Corticosteroid resistance is predetermined by early immune response dynamics at acute Graft-versus-Host disease onset

Steroid-resistant acute graft versus host disease (SR-aGVHD) is the leading life-threatening complication following allogeneic hematopoietic stem cell transplantation. Novel therapeutics development is impeded by scares knowledge on biological pathways leading to steroid resistance at time of aGVHD diagnosis. To gain insight into our understanding on circulating immune cell subsets and functions at time of aGVHD, a single cell deep phenotyping and transcriptome analysis was performed on peripheral blood mononuclear cells from patients with aGVHD before steroid treatment or without aGVHD. We aimed at identifying biological patterns associated with steroid resistance at early onset of aGVHD. First, circulating immune cell subsets were associated with increased incidence of aGVHD, but not with steroid sensitivity. Then, pathway analysis and inferred ligand/receptor interactions revealed major functional divergences between steroid-sensitive (SS-) and SR-aGVHD, including enrichment of TNFα activation in SR-GVHD, as well as TNF/TNFR, CCL3, CCL4 and IL18 signaling, and decreased interferon α and γ signaling pathways, suggesting that steroid resistance in an intrinsic property of immune cells before any treatment. To go deeper into the understanding of mechanisms at play during SR-aGVHD, we modeled immune trajectories within CD8 ⁺ T cells and evidenced specific direct transition, from an early naive state to a highly activated one. By contrast, SS-aGVHD involved specific gene signatures across multiple intermediate differentiation stages during cell-to-cell transitions. These findings provide evidence that steroid resistance is driven by intrinsic mechanisms already present at the onset of alloimmune response, that may serve as potential new therapeutic targets.