The invention relates to isolated polypeptides and nucleic acids encoding polypeptides which comprise a tim-3 IgV domain and a tim-3 intracellular domain, wherein the polypeptides do not comprise a tim-3 mucin domain or a tim-3 transmembrane domain. In addition, the invention relates to methods of modulating immune responses in a subject, comprising administering to the subject a therapeutically effective amount of an agent that modulates tim-3 activity. Immune responses include, but are not limited to, immune tolerance, transplantation tolerance, Th1 responses and Th2 responses.
