Development of a hydrogen peroxide-inactivated vaccine that protects against viscerotropic yellow fever in a non-human primate model.

Yellow fever virus (YFV) is endemic in >40 countries and causes viscerotropic disease with up to 20%-60% mortality. Successful live-attenuated yellow fever (YF) vaccines were developed in the mid-1930s, but their use is restricted or formally contraindicated in vulnerable populations including infants, the elderly, and people with compromised immune systems. In these studies, we describe the development of a next-generation hydrogen peroxide-inactivated YF vaccine and determine immune correlates of protection based on log neutralizing index (LNI) and neutralizing titer-50% (NT50) studies. In addition, we compare neutralizing antibody responses and protective efficacy of hydrogen peroxide-inactivated YF vaccine candidates to live-attenuated YFV-17D (YF-VAX) in a rhesus macaque model of viscerotropic YF. Our results indicate that an optimized, inactivated YF vaccine elicits protective antibody responses that prevent viral dissemination and lethal infection in rhesus macaques and may be a suitable alternative for vaccinating vulnerable populations who are not eligible to receive replicating live-attenuated YF vaccines.

An observer blinded, randomized, placebo-controlled, phase I dose escalation trial to evaluate the safety and immunogenicity of an inactivated West Nile virus Vaccine, HydroVax-001, in healthy adults.

BACKGROUND: West Nile virus (WNV) is the most common mosquito-borne infection in the United States. HydroVax-001 WNV is a hydrogen peroxide inactivated, whole virion (WNV-Kunjin strain) vaccine adjuvanted with aluminum hydroxide. METHODS: We performed a phase 1, randomized, placebo-controlled, double-blind (within dosing group), dose escalation clinical trial of the HydroVax-001 WNV vaccine administered via intramuscular injection. This trial evaluated 1 mcg and 4 mcg dosages of HydroVax-001 WNV vaccine given intramuscularly on day 1 and day 29 in healthy adults. The two dosing groups of HydroVax-001 were enrolled sequentially and each group consisted of 20 individuals who received HydroVax-001 and 5 who received placebo. Safety was assessed at all study days (days 1, 2, 4 and 15 post dose 1, and days 1, 2, 4, 15, 29, 57, 180 and 365 post dose 2), and reactogenicity was assessed for 14 days after administration of each dose. Immunogenicity was measured by WNV-specific plaque reduction neutralization tests (PRNT50) in the presence or absence of added complement or by WNV-specific enzyme-linked immunosorbent assays (ELISA). RESULTS: HydroVax-001 was safe and well-tolerated as there were no serious adverse events or concerning safety signals. At the 1 mcg dose, HydroVax-001 was not immunogenic by PRNT50 but elicited up to 41% seroconversion by WNV-specific ELISA in the per-protocol population (PP) after the second dose. At the 4 mcg dose, HydroVax-001 elicited neutralizing antibody responses in 31% of the PP following the second dose. In the presence of added complement, PRNT50 seroconversion rates increased to 50%, and 75% seroconversion was observed by WNV-specific ELISA. CONCLUSIONS: The HydroVax-001 WNV vaccine was found to be modestly immunogenic and well-tolerated at all dose levels.

Pre-clinical development of a hydrogen peroxide-inactivated West Nile virus vaccine.

West Nile virus (WNV) is a mosquito-transmitted pathogen with a wide geographical range that can lead to long-term disability and death in some cases. Despite the public health risk posed by WNV, including an estimated 3 million infections in the United States alone, no vaccine is available for use in humans. Here, we present a scaled manufacturing approach for production of a hydrogen peroxide-inactivated whole virion WNV vaccine, termed HydroVax-001WNV. Vaccination resulted in robust virus-specific neutralizing antibody responses and protection against WNV-associated mortality in mice or viremia in rhesus macaques (RM). A GLP-compliant toxicology study performed in rats demonstrated an excellent safety profile with clinical findings limited to minor and transient irritation at the injection site. An in vitro relative potency (IVRP) assay was developed and shown to correlate with in vivo responses following forced degradation studies. Long-term in vivo potency comparisons between the intended storage condition (2-8°C) and a thermally stressed condition (40±2°C) demonstrated no loss in vaccine efficacy or protective immunity over a 6-month span of time. Together, the positive pre-clinical findings regarding immunogenicity, safety, and stability indicate that HydroVax-001WNV is a promising vaccine candidate.

Durability of Vaccine-Induced Immunity Against Tetanus and Diphtheria Toxins: A Cross-sectional Analysis.

BACKGROUND: Many adult immunization schedules recommend that tetanus and diphtheria vaccination be performed every 10 years. In light of current epidemiological trends of disease incidence and rates of vaccine-associated adverse events, the 10-year revaccination schedule has come into question. METHODS: We performed cross-sectional analysis of serum antibody titers in 546 adult subjects stratified by age or sex. All serological results were converted to international units after calibration with international serum standards. RESULTS: Approximately 97% of the population was seropositive to tetanus and diphtheria as defined by a protective serum antibody titer of ≥0.01 IU/mL. Mean antibody titers were 3.6 and 0.35 IU/mL against tetanus and diphtheria, respectively. Antibody responses to tetanus declined with an estimated half-life of 14 years (95% confidence interval, 11-17 years), whereas antibody responses to diphtheria were more long-lived and declined with an estimated half-life of 27 years (18-51 years). Mathematical models combining antibody magnitude and duration predict that 95% of the population will remain protected against tetanus and diphtheria for ≥30 years without requiring further booster vaccination. CONCLUSIONS: These studies demonstrate that durable levels of protective antitoxin immunity exist in the majority of vaccinated individuals. Together, this suggests that it may no longer be necessary to administer booster vaccinations every 10 years and that the current adult vaccination schedule for tetanus and diphtheria should be revisited.

A hydrogen peroxide-inactivated virus vaccine elicits humoral and cellular immunity and protects against lethal West Nile virus infection in aged mice.

West Nile virus (WNV) is an emerging pathogen that is now the leading cause of mosquito-borne and epidemic encephalitis in the United States. In humans, a small percentage of infected individuals develop severe neuroinvasive disease, with the greatest relative risk being in the elderly and immunocompromised, two populations that are difficult to immunize effectively with vaccines. While inactivated and subunit-based veterinary vaccines against WNV exist, currently there is no vaccine or therapy available to prevent or treat human disease. Here, we describe the generation and preclinical efficacy of a hydrogen peroxide (H(2)O(2))-inactivated WNV Kunjin strain (WNV-KUNV) vaccine as a candidate for further development. Both young and aged mice vaccinated with H(2)O(2)-inactivated WNV-KUNV produced robust adaptive B and T cell immune responses and were protected against stringent and lethal intracranial challenge with a heterologous virulent North American WNV strain. Our studies suggest that the H(2)O(2)-inactivated WNV-KUNV vaccine is safe and immunogenic and may be suitable for protection against WNV infection in vulnerable populations.

Inhibition of dengue virus infections in cell cultures and in AG129 mice by a small interfering RNA targeting a highly conserved sequence.

The dengue viruses (DENVs) exist as numerous genetic strains that are grouped into four antigenically distinct serotypes. DENV strains from each serotype can cause severe disease and threaten public health in tropical and subtropical regions worldwide. No licensed antiviral agent to treat DENV infections is currently available, and there is an acute need for the development of novel therapeutics. We found that a synthetic small interfering RNA (siRNA) (DC-3) targeting the highly conserved 5' cyclization sequence (5'CS) region of the DENV genome reduced, by more than 100-fold, the titers of representative strains from each DENV serotype in vitro. To determine if DC-3 siRNA could inhibit DENV in vivo, an "in vivo-ready" version of DC-3 was synthesized and tested against DENV-2 by using a mouse model of antibody-dependent enhancement of infection (ADE)-induced disease. Compared with the rapid weight loss and 5-day average survival time of the control groups, mice receiving the DC-3 siRNA had an average survival time of 15 days and showed little weight loss for approximately 12 days. DC-3-treated mice also contained significantly less virus than control groups in several tissues at various time points postinfection. These results suggest that exogenously introduced siRNA combined with the endogenous RNA interference processing machinery has the capacity to prevent severe dengue disease. Overall, the data indicate that DC-3 siRNA represents a useful research reagent and has potential as a novel approach to therapeutic intervention against the genetically diverse dengue viruses.