Abstract
BackgroundThe recent swine-origin H1N1 pandemic illustrates the need to develop improved procedures for rapid production of influenza vaccines. One alternative to the current egg-based manufacture of influenza vaccine is to produce a hemagglutinin (HA) subunit vaccine using a recombinant expression system with the potential for high protein yields, ease of cloning new antigenic variants, and an established safety record in humans.Methodology/Principal FindingsWe generated a soluble HA (sHA), derived from the H3N2 virus A/Aichi/2/68, modified at the C-terminus with a GCN4pII trimerization repeat to stabilize the native trimeric structure of HA. When expressed in the baculovirus system, the modified sHA formed native trimers. In contrast, the unmodified sHA was found to present epitopes recognized by a low-pH conformation specific monoclonal antibody. We found that mice primed and boosted with 3 µg of trimeric sHA in the absence of adjuvants had significantly higher IgG and HAI titers than mice that received the unmodified sHA. This correlated with an increased survival and reduced body weight loss following lethal challenge with mouse-adapted A/Aichi/2/68 virus. In addition, mice receiving a single vaccination of the trimeric sHA in the absence of adjuvants had improved survival and body weight loss compared to mice vaccinated with the unmodified sHA.Conclusions/SignificanceOur data indicate that the recombinant trimeric sHA presents native trimeric epitopes while the unmodified sHA presents epitopes not exposed in the native HA molecule. The epitopes presented in the unmodified sHA constitute a “silent face” which may skew the antibody response to epitopes not accessible in live virus at neutral pH. The results demonstrate that the trimeric sHA is a more effective influenza vaccine candidate and emphasize the importance of structure-based antigen design in improving recombinant HA vaccines.
Highlights
Influenza virus is one of the most common causes of serious respiratory illness
Recombinant baculovirus derived Aichi/2/68 soluble HA is expressed as the HA0 precursor
Western blot analysis of the recombinant HA proteins using reference sera from A/Aichi/2/68 infected mice indicates that the recombinant proteins are antigenically similar to the viral HA (Figure 2A) and the anti-His monoclonal antibody binding demonstrates that the His-tag was included in the protein (Figure 2B)(Lane 1 = soluble HA (sHA), Lane 2 = sHA.GCN4pII)
Summary
Influenza virus is one of the most common causes of serious respiratory illness. Since the beginning of the 2009–2010 influenza season, the CDC has reported that all subtyped influenza A viruses isolated from hospitalizations were the novel 2009 H1N1 virus [1]. Influenza vaccine production in eggs requires the generation of high-yield egg growth reassortant viruses and a large supply of embryonated chicken eggs, and the vaccine has potential safety concerns in individuals with egg allergies [2,3,4,5]. For these reasons, efforts have been made to develop alternative vaccine production methods. One alternative to the current egg-based manufacture of influenza vaccine is to produce a hemagglutinin (HA) subunit vaccine using a recombinant expression system with the potential for high protein yields, ease of cloning new antigenic variants, and an established safety record in humans
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