A Prospective Evaluation of the Effects of Extracorporeal Photopheresis on Important Immunological Markers in Chronic Graft Versus Host Disease.
Authors: Bladon John , Taylor Peter C. 
Published: October 2019

Abstract
A major complication of allogeneic bone marrow or stem cell transplantation is the development of acute and chronic graft versus host disease (GvHD). Initial treatment includes corticosteroids and immunosuppressive agents. However, for steroid-refractory patients other non-conventional therapies are utilised. Recently, extracorporeal photopheresis (ECP) has shown efficacy for the treatment of acute and chronic GvHD unresponsive to standard therapy. ECP involves exposing white cells, harvested by selective leucopheresis, to 8 methoxypsoralen (8-MOP) and UVA light. The irradiated white cells are subsequently re-infused. The aetiology of GvHD involves the stimulation of proinflammatory cytokines; the levels of tumour necrosis factor alpha (TNFα) and Interferon gamma (IFNγ) have been closely linked to GvHD progression. The successful treatment of GvHD has also demonstrated changes in the ratio of CD4/CD8 T cells. The T-cell activation marker CD134 (OX40) has been observed in rats experiencing acute GvHD (aGvHD) and indicated to be a marker of steroid resistant acute and chronic GvHD. Natural Killer (NK) cells are believed to play an active role in suppressing GvHD. NK activity can be reduced in chronic GvHD (cGvHD) and animal models demonstrate GvHD suppression following NK cell transfer. Inhibitory natural killer cell receptors (NKRs) on NK cells can regulate NK and T cell function, including down-regulating target cell lysis. High levels of the NKR CD94 has been observed on patients without cGvHD. This prospective study was designed to determine if peripheral immunophenotypic markers associated with cGvHD are significantly altered by long term ECP therapy. New cGvHD referrals were tested prior to beginning therapy (0 months) and after 3, 6 and 12 months of treatment. On each occasion peripheral blood were tested for: CD4+, CD8+, CD4+/CD134+, CD8+CD134+, CD3+/CD94+, CD8+/CD94+, CD3−/CD56+ (NK), CD3+/IFNγ+, CD3+/TNFα and CD14+/TNFα. For 0–3 months n=16, for 0–6 months n=9 and for 0–12 months n=5. From 0–3 months a fall (p=0.031) in CD8 levels was observed, whilst CD4+ T cells increased from 0–12 months (p=0.040). At each testing stage an increase in the ratio of CD4/CD8 was observed, although these changes were not statistically significant. The percentage of CD4+/CD134+ and CD8+/CD134+ T cells decreased at each subsequent test, however significance was only observed between 0 and 12 months (p= 0.018 for both). NK cells (CD3−/CD56+) increased at 3, 6 and 12 months, however significance was only detected at 3 months (p=0.038). The percentage of CD3+ and CD8+ T cells expressing CD94 remained unchanged. A fall in T cells positive for IFNγ was observed at 3 months (p=0.047), however at each other testing stage the levels of CD3+/IFNγ+, CD3+/TNFα and CD14+/TNFα showed no significant change. Therefore, although increases in CD4/CD8 have been observed in cGvHD treated by ECP, this response remains controversial with many reports demonstrating conflicting data. Reduction of CD134 was observed following ECP, however at the tradition evaluation stage of 3 months no significant difference was observed. The levels of NK cells increased, consistent with previous reports, however CD94 expression was unaltered by ECP therapy. In the absence of a consistent phenotypic marker to demonstrate cGvHD response to ECP, continued monitoring will be based on clinical observations.