Extracorporeal photopheresis as a non-specific immune therapy of autoimmune diseases and skin T-cell lymphoma (a review of the literature and own studies)

Aim: To present well-known and disputable mechanisms of the effects of extracorporeal photopheresis (ECP) in heterogeneous clinical conditions, as well as to demonstrate its advantages over conventional hormonal, immunosuppressive and cytostatic treatments, with a recommendation to widely implement it into practical management of autoimmune disease and cutaneous T-cell lymphomas (CTCLs).

Key points: Despite convincing evidence of the ECP efficacy in the treatment of T-cell mediated disorders, a unifying concept of its mechanism has not been established so far. In this review, we attempted to determine the value of multiple, sometimes contradictory and equivocal points of view to immunobiochemical processes underlying the restoration of mechanism of immune tolerance in some autoimmune diseases and CTCLs. We focused our attention on our own clinical and immunological data obtained during a 20-years' experience with the use of ECP in clinical departments of MONIKI (Russia). Based on this, we have shown that ECP is more effective in autoimmune diseases than conventional treatment approaches with hormones, immunosuppressants and cytostatics. Unlike them, ECP is selectively targeted to auto-aggressive T-cells without induction of systemic immunosuppression. The leading role is played by the transformation of activated (immunogenic) myeloid dendrite cells (DC) into tolerogenic cell associated with their synthesis of inhibitor cytokines. The interplay of the cytokines with an antigen results in polarization of CD4⁺ Т lymphocytes via the Th2 pathway with restoration of the Th1/Th2 balance and their cytokine production. ECP triggers regulatory anti-clonotypic effector memory cells at the end stage of CD3⁺/CD8⁺/CD27^-/CD28^-/CD62L⁺ differentiation, that provide and maintain the peripheral immune tolerance, by deletion of the clone of auto-reactive cytotoxic lymphocytes and inducing their apoptosis. In autoimmune disorders, ECP results in reduction of the expression of integrin adhesion molecules on auto-reactive cell membranes with subsequent loss of their ability to migrate through the endothelium to their target cells. In its turn, it leads to decreasing immunoinflammatory response in the lesion. Both clinical and experimental data indicate that the mechanism of ECP action against CTCLs is characterized by activation of tumor cell apoptosis, unblocking of co-activation receptors on the antigen-presenting DC providing the functioning of the second signaling pathway for T lymphocyte activation. This results in proliferation of anti-tumor effector cells pool, production of DC activating cytokines that participate in the CD4⁺ polarization via Th1 pathway. In addition, this review considers the mechanism of the immunomodulating effect of ECP in the context of its influence at the levels of transcription and translation of proteins contributing to the pathophysiology of the disorders, based on molecular immunogenetic studies. Thus, ECP is able to induce antigen-specific immunological tolerance through the transformation of antigen-presenting cells, modulation of cytokine profile, adhesion and activation molecules, as well as through formatting of the regulatory T cells (Tregs).

Conclusion: Undoubtedly, the immunobiological ECP technique has significant advantages over well-known conventional hormonal, immunosuppressive, and cytostatic therapies of autoimmune diseases and CTCLs.