Abstract A51: Intradermal delivery of polymeric nanoparticle based vaccine formulation using a hollow microneedle system

Abstract

Abstract Introduction: Nanoparticle (NP)-based anticancer vaccine delivery systems provide a number of advantages including spatial repetitive display of the antigen, size dependent lymphatic and intracellular trafficking, and the depot effect of persistence and sustained release of antigens/adjuvants. However, the optimal NP delivery mode and route of administration need additional investigation. To achieve reproducible intradermal PLGA NP vaccine delivery using an in-vivo rat model, we used a hollow microneedle array system (1). The profile of the resulting humoral and cellular immune responses was compared to that resulting from conventional intramuscular (IM) injection of the same formulation. Methods: Immunostimulatory Nanoparticles (ISNPs) loaded with imiquimod and monophosphoryl Lipid A (MPL-A) were created using emulsion- solvent evaporation technique. All vaccine formulations for the in vivo study contained 2 mg of ISNPs as the adjuvant component. Antigen was given either in the form of soluble OVA solution or OVA encapsulated PLGA NPs at equivalent doses of OVA (16 µg). Two doses of vaccine (prime and boost) were administered to Crl:CD(SD) rats three weeks apart via IM or ID delivery. ID delivery was enabled by a plastic, hollow microneedle array with 18 microneedles, each <1mm in length, similar to those referenced previously (1). Blood collection was carried out three weeks after each dose. Serially-diluted serum was incubated with OVA coated plate for IgG1/IgG2a titer test by ELISA. Spleens were harvested at the endpoint of the experiment (three weeks after the booster dose) for splenocyte isolation. The T cell response was determined by pulsing the splenocyte culture with OVA antigen using a Mabtech rat Interferon gamma ELISpot kit. Results and Discussion: ISNPs promoted high antigen-specific antibody response in both IM and ID vaccination groups. Compared to the soluble form, antigen encapsulated in NPs triggered significantly stronger IgG1 antibody response three weeks after priming dose regardless of administration route. Not only did the NP formulation demonstrate faster kinetics in mounting antibody response, but the antibody avidity, determined by Urea ELISA, was also better in the OVA NP formulation when compared to the soluble OVA formulation, indicating quicker progress of antibody affinity maturation. However, three weeks after the boost, IgG1 level of all groups were comparable, reaching a titer plateau. In contrast to the IgG1 response, antigen OVA encapsulated in NPs and delivered intradermally via the microneedles resulted in the highest IgG2a titer among all experimental groups at both time points after both priming and booster doses. IgG2a is widely considered a surrogate biomarker for Th1 response, while IgG1 is a biomarker for Th2 response. The relative strength of Th1/Th2 response could be assessed from IgG1/IgG2a ratio (2). Among the different groups, ID delivery of the OVA NP formulation demonstrated the highest relative strength of Th1 response. This result was further confirmed by the secretion of Th1 cytokine Interferon gamma by splenocytes upon antigen recall response. These data suggest that for a NP vaccine carrier, the skin is a vaccination priming locus that enhances Th1 response, which is considered essential for effective induction of anti-tumor immunity. Conclusion: A polymer-based NP vaccine formulation delivered intradermally via hollow microneedles elicited robust humoral and cellular immunity. When compared to IM injection, the unique combination of the polymeric NP formulation and the ID route of administration led to an optimal Th1 immune response.