Project Summary Approximately 20% of all human cancers contain a mutation in the KRAS oncogene that drives their growth and metastasis. Novel KRAS inhibitors have recently been developed that disable these growth signals. Although they help patients live longer, KRAS inhibitors are unlikely to cure patients. For this reason, there is a need to identify more effective ways to treat KRAS mutant cancers. Based on the success of cancer immunotherapy, an appealing strategy has been to combine targeted therapies with agents that activate the immune system to attack. Macrophages are cells of the innate immune system and are often the most common infiltrating immune cell in solid tumors. The CD47/SIRPa axis is a key regulator of macrophage activation in the tumor microenvironment and acts as a “don’t eat me” signal. Anti-CD47 antibodies that block this macrophage immune checkpoint can stimulate macrophage activation against cancer. In this proposal, we hypothesize that KRAS inhibitors make cancer cells more vulnerable to macrophage-mediated destruction, and consequently, that KRAS inhibitors will synergize with anti-CD47 antibodies to eliminate KRAS mutant cancers. Our overall goal is to convert KRAS-targeted therapies into curative therapies by engaging macrophages as effectors. To investigate potential synergy between KRAS inhibitors and anti-CD47 antibodies, we have developed a novel in vitro co-culture assay to evaluate macrophage-mediated destruction of cancer. We will use this assay to measure synergy between KRAS inhibitors and anti-CD47 antibodies (Aim 1). We will investigate the mechanism of synergy by assessing how KRAS inhibitors change the expression and function of other immunoregulatory molecules on the surface of KRAS mutant cancer cells. Next, we will test the combination therapy in xenograft mouse models of KRAS mutant cancer to evaluate for enhanced anti-tumor immunity in vivo (Aim 2). Finally, we will investigate the effects of the combination therapy in immunocompetent, syngeneic tumor models to understand how the combination therapy alters interactions between the innate and adaptive immune systems. Overall, we propose a novel mechanism to enhance the efficacy of KRAS inhibitors by merging the fields of immuno-oncology and precision medicine. We expect our findings to provide the rationale for rapidly translating this combination strategy to the clinic to benefit patients with KRAS mutant cancer.