Multivalent protein nanocages improve the safety profile of cluster of differentiation 47 checkpoint blockade

Protein-based nanocages are emerging as promising platforms for next-generation medicine because of their programmable architecture, biocompatibility, and capacity for functional integration. In the field of immunotherapy, these properties offer a structural basis for overcoming key limitations of conventional antibody-based therapeutics, where potent checkpoint blockade activity is often accompanied by systemic toxicity. Here, we demonstrate that a ferritin-signal regulatory protein alpha (SIRPα) protein nanocage maintains the therapeutic function of cluster of differentiation 47 (CD47)-SIRPα blockade while reducing the hematologic liabilities associated with CD47-targeting monoclonal antibodies. Although the CD47-SIRPα axis is a compelling innate immune checkpoint target broadly implicated in tumor immune evasion, anti-CD47 antibodies have been limited by the widespread expression of CD47 on both tumor cells and normal erythrocytes, which can result in dose-limiting hematologic toxicity. By displaying multivalent SIRPα domains on a self-assembling ferritin scaffold, ferritin-SIRPα achieves CD47 engagement through a structurally distinct, Fc-independent nanocage architecture. In direct comparison with anti-CD47 antibody, ferritin-SIRPα showed no hemagglutination at equivalent or higher doses, preserved near-complete viability across diverse immune and hematopoietic cell types, and avoided the reduction in RBC counts observed with anti-CD47 antibody treatment in vivo. Ferritin-SIRPα induced macrophage-mediated tumor cell phagocytosis under single-agent conditions, with further enhancement observed upon combination with EGFR antibody-mediated opsonization, indicating that its innate immune engagement remains functionally intact. These findings demonstrate that multivalent protein nanocage architecture can decouple antitumor immune activity from erythrocyte-associated toxicity. Broadly, this study highlights the potential of protein nanocages as a versatile therapeutic platform for preserving functional efficacy while mitigating off-target adverse effects, offering a structural strategy that may help improve the therapeutic window of next-generation immunotherapies.