Abstract: Provided are modified microorganisms, such as live recombinant commensal bacteria, that express a non-native antigen, or are surface-labeled with a non-native antigen, and methods of using the modified microorganisms to induce an antigen-specific immune response to the non-native antigen. The modified microorganism can be used to induce a regulatory T cell immune response to the heterologous antigen to treat an autoimmune disease in a subject in need thereof, or can be used to induce an effector T cell immune response to the heterologous antigen to treat an infectious disease or proliferative disease in a subject in need thereof.