Higher Numbers of Circulating Dendritic Cells and T-Cells Predict Response to Extracorporeal Photopheresis in Patients with Chronic Graft-Versus-Host Disease

Background: Therapeutic options for steroid-refractory chronic graft-versus-host-disease (cGVHD) are limited. Extracorporeal photopheresis (ECP) is a photoimmune therapeutic modality to treat cGVHD that is tolerated relatively well, but its mechanism has not been fully defined. One model for the mechanism of ECP in cGVHD is dendritic cell (DC) depletion and T-cell modification (Alcindor, T, et al ., BLOOD 2001, 98:1622). We tested this hypothesis by determining the numbers of circulating DCs and T-cells prior to ECP and during therapy in patients with cGVHD, and correlating cell numbers with response. Methods: This study was IRB approved. We studied 25 adult pts (median age 43 yrs, range 23–71) with histories of hematological malignancies including NHL (n=7), AML (n=5), CML (n=5), ALL (n=3), MDS (n=3), Hodgkin’s lymphoma (n=1), and CLL (n=1), who developed cGVHD after allogeneic, HLA-matched HPCT. Ten pts had progressive, 9 pts had de novo , and 6 pts had interrupted cGVHD. Initial treatment of cGVHD included corticosteroids in all pts. At the time of ECP initiation, pts were either dependent upon corticosteroids for control of cGvHD (21 pts), or steroid-intolerant (4 pts). No pts had received ECP prior to this study. ECP was administered 2 consecutive days every week for the first 2 months, two times a week every other week for 2 months, and then two times a week once a month. In addition to ECP, pts received steroids (21), MMF (n=13), FK506 (n=15), cyclosporine (n=3), MTX (n=3), rapamycin (n=1), rituximab (n=1) or pentostatin (n=1). Sites of cGVHD included skin (n=25), oropharynx (n=7), liver (n=5), gut (n=4), lung (n=1), and eye (n=1). A good response was defined as having > 50% reduction in the corticosteroid dose within 4 months of starting ECP, with improved or stable lesions on skin and other sites. For steroid-intolerant pts, clinical parameters such as improvement in skin condition were used to identify responders. Peripheral blood mononuclear cells were analyzed before ECP began and every 2 months during ECP therapy. The numbers of plasmacytoid DCs (pDC, Lin− CD123+ CD11c− HLA-DR+), myeloid DCs (mDC, Lin− CD123− CD11c+ HLA-DR+), and CD4+ and CD8+ T-cells in blood were determined by flow cytometry. Results: Median follow up of the 25 pts was 47.1 months (range, 8.6–90.9) from the time of transplant. The median number of ECP treatments was 26 (range 2–68). Fourteen pts (56%) had good response, and 11 were non-responders. The median time between HPCT and onset of cGVHD was similar for responders (8.6 months, range 3.3–34.7) and non-responders (6.1, range 3.4–43.8, p=0.52). The median time between HPCT and ECP was also similar for the two groups (32.3 months, range 13.1–60.0, vs. 21.9 months, range 4.1–47.5, respectively, p=0.12). Responders had an estimated 2-yr survival of 88% after starting ECP, vs 18% for non-responders (p=0.004). Two responders died at 11.2 and 31.2 months after starting ECP, compared with 7 non-responders (median 4.4 months, range 2.8–22.1). Non-responders had a relative risk of death of 11.6 compared with responders (p=0.022). Average prednisone doses for responders and non-responders were comparable, averaging 24.3 and 41.8 mg/day, respectively (p=0.11). Responders had higher baseline numbers of pDCs (average 5.8 vs. 0.6 cells/mcL, p=0.025) and mDCs (average 15 vs. 3.8 cells/mcL, p= 0.01) compared with non-responders. Baseline CD4+ T-cell numbers were higher in responders compared with non-responders (average 623 vs. 178 cells/mcL, p=0.005), as were CD8+ T-cell numbers (712 vs. 251 cells/mcL, p=0.047). Contrary to the original hypothesis, there were no consistent changes in the numbers of circulating DCs and T-cells among responders over a 12-month period. Receiver-operator characteristics (ROC) analysis showed that baseline numbers of blood mDCs of >3.7 cells/mcL prior to ECP had 79% sensitivity and 82% specificity to predict response of cGvHD patients to ECP. Conclusion: Our results demonstrate that higher numbers of circulating DCs and T-cells predict response to ECP in pts with cGVHD. Response to ECP was significantly associated with improved survival in univariate and multivariate analyses (p<0.03). Our findings support a newer model for the mechanism of response to ECP therapy, involving interactions between donor-derived DCs and donor T-cells. The generation of regulatory T-cells by dendritic cells presenting antigens from apoptotic bodies will be discussed.