Immunomodulatory and physical effects of oil composition in vaccine adjuvant emulsions

Abstract

Squalene-based oil-in-water emulsions have been used for years in some seasonal and pandemic influenza vaccines. However, concerns have been expressed regarding squalene source and potential biological activities. Little information is available regarding the immunomodulatory activity of squalene in comparison with other metabolizable oils in the context of oil-in-water emulsions formulated with vaccines. The present work describes the manufacture and physical characterization of emulsions composed of different classes of oils, including squalene, long chain triglycerides, a medium chain triglyceride, and a perfluorocarbon, all emulsified with egg phosphatidylcholine. Some differences were apparent among the non-squalene oils in terms of emulsion stability, including higher size polydispersity in the perfluorocarbon emulsion, more rapid visual instability at 60 °C for the long-chain triglyceride and perfluorocarbon emulsions, and an increased creaming rate in the medium-chain triglyceride emulsion at 60 °C as detected by laser scattering optical profiling. The biological activity of each of these emulsions was compared when formulated with either a recombinant malaria antigen or a split-virus inactivated influenza vaccine. Overall, vaccines containing the squalene emulsion elicited higher antibody titers and more abundant long-lived plasma cells than vaccines containing emulsions based on other oils. Since squalene-based emulsions show higher adjuvant potency compared to the other oils tested, non-squalene oils may be more suitable as carriers of amphiphilic or hydrophobic immunostimulatory molecules (such as TLR agonists) rather than as stand-alone adjuvants.

Adjuvanted pandemic influenza vaccine: variation of emulsion components affects stability, antigen structure, and vaccine efficacy

“…In contrast, substitution of squalene with a MCT oil caused a dramatic loss in biological activity in virtually all assays conducted. This finding correlates well with related work where squalene was found to induce more adjuvant activity compared with multiple other biocompatible oils when formulated with a recombinant malaria antigen or a split‐inactivated influenza vaccine 3 . The mechanisms responsible for the enhanced adjuvant activity of squalene emulsions are not clear.…”

Immunomodulatory and Physical Effects of Phospholipid Composition in Vaccine Adjuvant Emulsions

“…Egg phosphatidylcholine (egg PC), POPC, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoylsn-glycero-3-phosphocholine (DMPC), and 1,2-dilauroylsn-glycero-3-phosphocholine (DLPC) were obtained from Avanti Polar Lipids, Inc. at 99% purity (Alabaster, AL, USA). All emulsion formulations were prepared by high-speed mixing an oil phase (containing squalene and phospholipid) and an aqueous phase followed by high-pressure homogenization, as described previously (8). The final concentration of phospholipid was 25 mM.…”

“…Formulations were monitored for stability over 6 months at 5°C, room temperature (RT), 37°C, and 60°C. Particle size, zeta potential, viscosity, hemolysis, and light scattering optical profiling measurements were performed as described previously (8). Briefly, particle size was determined at the indicated timepoints by diluting an aliquot of each emulsion 1:100-fold in water and measuring the scattering intensity-biased size average (Z-avg) by dynamic light scattering (Malvern Zetasizer APS).…”

“…(2) recombinant Plasmodium berghei circumsporozoite protein (PbCSP) produced in-house using the codon-harmonized construct developed by Walter Reed Army Institute of Research. Influenza and malaria vaccine formulations, immunization regimens, and serum collection were as described earlier (8), except that the influenza antigen dose was 0.02 μg total HA. All procedures were performed under specific pathogen-free conditions and in accordance with the regulations and guidelines of the Infectious Disease Research Institute animal care and use committee.…”

“…We have previously published the physical stability profile of squalene emulsions stabilized by egg PC (8,9). Moreover, we showed that synthetic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC; a main component of egg PC) provided equivalent stability to a squalene emulsion compared to egg PC.…”