Immunocontraceptive potential of recombinantly expressed minimized chicken riboflavin carrier protein (mini-RCP) in rodents

Chicken riboflavin carrier protein (RCP; 219 AA) harbours four linear epitopes, constituted by the peptide residues 3-23, 64-83, 130-147 and 200-219. Antibodies to these sequences bioneutralize maternal RCP and provide protection from pregnancy in rodents. In order to overcome the major histocompatibility complex-dependent variability in immune response often encountered with use of single peptides for vaccination in genetically outbred populations, we have assembled a novel synthetic gene, incorporating in tandem the nucleotide sequences coding for all the four neutralizing epitopes of chicken RCP and expressed in Escherichia coli. The gene product, mini-RCP has been characterized for its immunogenic properties and contraceptive potential in rodents. Immunization of rabbits and rats led to generation of antibodies against individual peptide components, as determined by enzyme-linked-immunosorbent assay (ELISA). However, immunized rats carried pregnancy to term and delivered healthy offsprings. Antisera from these rats exhibited decreased affinity of binding to the native protein. These findings suggest that the prospects of covalently-linked epitope peptides need to be cautiously evaluated during the design and development of peptide-based vaccines.