Changes in L-Selectin Expression by T Lymphocytes after Extracorporeal Photochemotherapy.

Extracorporeal photochemotherapy (ECP) is an emerging treatment modality for steroid-refractory acute and chronic graft versus host disease (GVHD). The mechanisms by which ECP works are still not fully understood, and modulation of dendritic cell subpopulations, a shift of cytokine profile from Th1 to Th2 and an increase of T-cell regulatory (Treg) cells have been related to the ECP beneficial effect. Changes on T-lymphocyte subsets other than Treg have been reported after ECP (

The clinical outcome of the patients was always positive, with more than 50% achieving complete remission. The proportion of L-selectin expressing T lymphocytes significantly diminished after ECP, both in CD4 and in CD8 cells. The reason for these changes are currently unknown. L-selectin is an important T-cell homing receptor for T-cell entry into lymph nodes via high endothelial venules. Expression of CD62L is rapidly lost following T-cell receptor activation, leading to exit from the lymph node into the periphery and sites of inflammation. CD62L^neg and CD62L^pos also differ in their functional abilities, such as cytokine secretion and cytolytic potential. Our results suggest that ECP may have an impact in the trafficking patterns of T lymphocytes, redirectioning T cells from lymphoid to extralymphoid organs. In addition, ECP was associated to a redistribution of the pool of non-naive T lymphocytes.