His research over the past 25 years has focused on understanding the basic processes that control T cell activation and immune tolerance in autoimmunity and organ transplantation. He and members of his lab have developed soluble receptor antagonists; monoclonal antibodies and animals deficient in individual members of TCR and co-stimulatory pathways to define their individual roles in transplant rejection and autoimmunity including a special emphasis on a specialized subset of T cells termed “regulatory T cells” (Treg). Tregs control fundamental aspect of immune homeostasis. During the last several years, his research has adapted the animal studies using biologics and cell based therapies to develop therapeutics that can be used in humans with autoimmunity and under conditions of allotransplant rejection. Moreover, a strong role for antigen-specific Tregs have been found in these model systems and further evidence in humanized mice and transplant patients that alloantigen-specific Tregs are more effective. Thus, the major goal of this work is to identify the antigen-specificity of thymic- and peripherally-derived Tregs with the expectation that these TCRs can be adapted for immunotherapy. Finally, his lab initiated several projects to determine mechanisms that control Treg stability. The goal is to develop approaches using pharmacogenomics to either stabilize or destabilize Tregs in autoimmunity and cancer.