote host- protective adaptive immunity that improves cancer therapy. In the current funding period we have 1) defined tumor cell based determinants of anti-tumor efficacy and promotion of antibody-dependent cellular cytotoxicity (ADCC) such as c-Abl and protein kinase C-, 2) demonstrated that effective antibody therapy promotes host-protective immune responses, and 3) employed a novel shRNA library screening strategy to identify Tex9 and other tumor cell-based determinants of immune rejection. We now propose to translate these findings into the clinic, and to develop innovative new approaches to improve antibody- initiated tumor rejection. The first aim is to define EGFR network-related signaling following therapy with cetuximab, nilotinib or the combination in a Phase I clinical trial of these drugs in patients with solid tumors.The second aim is to enhance antibody-dependent cellular cytotoxicity (ADCC) and improve its in vivo anti-tumor effects. We will test the hypotheses that 1) nilotinib therapy or protein kinase C- knockdown enhance ADCC and subsequent antigen presentation, and 2) strategies to enhance ADCC promote the anti-tumor effects of cetuximab.The third aim is to identify new tumor cell-based molecular determinants of immune rejection in murine models. We have screened a barcoded murine whole-genome shRNA library in vivo and identified genes whose knockdown in EO771 breast tumor cells selectively enriches or depletes such cells in tumors in NSG, WT C57Bl/6 and SCID C57Bl/6 mice. We hypothesize that in vivo genomic screening can identify new targets that alter immune rejection initiated by monoclonal antibody therapy or vaccination. The successful execution of this work will have high impact by 1) defining the value of synthetic lethal screening to identify MAb-based combinations (Aim 1), 2) demonstrating new ways to promote ADCC-induced host protection (Aim 2), and 3) defining new targets and pathways that regulate tumor cell-based sensitivity and resistance to antibody-initiated host immunity (Aim 3). These results will have resonance for the field of tumor immunity. RELEVANCE (See instructions): Monoclonal antibodies (MAb) are useful treatments for many tumor types, but new approaches are needed to improve therapy outcomes. We aim to improve the ability of MAb to directly kill cancer cells, and to stimulate the body's immune system so that people can be immunized against their cancers to prevent or delay relapse or disease worsening.