Single-cell RNA sequencing reveals an exhausted immune landscape in human sclerotic chronic graft-versus-host disease

Summary: We aimed to investigate the cell types and signals that produce human cutaneous sclerotic chronic graft-versus-host disease (cGVHD), a highly morbid complication of allogeneic hematopoietic stem cell transplantation. Using single-cell RNA sequencing, we compared the predominant skin cell populations of sclerotic cGVHD patients (n=8) and normal skin controls (n=8). An increased proportion of CD8+ T cells were identified in affected skin from sclerotic cGVHD patients compared to normal skin controls that were characterized by an exhausted phenotype, expressing <i>PDCD1</i>, <i>LAG3</i>, and <i>TNFRSF9, </i>with unaffected skin showing an intermediate phenotype<i>.</i> Additionally, a population of <i>CXCL13+ </i>T follicular helper cells was identified most prominently in sclerotic cGVHD skin, expressing <i>PDCD1, LAG3, </i>and<i> TIGIT</i>. These exhausted T cell populations are likely induced by chronic alloantigen stimulation in the setting of cGVHD, and published murine data suggest that exhausted progenitor CD8+ T cells maintain GVHD. Distinct profibrotic myeloid cell populations were also identified in affected skin, along with <i>SFRP4+/ADAM12</i>+ myofibroblasts, which have been identified in skin in systemic sclerosis. While sclerotic cGVHD pathogenesis is believed to be initiated by tissue damage, promoting innate immune activation, recruitment of alloreactive lymphocytes, macrophage activation and fibroblast extracellular matrix deposition, the specific mediators and cell types required for disease have not been defined, and this study identifies key subsets of cells in affected skin. Additionally, as cellular therapy is being investigated as a means to treat fibrosis, identifying distinct markers in fibrotic skin will provide potential drug targets in the future. Tracy Tabib⁴, Jaemin Byun¹, Paul Chu⁵, Steven Pavletic³, Edward Cowen², Binfeng Lu¹, Robert Lafyatis⁴, Jishnu Das⁴, Rachel Rosenstein¹ 1. Hackensack Meridian Hackensack University Medical Center, Hackensack, NJ, United States. 2. National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD, United States. 3. National Cancer Institute Center for Cancer Research, Bethesda, MD, United States. 4. University of Pittsburgh, Pittsburgh, PA, United States. 5. Bridge Dermpath, Tarrytown, NY, United States. Cell Communication Networks and Stromal Biology