Abstract
Influenza hemagglutinin (HA) is considered a major protective antigen of seasonal influenza vaccine but antigenic drift of HA necessitates annual immunizations using new circulating HA versions. Low variation found within conserved non-HA influenza virus (INFV) antigens may maintain protection with less frequent immunizations. Conserved antigens of influenza A virus (INFV A) that can generate cross protection against multiple INFV strains were evaluated in BALB/c mice using modified Vaccinia virus Ankara (MVA)-vectored vaccines that expressed INFV A antigens hemagglutinin (HA), matrix protein 1 (M1), nucleoprotein (NP), matrix protein 2 (M2), repeats of the external portion of M2 (M2e) or as tandem repeats (METR), and M2e with transmembrane region and cytoplasmic loop (M2eTML). Protection by combinations of non-HA antigens was equivalent to that of subtype-matched HA. Combinations of NP and forms of M2e generated serum antibody responses and protected mice against lethal INFV A challenge using PR8, pandemic H1N1 A/Mexico/4108/2009 (pH1N1) or H5N1 A/Vietnam/1203/2004 (H5N1) viruses, as demonstrated by reduced lung viral burden and protection against weight loss. The highest levels of protection were obtained with NP and M2e antigens delivered as MVA inserts, resulting in broadly protective immunity in mice and enhancement of previous natural immunity to INFV A.
Highlights
Despite the high rates of spontaneous mutation among RNA viruses, a rate close to the maximum value compatible with viability [1], control of disease from influenza virus (INFV), an RNA virus, is attempted by vaccination
Conserved antigens of influenza A virus (INFV A) that can generate cross protection against multiple INFV strains were evaluated in BALB/c mice using modified Vaccinia virus Ankara (MVA)-vectored vaccines that expressed INFV A antigens hemagglutinin (HA), matrix protein 1 (M1), nucleoprotein (NP), matrix protein 2 (M2), repeats of the external portion of M2 (M2e) or as tandem repeats (METR), and M2e with transmembrane region and cytoplasmic loop (M2eTML)
Relative protective capability as weight loss was more comparative than survival, resulting first in selection of bivalent NP with any M2 variation as potent vaccines, verification that heterologous INFV infection (PR8) prior to immunization with trivalent M1 + NP + METRC provided weight loss protection nearly equivalent to HA vaccine matched to H5 challenge INFV
Summary
Despite the high rates of spontaneous mutation among RNA viruses, a rate close to the maximum value compatible with viability [1], control of disease from INFV, an RNA virus, is attempted by vaccination. Seasonal influenza vaccines that are based upon matching to current HA types, have limitations, examples of which are: (a) a low pooled efficacy of 59% in adults aged 18–65 years [2]; (b) only 24% cross reactivity based upon seasonal influenza vaccine (2009–2010) for seroprotective HA-based titer to pandemic 2009 swine H1N1 influenza virus [3]; and (c) escape mutations, for example 42.9% of individuals who succumbed to pandemic influenza in 2009 had been infected with INFV that had one of two identified HA mutations [4] that may have assisted immune escape. Some INFV proteins have lower mutation rates compared to HA. The INFV matrix protein gene [5] has a lower rate of nucleotide substitution compared to HA [6]. The amino acid substitution rate per amino acid per year is 0.00074 for INFV NP [7] compared to 0.006 for human INFV A HA
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