Abstract: Disclosed are (1) a fused protein comprising heat-labile enterotoxin B subunit and a protein heterologous to heat-labile enterotoxin, (2) a recombinant DNA containing a nucleotide sequence coding for the above fused protein, (3) a transformant harboring the above recombinant DNA, (4) a method for producing the fused protein which comprises cultivating the above transformant, producing and accumulating the above fused protein in a culture, and collecting the fused protein, and (5) a method for purifying a fused protein comprising a herpes simplex virus surface antigen and heat-labile enterotoxin B subunit, which comprises cultivating a transformant harboring a recombinant DNA containing a nucleotide sequence coding for the fused protein, producing an accumulating the fused protein in a culture, collecting the fused protein and subjecting the collected fused protein to purification processes comprising cationic exchange chromatography and gel permeation chromatography.