Mucosal vaccine made from live, recombinant Lactococcus lactis protects mice against pharyngeal infection with Streptococcus pyogenes

Abstract

A novel vaccine (LL-CRR) made from live, nonpathogenic Lactococcus lactis that expresses the conserved C-repeat region (CRR) of M protein from Streptococcus pyogenes serotype 6 was tested in mice. Nasally vaccinated mice produced CRR-specific salivary immunoglobulin A (IgA) and serum IgG. Subcutaneously vaccinated mice produced CRR-specific serum IgG but not salivary IgA. A combined regimen produced responses similar to the salivary IgA of nasally vaccinated mice and serum IgG of subcutaneously vaccinated mice. Mice vaccinated nasally or with the combined regimen were significantly protected against pharyngeal infection following a nasal challenge with S. pyogenes M serotype 14. Mice vaccinated subcutaneously were not protected against pharyngeal infection. Mice in all three LL-CRR vaccination groups were significantly protected against the lethal effects of S. pyogenes. Only 1 of 77 challenged mice that were vaccinated with LL-CRR died, whereas 60 of 118 challenged mice that were vaccinated with a control strain or phosphate-buffered saline died. In conclusion, mucosal vaccination with LL-CRR produced CRR-specific salivary IgA and serum IgG, prevented pharyngeal infection with S. pyogenes, and promoted survival.

FIG. 1.

Salivary IgA. CRR-specific IgA in the saliva was measured by ELISA. The treatment groups are indicated: SubQ, subcutaneous; Nasal Hi, higher-dose groups 8 to 11. Shaded bars, LL-CRR; crosshatched bars, LL; horizontally striped bars, PBS. Error bars indicate standard errors of the means. **, highly significant (P < 0.01) difference from control group(s).

FIG. 2.

Serum IgG. CRR-specific IgG in the blood serum was measured by ELISA. The treatment groups are indicated: SubQ, subcutaneous; Nasal Hi, higher-dose groups 8 to 11. Shaded bars, LL-CRR; crosshatched bars, LL; horizontally striped bars, PBS. Error bars indicate standard errors of the means. **, highly significant (P < 0.01) difference from control group(s).

FIG. 3.

Pharyngeal infection. Vaccinated mice were challenged with S. pyogenes, and throat swabs were taken to measure pharyngeal infection (percent colonized). The treatment groups are indicated: SubQ, subcutaneous; Nasal Hi, higher-dose groups 8 to 11. Shaded bars, LL-CRR; crosshatched bars, LL; horizontally striped bars, PBS. #, highly significant (P < 0.01) difference from LL group and significant (P < 0.05) difference from PBS treatment groups; * and **, significant (P < 0.05) and highly significant (P < 0.01) difference from control group(s).