Construction and characterization of single chain variable fragment antibodies against C-type lectin receptor DEC 205 and complement receptor 1 for Streptococcus gordonii targeting to dendritic cells

Streptococcus gordonii, an oral commensal organism, is a candidate vector for oral vaccine development. However, previous studies have shown that recombinant S. gordonii expressing heterologous antigens are much more immunogenic when delivered systemically than intranasally. This is possibly due to a failure of the immune system to recognize the commensal organism. 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 aforementioned antigen. Dendritic cells, the principal APC, were targeted by developing single chain variable fragment antibodies (scFv) against the phagocytic receptors CR1 and DEC 205 which are expressed on the surface of immature dendritic cells. scFv expressed on recombinant phage particles or purified from Escherichia coli were able to bind to cells expressing the respective receptors. scFv anti-CR1 and -DEC 205 genes were sequenced and found to be consistent with VH and VL domains. In vivo function of the scFv anti-CR1 protein was assayed by immunizing mice with soluble scFv either subcutaneously or intranasally and determining the immune response against the hemagglutinin peptide located on the carboxy terminus of the scFv. (Abstract shortened by UMI.)...