Insights into Keratinocyte and Immunologic Landscape in Cutaneous Graft-Versus-Host Disease through Single-Cell Transcriptomics.

Cutaneous manifestations are the most common presenting sign of chronic graft-versus-host disease (GVHD), and the extent of cutaneous involvement is also highly correlated with prognosis. Very little is understood about the underlying pathogenesis underpinning injury at this location, especially the contribution of keratinocytes and other structural skin cells. We performed single-cell RNA sequencing to compare the transcriptome of epidermal and dermal chronic GVHD samples with that of healthy control samples. Our findings reveal unique nonimmunologic and immunologic changes in epidermal keratinocytes and dermal immune cells. Specifically, we observed upregulation of alarmins and inflammatory cytokines and downregulation of anti-reduction-oxidation and activator protein-1 pathway genes in the keratinocyte compartments. In dermal immune cell subsets, we showed increased CD8(+) T, CD4(+) T, CD4(+)Foxp3(+) regulatory T, and NK cells in chronic GVHD, accompanied by increased signals of leukocyte functions, inflammatory responses, cytolysis, and macrophage M1 polarization. Finally, we also delineated the donor versus recipient cellular origin of nonimmune and immune cell populations in sex-mismatched chronic GVHD. Taken together, these data reveal complex keratinocyte and immune responses in cutaneous chronic GVHD, supporting future studies of skin cell contributions to pathogenesis and potential local treatment strategies.