Enhanced immune response of DNA vaccine (VP1-pCDNA) adsorbed on cationic PLG for foot and mouth disease in guinea pigs

Foot and mouth disease (FMD) is the major constraint to international trade in livestock and animal products. Though conventional vaccine has shown to provide protection, it has several limitations, like short duration of immunity and poor cell mediated immune response compared to DNA vaccines, which are known to induce both cell mediated as well as humoral responses. The present work envisages the production of DNA vaccine construct with partial 1D gene (coding for VP1) of FMDV type 'A' and studied the efficacy of the vaccine coated on cationic PLGA micro-particles in guinea pigs. Sequence coding for VP1 of serotype 'A' was amplified by PCR and cloned into mammalian expression vector, pCDNA-containing FMDV IRES. Expression of the construct was confirmed by transfection of the plasmid into BHK-21 cells followed by the protein profile by SDS-PAGE and Western blotting of the cell lysate. Guinea pigs were immunized with 25 mu g of the vaccine construct intramuscularly, followed by a booster at 21st day. Sera from the animals of all the groups (pre-vaccinated, 14, 21, and 28 days of post-vaccination) was analyzed by ELISA and SNT. ELISA titers indicated significant improvement in the antibody titers in the PLG-coated DNA group (2.408 + 0.06), whereas the naked plasmid gave a titer of 1.505+. Serum neutralization titers were higher in PLG-coated vaccine group compared to the animals that received the naked DNA vaccine. Increased CTL response measured by MTT stimulation index (1.58 + 0.08) was observed in the case of PLG-coated DNA vaccine construct compared to the naked DNA vaccine (1.29 + 0.068). PLG-DNA vaccine construct conferred 100% protection to the animals when challenged with 100GpID50 of homologous virus compared to 50% protection in case of naked DNA vaccine construct. The present study has shown that adjuvantation with PLG markedly improved the efficacy of DNA vaccine against FMDV.