CD28⁺ CD8⁺ Tem cells with a STAT1-dependent glucocorticoid receptor deficit contribute to steroid-refractory acute GVHD

Steroid-refractory (SR) disease develops in a substantial fraction of patients with grade II-IV acute graft-versus-host disease (aGvHD) and is associated with poor long-term survival. Improved mechanistic insight is needed to identify reliable predictors of steroid resistance. We retrospectively profiled peripheral blood collected prior to glucocorticoid treatment from allogeneic hematopoietic cell transplantation recipients without aGvHD, with steroid-sensitive aGvHD, and with SR-aGvHD using an integrated multi-omics approach, and validated findings in an independent multicenter cohort. Mass cytometry revealed expansion of activated CD28+ CD8+ effector-memory T (Tem) cells in SR-aGvHD. Absolute counts of these cells at neutrophil engraftment predicted subsequent steroid resistance in the multicenter cohort and performed comparably to established clinical classifiers. This phenotype was associated with a proinflammatory milieu enriched for IL-2, IL-27, and IFN-γ. Single-cell RNA sequencing and functional assays implicated a STAT1-glucocorticoid receptor (GR) regulatory axis in which inflammatory cytokines induce STAT1 phosphorylation and suppress GR expression, consistent with intrinsic glucocorticoid resistance. JAK inhibition rescued cytokine-induced steroid resistance in vitro, while in SR-aGvHD patients, clinical response to ruxolitinib was accompanied by reduced STAT1 activation, restoration of GR expression, and contraction of the expanded CD8+ Tem pool. These findings identify immune dysregulation at SR-aGvHD centered on CD8+ Tem cells with a STAT1-dependent GR deficit and support a mechanistic link to steroid refractoriness. CD28+ CD8+ Tem cell counts may serve as a biomarker of SR-aGvHD and inform development of pre-emptive, pathway-targeted strategies.