Abstract
BackgroundH1N1 influenza viruses mutate rapidly, rendering vaccines developed in any given year relatively ineffective in subsequent years. Thus it is necessary to generate new vaccines every year, but this is time-consuming and resource-intensive. Should a highly virulent influenza strain capable of human-to-human transmission emerge, these factors will severely limit the number of people that can be effectively immunised against that strain in time to prevent a pandemic. An adjuvant and mode of administration capable of rendering ordinarily unprotective vaccine doses protective would thus be highly advantageous.MethodsThe carbohydrate mannan was conjugated to whole inactivated H1N1 influenza virus at a range of ratios, and mixed with it at a range of ratios, and various doses of the resulting preparations were administered to mice via the intranasal (IN) route. Serum immunity was assessed via antigen-specific IgG ELISA and the haemagglutination-inhibition (HI) assay, and mucosal immunity was assessed via IgA ELISA of bronchio-alveolar lavages.ResultsIN-administered inactivated H1N1 mixed with mannan induced higher serum IgG and respiratory-tract IgA than inactivated H1N1 conjugated to mannan, and HIN1 alone. Adjuvantation was mannan-dose-dependent, with 100 μg of mannan adjuvanting 1 μg of H1N1 more effectively than 10 or 50 μg of mannan. Serum samples from mice immunised with 1 μg H1N1 adjuvanted with 10 μg mannan did not inhibit agglutination of red blood cells (RBCs) at a dilution factor of 10 in the HI assay, but samples resulting from adjuvantation with 50 and 100 μg mannan inhibited agglutination at dilution factors of ≥ 40. Both serum IgG1 and IgG2a were induced by IN mannan-adjuvanted H1N1 vaccination, suggesting the induction of humoral and cellular immunity.ConclusionsMixing 100 μg of mannan with 1 μg of inactivated H1N1 adjuvanted the vaccine in mice, such that IN immunisation induced higher serum IgG and respiratory tract IgA than immunisation with virus alone. The serum from mice thus immunised inhibited H1N1-mediated RBC agglutination strongly in vitro. If mannan similarly adjuvants low doses of influenza vaccine in humans, it could potentially be used for vaccine ‘dose-sparing’ in the event that a vaccine shortage arises from an epidemic involving a highly virulent human-to-human transmissable influenza strain.
Highlights
H1N1 influenza viruses mutate rapidly, rendering vaccines developed in any given year relatively ineffective in subsequent years
We investigated the ability of mannan to adjuvant whole inactivated H1N1 (A/New Caledonia 20/ 1999) influenza virus in mice
Mucosal antibody responses to H1N1_OxMan conjugates and H1N1+ mannan mixes After immunising groups of 9 mice three times with 10 μg of H1N1 either alone, conjugated to 100 μg of mannan or mixed with 100 μg of mannan, serum was harvested from all mice 7 days after the final immunisation, and lung washes were performed on 5 mice from each group
Summary
H1N1 influenza viruses mutate rapidly, rendering vaccines developed in any given year relatively ineffective in subsequent years. Should a highly virulent influenza strain capable of human-to-human transmission emerge, these factors will severely limit the number of people that can be effectively immunised against that strain in time to prevent a pandemic. Recent threats of the potential large-scale emergence of human-to-human transmissible forms of virulent H5N1 (reviewed in Kaplan et al [4]) and H7N9 (reviewed in Wu et al [5]) avian influenza strains, and the actual emergence of widespread human-to-human transmissible variants of an H1N1 variant dubbed ‘swine-flu’ (reviewed in Dhama et al [6]) have highlighted the need for a nontoxic, cost-effective dose-sparing influenza vaccine adjuvant. An adjuvant that substantially reduces the amount of influenza virus normally required for protective vaccination would allow for faster immunisation of potentially high-risk sections of the population such as children and asthmatics, against a rapidly emerging, highly virulent influenza strain
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