Defining pathogenic IL-17 and CSF-1 gene expression signatures in chronic graft-versus-host disease

• Temporal single cell RNA sequencing of mouse blood identifies non-intuitive signatures of IL-17 and CSF-1 dysregulation during chronic GVHD.

• Analogous IL-17 and CSF-1 dysregulation signatures can be identified in patients' blood monocyte subsets at and prior to cGVHD diagnosis.

Chronic graft-versus-host disease (cGVHD) remains the leading cause of non-relapse morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Effective therapeutics agents targeting dysregulated cytokines including IL-17 and CSF-1 have been defined in preclinical models of cGVHD, and efficacy in subsequent clinical trials has led to their recent FDA approval. Despite this, these agents are effective in only a subset of patients, expensive, difficult to access outside the US, and used in a trial-and-error fashion. The ability to readily discern druggable, dysregulated immunity in these patients is desperately needed to facilitate the selection of appropriate treatment and to potentially identify high-risk individuals for preemptive therapy. We used single cell sequencing-based approaches in our informative preclinical cGVHD models to "reverse engineer" temporal IL-17 and CSF-1 signatures in mouse blood that could be used to interrogate patients. We defined distinct, non-intuitive IL-17 and CSF-1 signatures in mouse blood monocytes that could be identified in relevant monocytes within 70% of patients at diagnosis of cGVHD and in half of patients at day +100 post-HCT who subsequently developed cGVHD. These signatures can now be evaluated prospectively in clinical studies to help delineate potential responder and non-responders to relevant therapeutics targeting these pathways.