Abstract: The inventors have discovered a targeting signal that will direct proteins to the endosomal/lysosomal compartment, and they have demonstrated that chimeric proteins containing a luminal antigenic domain and a cytoplasmic endosomal/lysosomal targeting signal will effectively target antigens to that compartment, where the antigenic domain is processed and peptides from it are presented on the cell surface in association with major histocompatibility (MHC) class II molecules. Chimeric DNA encoding the antigen of interest, linked to an endosomal/lysosomal targeting sequence, inserted in an immunization vector, can introduce the chimeric genes into cells, where the recombinant antigens are expressed and targeted to the endosomal/lysosomal compartment. As a result, the antigens associate more efficiently with MHC class II molecules, providing enhanced in vivo stimulation of CD4.sup.+ T cells specific for the recombinant antigen.