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Cluster of differentiation 47 (CD47) delivers an inhibitory signal that suppresses phagocytosis and prevents immune clearance of tumor cells by interacting with signal regulatory protein alpha (SIRPα) on myeloid cells. Although blockade of the CD47-SIRPα axis is a promising immunotherapeutic strategy, clinical development has been hindered by on-target toxicities (e.g., severe anemia) and insufficient potency. Herein we report a third generation CD47-SIRPα inhibitor HCB101, a rationally designed SIRPα-Fc fusion protein generated from a large-scale screening of a structure-guided SIRPα extracellular domain (ECD) mutant library and fused to a human IgG4 Fc. HCB101 demonstrates high-affinity binding to CD47, robustly promotes macrophage-mediated phagocytosis of tumor cells without affecting red blood cells and exhibits unique advantages over current CD47-targeting agents, including Hu5F9-G4, TTI-622, and ALX148. In multiple xenograft cancer models, HCB101 induced significant inhibition of tumor growth as a single agent and showed synergistic anti-tumor effects when combined with anti-HER2 or anti-EGFR monoclonal antibodies. Additionally, HCB101 treatment increased the M1/M2 macrophage ratio in the tumor microenvironment, suggesting repolarization of tumor-associated macrophages (TAMs) toward a pro-inflammatory phenotype. No dose-limiting toxicities or hematologic adverse effects were observed in murine or non-human primate studies.