Abstract: The invention provides a method for designing protein immunogen, which comprises (a) modifying the amino acid sequence of the immunogen, and (b) determining whether the T-helper (Th) cell response to the modified immunogen is of the Th1 type or the Th2 type. The method is useful in identifying immunogens for use in immunotherapy of diseases. For example, chronic hepatitis is believed to be associated with a Th2-dominated response which fails to clear the virus, and switching the Th response to a Th1 response by administration of an immunogen that induces a Th1 response may help in clearing the virus.