A fusion protein comprising an antigen-presenting cell (APC)-binding domain or a CD91 receptor-binding domain, a translocation peptide, a fusion antigen, an endoplasmic reticulum retention sequence, and optionally a nuclear export signal is disclosed. The fusion antigen comprises a porcine reproductive and respiratory syndrome virus (PRRSV) ORF7 antigen, a PRRSV ORF1b antigen, a PRRSV ORF6 antigen, and a PRRSV ORF5 antigen. The fusion protein is useful for inducing antigen-specific cell-mediated and humoral responses.