Stability of poly(epsilon-caprolactone) microparticles containing Brucella ovis antigens as a vaccine delivery system against brucellosis.

In previous works, our research group has successfully proved the use of subcellular vaccines based on poly(epsilon-caprolactone) (PEC) microparticles containing an antigenic extract of Brucella ovis (HS) against experimental brucellosis in both mice and rams. However, the successful exploitation of pharmaceutical products, and therefore of this product as veterinary vaccine, requires preservation of both biological activity and native structure in all steps of development from purification to storage. In this context, we have carried out an accelerated stability study to evaluate the relative stability of HS when loading in PEC microparticles. For this purpose, freeze-dried microparticles were stored at 40 +/- 1 degrees C and 75% RH as a preliminary analysis of a stability testing. The results showed that both physico-chemical (size, morphology, antigen content, release profile) and biological (integrity and antigenicity of the HS) properties were preserved after 6 months of storage. On the contrary, after 1 year of storage, the HS release profile was dramatically affected probably due to a progressive loss of the polymer microstructure. In addition, the degradation and loss of the antigenicity of the HS components was also evident by SDS-PAGE and immunoblotting analysis. In fact, after 12 months of storage, only the integrity and antigenicity of two of the major protective proteins of the HS antigenic complex were preserved.