M. Grazia Revello

Human cytomegalovirus serum neutralizing antibodies block virus infection of endothelial/epithelial cells, but not fibroblasts, early during primary infection

A panel of human sera exhibited a >or=128-fold higher neutralizing potency against a human cytomegalovirus (HCMV) clinical isolate propagated and tested in endothelial (or epithelial) cells than against the same virus infecting human fibroblasts. In a group of 18 primary infections, the reverse geometric mean titre was in the range of 10-15 in human fibroblasts within the first 3 months after the onset of infection, whereas the endothelial cell infection-neutralizing activity was already present within the first 10 days, reaching median levels of 122, 320 and 545 at respectively 30, 60 and 90 days after onset, then declining slowly. This difference was also confirmed in the majority of reactivated and remote HCMV infections, as well as in a hyperimmune globulin preparation. The antibody response to HCMV pUL131A, pUL130 and pUL128 locus products, which are required for endothelial/epithelial cell infection, provided a potential molecular basis for such a differential neutralizing activity. In addition, monoclonal/monospecific antibodies raised against the pUL131A, pUL130 and pUL128 proteins were found to display an inhibitory activity on HCMV plaque formation and HCMV leukocyte transfer from HCMV-infected cells. Hence, conventional determination of the neutralizing activity of human sera in fibroblasts is misleading. Antibodies to pUL131A, pUL130 and pUL128 appear to display a major HCMV-neutralizing and dissemination-inhibiting activity.

The Human Cytomegalovirus Ribonucleotide Reductase Homolog UL45 Is Dispensable for Growth in Endothelial Cells, as Determined by a BAC-Cloned Clinical Isolate of Human Cytomegalovirus with Preserved Wild-Type Characteristics

ABSTRACT An endothelial cell-tropic and leukotropic human cytomegalovirus (HCMV) clinical isolate was cloned as a fusion-inducing factor X-bacterial artificial chromosome in Escherichia coli, and the ribonucleotide reductase homolog UL45 was deleted. Reconstituted virus RVFIX and RVΔUL45 grew equally well in human fibroblasts and human endothelial cells. Thus, UL45 is dispensable for growth of HCMV in both cell types.

Human cytomegalovirus tropism for endothelial/epithelial cells: Scientific background and clinical implications

Human cytomegalovirus (HCMV) has been routinely isolated from and propagated in vitro in human embryonic lung fibroblast (HELF) cell cultures, while in vivo it is known to infect predominantly endothelial and epithelial cells. In recent years, genetic determinants of the HCMV tropism for endothelial/epithelial cells were identified in the UL131A/UL130/UL128 locus of HCMV genome of wild‐type strains. UL131A‐UL128 gene products form a complex with glycoprotein H (gH) and L (gL) resulting in a gH/gL/UL131A‐UL128 complex that is required for HCMV entry into endothelial/epithelial cells. In contrast, virus entry into fibroblasts has its genetic determinants in the complex gH/gL/gO (or gH/gL). During primary HCMV infection, the neutralising antibody response measured in endothelial cells (EC) is potent, occurs very early and is directed mostly against combinations of two or three gene products of the UL131A‐128 locus. On the contrary, neutralising antibodies measured in fibroblasts appear late, are relatively weak in potency and are directed against gH and gB. The T‐cell immune response to UL131A‐UL128 gene products remains to be investigated. Recently, a role has been proposed for neutralising antibody in conferring prevention/protection against HCMV infection/disease in pregnant women with primary HCMV infection. However, the level of cooperation between humoral immunity and the well‐established T‐cell protection remains to be defined. Copyright

In vitro selection of human cytomegalovirus variants unable to transfer virus and virus products from infected cells to polymorphonuclear leukocytes and to grow in endothelial cells

Four human cytomegalovirus (HCMV) isolates from different clinical sources were extensively propagated in human embryonic lung fibroblasts (HELF). Plaque isolates from each of the four virus strains were evaluated for their ability to be transferred to polymorphonuclear leukocytes (PMNL) and to grow in endothelial cells (EC). While all four of the clinical strains were found to be both PMNL- and EC-tropic, variants were identified from each of the four strains that lacked both biological properties, while three of the four parental strains lost their transfer capacity before passage 50 in HELF. It was demonstrated that one of the four field isolates (VR6110) and its transfer-deficient variant were genetically related, but showed different curves of virus yield in HELF. In addition, neither the immediate-early (IE) mRNA nor the IE protein p72 were found to be transferred to PMNL before 72 h post-infection (late in infection) or in the presence of viral DNA replication inhibitors. These findings link EC and PMNL tropism and suggest that PMNL tropism is a late HCMV function.

Impact of human metapneumovirus and human cytomegalovirus versus other respiratory viruses on the lower respiratory tract infections of lung transplant recipients

Viral respiratory tract infections in lung transplant recipients may be severe. During three consecutive winter‐spring seasons, 49 symptomatic lung transplant recipients with suspected respiratory viral infection, and 26 asymptomatic patients were investigated for presence of respiratory viruses either in 56 nasopharyngeal aspirate or 72 bronchoalveolar lavage samples taken at different times after transplantation. On the whole, 1 asymptomatic (3.4%) and 28 symptomatic (57.1%) patients were positive for human metapneumovirus (hMPV, 4 patients), influenza virus A (3 patients), and B (2 patients), respiratory syncytial virus (2 patients), human coronavirus (2 patients), human parainfluenza virus (2 patients), rhinovirus (5 patients), while 4 patients were coinfected by 2 respiratory viruses, and 5 were infected sequentially by 2 or more respiratory viruses. In bronchoalveolar lavage samples, hMPV predominated by far over the other viruses, being responsible for 60% of positive specimens, whereas other viruses were present in nasopharyngeal aspirates at a comparable rate. RT‐PCR (detecting 43 positive samples/128 examined) was largely superior to monoclonal antibodies (detecting 17 positive samples only). In addition, HCMV was detected in association with a respiratory virus in 4/18 HCMV‐positive patients, and was found at a high concentration (>105 DNA copies/ml) in 3/16 (18.7%) patients with HCMV‐positive bronchoalveolar lavage samples and pneumonia. Coinfections and sequential infections by HCMV and respiratory viruses were significantly more frequent in patients with acute rejection and steroid treatment. In conclusion: (i) about 50% of respiratory tract infections of lung transplant recipients were associated with one or more respiratory viruses; (ii) hMPV largely predominates in bronchoalveolar lavage of symptomatic lung transplant recipients, thus suggesting a causative role in lower respiratory tract infections; (iii) RT‐PCR appears to be the method of choice for detection of respiratory viruses in lung transplant recipients, (iv) a high HCMV load in bronchoalveolar lavage is a risk factor for viral pneumonia, suggesting some measure of intervention for the control of viral infection. J. Med. Virol. 78:408–416, 2006.

Nuclear expression of the lower matrix protein of human cytomegalovirus in peripheral blood leukocytes of immunocompromised viraemic patients

Peripheral blood leukocytes (PBL), namely polymorphonuclear leukocytes (PMNL), are the major carrier of human cytomegalovirus (HCMV) in the blood of immunocompromised patients with HCMV viraemia. By using monoclonal antibodies (MAbs) directed against different early and late viral proteins, we showed that the protein accumulating in PBL, originally reported to be an immediate early (IE) gene product, is the 65K lower matrix early structural protein (ep65). This protein is detectable by immunofluorescence before IE proteins during early stages of the replication cycle of HCMV in permissive human embryonic lung fibroblast cells. However, the appearance of ep65 in the nucleus within 1 h post-infection in the presence of cycloheximide indicates that it represents uptake from the virus inoculum rather than newly synthetized protein. The ep65 MAbs staining PBL did not react with Vero cells infected with a recombinant vaccinia virus encoding the major IE gene (IE1) product, whereas MAbs reactive with the 72K major IE protein stained only faintly a small number of infected PBL. A group of four ep65 MAbs was tested in competitive binding assays to show that ep65 possesses at least three distinct epitopes. These were recognized by all four MAbs in AD169-infected Vero cell cultures when fixed with formaldehyde, whereas only one MAb recognizing a distinct epitope was reactive with methanol-acetone (MA)-fixed AD169-infected Vero cells. In formalin-fixed PBL the number of infected cells stained by the four ep65 MAbs was about twofold that found using MA-fixed cells. Using fluorescence-activated cell sorter-purified leukocyte subpopulations from viraemic patients with different levels of viraemia, the ratio of ep65-positive to ep65-negative cells was found to be 1:100 to 1:100,000 for PMNL, and only 1:10,000 to 1:100,000 for mononuclear cells.

Monoclonal antibodies versus reverse transcription-PCR for detection of respiratory viruses in a patient population with respiratory tract infections admitted to hospital

In the winter season 2001–2002, 239 nasopharyngeal aspirate and 15 bronchoalveolar lavage samples from 208 patients (135 pediatric and 73 adults, including 19 lung transplant recipients) admitted to hospital because of an acute respiratory tract infection were examined for rapid diagnosis of respiratory viruses by two diagnostic approaches: immunological, using specific monoclonal antibodies (MAb); and molecular, using specific reverse transcription (RT)‐PCR assays. Both methods detected influenza viruses A (H1N1 and H3N2) and B, human parainfluenza virus types 1 to 3, human respiratory syncytial virus (hRSV) types A and B, and human adenoviruses. In addition, human coronavirus (hCoV) groups I (229E‐like) and II (OC43‐like), as well as the new human metapneumovirus (hMPV), types A and B, were searched for by RT‐PCR alone. When results obtained by both methods were added, the overall percentage of patients positive for at least one respiratory virus peaked at 44.2%, involving 92/208 patients (81 pediatric, and 11 adults), while 116 patients (55.8%) were negative for any respiratory virus tested. The most common circulating virus was hRSV, infecting 54 (25.9%) patients (24 type A, and 30 type B strains), followed by hMPV, infecting 12 (5.8%) patients (7 type A and 5 type B strains). Coinfections by two respiratory viruses interested 11 (5.3%) patients, and 9 (81.8%) of these were infected by hRSV in association with another respiratory virus. In the great majority of infected children, hRSV and hMPV were associated with lower respiratory tract infections. In lung transplant recipients, viruses present in bronchoalveolar lavage appeared to be associated frequently with lower respiratory tract infections. In conclusion: the combination of immunological and molecular assays is the most sensitive approach to the diagnosis of respiratory viral infections; and infections caused by the less investigated hCoVs and hMPVs represent a fair proportion of respiratory infections. J. Med. Virol. 75:336–347, 2005.

Rapid Detection of Human Metapneumovirus Strains in Nasopharyngeal Aspirates and Shell Vial Cultures by Monoclonal Antibodies

ABSTRACT Monoclonal antibodies to human metapneumovirus (hMPV) were developed for direct fluorescent antibody (DFA) staining of nasopharyngeal aspirates from 40 infants with respiratory infections, as well as for hMPV identification in shell vial cultures. With reference to reverse transcription-PCR, DFA staining showed sensitivity, specificity, and positive and negative predictive values of 73.9%, 94.1%, 94.4%, and 72.7%, respectively. Monoclonal antibodies are useful for direct hMPV detection.

Detection and pathogenicity of human metapneumovirus respiratory infection in pediatric Italian patients during a winter–spring season

Abstract Background Some diagnostic, epidemiological and clinical features of the recently discovered human metapneumovirus remain to be investigated. Objectives To study the best approach for the diagnosis of human metapneumovirus infections by both conventional and molecular methods, along with the human metapneumovirus circulation rate in northern Italy and the severity of human metapneumovirus respiratory infections in a pediatric patient population. Study design Nasopharyngeal aspirates (NPA) were taken from 306 pediatric patients during the winter–spring season 2003–2004, and examined for conventional respiratory viruses by direct fluorescent staining and cell culture, while human coronavirus and human metapneumovirus were sought by RT-PCR. Results RT-PCR detected human metapneumovirus in 40/306 (13.1%) children positive for respiratory viruses, with an incidence intermediate between that of respiratory syncytial virus (58 patients, 18.9%) and that of influenzavirus infections (29 patients, 9.5%). Phylogenetic analysis showed cocirculation of both human metapneumovirus types (A and B) as well as their relevant subtypes (A1–A2 and B1–B2). Clinically, human metapneumovirus was found to be second to human respiratory syncytial virus alone, as a cause of respiratory tract infections, while duration of virus excretion appeared to correlate with severity of infection, and virus load in NPA with the stage of respiratory infection. Conclusion (i) Human metapneumovirus is a major viral pathogen in the Italian pediatric patient population; (ii) the severity of lower respiratory tract infections approaches that of human respiratory syncytial virus; (iii) there are preliminary indications that the duration of virus excretion may reach 2–3 weeks and that the level of viral load in NPA correlates with the clinical stage of human metapneumovirus infection.

Serum antibody response to the gH/gL/pUL128-131 five-protein complex of human cytomegalovirus (HCMV) in primary and reactivated HCMV infections

BACKGROUND Recently, a new human cytomegalovirus (HCMV) glycoprotein complex has been identified and potentially proposed as a vaccine. OBJECTIVE The aim of this study was to determine whether the HCMV gH/gL/pUL128-pUL130-pUL131 (gH/gL/pUL128-131) 5-protein (pentameric) complex (which has been recently found to be indispensable for the infection of endothelial and epithelial cells) is able to elicit a consistent antibody response in both primary and reactivated HCMV infections. STUDY DESIGN The antibody response was determined by both indirect immunofluorescence (IFA) and ELISA, using fixed (IFA) or lysed (ELISA) epithelial (ARPE-19) cells infected with one or more adenoviral vectors, each carrying one HCMV gene and, in parallel, with a control adenovirus vector. RESULTS The specificity of results was determined by the reactivity of human neutralizing mAbs recognizing two, three, or four proteins of the complex. In 14 cases of primary infection, an IgG antibody seroconversion to the UL128-131 gene products was consistently detected within 2-4 weeks after onset of infection, while antibodies persisted for at least 12 months. The IgG antibody response to UL128-131 gene products was generally superior to the response to gH and appeared to follow the neutralizing antibody response (as determined in epithelial cells). In reactivated infections, the antibody response showed a trend reminiscent of a booster response. IgG antibodies were detected in HCMV-seropositive healthy adult controls, but not in HCMV-seronegative individuals. CONCLUSIONS The IgG antibody response to the pentameric complex could be a major target for the evaluation of the antibody response to a pentamer-based vaccine.