In this study the investigators are proposing to treat patients with steroid-refractory Graft-versus-host Disease (GVHD) in a manner designed to promote CD4+CD25+FoxP3+ Tregs. The profound immune suppression which follows the most common salvage treatment for GVHD have unfortunately lead to very poor outcomes because of high infection rates. A more targeted approach based on the promotion and stabilization of Tregs is hoped to allow GVHD control without the profound immunosuppression usually seen. High-dose cyclophosphamide and sirolimus have been successfully used for the prevention of GVHD and have shown to enhance the Tregs subpopulation. The addition of low dose IL-2 and a demethylating agent such as azacitidine will also be studied in an attempt to promote and stabilize the FoxP3 expression of Tregs.