Synergistic effect of formulated plasmid and needle-free injection for genetic vaccines

Purpose. A plasmid-based gene expression system was complexed with protecti ve, interactive, and non-condensing (PINC(TM)) polymer system and administe red with Medi-Jector(TM), a needle-free injection device (NFID), to achieve high and sustained levels of antigen-specific antibodies in blood circulat ion. Methods. Human growth hormone (hGH) or bacterial beta-galactosidase gene ex pression plasmids driven by a cytomegalovirus (CMV) promoter were formulate d in saline or complexed with a PINC polymer, polyvinylpyrrolidone (PVP), a nd intramuscularly or subcutaneously administered into dogs and pigs using a 22-gauge needle or a NFID. The hGH-specific IgG titers in serum were meas ured by an ELISA. beta-galactosidase expression was measured in injected mu scles by an enzymatic assay or immunohistochemistry. The effect of NFID on DNA stability and topology was assessed by gel electrophoresis. Results. Intramuscular (i.m.) or subcutaneous (s.c.) injection of a hGH exp ression plasmid pCMV-hGH (0.05-0.5 mg/kg) in dogs and pigs elicited antigen -specific IgG antibody titers to expressed hGH. With both routes of injecti on, pDNA delivery by a NFID was superior to pDNA injection by needle. The m agnitude of hGH-specific IgG titers with NFID was 15-20-fold higher than ne edle injection when pDNA was complexed with PVP, and only 3-4-fold higher w ith pDNA in saline. The transfection efficiency in the injected muscle, as measured by beta-galactosidase expression, following i.m. injection of pCMV -beta-galactosidase/PVP, was not significantly different between needle and NFID-injected groups. Conclusions. These data demonstrate that the combination of pDNA/PVP comple xes and a NFID act synergistically to achieve high and sustained levels of antigen-specific IgG response to expressed antigen. This gene delivery appr oach may offer advantage over needle injection of naked DNA for the develop ment of genetic vaccines.