A live attenuated H7N7 candidate vaccine virus induces neutralizing antibody that confers protection from challenge in mice, ferrets, and monkeys.

A live attenuated H7N7 candidate vaccine virus was generated by reverse genetics using the modified hemagglutinin (HA) and neuraminidase (NA) genes of highly pathogenic (HP) A/Netherlands/219/03 (NL/03) (H7N7) wild-type (wt) virus and the six internal protein genes of the cold-adapted (ca) A/Ann Arbor/6/60 ca (AA ca) (H2N2) virus. The reassortant H7N7 NL/03 ca vaccine virus was temperature sensitive and attenuated in mice, ferrets, and African green monkeys (AGMs). Intranasal (i.n.) administration of a single dose of the H7N7 NL/03 ca vaccine virus fully protected mice from lethal challenge with homologous and heterologous H7 viruses from Eurasian and North American lineages. Two doses of the H7N7 NL/03 ca vaccine induced neutralizing antibodies in serum and provided complete protection from pulmonary replication of homologous and heterologous wild-type H7 challenge viruses in mice and ferrets. One dose of the H7N7 NL/03 ca vaccine elicited an antibody response in one of three AGMs that was completely protected from pulmonary replication of the homologous wild-type H7 challenge virus. The contribution of CD8(+) and/or CD4(+) T cells to the vaccine-induced protection of mice was evaluated by T-cell depletion; T lymphocytes were not essential for the vaccine-induced protection from lethal challenge with H7 wt viruses. Additionally, passively transferred neutralizing antibody induced by the H7N7 NL/03 ca virus protected mice from lethality following challenge with H7 wt viruses. The safety, immunogenicity, and efficacy of the H7N7 NL/03 ca vaccine virus in mice, ferrets, and AGMs support the evaluation of this vaccine virus in phase I clinical trials.