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

Chronic graft-versus-host disease (cGVHD) remains the leading cause of nonrelapse morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Effective therapeutic agents targeting dysregulated cytokines including interleukin-17 (IL-17) and colony-stimulating factor 1 (CSF-1) have been defined in preclinical models of cGVHD, and efficacy in subsequent clinical trials has led to their recent US Food and Drug Administration approval. Despite this, these agents are effective in only a subset of patients, expensive, difficult to access outside the United States, 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, nonintuitive IL-17 and CSF-1 signatures in mouse blood monocytes that could be identified in relevant monocyte populations within 70% of patients at diagnosis of cGVHD and in half of patients at day +100 after HCT who subsequently developed cGVHD. These signatures can now be evaluated prospectively in clinical studies to help delineate potential responder and nonresponders to relevant therapeutics targeting these pathways.