Extracorporeal photochemotherapy induces arginase 1 in patients with graft versus host disease

Abstract

The benefits of extracorporeal photochemotherapy (ECP; psoralen and UVA exposure of blood mononuclear cells) in graft-versus-host-disease (GVHD) are well-recognized, but the mechanisms of action remain elusive. As the metabolism of l-arginine in immune cells is known to play a role in immune tolerance, we investigated the effect of ECP on arginine metabolism, and the influence of extracellular l-arginine concentration on the response to ECP in cells from patients on therapy by ECP for a GVHD and healthy donors cultured before and after ECP in the presence of different concentrations of arginine (0, 50, 100, 200 and 1000 μmol/l). At baseline arginine was not metabolized through the same pathway in patients and donors. When cells were exposed to ECP, the production of ornithine but not NO° was enhanced, while mRNA of arginase 1 was up-regulated but not INOS. In GVHD patients, increasing arginine concentration resulted in down-regulation of IFNγ and TNFα mRNA expression, whereas IL10 was up-regulated especially at physiological plasma levels (between 0 and 100 μM). Overall, our study shows that ECP orients the metabolism of arginine toward the arginase pathway together with shifting the cytokine profile toward IL-10, providing new insights into the enigmatic mechanism of action of ECP.

Extracorporeal photopheresis increases neutrophilic myeloid-derived suppressor cells in patients with GvHD

“…Mechanistically, the effect of ECP on percentages of PMNMDSCs was paralleled by an enhancement of the suppressive function of MDSCs on effector T cells and an increased arginase activity both at cellular and extracellular level, suggesting that (i) ECP has a dual effect on MDSC numbers and function and (ii) ECP-mediated immunomodulation may involve an arginasemediated mechanism, consistent with previous observations. 31 Arginase depletes arginine from the surrounding microenvironment and thereby impairs T-cell functionalities. MDSCs have been described to express and actively utilize arginase I 38,39 and BM MDSCs were found to inhibit GvHD via an arginase-1-dependent mechanism.…”

“…Several factors have been involved into the generation and functionality of MDSCs, particularly arginase, Signal Transducer and Activator of Transcription 3 (STAT3), indoleamine 2,3-dioxygenase (IDO), reactive oxygen species and others. 18,19 As previous studies found that ECP enhances arginase I mRNA expression and enzyme activity in GvHD patients, 31 we focused on this pathway in our study. Our analyses demonstrated that ECP treatment increased arginase I activity both extracellularly in serum and intracellularly in the PMN-MDSC-containing PBMC fraction in GvHD patients, with PMN-MDSCs showing tendentially higher arginase I activity compared with autologous PBMCs (Figure 2c and Supplementary Figure 7).…”

Guidelines on the use of extracorporeal photopheresis

“…The above‐mentioned findings, however, cannot explain the effects of ECP in these patients and, as these conditions respond to immunosuppressive therapies, it was surmised that ECP might also exert inhibitory effects on the immune system. Furthermore, in patients with GVHD, ECP was shown to induce IL‐10 via modulation of arginine metabolism . In contrast to immunosuppressive therapy, ECP is not associated with any major side‐effects, including opportunistic infections.…”

Leptin modulates dose‐dependently the metabolic and cytolytic activities of NK‐92 cells

“…After 48 h of culture in absence or presence of leptin (10, 100, and 200 ng/ml), NK cells (1 Â 10 6 /ml) were harvested, and total RNA was isolated with TRIzol 1 Reagent (Invitrogen) according to the manufacturer's instructions. Reverse transcription was performed with 1 mg of total RNA, giving rise to 20 ml of cDNA, as previously reported (Merlin et al, 2011). Primers for Ob-R, perforin, granzyme B, IFN-g, Fas-L, and TRAIL are given in Table 1.…”