Investigation of adjuvant effect of poly(D, l-lactic-co-glycolic acid) (PLGA) biopolymer in the production of bacterial vaccine

In this study, immunity levels of the vaccines produced by using aluminum hydroxide and Poly (D, L-Lactic-Co-Glycolic Acid) (PLGA) adjuvants against infectious necrotic hepatitis of sheep were compared in guinea pigs. Toxoid was produced by using C. oedematiens type A (UK) strain. Toxoid vaccines adsorbed onto aluminum hydroxide and encapsulated in PLGA (lactide/glycolide ratio: (50/50), molecular weight: 30,000-60,000 dalton) were prepared. Encapsulation of toxoid in PLGA particles was performed by double emulsion solvent evaporation method. Trehalose and Mg(OH)2 were used to protect the toxoid structure in the encapsulation process. At the end of the encapsulation process, the loading capacity of protein antigen into the microspheres was found to be approximately 88%. Male guinea pigs were used to determine the immune response to vaccination. Animals were divided into 3 groups with 10 in each group. The first group received double dose aluminum hydroxide-adsorbed vaccine (2 ml + 2 ml) with 21 days intervals, the second group received a single PLGA microsphere vaccine (2 ml) and the third group received a half dose PLGA microsphere vaccine (1 ml) subcutaneously. At 15th, 30th and 45th days after booster dose in the first group and a single dose in the other groups, blood samples were taken and pooled serum samples were obtained. Antibody levels in the pooled serum samples were determined by the mouse TNT (Toxin Neutralization Test). The same antibody level (8 IU /ml) was determined at 30th and 45th days after vaccination with double dose aluminum hydroxide-adsorbed vaccine and a single dose PLGA microsphere vaccine. However, on day 15, the antibody level of the double dose aluminum hydroxide-adsorbed vaccine was 4 IU/ml and the antibody level of the single dose PLGA microsphere vaccine was found to be 2 IU/ml. A half dose of PLGA microsphere vaccine did not produce a sufficient immun response (antibody titer ˂ 2.5 IU/ml). The results of this study show that PLGA biopolymer can be used in the development of single dose veterinary vaccines. However, more extensive studies should be done by using different polymer types and encapsulation methods in vaccine development studies.