Giuseppe Gerna

Diagnosis and Management of Human Cytomegalovirus Infection in the Mother, Fetus, and Newborn Infant

SUMMARY Human cytomegalovirus (HCMV) is the leading cause of congenital viral infection and mental retardation. HCMV infection, while causing asymptomatic infections in most immunocompetent subjects, can be transmitted during pregnancy from the mother with primary (and also recurrent) infection to the fetus. Hence, careful diagnosis of primary infection is required in the pregnant woman based on the most sensitive serologic assays (immunoglobulin M [IgM] and IgG avidity assays) and conventional virologic and molecular procedures for virus detection in blood. Maternal prognostic markers of fetal infection are still under investigation. If primary infection is diagnosed in a timely manner, prenatal diagnosis can be offered, including the search for virus and virus components in fetal blood and amniotic fluid, with fetal prognostic markers of HCMV disease still to be defined. However, the final step for definite diagnosis of congenital HCMV infection is detection of virus in the blood or urine in the first 1 to 2 weeks of life. To date, treatment of congenital infection with antiviral drugs is only palliative both prior to and after birth, whereas the only efficacious preventive measure seems to be the development of a safe and immunogenic vaccine, including recombinant, subunit, DNA, and peptide-based vaccines now under investigation. The following controversial issues are discussed in the light of the most recent advances in the field: the actual perception of the problem; universal serologic screening before pregnancy; the impact of correct counseling on decision making by the couple involved; the role of prenatal diagnosis in ascertaining transmission of virus to the fetus; the impact of preconceptional and periconceptional infections on the prevalence of congenital infection; and the prevalence of congenitally infected babies born to mothers who were immune prior to pregnancy compared to the number born to mothers undergoing primary infection during pregnancy.

Human Cytomegalovirus UL131-128 Genes Are Indispensable for Virus Growth in Endothelial Cells and Virus Transfer to Leukocytes

ABSTRACT Human cytomegalovirus (HCMV), a ubiquitous human pathogen, is the leading cause of birth defects and morbidity in immunocompromised patients and a potential trigger for vascular disease. HCMV replicates in vascular endothelial cells and drives leukocyte-mediated viral dissemination through close endothelium- leukocyte interaction. However, the genetic basis of HCMV growth in endothelial cells and transfer to leukocytes is unknown. We show here that the UL131-128 gene locus of HCMV is indispensable for both productive infection of endothelial cells and transmission to leukocytes. The experimental evidence for this is based on both the loss-of-function phenotype in knockout mutants and natural variants and the gain-of-function phenotype by trans-complementation with individual UL131, UL130, and UL128 genes. Our findings suggest that a common mechanism of virus transfer may be involved in both endothelial cell tropism and leukocyte transfer and shed light on a crucial step in the pathogenesis of HCMV infection.

Human Cytomegalovirus Replicates Abortively in Polymorphonuclear Leukocytes after Transfer from Infected Endothelial Cells via Transient Microfusion Events

ABSTRACT Using a recently developed model for in vitro generation of pp65-positive polymorphonuclear leukocytes (PMNLs), we demonstrated that PMNLs from immunocompetent subjects may harbor both infectious human cytomegalovirus (HCMV) and viral products (pp65, p72, DNA, and immediate-early [IE] and pp67 late mRNAs) as early as 60 min after coculture with human umbilical vein endothelial cells (HUVEC) or human embryonic lung fibroblasts (HELF) infected with a clinical HCMV isolate (VR6110) or other wild-type strains. The number of PMNLs positive for each viral parameter increased with coculture time. Using HELF infected with laboratory-adapted HCMV strains, only very small amounts of viral DNA and IE and late mRNAs were detected in PMNLs. A cellular mRNA, the vascular cell adhesion molecule-1 mRNA, which is abundantly present in both infected and uninfected HUVEC, was detected in much larger amounts in PMNLs cocultured with VR6110-infected cells than in controls. Coculture of PMNLs with VR6110-infected permissive cells in the presence or absence of RNA, protein, and viral DNA synthesis inhibitors showed that only IE genes were transcribed in PMNLs during coculture. Synthesis of IE transcripts in PMNLs was also supported by the finding that only the copy number of IE mRNA (and not the DNA or the pp67 mRNA) per infected PMNL increased markedly with time, and the pp67 to IE mRNA copy number ratio changed from greater than 10 in infected HUVEC to less than 1 in cocultured PMNLs. Fluorescent probe transfer experiments and electron microscopy studies indicated that transfer of infectious virus and viral products from infected cells to PMNLs is likely to be mediated by microfusion events induced by wild-type strains only. In addition, HCMV pp65 and p72 were both shown to localize in the nucleus of the same PMNLs by double immunostaining. Two different mechanisms may explain the virus presence in PMNLs: (i) one major mechanism consists of transitory microfusion events (induced by wild-type strains only) of HUVEC or HELF and PMNLs with transfer of viable virus and biologically active viral material to PMNLs; and (ii) one minor mechanism, i.e., endocytosis, occurs with both wild-type and laboratory strains and leads to the acquisition of very small amounts of viral nucleic acids. In conclusion, HCMV replicates abortively in PMNLs, and wild-type strains and their products (as well as cellular metabolites and fluorescent dyes) are transferred to PMNLs, thus providing evidence for a potential mechanism of HCMV dissemination in vivo.

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.

Circulating endothelial giant cells permissive for human cytomegalovirus (HCMV) are detected in disseminated HCMV infections with organ involvement.

Giant cells fully permissive for human cytomegalovirus (HCMV) were found to circulate, at a variable proportion, in peripheral blood of 21 out of 25 immunocompromised patients with disseminated HCMV infection. Circulating endothelial giant cells (EGC) were identified by a specific monoclonal antibody of endothelial origin and shown to express immediate-early, early, and late viral proteins. Immunostaining patterns of different viral proteins were comparable to those detected in vitro in cultured human umbilical vein endothelial cells. EGC counts > 10 were associated with high levels (> 100) of HCMV viremia and antigenemia, as well as with an overt clinical syndrome in transplanted patients, and to an untreated long lasting organ localization in AIDS patients. On the other hand, EGC counts were < 10 during disseminated HCMV infections of both transplant recipients with no apparent organ syndrome and AIDS patients with recent organ involvement. In tissue sections from AIDS patients, infected endothelial cells were found to progressively enlarge till detaching from the small vessel wall and entering blood stream. HCMV-infected EGC represent a new systemic parameter suitable for the diagnosis of HCMV organ involvement and for the study of the pathogenesis of disseminated infections.

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.

Diagnostic and prognostic value of human cytomegalovirus load and IgM antibody in blood of congenitally infected newborns

BACKGROUND Diagnosis of congenital human cytomegalovirus (HCMV) infection relies on virus isolation from urine collected in the first 3 weeks of life. However, very little is known about the presence, levels and duration of HCMV pp65 antigenemia, viremia and DNAemia in congenitally infected newborns. OBJECTIVES To investigate the diagnostic and prognostic value of HCMV load determination in blood of newborns/infants with congenital HCMV infection. STUDY DESIGN HCMV pp65 antigenemia, viremia and DNAemia were investigated in 116 sequential peripheral blood leukocytes (PBL) samples from 41 newborns/infants with congenital HCMV infection and in 34 PBL samples from 34 uninfected newborn. Virus-specific IgM were determined in parallel on 145 sequential serum samples. RESULTS Compared to virus isolation from urine, sensitivities of DNAemia, antigenemia, viremia, and IgM determination were 100, 42.5, 28.2, and 70.7%, respectively. Specificity was 100% for all assays. Antigenemia, viremia and DNAemia levels were significantly higher and persisted longer in newborns with symptomatic infection compared to subclinically infected babies, whereas no difference was observed for virus-specific IgM antibody between the two groups. CONCLUSIONS (i) determination of viral DNA in blood at birth appears to be a sensitive and specific marker for diagnosis of congenital HCMV infection; (ii) significantly higher levels of HCMV load were detected in infants with symptomatic HCMV infection; and (iii) virus clearance from blood occurs spontaneously both in symptomatic and subclinically infected infants. However, the process takes longer in infants presenting with symptoms at birth.

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

Diagnosis and Outcome of Preconceptional and Periconceptional Primary Human Cytomegalovirus Infections

Primary human cytomegalovirus (HCMV) infection occurring in pregnant women within 3 months before (preconceptional) or within 4 weeks after (periconceptional) the last menstrual period represents an as-yet-undefined risk to the fetus. One (9.1%) of 11 newborns born to 12 women with preconceptional infection was subclinically infected (1 aborted fetus was not examined for infection). Of 20 pregnancies in women with periconceptional infection, 7 were terminated before 12 weeks of gestation (aborted fetus was not examined), 1 was terminated at 23 weeks after prenatal diagnosis of congenital infection, and 12 continued to term. Of those 12, 3 resulted in newborns who were congenitally infected. Thus, in the periconceptional group, intrauterine transmission occurred in 4 (30.8%) of 13 pregnancies for which the virologic outcome was known. One newborn was symptomatic at birth, and disseminated HCMV infection was diagnosed in an aborted fetus. Periconceptional primary HCMV infection seems to bear a higher risk of unfavorable outcome than preconceptional infection, and counseling should be adjusted accordingly.

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.