AS03-Adjuvanted, Very-Low-Dose Influenza Vaccines Induce Distinctive Immune Responses Compared to Unadjuvanted High-Dose Vaccines in BALB/c Mice

Abstract

During the 2009–2010 influenza pandemic, an adjuvanted, dose-sparing vaccine was recommended for most Canadians. We hypothesize that differences exist in the responses to AS03-adjuvanted, low antigen (Ag) dose versus unadjuvanted, full-dose vaccines. We investigated the relationship between Ag dose and the oil-in-water emulsion Adjuvant System AS03. BALB/c mice received two IM doses of AS03A or AS03B with exaggerated dilutions of A/Uruguay/716/2007 H3N2 split virion vaccine Ag. Immune responses were assessed 3 weeks after the booster. Unadjuvanted “high” (3 μg) and low-dose (0.03–0.003 μg) vaccines generated similar serum antibody titers and cytokine secretion patterns in restimulated splenocytes. Compared to unadjuvanted “high-dose” vaccination, both AS03A and AS03B-adjuvanted low-dose vaccines tended to elicit higher serum antibody titers, broader induction of cytokine secretion and generated more influenza-specific antibody secreting cells and cytokine-secreting CD4 and CD8 T cells in splenocytes. We show that varying Ag and/or AS03 dose in this influenza vaccination mouse model can strongly influence both the magnitude and pattern of the immune response elicited. These findings are highly relevant given the likelihood of expanded use of adjuvanted, dose-sparing vaccines and raise questions about the use of “standard” doses of vaccines in pre-clinical vaccine studies.

Low hemagglutinin antigen dose influenza vaccines adjuvanted with AS03 alter the long-term immune responses in BALB/c mice

“…The mice vaccinated with the lowest-doseCAS03 generally had intermediate serologic response between the 0.03 mg HACAS03 and the HD-unadjuvanted groups. Similar to what we observed in the short-term study, 6 high HA-specific antibody avidity was present by 1 week pb in all groups and remained elevated throughout the 34 week study (Fig. 1D).…”

“…These trends confirm and extend our splenocyte observations with LDCAS03 formulations at 3 weeks pb. 6 In apparent contradiction to the numbers of ASCs detected by ELISpot in response to the different vaccines, ELISpot size tended to be greatest in the HD-unadjuvanted animals at later timepoints. The size of spots in the ELISpot assay is thought to reflect the amount of antibody secreted by each cell.…”

“…This body of work has demonstrated that AS03-adjuvanted, dose-sparing formulations can induce strong serum antibody responses that persist for at least 12 months in healthy children, [13][14][15][16][17] adults [18][19][20][21][22][23] and the elderly, [24][25][26] and that influenza-specific, poly-functional CD4C T cells can be detected in human PBMC samples for at least 6 months after vaccination. [27][28][29] We have previously shown that AS03 can induce powerful humoral 6,12 and cellular responses 6 to influenza antigens over a surprisingly wide range of Ag doses (100-to 1000-fold lower than a 'standard' 3 mg HA dose in mice) at 3 weeks after a booster immunization The objective of this study was to determine the persistence of these responses up to 34 weeks after LD-AS03-adjuvanted vs. HD-unadjuvanted vaccination. We observed the same trends for AS03 effects seen at 3 weeks post-boost (i.e.…”

“…6,[10][11][12] The pandemic experience created the unusual situation in which much of what we know about the immunological impact of AS03 is derived from human studies. This body of work has demonstrated that AS03-adjuvanted, dose-sparing formulations can induce strong serum antibody responses that persist for at least 12 months in healthy children, [13][14][15][16][17] adults [18][19][20][21][22][23] and the elderly, [24][25][26] and that influenza-specific, poly-functional CD4C T cells can be detected in human PBMC samples for at least 6 months after vaccination.…”

“…This previous work found that even extremely low doses of Ag administered with AS03 could generate a humoral response equivalent to that induced by a higher ('standard') dose (3 mg HA) but with much broader activation of cytokines. 6 This work suggested that both Ag and adjuvant dose in AS03-adjuvanted formulations could strongly influence the quality and quantity of immune responses elicited. We next sought to investigate the durability of the responses induced in our very low-dose vaccine model.…”