Isolated polypeptides related to endogenous anti-viral polypeptides and compositions, including immunogenic compositions, comprising a subject isolated polypeptide are disclosed herein. A subject isolated polypeptide comprises an amino acid sequence having substantial amino acid sequence identity to a contiguous stretch of amino acids of one or more endogenous anti-viral polypeptides, wherein the endogenous anti-viral polypeptides are polypeptides subject to proteolytic degradation as a result of the activity of one or more viral proteins. Also provided are diagnostic and treatment methods using the subject isolated polypeptides and compositions.