An inactivated enterovirus 71 vaccine is safe and immunogenic in healthy adults: A phase I, double blind, randomized, placebo-controlled, study of two dosages.

BACKGROUND: Hand, foot and mouth disease (HFMD), especially that caused by enterovirus 71 (EV71) infection, is a public health concern in the Asia-Pacific region. We report a phase I clinical trial of an EV71 candidate vaccine (INV21) based on a binary ethylenimine inactivated B2 sub-genotype formulated with aluminum hydroxide. METHODS: In this double-blind, placebo-controlled, randomized, dose escalation study adult volunteers received two vaccinations 28 days apart of low or high dose formulations of the candidate vaccine and were then monitored for safety and reactogenicity for four weeks after each dose, and for their immune responses up to 28 weeks. RESULTS: Of 36 adults enrolled, 35 completed the study as planned. Either no or mild adverse events were observed, mainly injection site pain and tiredness. Seroconversion was 100% after two vaccinations. High geometric mean neutralizing antibody titers (GMT) were observed 14 days post first dose, peaking 14 days post second dose (at Day 42) in both high and low dose groups; GMTs on days 14, 28, 42, and 56 were 128, 81, 323, 203 and 144, 100, 451, 351 in low- and high-dose groups, respectively. Titers for both doses declined gradually to Day 196 but remained higher than baseline and the placebo groups, which had low GMTs throughout the duration of the study. Cross-neutralizing antibody activity against heterologous sub-genotypes was demonstrated. CONCLUSION: These data show that the EV71 candidate vaccine is safe and immunogenic in adults and supports further clinical development as a potential pediatric vaccine by initiating a dose-escalation study for determining the dose-dependent safety and immunogenicity of the vaccine in young naïve children.

Heterologous Immunization With Defined RNA and Subunit Vaccines Enhances T Cell Responses That Protect Against Leishmania donovani.

The rapid generation of strong T cell responses is highly desirable and viral vectors can have potent CD8+ T cell-inducing activity. Immunity to leishmaniasis requires selective T cell responses, with immunization schemes that raise either CD4 or CD8 T cell responses being protective in small animal models. We have defined the leishmaniasis vaccine candidate recombinant fusion antigens, LEISH-F2 and LEISH-F3+, that when formulated in a stable emulsion with a Toll-like receptor (TLR) 4 agonist, induce protective CD4+ T cell responses in animal models as well as providing therapeutic efficacy in canine leishmaniasis and in clinical trials in leishmaniasis patients. We used the genetic sequences of these validated vaccine antigens to design RNA vaccine constructs. Immunization of mice with the RNA replicons induced potent, local innate responses that were surprisingly independent of TLR7 and activated antigen-presenting cells (APC) to prime for extremely potent antigen-specific T helper 1 type responses upon heterologous boosting with either of the subunit vaccines (recombinant antigen with second generation glucopyranosyl lipid A in stable oil-in-water emulsion; SLA-SE). Inclusion of RNA in the immunization schedule also generated MHCI-restricted T cell responses. Immunization with LEISH-F2-expressing RNA vaccine followed later by subunit vaccine afforded protection against challenge with Leishmania donovani. Together, these data indicate the utility of heterologous prime-boost immunization schemes for the induction of potent antigen-specific CD4 and CD8 T cell responses for protection against intracellular pathogens.

A combination of TLR-4 agonist and saponin adjuvants increases antibody diversity and protective efficacy of a recombinant West Nile Virus antigen.

Members of the Flaviviridae family are the leading causes of mosquito-borne viral disease worldwide. While dengue virus is the most prevalent, the recent Zika virus outbreak in the Americas triggered a WHO public health emergency, and yellow fever and West Nile viruses (WNV) continue to cause regional epidemics. Given the sporadic nature of flaviviral epidemics both temporally and geographically, there is an urgent need for vaccines that can rapidly provide effective immunity. Protection from flaviviral infection is correlated with antibodies to the viral envelope (E) protein, which encodes receptor binding and fusion functions. TLR agonist adjuvants represent a promising tool to enhance the protective capacity of flavivirus vaccines through dose and dosage reduction and broadening of antiviral antibody responses. This study investigates the ability to improve the immunogenicity and protective capacity of a promising clinical-stage WNV recombinant E-protein vaccine (WN-80E) using a novel combination adjuvant, which contains a potent TLR-4 agonist and the saponin QS21 in a liposomal formulation (SLA-LSQ). Here, we show that, in combination with WN-80E, optimized SLA-LSQ is capable of inducing long-lasting immune responses in preclinical models that provide sterilizing protection from WNV challenge, reducing viral titers following WNV challenge to undetectable levels in Syrian hamsters. We have investigated potential mechanisms of action by examining the antibody repertoire generated post-immunization. SLA-LSQ induced a more diverse antibody response to WNV recombinant E-protein antigen than less protective adjuvants. Collectively, these studies identify an adjuvant formulation that enhances the protective capacity of recombinant flavivirus vaccines.

A Nanostructured Lipid Carrier for Delivery of a Replicating Viral RNA Provides Single, Low-Dose Protection against Zika.

Since the first demonstration of in vivo gene expression from an injected RNA molecule almost two decades ago,1 the field of RNA-based therapeutics is now taking significant strides, with many cancer and infectious disease targets entering clinical trials.2 Critical to this success has been advances in the knowledge and application of delivery formulations. Currently, various lipid nanoparticle (LNP) platforms are at the forefront,3 but the encapsulation approach underpinning LNP formulations offsets the synthetic and rapid-response nature of RNA vaccines.4 Second, limited stability of LNP formulated RNA precludes stockpiling for pandemic readiness.5 Here, we show the development of a two-vialed approach wherein the delivery formulation, a highly stable nanostructured lipid carrier (NLC), can be manufactured and stockpiled separate from the target RNA, which is admixed prior to administration. Furthermore, specific physicochemical modifications to the NLC modulate immune responses, either enhancing or diminishing neutralizing antibody responses. We have combined this approach with a replicating viral RNA (rvRNA) encoding Zika virus (ZIKV) antigens and demonstrated a single dose as low as 10 ng can completely protect mice against a lethal ZIKV challenge, representing what might be the most potent approach to date of any Zika vaccine.

Early Transcriptional Signatures of the Immune Response to a Live Attenuated Tetravalent Dengue Vaccine Candidate in Non-human Primates.

BACKGROUND: The development of a vaccine against dengue faces unique challenges, including the complexity of the immune responses to the four antigenically distinct serotypes. Genome-wide transcriptional profiling provides insight into the pathways and molecular features that underlie responses to immune system stimulation, and may facilitate predictions of immune protection. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we measured early transcriptional responses in the peripheral blood of cynomolgus macaques following vaccination with a live, attenuated tetravalent dengue vaccine candidate, TDV, which is based on a DENV-2 backbone. Different doses and routes of vaccine administration were used, and viral load and neutralizing antibody titers were measured at different time-points following vaccination. All 30 vaccinated animals developed a neutralizing antibody response to each of the four dengue serotypes, and only 3 of these animals had detectable serum viral RNA after challenge with wild-type dengue virus (DENV), suggesting protection of vaccinated animals to DENV infection. The vaccine induced statistically significant changes in 595 gene transcripts on days 1, 3, 5 and 7 as compared with baseline and placebo-treated animals. Genes involved in the type I interferon (IFN) response, including IFI44, DDX58, MX1 and OASL, exhibited the highest fold-change in transcript abundance, and this response was strongest following double dose and subcutaneous (versus intradermal) vaccine administration. In addition, modules of genes involved in antigen presentation, dendritic cell activation, and T cell activation and signaling were enriched following vaccination. Increased abundance of gene transcripts related to T cell activation on day 5, and the type I IFN response on day 7, were significantly correlated with the development of high neutralizing antibody titers on day 30. CONCLUSIONS/SIGNIFICANCE: These results suggest that early transcriptional responses may be predictive of development of adaptive immunity to TDV vaccination in cynomolgus macaques, and will inform studies of human responses to dengue vaccines.

Safety and Immunogenicity of a Tetravalent Dengue Vaccine Candidate in Healthy Children and Adults in Dengue-Endemic Regions: A Randomized, Placebo-Controlled Phase 2 Study.

BACKGROUND: A safe, effective tetravalent dengue vaccine is a global health priority. The safety and immunogenicity of a live attenuated, recombinant tetravalent dengue vaccine candidate (TDV) were evaluated in healthy volunteers from dengue-endemic countries. METHODS: This multicenter, double-blind, phase 2 study was conducted in Puerto Rico, Colombia, Singapore, and Thailand. During stage I, 148 volunteers aged 1.5-45 years were sequentially enrolled into 4 age-descending groups and randomized at a ratio of 2:1 to receive TDV or placebo. In stage II (group 5), 212 children aged 1.5-11 years were randomized at a ratio of 3:1 to receive TDV or placebo. Participants received a subcutaneous injection of TDV or placebo on days 0 and 90 and were followed for analysis of safety, seropositivity, and neutralizing antibodies to DENV-1-4. RESULTS: Injection site pain, itching, and erythema (mostly mild) were the only solicited adverse events more frequently reported with TDV than with placebo in all age groups. After 2 TDV doses, seropositivity was >95% in all 5 groups for DENV-1-3 and 72.7%-100% for DENV-4; geometric mean titers ranged from 582 to 1187 for DENV-1, from 582 to 1187 for DENV-2, from 196 to 630 for DENV-3, and from 41 to 210 for DENV-4 among the 5 groups. CONCLUSIONS: TDV was well tolerated and immunogenic in volunteers aged 1.5-45 years, irrespective of prevaccination dengue exposure.

A recombinant, chimeric tetravalent dengue vaccine candidate based on a dengue virus serotype 2 backbone.

Dengue fever is caused by infection with one of four dengue virus (DENV) serotypes (DENV-1-4), necessitating tetravalent dengue vaccines that can induce protection against all four DENV. Takeda's live attenuated tetravalent dengue vaccine candidate (TDV) comprises an attenuated DENV-2 strain plus chimeric viruses containing the prM and E genes of DENV-1, -3 and -4 cloned into the attenuated DENV-2 'backbone'. In Phase 1 and 2 studies, TDV was well tolerated by children and adults aged 1.5-45 years, irrespective of prior dengue exposure; mild injection-site symptoms were the most common adverse events. TDV induced neutralizing antibody responses and seroconversion to all four DENV as well as cross-reactive T cell-mediated responses that may be necessary for broad protection against dengue fever.

Development of a recombinant, chimeric tetravalent dengue vaccine candidate.

Dengue is a significant threat to public health worldwide. Currently, there are no licensed vaccines available for dengue. Takeda Vaccines Inc. is developing a live, attenuated tetravalent dengue vaccine candidate (TDV) that consists of an attenuated DENV-2 strain (TDV-2) and three chimeric viruses containing the prM and E protein genes of DENV-1, -3 and -4 expressed in the context of the attenuated TDV-2 genome backbone (TDV-1, TDV-3, and TDV-4, respectively). TDV has been shown to be immunogenic and efficacious in nonclinical animal models. In interferon-receptor deficient mice, the vaccine induces humoral neutralizing antibody responses and cellular immune responses that are sufficient to protect from lethal challenge with DENV-1, DENV-2 or DENV-4. In non-human primates, administration of TDV induces innate immune responses as well as long lasting antibody and cellular immunity. In Phase 1 clinical trials, the safety and immunogenicity of two different formulations were assessed after intradermal or subcutaneous administration to healthy, flavivirus-naïve adults. TDV administration was generally well-tolerated independent of dose and route. The vaccine induced neutralizing antibody responses to all four DENV serotypes: after a single administration of the higher formulation, 24-67%% of the subjects seroconverted to all four DENV and >80% seroconverted to three or more viruses. In addition, TDV induced CD8(+) T cell responses to the non-structural NS1, NS3 and NS5 proteins of DENV. TDV has been also shown to be generally well tolerated and immunogenic in a Phase 2 clinical trial in dengue endemic countries in adults and children as young as 18 months. Additional clinical studies are ongoing in preparation for a Phase 3 safety and efficacy study.

Safety and immunogenicity of different doses and schedules of a live attenuated tetravalent dengue vaccine (TDV) in healthy adults: A Phase 1b randomized study.

INTRODUCTION: A safe, effective dengue vaccine that can simultaneously induce immunity to all four dengue virus serotypes (DENV-1-4) is a public health priority. A chimeric tetravalent dengue vaccine (TDV) based on an attenuated DENV-2 serotype backbone was evaluated in healthy, flavivirus-seronegative adults. METHODS: In this randomized, multicenter, Phase 1b study conducted in the United States, the safety and immunogenicity of TDV were evaluated in 140 participants aged 18-45 years in six dosing regimen study groups. Participants were injected subcutaneously on Days 0 and 90; placebo (saline) was injected where appropriate to maintain double blinding. Three different TDV dosages (TDV, a vaccine in which TDV-4 had been increased three-fold, and a one-tenth TDV dose), and single or double dosing were evaluated in one and/or both arms. Primary endpoints were solicited and unsolicited adverse events (AEs) and seroconversion rates to DENV-1-4 at Day 120. RESULTS: The severity of all AEs was generally mild. The most common unsolicited AEs were headache (52%), fatigue (43%) and myalgia (29%). The incidence of injection site pain ranged from 29 to 64% and 5 to 52% among study groups after the first and second doses, respectively. At Day 120, the ranges of seroconversion rates among the groups were DEN-1: 84-100%; DEN-2: 96-100%; DEN-3: 83-100%; and DEN-4: 33-77%. More than 80% of participants in each group seroconverted to at least three dengue serotypes. Substantial GMT increases from baseline were observed for DEN-1-3 at all time points from Day 30 onward; DEN-4 GMT increases were lower. Increasing TDV-4 slightly increased DEN-4 GMT, did not impact DEN-2 and DEN-3 GMT, but reduced DEN-1 GMT. Neither multiple dosing in both arms, nor one-tenth TDV dosing meaningfully impacted GMT increases relative to TDV. CONCLUSIONS: All TDV doses and dosing schedules were well tolerated and immunogenic in healthy flavivirus-naive adults (ClinicalTrials.gov NCT01511250).

CD8+ T-cell Responses in Flavivirus-Naive Individuals Following Immunization with a Live-Attenuated Tetravalent Dengue Vaccine Candidate.

We are developing a live-attenuated tetravalent dengue vaccine (TDV) candidate based on an attenuated dengue 2 virus (TDV-2) and 3 chimeric viruses containing the premembrane and envelope genes of dengue viruses (DENVs) -1, -3, and -4 expressed in the context of the attenuated TDV-2 genome (TDV-1, TDV-3, and TDV-4, respectively). In this study, we analyzed and characterized the CD8(+) T-cell response in flavivirus-naive human volunteers vaccinated with 2 doses of TDV 90 days apart via the subcutaneous or intradermal routes. Using peptide arrays and intracellular cytokine staining, we demonstrated that TDV elicits CD8(+) T cells targeting the nonstructural NS1, NS3, and NS5 proteins of TDV-2. The cells were characterized by the production of interferon-γ, tumor necrosis factor-α, and to a lesser extent interleukin-2. Responses were highest on day 90 after the first dose and were still detectable on 180 days after the second dose. In addition, CD8(+) T cells were multifunctional, producing ≥2 cytokines simultaneously, and cross-reactive to NS proteins of the other 3 DENV serotypes. Overall, these findings describe the capacity of our candidate dengue vaccine to elicit cellular immune responses and support the further evaluation of T-cell responses in samples from future TDV clinical trials.

Safety and Immunogenicity of a Live Attenuated Tetravalent Dengue Vaccine Candidate in Flavivirus-Naive Adults: A Randomized, Double-Blinded Phase 1 Clinical Trial.

BACKGROUND: Dengue viruses (DENVs) infect >300 million people annually, causing 96 million cases of dengue disease and 22 000 deaths [1]. A safe vaccine that protects against DENV disease is a global health priority [2]. METHODS: We enrolled 72 flavivirus-naive healthy adults in a phase 1 double-blinded, randomized, placebo-controlled dose-escalation trial (low and high dose) of a live attenuated recombinant tetravalent dengue vaccine candidate (TDV) given in 2 doses 90 days apart. Volunteers were followed for safety, vaccine component viremia, and development of neutralizing antibodies to the 4 DENV serotypes. RESULTS: The majority of adverse events were mild, with no vaccine-related serious adverse events. Vaccinees reported injection site pain (52% vs 17%) and erythema (73% vs 25%) more frequently than placebo recipients. Low levels of TDV-serotype 2 (TDV-2), TDV-3, and TDV-4 viremia were observed after the first but not second administration of vaccine. Overall seroconversion rates and geometric mean neutralization titers after 2 doses were 84.2% and 54.1, respectively, for DENV serotype 1 (DENV-1); 92.1% and 292.8, respectively, for DENV-2; 86.8% and 32.3, respectively, for DENV-3; and 71.1% and 15.0, respectively, for DENV-4. More than 90.0% of high-dose recipients had trivalent or broader responses. CONCLUSIONS: TDV was generally well tolerated, induced trivalent or broader neutralizing antibodies to DENV in most flavivirus-naive vaccinees, and is undergoing further development. CLINICAL TRIALS REGISTRATION: NCT01110551.

Modified vaccinia virus Ankara encoding influenza virus hemagglutinin induces heterosubtypic immunity in macaques.

UNLABELLED: Current influenza virus vaccines primarily aim to induce neutralizing antibodies (NAbs). Modified vaccinia virus Ankara (MVA) is a safe and well-characterized vector for inducing both antibody and cellular immunity. We evaluated the immunogenicity and protective efficacy of MVA encoding influenza virus hemagglutinin (HA) and/or nucleoprotein (NP) in cynomolgus macaques. Animals were given 2 doses of MVA-based vaccines 4 weeks apart and were challenged with a 2009 pandemic H1N1 isolate (H1N1pdm) 8 weeks after the last vaccination. MVA-based vaccines encoding HA induced potent serum antibody responses against homologous H1 or H5 HAs but did not stimulate strong T cell responses prior to challenge. However, animals that received MVA encoding influenza virus HA and/or NP had high frequencies of virus-specific CD4(+) and CD8(+) T cell responses within the first 7 days of H1N1pdm infection, while animals vaccinated with MVA encoding irrelevant antigens did not. We detected little or no H1N1pdm replication in animals that received vaccines encoding H1 (homologous) HA, while a vaccine encoding NP from an H5N1 isolate afforded no protection. Surprisingly, H1N1pdm viral shedding was reduced in animals vaccinated with MVA encoding HA and NP from an H5N1 isolate. This reduced shedding was associated with cross-reactive antibodies capable of mediating antibody-dependent cellular cytotoxicity (ADCC) effector functions. Our results suggest that ADCC plays a role in cross-protective immunity against influenza. Vaccines optimized to stimulate cross-reactive antibodies with ADCC function may provide an important measure of protection against emerging influenza viruses when NAbs are ineffective. IMPORTANCE: Current influenza vaccines are designed to elicit neutralizing antibodies (NAbs). Vaccine-induced NAbs typically are effective but highly specific for particular virus strains. Consequently, current vaccines are poorly suited for preventing the spread of newly emerging pandemic viruses. Therefore, we evaluated a vaccine strategy designed to induce both antibody and T cell responses, which may provide more broadly cross-protective immunity against influenza. Here, we show in a translational primate model that vaccination with a modified vaccinia virus Ankara encoding hemagglutinin from a heterosubtypic H5N1 virus was associated with reduced shedding of a pandemic H1N1 virus challenge, while vaccination with MVA encoding nucleoprotein, an internal viral protein, was not. Unexpectedly, this reduced shedding was associated with nonneutralizing antibodies that bound H1 hemagglutinin and activated natural killer cells. Therefore, antibody-dependent cellular cytotoxicity (ADCC) may play a role in cross-protective immunity to influenza virus. Vaccines that stimulate ADCC antibodies may enhance protection against pandemic influenza virus.

Safety and immunogenicity of a recombinant live attenuated tetravalent dengue vaccine (DENVax) in flavivirus-naive healthy adults in Colombia: a randomised, placebo-controlled, phase 1 study.

BACKGROUND: Dengue virus is the most serious mosquito-borne viral threat to public health and no vaccines or antiviral therapies are approved for dengue fever. The tetravalent DENVax vaccine contains a molecularly characterised live attenuated dengue serotype-2 virus (DENVax-2) and three recombinant vaccine viruses expressing the prM and E structural genes for serotypes 1, 3, and 4 in the DENVax-2 genetic backbone. We aimed to assess the safety and immunogenicity of tetravalent DENVax formulations. METHODS: We undertook a randomised, double-blind, phase 1, dose-escalation trial between Oct 11, 2011, and Nov 9, 2011, in the Rionegro, Antioquia, Colombia. The first cohort of participants (aged 18-45 years) were randomly assigned centrally, via block randomisation, to receive a low-dose formulation of DENvax, or placebo, by either subcutaneous or intradermal administration. After a safety assessment, participants were randomly assigned to receive a high-dose DENVax formulation, or placebo, by subcutaneous or intradermal administration. Group assignment was not masked from study pharmacists, but allocation was concealed from participants, nurses, and investigators. Primary endpoints were frequency and severity of injection-site and systemic reactions within 28 days of each vaccination. Secondary endpoints were the immunogenicity of DENVax against all four dengue virus serotypes, and the viraemia due to each of the four vaccine components after immunisation. Analysis was by intention to treat for safety and per protocol for immunogenicity. Because of the small sample size, no detailed comparison of adverse event rates were warranted. The trial is registered with ClinicalTrials.gov, number NCT01224639. FINDINGS: We randomly assigned 96 patients to one of the four study groups: 40 participants (42%) received low-dose vaccine and eight participants (8%) received placebo in the low-dose groups; 39 participants (41%) received high-dose vaccine, with nine (9%) participants assigned to receive placebo. Both formulations were well tolerated with mostly mild and transient local or systemic reactions. No clinically meaningful differences were recorded in the overall incidence of local and systemic adverse events between patients in the vaccine and placebo groups; 68 (86%) of 79 participants in the vaccine groups had solicited systemic adverse events compared with 13 (76%) of 17 of those in the placebo groups. By contrast, 67 participants (85%) in the vaccine group had local solicited reactions compared with five (29%) participants in the placebo group. Immunisation with either high-dose or low-dose DENVax formulations induced neutralising antibody responses to all four dengue virus serotypes; 30 days after the second dose, 47 (62%) of 76 participants given vaccine seroconverted to all four serotypes and 73 (96%) participants seroconverted to three or more dengue viruses. Infectious DENVax viruses were detected in only ten (25%) of 40 participants in the low-dose group and 13 (33%) of 39 participants in the high-dose group. INTERPRETATION: Our findings emphasise the acceptable tolerability and immunogenicity of the tetravalent DENVax formulations in healthy, flavivirus-naive adults. Further clinical testing of DENVax in different age groups and in dengue-endemic areas is warranted. FUNDING: Takeda Vaccines.

A rapid immunization strategy with a live-attenuated tetravalent dengue vaccine elicits protective neutralizing antibody responses in non-human primates.

Dengue viruses (DENVs) cause approximately 390 million cases of DENV infections annually and over 3 billion people worldwide are at risk of infection. No dengue vaccine is currently available nor is there an antiviral therapy for DENV infections. We have developed a tetravalent live-attenuated DENV vaccine tetravalent dengue vaccine (TDV) that consists of a molecularly characterized attenuated DENV-2 strain (TDV-2) and three chimeric viruses containing the pre-membrane and envelope genes of DENV-1, -3, and -4 expressed in the context of the TDV-2 genome. To impact dengue vaccine delivery in endemic areas and immunize travelers, a simple and rapid immunization strategy (RIS) is preferred. We investigated RIS consisting of two full vaccine doses being administered subcutaneously or intradermally on the initial vaccination visit (day 0) at two different anatomical locations with a needle-free disposable syringe jet injection delivery devices (PharmaJet) in non-human primates. This vaccination strategy resulted in efficient priming and induction of neutralizing antibody responses to all four DENV serotypes comparable to those elicited by the traditional prime and boost (2 months later) vaccination schedule. In addition, the vaccine induced CD4(+) and CD8(+) T cells producing IFN-γ, IL-2, and TNF-α, and targeting the DENV-2 NS1, NS3, and NS5 proteins. Moreover, vaccine-specific T cells were cross-reactive with the non-structural NS3 and NS5 proteins of DENV-4. When animals were challenged with DENV-2 they were protected with no detectable viremia, and exhibited sterilizing immunity (no increase of neutralizing titers post-challenge). RIS could decrease vaccination visits and provide quick immune response to all four DENV serotypes. This strategy could increase vaccination compliance and would be especially advantageous for travelers into endemic areas.

Deciphering the protective role of adaptive immunity to CHIKV/IRES a novel candidate vaccine against Chikungunya in the A129 mouse model.

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, recently re-emerged in Africa and spread to islands in the Indian Ocean, the Indian subcontinent, and to South East Asia. Viremic travelers have also imported CHIKV to the Western hemisphere highlighting the importance of CHIKV in public health. In addition to the great burden of arthralgic disease, which can persist for months or years, epidemiologic studies have estimated case-fatality rates of ∼0.1%, principally from neurologic disease in older patients. There are no licensed vaccines or effective therapies to prevent or treat human CHIKV infections. We have developed a live CHIKV vaccine (CHIKV/IRES) that is highly attenuated yet immunogenic in mouse models, and is incapable of replicating in mosquito cells. In this study we sought to decipher the role of adaptive immunity elicited by CHIKV/IRES in protection against wild-type CHIKV infection. A single dose of vaccine effectively activated T cells with an expansion peak on day 10 post immunization and elicited memory CD4(+) and CD8(+) T cells that produced IFN-γ, TNF-α and IL-2 upon restimulation with CHIKV/IRES. Adoptive transfer of CHIKV/IRES-immune CD4(+) or CD8(+) T cells did not confer protection against wtCHIKV-LR challenge. By contrast, passive immunization with anti-CHIKV/IRES immune serum provided protection, and a correlate of a minimum protective neutralizing antibody titer was established. Overall, our findings demonstrate the immunogenic potential of the CHIKV/IRES vaccine and highlight the important role that neutralizing antibodies play in protection against an acute CHIKV infection.

Genetic and phenotypic characterization of manufacturing seeds for a tetravalent dengue vaccine (DENVax).

BACKGROUND: We have developed a manufacturing strategy that can improve the safety and genetic stability of recombinant live-attenuated chimeric dengue vaccine (DENVax) viruses. These viruses, containing the pre-membrane (prM) and envelope (E) genes of dengue serotypes 1-4 in the replicative background of the attenuated dengue-2 PDK-53 vaccine virus candidate, were manufactured under cGMP. METHODOLOGY/PRINCIPAL FINDINGS: After deriving vaccine viruses from RNA-transfected Vero cells, six plaque-purified viruses for each serotype were produced. The plaque-purified strains were then analyzed to select one stock for generation of the master seed. Full genetic and phenotypic characterizations of the master virus seeds were conducted to ensure these viruses retained the previously identified attenuating determinants and phenotypes of the vaccine viruses. We also assessed vector competence of the vaccine viruses in sympatric (Thai) Aedes aegypti mosquito vectors. CONCLUSION/SIGNIFICANCE: All four serotypes of master vaccine seeds retained the previously defined safety features, including all three major genetic loci of attenuation, small plaques, temperature sensitivity in mammalian cells, reduced replication in mosquito cell cultures, and reduced neurovirulence in new-born mice. In addition, the candidate vaccine viruses demonstrated greatly reduced infection and dissemination in Aedes aegypti mosquitoes, and are not likely to be transmissible by these mosquitoes. This manufacturing strategy has successfully been used to produce the candidate tetravalent vaccine, which is currently being tested in human clinical trials in the United States, Central and South America, and Asia.

Cross-protective immunity against multiple influenza virus subtypes by a novel modified vaccinia Ankara (MVA) vectored vaccine in mice.

Development of an influenza vaccine that provides cross-protective immunity remains a challenge. Candidate vaccines based on a recombinant modified vaccinia Ankara (MVA) viral vector expressing antigens from influenza (MVA/Flu) viruses were constructed. A vaccine candidate, designated MVA/HA1/C13L/NP, that expresses the hemagglutinin from pandemic H1N1 (A/California/04/09) and the nucleoprotein (NP) from highly pathogenic H5N1 (A/Vietnam/1203/04) fused to a secretory signal sequence from vaccinia virus was highly protective. The vaccine elicited strong antibody titers to homologous H1N1 viruses while cross-reactive antibodies to heterologous viruses were not detectable. In mice, this MVA/HA1/C13L/NP vaccine conferred complete protection against lethal challenge with A/Vietnam/1203/04 (H5N1), A/Norway/3487-2/09 (pandemic H1N1) or A/Influenza/Puerto Rico/8/34 (seasonal H1N1) and partial protection (57.1%) against challenge with seasonal H3N2 virus (A/Aichi/68). The protective efficacy of the vaccine was not affected by pre-existing immunity to vaccinia. Our findings highlight MVA as suitable vector to express multiple influenza antigens that could afford broad cross-protective immunity against multiple subtypes of influenza virus.

Chikungunya virus and prospects for a vaccine.

In 2004, chikungunya virus (CHIKV) re-emerged from East Africa to cause devastating epidemics of debilitating and often chronic arthralgia that have affected millions of people in the Indian Ocean Basin and Asia. More limited epidemics initiated by travelers subsequently occurred in Italy and France, as well as human cases exported to most regions of the world, including the Americas where CHIKV could become endemic. Because CHIKV circulates during epidemics in an urban mosquito-human cycle, control of transmission relies on mosquito abatement, which is rarely effective. Furthermore, there is no antiviral treatment for CHIKV infection and no licensed vaccine to prevent disease. Here, we discuss the challenges to the development of a safe, effective and affordable chikungunya vaccine and recent progress toward this goal.

Cross-protective immunity against o'nyong-nyong virus afforded by a novel recombinant chikungunya vaccine.

Emerging mosquito-borne alphavirus infections caused by chikungunya virus (CHIKV) or o'nyong-nyong virus (ONNV) are responsible for sporadic and sometimes explosive urban outbreaks. Currently, there is no licensed vaccine against either virus. We have developed a highly attenuated recombinant CHIKV candidate vaccine (CHIKV/IRES) that in preclinical studies was demonstrated to be safe, immunogenic and efficacious. In this study we investigated the potential of this vaccine to induce cross-protective immunity against the antigenically related ONNV. Our studies demonstrated that a single dose of CHIKV/IRES elicited a strong cross-neutralizing antibody response and conferred protection against ONNV challenge in the A129 mouse model. Moreover, CHIKV/IRES immune A129 dams transferred antibodies to their offspring that were protective, and passively transferred anti-CHIKV/IRES immune serum protected AG129 mice, independently of a functional IFN response. These findings highlight the potential of the CHIKV/IRES vaccine to protect humans against not only CHIKV but also against ONNV-induced disease.

Immunogenicity and efficacy of chimeric dengue vaccine (DENVax) formulations in interferon-deficient AG129 mice.

Formulations of chimeric dengue vaccine (DENVax) viruses containing the pre-membrane (prM) and envelope (E) genes of serotypes 1-4 expressed in the context of the attenuated DENV-2 PDK-53 genome were tested for safety, immunogenicity and efficacy in interferon receptor knock-out mice (AG129). Monovalent formulations were safe and elicited robust neutralizing antibody responses to the homologous virus and only limited cross-reactivity to other serotypes. A single dose of monovalent DENVax-1, -2, or -3 vaccine provided eighty or greater percent protection against both wild-type (wt) DENV-1 (Mochizuki strain) and DENV-2 (New Guinea C strain) challenge viruses. A single dose of monovalent DENVax-4 also provided complete protection against wt DENV-1 challenge and significantly increased the survival times after challenge with wt DENV-2. In studies using tetravalent mixtures, DENVax ratios were identified that: (i) caused limited viremia, (ii) induced serotype-specific neutralizing antibodies to all four DENV serotypes with different hierarchies, and (iii) conferred full protection against clinical signs of disease following challenge with either wt DENV-1 or DENV-2 viruses. Overall, these data highlight the immunogenic profile of DENVax, a novel candidate tetravalent dengue vaccine and the advantage of sharing a common attenuated genomic backbone among the DENVax monovalent vaccines that confer protection against homologous or heterologous virus challenge.