Azacytidine and Decitabine prevent experimental sclerodermic chronic graft-versus-host disease

Introduction: Graft-versus-host disease (GVHD) remains a major complication of allogeneic hematopoietic stem cell transplantation (HSCT). Following allo-transplantation, 60% of the patients experience chronic GVHD while approximately 15% of them develop a sclerodermic form of chronic GVHD characterized by multiple organ fibrosis and loss of skin elasticity. Regulatory T cells (Tregs) play a pivotal protective role in the pathogenesis of chronic GVHD by inhibiting alloreactive conventional T cells (Tconvs). Several studies have shown that hypomethylating agents such as Azacytidine (AZA) or Decitabine (DAC) can demethylate the master transcription factor of Treg (FoxP3), thus promoting Treg differentiation from Tconvs. This work investigates the impact of AZA and DAC in a murine model of sclerodermic chronic GVHD. Methods: Lethally irradiated (7 Gy) BALB/cJ recipient mice were injected with 107 bone marrow cells + 7.107splenocytes from B10.D2 donor mice to induce scl-cGVHD. Recipients were injected with 0.5 or 2 mg/kg of AZA or 0.75 mg/kg of DAC every 48h from day 10 to 30 following transplantation. GVHD was scored using a five criteria scale (weight loss, activity, fibrosis, hair loss and mice posture; 0-1-2 points/criteria). Mice were sacrificed at a score of 8/10. Results: Mice treated with AZA 0.5 mg/kg (n=14) or 2 mg/kg (n=17) or DAC 0.75 mg/kg (n=5) had lower clinical scores of GVHD compared to control (n=15). FACS analyses showed a higher proportion of Treg in the blood of AZA 0.5 or 2 mg/kg or DAC 0.75 mg/kg mice than in control at day 35. Results also showed a decreased number of Tconv and CD8 in AZA and DAC treated mice while proliferation of these cells expressing Ki67 was lower during AZA/DAC treatment but higher after discontinuation. Histological analyses showed less skin fibrosis in mice treated with 2 mg/kg of AZA. Finally, analyses of the blood components demonstrated that AZA mice were leuco- and lymphopenic as compared to control at day 21 and 35. Conclusion : AZA and DAC prevented sclerodermic GVHD in this murine model