The effect of co-administration of adjuvants with a nanoparticle-based genetic vaccine delivery system on the resulting immune responses

Abstract

Previously, we reported on a novel cationic nanoparticle-based DNA vaccine delivery system. In the present studies, the effects of co-administration of two well-known adjuvants, cholera toxin (CT) and lipid A (LA), with plasmid DNA (pDNA)-coated nanoparticles were investigated. Balb/C mice ( n=6) were immunized with either pDNA alone (cytomegalovirus-β-galactosidase, 5 μg) or pDNA-coated nanoparticles with either 0 or 50 μg of LA on days 0, 7, and 14 subcutaneously (s.c.), or topically on shaved skin with either pDNA (5 μg) alone or pDNA-coated nanoparticles with 0, 10, or 100 μg of CT on days 0, 6, 21, and 35. Mice were sacrificed on day 28 or day 45. Serum IgG titer, in vitro cytokine release and cell proliferation of the isolated splenocytes were determined. By the topical route, immunization of mice with ‘naked’ pDNA together with 10 and 100 μg of CT significantly enhanced the antigen-specific serum IgG titer by four- and 20-fold, respectively, compared to immunization with pDNA alone. Moreover, co-administration of 100 μg CT with the pDNA-nanoparticles enhanced the IgG titer by more than 300-fold over immunization with ‘naked’ pDNA alone with no CT. In vitro interferon-γ (IFN)-γ release from splenocytes isolated from mice immunized with pDNA-coated nanoparticles with CT (100 μg) was increased by three-fold over immunization with pDNA-nanoparticles without CT. Similarly, in vitro IFN-γ release from splenocytes isolated from mice immunized with ‘naked’ pDNA with CT (100 μg) was increased by two-fold over immunization with ‘naked’ pDNA without CT. Finally, pDNA-coated nanoparticles adjuvanted with 10 μg CT resulted in the strongest splenocyte proliferation. By the s.c. route, co-administration of LA (50 μg) with pDNA resulted in more than 16-fold enhancement in IgG titer over immunization with ‘naked’ pDNA alone. Immunization with pDNA-coated nanoparticles with LA (50 μg) led to 16-fold enhancement in specific serum IgG titer over immunization with pDNA-coated nanoparticles with no LA, and more than 250-fold enhancement over immunization with ‘naked’ pDNA alone with no LA. Moreover, in vitro IFN-γ release and proliferation by splenocytes isolated from LA co-immunized mice was also significantly enhanced. In conclusion, CT (topical) and LA (s.c.) are potential adjuvants to further enhance immune responses using a novel cationic nanoparticle-based DNA vaccine delivery system.