Bone Morphogenetic Protein Signaling Pathway Modulation by Blocking Anti-Repulsive Guidance Molecule B Antibody Promotes Tolerance in Graft-Versus-Host Disease

Graft-versus-host disease (GvHD) is a major complication after allogeneic hematopoietic stem cell transplantation (HSCT). Current strategies to prevent GvHD with immunosuppressive drugs carry significant morbidity and may affect the graft-versus-tumor (GVT) effect. Bone morphogenetic protein (BMP) signaling plays an important role in developmental, physiologic, and pathologic processes. Repulsive guidance molecule b (RGMb) is a signaling hub and coreceptor that enhances BMP2, BMP4 and neogenin signaling in several cell types including antigen-presenting cells. Interaction between BMP2/BMP4/neogenin and RGMb molecules during antigen presentation can influence T cell responses in models of allergic airway disease. We hypothesized that neutralization of RGMb signaling using a monoclonal antibody suppressed GvHD allo-transplantation in vivo. RGMb expression was significantly increased in murine small intestine at 24 h post total body irradiation (TBI). In a HSCT murine model, anti-RGMb antibody was injected into the recipient mice with 3 doses on day −1, +3 and +7 post HSCT. Treatment with anti-RGMb but not the isotype control protected the recipient mice against Tcon-induced GvHD with statistically higher body weights and improved survival rate (75% versus 30% at 60 days post-HSCT, P < .05), while the GVT effect remains intact. Allogeneic Tcon transplantation induced cytokine expression of IFN-gamma, BMP2, and BMP4 in small intestine tissue. The expression was mitigated by anti-RGMb therapy via induction of IL-10 expression. Bioluminescence imaging showed that anti-RGMb reduced Tcon proliferation in vivo, but also, enhance CD4+ versus CD8+ T cells polarization. The phenotype was further confirmed in vitro that anti-RGMb treatment reduced both naïve CD4+ and naïve CD8+ T cell differentiation in the mixed lymphocyte reaction assay. This effect is also seen in the xenograft mice model with human PBMC transplanted into immuno-deficient NSG mice. The present study demonstrates the potent effects of blocking anti-RGMb antibody therapy to modulate the allograft immune responses. This therapy can be a target in prevention of GvHD following HSCT retaining GVT effect and possibly for other immune disorders likes autoimmunity.