A Whole Virus Pandemic Influenza H1N1 Vaccine Is Highly Immunogenic and Protective in Active Immunization and Passive Protection Mouse Models

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

Immunogenicity and protective efficacy of a Vero cell culture-derived whole-virus H7N9 vaccine in mice and guinea pigs.

A novel avian H7N9 virus with a high case fatality rate in humans emerged in China in 2013. We evaluated the immunogenicity and protective efficacy of a candidate Vero cell culture-derived whole-virus H7N9 vaccine in small animal models.Antibody responses induced in immunized DBA/2J mice and guinea pigs were evaluated by hemagglutination inhibition (HI), microneutralization (MN), and neuraminidase inhibition (NAi) assays. T-helper cell responses and IgG subclass responses in mice were analyzed by ELISPOT and ELISA, respectively. Vaccine efficacy against lethal challenge with wild-type H7N9 virus was evaluated in immunized mice. H7N9-specific antibody responses induced in mice and guinea pigs were compared to those induced by a licensed whole-virus pandemic H1N1 (H1N1pdm09) vaccine.The whole-virus H7N9 vaccine induced dose-dependent H7N9-specific HI, MN and NAi antibodies in mice and guinea pigs. Evaluation of T-helper cell responses and IgG subclasses indicated the induction of a balanced Th1/Th2 response. Immunized mice were protected against lethal H7N9 challenge in a dose-dependent manner. H7N9 and H1N1pdm09 vaccines were similarly immunogenic.The induction of H7N9-specific antibody and T cell responses and protection against lethal challenge suggest that the Vero cell culture-derived whole-virus vaccine would provide an effective intervention against the H7N9 virus

HA and NA antibody responses induced by H7N9 and H1N1pdm09 vaccines in DBA/2J mice.

<p>^a20 animals per dose group for both vaccines.</p><p>^b10 animals per dose group for both vaccines.</p><p>^c20 animals per dose group for H7N9 vaccine; 10 animals per dose group for H1N1 pdm09 vaccine.</p><p>^dGeometric mean titer</p><p>^eSeroconversion (≥4-fold increase in antibody titer and antibody titer ≥ 1:40)</p><p>n.d., not done; n.a., not applicable.</p><p>HA and NA antibody responses induced by H7N9 and H1N1pdm09 vaccines in DBA/2J mice.</p

Dose-dependent protection against disease symptoms and death in H7N9-challenged DBA/2J mice immunized with whole-virus H7N9 vaccine.

<p>(A) Kaplan-Meier survival curves, (B) Severity and duration of disease symptoms</p

HA and NA antibody responses induced by H7N9 and H1N1pdm09 vaccines in guinea pigs.

<p>^a10 animals per dose group for both vaccines.</p><p>^bGeometric mean titer</p><p>^cSeroconversion (≥4-fold increase in antibody titer and antibody titer ≥ 1:40)</p><p>n.d., not done; n.a., not applicable</p><p>HA and NA antibody responses induced by H7N9 and H1N1pdm09 vaccines in guinea pigs.</p

Th-1 and Th-2 cytokine and IgG subclass responses in mice immunized with pandemic H7N9.

<p>DBA/2J mice were immunized with whole-virus (WV) H7N9 vaccine or buffer as control on days 0 and 21. Spleen cells were collected 7 days after the first, or 21 days after the booster immunization (i.e. 42 days after the first), and stimulated with whole-virus (WV) H7N9 vaccine or recombinant H7 HA (rHA) for the determination of cells responding to the antigens by secretion of either IFN-γ (A) or IL-4 (B) using an ELISPOT assay. Statistically significant differences of comparisons between T cell responses in mice receiving H7N9 vaccine or buffer are shown. H7 HA-specific IgG subclass responses were analyzed by ELISA using sera collected on day 42 (C). IgG subclass responses on day 42 were compared by ANOVA. ***, p<0.0001; ns, not significant.</p