Oral immunization with a model protein entrapped in microspheres prepared from derivatized α-amino acids

A model antigen, ovalbumin (OVA), was encapsulated in microspheres prepared from derivatized α-amino acids and administered orally to mice. These microspheres are quickly and easily prepared, without the use of organic solvents, high temperatures, or complex purification techniques. Immunological responses included induction of OVA-specific antibodies in both sera (IgG) and in intestinal secretions (sIgA), as well as antigen-dependent proliferation of splenic CD4⁺ T cells following, in some cases, as little as a single oral priming dose containing 0.1 mg OVA. Oral administration of microspheres was also found to be effective as a secondary immunization following a subcutaneous prime with soluble antigen. In addition, the protective effect of co-encapsulation of cholera toxin, a mucosal adjuvant, was demonstrated in a whole virus model (infectious bursal disease in chickens). These results indicate that oral administration of antigen-loaded derivatized α-amino acid microspheres can induce local and systemic antibody production and/or stimulation of effector cells.