Relationship of human cytomegalovirus-infected endothelial cells and circulating leukocytes in the pathogenesis of disseminated human cytomegalovirus infection: A narrative review.

Among the leucocyte subpopulations circulating in peripheral blood of immune-compromised patients with disseminated Human cytomegalovirus (HCMV) infection, polymorphonuclear leuckocytes (PMNL) and M/M may carry infectious virus. While only in PMNL early HCMV replicative events do occur, monocytes are susceptible to complete virus replication when they enter human organs, where as macrophages become a site of active complete virus replication. In vivo leucocytes and endothelial cells interact continuously, as suggested by several in vitro experimental findings showing the bidirectional HCMV transmission from leucocytes to and from endothelial cells with the critical aid of adhesion molecules. Recently, the neutralising antibody response in sera from subjects with primary HCMV infection was reported to be much higher and earlier than in human embryonic lung fibroblasts (HELF) cells when measured in endothelial cells and epithelial cells, where virus entry is mediated mostly by the pentamer complex gH/gL/pUL128/pUL130/pUL131, whereas it was much lower and delayed when determined in HELF, where virus entry is mediated mostly by the trimer complex gH/gL/gO. Thus, these results suggested that products of UL128L were the molecules primary responsible for the differential neutralising antibody response. This conclusion was confirmed by a series of polyclonal and monoclonal antibodies directed to the components of pUL128L. Very recently, based on two sets of experiments including inhibition and immunoblotting assays, the pentamer complex/trimer complex ratio has been finally identified as the main factor of the neutralising antibody response. This ratio may change with the virus suspension producer and target cell system as well as number of cell culture passages.

Fibroblast, Epithelial and Endothelial Cell-Derived Human Cytomegalovirus Strains Display Distinct Neutralizing Antibody Responses and Varying Levels of gH/gL Complexes.

In sequential sera from pregnant women with HCMV primary infection (PI), the serum neutralizing activity is higher against virions produced in epithelial and endothelial cells than in fibroblasts. Immunoblotting shows that the pentamer complex/trimer complex (PC/TC) ratio varies according to the producer cell culture type used for the virus preparation to be employed in the neutralizing antibody (NAb) assay, and is lower in fibroblasts and higher in epithelial, and especially endothelial cells. The blocking activity of TC- and PC-specific inhibitors varies according to the PC/TC ratio of virus preparations. The rapid reversion of the virus phenotype following its back passage to the original cell culture (fibroblasts) potentially argues in favor of a producer cell effect on virus phenotype. However, the role of genetic factors cannot be overlooked. In addition to the producer cell type, the PC/TC ratio may differ in single HCMV strains. In conclusion, the NAb activity not only varies with different HCMV strains, but is a dynamic parameter changing according to virus strain, type of target and producer cells, and number of cell culture passages. These findings may have some important implications for the development of both therapeutic antibodies and subunit vaccines.

Slow cytomegalovirus-specific CD4+ and CD8+ T-cell differentiation: 10-year follow-up of primary infection in a small number of immunocompetent hosts.

Differentiation of human cytomegalovirus specific T cells is a slow process requiring years. In the acute phase, EM predominate; subsequently, no contraction occurs (memory inflation) and TEMRA increase, especially among CD8+ T cells, while few LTM T cells appear. After some years, LTM stabilizes and predominate among CD4+ .

Human Cytomegalovirus Genomes Sequenced Directly From Clinical Material: Variation, Multiple-Strain Infection, Recombination, and Gene Loss.

The genomic characteristics of human cytomegalovirus (HCMV) strains sequenced directly from clinical pathology samples were investigated, focusing on variation, multiple-strain infection, recombination, and gene loss. A total of 207 datasets generated in this and previous studies using target enrichment and high-throughput sequencing were analyzed, in the process enabling the determination of genome sequences for 91 strains. Key findings were that (i) it is important to monitor the quality of sequencing libraries in investigating variation; (ii) many recombinant strains have been transmitted during HCMV evolution, and some have apparently survived for thousands of years without further recombination; (iii) mutants with nonfunctional genes (pseudogenes) have been circulating and recombining for long periods and can cause congenital infection and resulting clinical sequelae; and (iv) intrahost variation in single-strain infections is much less than that in multiple-strain infections. Future population-based studies are likely to continue illuminating the evolution, epidemiology, and pathogenesis of HCMV.

Human cytomegalovirus (HCMV) infection/re-infection: development of a protective HCMV vaccine.

In recent years, one of the main objectives in the field of medical virology has been the development of a human cytomegalovirus (HCMV) vaccine that can prevent congenital HCMV infection in the offspring of pregnant women as well as systemic and end-organ disease in immunocompromised (AIDS and transplanted) patients. Major obstacles to the development of an efficacious HCMV vaccine are lack of protection provided by immune memory cells against HCMV re-activation (replication relapse of a latent strain following primary infection) and HCMV re-infection (infection of a seropositive individual by a new virus strain). Thus, while initial efforts were directed at the development of a vaccine for the prevention of primary infection, in the last decade the primary vaccine development endpoint was the prevention of primary HCMV infection, as well as HCMV re-activation and re-infection. Along this line of research, both HCMV live (including Towne, AD169 and its derivatives, Towne/Toledo chimeras, Viral-Vectored vaccines, and Virus Replicon Particles) and non-living vaccines (including the recombinant gB subunit, DNA- and RNA-based vaccines, Virus-like particles, Dense bodies, Peptide vaccines, and the Pentamer Complex) have been developed. To date, Phase I, II, and III clinical trials have been variably conducted in humans, and experimental inoculation in different animal models has been performed with different vaccine formulations. Notwithstanding the variable research conditions, clinical and experimental results achieved thus far predict that the ideal HCMV vaccine should be able to elicit both robust humoral (both neutralizing and binding) and HCMV-specific CD4+ and CD8+ T-cell responses. This vaccine should hypothetically contain: 1) gB, inducing both humoral and T-cell responses; 2) the pentameric complex (PC), inducing the most potent neutralizing antibody response; 3) pp65, inducing the most potent HCMV-specific T-cell response. Although the protective role of cell-mediated immunity has been repeatedly documented, while the protective effect of (mostly neutralizing) antibodies remains partly to be documented, a vaccine stimulating both arms of the immune response would likely confer the highest level of protection against HCMV infection/disease in both HCMV-seronegative and -seropositive individuals.

Human cytomegalovirus (HCMV)-specific T cell but not neutralizing or IgG binding antibody responses to glycoprotein complexes gB, gHgLgO, and pUL128L correlate with protection against high HCMV viral load reactivation in solid-organ transplant recipients.

Immune correlates of protection against human cytomegalovirus (HCMV) infection are still debated. This study aimed to investigate which arm of the immune response plays a major role in protection against HCMV infection in kidney transplant recipients (n = 40) and heart transplant recipients (n = 12). Overall, patients were divided into 2 groups: one including 37 patients with low viral load (LVL), and the other including 15 patients with high viral load (HVL). All LVL patients resolved the infection spontaneously, whereas HVL patients were all treated with one or more courses of antivirals. In HVL patients, viral DNAemia, which was more than 100 times higher than LVL, appeared and peaked at significantly earlier times, but disappeared much later than in LVL patients. During a 1-year follow-up, all LVL patients had levels of HCMV-specific CD4+ (and CD8+ ) T cells significantly higher than HVL patients. On the contrary, titers of neutralizing antibodies and enzyme-linked immunosorbent assay-IgG antibodies to gB, gHgLgO, and pentamer gHgLpUL128L were overlapping in the 2 patient groups. In conclusion, while a valid HCMV-specific T-cell response was detected in more than 90% of LVL patients, >90% of HVL patients lacked an adequate T-cell response. Antibody responses did not appear to be associated directly or indirectly with protection.

Maternal immune correlates of protection from human cytomegalovirus transmission to the fetus after primary infection in pregnancy.

Immune control of primary human cytomegalovirus (HCMV) infection appears to depend on the interaction of humoral and T-cell responses. In this review, we have separately explored the 2 arms of the immune response to primary HCMV infection in HCMV-seronegative pregnant women transmitting (T) or not transmitting (NT) the infection to the fetus, with the objective of correlating the immune risk factors associated with vertical HCMV transmission. As for the humoral response, the following findings were documented: (i) in competitive binding assays, antibody titers to different antigenic sites of the gH pentamer complex were significantly lower in T compared with NT women; (ii) in addition, the number of neutralization sites recognized by T was significantly lower compared with NT women; (iii) the plaque formation inhibition assay showed a faster kinetics and a higher titer in NT women. As for T-cell immunity, the delayed expression of 3 immunological parameters (lymphoproliferative response, CD45RA reexpression in both CD4+ and CD8+ HCMV-specific T cells, and interleukin-2 production by HCMV-specific CD4+ T cells) were significantly associated with vertical transmission. This overview provides important information at the population level, which may help to inform the evaluation of interventions such as vaccination or treatments designed to interrupt intrauterine transmission of HCMV during primary infection. However, although we are waiting for an HCMV vaccination to become available, we emphasize that none of these parameters can be prognostically used on an individual basis because of the great variation in values among women.

Comparison of the T-cell response to human cytomegalovirus (HCMV) as detected by cytokine flow cytometry and QuantiFERON-CMV assay in HCMV-seropositive kidney transplant recipients.

Human cytomegalovirus (HCMV)-specific T-cell response in kidney transplant recipients (KTR) helps to identify patients at risk for severe infection. To assess the T-cell response, this study compared our in-house developed reference test, based on T-cell (both CD4+ and CD8+) stimulation by autologous HCMV-infected dendritic cells (iDC) and subsequent detection by cytokine flow cytometry (CFC-iDC), with the Quanti-FERON-CMV (QF-CMV) assay. Fifty-three HCMV-seropositive KTR were enrolled. At the DNAemia peak, 33 (62%) had low viral load (LVL, <3x105 DNA copies/mL) self-resolving infection, 19 (36%) high viral load (HVL, >3x105 DNA copies/mL) infection treated with antivirals, and one LVL patient (2%) tissue-invasive disease alone. Both assays showed a delayed recovery of HCMV-specific T-cell immunity in HVL vs LVL patients. Immune reconstitution kinetics did not significantly differ between the two assays in HVL patients. QF-CMV and CFC-iDC showed comparable sensitivities, but QF-CMV had a lower (although not significantly) specificity. Indeed, 7/19 HVL patients (37%) were erroneously considered protected from severe infection by QF-CMV, whereas CFC-iDC misidentified only 3/19 (16%) patients as protected. Although our reference test takes longer to complete, it appears slightly better at predicting patients at risk for severe HCMV infection. Moreover, QF-CMV may provide false negative results with some HLA types.

The pentameric complex of human Cytomegalovirus: cell tropism, virus dissemination, immune response and vaccine development.

Between the 1980s and 1990s, three assays were developed for diagnosis of human cytomegalovirus (HCMV) infections: leuko (L)-antigenemia, l-viremia and l-DNAemia, detecting viral protein pp65, infectious virus and viral DNA, respectively, in circulating leukocytes Repeated initial attempts to reproduce the three assays in vitro using laboratory-adapted strains and infected cell cultures were consistently unsuccessful. Results were totally reversed when wild-type HCMV strains were used to infect either fibroblasts or endothelial cells. Careful analysis and sequencing of plaque-purified viruses from recent clinical isolates drew attention to the ULb' region of the HCMV genome. Using bacterial artificial chromosome technology, it was shown by both gain-of-function and loss-of-function experiments that UL131-128 genes are indispensable for virus growth in endothelial cells and virus transfer to leukocytes. In addition, a number of clinical isolates passaged in human fibroblasts had lost both properties (leuko-tropism and endothelial cell-tropism) when displaying a mutation in the UL131-128 locus (referred to as UL128L). In the following years, it was shown that pUL128L was complexed with gH and gL to form the pentameric complex (PC), which is required to infect endothelial, epithelial and myeloid cells. The immune response to PC was studied extensively, particularly its humoral component, showing that the great majority of the neutralizing antibody response is directed to PC. Although anti-HCMV antibodies may act with other mechanisms than mere neutralizing activity, these findings definitely favour their protective activity, thus paving the way to the development of a potentially protective HCMV vaccine.

A randomized trial of hyperimmune globulin to prevent congenital cytomegalovirus.

BACKGROUND: Congenital infection with human cytomegalovirus (CMV) is a major cause of morbidity and mortality. In an uncontrolled study published in 2005, administration of CMV-specific hyperimmune globulin to pregnant women with primary CMV infection significantly reduced the rate of intrauterine transmission, from 40% to 16%. METHODS: We evaluated the efficacy of hyperimmune globulin in a phase 2, randomized, placebo-controlled, double-blind study. A total of 124 pregnant women with primary CMV infection at 5 to 26 weeks of gestation were randomly assigned within 6 weeks after the presumed onset of infection to receive hyperimmune globulin or placebo every 4 weeks until 36 weeks of gestation or until detection of CMV in amniotic fluid. The primary end point was congenital infection diagnosed at birth or by means of amniocentesis. RESULTS: A total of 123 women could be evaluated in the efficacy analysis (1 woman in the placebo group withdrew). The rate of congenital infection was 30% (18 fetuses or infants of 61 women) in the hyperimmune globulin group and 44% (27 fetuses or infants of 62 women) in the placebo group (a difference of 14 percentage points; 95% confidence interval, -3 to 31; P=0.13). There was no significant difference between the two groups or, within each group, between the women who transmitted the virus and those who did not, with respect to levels of virus-specific antibodies, T-cell-mediated immune response, or viral DNA in the blood. The clinical outcome of congenital infection at birth was similar in the two groups. The number of obstetrical adverse events was higher in the hyperimmune globulin group than in the placebo group (13% vs. 2%). CONCLUSIONS: In this study involving 123 women who could be evaluated, treatment with hyperimmune globulin did not significantly modify the course of primary CMV infection during pregnancy. (Funded by Agenzia Italiana del Farmaco; CHIP ClinicalTrials.gov number, NCT00881517; EudraCT no. 2008-006560-11.).

Monoclonal Antibodies to Different Components of the Human Cytomegalovirus (HCMV) Pentamer gH/gL/pUL128L and Trimer gH/gL/gO as well as Antibodies Elicited during Primary HCMV Infection Prevent Epithelial Cell Syncytium Formation.

UNLABELLED: Human cytomegalovirus (HCMV) may cause disseminated/end-organ disease in congenitally infected newborns and immunosuppressed transplant recipients. Two glycoprotein complexes, gH/gL/gO and gH/gL/pUL128/pUL130/pUL131 (gH/gL/pUL128L; referred to as the pentamer), are required for HCMV entry into fibroblasts and endothelial/epithelial cells, respectively, in the presence of the viral fusion protein gB. In addition, gH/gL/gO was recently reported to also be required for infection of endothelial/epithelial cells. Virus entry into human fibroblasts involves fusion of the virus envelope with the plasma membrane, whereas entry into endothelial/epithelial cells involves macropinocytosis or endocytosis and low-pH-dependent fusion with endosomes. A large set of neutralizing monoclonal antibodies (MAbs), directed to gH, gB, and multiple components of the pentamer, was developed. In addition, novel anti-gO human monoclonal antibodies were recently isolated. It is known that epithelial cell infection with a wild HCMV strain at a high multiplicity of infection produces a large number of syncytia. Incubation of heavily HCMV VR1814-infected ARPE-19 epithelial cells with neutralizing MAbs to one, two, or three components of the pUL128L portion of the pentamer blocked syncytium formation at an antibody concentration of 10 µg/ml, whereas only a partial inhibitory effect was displayed for MAbs to gO, gH, or gB at the same concentration. A blocking effect was also exhibited by convalescent-phase sera from primary HCMV infections. These findings indicate that the pentamer is required for syncytium formation in epithelial cells. IMPORTANCE: Human cytomegalovirus (HCMV) mostly infects epithelial and endothelial cells in vivo Recently, the pentamer protein complex (gH/gL/pUL128L) was identified as being required for infection of these cells, in association with the other protein complex, gH/gL/gO. In primary infections, HCMV migrates to endothelial cells and then to leukocytes, which disseminate the infection throughout the body. The virus then spreads to organs and tissues, mostly infecting either single cells or multinucleated epithelial giant cells (syncytia), depending on the viral load. Potent neutralizing human MAbs directed to distinct binding sites of the pUL128L portion of the pentamer were shown in the past to block virus dissemination. In the present study, MAbs to pUL128L were shown to block syncytium formation with a higher potency than that of MAbs to gO, gH, or gB, thus suggesting their role in limiting virus dissemination. This finding provides additional information useful for the development of anti-HCMV therapeutic antibodies and subunit vaccines.

Antibody-driven design of a human cytomegalovirus gHgLpUL128L subunit vaccine that selectively elicits potent neutralizing antibodies.

The use of neutralizing antibodies to identify the most effective antigen has been proposed as a strategy to design vaccines capable of eliciting protective B-cell immunity. In this study, we analyzed the human antibody response to cytomegalovirus (human cytomegalovirus, HCMV) infection and found that antibodies to glycoprotein (g)B, a surface glycoprotein that has been developed as a HCMV vaccine, were primarily nonneutralizing. In contrast, most of the antibodies to the complex formed by gH, gL, protein (p)UL128, pUL130, and pUL131 (the gHgLpUL128L pentamer) neutralized HCMV infection with high potency. Based on this analysis, we developed a single polycistronic vector encoding the five pentamer genes separated by "self-cleaving" 2A peptides to generate a stably transfected CHO cell line constitutively secreting high levels of recombinant pentamer that displayed the functional antigenic sites targeted by human neutralizing antibodies. Immunization of mice with the pentamer formulated with different adjuvants elicited HCMV neutralizing antibody titers that persisted to high levels over time and that were a hundred- to thousand-fold higher than those found in individuals that recovered from primary HCMV infection. Sera from mice immunized with the pentamer vaccine neutralized infection of both epithelial cells and fibroblasts and prevented cell-to-cell spread and viral dissemination from endothelial cells to leukocytes. Neutralizing monoclonal antibodies from immunized mice showed the same potency as human antibodies and targeted the same as well as additional sites on the pentamer. These results illustrate with a relevant example a general and practical approach of analytic vaccinology for the development of subunit vaccines against complex pathogens.

Follicular helper T-cells and virus-specific antibody response in primary and reactivated human cytomegalovirus infections of the immunocompetent and immunocompromised transplant patients.

Analysis of human cytomegalovirus (HCMV) primary infection in immunocompetent (n=40) and immunocompromised transplant patients (n=20) revealed that the median peak antibody titre neutralizing infection of epithelial cells was 16-fold higher in immunocompromised patients. The mechanism of this finding was investigated by measuring: (i) HCMV DNAemia; (ii) HCMV neutralizing antibodies; (iii) ELISA IgG antibody titre to HCMV glycoprotein complexes gHgLpUL128L, gHgLgO and gB; and (iv) HCMV-specific (IFN-γ+) CD4+ and CD8+ T-cells. Circulating CXCR5+ CD4+ (memory T follicular helper - TFH-cells) were identified as activated TFH (ICOS+PD-1++CCR7lo) and quiescent cells. In the early stages of primary infection, activated TFH cells increased in number. Concomitantly, both neutralizing and IgG antibodies to HCMV glycoproteins reached a peak, followed by a plateau. A stop in antibody rise occurred upon appearance of HCMV-specific CD4+ T-cells, HCMV clearance and progressive reduction in activated TFH cells. The main differences between healthy and transplant patients were that the latter had a delayed DNA peak, a much higher DNA load and delayed activated TFH cells and antibody peaks. Similar events were observed in clinically severe HCMV reactivations of transplant patients. A preliminary analysis of the specificity of the activated TFH cell response to viral proteins showed a major response to the pentamer gHgLpUL128L and gB. In conclusion, in the absence of T-cell immunity, one of the first lines of defence, during primary infection, is conferred by antibodies produced through the interaction of TFH cells and B-cells of germinal centres, resulting in differentiation of B-cells into antibody producing plasma cells.

Comparative magnitude and kinetics of human cytomegalovirus-specific CD4⁺ and CD8⁺ T-cell responses in pregnant women with primary versus remote infection and in transmitting versus non-transmitting mothers: Its utility for dating primary infection in pregnancy.

To discriminate between primary (PI) and remote (RI) human cytomegalovirus (HCMV) infection, several immunological parameters were monitored for a 2-year period in 53 pregnant women with PI, and 33 pregnant women experiencing HCMV PI at least 5 years prior. Cytokine (IFN-γ and IL-2) production by and phenotype (effector/memory CD45RA(+)) of HCMV-specific CD4(+) and CD8(+) T-cells as well as the lymphoproliferative responses (LPR) were evaluated, with special reference to the comparison between a group of women transmitting (T) and a group of non-transmitting (NT) the infection to fetus. While HCMV-specific CD4(+) T-cells reached at 90 days post-infection (p.i.) values comparable to RI, CD8(+) T-cells reached at 60 days p.i. levels significantly higher and persisting throughout the entire follow-up. Instead, IL-2 production and lymphoproliferative responses were lower in PI than RI for the entire follow-up period. Effector memory CD45RA(+) CD4(+) and CD8(+) HCMV-specific T-cells increased until 90 days p.i., reaching and maintaining levels higher than RI. The comparison between T and NT women showed that, at 30 days p.i., in NT women there was a significantly higher IL-2 production by HCMV-specific CD4(+) T-cells, and at 60 days p.i. a significantly higher frequency of both specific CD4(+) and CD8(+) CD45RA(+) T-cells. HCMV T-cell response appears to correlate with virus transmission to fetus and some parameters (CD4(+) lymphoproliferation, and frequency of HCMV-specific CD8(+) IL2(+) T-cells) may help in dating PI during pregnancy.

Predictive value of human cytomegalovirus (HCMV) T-cell response in the control of HCMV infection by seropositive solid-organ transplant recipients according to different assays and stimuli.

Human cytomegalovirus (HCMV) is still the most common viral infection in solid-organ transplant recipients (SOTR). Our study aimed to identify the predictive values of the T-cell response able to protect from HCMV disease, according to different assays. Viral DNA was determined by real-time PCR. The T-cell immune response to HCMV infection was investigated in SOTR according to the following assays and stimuli: cytokine flow cytometry (CFC) after peripheral blood mononuclear cell (PBMC) stimulation with autologous HCMV-infected dendritic cells (iDC) vs three ELISPOT assays using PBMCs stimulated with: 1. HCMV-infected cell lysate (iCL); 2. a pool of 34 epitopic peptides (PP) from different HCMV proteins; 3. a commercial pp65 peptide pool (CPM). ELISPOT results were normalized to T-cell counts. Overall, 51 SOTR were enrolled: 29 (57%) had low viral load (LVL) self-resolving infections, 19 (37%) high viral load (HVL) infections treated with antiviral drugs, and 3 (6%) tissue-invasive disease (TID). At DNAemia peak, ROC analysis showed that CFC-iDC CD4+ and the ELISPOT-iCL assays yielded overlapping area under the curve (AUC) results. The time needed to reconstitute protective T-cell immunity in SOTR with HVL infections was significantly longer with each assay compared to LVL infections. Using the CFC-iDC assay as a reference test (requiring 7 days to complete), the 24h ELISPOT-iCL assay provides similar results in terms of protection prediction from HCMV infection.

Reconstitution of Human Cytomegalovirus-Specific CD4+ T Cells is Critical for Control of Virus Reactivation in Hematopoietic Stem Cell Transplant Recipients but Does Not Prevent Organ Infection.

The relative contribution of human cytomegalovirus (HMCV)-specific CD4(+) and CD8(+) T cells to the control of HCMV infection in hematopoietic stem cell transplant (HSCT) recipients is still controversial. HCMV reactivation and HCMV-specific CD4(+) and CD8(+) T cell reconstitution were monitored for 1 year in 63 HCMV-seropositive patients receiving HSCT. HCMV reactivation was detected in all but 2 patients. In 20 of 63 (31.7%) patients (group 1) HCMV infection resolved spontaneously, whereas 32 of 63 (50.8%) patients (group 2) controlled the infection after a single short-course of pre-emptive therapy and the remaining 9 (14.3%) patients (group 3) suffered from relapsing episodes of HCMV infection, requiring multiple courses of antiviral therapy. The kinetics and magnitude of HCMV-specific CD8(+) T cell reconstitution were comparable among the 3 groups, but HCMV-specific CD4(+) T cells were lower in number in patients requiring antiviral treatment. HCMV-seronegative donors, as well as unrelated donors (receiving antithymocyte globulin) and acute graft-versus-host disease (GVHD) were associated with both delayed HCMV-specific CD4(+) T cell reconstitution and severity of infection. Conversely, these risk factors had no impact on HCMV-specific CD8(+) T cells. Eight patients with previous GVHD suffered from HCMV gastrointestinal disease, although in the presence of HCMV-specific CD4(+) and CD8(+) systemic immunity and undetectable HCMV DNA in blood. Reconstitution of systemic HCMV-specific CD4(+) T cell immunity is required for control of HCMV reactivation in adult HSCT recipients, but it may not be sufficient to prevent late-onset organ localization in patients with GVHD. HCMV-specific CD8(+) T cells contribute to control of HCMV infection, but only after HCMV-specific CD4(+) T cell reconstitution.

Differential kinetics of human cytomegalovirus load and antibody responses in primary infection of the immunocompetent and immunocompromised host.

The comparative long-term kinetics of human cytomegalovirus (HCMV) load and HCMV-specific antibody responses in the immunocompetent and immunocompromised solid-organ transplanted host during primary HCMV infection was investigated. In total, 40 immunocompetent subjects and 17 transplanted patients were examined for viral load as well as for IgG antibody responses to HCMV glycoproteins gH/gL/pUL128L, gH/gL and gB, and neutralizing antibodies in ARPE-19 epithelial cells and human fibroblasts. In parallel, the CD4(+) and CD8(+) HCMV-specific T-cell responses were determined by cytokine flow cytometry. Transplanted patients reached significantly higher viral DNA peaks, which persisted longer than in immunocompetent subjects. The ELISA-IgG responses to the pentamer, gH/gL and gB were significantly higher in primary infections of the immunocompetent until six months after onset, with the two antibody levels then overlapping from six to 12 months. Antibody levels neutralizing infection of epithelial cells were significantly higher in transplanted patients after six months, persisting for up to a year after transplantation. This trend was not observed for antibodies neutralizing infection of human fibroblasts, which showed higher titres in the immunocompetent over the entire one-year follow-up. In conclusion, in immunocompromised patients the viral load peak was much higher, while the neutralizing antibody response exceeded that detected in the immunocompetent host starting six months after onset of follow-up, often concomitantly with a lack of specific CD4(+) T cells. In this setting, the elevated antibody response occurred in the presence of differentiated follicular helper T cells in the blood, which decreased in number as did antibody titres upon reappearance of HCMV-specific CD4(+) T cells.

Polyfunctional analysis of human cytomegalovirus (HCMV)-specific CD4(+) and CD8 (+) memory T-cells in HCMV-seropositive healthy subjects following different stimuli.

PURPOSE: Following primary human cytomegalovirus (HCMV) infection, both humoral and T-cell-mediated immune responses develop in immunocompetent subjects. However, while antibodies may be measured by different methodologies, the T-cell-mediated response remains to be analyzed in its polyfunctional aspects, in view of defining (following different stimuli) the optimal assay to monitor the HCMV-specific T-cell response in HCMV-seropositive subjects. METHODS: In a group of 30 HCMV-seropositive adults, T-cell response revealed by the HCMV-infected dendritic cell (iDC) stimulus was compared with those given by the HCMV-infected cell lysate (iCL), and by a 34-peptide pool (PP). RESULTS: All HCMV-seropositive subjects showed presence of both HCMV-specific CD4(+) and CD8(+) T-cells in peripheral blood following iDC stimulation. One subject did not respond to PP. As compared to iDC, the number of HCMV-specific stimulated T-cells/µl blood was slightly lower for iCL (P = 0.195) and significantly lower for PP (P = 0.001). Polyfunctional analysis of the T-cell response indicated that the lower number of CD4(+) T-cells stimulated by iCL was due to the bifunctional (IFN-γ(+) TNF-α(+)) and CD40L-negative T-cell reduction, while the reduction in specific PP-stimulated CD8(+) T-cells was attributable to the reduction in tri-(IFN-γ(+) TNF-α(+) IL2(+)), bi-(IFN-γ(+) TNF-α(+)) and mono-(IFN-γ(+)) functional T-cells. In addition, 15/30 (50 %) subjects showed a CD4(+) cross-response to PP, and 11/30 (37 %) a CD8(+) cross-response to iCL. CONCLUSIONS: HCMV-specific stimulus given by iDC is not significantly different from that of iCL on CD4(+) and is significantly superior to that of PP on CD8+ T-cells. However, iCL may contribute significantly to CD8(+), and PP to CD4(+) T-cell stimulation.

Slow increase in IgG avidity correlates with prevention of human cytomegalovirus transmission to the fetus.

Following primary human cytomegalovirus (HCMV) infection, virus-specific IgG antibody shift from low to high avidity with individual variations in the rate of avidity maturation. The kinetics of the avidity maturation of IgG specific for HCMV nuclear antigen in pregnant women with primary infection was investigated. Absorbance values used for avidity index calculation of 286 sequential sera collected from 69 pregnant women with primary HCMV infection were retrieved. Percent difference in absorbance values of IgG antibody bound to the solid phase after urea treatment (IgG avidity) between early (T1, 0-90, median 31 days) and late (T2, 91-180, median 136 days) serum samples was calculated for each woman. Three groups of women were identified: 24/69 (34.8%) women showed high (>100%) avidity increase between T1 and T2 (pattern H), 29/69 (42%) low (<50%) increase (pattern L), and 16/69 (23.2%) intermediate increase (pattern I). Avidity values in T1 samples were significantly higher in women with pattern L compared to women with pattern H (P=0.01). Altogether, 28/69 (40.6%) women transmitted HCMV infection to their fetuses. Fetal infection preferentially occurred (P<0.01) in women with pattern H (15/24, 62.5%) compared with women with pattern L (7/29, 24.1%). In conclusion, different patterns of IgG avidity maturation can be detected following primary HCMV infection. Pregnant women with pattern H (rapid IgG avidity increase) appear to be at higher risk for fetal infection, whereas, pregnant women developing early antibody with high avidity appear to be at a lower risk of vertical transmission.

Systemic and local human cytomegalovirus-specific T-cell response in lung transplant recipients.

It is debated whether human cytomegalovirus (HCMV) infection/disease of the pulmonary compartment in lung transplant recipients (LTRs) may be controlled by the HCMV-specific systemic T-cell response or requires a local (lung) T-cell response. Systemic and local HCMV loads were investigated in parallel by real-time PCR in 20 LTRs. T-cell responses were measured by intracellular cytokine staining of HCMV-specific IFN-? + CD4+ and CD8+ T-cells in PBMC, and by enzyme-linked immunospot (ELISpot) assay in lung (BAL) mononuclear cells. Patients were grouped at time of peak of infection based on viral load in blood and BAL. Immunological testing results showed that five patients with no HCMV infection (either local or systemic) had both local and systemic T-cell responses; four patients with systemic infection had no systemic T-cell response; five patients with both systemic and lung infection had neither local nor systemic T-cell responses; and six patients with lung infection had no local and a partial (only CD8+ in the absence of CD4+) systemic T-cell response. These results indicate that local immunity is associated with resolution of lung infection. Systemic T-cell response alone is not sufficient to provide lung protection from HCMV infection.