Methods for eliciting or enhancing immune responses to antigens, including tumor antigens, and/or DNA vaccines are provided. The methods employ polypeptides or nucleic acid compositions that contain at least a biologically active portion of a Leishmania braziliensis or Leishmania major homologue of the eukaryotic initiation factor 4A, or a variant thereof. Such polypeptides and compositions are useful for enhancing or eliciting a patient's cellular and/or humoral immune response, for instance within methods for treating tumors.