Sirp-α Antibody Inhibits Renal Cell Carcinoma Progression via Akt1/Akt2 Modulation in Tumor-Associated Macrophages.

Introduction and aim: Immunotherapies targeting tumor-associated macrophages (TAM) to improve antitumor immunity, are promising treatment strategies for many types of cancer. The signal-regulatory protein-α (Sirp-α)/CD47 axis is a key innate immune checkpoint target important in regulating phagocytosis in macrophages. We aimed to determine whether a Sirp-α monoclonal antibody (mAb) could prevent renal cell carcinoma (RCC) progression by acting on macrophages and modifying their phenotype.

Methods: We explored the gene expression signature of macrophages in the RCC microenvironment by analyzing transcriptome data of blood monocytes from patients with RCC vs healthy donors, and macrophages vs non-immune cells in RCC from public databases. We characterized the prevailing macrophage polarization phenotypes and the different ratios of Akt1 and Akt2 in RCC according to cell surface markers and expression profiles, prior to examining the effect of Sirp-α mAb on the M2 macrophage polarization in an in vitro co-culture model of RCC cells with macrophages. The co-culture model included human RCC cell lines and induced M2 macrophages, including a subset that had been transfected to overexpress phosphoinositide 3-kinase (PI3K).

Results and conclusion: Treatment of RCC with Sirp-α mAb counteracted the enhanced migration and invasion of RCC as measured in wound healing and transwell assays and in vivo model. Collectively, our data showed that the different ratio of Akt1 and Akt2 of the PI3K/Akt pathway is involved in the RCC-induced M2 polarization of macrophages and that a new mechanism that the Sirp-α mAb inhibited M2 macrophage polarization by regulating components of the PI3K/Akt pathway. Elucidating the mechanism by which Sirp-α mAb inhibits the development of RCC allows us to provide a new theoretical basis for the study of the mAb in RCC immunotherapy.