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Robert H Purcell

Publications and source records attributed to Robert H Purcell.

17 recordsLinked to original sources
PubMed2003

Pre-clinical immunogenicity and efficacy trial of a recombinant hepatitis E vaccine.

We have demonstrated that recombinant hepatitis E vaccine suitable for clinical evaluation was highly immunogenic and efficacious in preventing hepatitis E and even infection in rhesus macaques following intravenous challenge with three different genotypes of hepatitis E virus (HEV). Two doses of vaccine were essential for optimal protection; the two-dose regimen was more important than the formulation of the vaccine for achieving efficacy. The titers of anti-HEV that were protective in this study were quantified against a World Health Organization (WHO) standard. This permits direct comparison of the results with other studies. The results of this pre-clinical trial of a candidate hepatitis E vaccine strongly suggest that it will be highly efficacious for preventing hepatitis E in the field trial of this vaccine that is currently in progress in Nepal.

Animals↗
PubMed2003

CD8(+) T cells mediate viral clearance and disease pathogenesis during acute hepatitis B virus infection.

Although the CD4(+)- and CD8(+)-T-cell responses to the hepatitis B virus (HBV) are thought to be crucial for the control of HBV infection, the relative contribution of each T-cell subset as an effector of viral clearance is not known. To examine this question, we monitored the course of HBV infection in control, CD4-depleted, and CD8-depleted chimpanzees. Our results demonstrate that CD8(+) cells are the main effector cells responsible for viral clearance and disease pathogenesis during acute HBV infection, and they suggest that viral clearance is mediated by both noncytolytic and cytolytic effector functions of the CD8(+)-T-cell response.

Acute Disease↗
PubMed2002

Genomic analysis of the host response to hepatitis C virus infection.

We have examined the progression of hepatitis C virus (HCV) infections by gene expression analysis of liver biopsies in acutely infected chimpanzees that developed persistent infection, transient viral clearance, or sustained clearance. Both common responses and outcome-specific changes in expression were observed. All chimpanzees showed gene expression patterns consistent with an IFN-alpha response that correlated with the magnitude and duration of infection. Transient and sustained viral clearance were uniquely associated with induction of IFN-gamma-induced genes and other genes involved in antigen processing and presentation and the adaptive immune response. During the early stages of infection, host genes involved in lipid metabolism were also differentially regulated. We also show that drugs that affect these biosynthetic pathways can regulate HCV replication in HCV replicon systems. Our results reveal genome-wide transcriptional changes that reflect the establishment, spread, and control of infection, and they reveal potentially unique antiviral programs associated with clearance of HCV infection.

Animals↗
PubMed2002

Viral and immunological determinants of hepatitis C virus clearance, persistence, and disease.

To define the early events that determine the outcome of acute hepatitis C virus (HCV) infection, we compared the course of viremia with the peripheral and intrahepatic T cell response and intrahepatic cytokine profile in six acutely infected chimpanzees. Three different outcomes were observed after peak viral titers were reached: sustained viral clearance, transient viral clearance followed by chronic infection, and chronic infection that persisted at initial peak titers. The results indicate that HCV spread outpaces the T cell response and that HCV rapidly induces but is not controlled by IFN-alphabeta; that viral clearance follows the entry and accumulation of HCV-specific IFN-gamma-producing T cells in the liver; and that it may not require the destruction of infected cells.

Acute Disease↗
PubMed2002

Prevalence study of antibody to ratborne pathogens and other agents among patients using a free clinic in downtown Los Angeles.

Norway rats (Rattus norvegicus) are hosts for various microbes. Homeless people who have contact with rats may be at risk of infection by them. The Los Angeles County Department of Health Services initiated a seroepidemiologic study among patients who used a free clinic in downtown Los Angeles; 200 serum specimens obtained for other routine assays were tested for antibodies to ratborne pathogens and other agents. The seroprevalence of antibody to hepatitis E virus in this population was 13.6%; to Bartonella elizabethae, 12.5%; to B. quintana, 9.5%; to B. henselae, 3.5%; to Seoul virus, 0.5%; and to Rickettsia typhi, 0.0%. This study found that patients and locally trapped rats had antibodies to some of the same agents.

Adult↗
PubMed2002

DNA-based vaccination against hepatitis C virus (HCV): effect of expressing different forms of HCV E2 protein and use of CpG-optimized vectors in mice.

DNA-based immunization may be of prophylactic and therapeutic value for hepatitis C virus (HCV) infection. In efforts to improve the immunogenicity of a plasmid expressing the second envelope protein (E2) of HCV, we evaluated in mice the role of the antigen localization and demonstrated that membrane-bound and secreted forms induced higher titers of E2-specific antibodies, as well as earlier and higher seroconversion rates, than the intracellular form, but all three forms induced strong CTL. We also investigated whether E2-specific antibody responses could be enhanced by CpG optimization of the plasmid backbone and showed that removal of neutralizing CpG dinucleotides did not have a significant effect but addition of 64 immunostimulatory CpG motifs significantly enhanced anti-E2 titers. These results may have implications for the design and development of HCV DNA vaccines.

Animals↗
PubMed2002

Recombinant vaccine against hepatitis E: duration of protective immunity in rhesus macaques.

Hepatitis E virus (HEV) is an enterically transmitted virus that causes acute hepatitis. A candidate vaccine containing recombinant HEV capsid protein (56kDa) expressed in insect cells was shown previously to be highly immunogenic when administered in two doses to rhesus monkeys and to protect them from hepatitis E when challenged with a large intravenous dose of homologous or heterologous HEV. In the present study, the effect of a third dose of the same vaccine lot was evaluated and more importantly, the duration of protection following two doses was determined. Rhesus monkeys vaccinated twice with the 56kDa capsid protein were challenged with homologous virus 6 or 12 months after the last vaccination: 3 of 4 monkeys challenged 6 or 12 months later, respectively were protected against viral hepatitis. Similarly, all four of the rhesus monkeys given a third dose of vaccine 1 month prior to challenge were protected against hepatitis. In contrast, all four monkeys given placebo developed hepatitis following challenge. In summary, two doses of HEV vaccine partially protected rhesus monkeys from hepatitis E following intravenous challenge 6 or 12 months after vaccination.

Animals↗
PubMed2002

Relative infectivity of hepatitis A virus by the oral and intravenous routes in 2 species of nonhuman primates.

Hepatitis A virus (HAV) is naturally transmitted by the fecal-oral route but can also be transmitted intravenously. To determine the relative infectivity of these 2 routes, an infectivity titration of a standard challenge pool of virulent HAV was performed in tamarins and chimpanzees. In both species, 1 oral dose of HAV was equivalent to 10(4.5) intravenous doses. These findings have relevance for attempts to develop live, attenuated HAV vaccines that can be administered orally.

Animals↗
PubMed2002

Early changes in hepatitis C viral quasispecies during interferon therapy predict the therapeutic outcome.

Despite recent treatment advances, the majority of patients with chronic hepatitis C fail to respond to antiviral therapy. Although the genetic basis for this resistance is unknown, accumulated evidence suggests that changes in the heterogeneous viral population (quasispecies) may be an important determinant of viral persistence and response to therapy. Sequences within hepatitis C virus (HCV) envelope 1 and envelope 2 genes, inclusive of the hypervariable region 1, were analyzed in parallel with the level of viral replication in serial serum samples obtained from 23 patients who exhibited different patterns of response to therapy and from untreated controls. Our study provides evidence that although the viral diversity before treatment does not predict the response to treatment, the early emergence and dominance of a single viral variant distinguishes patients who will have a sustained therapeutic response from those who subsequently will experience a breakthrough or relapse. A dramatic reduction in genetic diversity leading to an increasingly homogeneous viral population was a consistent feature associated with viral clearance in sustained responders and was independent of HCV genotype. The persistence of variants present before treatment in patients who fail to respond or who experience a breakthrough during therapy strongly suggests the preexistence of viral strains with inherent resistance to IFN. Thus, the study of the evolution of the HCV quasispecies provides prognostic information as early as the first 2 weeks after starting therapy and opens perspectives for elucidating the mechanisms of treatment failure in chronic hepatitis C.

Adult↗
PubMed2002

High prevalence of hepatitis E antibodies among Danish prisoners and drug users.

Injecting drug users and prisoners have high prevalences of antibodies to hepatitis A-C. The aim of this study was to determine the prevalence of antibodies to hepatitis E virus (anti-HEV) in two Danish high-risk populations and correlate anti-HEV with risk factors for transmission. Three hundred thirty male prisoners and 137 patients at a drug treatment center were tested for anti-HEV with an in-house enzyme-linked immunoassay (EIA) utilizing antigens derived from open reading frame 2 (ORF2). This was compared with a commercial test with antigens derived from ORF2 and ORF3 (Abbott HEV EIA). In addition the samples were tested for antibodies against hepatitis A-C viruses, human immunodeficiency virus (HIV) 1 and 2, human T lymphotropic virus (HTLV) I and II and herpes simplex virus type 2 (HSV2). The participants were interviewed about risk factors for transmission. The anti-HEV prevalence was 16.9% (95% CI 14-21) for the in-house assay compared to 4.1% (95% CI 2.5-6.3) with the commercial assay. The correlation between the two assays was low (87% overall agreement; kappa value 0.32). One sample was strongly anti-HEV IgM positive, suggesting recent HEV infection inside Denmark. The presence of anti-HEV was associated significantly with anti-HAV among prisoners and increased with age in both groups. In contrast, associations were not found with injecting drug use or sexual risk factors. With the commercial assay an increased prevalence of anti-HEV was found among participants who had spent more than 5 years outside Northern Europe. In conclusion, anti-HEV was highly prevalent among Danish prisoners and drug users but not related to risk factors for blood-borne or sexual transmission.

Adult↗
PubMed2002

Identification of VP1/2A and 2C as virulence genes of hepatitis A virus and demonstration of genetic instability of 2C.

Fourteen different chimeric virus genomes were constructed from two infectious cDNA clones encoding a virulent and an attenuated isolate, respectively, of the HM175 strain of hepatitis A virus. The ability of each recombinant virus to infect tamarins and to cause acute hepatitis was determined. Comparisons of the genotype and phenotype of each virus suggested that VP1/2A and 2C genes were responsible for virulence. The 2C gene derived from the attenuated parent virus was unstable, and one or more mutations arose in this gene during the first passage in tamarins.

Animals↗
PubMed2002

Epidemic of hepatitis E in a military unit in Abbotrabad, Pakistan.

An outbreak of hepatitis caused by hepatitis E virus (HEV) in Abbottabad, Pakistan was traced to fecal contamination of a water system. Of 109 men hospitalized with hepatitis, 104 (95%) had serologic evidence of acute hepatitis E (IgM antibody to HEV [anti-HEV]), three (3%) probably had acute hepatitis E (high titers of IgG anti-HEV without IgM), and two had acute hepatitis A. Among a subset of 44 men with acute hepatitis E from whom three serum specimens were obtained over a four-month period, the anti-HEV IgG geometric mean titers (GMTs) decreased from 1,519 during the outbreak to 657 at four months. The IgM anti-HEV was detected in 40 (91%) of 44 sera obtained at admission (GMT = 533 during acute disease), but in only six (14%) four months later. The prevalence of anti-HEV in this population before the outbreak was estimated to be 30%. The presence of IgG anti-HEV appeared to protect against clinical hepatitis or development of serologic evidence of new infection with HEV. This is the second major epidemic of hepatitis E in the Pakistani military confirmed by an anti-HEV enzyme-linked immunosorbent assay (ELISA). Evidence that pre-existing antibody as measured by this ELISA protects against disease is important for assessment of vaccine development.

Adolescent↗
PubMed2001

Acute hepatitis caused by a novel strain of hepatitis E virus most closely related to United States strains.

A unique hepatitis E virus (HEV) strain was identified as the aetiological agent of acute hepatitis in a United States (US) patient who had recently returned from vacation in Thailand, a country in which HEV is endemic. Sequence comparison showed that this HEV strain was most similar, but not identical, to the swine and human HEV strains recovered in the US. Phylogenetic analysis revealed that this new HEV isolate was closer to genotype 3 strains than to the genotype 1 strains common in Asia. The fact that this HEV was closely related to strains recovered in countries where HEV is not endemic and was highly divergent from Asian HEV strains raises the questions of where the patient's infection was acquired and of whether strains are geographically as localized as once thought.

Animals↗
PubMedDate not supplied

Hepatitis E virus.

Hepatitis E virus (HEV) is a positive-stranded RNA virus with a 7.2 kb genome that is capped and polyadenylated. The virus is currently unclassified: the organisation of the genome resembles that of the Caliciviridae but sequence analyses suggest it is more closely related to the Togaviridae. Hepatitis E virus is an enterically transmitted virus that causes both epidemics and sporadic cases of acute hepatitis in many countries of Asia and Africa but only rarely causes disease in more industrialised countries. Initially the virus was believed to have a limited geographical distribution. However, serological studies suggest that HEV may be endemic also in the United States and Europe even though it infrequently causes overt disease in these countries. Many different animal species worldwide recently have been shown to have antibodies to HEV suggesting that hepatitis E may be zoonotic. Although two related strains have been experimentally transmitted between species, direct transmission from an animal to a human has not been documented. There are four currently recognised genotypes and two of the four contain viruses isolated from swine as well as from humans. Regardless of country of origin or genotype of the virus, most, if not all, strains belong to a single serotype. A promising recombinant vaccine candidate comprised of a truncated capsid protein is currently under evaluation in Nepal.

Animals↗