Extended report Ann Rheum Dis 2010;69:1519–1526. doi:10.1136/ard.2009.121111 1519 ABSTRACT Background It has been widely demonstrated that a quantitative and/or qualitative impairment of regulatory T cells (T regs ) play a fundamental role in the initiation and persistence of rheumatoid arthritis (RA) in animal models and in patients. In the present work it is demonstrated that partial myeloablation induces a relative expansion of T regs that is sufficient to mediate immunological tolerance. Objectives (1) To test the ability of low-intensity myeloablation mediated T reg activation to prevent and/or to treat experimental arthritis using the collagen-induced arthritis (CIA) model and (2) to clarify the role of T reg in mediating the beneficial effect. Methods Low-dose irradiation was used before the induction of arthritis or at the onset of disease. The role of T regs (CD4CD25forkhead box P3 (FoxP3) + cells) and their suppressive activity was assessed by testing their functional activities ex vivo after the treatment and by their in vivo depletion before the treatment. Results It was observed that irradiation ameliorated CIA before or after disease induction. T regs appear to play a fundamental role in the therapeutic efficacy of irradiation, because the depletion of CD25 or folate receptor (FR)4 + cells with specific antibodies before the treatment abolished the beneficial effects. The therapeutic efficacy was associated with an increment in the proportion of T regs despite the overall reduction in lymphocyte counts. Furthermore, a decline in the percentage of CD4CD25FoxP3 + T regs was associated with disease flare. Conclusion In vivo T reg expansion is a feasible and effective approach in the treatment of autoimmune diseases. INTRODUCTION Rheumatoid arthritis (RA) is an autoimmune disease characterised by persistent chronic inflammation manifesting as joint destruction and chronic disabil- ity. Despite the success of biological treatments, a substantial proportion of patients fail to respond 1 2 and novel treatments would therefore be desirable. An attractive possibility would be to potentiate the immunoregulatory networks involved in the control of self-reactive immune responses. CD4 regulatory T cells (T regs ) are the main effectors of immunological tolerance in adult life. T regs can be divided into ‘naturally occurring’ thymus-derived T regs and those generated in the periphery known as ‘adaptive or induced’ T regs. 3 In general, T regs can be reasonably identified as expressing the interleu- kin (IL)2 receptor α chain (CD25) 4 and the forkhead box P3 (FoxP3) gene product. Other features include the expression of glucocorticoid-induced tumour The therapeutic activity of low-dose irradiation on experimental arthritis depends on the induction of endogenous regulatory T cell activity Ling Weng, 1,2 Richard O. Williams, 1 Pedro L Vieira, 3 Gavin Screaton, 3 Marc Feldmann, 1 Francesco Dazzi 1,2 1 Kennedy Institute of Rheumatology, Imperial College, London, UK 2 Department of Haematology, Imperial College, London, UK 3 Department of Immunology, Imperial College, London, UK Correspondence to Francesco Dazzi, Department of Haematology, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK; f.dazzi@imperial.ac.uk Accepted 24 January 2010 necrosis factor receptor (GITR) and the absence of CD127. More recently, folate receptor 4 (FR4) has been proposed as their most specific marker. 5 Several studies have indicated that quantitative and qualitative abnormalities of regulatory T regs contribute to the pathogenesis of collagen-induced arthritis (CIA) 6 7 and in a spontaneous model of RA. 8 Studies conducted in humans have docu- mented quantitative changes in T reg numbers or function in the peripheral blood and/or the syno- vial fluid of patients with RA. 9–11 Furthermore, T regs isolated from patients with active RA, although displaying an anergic phenotype, are unable to inhibit proinflammatory cytokine secretion from activated T cells and monocytes. There is evidence that the local proinflammatory environment is fun- damental in imparting a T reg defect, because the treatment with anti-tumour necrosis factor (TNF) α may restore their function 12 by generating trans- forming growth factor (TGF)β producing T regs . 13 This hypothesis has gained further evidence by a study showing that cytotoxic T lymphocyte anti- gen 4 (CTLA4) expression on T regs in patients with RA is significantly reduced, and artificial induction of CTLA4 expression on RA T regs can restore their suppressive capacity. 14 Therefore, generating func- tionally effective T regs may provide an effective approach for the treatment of RA. The adoptive transfer of T regs can be efficacious in the treatment of autoimmune diseases in pre- clinical models, 15 but the major limitation of such a strategy is that, in order to obtain a dose sufficient for clinical use, T regs need to be expanded in vitro with implications on their functionality. 16 An alternative strategy is to increase the number of T regs by exploiting the selective advantage of T regs over conventional T cells during homeostatic recon- stitution following cell ablative treatments. 17 18 We have previously reported that even non-myeloabla- tive doses of irradiation are sufficient to determine a selective retention/expansion of T regs capable of producing an immunosuppressive activity against donor haematopoietic antigens, thus facilitating their engraftment. 19 Therefore, we hypothesised that partial myeloablation could also generate the conditions to control autoimmune diseases. MATERIALS AND METHODS Mice and CIA DBA/1 male mice (Olac, Oxford, UK), 12 weeks old, received a single intradermal injection at the base of the tail of bovine type II collagen group.bmj.com on March 19, 2015 - Published by http://ard.bmj.com/ Downloaded from