Expression of a Functional Single Chain Variable Fragment Antibody against the Complement Receptor 1 in Streptococcus gordonii

Department of Microbiology and Immunology, Faculty of Medicine, Department of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, Department of Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, NS, Canada

^* To whom correspondence should be addressed. Email: Song.Lee{at}Dal.Ca.

	Abstract

Streptococcus gordonii, an oral commensal organism, is a candidate vector for oral vaccine development. Previous studies have shown that recombinant S. gordonii expressing heterologous antigens were weakly immunogenic when delivered intranasally. In this study, antigen was specifically targeted to antigen presenting cells (APC) in order to potentiate antigen-APC interactions and increase the humoral immune response to the antigen. To achieve this goal, a single chain variable fragment antibody (scFv) against the complement receptor 1 (CR1) was constructed. Anti-CR1 scFv purified from Escherichia coli was able to bind to mouse mixed lymphocytes and bone marrow-derived dendritic cells. In vivo function of the anti-CR1 scFv protein was assessed by immunizing mice intranasally with soluble scFv and determining the immune response against the hemagglutinin (HA) peptide located on the carboxy terminus of the scFv. The serum anti-HA IgG immune response was dose-dependent with as low as 100 ng of anti-CR1 scFv induced a significant IgG immune response while such a response was minimal when the animals were given an unrelated scFv. The anti-CR1 scFv was expressed in S. gordonii as a secreted protein, which was functional as it bound to dendritic cells. Mice orally colonized by the anti-CR1 secreting S. gordonii produced an anti-HA IgG immune response indicating that such an approach can be used to increase immune response to antigens produced by this bacterium.