Host Tissue PD-L1 Separates GVL Effect from Gvhd after Temporary Depletion of Donor CD4 + T Cells Early after HCT

Recipient tissue expression of programmed death-ligand 1 (PD-L1, B7H1) down-regulates graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT), but this information has not been translated clinically. Here we demonstrate a critical role for recipient PD-L1 expression in preventing both acute and chronic GVHD while preserving graft-versus-leukemia (GVL) effects when donor CD4 + T cells are temporarily depleted in vivo early after HCT. Depletion of donor CD4 + T cells increases serum IFN-γ concentrations and enhances recipient tissue expression of PD-L1 and donor CD8 + T cell expression of the PD-L1 receptors CD80 and PD-1. In GVHD target tissues, depletion of CD4 + T cells increases anergy and apoptosis of infiltrating CD8 + T cells in a manner that depends on recipient PD-L1 expression, thereby preventing damage to intestinal Paneth cells and stem cells, hepatocytes, and thymic medullary epithelial cells, and preventing both acute and chronic GVHD. In lymphoid tissues, depletion of CD4 + T cells augments CD8 + T cell proliferation without increasing CD8 + T cell anergy or apoptosis, resulting in expansion of donor CD8 + T cells and strong GVL effects. Therefore, temporary depletion of donor CD4 + T cells early after HCT represents a novel approach for preventing GVHD while preserving GVL effects. This work was supported by NIH R01 AI066008 and Nesvig Lymphoma Fundation (to D.Z.) and by NSFC 81090413, 81270638 (to J.W.). Disclosures Forman: Amgen: Consultancy; Mustang: Research Funding. Martin: Neovii: Research Funding; RegImmune: Research Funding; Enlivex: Consultancy; Janssen: Consultancy; Pfizer: Consultancy; Pharmacyclics: Consultancy.