Passive immunization against oral pathogens

Abstract

Dental caries is one of the most common infectious diseases and Streptococcus mutans (S. mutans) is considered to be the main etiological agent of dental caries. S. mutans possesses a variety of virulence factors that enables it to establish and initiate disease. SAI/II a 185-kDa cell surface localized protein involved in the initial attachment to the tooth pellicle and glucosyltransferases (Gtf´s), a series of enzymes involved in the production of glucans have both been shown to be important factors in the pathogenesis of dental caries.

The effects of passive immunization against S. mutans, has previously been explored using topical oral administration of antibodies derived from both animals and plants. Lactobacilli have previously been used to deliver vaccine components for active immunization in vivo and are well recognized for their health promoting effects in the oral and gastro-intestinal tract.

We have constructed a series of expression vectors where single-chain (scFv) antibody fragments, directed against the SAI/II antigen of S. mutans, are expressed on the surface of Lactohacillus casei, anchored or secreted. In vitro we verified the expression of functional scFvs and in vivo could show that when administered to rats, the development of dental caries was lower in comparison to controls. Furthermore, we constructed a second set of vectors containing a constitutive promoter region giving rise to a continuous expression of scFv, directed against the same SAI/II antigen of S. mutans. The continuous expression of scFv was compared to the previous inducible lactobacilli construct and was found to be protective against caries in vivo and the anti-cariogenic effect was slightly better than the effect obtained with the initial lactobacilli constructs.

We have also demonstrated that polyclonal chicken derived antibodies against Gtf were protective against dental caries when administered in the drinking water to desalivated rats an important step verifying that antibodies were protective in a drymouth environment. Llama, dromedaries and camels produce IgG antibodies devoid of light chains and consisting of only the heavy chain part of the immunoglobulin molecule. Llama VHHs (heavy chain variable fragment) directed against the SAI/II antigen of S. mutans, fused with glucose oxidase, were constructed and produced in yeast. Rats receiving a daily oral dose of llama VHH or VHH-GOx had a lower development of caries. From the experiments performed herein, we have been able to establish a safe, local, and cost-efficient passive immunotherapy against dental caries.