Genetic engineering of Streptococcus gordonii for the simultaneous display of two heterologous proteins at the bacterial surface

The Gram-positive bacterium Streptococcus gordonii has been genetically engineered to allow the simultaneous expression of two heterologous proteins at the cell surface. A family of recombinant streptococci displaying two different antigens was constructed. All the strains were genetically stable and expressed both proteins at the surface of the same bacterial cell. S. gordonii co-expressing the immunomodulating molecule LTB (B monomer of Escherichia coli heat-labile toxin) and the V3 domain of HIV-1 gp120 were inoculated subcutaneously to BALB/c mice. Animals were capable of responding to both antigens, producing LTB- and V3-specific serum IgG. The V3-specific IgG titer was four-fold higher in mice immunised with the double protein-expressing bacteria, as compared to control animals inoculated either with S. gordonii expressing the V3 domain alone or with a mixture of the two strains expressing LTB and V3, separately. Therefore, LTB was able to potentiate the antibody response towards the V3 domain, and this effect was observed only when LTB was co-expressed on the same bacterial cell.