Fusion antigen used as vaccine. The invention relates to a fusion antigen specific for a target cell. The fusion antigen contains a ligand moiety, a Pseudomonas exotoxin A translocation domain II, an antigenic moiety, and a carboxyl terminal moiety. The ligand moiety is capable of reacting, recognizing or binding to receptors on the target cell. The carboxyl terminal moiety permits retention and processing of the fusion antigen in the endoplasmic reticulum (ER) membrane of the target cell. Pharmaceutical compositions and methods of inducing an immune response using the same are also disclosed.