Extracorporeal photopheresis (ECP) has been proposed as a possible alternative therapy for patients with bronchiolitis obliterans syndrome (BOS), with some evidence of efficacy. Although the mechanism by which ECP exerts its protective effects remains to be determined, two recent studies suggest that the modulation of transplant immune rejection may depend on the capacity to increase the number of peripheral T-regulatory (Treg) cells. We evaluated the effect of ECP treatment on the number of naturally occurring CD4(+)CD25(+) Treg cells in the peripheral blood of six lung transplant recipients: in five cases after failure of augmented or changed immunosuppression for BOS, and in one case owing to persistent acute rejection in a patient who contracted chronic hepatitis C viral infection after lung transplant. A functional stabilization was observed in three of our five patients with BOS, which was accompanied by a slight increase or stabilization of the number of peripheral blood CD4(+)CD25(high) cells with in vitro features of Treg cells. On the contrary, two patients with BOS who did not experience graft functional stabilization also showed a decline in the peripheral Treg subset. In the last patient Treg cell kinetics showed stabilization during the first 5 months of ECP treatment when lung function remained stable and graft histology normalized but showed a subsequent decrease, predating BOS diagnosis. In all, our results indicate that ECP may modulate peripheral Treg cell number but the time course of peripheral Treg cells varies according to graft function.
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