PD-1H/VISTA expressed on host myeloid cells regulates acute graft-versus-host disease (aGVHD)

Abstract

Abstract Programmed Death-1 Homolog (PD-1H, also known as VISTA) is a co-inhibitory molecule of the immunoglobulin superfamily and broadly found in hematopoietic cells. We previously demonstrated that PD-1H agonists prevent aGVHD in a murine MHC mismatched bone marrow (BM) transplantation model. aGVHD occurs when donor T cells are primed and activated by host antigen-presenting cells (APCs). PD-1H agonism suppressed donor allogeneic T cell activation leading to the suppression of aGVHD. However, it remains unknown whether PD-1H agonists also suppress host myeloid APCs, in which PD-1H is highly expressed. To test this, we adoptively transferred wildtype (WT) C57B/L6 (B6) BM into either PD-1H knock-out (KO) or WT BALB/c mice as hosts. PD-1H KO host mice had more severe aGVHD clinical scores and a worse survival rate when compared to WT host mice. To determine whether PD-1H agonism impacts host immune cells, we transferred B6 PD-1H KO BM into BALB/c WT host mice and treated host recipients with or without PD-1H agonists. Consistent with prior data, host mice treated with PD-1H agonists suppressed aGVHD and extended survival compared with isotype control treated mice. To test which cell subsets expressing PD-1H in host mice regulate aGVHD, we transferred WT BALB/c BM into myeloid lineage specific KO of PD-1H or WT littermate hosts. Interestingly, the myeloid lineage specific KO mice host had significantly worse survival rates and worse aGVHD symptoms compared with WT littermates. Our studies indicate that PD-1H expression on host myeloid cells regulates aGVHD in addition to donor T cell PD-1H. Finding new mechanisms of PD-1H agonism on aGVHD enables development of future therapeutic approaches for aGVHD treatment, such as myeloid APC suppression. Supported by an Edward P. Evans Foundation Young Investigator Award, a Conquer Cancer Foundation American Society of Clinical Oncology Career Development Grant, and an American Cancer Society Clinician Scientist Development Grant