Leo L M Poon

The University of Hong Kong, Hong Kong, Hong Kong

Are you Leo L M Poon?

Claim your profile

Publications (150)1311.24 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Sequence analyses of influenza PB2 sequences indicate that the 627 position almost exclusively contains either lysine (K) or glutamic acid (E), suggesting a high sequence constraint at this genetic marker. Here, we used a site-directed random mutagenesis method to demonstrate that PB2-627 position has a high sequence plasticity. Recombinant viruses carrying various amino acid residues at this position are viable in cell cultures. These PB2-627 mutants showed various polymerase activities and replication kinetics in mammalian and avian cells as well as pathogenicity in mice. Serially passaging these mutants in MDCK cells generated some compensatory PB2 mutations that can restore polymerase activities of the PB2-627 mutants. Of these, PB2-D309N was identified as a novel one. Besides showing that influenza virus can tolerate a wide range of amino acid residues at the PB2-627 position, this study also demonstrates a potential strategy to identify novel mutations that can enhance viral polymerase.
    Virology. 09/2014; 468-470C:545-555.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Avian H7N9 influenza viruses may pose a further threat to humans by reassortment with human viruses, which could lead to generation of novel reassortants with enhanced polymerase activity. We previously established a novel statistical approach to study the polymerase activity of reassorted vRNPs (Influenza Other Respir Viruses. 2013;7:969-78). Here, we report the use of this method to study recombinant vRNPs with subunits derived from human H1N1, H3N2, and H7N9 viruses. Our results demonstrate that some reassortant vRNPs with subunits derived from the H7N9 and other human viruses can have much higher polymerase activities than the wild-type levels.
    Influenza and Other Respiratory Viruses 07/2014; · 1.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A prospective study of a dromedary camel herd during the 2013-14 calving season showed Middle East respiratory syndrome coronavirus infection of calves and adults. Virus was isolated from the nose and feces but more frequently from the nose. Preexisting neutralizing antibody did not appear to protect against infection.
    Emerging infectious diseases. 07/2014; 20(7).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We identified the near-full-genome sequence (29,908 nt, >99%) of Middle East respiratory syndrome coronavirus (MERS-CoV) from a nasal swab specimen from a dromedary camel in Egypt. We found that viruses genetically very similar to human MERS-CoV are infecting dromedaries beyond the Arabian Peninsula, where human MERS-CoV infections have not yet been detected.
    Emerging infectious diseases. 06/2014; 20(6):1049-53.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Human disease caused by highly pathogenic avian influenza A (HPAI) (H5N1) is associated with fulminant viral pneumonia and mortality rates in excess of 60%. Acute respiratory syndrome (ARDS) has been found to be the most severe form of acute lung injury caused by H5N1 virus infection while cytokine dysregulation and viral replication are thought to contribute to its pathogenesis. In this study, the anti-viral and anti-inflammatory effects of two indirubin derivatives: indirubin-3'-oxime (IM) and E804 on primary human peripherial blood-derived macrophages and type-I like pneumocytes (human alveolar epithelial cells) during influenza A (H5N1) virus infection were investigated. We found that both of the indirubin derivatives strongly suppress the pro-inflammatory cytokines including IP-10 (CXCL10), one of the key factors which contribute to the lung inflammation during H5N1 virus infection. In addition, we also demonstrated that the indirubin derivative delays the virus replication in the primary cell culture models. Our results showed that indirubin derivatives have a potential to be used as an adjunct to antiviral therapy for the treatment of severe human H5N1 disease.
    Antiviral research 04/2014; · 3.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Contemporary influenza B viruses are classified into two groups known as Yamagata and Victoria lineages. The co-circulation of two viral lineages in recent years urges for a robust and simple diagnostic test for detecting influenza B viruses and for lineage differentiation. In this study, a SYBR green-based asymmetric PCR assay has been developed for influenza B virus detection. Apart from identifying influenza B virus, the assay contains sequence-specific probes for lineage differentiation. This allows identifying influenza B virus and detecting influenza B viral lineage in a single reaction. The test has been evaluated by a panel of respiratory specimens. Of 108 influenza B virus-positive specimens, 105 (97%) were positive in this assay. None of the negative control respiratory specimens were positive in the test (N = 60). Viral lineages of all samples that are positive in the assay (N = 105) can also be classified correctly. These results suggest that this assay has a potential for routine influenza B virus surveillance. J. Med. Virol. © 2014 Wiley Periodicals, Inc.
    Journal of Medical Virology 04/2014; · 2.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Current influenza vaccines are ineffective against novel viruses and the source or the strain of the next outbreak of influenza is unpredictable; therefore, establishing universal immunity by vaccination to limit the impact of influenza remains a high priority. To meet this challenge, a novel vaccine has been developed using the immunogenic live vaccinia virus as a vaccine vector, expressing multiple H5N1 viral proteins (HA, NA, M1, M2, and NP) together with IL-15 as a molecular adjuvant. Previously, this vaccine demonstrated robust sterile cross-clade protection in mice against H5 influenza viruses, and herein its use has been extended to mediate heterosubtypic immunity toward viruses from both group 1 and 2 HA lineages. The vaccine protected mice against lethal challenge by increasing survival and significantly reducing lung viral loads against the most recent human H7N9, seasonal H3N2, pandemic-2009 H1N1, and highly pathogenic H7N7 influenza A viruses. Influenza-specific antibodies elicited by the vaccine failed to neutralize heterologous viruses and were unable to confer protection by passive transfer. Importantly, heterologous influenza-specific CD4(+) and CD8(+) T-cell responses that were elicited by the vaccine were effectively recalled and amplified following viral challenge in the lungs and periphery. Selective depletion of T-cell subsets in the immunized mice revealed an important role for CD4(+) T cells in heterosubtypic protection, despite low sequence conservation among known MHC-II restricted epitopes across different influenza viruses. This study illustrates the potential utility of our multivalent Wyeth/IL-15/5Flu as a universal influenza vaccine with a correlate of protective immunity that is independent of neutralizing antibodies.
    Proceedings of the National Academy of Sciences 03/2014; · 9.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel avian-origin influenza A/H7N9 virus emerged in 2013 to cause more than 130 cases of zoonotic human disease with an overall case fatality of around 30% in cases detected. It has been shown that an amino acid change at the residue E627K of polymerase basic protein 2 (PB2) occurred frequently in the H7N9 isolates obtained from humans but not in viruses isolated from poultry. Although this mutation has been reported to confer increased mammalian pathogenicity in other avian influenza subtypes, it has not been experimentally investigated in the H7N9 virus. In this study, we determined the contribution of the PB2-E627K in H7N9 virus to the pathogenicity in mammalian hosts. In addition, the compensatory role of the other PB2 mutations at positions T271A, Q591K and D701N in H7N9 virus was investigated. We characterized the activity of polymerase complexes with these PB2 mutations and found that they enhance the polymerase activity in human 293T cells. The rescued mutants enhanced growth in mammalian cells in vitro. Mice infected with the H7N9 mutant containing avian signature PB2-627E showed marked decrease of disease severity (weight loss) and pathology compared to mice infected with the wild type strain (PB2-627K) or other PB2 mutants. Also, mutant with the PB2-627E showed lower virus replication and pro-inflammatory cytokine responses in the lungs of the virus-infected mice which may contribute to pathogenicity. Our results suggest that these amino acid substitutions contributes to mouse pathogenicity and mammalian adaptation.
    Journal of Virology 01/2014; · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is the etiological agent for the infectious disease, SARS, which first emerged 10 years ago. SARS-CoV is a zoonotic virus that has crossed the species barriers to infect humans. Bats, which harbour a diverse pool of SARS-like CoVs (SL-CoVs), are believed to be the natural reservoir. The SARS-CoV surface Spike (S) protein is a major antigenic determinant in eliciting neutralizing antibody production during SARS-CoV infection. In our previous work, we showed that a panel of murine monoclonal antibodies (mAbs) that target the S2 subunit of the S protein are capable of neutralizing SARS-CoV infection in vitro (Lip KM et al, J Virol. 2006 Jan; 80(2): 941-50). In this study, we report our findings on the characterization of one of these mAbs, known as 1A9, which binds to the S protein at a novel epitope within the S2 subunit at amino acids 1111-1130. MAb 1A9 is a broadly neutralizing mAb that prevents viral entry mediated by the S proteins of human and civet SARS-CoVs as well as bat SL-CoVs. By generating mutant SARS-CoV that escapes the neutralization by mAb 1A9, the residue D1128 in S was found to be crucial for its interaction with mAb 1A9. S protein containing the substitution of D1128 with alanine (D1128A) exhibited a significant decrease in binding capability to mAb 1A9 compared to wild-type S protein. By using a pseudotyped viral entry assay, it was shown that the D1128A substitution in the escape virus allows it to overcome the viral entry blockage by mAb 1A9. In addition, the D1128A mutation was found to exert no effects on the S protein cell surface expression and incorporation into virion particles, suggesting that the escape virus retains the same viral entry property as the wild-type virus.
    PLoS ONE 01/2014; 9(7):e102415. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic infection causing severe viral pneumonia, with index cases having resided in or recently travelled to the Arabian peninsula, and is a global concern for public health. Limited human-to-human transmission, leading to some case clusters, has been reported. MERS-CoV has been reported in dromedary camels but phenotypic characterisation of such viruses is limited. We aimed to compare MERS-CoV isolates from dromedaries in Saudi Arabia and Egypt with a prototype human MERS-CoV to assess virus replication competence and cell tropism in ex-vivo cultures of human bronchus and lung. Methods We characterised MERS-CoV viruses from dromedaries in Saudi Arabia and Egypt and compared them with a human MERS-CoV reference strain. We assessed viral replication kinetics and competence in Vero-E6 cells (rhesus monkey), tissue tropism in cultures of ex-vivo human bronchial and lung tissues, and cytokine and chemokine induction, gene expression, and quantification of viral RNA in Calu-3 cells (human respiratory tract). We used mock-infected tissue as negative controls for ex-vivo experiments and influenza A H5N1 as a positive control for cytokine and chemokine induction experiments in Calu-3 cells. Findings We isolated three dromedary strains, two from Saudi Arabia (Dromedary/Al-Hasa-KFU-HKU13/2013 [AH13] and Dromedary/Al-Hasa-KFU-HKU19D/2013 [AH19D]), and one from Egypt (Dromedary/Egypt-NRCE-HKU270/2013 [NRCE-HKU270]). The human and dromedary MERS-CoV strains had similar viral replication competence in Vero-E6 cells and respiratory tropism in ex-vivo cultures of the human respiratory tract, and had similar ability to evade interferon responses in the human-respiratory-tract-derived cell line Calu-3. Interpretation The similarity of virus tropism and replication competence of human and dromedary MERS-CoV from the Arabian peninsula, and genetically diverse dromedary viruses from Egypt, in ex-vivo cultures of the human respiratory tract suggests that dromedary viruses from Saudi Arabia and Egypt are probably infectious to human beings. Exposure to zoonotic MERS-CoV is probably occurring in a wider geographical region beyond the Arabian peninsula. Funding King Faisal University, Egyptian National Research Centre, Hong Kong Food and Health Bureau, National Institute of Allergy and Infectious Diseases, and European Community Seventh Framework Program.
    The Lancet Respiratory Medicine. 01/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Genetic diversity of influenza A viruses (IAV) acquired through the error-prone RNA-dependent RNA polymerase (RdRP) or through genetic reassortment enables perpetuation of IAV in humans through epidemics or pandemics. Here, to assess the biological significance of genetic diversity acquired through RdRP, we characterize an IAV fidelity variant derived from passaging a seasonal H3N2 virus in the presence of ribavirin, a purine analogue that increases guanosine-to-adenosine mutations. We demonstrate that a single PB1-V43I mutation increases selectivity to guanosine in A/Wuhan/359/95 (H3N2) and A/Vietnam/1203/04 (H5N1) viruses. The H5N1 PB1-V43I-recombinant virus replicates to comparable titres as the wild-type virus in vitro or in the mouse lungs. However, a decrease in viral population diversity at day 3 post inoculation is associated with a tenfold reduced lethality and neurotropism in mice. Applying a fidelity variant with reduced mutational frequency, we provide direct experimental evidence for the role of genetic diversity in IAV pathogenesis.
    Nature Communications 01/2014; 5:4794. · 10.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel H7N9 influenza A virus first detected in March 2013 has since caused more than 130 human infections in China, resulting in 40 deaths. Preliminary analyses suggest that the virus is a reassortant of H7, N9 and H9N2 avian influenza viruses, and carries some amino acids associated with mammalian receptor binding, raising concerns of a new pandemic. However, neither the source populations of the H7N9 outbreak lineage nor the conditions for its genesis are fully known. Using a combination of active surveillance, screening of virus archives, and evolutionary analyses, here we show that H7 viruses probably transferred from domestic duck to chicken populations in China on at least two independent occasions. We show that the H7 viruses subsequently reassorted with enzootic H9N2 viruses to generate the H7N9 outbreak lineage, and a related previously unrecognized H7N7 lineage. The H7N9 outbreak lineage has spread over a large geographic region and is prevalent in chickens at live poultry markets, which are thought to be the immediate source of human infections. Whether the H7N9 outbreak lineage has, or will, become enzootic in China and neighbouring regions requires further investigation. The discovery here of a related H7N7 influenza virus in chickens that has the ability to infect mammals experimentally, suggests that H7 viruses may pose threats beyond the current outbreak. The continuing prevalence of H7 viruses in poultry could lead to the generation of highly pathogenic variants and further sporadic human infections, with a continued risk of the virus acquiring human-to-human transmissibility.
    Nature 08/2013; · 38.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The emergence of the H7N9 influenza virus in humans in Eastern China has raised concerns that a new influenza pandemic could occur. Here, we used a ferret model to evaluate the infectivity and transmissibility of A/Shanghai/2/2013 (SH2), a human H7N9 virus isolate. This virus replicated in the upper and lower respiratory tracts of the ferrets and was shed at high titers for 6 to 7 days, with ferrets showing relatively mild clinical signs. SH2 was efficiently transmitted via direct contact, but less efficiently by airborne exposure. Pigs could be productively infected by SH2 and shed virus for 6 days but were unable to transmit the virus to other animals. Under appropriate conditions human-to-human transmission of the H7N9 virus may be possible.
    Science 05/2013; · 31.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: During the summer of 2012, in Jeddah, Saudi Arabia a hitherto unknown coronavirus was isolated from the sputum of a patient with acute pneumonia and renal failure (1, 2).…
    Journal of Virology 05/2013; · 5.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: A novel subtype of influenza A virus (H7N9) was recently identified in humans. The virus is a reassortant of avian viruses, but these human isolates contain mutations [hemagglutinin (HA) Q226L and PB2 E627K] that might make it easier for the virus to adapt to mammalian hosts. Molecular tests for rapid detection of this virus are urgently needed.METHODS: We developed a 1-step quantitative real-time reverse-transcription PCR assay to detect the novel human H7N9 virus. The primer set was specific to the hemagglutinin (HA) gene of the H7N9 viruses currently causing the outbreak in China and had mismatches to all previously known avian or mammalian H7 HA sequences. In addition, the assay was evaluated using influenza A viruses of various genetic backgrounds and other negative controls.RESULTS: The detection limit of the assay was approximately 0.04 TCID50 (median tissue culture infective dose) per reaction. The assay specificity was high and all negative control samples, including 8 H7 viruses not closely related to the human H7N9 virus, tested negative.CONCLUSIONS: The established assay allows rapid detection of the novel human H7N9 virus, thereby allowing better pandemic preparedness.
    Clinical Chemistry 05/2013; · 7.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVES: Reassortment of influenza A viruses can give rise to viral ribonucleoproteins (vRNPs) with elevated polymerase activity and the previous three pandemic influenza viruses contained reassorted vRNPs of different origins. These suggest that reassorted vRNP may be one of the factors leading to a pandemic virus. In this study, we reconstituted chimeric vRNPs with three different viral strains isolated from avian, human and swine hosts. We applied a statistical strategy to identify the effect that the origin of a single vRNP protein subunit or the interactions between these subunits on polymerase activity. DESIGN: Eighty one chimeric vRNPs were reconstituted in 293T cells at different temperatures. Polymerase activity was determined by luciferase reporter assay and the results were analysed by multiway anova and other statistical methods. RESULTS: It was found that PB2, PB1, NP, PB2-PB1 interaction, PB2-PA interaction and PB1-NP interaction had significant effect on polymerase activity at 37°C and several single subunits and interactions were identified to lead to elevation of polymerase activity. Furthermore, we studied 27 out of these 81 different chimieric vRNPs in different combinations via fractional factorial design approach. Our results suggested that the approach can identify the major single subunit or interaction factors that affect the polymerase activity without the need to experimentally reproduce all possible vRNP combinations. CONCLUSIONS: Statistical approach and fractional factorial design are useful to identify the major single subunit or interaction factors that can modulate viral polymerase activity.
    Influenza and Other Respiratory Viruses 05/2013; · 1.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Coronaviruses are found in a diverse array of bat and bird species, which are believed to act as natural hosts. Molecular clock dating analyses of coronaviruses suggest that the most recent common ancestor for these viruses existed around 10,000 years ago. This relatively young age is in sharp contrast with the ancient evolutionary history of their putative natural hosts, which began diversifying tens of millions of years ago. Here, we attempted to resolve this discrepancy by applying more realistic evolutionary models that have previously revealed the ancient evolutionary history of other RNA viruses. By explicitly modeling variation in the strength of natural selection over time, and thereby improving the modeling of substitution saturation, we found that the time of most recent common ancestor for all coronaviruses is likely far more ancient (millions of years old) than the previously inferred range.
    Journal of Virology 04/2013; · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Since April 2012, there have been thirteen laboratory-confirmed human cases of respiratory disease associated with a newly recognized human betacoronavirus lineage C (HCoV-EMC) virus, seven of them fatal. The transmissibility and pathogenesis of HCoV-EMC remains poorly understood and elucidating its cellular tropism in human respiratory tissues will provide mechanistic insights into the key cellular targets for virus propagation and spread.We utilized ex vivo organ cultures of human bronchus and lung to investigate the tissue tropism, virus replication kinetics following experimental infection with HCoV-EMC, compared with human coronavirus 229E (HCoV-229E) and SARS coronavirus (SARS-CoV). Innate immune responses elicited by HCoV-EMC were also investigated.HCoV-EMC productively replicated in human bronchial and lung ex vivo organ cultures. While SARS-CoV productively replicated in lung tissue, replication in human bronchial tissue was limited. Immunohistochemistry revealed that HCoV-EMC infected non-ciliated bronchial epithelium, bronchiolar epithelial cells, alveolar epithelial cells and endothelial cells. Transmission electron microscopy showed virions within the cytoplasm of bronchial epithelial cells and budding virions from alveolar epithelial cells (type II). In contrast, there was minimal HCoV-229E infection in these tissues.HCoV-EMC failed to elicit strong type I or III interferon or pro-inflammatory innate immune responses in ex vivo respiratory cultures. Treatment of human lung ex vivo organ cultures with type I interferons (IFN α and β) at 1 hour post-infection reduced the replication of HCoV-EMC suggesting a potential therapeutic use of IFNs for treatment of human infection.
    Journal of Virology 04/2013; · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To study influenza viruses in pigs in Sri Lanka, we examined samples from pigs at slaughterhouses. Influenza (H3N2) and A(H1N1)pdm09 viruses were prevalent during 2004-2005 and 2009-2012, respectively. Genetic and epidemiologic analyses of human and swine influenza viruses indicated 2 events of A(H1N1)pdm09 virus spillover from humans to pigs.
    Emerging Infectious Diseases 03/2013; 19(3):481-4. · 6.79 Impact Factor
  • Source
    Renee W Y Chan, Leo L M Poon
    [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT A novel betacoronavirus, human coronavirus (HCoV-EMC), has recently been detected in humans with severe respiratory disease. Further characterization of HCoV-EMC suggests that this virus is different from severe acute respiratory syndrome coronavirus (SARS-CoV) because it is able to replicate in multiple mammalian cell lines and it does not use angiotensin-converting enzyme 2 as a receptor to achieve infection. Additional research is urgently needed to better understand the pathogenicity and tissue tropism of this virus in humans. In their recent study published in mBio, Kindler et al. shed some light on these important topics (E. Kindler, H. R. Jónsdóttir, M. Muth, O. J. Hamming, R. Hartmann, R. Rodriguez, R. Geffers, R. A. Fouchier, C. Drosten, M. A. Müller, R. Dijkman, and V. Thiel, mBio 4[1]:e00611-12, 2013). These authors report the use of differentiated pseudostratified human primary airway epithelial cells, an in vitro model with high physiological relevance to the human airway epithelium, to characterize the cellular tropism of HCoV-EMC. More importantly, the authors demonstrate the potential use of type I and type III interferons (IFNs) to control viral infection.
    mBio 01/2013; 4(2). · 6.88 Impact Factor

Publication Stats

12k Citations
1,311.24 Total Impact Points

Institutions

  • 2004–2014
    • The University of Hong Kong
      • • Centre of Influenza Research
      • • Department of Microbiology
      Hong Kong, Hong Kong
  • 2013
    • University of California, San Diego
      • Department of Pathology
      San Diego, CA, United States
  • 2011
    • The Scripps Research Institute
      • Department of Cell and Molecular Biology
      La Jolla, CA, United States
    • Australian Animal Health Laboratory
      Geelong, Victoria, Australia
    • Guangxi Medical University
      Yung-ning, Guangxi Zhuangzu Zizhiqu, China
  • 2009–2010
    • Lands Department of The Government of the Hong Kong Special Administrative Region
      Hong Kong, Hong Kong
  • 2003–2010
    • Queen Mary Hospital
      Hong Kong, Hong Kong
    • St. Jude Children's Research Hospital
      • Department of Infectious Diseases
      Memphis, Tennessee, United States
  • 2008
    • MRC-Holland b.v.
      Amsterdamo, North Holland, Netherlands
  • 2007
    • East China Normal University
      • School of Life Sciences
      Shanghai, Shanghai Shi, China
  • 2003–2007
    • Shantou University
      • • International Institute of Infection and Immunity
      • • Department of Microbiology and Immunology
      Swatow, Guangdong, China
  • 2006
    • Crucell
      Leyden, South Holland, Netherlands
    • University of East Anglia
      • Centre for Ecology, Evolution and Conservation
      Norwich, ENG, United Kingdom
  • 2000–2003
    • The Chinese University of Hong Kong
      • • Prince of Wales Hospital
      • • Department of Obstetrics and Gynaecology
      Hong Kong, Hong Kong