Survival of dendritic cell subsets is differentially affected by ECP treatment in vitro

Background

Extracorporeal photopheresis (ECP) can induce both an activating as well as regulatory immune response depending on the clinical context. Current studies indicate that dendritic cells (DC) – key players in the regulation of T cell immunity – are critical for ECP efficacy. However, contribution of DC subsets to ECP efficacy is scarcely investigated. This study examined the direct effect of ECP treatment on plasmacytoid DC (pDC) and conventional DC type 1 (cDC1) and type 2 (cDC2) in vitro.

Methods

To address the effect of ECP treatment on DC subsets, human peripheral blood mononuclear cells (PBMC) of healthy blood donors were treated with 200ng/ml 8-Methoxypsoralen (8-MOP) for 30 min and then irradiated with 2J/cm2 UVA in vitro. Untreated, UVA or 8-MOP treated PBMCs served as controls. After 24 and 48 hours quantity and quality of cell death of pDC, cDC1 and cDC2 was evaluated via flow cytometry and compared to the survival of other leukocytes. To reliably identify cDC1 within PBMCs after in vitro culture, staining with XCR1, CLEC9A and CD141 was compared via flow cytometry.

Results

Staining of PBMC with CD141 was superior to CLEC9A and XCR1 to identify cDC1 after in vitro culture. Thus, after exclusion of CD45+Lin+CD14+CD16+ cells, CD123+HLA+ were defined as pDC, CD123-CD11c+HLA+CD1c+ cells as cDC2 and CD123-CD11c+HLA+CD141+ cells as cDC1. cDC1 and cDC2 were more sensitive to cell death due to in vitro culture compared to pDC and other leukocyte subsets over time. T cells, B cells and pDCs were similar susceptible to ECP treatment. Relative amount and absolute number of these populations was substantially reduced within 48h. In contrast, cDCs were less affected by ECP induced cell death.

Conclusion

The results of this study indicate that DC subsets respond differentially to ECP treatment. Thus, it seems to be worth to further investigate the role of pDC, cDC1 and cDC2 during ECP treatment in more detail. Such studies will help to get a better understanding of the immunological mechanism of action of ECP and therefore can contribute to improve this therapy.

Offenlegung Interessenkonflikt:

The authors declare that they have no competing interests.