We demonstrate herein that neuritin controls the homeostasis of regulatory T cells in an antigen dependent manner. Based on this discovery, we describe herein the application of neuritin as a therapeutic agent to manipulate antigen specific regulatory T cells in various disease settings is described. Thus manipulation of Treg cells and DCs through neuritin can be used to enhance immunotherapy of autoimmune diseases, cancer and infectious diseases, as well as enhance lymphocyte engraftment in settings of donor lymphocyte infusion, bone marrow transplant, as well as other types of transplants, and adoptive transfer.