Critical role of host γδ T cells in experimental acute graft-versus-host disease

γδ T cells localize to target tissues of gratt-versus-host disease (GVHD) and therefore we investigated the role of host γδ T cells in the pathogenesis of acute GVHD in several well-characterized allogeneic bone marrow transplantation (BMT) models. Depletion of host γδ cells in wild-type (wt) B6 recipients by administration of anti-T-cell receptor (TCR) γδ monoclonal antibody reduced GVHD, and γδ T-cell-deficient (γδ^-/-) BM transplant recipients experienced markedly improved survival compared with normal controls (63% vs 10%, P < .001). γδ T cells were responsible for this difference because reconstitution of γδ^-/- recipients with γδ T cells restored GVHD mortality. γδ^-/- recipients showed decreased serum levels of tumor necrosis factor α (TNF-α), less GVHD histopathologic damage, and reduced donor T-cell expansion. Mechanistic analysis of this phenomenon demonstrated that dendritic cells (DCs) from γδ^-/-recipients exhibited less allostimulatory capacity compared to wt DCs after irradiation. Normal DCs derived from BM caused greater allogeneic T-cell proliferation when cocultured with γδ cells than DCs cocultured with medium alone. This enhancement did not depend on interferon γ (IFN-γ), TNF-α, or CD40 ligand but did depend on cell-to-cell contact. These data demonstrated that the host γδ T cells exacerbate GVHD by enhancing the allostimulatory capacity of host antigen-presenting cells.