Receiver operating characteristic curve analysis of circulating blood dendritic cell precursors and T cells predicts response to extracorporeal photopheresis in patients with chronic graft‐versus‐host disease

BACKGROUND: One proposed mechanism of extracorporeal photopheresis (ECP) in reducing chronic graft-versus-host disease (cGVHD) is alteration in numbers of circulating dendritic cells (DCs). This hypothesis was tested by correlating numbers of DC precursors and T cells in the blood before and during ECP therapy with response of cGVHD. STUDY DESIGN AND METHODS: Twenty-five patients with cGVHD were treated with ECP. Data were collected with emphasis on blood cellular markers, clinical response to ECP, and overall survival. RESULTS: Fourteen patients (56%) responded and had better 2-year survival than nonresponders (88% vs. 18%, p=0.003). Responders had higher baseline circulating myeloid DC (mDC) and plasmacytoid DC precursors and CD4+ and CD8+ T cells compared with nonresponders. Receiver operating characteristic curve analyses showed that the best baseline cutoff values to predict response to ECP were mDC counts of 3.7 cells/µL (79% sensitivity, 82% specificity) and CD4+ T-cell counts of 104 cells/µL (71% sensitivity, 82% specificity). CD4+ T cells declined in responders over time, but not in nonresponders, and no significant changes were seen in CD8 T-cell or DC numbers over a 12-month period in responder or nonresponder groups. CONCLUSIONS: Higher baseline numbers of circulating DCs and T cells may predict clinical response to ECP in patients with cGVHD.