Semaphorin 3A reduces the severity of aGVHD by promoting M2 macrophage polarization

Acute graft-versus-host disease (aGVHD) remains a serious complication allogeneic hematopoietic stem cell transplantation (allo-HSCT) and significantly impacts nonrelapse mortality (NRM). While Semaphorin 3A (Sema3A) is implicated in immune regulation during inflammatory conditions, its role in aGVHD pathogenesis was unclear. Using an aGVHD mouse model, intravenous recombinant Sema3A administration demonstrated therapeutic effects, significantly reducing tissue damage in target organs observed via histopathological analysis. Flow cytometry and immunofluorescence staining revealed an increased proportion of M2 macrophages (CD206⁺) in vivo. In vitro treatment of RAW264.7 murine macrophages with Sema3A promoted polarization towards the M2 phenotype, characterized by elevated expression of Arg1 and IL-10, and inhibited T cell function. Transcriptome sequencing of treated macrophages identified suppressed IL-17 signaling, which was validated by qPCR and western blot showing significant decreases in mRNA and protein levels of both IL-17A and its receptor IL-17RA. These findings indicate that Sema3A mitigates aGVHD by driving M2 macrophage polarization through inhibition of the IL-17 signaling pathway, thereby suppressing pathogenic T cell responses, highlighting its potential as a therapeutic target.