Investigating the use of polyglutamic acid for enteric delivery of idiotypic antibodies

The success of an oral vaccine depends upon the ability of the antigen to target the Peyer\u27s Patches of the small intestine, uptake and presentation of the antigen to local immune effector cells, and the antigenicity of the antigen. Most proteins are poor mucosal immunogens and therefore have been coupled to a carrier molecule to target the Peyer\u27s Patches. However, the carrier molecule must be immunologically inert so that it may be used for successive immunizations. Additionally many pathogenic bacteria are coated with carbohydrates and lipids which are weak immunogens. Therefore it is of value to develop vaccine strategies which employ proteins which mimic these antigens. These experiments investigated poly-D,L-glutamic acid for use as a delivery vehicle for oral immunization with protein antigens, and attempted to induce an idiotypic specific immune response at mucosal surfaces using idiotypic antibodies. Tetanus toxoid mimicking anti-idiotypic antibodies were produced in a horse by immunizing it with anti-tetanus toxoid antibodies isolated from immune guinea pig sera. The anti-idiotypic antibodies were affinity purified using horse anti-tetanus toxoid antibodies. These anti-idiotypic antibodies specifically inhibited the binding of labelled tetanus toxoid to immobilized horse anti-tetanus toxoid antibodies. Poly-D,L-glutamic acid produced by Bacillus licheniformis was isolated by ethanol precipitation and coupled with idiotypic antibodies for both parental and oral immunization. Horse antibodies coupled to the polymer retained antigen binding specificity as determined by binding to labelled antigen, and induced the same anti-xenotypic response as carrier free horse antibodies when injected into guinea pigs and rabbits. Idiotypic antibody-polymer complexes were packaged in enteric coated gelatin capsules, tablets or suspended in NaHCO$\sb3$ and used to orally immunize primates, guinea pigs and mice respectively. No anti-xenotypic or anti-idiotypic antibodies were detected in the serum or secretion samples collected. These studies demonstrate that poly-D,L-glutamic acid does not optimize nonspecific uptake of protein antigen by Peyer\u27s Patches but do not rule out the use of anti-idiotypic antibodies to induce immunity at mucosal surfaces