A Randomized Dose-Escalating Phase I Trial of a Replication-Deficient Lymphocytic Choriomeningitis Virus Vector-Based Vaccine Against Human Cytomegalovirus.

BACKGROUND: A vaccine (HB-101) consisting of 2 nonreplicating lymphocytic choriomeningitis virus (LCMV) vectors expressing the human cytomegalovirus antigens glycoprotein B (gB) and the 65-kD phosphoprotein (pp65), respectively, is in development to prevent cytomegalovirus infection. METHODS: HB-101 was tested in cytomegalovirus-naive, healthy adults in a randomized, double-blind, placebo-controlled, dose-escalation Phase I trial. Fifty-four subjects received low, medium, or high dose of HB-101 or placebo by intramuscular administration at Month 0, 1, and 3. Safety and immunogenicity were the respective primary and secondary endpoints. Subjects were followed for 12 months after the initial immunization. RESULTS: Vaccination was associated with transient mild to moderate adverse events. HB-101 administration induced dose-dependent gB- and pp65-specific cellular responses, dominated by pp65-specific CD8 T cells, a high fraction of which were polyfunctional. Two administrations were sufficient to elicit dose-dependent gB-binding and cytomegalovirus-neutralizing antibodies (Abs). Cytomegalovirus-specific immune responses were boosted after each administration. Only 1 of 42 vaccine recipients mounted a transient LCMV vector-neutralizing Ab response. CONCLUSIONS: HB-101 was well tolerated and induced cytomegalovirus-specific polyfunctional CD8 T-cell and neutralizing Ab responses in the majority of subjects. Lack of vector-neutralizing Ab responses should facilitate booster vaccinations. These results justify further clinical evaluation of this vaccine candidate.

Additive Protection against Congenital Cytomegalovirus Conferred by Combined Glycoprotein B/pp65 Vaccination Using a Lymphocytic Choriomeningitis Virus Vector.

Subunit vaccines for prevention of congenital cytomegalovirus (CMV) infection based on glycoprotein B (gB) and pp65 are in clinical trials, but it is unclear whether simultaneous vaccination with both antigens enhances protection. We undertook evaluation of a novel bivalent vaccine based on nonreplicating lymphocytic choriomeningitis virus (rLCMV) vectors expressing a cytoplasmic tail-deleted gB [gB(dCt)] and full-length pp65 from human CMV in mice. Immunization with the gB(dCt) vector alone elicited a comparable gB-binding antibody response and a superior neutralizing response to that elicited by adjuvanted subunit gB. Immunization with the pp65 vector alone elicited robust T cell responses. Comparable immunogenicity of the combined gB(dCt) and pp65 vectors with the individual monovalent formulations was demonstrated. To demonstrate proof of principle for a bivalent rLCMV-based HCMV vaccine, the congenital guinea pig cytomegalovirus (GPCMV) infection model was used to compare rLCMV vectors encoding homologs of pp65 (GP83) and gB(dCt), alone and in combination versus Freund's adjuvanted recombinant gB. Both vectors elicited significant immune responses, and no loss of gB immunogenicity was noted with the bivalent formulation. Combined vaccination with rLCMV-vectored GPCMV gB(dCt) and pp65 (GP83) conferred better protection against maternal viremia than subunit or either monovalent rLCMV vaccine. The bivalent vaccine also was significantly more effective in reducing pup mortality than the monovalent vaccines. In summary, bivalent vaccines with rLCMV vectors expressing gB and pp65 elicited potent humoral and cellular responses and conferred protection in the GPCMV model. Further clinical trials of LCMV-vectored HCMV vaccines are warranted.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

A Novel multivalent OspA vaccine against Lyme borreliosis is safe and immunogenic in an adult population previously infected with Borrelia burgdorferi sensu lato.

Lyme borreliosis (LB) patients who recover, as well as previously infected asymptomatic individuals, remain vulnerable to reinfection with Borrelia burgdorferi sensu lato. There is limited information available about the use of OspA vaccines in this population. In this study, a randomized double-blind phase I/II trial was performed to investigate the safety and immunogenicity of a novel multivalent OspA vaccine in healthy adults who were either seronegative or seropositive for previous B. burgdorferi sensu lato infection. The participants received three monthly priming immunizations with either 30 µg or 60 µg alum-adjuvanted OspA antigen and a booster vaccination either 6 months or 9 to 12 months after the first immunization. The antibody responses to the six OspA serotypes included in the vaccine were evaluated. Adverse events were predominantly mild and transient and were similar in the seronegative and seropositive populations. Substantial enzyme-linked immunosorbent assay (ELISA) and surface-binding antibody responses against all six OspA antigens were induced after the primary immunization schedule in both populations, and they were substantially increased with both booster schedules. The antibody responses induced by the two doses were similar in the seronegative population, but there was a significant dose response in the seropositive population. These data indicate that the novel multivalent OspA vaccine is well tolerated and immunogenic in individuals previously infected with B. burgdorferi sensu lato. (This study is registered at ClinicalTrials.gov under registration no. NCT01504347.).

MVA vectors expressing conserved influenza proteins protect mice against lethal challenge with H5N1, H9N2 and H7N1 viruses.

BACKGROUND: The availability of a universal influenza vaccine able to induce broad cross-reactive immune responses against diverse influenza viruses would provide an alternative to currently available strain-specific vaccines. We evaluated the ability of vectors based on modified vaccinia virus Ankara (MVA) expressing conserved influenza proteins to protect mice against lethal challenge with multiple influenza subtypes. METHODS: Mice were immunized with MVA vectors expressing H5N1-derived nucleoprotein (NP), the stem region of hemagglutinin (HA), matrix proteins 1 and 2 (M1 and M2), the viral polymerase basic protein 1 (PB1), or the HA stem fused to a quadrivalent matrix protein 2 extracellular domain (M2e). Immunized mice were challenged with lethal doses of H5N1, H7N1 or H9N2 virus and monitored for disease symptoms and weight loss. To investigate the influence of previous exposure to influenza virus on protective immune responses induced by conserved influenza proteins, mice were infected with pandemic H1N1 virus (H1N1pdm09) prior to immunization and subsequently challenged with H5N1 virus. Antibody and T cell responses were assessed by ELISA and flow cytometry, respectively. RESULTS: MVA vectors expressing NP alone, or co-expressed with other conserved influenza proteins, protected mice against lethal challenge with H5N1, H7N1 or H9N2 virus. Pre-exposure to H1N1pdm09 increased protective efficacy against lethal H5N1 challenge. None of the other conserved influenza proteins provided significant levels of protection against lethal challenge. NP-expressing vectors induced high numbers of influenza-specific CD4(+) and CD8(+) T cells and high titer influenza-specific antibody responses. Higher influenza-specific CD4(+) T cell responses and NP-specific CD8(+) T cell responses were associated with increased protective efficacy. CONCLUSIONS: MVA vectors expressing influenza NP protect mice against lethal challenge with H5N1, H7N1 and H9N2 viruses by a mechanism involving influenza-specific CD4(+) and CD8(+) T cell responses.

Evaluation of OspA vaccination-induced serological correlates of protection against Lyme borreliosis in a mouse model.

BACKGROUND: For clinical development of a novel multivalent OspA vaccine against Lyme borreliosis, serological assays are required which can be used to establish immune correlates of protection against infection with Borrelia. METHODS: Four assays (an OspA IgG ELISA, a competitive inhibition (CI) ELISA, a Borrelia surface-binding (SB) assay and a Borrelia killing assay) were used to evaluate the correlation between immune responses induced by rOspA 1/2 (a chimeric immunogen containing protective epitopes from OspA serotypes 1 and 2), and protective immunity against infection by B. burgdorferi s.s. (OspA-1) and B. afzelii (OspA-2). Mice were immunized with OspA 1/2 doses ranging from 0.3 ng to 100 ng, to induce a range of OspA antibody titers, and exposed to needle challenge with B. burgdorferi s.s. or tick challenge with B. afzelii. Receiver operator characteristics (ROC) curves were constructed for each assay, and the area under the curve (AUC), sensitivity, specificity and Youden Index were calculated. Potential cutoff antibody titers which could be used as correlates of vaccine-induced protection were derived from the maximum Youden Index. RESULTS: Immunization with OspA-1/2 provided dose-dependent protection against infection with B. burgdorferi s.s. and B. afzelii. Antibody responses detected by all four assays were highly significantly correlated with protection from infection by either B. burgdorferi s.s. (p<0.0001 to 0.0062) or B. afzelii (p<0.0001). ROC analyses of the diagnostic effectiveness of each assay showed the AUC to range between 0.95 and 0.79, demonstrating that all assays distinguish well between infected and non-infected animals. Based on sensitivity, specificity and AUC, the OspA IgG ELISA and SB assays best discriminated between infected and non-infected animals. CONCLUSIONS: All four assays differentiate well between Borrelia-infected and non-infected animals. The relatively simple, high throughput IgG ELISA would be suitable to establish immune correlates of protection for the novel OspA vaccine in clinical trials.

Preclinical evaluation of Vaxfectin-adjuvanted Vero cell-derived seasonal split and pandemic whole virus influenza vaccines.

Increasing the potency and supply of seasonal and pandemic influenza vaccines remains an important unmet medical need which may be effectively accomplished with adjuvanted egg- or cell culture-derived vaccines. Vaxfectin, a cationic lipid-based adjuvant with a favorable safety profile in phase 1 plasmid DNA vaccines trials, was tested in combination with seasonal split, trivalent and pandemic whole virus, monovalent influenza vaccines produced in Vero cell cultures. Comparison of hemagglutination inhibition (HI) antibody titers in Vaxfectin-adjuvanted to nonadjuvanted vaccinated mice and guinea pigs revealed 3- to 20-fold increases in antibody titers against each of the trivalent influenza virus vaccine strains and 2- to 8-fold increases in antibody titers against the monovalent H5N1 influenza virus vaccine strain. With the vaccine doses tested, comparable antibody responses were induced with formulations that were freshly prepared or refrigerated at conventional 2-8°C storage conditions for up to 6 mo. Comparison of T-cell frequencies measured by interferon-gamma ELISPOT assay between groups revealed increases of between 2- to 10-fold for each of the adjuvanted trivalent strains and up to 22-fold higher with monovalent H5N1 strain. Both trivalent and monovalent vaccines were easy to formulate with Vaxfectin by simple mixing. These preclinical data support further testing of Vaxfectin-adjuvanted Vero cell culture vaccines toward clinical studies designed to assess safety and immunogenicity of these vaccines in humans.

Safety and immunogenicity of a novel multivalent OspA vaccine against Lyme borreliosis in healthy adults: a double-blind, randomised, dose-escalation phase 1/2 trial.

BACKGROUND: Lyme borreliosis is caused by Borrelia burgdorferi sensu stricto in the USA and by several Borrelia species in Europe and Asia, but no human vaccine is available. We investigated the safety and immunogenicity of adjuvanted and non-adjuvanted vaccines containing protective epitopes from Borrelia species outer surface protein A (OspA) serotypes in healthy adults. METHODS: Between March 1, 2011, and May 8, 2012, we did a double-blind, randomised, dose-escalation phase 1/2 study at four sites in Austria and Germany. Healthy adults aged 18-70 years who were seronegative for B. burgdorferi sensu lato were eligible for inclusion. Participants were recruited sequentially and randomly assigned to one of six study groups in equal ratios via an electronic data capture system. Participants and investigators were masked to group allocation. Participants received three vaccinations containing 30 µg, 60 µg, or 90 µg OspA antigen with or without an adjuvant, with intervals of 28 days, and a booster 9-12 months after the first immunisation. The coprimary endpoints were the frequency and severity of injection-site and systemic reactions within 7 days of each vaccination, and the antibody responses to OspA serotypes 1-6, as established by ELISA. This study is registered with ClinicalTrials.gov, number NCT01504347. FINDINGS: 300 participants were randomly assigned: 151 to adjuvanted vaccines (50 to 30 µg, 51 to 60 µg, and 50 to 90 µg doses), and 149 to non-adjuvanted vaccines (50 to 30 µg, 49 to 60 µg, and 50 to 90 µg doses). Adverse reactions were predominantly mild, and no vaccine-related serious adverse events were reported. The risk of systemic reactions (risk ratio 0·54 [95% CI 0·41-0·70]; p<0·0001) and of moderate or severe systemic reactions (0·35 [0·13-0·92]; p=0·034) was significantly lower for adjuvanted than non-adjuvanted formulations. The 30 µg adjuvanted formulation had the best tolerability profile; only headache (five [10%, 95% CI 4-20] of 50), injection-site pain (16 [32%, 21-45]), and tenderness (17 [34%, 23-47]) affected more than 6% of patients. All doses and formulations induced substantial mean IgG antibody titres against OspA serotypes 1-6 after the first three vaccinations (range 6944-17,321) and booster (19,056-32,824) immunisations. The 30 µg adjuvanted formulation induced the highest antibody titres after the booster: range 26,143 (95% CI 18,906-36,151) to 42,381 (31,288-57,407). INTERPRETATION: The novel multivalent OspA vaccine could be an effective intervention for prevention of Lyme borreliosis in Europe and the USA, and possibly worldwide. Larger confirmatory formulation studies will need to be done that include individuals seropositive for Borrelia burgdorferi sensu lato before placebo-controlled phase 3 efficacy studies can begin. FUNDING: Baxter.

A cell culture-derived whole-virus H5N1 vaccine induces long-lasting cross-clade protective immunity in mice which is augmented by a homologous or heterologous booster vaccination.

BACKGROUND: Preparation for an H5N1 influenza pandemic in humans could include priming the population in the pre-pandemic period with a vaccine produced from an existing H5N1 vaccine strain, with the possibility of boosting with a pandemic virus vaccine when it becomes available. We investigated the longevity of the immune response after one or two priming immunizations with a whole-virus H5N1 vaccine and the extent to which this can be boosted by later immunization with either a homologous or heterologous vaccine. METHODS: Mice received one or two priming immunizations with a Vero cell culture-derived, whole-virus clade 1 H5N1 vaccine formulated to contain either 750 ng or 30 ng hemagglutinin. Six months after the first priming immunization, mice received either a booster immunization with the same clade 1 vaccine or a heterologous clade 2.1 vaccine, or buffer. Humoral and cellular immune responses were evaluated before and at regular intervals after immunizations. Three weeks after booster immunization, mice were challenged with a lethal dose of wild-type H5N1 virus from clades 1, 2.1 or 2.2 and survival was monitored for 14 days. RESULTS: One or two priming immunizations with the 750 ng or 30 ng HA formulations, respectively, induced H5N1-neutralizing antibody titers which were maintained for ≥ 6 months and provided long-term cross-clade protection against wild-type virus challenge. Both humoral and cellular immune responses were substantially increased by a booster immunization after 6 months. The broadest protective immunity was provided by an immunization regimen consisting of one or two priming immunizations with a clade 1 vaccine and a boosting immunization with a clade 2.1 vaccine. CONCLUSIONS: These data support the concept that pre-pandemic vaccination can provide robust and long-lasting H5N1 immunity which could be effectively boosted by immunization either with another pre-pandemic vaccine or with the pandemic strain vaccine.

Pre-clinical efficacy and safety of experimental vaccines based on non-replicating vaccinia vectors against yellow fever.

BACKGROUND: Currently existing yellow fever (YF) vaccines are based on the live attenuated yellow fever virus 17D strain (YFV-17D). Although, a good safety profile was historically attributed to the 17D vaccine, serious adverse events have been reported, making the development of a safer, more modern vaccine desirable. METHODOLOGY/PRINCIPAL FINDINGS: A gene encoding the precursor of the membrane and envelope (prME) protein of the YFV-17D strain was inserted into the non-replicating modified vaccinia virus Ankara and into the D4R-defective vaccinia virus. Candidate vaccines based on the recombinant vaccinia viruses were assessed for immunogenicity and protection in a mouse model and compared to the commercial YFV-17D vaccine. The recombinant live vaccines induced γ-interferon-secreting CD4- and functionally active CD8-T cells, and conferred full protection against lethal challenge already after a single low immunization dose of 10(5) TCID(50). Surprisingly, pre-existing immunity against wild-type vaccinia virus did not negatively influence protection. Unlike the classical 17D vaccine, the vaccinia virus-based vaccines did not cause mortality following intracerebral administration in mice, demonstrating better safety profiles. CONCLUSIONS/SIGNIFICANCE: The non-replicating recombinant YF candidate live vaccines induced a broad immune response after single dose administration, were effective even in the presence of a pre-existing immunity against vaccinia virus and demonstrated an excellent safety profile in mice.

Vectors based on modified vaccinia Ankara expressing influenza H5N1 hemagglutinin induce substantial cross-clade protective immunity.

BACKGROUND: New highly pathogenic H5N1 influenza viruses are continuing to evolve with a potential threat for an influenza pandemic. So far, the H5N1 influenza viruses have not widely circulated in humans and therefore constitute a high risk for the non immune population. The aim of this study was to evaluate the cross-protective potential of the hemagglutinins of five H5N1 strains of divergent clades using a live attenuated modified vaccinia Ankara (MVA) vector vaccine. METHODOLOGY/PRINCIPAL FINDINGS: The replication-deficient MVA virus was used to express influenza hemagglutinin (HA) proteins. Specifically, recombinant MVA viruses expressing the HA genes of the clade 1 virus A/Vietnam/1203/2004 (VN/1203), the clade 2.1.3 virus A/Indonesia/5/2005 (IN5/05), the clade 2.2 viruses A/turkey/Turkey/1/2005 (TT01/05) and A/chicken/Egypt/3/2006 (CE/06), and the clade 2.3.4 virus A/Anhui/1/2005 (AH1/05) were constructed. These experimental live vaccines were assessed in a lethal mouse model. Mice vaccinated with the VN/1203 hemagglutinin-expressing MVA induced excellent protection against all the above mentioned clades. Also mice vaccinated with the IN5/05 HA expressing MVA induced substantial protection against homologous and heterologous AH1/05 challenge. After vaccination with the CE/06 HA expressing MVA, mice were fully protected against clade 2.2 challenge and partially protected against challenge of other clades. Mice vaccinated with AH1/05 HA expressing MVA vectors were only partially protected against homologous and heterologous challenge. The live vaccines induced substantial amounts of neutralizing antibodies, mainly directed against the homologous challenge virus, and high levels of HA-specific IFN-γ secreting CD4 and CD8 T-cells against epitopes conserved among the H5 clades and subclades. CONCLUSIONS/SIGNIFICANCE: The highest level of cross-protection was induced by the HA derived from the VN/1203 strain, suggesting that pandemic H5 vaccines utilizing MVA vector technology, should be based on the VN/1203 hemagglutinin. Furthermore, the recombinant MVA-HA-VN, as characterized in the present study, would be a promising candidate for such a vaccine.

Evaluation of the cellular immune responses induced by a non-adjuvanted inactivated whole virus A/H5N1/VN/1203 pandemic influenza vaccine in humans.

In the present study the homologous and heterologous type and subtype specific cellular immune response induced by a wild type inactivated whole virus H5N1 Influenza (A/Vietnam/1203/2004) vaccine was evaluated. Two immunizations with the Vero cell derived H5N1 influenza vaccine on Day 0 and Day 21 induced significant H5N1 vaccine specific and H5 haemagglutinin specific clade and cross-clade reactive CD4(+) T cell responses, which were maintained at significant levels for at least 6 months. The H5N1 vaccine specific response cross-reacted with the H1N1, but not with H3N2 or B seasonal Influenza strains. The vaccine significantly increased the number of H5N1 specific and H5 haemagglutinin specific memory B cells, 6 months after the primary immunization, however no H1N1 specific cross-reactivity was observed. Importantly, the inactivated whole virus H5N1 vaccine was just as effective in inducing CD4(+) T cell and memory B cell response in the elderly (60 years or over) as in the adult population (18-59 years).

A pandemic influenza H1N1 live vaccine based on modified vaccinia Ankara is highly immunogenic and protects mice in active and passive immunizations.

BACKGROUND: The development of novel influenza vaccines inducing a broad immune response is an important objective. The aim of this study was to evaluate live vaccines which induce both strong humoral and cell-mediated immune responses against the novel human pandemic H1N1 influenza virus, and to show protection in a lethal animal challenge model. METHODOLOGY/PRINCIPAL FINDINGS: For this purpose, the hemagglutinin (HA) and neuraminidase (NA) genes of the influenza A/California/07/2009 (H1N1) strain (CA/07) were inserted into the replication-deficient modified vaccinia Ankara (MVA) virus--a safe poxviral live vector--resulting in MVA-H1-Ca and MVA-N1-Ca vectors. These live vaccines, together with an inactivated whole virus vaccine, were assessed in a lung infection model using immune competent Balb/c mice, and in a lethal challenge model using severe combined immunodeficient (SCID) mice after passive serum transfer from immunized mice. Balb/c mice vaccinated with the MVA-H1-Ca virus or the inactivated vaccine were fully protected from lung infection after challenge with the influenza H1N1 wild-type strain, while the neuraminidase virus MVA-N1-Ca induced only partial protection. The live vaccines were already protective after a single dose and induced substantial amounts of neutralizing antibodies and of interferon-gamma-secreting (IFN-gamma) CD4- and CD8 T-cells in lungs and spleens. In the lungs, a rapid increase of HA-specific CD4- and CD8 T cells was observed in vaccinated mice shortly after challenge with influenza swine flu virus, which probably contributes to the strong inhibition of pulmonary viral replication observed. In addition, passive transfer of antisera raised in MVA-H1-Ca vaccinated immune-competent mice protected SCID mice from lethal challenge with the CA/07 wild-type virus. CONCLUSIONS/SIGNIFICANCE: The non-replicating MVA-based H1N1 live vaccines induce a broad protective immune response and are promising vaccine candidates for pandemic influenza.

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.

Seasonal influenza vaccine elicits heterosubtypic immunity against H5N1 that can be further boosted by H5N1 vaccination.

Recent findings indicate that seasonal influenza vaccination or infection of healthy humans may contribute to heterosubtypic immunity against new influenza A subtypes, such as H5N1. Here, we investigated whether seasonal influenza vaccination in a mouse model could induce any immunity against the H5N1 subtype. It could be demonstrated that, largely due to the H1N1 component strain A/NewCaledonia/20/99, parenteral immunization of mice with a trivalent seasonal influenza vaccine elicited heterosubtype H5-reactive antibodies able to confer partial protection against H5N1 influenza virus infection. Furthermore, the trivalent seasonal influenza vaccine was found to be compatible with a whole virus H5N1 vaccine in a heterologous prime-boost immunization regimen, achieving superior efficacy compared to a single immunization with an equivalent low-dose of the H5N1 vaccine.

Nonreplicating vaccinia virus vectors expressing the H5 influenza virus hemagglutinin produced in modified Vero cells induce robust protection.

The timely development of safe and effective vaccines against avian influenza virus of the H5N1 subtype will be of the utmost importance in the event of a pandemic. Our aim was first to develop a safe live vaccine which induces both humoral and cell-mediated immune responses against human H5N1 influenza viruses and second, since the supply of embryonated eggs for traditional influenza vaccine production may be endangered in a pandemic, an egg-independent production procedure based on a permanent cell line. In the present article, the generation of a complementing Vero cell line suitable for the production of safe poxviral vaccines is described. This cell line was used to produce a replication-deficient vaccinia virus vector H5N1 live vaccine, dVV-HA5, expressing the hemagglutinin of a virulent clade 1 H5N1 strain. This experimental vaccine was compared with a formalin-inactivated whole-virus vaccine based on the same clade and with different replicating poxvirus-vectored vaccines. Mice were immunized to assess protective immunity after high-dose challenge with the highly virulent A/Vietnam/1203/2004(H5N1) strain. A single dose of the defective live vaccine induced complete protection from lethal homologous virus challenge and also full cross-protection against clade 0 and 2 challenge viruses. Neutralizing antibody levels were comparable to those induced by the inactivated vaccine. Unlike the whole-virus vaccine, the dVV-HA5 vaccine induced substantial amounts of gamma interferon-secreting CD8 T cells. Thus, the nonreplicating recombinant vaccinia virus vectors are promising vaccine candidates that induce a broad immune response and can be produced in an egg-independent and adjuvant-independent manner in a proven vector system.