Earlier may be better: the role of extracorporeal photopheresis (ECP) as prevention of GVHD after allogeneic transplant

Extracorporeal Therapy in Dermatology

Extracorporeal therapy is a treatment modality where human blood undergoes favorable technical modifications and is reintroduced into the same patient. Since the last four decades this technique has been deployed in the management of difficult and refractory disorders in dermatology. Over a period of time newer techniques like immunoadsorption has emerged and opened new vistas in management of morbid dermatoses. In extracorporeal photopheresis a patient's leukocytes are separated and treated outside with Ultra Violet A in presence of 8-methoxypsoralen. Double filtration plasmapheresis and Immunoadsorption are techniques to remove offending immune complexes. They are safe and reduce the need of toxic medications that are conventionally used in recalcitrant skin diseases. In recent years immunoadsorption is emerging as first-line therapy in condition like immunobullous diseases. High cost is one of the important factors limiting their wider use in developing countries like India. Our review discusses different extracorporeal therapies, their applications, recommendations and guidelines based on various clinical trials.

Thymopoiesis, Alterations in Dendritic Cells and Tregs, and Reduced T Cell Activation in Successful Extracorporeal Photopheresis Treatment of GVHD

Acute graft-versus-host disease (aGVHD) is a significant complication of allogeneic hematopoietic stem cell transplant (HSCT) and negatively affects T cell reconstitution. Extracorporeal photopheresis (ECP) reduces aGVHD, but the mechanisms remain incompletely understood. Our objective was to examine the impact of ECP on thymopoiesis in pediatric aGVHD and the mechanisms at a cellular and transcriptional level. Sixteen pediatric HSCT patients were recruited: 6 with ECP-treated aGVHD, 5 without aGVHD, and 5 with aGVHD treated with corticosteroids only. Thymopoiesis was evaluated by measuring naive T cells, TRECs, IL-7, and T cell receptor repertoire diversity. Regulatory T cell (Treg) enumeration and function and dendritic cell (DC) enumeration and phenotype were analyzed using flow cytometry. T cell transcriptome analysis was performed on ECP patients after treatment and responders pre- and post-treatment. Four ECP responders demonstrated thymic-dependent T cell recovery, and superior median naïve T cell numbers at 8 and 12 months post-HSCT compared to the aGVHD corticosteroid group. Increased Tregs and Treg suppressive function, reduced cDC/pDC and DC co-stimulatory marker expression in ECP responders suggest upregulated peripheral tolerance; these findings were not observed in partial responders. Responder post-ECP CD3+ T cell transcriptional profile demonstrated 3333 downregulated and 364 upregulated genes, with significant downregulation of ERRα and GαS pathways, and reduced expression of pro-inflammatory and adhesion proteins.

Thymic function improves with successful ECP treatment. ECP reduces T cell activation and impacts peripheral tolerance via DCs and Tregs. Differences in thymic recovery, DC, and Treg cellular patterns and the T cell transcriptome were observed between ECP responders and partial responders and require further validation and investigation in additional patients.

CD8+ T cells mediate ultraviolet A-induced immunomodulation in a model of extracorporeal photochemotherapy

Extracorporeal photochemotherapy (ECP) that takes advantage of the immunomodulatory effects of UV light has been extensively used for many years for the treatment of several T cell-mediated diseases, including graft-versus-host disease (GvHD) and systemic scleroderma. Immune mechanisms that lead to the establishment of T cell tolerance in ECP-treated patients remain poorly known. In this study, we have tested the effect of UV/psoralen-treated BM-derived dendritic cells, referred to as ECP-BMDCs on the outcome of an antigen-specific T cell-mediated reaction, that is, contact hypersensitivity (CHS), which is mediated by CD8⁺ effector T cells (CD8⁺ T_eff ). The intravenous (i.v.) injection of antigen-pulsed ECP-BMDCs in recipient C57BL/6 mice induced specific CD8⁺ T cells endowed with immunomodulatory properties (referred to as CD8⁺ T_ECP ), which prevented the priming of CD8⁺ T_eff and the development of CHS, independently of conventional CD4⁺ regulatory T cells. CD8⁺ T_ECP mediated tolerance by inhibiting the migration and functions of skin DC and subsequently the priming of CD8⁺ T_eff . CD8⁺ T_ECP displayed none of the phenotypes of the usual CD8⁺ T regulatory cells described so far. Our results reveal an underestimated participation of CD8⁺ T cells to ECP-induced immunomodulation that could explain the therapeutic effects of ECP in T cell-mediated diseases.

Extracorporeal Photopheresis-An Overview

Extracorporeal photopheresis (ECP) has been in clinical use for over three decades after receiving FDA approval for the palliative treatment of the Sézary Syndrome variant of cutaneous T-cell lymphoma (CTCL) in 1988. After the first positive experiences with CTCL, additional indications have been successfully explored including areas such as graft-vs.-host disease (GVHD), scleroderma, and solid organ transplantation. The mechanism of action is still not fully resolved, but important steps in understanding ECP in recent years have been very informative. Originally, the primary hypothesis stated that psoralen and ultraviolet A (UVA) in combination induce apoptosis in the treated immune cells. This view shifted in favor of dendritic cell initiation, modification of the cytokine profile and stimulation of several T-cell lineages, in particular regulatory T-cells. A number of ECP guidelines have been produced to optimize treatment regimens in the clinical context. In CTCL, enough evidence is available for the use of ECP as a first line treatment for Sézary Syndrome (SS), but also as a second line or rescue treatment in therapy-refractory forms of mycosis fungoides (MF). ECP in the treatment of acute and chronic GVHD has shown promising results as second line therapy in steroid-refractory presentations. In solid organ transplantation, ECP has been used to increase tissue tolerance and decrease infections with opportunistic pathogens, attributed to the use of high doses of immunosuppressive medication. Infection with cytomegalovirus (CMV) remains a limiting factor affecting survival in solid organ transplantation and the role of ECP will be discussed in this review. A trend toward prophylactic use of ECP can be observed and may further contribute to improve the outcome in many patients. To further deepen our knowledge of ECP and thus facilitate its use in patients that potentially benefit most from it, future prospective randomized trials are urgently needed in this rapidly growing field. The aim of this review is to (1) introduce the method, (2) give an overview where ECP has shown promising effects and has become an essential part of treatment protocols, and (3) to give recommendations on how to proceed in numerous indications.