Showing papers on "Viral Vaccine published in 2007"

Recombinant gp350 Vaccine for Infectious Mononucleosis: A Phase 2, Randomized, Double- Blind, Placebo-Controlled Trial to Evaluate the Safety, Immunogenicity, and Efficacy of an Epstein- Barr Virus Vaccine in Healthy Young Adults

Abstract: BACKGROUND: To date, there is no commercially available vaccine to prevent infectious mononucleosis, a disease frequently induced by Epstein-Barr virus (EBV) infection in adolescents or adults devoid of preexisting immunity to the virus. METHODS: A total of 181 EBV-seronegative, healthy, young adult volunteers were randomized in a double-blind fashion to receive either placebo or a recombinant EBV subunit glycoprotein 350 (gp350)/aluminum hydroxide and 3-O-desacyl-4'-monophosphoryl lipid A (AS04) candidate vaccine in a 3-dose regimen. RESULTS: The vaccine had demonstrable efficacy (mean efficacy rate, 78.0% [95% confidence interval {CI}, 1.0%-96.0%]) in preventing the development of infectious mononucleosis induced by EBV infection, but it had no efficacy in preventing asymptomatic EBV infection. One month after receipt of the final dose of gp350 vaccine, 98.7% of subjects showed seroconversion to anti-gp350 antibodies (95% CI, 85.5%-97.9%), and they remained anti-gp350 antibody positive for >18 months. Furthermore, there were no concerns regarding the safety or reactogenicity of the gp350/AS04 vaccine. CONCLUSION: These data support the clinical feasibility of using an EBV vaccine to prevent infectious mononucleosis. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00430534.

Newcastle Disease Virus-Based Live Attenuated Vaccine Completely Protects Chickens and Mice from Lethal Challenge of Homologous and Heterologous H5N1 Avian Influenza Viruses

Abstract: H5N1 highly pathogenic avian influenza virus (HPAIV) has continued to spread and poses a significant threat to both animal and human health. Current influenza vaccine strategies have limitations that prevent their effective use for widespread inoculation of animals in the field. Vaccine strains of Newcastle disease virus (NDV), however, have been used successfully to easily vaccinate large numbers of animals. In this study, we used reverse genetics to construct a NDV that expressed an H5 subtype avian influenza virus (AIV) hemagglutinin (HA). Both a wild-type and a mutated HA open reading frame (ORF) from the HPAIV wild bird isolate, A/Bar-headed goose/Qinghai/3/2005 (H5N1), were inserted into the intergenic region between the P and M genes of the LaSota NDV vaccine strain. The recombinant viruses stably expressing the wild-type and mutant HA genes were found to be innocuous after intracerebral inoculation of 1-day-old chickens. A single dose of the recombinant viruses in chickens induced both NDV- and AIV H5-specific antibodies and completely protected chickens from challenge with a lethal dose of both velogenic NDV and homologous and heterologous H5N1 HPAIV. In addition, BALB/c mice immunized with the recombinant NDV-based vaccine produced H5 AIV-specific antibodies and were completely protected from homologous and heterologous lethal virus challenge. Our results indicate that recombinant NDV is suitable as a bivalent live attenuated vaccine against both NDV and AIV infection in poultry. The recombinant NDV vaccine may also have potential use in high-risk human individuals to control the pandemic spread of lethal avian influenza.

Pathogenic epitopes, heterologous immunity and vaccine design.

Abstract: Substantial research has been directed towards the development of a new generation of vaccines that are based on the inclusion of immunogenic epitopes in recombinant vectors. Here we examine the evidence that under certain conditions immunogenic epitopes can do more harm than good and might therefore be considered pathogenic. We suggest that the specific removal of such pathogenic epitopes from vaccines might increase their prophylactic potential, while minimizing the risk of side-effects from vaccine use.

Coping with viral diversity in HIV vaccine design.

Abstract: The ability of human immunodeficiency virus type 1 (HIV-1) to develop high levels of genetic diversity, and thereby acquire mutations to escape immune pressures, contributes to the difficulties in producing a vaccine. Possibly no single HIV-1 sequence can induce sufficiently broad immunity to protect against a wide variety of infectious strains, or block mutational escape pathways available to the virus after infection. The authors describe the generation of HIV-1 immunogens that minimizes the phylogenetic distance of viral strains throughout the known viral population (the center of tree [COT]) and then extend the COT immunogen by addition of a composite sequence that includes high-frequency variable sites preserved in their native contexts. The resulting COT+ antigens compress the variation found in many independent HIV-1 isolates into lengths suitable for vaccine immunogens. It is possible to capture 62% of the variation found in the Nef protein and 82% of the variation in the Gag protein into immunogens of three gene lengths. The authors put forward immunogen designs that maximize representation of the diverse antigenic features present in a spectrum of HIV-1 strains. These immunogens should elicit immune responses against high-frequency viral strains as well as against most mutant forms of the virus.

Antibody-based HIV-1 vaccines: recent developments and future directions.

Abstract: The Global HIV Vaccine Enterprise convened a two-day workshop in May of 2007 to discuss humoral immune responses to HIV and approaches to design vaccines that induce viral neutralizing and other potentially protective antibody responses. The goals of this workshop were to identify key scientific issues, gaps, and opportunities that have emerged since the Enterprise Strategic Plan was first published in 2005 [1], and to make recommendations that Enterprise stakeholders can use to plan new activities. Most effective viral vaccines work, at least in part, by generating antibodies that inactivate or neutralize the invading virus, and the existing data strongly suggest that an optimally effective HIV-1 vaccine should elicit potent antiviral neutralizing antibodies. However, unlike acute viral pathogens, HIV-1 chronically replicates in the host and evades the antibody response. This immune evasion, along with the large genetic variation among HIV-1 strains worldwide, has posed major obstacles to vaccine development. Current HIV vaccine candidates do not elicit neutralizing antibodies against most circulating virus strains, and thus the induction of a protective antibody response remains a major priority for HIV-1 vaccine development. For an antibody-based HIV-1 vaccine, progress in vaccine design is generally gauged by in vitro assays that measure the ability of vaccine-induced antibodies to neutralize a broad spectrum of viral isolates representing the major genetic subtypes (clades) of HIV-1 [2]. Although it is not known what magnitude and breadth of neutralization will predict protection in vaccine recipients, it is clear that current vaccine immunogens elicit antibodies that neutralize only a minority of circulating isolates. Thus, much progress needs to be made in this area. Also, though virus neutralization is considered a critical benchmark for a vaccine, this may not be the only benchmark for predicting success with antibody-based HIV-1 vaccine immunogens. The main targets for neutralizing antibodies to HIV-1 are the surface gp120 and trans-membrane gp41 envelope glycoproteins (Env) that mediate receptor and coreceptor binding and the subsequent membrane fusion events that allow the virus to gain entry into cells [3]. Antibodies neutralize the virus by binding these viral spikes and blocking virus entry into susceptible cells, such as CD4+ T cells [4,5]. In order to chronically replicate in the host, the virus exploits several mechanisms to shield itself against antibody recognition, including a dense outer coating of sugar molecules (N-linked glycans) and the strategic positioning of cysteine–cysteine loop structures on the gp120 molecule [6–8]. These shielding mechanisms, although highly effective, have vulnerabilities imposed by fitness constraints. Information on the precise location and molecular structure of these vulnerable regions could be valuable for the rational design of improved vaccine immunogens. Participants in the workshop identified four areas that, if given proper attention, could provide key information that would bring the field closer to an effective antibody-based HIV-1 vaccine: (1) structure-assisted immunogen design, (2) role of Fc receptors and complement, (3) assay standardization and validation, and (4) immunoregulation of B cell responses.

Optimizing the dose of pre-pandemic influenza vaccines to reduce the infection attack rate.

Abstract: Background The recent spread of avian influenza in wild birds and poultry may be a precursor to the emergence of a 1918-like human pandemic. Therefore, stockpiles of human pre-pandemic vaccine (targeted at avian strains) are being considered. For many countries, the principal constraint for these vaccine stockpiles will be the total mass of antigen maintained. We tested the hypothesis that lower individual doses (i.e., less than the recommended dose for maximum protection) may provide substantial extra community-level benefits because they would permit wider vaccine coverage for a given total size of antigen stockpile. Methods and Findings We used a mathematical model to predict infection attack rates under different policies. The model incorporated both an individual's response to vaccination at different doses and the process of person-to-person transmission of pandemic influenza. We found that substantial reductions in the attack rate are likely if vaccines are given to more people at lower doses. These results are applicable to all three vaccine candidates for which data are available. As a guide to the magnitude of the effect, we simulated epidemics based on historical studies of immunogenicity. For example, for one of the vaccines for which data are available, the attack rate would drop from 67.6% to 58.7% if 160 out of the total US population of 300 million were given an optimal dose rather than 20 out of 300 million given the maximally protective dose (as promulgated in the US National Pandemic Preparedness Plan). Our results are conservative with respect to a number of alternative assumptions about the precise nature of vaccine protection. We also considered a model variant that includes a single high-risk subgroup representing children. For smaller stockpile sizes that allow vaccine to be offered only to the high-risk group at the optimal dose, the predicted benefits of using the homogenous model formed a lower bound in the presence of a risk group, even when the high-risk group was twice as infective and twice as susceptible. Conclusions In addition to individual-level protection (i.e., vaccine efficacy), the population-level implications of pre-pandemic vaccine programs should be considered when deciding on stockpile size and dose. Our results suggest that a lower vaccine dose may be justified in order to increase population coverage, thereby reducing the infection attack rate overall.

Replication and Transmission of Live Attenuated Infectious Laryngotracheitis Virus (ILTV) Vaccines

Abstract: The aim of this study was to evaluate the replication of live attenuated infectious laryngotracheitis virus vaccines in selected tissues and their ability to transmit to contact-exposed birds. Four-week-old specific-pathogen-free chickens were eye drop-inoculated with tissue culture origin (TCO) and chicken embryo origin (CEO) vaccines. Contact-exposed chickens were housed in direct contact with eye drop-inoculated chickens from the first day postinoculation. Virus isolation and real-time polymerase chain reaction were used to detect the presence of live virus and viral DNA, respectively, in the trachea, trigeminal ganglia, eye conjunctiva, cecal tonsils, and cloaca from eye drop-inoculated and contact-exposed birds at days 2, 4, 5 to 10, 14, 18, 21, 24, and 28 postinoculation. No differences were observed in the ability of the TCO and CEO vaccines to replicate in the examined tissues. Both vaccines presented a localized replication in the eye conjunctiva and the trachea. Both vaccines were capable of transmitting to contact-exposed birds, attaining peaks of viral DNA as elevated as those observed in inoculated birds. The CEO vaccine replicated faster and reached higher viral genome copy number than the TCO vaccine in the conjunctiva and trachea of eye drop-inoculated and contact-exposed birds. The viral DNA from both vaccines migrated to the trigeminal ganglia during early stages of infection. Although the CEO and TCO vaccines were not recovered from the cecal tonsils and the cloaca, low levels of viral DNA were detected at these sites during the peak of viral replication in the upper respiratory tract.

H5N1 Viruses and Vaccines

Abstract: The establishment and spread of highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype in birds and coincident infections in humans since 2003 have raised concerns that we may be facing an influenza pandemic caused by an H5N1 influenza virus. In this brief Opinion piece, we consider the pandemic threat posed by H5N1 viruses and review the published data on the evaluation of H5N1 vaccines in preclinical and clinical studies. HPAI H5N1 viruses have been isolated from avian species in more than 50 countries. As of 29 January 2007, 270 laboratory-confirmed cases of H5N1 infection in humans had been reported by the World Health Organization, 164 of which were fatal [1], resulting in a case fatality rate of approximately 60%. In order to cause a pandemic, H5N1 viruses will have to acquire the ability to transmit efficiently from person to person. The H5 hemagglutinin (HA) is found in influenza viruses that typically infect avian species, so efficient person-to-person spread could happen if the H5N1 virus reassorts, or exchanges genes, with circulating human influenza viruses giving rise to a virus with the H5 HA (to which the population is not immune) in a gene constellation that confers the property of transmissibility. Alternatively, efficient person-to-person spread could occur if the H5N1 virus evolves and adapts to more efficient replication and transmissibility in the human population. Two observations have led to questions about the likelihood of a reassortant H5N1 virus causing a pandemic. First, reassortant viruses have not been isolated despite ongoing H5N1 outbreaks in birds and infections in humans, even with concurrent circulation of human influenza viruses since 2003. Second, laboratory studies have found that reassortant viruses that derived the surface glycoprotein genes from an H5N1 virus and internal protein genes from an H3N2 influenza A virus were not efficiently transmitted and were somewhat less infectious to ferrets (an animal model for human influenza) than the wild-type H5N1 viruses [2]. The concern that an H5N1 virus could adapt to the human host and acquire mutations that confer transmissibility prompts very careful analysis of each cluster of human H5N1 infections that is reported ( [1,3–5]). At present, the data suggest that human-to-human transmission is inefficient and very limited. Nevertheless, from the standpoint of public health preparedness, it is important to move forward in developing approaches for dealing with H5N1 in humans. Vaccination is the preferred strategy for prevention and control of influenza. The most expeditious way to generate an H5N1 vaccine is to use licensed technology, such as inactivated or live attenuated vaccines. However, several practical and scientific challenges to the development of H5N1 vaccines exist. These include high pathogenicity of wild-type H5N1 influenza viruses, reduced yield of candidate vaccine viruses in embryonated hens' eggs compared to that of human influenza viruses, limited manufacturing capacity, and poor immunogenicity of the H5 HA. Despite these obstacles, several approaches have been used to generate candidate vaccines and a few have advanced to clinical trials (Table 1). Table 1 also includes data published on vaccines that are being developed for veterinary use. Table 1 Vaccine Strategies against H5N1 Influenza that Have Been Evaluated in Preclinical and Clinical Studies Perhaps the most significant scientific challenge for the development and licensure of pandemic vaccines for humans is that assessment of vaccine efficacy for humans will have to be inferred from preclinical studies in experimental animals and immunogenicity studies in humans, as it will not be possible to assess the efficacy of a pandemic vaccine in a clinical trial before a pandemic begins. Table 2 summarizes the preclinical and clinical findings from inactivated H5N1 vaccines evaluated in humans to date. Preclinical studies of influenza vaccines are generally conducted in mice or ferrets. In most cases, the 1997 and 2003 H5N1 vaccine candidates were promising in terms of immunogenicity and efficacy, with complete protection of animals from lethal H5N1 infection, and significant, if not complete, reduction of pulmonary viral replication following challenge. Preclinical data in ferrets have not been published on the 2004 H5N1 vaccines that were evaluated in clinical trials, so data are not available to directly assess how accurately preclinical studies would have predicted the outcome of evaluation of these vaccines in humans. Table 2 Summary of Preclinical and Clinical Findings for Inactivated H5N1 Virus Vaccines Evaluated in Humans In clinical trials, inactivated virus vaccines based on H5N1 viruses isolated in 2004 [6,7], a recombinant H5 HA subunit vaccine based on an H5N1 virus isolated in 1997 expressed in a baculovirus vector [8], and an inactivated virus vaccine based on a surrogate low pathogenicity avian H5N3 virus [9–11], were poorly immunogenic when administered to volunteers without adjuvant. Clinical trials of H1N1 influenza vaccines in 1977 established that whole virion vaccines are more immunogenic than split-virion vaccines (in which the virus particles are disrupted by detergent treatment to obtain a preparation enriched for the surface antigens) [12,13]; however, the former are also more reactogenic than the latter. Consistent with this observation, in recent trials in humans of an alum-adjuvanted inactivated H5N1 virus vaccine, much lower doses of a whole virion vaccine elicited higher levels of antibody compared to a split-virion vaccine [7,14]. Despite the fact that the difference in immunogenicity of whole virion and split-virion vaccines was well established, preclinical studies of inactivated H5 virus vaccines in mice and ferrets have generally been performed using whole virion preparations with adjuvant, while the vaccine preparation evaluated in clinical trials is a purified split-virion vaccine. It is important to note that preclinical data will not be predictive of clinical trial results if the vaccine formulations that are tested in preclinical studies are different from those evaluated in clinical trials. Clinical trials have demonstrated that the immunogenicity of H5 vaccines can be enhanced by an increased dose of the HA, the use of adjuvants, use of multiple doses, or use of a whole virion vaccine. More studies are needed to directly compare findings from preclinical and clinical evaluation of pandemic influenza vaccines to establish whether animal models can be used to guide decisions on which vaccine candidates to take forward for evaluation in humans. Although there is no evidence that H5N1 viruses have yet acquired pandemic potential, the consequences of such an event are serious enough that preparation for a possible pandemic is essential.

Combination of protein and viral vaccines induces potent cellular and humoral immune responses and enhanced protection from murine malaria challenge.

Abstract: The search for an efficacious vaccine against malaria is ongoing, and it is now widely believed that to confer protection a vaccine must induce very strong cellular and humoral immunity concurrently. We studied the immune response in mice immunized with the recombinant viral vaccines fowlpox strain FP9 and modified virus Ankara (MVA), a protein vaccine (CV-1866), or a combination of the two; all vaccines express parts of the same preerythrocytic malaria antigen, the Plasmodium berghei circumsporozoite protein (CSP). Mice were then challenged with P. berghei sporozoites to determine the protective efficacies of different vaccine regimens. Two immunizations with the protein vaccine CV-1866, based on the hepatitis B core antigen particle, induced strong humoral immunity to the repeat region of CSP that was weakly protective against sporozoite challenge. Prime-boost with the viral vector vaccines, FP9 followed by MVA, induced strong T-cell immunity to the CD8+ epitope Pb9 and partially protected animals from challenge. Physically mixing CV-1866 with FP9 or MVA and then immunizing with the resultant combinations in a prime-boost regimen induced both cellular and humoral immunity and afforded substantially higher levels of protection (combination, 90%) than either vaccine alone (CV-1866, 12%; FP9/MVA, 37%). For diseases such as malaria in which different potent immune responses are required to protect against different stages, using combinations of partially effective vaccines may offer a more rapid route to achieving deployable levels of efficacy than individual vaccine strategies.

MVA E2 recombinant vaccine in the treatment of human papillomavirus infection in men presenting intraurethral flat condyloma: a phase I/II study.

Abstract: Human papillomavirus (HPV) is the etiologic agent for warts and cervical cancer. In Mexico, the death rate from cervical cancer is extremely high, and statistical data show that since 1990 the number of deaths is increasing. Condylomas and cancer of the penis are the most common lesions presented in men; bladder and prostate cancer in men are also associated with the presence of HPV. Since HPV is transmitted by sexual intercourse, treating both partners is necessary in order to eliminate the virus in the population. Approaches to this include preventative vaccines such as Gardasil®, and therapeutic vaccines to treat established infections in both men and women. This will be the only way to decrease the numbers of deaths due to this malignancy. We conducted a phase I/II clinical trial to evaluate the potential use of the recombinant vaccinia viral vaccine MVA E2 (composed of modified vaccinia virus Ankara [MVA] expressing the E2 gene of bovine papillomavirus) to treat flat condyloma lesions associated with oncogenic HPV in men. Fifty male patients with flat condyloma lesions were treated with either MVA E2 therapeutic vaccine or fluorouracil (5-fluorouracil). Thirty men received the therapeutic vaccine, at a total of 106 virus particles per dose, administered directly into the urethra once every week over a 4-week period. Twenty control patients were treated with 5% fluorouracil 1mL twice weekly over a 4-week period directly into the urethra. Reduction of lesions or absence of papillomavirus infection was monitored by colposcopy and histologic analysis. The immune response after MVA E2 treatment was determined by measuring the antibodies against the MVA E2 virus and by analyzing the lymphocyte cytotoxic activity against cancer cells bearing oncogenic papillomavirus. Presence of papillomavirus was determined by the Hybrid Capture® method. Twenty-eight of 30 patients showed no lesion or presence of papillomavirus as diagnosed by colposcopy and brush histologic examination after 4 weeks of MVA E2 treatment. These patients showed complete elimination of flat condyloma in the urethra and no acetowhite spots were detected over the prepuce. In two other patients the acetowhite spots and flat condyloma did not diminish. All patients developed antibodies against the MVA E2 vaccine and E2 protein, and generated a specific cytotoxic response against papilloma-transformed cells. Viral DNA was not detected in MVA E2-treated patients. In the control group, 13 of 20 patients were free of lesions. Three of these patients had recurrence of lesions after 3 months of treatment and none of the patients developed specific antibodies against cancer cells. In contrast, patients treated with MVA E2 did not show any recurrence of lesions after 1 year of treatment. In addition, none of the patients had local or systemic adverse effects according to the WHO classification 1–4. Therapeutic vaccination with MVA E2 proved to be very effective in stimulating the immune system against papillomavirus, and in generating regression of flat condyloma lesions in men.

A Heterologous DNA Prime-Venezuelan Equine Encephalitis Virus Replicon Particle Boost Dengue Vaccine Regimen Affords Complete Protection from Virus Challenge in Cynomolgus Macaques

Abstract: A candidate vaccine (D1ME-VRP) expressing dengue virus type 1 premembrane and envelope proteins in a Venezuelan equine encephalitis (VEE) virus replicon particle (VRP) system was constructed and tested in conjunction with a plasmid DNA vaccine (D1ME-DNA) expressing identical dengue virus sequences. Cynomolgus macaques were vaccinated with three doses of DNA (DDD), three doses of VRP (VVV group), or a heterologous DNA prime-VRP boost regimen (DDV) using two doses of DNA vaccine and a third dose of VRP vaccine. Four weeks after the final immunization, the DDV group produced the highest dengue virus type 1-specific immunoglobulin G antibody responses and virus-neutralizing antibody titers. Moderate T-cell responses were demonstrated only in DDD- and DDV-vaccinated animals. When vaccinated animals were challenged with live virus, all vaccination regimens showed significant protection from viremia. DDV-immunized animals were completely protected from viremia (mean time of viremia = 0 days), whereas DDD- and VVV-vaccinated animals had mean times of viremia of 0.66 and 0.75 day, respectively, compared to 6.33 days for the control group of animals.