Purpose: To enhance the water affinity of W/O emulsion-adjuvanted vaccines, we used three bioresorbable polymers named PEG-b-PLA, PEG-b-PCL, and PEG-b-PLACL as hydrophilic emulsifier to stabilize the interfaces between the oily Montanide ISA 51 adjuvant and the antigen media. Methods: Polymers were synthesized by ring-opening polymerization of lactide and/or ε-caprolactone in the presence of monomethoxy PEG. 1H NMR and GPC data showed that obtained polymers consisted of 70 wt.% hydrophilic PEG block and 30 wt.% lipophilic PLA, PCL, PLACL block with molecular weights of 7,000. Results: The polymer-stabilized ISA51 emulsions have high affinity to water, such that the stock of antigen-encapsulating emulsion could be re-dispersed into PBS before injection, thus yielding stable and injectable W/O/W emulsion nanoparticles. Immunogenicity studies showed that PEG-b-PLACL/ISA51/PBS-formulated ovalbumin with only 5% of ISA51 oily adjuvant could induce the same level of antibody titers as those induced by PBS/ISA51-formulated ovalbumin. Conclusions: The novel multi-phase emulsions increase fluidity and conceptually diminish local reactions with respect to the W/O type vaccines produced from the same oil. These features are of great interest for applications in candidate vaccine delivery, especially for further optimization of alternative immunization routes, such as intramuscular, transdermal or mucosal administration.
