PROLONGED IMMUNE-RESPONSE EVOKED BY A SINGLE SUBCUTANEOUS INJECTION OF MICROCAPSULES HAVING A MONOPHASIC ANTIGEN RELEASE

A model antigen, bovine serum albumin (BSA), was successfully incorpor ated into microcapsules fabricated from blends of poly(d,l-lactide-co- glycolide) and poly(d,l-lactide). The microcapsules possessed diameter s ranging from 10 to 100 mu m and exhibited a continuous monophasic re lease of the protein in vitro for 3 weeks. They were found to enhance its immunogenicity, thereby potentiating the anti-BSA antibody respons e following a single subcutaneous injection in mice and rabbits. Enzym e-linked immunosorbent assays demonstrated that the microcapsules prov oked high-titre and long-lived immunoglobulin G immune a responses ove r a period of 192 days in mice. When rabbits were immunized by a singl e subcutaneous injection of BSA-loaded microcapsules, a high level of anti-BSA antibody was still present in the sera obtained at 17 weeks p ost-injection. The immunization protocol using the BSA-loaded microcap sules was superior to that using BSA dissolved in saline or adsorbed t o alum. These microcapsules providing the controlled release of antige ns may be valuable in designing better vaccine formulations.