ABSTRACT
The recent emergence and rapid spread of a novel swine-derived H1N1 influenza virus has resulted in the first influenza pandemic of this century. Monovalent vaccines have undergone preclinical and clinical development prior to initiation of mass immunization campaigns. We have carried out a series of immunogenicity and protection studies following active immunization of mice, which indicate that a whole virus, nonadjuvanted vaccine is immunogenic at low doses and protects against live virus challenge. The immunogenicity in this model was comparable to that of a whole virus H5N1 vaccine, which had previously been demonstrated to induce high levels of seroprotection in clinical studies. The efficacy of the H1N1 pandemic vaccine in protecting against live virus challenge was also seen to be equivalent to that of the H5N1 vaccine. The protective efficacy of the H1N1 vaccine was also confirmed using a severe combined immunodeficient (SCID) mouse model. It was demonstrated that mouse and guinea pig immune sera elicited following active H1N1 vaccination resulted in 100% protection of SCID mice following passive transfer of immune sera and lethal challenge. The immune responses to a whole virus pandemic H1N1 and a split seasonal H1N1 vaccine were also compared in this study. It was demonstrated that the whole virus vaccine induced a balanced Th-1 and Th-2 response in mice, whereas the split vaccine induced mainly a Th-2 response and only minimal levels of Th-1 responses. These data supported the initiation of clinical studies with the same low doses of whole virus vaccine that had previously been demonstrated to be immunogenic in clinical studies with a whole virus H5N1 vaccine.
Subject(s)
Influenza A Virus, H1N1 Subtype/immunology , Influenza Vaccines/immunology , Orthomyxoviridae Infections/immunology , Vaccination/methods , Viral Vaccines/immunology , Animals , Disease Models, Animal , Disease Outbreaks , Humans , Influenza A Virus, H5N1 Subtype/immunology , Influenza Vaccines/administration & dosage , Influenza, Human/epidemiology , Influenza, Human/immunology , Influenza, Human/prevention & control , Mice , Mice, Inbred BALB C , Mice, SCID , Orthomyxoviridae Infections/prevention & control , Swine/virology , Th1 Cells/immunology , Th2 Cells/immunology , Treatment Outcome , Viral Vaccines/administration & dosage , Viremia/immunology , Viremia/prevention & controlABSTRACT
We discovered a unique, single amino acid mutation in the influenza B M1 protein promoting viral growth of NS1 truncation mutants in Vero cells. Due to this mutation, we were able to generate an influenza B virus lacking the complete NS1 open reading frame (DeltaNS1-B virus) by reverse genetics, which was growing to titers of 8log(10)TCID(50)/ml in a Vero cell culture-based micro-carrier fermenter. The DeltaNS1-B vaccine candidate was attenuated in IFN-competent hosts such as human alveolar epithelial cells (A549) similar to influenza A DeltaNS1 viruses. In ferrets, the DeltaNS1-B virus was replication-deficient and did not provoke any clinical symptoms. Importantly, a single intranasal immunization of ferrets at a dose as low as 6 log(10)TCID(50)/animal induced a significant HAI response and provided protection against challenge with wild-type influenza B virus. So far, the lack of a DeltaNS1-B virus component growing to high titers in cell culture has been limiting the possibility to formulate a trivalent vaccine based on deletion of the NS1 gene. Our study closes this gap and paves the way for the clinical evaluation of a seasonal, trivalent, live replication-deficient DeltaNS1 intranasal influenza vaccine.
Subject(s)
Influenza B virus/immunology , Influenza Vaccines/administration & dosage , Influenza Vaccines/immunology , Viral Nonstructural Proteins/immunology , Administration, Intranasal , Animals , Base Sequence , Cell Line , Chlorocebus aethiops , Ferrets/immunology , Humans , Influenza B virus/genetics , Influenza B virus/metabolism , Mutation/genetics , Orthomyxoviridae Infections/immunology , Orthomyxoviridae Infections/prevention & control , Vaccines, Attenuated/genetics , Vaccines, Attenuated/immunology , Vaccines, Attenuated/metabolism , Viral Nonstructural Proteins/genetics , Viral Nonstructural Proteins/metabolism , Virus ReplicationABSTRACT
The rapid spread and the transmission to humans of avian influenza virus (H5N1) have induced world-wide fears of a new pandemic and raised concerns over the ability of standard influenza vaccine production methods to rapidly supply sufficient amounts of an effective vaccine. We report here on a robust and flexible strategy which uses wild-type virus grown in a continuous cell culture (Vero) system to produce an inactivated whole virus vaccine. Candidate vaccines based on clade 1 and clade 2 influenza H5N1 strains were developed and demonstrated to be highly immunogenic in animal models. The vaccines induce cross-neutralising antibodies, highly cross-reactive T-cell responses and are protective in a mouse challenge model not only against the homologous virus but also against other H5N1 strains, including those from another clade. These data indicate that cell culture-grown whole virus vaccines, based on the wild-type virus, allow the rapid high yield production of a candidate pandemic vaccine.
