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

Corticosteroid-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 and before steroid initiation, a single cell deep phenotyping and transcriptome analysis was performed on peripheral blood mononuclear cells from aGVHD patients before first line treatment, and from patients without aGVHD. We first explored immune cell subsets as a global signature, called immunotype. One immunotype enriched in monocytes expressing CD11b was associated with increased incidence of aGVHD (72% at day 100, log-rank p=0.005), but immunotypes were not associated with steroid sensitivity. Pathway analysis and inferred ligand/receptor interactions revealed major divergence between steroid sensitive and SR-aGVHD, including enrichment of TNFα activation in SR-GVHD, as well as TNF/TNFR, CCL3, CCL4 and IL18 signaling. Interferon α and γ pathways activation were decreased in SR-aGVHD patients. Finally, trajectory inferences within CD8 ⁺ T cells evidenced specific transition during SR-aGVHD, from an early differentiated state to a highly activated and differentiated one, without slight differentiation across intermediate stages, involving specific gene signature during state transition. These findings provide evidence that corticosteroid resistance is an intrinsic mechanism already present at the onset of alloimmune response. This comprehensive overview of pathways underlying corticosteroid resistance highlights specific patterns that may serve as potential new therapeutic targets.