Biodegradable microparticles with different release profiles: effect on the immune response after a single administration via intranasal and intramuscular routes.

In the development of single-dose microparticulate vaccines, identification of the type of protein release profile required to elicit high and sustainable immune responses is important. Microparticles exhibiting different protein release profiles (continuous, pulsatile and plateau) were made by solvent evaporation or solvent extraction methods from biodegradable polymers encapsulating the model antigen, bovine serum albumin (BSA). The immune responses obtained after a single intranasal or intramuscular administration of microparticles were determined, and also after a subcutaneous boost after 11 months. Microparticles were manufactured with acceptable protein loading and average volume size ranging from 1 to 10 microm. The integrity of BSA extracted and released from microparticles after 2 months incubation was retained. Microparticulate preparations administered by either intranasal or intramuscular routes, evoked rapid, high titre and long-lived (up to 11 months after priming) specific serum IgG responses which were significantly greater than for free BSA. The type of protein release from microparticles had no significant effect on the systemic immune responses. Interestingly, a formulation exhibiting a plateau-release profile was the only microparticulate system capable of inducing significantly greater IgA responses than free BSA after intranasal immunization. This study shows the benefit of microencapsulation in inducing high and long-lasting systemic immune responses after a single dose by both parenteral and mucosal delivery. We conclude that of the microparticles tested, the longevity and magnitude of humoral responses was not effected by the type of in-vitro protein release profile.