Replication and Immunogenicity of Swine, Equine, and Avian H3 Subtype Influenza Viruses in Mice and Ferrets

Abstract

Since it is difficult to predict which influenza virus subtype will cause an influenza pandemic, it is important to prepare influenza virus vaccines against different subtypes and evaluate the safety and immunogenicity of candidate vaccines in preclinical and clinical studies prior to a pandemic. In addition to infecting humans, H3 influenza viruses commonly infect pigs, horses, and avian species. We selected 11 swine, equine, and avian H3 influenza viruses and evaluated their kinetics of replication and ability to induce a broadly cross-reactive antibody response in mice and ferrets. The swine and equine viruses replicated well in the upper respiratory tract of mice. With the exception of one avian virus that replicated poorly in the lower respiratory tract, all of the viruses replicated in mouse lungs. In ferrets, all of the viruses replicated well in the upper respiratory tract, but the equine viruses replicated poorly in the lungs. Extrapulmonary spread was not observed in either mice or ferrets. No single virus elicited antibodies that cross-reacted with viruses from all three animal sources. Avian and equine H3 viruses elicited broadly cross-reactive antibodies against heterologous viruses isolated from the same or other species, but the swine viruses did not. We selected an equine and an avian H3 influenza virus for further development as vaccines.

Hemagglutinin Stalk-Based Universal Vaccine Constructs Protect against Group 2 Influenza A Viruses

“…These antibodies were not only protective against a panel of H3N2 strains and an H3N8 virus but also provided robust protection against a heterosubtypic challenge with avian H7N1 and H10N7 isolates, demonstrating a breadth that spans both clades of the group 2 HA-expressing viruses. This breadth is important in light of growing concerns about the pandemic potential of H3N2 variant (H3N2v) viruses and H3N8 viruses isolated from New England harbor seals and other zoonotic H3 strains (12,34,38), as well as H4-, H7-, and H10-expressing viruses that infect humans occasionally (11,(39)(40)(41)(42)(43). Importantly, this vaccination strategy also induced high titers of stalk-reactive antibodies against the H7 HA from the emerging Chinese H7N9 virus (10).…”

“…Low vaccine efficacy was also observed in the elderly during the 2012-2013 epidemic (caused mostly by H3N2 strains) (8). Furthermore, mismatch-independent vaccine failure in certain populations (9) and the pandemic threat from avian viruses like H7N9 and other zoonotic influenza viruses (10)(11)(12) warrant the development of better, longer-lasting, and broader vaccines.…”

A Single Dose of an Avian H3N8 Influenza Virus Vaccine Is Highly Immunogenic and Efficacious against a Recently Emerged Seal Influenza Virus in Mice and Ferrets

“…The H3N2 viruses that we selected circulated during the 1960s (A/HK/68), 1970s (A/PC/73), 1980s (A/LA/87), 1990s (A/WU/ 95), 2000s (A/CA/04), and 2010s (A/TX/12). Sera from ferrets infected with the tl/TX/079/07 virus in a previous study (14) served as a positive control. The results are presented in Fig.…”

“…On days 3 and 5 p.c., groups of three ferrets were euthanized, and the NTs and lungs (right middle lobe and the caudal portion of the left cranial lobe) were harvested and stored at Ϫ80°C. We chose these time points based on previous observations in our laboratory that replication of avian wt viruses was detected at high titers in the NTs and lungs of ferrets from days 1 to 5 after infection (14).…”

“…), and lungs and nasal turbinates (NTs) were harvested and stored at Ϫ80°C. We chose these time points based on previous observations that replication of the tl/TX/079/07 and npin/AK/06 wt viruses was detected at moderate to high titers in the lungs of mice from days 2 to 4 after infection (14). Lungs and NTs were weighed and homogenized in L15 medium containing 2ϫ antibiotic-antimycotic (penicillin, streptomycin, and amphotericin B) (Invitrogen-GIBCO) to make 10% and 5% (wt/vol) tissue homogenates, respectively.…”