Th22 and Tfh Cell Elevation Is Associated with Clinical Response of Photopheresis Therapy in Patients with Steroid-Refractory/ Resistant Graft-Versus-Host Disease (GvHD)

In patients with steroid-refractory/resistant graft-versus-host disease (GvHD), extracorporeal photopheresis (ECP) has been identified as a promising therapeutic strategy due to its safety profile and convincing clinical response rates.

While previous studies have reported on the role of Th1, Th2 and Treg cells in ECP therapy, further comprehensive analysis of T helper cells is necessary to provide better understanding of the underlying mechanisms. In this study, we thus investigated the influence of long-term ECP treatment on both Th cells as well as on immune checkpoint molecules and apoptosis. Overall, we investigated 27 patients with GvHD treated by ECP therapy, containing 13 patients with acute GvHD and 14 patients with chronic GvHD. 10/13 (76.9%) of aGvHD and 9/14 (64.3%) of cGvHD patients clinically responded to ECP therapy. Three (23.1%) patients reached CR and seven (53.8%) patients achieved PR under ECP treatment in patients with aGvHD, while in patients with cGvHD CR was achieved in one (7.1%) and PR in eight (57.1%) patients. Stabilization of disease was observed in five (35.7%) patients.

On an immunological level, aGvHD, cGvHD and healthy donors (HD) patients showed different profiles of Th populations. In GvHD patients, significantly higher levels for Th2 (aGvHD vs. HD: 36.26% vs. 13.88%, p = 0.014; cGvHD vs. HD: 30.71% vs. 13.88%, p = 0.026), Th17 (aGvHD vs. HD: 19.21% vs. 7.49%, p = 0.038), Th22 (aGvHD vs. HD: 1.22% vs. 0.11%，p = 0.011; cGvHD vs. HD: 0.64% vs. 0.11%, p = 0.012) and GM-CSF ⁺ Th cells (aGvHD vs. HD: 1.15% vs. 0.14%, p = 0.022; cGvHD vs. HD: 0.84% vs. 0.14%，p = 0.012) and clearly lower levels for T follicular helper (Tfh) cells including Th1- (aGvHD vs. HD: 0.37% vs. 2.04%, p = 0.002; cGvHD vs. HD: 1.28% vs. 2.04%, p = 0.03) and Th2-like cells (aGvHD vs. HD: 1.17% vs. 4.19%, p = 0.033) were observed in comparison to HDs. This suggests Th cells account for a crucial role in GvHD pathogenesis. ECP therapy was able to accelerate recovery of Tfh cells, including Th1- (Time point 1 vs. Time point 2 in aGvHD: 0.37% vs. 0.97%, p = 0.028), Th2- (T1 vs. T2 in aGvHD: 1.17% vs. 1.35%, p = 0.049; T1 vs. T2 in cGvHD: 2.08% vs. 3.15%, p = 0.048) and Th17-like Tfh cells (T1 vs. T2 in aGvHD: 1.82% vs. 2.70%, p = 0.034), facilitating immune reconstitution after allo-HSCT and thereby alleviating GvHD. Clinical response in aGvHD patients was strongly associated with elevation of Th22 cells by ECP therapy showing 51% upregulation (T1 vs. T2: 0.86% vs. 1.3%，p=0.007). In addition, we also found that the expression of the Fas receptor on effector T cells could be further upregulated with ECP treatment (T1 vs. T2 in cGvHD: 49.65% vs. 56.46%, p = 0.011), which increases the susceptibility of these effectors T cells to Fas-mediated apoptosis. This could lead to the elimination of these overactivated effector T cells and the perseverance of immunological tolerance by triggering activation-induced cell death. In addition, a reduction of Tim-3-expressing effector T cells, which are associated with the severity of GvHD, with ECP therapy (T1 vs. T2 for aGvHD: 18.09% vs. 15.10%, p = 0.044) was discovered.

In conclusion, ECP therapy exerts immunomodulatory effects by promoting balanced immune reconstitution and inducing immune tolerance, making it an attractive and promising treatment option for patients with GvHD.