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.

Virus-like-particle (VLP) influenza vaccines can be given intramuscularly (i.m.) or intranasally (i.n.) and may have advantages over split-virion formulations in the elderly. We tested a plant-made VLP vaccine candidate bearing the viral hemagglutinin (HA) delivered either i.m. or i.n. in young and aged mice. Young adult (5-to 8-week-old) and aged (16-to 20-month-old) female BALB/c mice received a single 3-g dose based on the HA (A/California/07/2009 H1N1) content of a plant-made H1-VLP (i.m. or i.n.) split-virion vaccine (i.m.) or were left naive. After vaccination, humoral and splenocyte responses were assessed, and some mice were challenged. Both VLP and split vaccines given i.m. protected 100% of the young animals, but the VLP group lost the least weight and had stronger humoral and cellular responses. Compared to split-vaccine recipients, aged animals vaccinated i.m. with VLP were more likely to survive challenge (80% versus 60%). The lung viral load postchallenge was lowest in the VLP i.m. groups. Mice vaccinated with VLP i.n. had little detectable immune response, but survival was significantly increased. In both age groups, i.m. administration of the H1-VLP vaccine elicited more balanced humoral and cellular responses and provided better protection from homologous challenge than the splitvirion vaccine.KEYWORDS aged-mouse model, influenza, virus-like particles (VLPs), plant-made vaccines A ccording to the World Health Organization, influenza epidemics account for 250,000 to 500,000 deaths worldwide every year (http://www.who.int/mediacentre/factsheets/ fs211/en/). Although vaccines are widely recommended to protect against influenza, the elderly often respond poorly, in part due to prior experience with influenza virus antigens (Ag) (1), but also as a result of immunosenescence (2). The latter affects both innate and adaptive immune responses and has broad implications for both natural infection and vaccination (1, 2).Influenza vaccines for adults are administered by either intramuscular (i.m.) or intradermal injection of detergent-split virions at a fixed dose of 15 g hemagglutinin (HA)/strain (3). These vaccines typically elicit strong antibody responses in healthy young adults and achieve vaccine efficacy (VE) that varies between strains and years but averages 50 to 60% (4). These formulations work less well in the elderly (5

Clostridium difficile disease is mediated primarily by toxins A and B (TcdA and TcdB, respectively). The receptor binding domains (RBD) of TcdA and TcdB are immunogenic, and anti-RBD antibodies are protective. Since these toxins act locally, an optimal C. difficile vaccine would generate both systemic and mucosal responses. We have repurposed an attenuated Salmonella enterica serovar Typhimurium strain (YS1646) to produce such a vaccine. Plasmid-based candidates expressing either the TcdA or TcdB RBD were screened. Different vaccine routes and schedules were tested to achieve detectable serum and mucosal antibody titers in C57BL/6J mice. When given in a multimodality schedule over 1 week (intramuscularly and orally [p.o.] on day 0 and p.o. on days 2 and 4), several candidates provided 100% protection against lethal challenge. Substantial protection (82%) was achieved with combined p.o. TcdA and TcdB vaccination alone (days 0, 2, and 4). These data demonstrate the potential of the YS1646-based vaccines for C. difficile and strongly support their further development.

Potential financial conflict of interest: D. Vinh is supported by the Clinician-Scientist Scholar Junior 2 program of the Fonds de la recherche en santé du Québec and has received research support from Cidara Therapeutics, CSL Behring and Janssen Pharmaceutical, and consulting or speaker honoraria from CSL Behring, Novartis Canada, and UCB Biosciences GmbH. None of these entities were involved in any aspect of the research in this manuscript. D. Vinh has a patent application pending (EFS ID: 40101099), unrelated to the research in this manuscript. M. Ndao reports having filed on April 2, 2019 the McGill report of invention ROI 2019-107, unrelated to the research in this manuscript. A report of invention has been submitted by D. Vinh, on behalf of D. Vinh, M. Golizeh, and M. Ndao, to McGill University for the work in this manuscript (Track code: D2021-0043). 10 V. Loo has received consulting fees for Merck Canada Inc.