Anti-tumor immunity mediated by cytotoxic CD8+ T lymphocytes (CTL) is thought to underlie the efficacy of extracorporeal photopheresis (ECP) for cutaneous T cell lymphoma (CTCL). In contrast, induction of immune tolerance mediated by regulatory T cells (Treg) is hypothesized to underlie the effect of ECP for graft-versus-host disease (GVHD). In this translational research study, peripheral blood mononuclear cells (PBMC) from patients (Pt) with Sézary Syndrome (SS), a leukemic form of CTCL, and GVHD pre- and post-ECP were studied for expression of the CTL cytokine IFN-gamma and of the nuclear transcription factor forkhead box P3 (Foxp3), a specific marker of Treg. Total RNA from PBMCs at pre-ECP, 2 day, 1 month, 3 months, and 6 months post- ECP were quantitated by real-time quantitative reverse transcript-PCR (RT-Q-PCR) for Foxp3 and IFN-gamma mRNA expression levels, normalized to endogenous control gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Foxp3 levels at baseline varied but increased at 2 day and 1 month post-ECP in GVHD by 9.5-fold and 27.6-fold, respectively (Fig.1). Similarly,foxp3 also increased in 3 of 4 CTCL patients (Pt#1, #2 and #4). Foxp3 levels rose steadily in clinical responders, Pt#1 and Pt#2, during the treatment course, and highest levels were detected at 6 months post-ECP with 13.1-fold and 17.4-fold increase, respectively. Pt#1 and #2 experienced partial clinical response and decreased circulating tumor cells with ECP. The levels of interferon-gamma had only < 2-fold up or down over the treatment course from baseline among CTCL post-ECP samples. While the level of IFN-gamma was decreased by half at 2 day and 1 month post-ECP in GVHD compared to that in pre-ECP (Fig.2). These results suggest that Tregs (detected by Foxp3) but not IFN-gamma are induced during ECP in responding CTCL patients as in GVHD. ECP might thus have common mechanisms in these two T cell mediated diseases. The study will continue to enroll patients to further study the effects of ECP.
Disclosures: Ni:Therakos,Inc.: Research Funding. Duvic:Therakos,Inc: Research Funding.