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Biomedical subjects

Mike Bray

Publications and source records attributed to Mike Bray.

At least 19 recordsLinked to original sources
PubMed2006

Subunit recombinant vaccine protects against monkeypox.

The smallpox vaccine Dryvax, a live vaccinia virus (VACV), protects against smallpox and monkeypox, but is contraindicated in immunocompromised individuals. Because Abs to VACV mediate protection, a live virus vaccine could be substituted by a safe subunit protein-based vaccine able to induce a protective Ab response. We immunized rhesus macaques with plasmid DNA encoding the monkeypox orthologs of the VACV L1R, A27L, A33R, and B5R proteins by the intradermal and i.m. routes, either alone or in combination with the equivalent recombinant proteins produced in Escherichia coli. Animals that received only DNA failed to produce high titer Abs, developed innumerable skin lesions after challenge, and died in a manner similar to placebo controls. By contrast, the animals vaccinated with proteins developed moderate to severe disease (20-155 skin lesions) but survived. Importantly, those immunized with DNA and boosted with proteins had mild disease with 15 or fewer lesions that resolved within days. DNA/protein immunization elicited Th responses and binding Ab titers to all four proteins that correlated negatively with the total lesion number. The sera of the immunized macaques recognized a limited number of linear B cell epitopes that are highly conserved among orthopoxviruses. Their identification may guide future efforts to develop simpler, safer, and more effective vaccines for monkeypox and smallpox.

Amino Acid Sequence↗
PubMed2006

Molecular determinants of Ebola virus virulence in mice.

Zaire ebolavirus (ZEBOV) causes severe hemorrhagic fever in humans and nonhuman primates, with fatality rates in humans of up to 90%. The molecular basis for the extreme virulence of ZEBOV remains elusive. While adult mice resist ZEBOV infection, the Mayinga strain of the virus has been adapted to cause lethal infection in these animals. To understand the pathogenesis underlying the extreme virulence of Ebola virus (EBOV), here we identified the mutations responsible for the acquisition of the high virulence of the adapted Mayinga strain in mice, by using reverse genetics. We found that mutations in viral protein 24 and in the nucleoprotein were primarily responsible for the acquisition of high virulence. Moreover, the role of these proteins in virulence correlated with their ability to evade type I interferon-stimulated antiviral responses. These findings suggest a critical role for overcoming the interferon-induced antiviral state in the pathogenicity of EBOV and offer new insights into the pathogenesis of EBOV infection.

Animals↗
PubMed2005

Smallpox vaccine-induced antibodies are necessary and sufficient for protection against monkeypox virus.

Vaccination with live vaccinia virus affords long-lasting protection against variola virus, the agent of smallpox. Its mode of protection in humans, however, has not been clearly defined. Here we report that vaccinia-specific B-cell responses are essential for protection of macaques from monkeypox virus, a variola virus ortholog. Antibody-mediated depletion of B cells, but not CD4+ or CD8+ T cells, abrogated vaccine-induced protection from a lethal intravenous challenge with monkeypox virus. In addition, passive transfer of human vaccinia-neutralizing antibodies protected nonimmunized macaques from severe disease. Thus, vaccines able to induce long-lasting protective antibody responses may constitute realistic alternatives to the currently available smallpox vaccine (Dryvax).

Animals↗
PubMed2005

Potential applications of conventional and molecular imaging to biodefense research.

Imaging methods that visualize the structure and function of the living body are widely used in patient care and biomedical research, but their full potential has not yet been applied to the study and treatment of the severe illnesses caused by pathogens of biodefense concern. "Conventional" imaging techniques (e.g., radiography, computed tomography, ultrasound, or magnetic resonance imaging) delineate anatomic changes in tissues, whereas "molecular" methods employ magnetic resonance, positron emission tomography, single-photon emission computed tomography, or optical (fluorescence or bioluminescence) imaging to detect biochemical reactions that accompany pathogen replication or host responses. We review the basic principles of these methods, describe the diseases caused by 6 pathogens classified as category A or B bioterror agents (anthrax, plague, tularemia, filoviral hemorrhagic fever, smallpox, and aerosolized equine encephalitis virus infection), and discuss how imaging could be used to study their pathogenesis in laboratory animals and to diagnose and monitor infection in humans.

Bioterrorism↗
PubMed2005

Ebola virus: the role of macrophages and dendritic cells in the pathogenesis of Ebola hemorrhagic fever.

Ebola hemorrhagic fever is a severe viral infection characterized by fever, shock and coagulation defects. Recent studies in macaques show that major features of illness are caused by effects of viral replication on macrophages and dendritic cells. Infected macrophages produce proinflammatory cytokines, chemokines and tissue factor, attracting additional target cells and inducing vasodilatation, increased vascular permeability and disseminated intravascular coagulation. However, they cannot restrict viral replication, possibly because of suppression of interferon responses. Infected dendritic cells also secrete proinflammatory mediators, but cannot initiate antigen-specific responses. In consequence, virus disseminates to these and other cell types throughout the body, causing multifocal necrosis and a syndrome resembling septic shock. Massive "bystander" apoptosis of natural killer and T cells further impairs immunity. These findings suggest that modifying host responses would be an effective therapeutic strategy, and treatment of infected macaques with a tissue-factor inhibitor reduced both inflammation and viral replication and improved survival.

Animals↗
PubMed2005

Smallpox vaccine does not protect macaques with AIDS from a lethal monkeypox virus challenge.

It is unknown whether smallpox vaccination would protect human immunodeficiency virus type 1 (HIV-1)-infected individuals, because helper CD4(+) cells, the targets of HIV-1 infection, are necessary for the induction of both adaptive CD8(+) cell and B cell responses. We have addressed this question in macaques and have demonstrated that, although smallpox vaccination is safe in immunodeficient macaques when it is preceded by immunization with highly attenuated vaccinia strains, the macaques were not protected against lethal monkeypox virus challenge if their CD4(+) cell count was <300 cells/mm(3). The lack of protection appeared to be associated with a defect in vaccinia-specific immunoglobulin (Ig) switching from IgM to IgG. Thus, vaccination strategies that bypass CD4(+) cell help are needed to elicit IgG antibodies with high affinity and adequate tissue distribution and to restore protection against smallpox in severely immunocompromised individuals.

Animals↗
PubMed2005

Pathogenesis of viral hemorrhagic fever.

Single-stranded RNA viruses from four different families cause a syndrome of fever and malaise, 'capillary leak' with loss of plasma volume, and coagulation defects which can lead to bleeding. Although direct cytopathic effects can contribute to disease severity, most features of illness are caused by innate immune responses, as the systemic spread of virus to macrophages and dendritic cells leads to the release of mediators that modify vascular function and have procoagulant activity. The synthesis of tissue factor by infected cells can also trigger coagulation. Failure of adaptive immunity through impaired dendritic cell function and lymphocyte apoptosis can have a crucial role in fatal infection.

Animals↗
PubMed2004

Antiviral prophylaxis of smallpox.

Proof-of-concept studies suggest that current defences against smallpox could be strengthened by supplementing vaccination with antiviral drug prophylaxis, based on aerosolized or orally available forms of the long-acting medication cidofovir. Delivery of aerosolized cidofovir to mice results in its prolonged retention in respiratory tissues and protection against lethal intranasal or aerosol poxviral challenge. Although cidofovir itself is not orally available, the addition of an alkoxyalkanol ether side-chain allows it to be absorbed from the gastrointestinal tract. This also markedly increases its antiviral activity and lengthens its intracellular half-life from roughly 3 to 8-10 days. Oral treatment also protected mice against lethal poxviral challenge. These results suggest that a single aerosol dose of cidofovir (or an alkoxyalkanol-ether derivative) could provide prolonged protection against initiation of smallpox infection, whereas oral treatment could prevent both initiation of infection and internal dissemination of virus. Both approaches may avoid the nephrotoxicity that occasionally results from intravenous cidofovir therapy.

Antiviral Agents↗
PubMed2004

Looking back at smallpox.

Smallpox apparently arose through transfer of variola virus to humans from another animal species. By causing a brief infection that required close contact for transmission and engendered solid immunity, the agent was always vulnerable to simple isolation measures. The high replicative fidelity of the viral DNA polymerase limited variola's ability to adapt to humans and preserved orthopoxviral antigenic cross-reactivity, so that vaccinia vaccination protected against smallpox. Host-derived genes encoding immunomodulatory proteins helped shelter viral replication from innate immune responses. Examination of clinical variants suggests that severity of illness was usually determined by host responses during the incubation period. Control of viral replication was aided by early postexposure vaccination and might be strengthened by additional immunological interventions. Massive inflammatory responses were responsible for major features of illness. Some patients with high levels of circulating virus developed hemorrhagic disease resembling septic shock. Continued study of virus-host interactions is needed to defend against genetically modified agents.

Bioterrorism↗
PubMed2004

A simple assay for determining antiviral activity against Crimean-Congo hemorrhagic fever virus.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus that is emerging as a significant human pathogen in many regions of the world, including Africa, Asia, and Europe. In this report, we describe a simple screening method for discovering new antiviral compounds directed against CCHFV. Antiviral activity was determined by assaying infected SW-13 cells (human adrenal gland carcinoma) for protection from cytopathic effect (CPE). By using an in vitro neutral red uptake assay, we were able to quantitatively measure CPE induced by CCHFV. As a proof of concept, we used this method to evaluate the antiviral activity of ribavirin and a series of structural analogs (ribamidine, 6-azauridine, selenazofurin, and tiazofurin) against four geographically diverse strains of CCHFV. Ribavirin inhibited the replication of CCHFV as reported previously using plaque reduction assays. One drug, ribamidine, showed antiviral activity that was 4.5- to 8-fold less than that of ribavirin, and the other three drugs (6-azauridine, selenazofurin, and tiazofurin) did not show significant antiviral activity. There were no significant differences in drug sensitivities among the CCHFV strains. Development of this simple and reliable assay will potentially allow high-throughput screening for discovering additional antiviral drugs to combat this important public health threat.

Animals↗
PubMed2004

Pathogenesis of filoviral haemorrhagic fevers.

The filoviruses, marburgvirus and ebolavirus, cause epidemics of haemorrhagic fever with high case-fatality rates. The severe illness results from a complex of pathogenetic mechanisms that enable the virus to suppress innate and adaptive immune responses, infect and kill a broad variety of cell types, and elicit strong inflammatory responses and disseminated intravascular coagulation, producing a syndrome resembling septic shock. Most experimental data have been obtained on Zaire ebolavirus, which causes uniformly lethal disease in experimentally infected non-human primates but produces a broader range of outcomes in naturally infected human beings. 10-30% of patients can survive the illness by mobilising adaptive immune responses, and there is limited evidence that mild or symptomless infections also occur. The other filoviruses that have caused human disease, Sudan ebolavirus, Ivory Coast ebolavirus, and marburgvirus, produce a similar illness but with somewhat lower case-fatality rates. Variations in outcome during an epidemic might be due partly to genetically determined differences in innate immune responses to the viruses. Recent studies in non-human primates have shown that blocking of certain host responses, such as the coagulation cascade, can result in reduced viral replication and improved host survival.

Africa↗
PubMed2003

Modeling a safer smallpox vaccination regimen, for human immunodeficiency virus type 1-infected patients, in immunocompromised macaques.

We have modeled smallpox vaccination with Dryvax (Wyeth) in rhesus macaques that had depletion of CD4(+) T cells induced by infection with simian immunodeficiency virus or simian/human immunodeficiency virus. Smallpox vaccination induced significantly larger skin lesions in immunocompromised macaques than in healthy macaques. Unexpectedly, "progressive vaccinia" was infrequent. Vaccination of immunocompromised macaques with the genetically-engineered, replication-deficient poxvirus NYVAC, before or after retrovirus infection, was safe and lessened the severity of Dryvax-induced skin lesions. Neutralizing antibodies to vaccinia were induced by NYVAC, even in macaques with severe CD4(+) T cell depletion, and their titers inversely correlated with the time to complete resolution of the skin lesions. Together, these results provide the proof of concept, in macaque models that mirror human immunodeficiency virus type 1 infection, that a prime-boost approach with a highly attenuated poxvirus followed by Dryvax increases the safety of smallpox vaccination, and they highlight the importance of neutralizing antibodies in protection against virulent poxvirus.

Animals↗
PubMed2003

Comparison of individual and combination DNA vaccines for B. anthracis, Ebola virus, Marburg virus and Venezuelan equine encephalitis virus.

Multiagent DNA vaccines for highly pathogenic organisms offer an attractive approach for preventing naturally occurring or deliberately introduced diseases. Few animal studies have compared the feasibility of combining unrelated gene vaccines. Here, we demonstrate that DNA vaccines to four dissimilar pathogens that are known biowarfare agents, Bacillus anthracis, Ebola (EBOV), Marburg (MARV), and Venezuelan equine encephalitis virus (VEEV), can elicit protective immunity in relevant animal models. In addition, a combination of all four vaccines is shown to be equally as effective as the individual vaccines for eliciting immune responses in a single animal species. These results demonstrate for the first time the potential of combined DNA vaccines for these agents and point to a possible method of rapid development of multiagent vaccines for disparate pathogens such as those that might be encountered in a biological attack.

Animals↗
PubMed2003

Protection from lethal infection is determined by innate immune responses in a mouse model of Ebola virus infection.

A mouse-adapted strain of Ebola Zaire virus produces a fatal infection when BALB/cj mice are infected intraperitoneally (ip) but subcutaneous (sc) infection with the same virus fails to produce illness and confers long-term protection from lethal ip rechallenge. To identify immune correlates of protection in this model, we compared viral replication and cytokine/chemokine responses to Ebola virus in mice infected ip (10 PFU/mouse), or sc (100 PFU/mouse) and sc "immune" mice rechallenged ip (10(6) PFU/mouse) at several time points postinfection (pi). Ebola viral antigens were detected in the serum, liver, spleen, and kidneys of ip-infected mice by day 2 pi, increasing up to day 6. Sc-infected mice and immune mice rechallenged ip had no detectable viral antigens until day 6 pi, when low levels of viral antigens were detected in the livers of sc-infected mice only. TNF-alpha and MCP-1 were detected earlier and at significantly higher levels in the serum and tissues of ip-infected mice than in sc-infected or immune mice challenged ip. In contrast, high levels of IFN-alpha and IFN-gamma were found in tissues within 2 days after challenge in sc-infected and immune mice but not in ip-infected mice. Mice became resistant to ip challenge within 48 h of sc infection, coinciding with the rise in tissue IFN-alpha levels. In this model of Ebola virus infection, the nonlethal sc route of infection is associated with an attenuated inflammatory response and early production of antiviral cytokines, particularly IFN-alpha, as compared with lethal ip infection.

Animals↗