Provided are polynucleotides and viral vectors, particularly, alphavirus vectors such as Sindbis viral vectors, which encode multiple, e.g., two or more, epitopes of at least one tumor associated antigen in which each epitope is separated by a processing or enzyme cleavage site. The multiple epitopes of the two or more tumor associated antigens encoded by the described polynucleotides and viral vectors may be the same or different. Methods of treating mammalian subjects having a cancer or tumor expressing the tumor associated antigen epitopes are provided, in which the viral vectors encoding the multiple epitopes, as well as other immunostimulatory or immunomodulatory components, generate an anti-cancer or anti-tumor immune response in which high levels of effector T cells increase the survivability of tumored mammalian subjects and result in epitope spreading, thus providing a further enhancement of the immune response.
