In vitrotreatment of monocytes with 8-methoxypsolaren and ultraviolet A light induces dendritic cells with a tolerogenic phenotype

Abstract

SummaryExtracorporeal photopheresis (ECP) has been considered an efficient dendritic cell (DC) therapy, used for treating both T cell malignancy, as well as T cell-mediated diseases. During the ECP procedure leucocytes are exposed to photoactivable agent 8-methoxypsolaren (8-MOP) and ultraviolet (UV) A radiation (PUVA) prior to reinfusion. Despite its clinical efficacy the mechanism of action remains elusive. As it has been reported that ECP might promote the differentiation of monocytes into immature DCs, we investigated the effects of UVA light (2 J/cm 2 ) and 8-MOP (100 ng/ml) on in vitro monocyte-to-DC differentiation from normal donors. DCs were generated from human purified CD14 + cells. Because monocytes are killed by PUVA and taking into account that only 5-10% of circulating mononuclear cells are exposed to PUVA during the ECP procedure, we developed an assay in which 10% of PUVA-treated monocytes were co-cultured with untreated monocytes. We first demonstrate that the presence of 10% apoptotic cells and monocyte activation were not enough to induce monocyte differentiation into DCs. Adding cytokines to our culture system, we obtained immature DCs characterized by significantly higher phagocytic activity and human leucocyte antigen D-related (HLA-DR) expression. These DCs preserved the capacity to be activated by lipopolysaccharide, but showed a reduced capacity to induce allogeneic T cell proliferation when first co-cultured with 10% of PUVAtreated cells. Our experimental design provides a novel insight into the real action of 8-MOP and UVA light on dendritic cell biology, suggesting an additional mechanism by which 8-MOP and UVA light exposure may influence immune responses.

Recognition of Live Phosphatidylserine-Labeled Tumor Cells by Dendritic Cells: A Novel Approach to Immunotherapy of Skin Cancer

“…2 B ). This is in line with the known facts that UV irradiation induces early apoptosis of tumor cells resulting in phagocytosis of dying tumor cells by APC (37). However, phagocytosis of UV-irradiated apoptotic B16 cells was less effective than phagocytosis of tumor cells after treatment with phosphatidylserine-containing liposomes (Fig.…”

Dendritic Cell Apoptosis: Regulation of Tolerance versus Immunity

“…Immature human DCs have a higher susceptibility to ECP-induced apoptosis, with up to 50% of DCs undergoing apoptosis within 24 h of treatment and .90% undergoing apoptosis within 72 h of ECP treatment (55). Thereafter, the remaining viable DCs become tolerogenic with a severely diminished ability to undergo maturation in response to LPS, with a defect in inducing T cell proliferation (56). Concomitantly, there is also an increase in the levels of Tregs (57).…”

Extracorporeal Photopheresis Efficiently Impairs the Proinflammatory Capacity of Human 6-Sulfo LacNAc Dendritic Cells

“…Thus, it has been demonstrated that DCs, which were co-cultured with ECP-treated lymphocytes, display a reduced ability to upregulate costimulatory molecules and produce more interleukin (IL)-10 (10). In addition, it has been documented that the incubation of DCs with ECP-treated monocytes resulted in a reduced ca pacity of DCs to induce allogeneic T-cell proliferation (11). Whereas these reports are based on DCs, which are differentiated from monocytes after several days in the presence of various cytokines, studies investigating the direct influence of ECP on the immunostimulatory capacity of native human DCs are limited.…”