Absence of CD47 in the tumor microenvironment modulates tumor metabolism and immunosuppressive signatures limiting breast cancer progression.

Abstract

The majority of breast cancers are generally considered immune-deprived tumors. This lack of immunogenicity severely hinders effectiveness of current immunotherapy approaches limiting therapeutic options to control disease. Therefore, we need new biomarkers to determine and enhance immune responses to improve the outcome of cancer patients experiencing invasive disease. Our data in matched human patient biopsies show that CD47 expression increases from primary to metastatic tumors. CD47 is an integral membrane protein that impairs antitumor immunosurveillance and influences normal tissue metabolism. However, whether CD47 plays a role in regulating tumor bioenergetics is unknown. A carcinogen-induced mouse mammary carcinogenesis model demonstrates that the absence of CD47 reduces tumor burden, which is associated with a distinct metabolic signature compared to WT tumors. Depletion of several lipid metabolites was observed in the absence of CD47, and metabolic dependency experiments suggest that anti-sense blockade of CD47 limits reliance on fatty acid oxidation as a fuel supporting cellular respiration on cancer cells. Our global metabolomics analysis also implicated the absence of CD47 in downregulation of immunosuppressive metabolites of the tryptophan and prostaglandin pathways. Spatial proteomic analysis revealed increased immune infiltrate and substantial reduction in immunosuppressive immune checkpoint proteins in the absence of CD47 with the highest reduction in intra-tumoral PD-L1 expression. Since anti-PD-L1 therapy is used in the current strategy to treat triple-negative breast cancer (TNBC), we targeted CD47 in an EMT-6 syngeneic TNBC model. The in vivo knockdown of CD47 sensitized tumors to anti-PD-L1 therapy to decrease tumor burden and increase intratumoral cytotoxic T cells. Therefore, targeting CD47 may be a suitable immunotherapeutic option to limit immunosuppression and enhance the efficacy of immune checkpoint blockade.