Correlation between in vitro release and in vivo immune response from biodegradable polymer particles entrapping...

Release of immunoreactive antigen from biodegradable polymer particles in a manner mimicking the normal vaccination schedule is one of the most important requirements for the successful development of single dose vaccine formulation. Tetanus toxoid (TT) was used as a model antigen to develop single dose vaccine formulations using poly(lactide-co-glycolide) and poly(lactide)polymers. An amphiphilic stabilizer such as RSA or PVA was used at an optimal concentration in the internal aqueous phase during preparation of immunoreactive TT particles using the multiple emulsion solvent evaporation method. Particles made from different polymers released immunoreactive TT continuously for more than 4 months in vitro and release profiles were in accordance with the degradation characteristics of the polymer. Initial burst release of antigen from the particles was controlled by incorporation of different concentrations of PVA in the internal aqueous phase during particle formulation. The extent of antigen release from the particles was varied by changing the aqueous to organic phase volume during the primary emulsification stage of particles formulation. Use of above formulation variables resulted in the formulation of polymer particles having different in vitro release characteristics. Anti-TT antibody titers in vivo were also in accordance with the in vitro release characteristics of immunoreactive TT from the particles. Anti-TT antibody titers from the stabilized particles were much better than that observed from particles made without stabilizers. These results indicate the importance of stabilizers and different formulation variables for the preparation of polymer particles having desired in vitro release characteristics.