A cDNA fragment encoding the V3 loop of human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein gp120 was fused to the cholera toxin B subunit gene (CTB-gp120) and transferred into Solanum tuberosum cells by Agrobacterium tumefaciens-mediated transformation. The CTB-gp 120 fusion gene was detected in genomic DNA from transformed potato leaves by PCR DNA amplification. Synthesis and assembly of the CTB-gp120 fusion protein into oligomeric structures of pentamer size was detected in transformed tuber extracts by immunoblot analysis. The binding of CTB-gp120 fusion protein pentamers to intestinal epithelial cell membrane glycolipid receptors was quantified by G(M1)-ganglioside enzyme-linked immunosorbent assay (G(M1)-ELISA). The ELISA results indicated that CTB-gp120 fusion protein made up 0.002-0.004% of the total soluble tuber protein. Synthesis of CTB-gp120 monomers and their assembly into biologically active oligomers in transformed potato tuber tissues demonstrates for the first time the expression of HIV-1 gp120 in plants and emphasizes the feasibility of using edible plant-based vaccination for protection against HIV-1 infection. (C) 2004 Elsevier Inc. All rights reserved.