HCMV-seropositive Individuals Research Articles

Evaluation of the In Vitro Capacity of Anti-Human Cytomegalovirus Antibodies to Initiate Antibody-Dependent Cell Cytotoxicity

In the setting of infectious diseases, antibodies show different functions beyond neutralizing activity. In this study, we investigated the activation of NK cells in vitro in the presence of human cytomegalovirus (HCMV)-specific antibodies and their potential role in the control of HCMV infection through antibody-dependent cell cytotoxicity (ADCC). Retinal pigmented epithelial cells (ARPE-19) infected with the HCMV strain VR1814 were co-cultured with cytokine-activated peripheral blood mononuclear cells (PBMCs) in the presence of sera collected from 23 HCMV-seropositive and 9 HCMV-seronegative donors. Moreover, 13 pregnant women sampled 3 and 6 months after HCMV primary infection and 13 pregnant women with pre-conception immunity were tested and compared. We determined the percentage of activated NK cells via the analysis of CD107a expression as a marker of degranulation. Significantly higher levels of NK-cell activation were observed using 1/100 and 1/10 dilutions of sera from HCMV-seropositive individuals, and when cells were infected for 96 and 120 h, suggesting that NK cells are activated by antibodies directed against late antigens. In the absence of serum NK cells, activation was negligible. In seropositive subjects, the median percentages of CD107a-positive NK cells in the presence of autologous serum and pooled HCMV-positive serum were similar (14.03% [range 0.00–33.56] and 12.42% [range 1.01–46.00], respectively), while NK-cell activation was negligible using an HCMV-negative serum pool. In HCMV-seronegative subjects, the median percentage of activated NK cells was 0.90% [range 0.00–3.92] with autologous serum and 2.07% [0.00–5.76] in the presence of the HCMV-negative serum pool, while it was 8.97% [0.00–26.49] with the pool of HCMV-positive sera. NK-cell activation using hyperimmune globulin is comparable to what is obtained using autologous serum. Sera from subjects at 3 and 6 months post primary infection showed a lower capacity of NK-cell activation than sera from subjects with past infection (p < 0.001). NK activation against HCMV-infected epithelial cells is dependent on the presence of HCMV-specific antibodies. This serum activity increases with time after the onset of HCMV infection. The protective role of NK-cell activation by HCMV-specific serum antibodies should be verified in clinical settings.

Autologous T-Cell-Free Antigen Presentation System Unveils hCMV-Specific NK Cell Response.

NK cells play a decisive role in controlling hCMV infection by combining innate and adaptive-like immune reactions. The hCMV-derived VMAPRTLFL (LFL) peptide is a potent activator of NKG2C+ NK cells. Proposed here is an autologous system of LFL stimulation without T lymphocytes and exogenous cytokines that allows us to evaluate NK-cell hCMV-specific responses in more native settings. In this model, we evaluated LFL-induced IFNγ production, focusing on signaling pathways and the degranulation and proliferation of NK cells orchestrated by microenvironment cytokine production and analyzed the transcriptome of expanded NK cells. NK cells of individuals having high anti-hCMV-IgG levels, in contrast to NK cells of hCMV-seronegative and low-positive donors, displayed increased IFNγ production and degranulation and activation levels and enhanced proliferation upon LFL stimulation. Cytokine profiles of these LFL-stimulated cultures demonstrated a proinflammatory shift. LFL-induced NK-cell IFNγ production was dependent on the PI3K and Ras/Raf/Mek signaling pathways, independently of cytokines. In hCMV-seropositive individuals, this model allowed obtaining NK-cell antigen-specific populations proliferating in response to LFL. The transcriptomic profile of these expanded NK cells showed increased adaptive gene expression and metabolic activation. The results complement the existing knowledge about hCMV-specific NK-cell response. This model may be further exploited for the identification and characterization of antigen-specific NK cells.

Spanish HCMV Seroprevalence in the 21st Century.

Human cytomegalovirus (HCMV) is linked to age-related diseases like cardiovascular disease, neurodegenerative conditions, and cancer. It can also cause congenital defects and severe illness in immunocompromised individuals. Accurate HCMV seroprevalence assessment is essential for public health planning and identifying at-risk individuals. This is the first HCMV seroprevalence study conducted in the general Spanish adult population in 30 years. We studied HCMV seroprevalence and HCMV IgG antibody titres in healthy adult donors (HDs) and HCMV-related disease patients from 2010 to 2013 and 2020 to 2023, categorized by sex and age. We compared our data with 1993 and 1999 studies in Spain. The current HCMV seroprevalence among HDs in Spain is 73.48%. In women of childbearing age, HCMV seroprevalence has increased 1.4-fold in the last decade. HCMV-seropositive individuals comprise 89.83% of CVD patients, 69% of SMI patients, and 70.37% of COVID-19 patients. No differences in HCMV seroprevalence or HCMV IgG antibody titres were observed between patients and HDs. A significant reduction in Spanish HCMV seroprevalence among HDs was observed in 1993. However, women of childbearing age have shown an upturn in the last decade that may denote a health risk in newborns and a change in HCMV seroprevalence trends.

Non-classical HLA-E restricted CMV 15-mer peptides are recognized by adaptive NK cells and induce memory responses.

Human cytomegalovirus (HCMV) reactivation causes complications in immunocompromised patients after hematopoietic stem cell transplantation (HSCT), significantly increasing morbidity and mortality. Adaptive Natural Killer (aNK) cells undergo a persistent reconfiguration in response to HCMV reactivation; however, the exact role of aNK cell memory in HCMV surveillance remains elusive. We employed mass spectrometry and computational prediction approaches to identify HLA-E-restricted HCMV peptides that can elucidate aNK cell responses. We also used the K562 cell line transfected with HLA-E0*0103 for specific peptide binding and blocking assays. Subsequently, NK cells were cocultured with dendritic cells (DCs) loaded with each of the identified peptides to examine aNK and conventional (c)NK cell responses. Here, we discovered three unconventional HLA-E-restricted 15-mer peptides (SEVENVSVNVHNPTG, TSGSDSDEELVTTER, and DSDEELVTTERKTPR) derived from the HCMV pp65-protein that elicit aNK cell memory responses restricted to HCMV. aNK cells displayed memory responses towards HMCV-infected cells and HCMV-seropositive individuals when primed by DCs loaded with each of these peptides and predicted 9-mer versions. Blocking the interaction between HLA-E and the activation NKG2C receptor but not the inhibitory NKG2A receptor abolished these specific recall responses. Interestingly, compared to the HLA-E complex with the leader peptide VMAPRTLIL, HLA-E complexes formed with each of the three identified peptides significantly changed the surface electrostatic potential to highly negative. Furthermore, these peptides do not comprise the classical HLA-E-restriction motifs. These findings suggest a differential binding to NKG2C compared to HLA-E complexes with classical leader peptides that may result in the specific activation of aNK cells. We then designed six nonameric peptides based on the three discovered peptides that could elicit aNK cell memory responses to HCMV necessary for therapeutic inventions. The results provide novel insights into HLA-E-mediated signaling networks that mediate aNK cell recall responses and maximize their reactivity.

FcRγ- NK Cell Induction by Specific Cytomegalovirus and Expansion by Subclinical Viral Infections in Rhesus Macaques.

"Adaptive" NK cells, characterized by FcRγ deficiency and enhanced responsiveness to Ab-bound, virus-infected cells, have been found in certain hCMV-seropositive individuals. Because humans are exposed to numerous microbes and environmental agents, specific relationships between hCMV and FcRγ-deficient NK cells (also known as g-NK cells) have been challenging to define. Here, we show that a subgroup of rhesus CMV (RhCMV)-seropositive macaques possesses FcRγ-deficient NK cells that stably persist and display a phenotype resembling human FcRγ-deficient NK cells. Moreover, these macaque NK cells resembled human FcRγ-deficient NK cells with respect to functional characteristics, including enhanced responsiveness to RhCMV-infected target in an Ab-dependent manner and hyporesponsiveness to tumor and cytokine stimulation. These cells were not detected in specific pathogen-free (SPF) macaques free of RhCMV and six other viruses; however, experimental infection of SPF animals with RhCMV strain UCD59, but not RhCMV strain 68-1 or SIV, led to induction of FcRγ-deficient NK cells. In non-SPF macaques, coinfection by RhCMV with other common viruses was associated with higher frequencies of FcRγ-deficient NK cells. These results support a causal role for specific CMV strain(s) in the induction of FcRγ-deficient NK cells and suggest that coinfection by other viruses further expands this memory-like NK cell pool.

NK cells expansion <i>in vitro</i> is followed by loss of inhibitory KIR expression

NK cells are innate lymphocytes that are able to eliminate altered cells, which makes them promising for the immunotherapy of viral diseases and tumors. The NK cell population is characterized by high phenotypic and functional diversity. In particular, in the pool of highly differentiated NK cells in the presence of cytomegalovirus (HCMV), a population of adaptive cells can be formed, characterized by a high lifespan and high cytotoxicity. However, in order to carry out a cytotoxic reaction, a NK cell must undergo a licensing process, during which it acquires the expression of NKG2A and KIRs. Currently, there are many effective methods of NK cell accumulation for subsequent use in therapy, one of them is the stimulation with IL-2 and K562-mbIL21 feeder cells. Highly differentiated adaptive-like NK cells are able to expand in respond to such stimulation. However, the phenotype of actively expanding NK cells dynamically changes. Loss of inhibitory KIR expression during intense proliferation of NK cells may adversely affect their cytotoxic potential. This work shows that highly differentiated CD56dimNKG2C+ NK cells from HCMV-seropositive individuals have a high proportion of KIR2DL2/3+ cells. This may indicate a high stability of KIR receptor expression in this population. We have shown that CD56dimNKG2C+ clonal cultures obtained by stimulation with IL-2 and K562- mbIL21 are characterized by high stability of KIR2DL2/3 expression compared to NKG2C-negative and less differentiated CD56brightNKG2C+. Also, in heterogeneous cultures of adaptive NK cells precursors CD57- CD56dimNKG2C+, a higher expression level of KIR2DL2/3 was observed in comparison with NKG2C-negative cultures of CD57-CD56dimNKG2C-. Thus, the accumulation of NK cells upon stimulation with IL-2 and K562- mbIL2 feeder cells can lead to loss of expression of KIR receptors and a decrease in their functional activity. However, cultures of highly differentiated NK cells of HCMV-seropositive individuals CD56dimNKG2C+, as well as cultures of precursors of adaptive NK cells CD57-CD56dimNKG2C+, are characterized by a greater stability of KIR2DL2/3 expression. As a result, stimulation with IL-2 and K562-mbIL21 feeder cells can be used to accumulate adaptive-like cells and their progenitors with stable inhibitory KIR expression and high cytotoxic potential.

Human cytomegalovirus expands a CD8+ T cell population with loss of BCL11B expression and gain of NK cell identity.

CD8+ T cells not only are critical mediators of adaptive immunity but also may exhibit innate-like properties such as surface expression of NKG2C, an activating receptor typically associated with natural killer (NK) cells. We demonstrate that, similar to NK cells, NKG2C+TCRαβ+CD8+ T cells are associated with prior human cytomegalovirus (HCMV) exposure. In addition to expressing several NK cell markers such as CD56 and KIR, NKG2C+CD8+ T cells are oligoclonal and do not up-regulate PD-1 even in response to persistent activation. Furthermore, we found that NKG2C+CD8+ T cells from some individuals exhibited strong effector function against leukemia cells and HCMV-infected fibroblasts, which was dictated by both NKG2C and TCR specificity. Transcriptomic analysis revealed that the transcription factor BCL11B, a regulator of T cell developmental fate, is down-regulated in NKG2C+CD8+ T cells when compared with conventional NKG2C−CD8+ T cells. BCL11B deletion in conventional CD8+ T cells resulted in the emergence of a similar innate-like CD56+CD94+DAP12+NKG2C+CD45RA+CCR7−PD-1−/low T cell population with activity against HLA-E+ targets. On the basis of their intrinsic capacity to recognize diseased cells coupled with lack of PD-1 induction, NKG2C+CD8+ T cells represent a lymphocyte population that resides at the boundary between innate and adaptive immunity, presenting an attractive alternative for cellular therapy, including CAR T cell–based therapies.

Targeting the latent human cytomegalovirus reservoir for T-cell-mediated killing with virus-specific nanobodies

Latent human cytomegalovirus (HCMV) infection is characterized by limited gene expression, making latent HCMV infections refractory to current treatments targeting viral replication. However, reactivation of latent HCMV in immunosuppressed solid organ and stem cell transplant patients often results in morbidity. Here, we report the killing of latently infected cells via a virus-specific nanobody (VUN100bv) that partially inhibits signaling of the viral receptor US28. VUN100bv reactivates immediate early gene expression in latently infected cells without inducing virus production. This allows recognition and killing of latently infected monocytes by autologous cytotoxic T lymphocytes from HCMV-seropositive individuals, which could serve as a therapy to reduce the HCMV latent reservoir of transplant patients.

Cytomegalovirus and cancer-related mortality in the national health and nutritional examination survey.

Cytomegalovirus (HCMV) is a common viral infection that shapes lifelong immunity. A history of infection with HCMV has been associated with many chronic diseases, including cancer. In addition, prospective cohort studies have established that HCMV is associated with all-cause mortality. However, there are limited data regarding HCMV and cancer mortality. Data were obtained from the National Health and Nutrition Examination Survey (NHANES) III study (1988-1994): subjects aged 18 to 98, who had HCMV serology results, did not report having cancer at baseline, and were eligible for mortality follow-up (n = 14,498). Mortality was ascertained until December 2011 using National Death Index (NDI) linkage. The unadjusted risk of all-cancer mortality was higher in HCMV seropositive individuals (HR 2.74, 95% CI 2.05-3.64). This association was attenuated after adjusting for age (HR 1.39, 95% CI 1.02-1.92), and other covariates (age, sex, race/ethnicity, smoking status, BMI, education, and C-reactive protein (CRP); HR 1.21, 95% CI 0.91-1.81). There was a statistically significant interaction between HCMV and sex (p = 0.01): HCMV seropositivity was associated with increased cancer mortality in men (HR 1.65, 95% CI 0.99-2.73) but not in women (HR 0.95, 95% CI 0.59-1.54). Consistent with prior reports, HCMV seropositivity may be associated with an increased risk of cancer-related mortality but the association is partially driven by socioeconomic status and other risk factors. Future research is needed to determine whether HCMV is a risk factor for cancer, as well as identify the specific cancer types where HCMV increases mortality.

Novel Approach to Cell Surface Discrimination Between KIR2DL1 Subtypes and KIR2DS1 Identifies Hierarchies in NK Repertoire, Education, and Tolerance.

Cumulative activating and inhibitory receptor signaling controls the functional output of individual natural killer (NK) cells. Investigation of how competing signals impact response, however, has been hampered by the lack of available antibodies capable of distinguishing inhibitory and activating receptors with highly homologous ectodomains. Utilizing a novel combination of monoclonal antibodies with specificity for discrete inhibitory KIR2DL1 and activating KIR2DS1 allotypes found among 230 healthy donors, we investigated allele-specific receptor expression and function driven by KIR2DL1 and KIR2DS1 alleles. We found that co-expression of the HLA-C2 ligand diminishes KIR2DL1, but not KIR2DS1, cell surface staining, but does not impact the respective frequencies of KIR2DL1- and KIR2DS1-expressing cells within the NK repertoire. We can distinguish by flow cytometry NK cell populations expressing the most common KIR2DL1-C245 allotypes from those expressing the most common KIR2DL1-R245 allotypes, and we show that the informative differential binding anti-KIR2DL1/S1 clone 1127B is determined by amino acid residue T154. Although both KIR2DL1-C245 and KIR2DL1-R245 subtypes can be co-expressed in the same cell, NK cells preferentially express one or the other. Cells expressing KIR2DL1-C245 exhibited a lower KIR2DL1 cell surface density and lower missing-self reactivity in comparison to cells expressing KIR2DL1-R245. We found no difference, however, in sensitivity to inhibition or cell surface stability between the two KIR2DL1 isoforms, and both demonstrated similar expansion among NKG2C+ KIR2DL1+ NK cells in HCMV-seropositive healthy individuals. In addition to cell surface density of KIR2DL1, copy number of cognate HLA-C2 hierarchically impacted the effector capacity of both KIR2DL1+ cells and the tolerization of KIR2DS1+ NK cells. HLA-C2 tolerization of KIR2DS1+ NK cells could be overridden, however, by education via co-expressed self-specific inhibitory receptors, such as the heterodimer CD94/NKG2A. Our results demonstrate that effector function of NK cells expressing KIR2DL1 or KIR2DS1 is highly influenced by genetic variability and is calibrated by co-expression of additional NK receptors and cognate HLA-C2 ligands. These findings define the molecular conditions under which NK cells are activated or inhibited, potentially informing selection of donors for adoptive NK therapies.

Large-Scale Screening of HCMV-Seropositive Blood Donors Indicates that HCMV Effectively Escapes from Antibodies by Cell-Associated Spread.

Immunoglobulins are only moderately effective for the treatment of human cytomegalovirus (HCMV) infections, possibly due to ineffectiveness against cell-associated virus spread. To overcome this limitation, we aimed to identify individuals with exceptional antibodies in their plasma that can efficiently block the cell-associated spread of HCMV. A Gaussia luciferase-secreting mutant of the cell-associated HCMV strain Merlin was generated, and luciferase activity evaluated as a readout for the extent of cell-associated focal spread. This reporter virus-based assay was then applied to screen plasma samples from 8400 HCMV-seropositive individuals for their inhibitory effect, including direct-acting antiviral drugs as positive controls. None of the plasmas reduced virus spread to the level of these controls. Even the top-scoring samples that partially reduced luciferase activity in the screening assay failed to inhibit focal growth when reevaluated with a more accurate, immunofluorescence-based assay. Selected sera with high neutralizing capacity against free viruses were analyzed separately, and none of them prevented the focal spread of three recent clinical HCMV isolates nor reduced the number of particles transmitted, as demonstrated with a fluorescent Merlin mutant. We concluded that donors with cell-to-cell-spread-inhibiting plasma are nonexistent or extremely rare, emphasizing cell-associated spread as a highly efficient immune escape mechanism of HCMV.

NK cells generate memory-type responses to human cytomegalovirus-infected fibroblasts.

Natural killer (NK) cells are cytotoxic lymphocytes that selectively respond against abnormal cells. Human cytomegalovirus (HCMV) infection causes expansion of NKG2C+ CD57+ NK cells in vivo and NKG2C+ NK cells proliferate when cultured with HCMV-infected cells. This raises the possibility of an NK-cell subset selectively responding against a specific pathogen and accruing memory. To test this possibility, we compared proliferation, natural cytotoxicity and interferon-γ (IFN-γ) production of NK cells from HCMV-seropositive and HCMV-seronegative individuals co-cultured with HCMV-infected or uninfected MRC-5 cells. There was no significant difference in proliferation of NK cells from HCMV-seropositive or seronegative individuals against uninfected MRC-5 cells, but significantly more NK cells from the HCMV-seropositive group proliferated in response to HCMV-infected MRC-5 cells. Natural cytotoxicity of NK cells against K562 cells increased following co-culture with HCMV-infected versus uninfected MRC-5 only for the HCMV-seropositive group. After co-culture with HCMV-infected MRC-5 cells, proliferating NK cells from HCMV-seropositive donors selectively produced IFN-γ when re-exposed to HCMV-infected MRC-5 cells. Both NKG2C+ and NKG2C- NK cells proliferated in co-culture with HCMV-infected MRC-5 cells, with the fraction of proliferating NKG2C+ NK cells directly correlating with the circulating NKG2C+ fraction. These data illustrate an at least partly NKG2C-independent human NK-cell memory-type response against HCMV.

Formation of FcRγ-deficient NK cell subset associated with HCMV-reactivation in hematopoietic cell transplant recipients.

131 Background: We have previously identified a novel subset of human NK cells that lacks FcRγ, a transmembrane signaling adaptor associated with CD16, the Fc receptor for IgG. These FcRγ-deficient NK cells (termed g-NK cells) display enhanced functional activity against target cells, including virus-infected cells, in concert with target-specific antibody molecules. The presence of g-NK cells in humans is associated with prior infection by human cytomegalovirus (HCMV). Additionally, g-NK cells are activated and expand robustly against HCMV-infected cells in the presence of HCMV-specific antibodies, consistent with predicted features of memory-like or adaptive NK cells. Recent studies have reported that expansion of a specific subset of NK cells with an adaptive phenotype can occur in response to HCMV reactivation after hematopoietic cell transplantation. Remarkably, patients with the expanded subset of NK cells showed reduced incidence of leukemia relapse and improved disease-free survival. Methods: Using blood samples obtained from BMT patients pre- and post-transplant, we have performed FACS-based phenotyping and ELISA-based serotyping analyses to explore whether HCMV-reactivation correlates with the generation of FcRγ-deficient NK cells in a bone marrow transplantation (BMT) setting. Results: Our data demonstrate that FcRγ-deficient NK cells appear in transplant patients following HCMV-reactivation, but not in the BMT patients without HCMV-reactivation. Phenotypic analysis indicates that these FcRγ-deficient NK cells display characteristics consistent with those observed in g-NK cells obtained from healthy HCMV-seropositive individuals, e.g. decreased expression of tyrosine kinase SYK. Conclusions: These results provide evidence in support of a causal relationship between HCMV infection and the generation of g-NK cells. Given the enhanced functional capability of g-NK cells against HCMV-infected target cells, the formation and functional activity of g-NK cells within BMT patients may contribute to the control of HCMV infection during the transplant procedure, and impact recovery from other diseases.

Comparative analysis of NK cell receptor repertoire in adults and very elderly subjects with cytomegalovirus infection

Human cytomegalovirus (HCMV) infection in children and young adults has been associated with changes in the innate immune system. We herein analyzed the possible effect of very long term HCMV infection on the expression of several NK cell receptors. Ninety HCMV-seropositive individuals were included and classified as young adults (n=30), elderly (n=30) and very elderly subjects (n=30). A peripheral blood sample was obtained and the expression of NK cell receptors (NKG2A, NKG2C, ILT2, CD161, KIR2DL1, KIR3DL1, and KIR3DL2) by NK and other lymphocyte subsets was assessed by flow cytometry. In addition, the frequency of the sixteen KIR genes was analyzed by polymerase chain reaction. We found a significant increase in the number of NKG2C+ NK and T cells in elderly individuals compared to young adults accompanied by an opposite trend in the number of NKG2A+ lymphocytes, and ILT2+ cells were also increased in elderly individuals. A significant increase in the levels of CD3-CD56+NKG2C+CD57+ cells was also detected in the elderly groups. Finally, KIR gene analysis revealed that the KIR genotype 2 was significantly less frequent in the elderly individuals. Our results support that long-term infection by HCMV exerts a significant progressive effect on the innate immune system.

Association of Human Immunoglobulin G1 Heavy Chain Variants With Neutralization Capacity and Antibody-Dependent Cellular Cytotoxicity Against Human Cytomegalovirus.

Human cytomegalovirus (HCMV) infection is limited by HCMV-specific antibody functions. Here the association between the genetic marker (GM) 3/17 variants in the immunoglobulin G1 (IgG1) heavy chain constant region, virus neutralization, and natural killer (NK)-cell activation was investigated. In 100 HCMV-seropositive individuals, the GM3/17 polymorphism, serum 50% HCMV antibody neutralization titer (NT50), and in vitro HCMV-specific antibody NK-cell activation were assessed. The HCMV NT50 was higher in heterozygous GM3/17 persons than in GM3/3 persons (P = .0276). Furthermore, individuals expressing GM3/17 exhibited significantly higher NK-cell activation than persons carrying GM3/3 (P < .0001) or GM17/17 (P = .0095). Thus, persons expressing GM3/17 have potentially a selective advantage in HCMV defense.

Influenza Vaccination Generates Cytokine-Induced Memory-like NK Cells: Impact of Human Cytomegalovirus Infection.

Human NK cells are activated by cytokines, immune complexes, and signals transduced via activating ligands on other host cells. After vaccination, or during secondary infection, adaptive immune responses can enhance both cytokine-driven and Ab-dependent NK cell responses. However, induction of NK cells for enhanced function after in vitro exposure to innate inflammatory cytokines has also been reported and may synergize with adaptive signals to potentiate NK cell activity during infection or vaccination. To test this hypothesis, we examined the effect of seasonal influenza vaccination on NK cell function and phenotype in 52 previously unvaccinated individuals. Enhanced, IL-2–dependent, NK cell IFN-γ responses to Influenza A/California/7/2009 virus were detected up to 4 wk postvaccination and higher in human CMV (HCMV)-seronegative (HCMV−) individuals than in HCMV-seropositive (HCMV+) individuals. By comparison, robust NK cell degranulation responses were observed both before and after vaccination, due to high titers of naturally occurring anti-influenza Abs in human plasma, and did not differ between HCMV+ and HCMV− subjects. In addition to these IL-2–dependent and Ab-dependent responses, NK cell responses to innate cytokines were also enhanced after influenza vaccination; this was associated with proliferation of CD57− NK cells and was most evident in HCMV+ subjects. Similar enhancement of cytokine responsiveness was observed when NK cells were cocultured in vitro with Influenza A/California/7/2009 virus, and this was at least partially dependent upon IFN-αβR2. In summary, our data indicate that attenuated or live viral vaccines promote cytokine-induced memory-like NK cells and that this process is influenced by HCMV infection.

Preclinical evaluations of peptide-conjugate vaccines targeting the antigenic domain-2 of glycoprotein B of human cytomegalovirus

ABSTRACTThe Antigenic Domain 2 (AD-2) is a short region near the N-terminus of glycoprotein B of human cytomegalovirus (HCMV). AD-2 has been shown to contain linear epitopes that are targets for neutralizing monoclonal antibodies from human subjects with natural HCMV infection. However, AD-2 appears to be masked by the adjacent immunodominant AD-1 region. We assessed a serum panel from HCMV-seropositive individuals and found a wide range of antibody titers to AD-2; these did not correlate to serum neutralization. To expose potential epitopes in AD-2, we constructed a series of AD-2 peptide-conjugate vaccines. Mice were immunized 3 times and produced high and sustained antibody titers to AD-2 peptides, but neutralization was weak even after a single boost with whole HCMV virions. Rabbits were likewise immunized with AD-2 peptide vaccines, and produced a robust antibody response, but neutralization was inferior to a recombinant gB vaccine with an oil-in-water adjuvant. These results highlight the challenges of developing a peptide-based vaccine specific to the HCMV gB AD-2 region.

NKG2C zygosity influences CD94/NKG2C receptor function and the NK‐cell compartment redistribution in response to human cytomegalovirus

Human cytomegalovirus (HCMV) infection promotes a persistent expansion of a functionally competent NK-cell subset expressing the activating CD94/NKG2C receptor. Factors underlying the wide variability of this effect observed in HCMV-seropositive healthy individuals and exacerbated in immunocompromized patients are uncertain. A deletion of the NKG2C gene has been reported, and an apparent relation of NKG2C genotype with circulating NKG2C(+) NK-cell numbers was observed in HCMV(+) children. We have assessed the influence of NKG2C gene dose on the NK-cell repertoire in a cohort of young healthy adults (N = 130, median age 19 years). Our results revealed a relation of NKG2C copy number with surface receptor levels and with NKG2C(+) NK-cell numbers in HCMV(+) subjects, independently of HLA-E dimorphism. Functional studies showed quantitative differences in signaling (i.e. iCa(2+) influx), degranulation, and IL-15-dependent proliferation, in response to NKG2C engagement, between NK cells from NKG2C(+/+) and hemizygous subjects. These observations provide a mechanistic interpretation on the way the NKG2C genotype influences steady-state NKG2C(+) NK-cell numbers, further supporting an active involvement of the receptor in the HCMV-induced reconfiguration of the NK-cell compartment. The putative implications of NKG2C zygosity over viral control and other clinical variables deserve attention.

A Vaccine Based on the Rhesus Cytomegalovirus UL128 Complex Induces Broadly Neutralizing Antibodies in Rhesus Macaques

Neutralizing antibodies (NAb) are important for interfering with horizontal transmission of human cytomegalovirus (HCMV) leading to primary and congenital HCMV infection. Recent findings have shown that a pentameric virion complex formed by the glycoproteins gH/gL, UL128, UL130, and UL131A (UL128C) is required for HCMV entry into epithelial/endothelial cells (Epi/EC) and is the target of potent NAb in HCMV-seropositive individuals. Using bacterial artificial chromosome technology, we have generated a modified vaccinia Ankara virus (MVA) that stably coexpresses all 5 rhesus CMV (RhCMV) proteins homologous to HCMV UL128C, termed MVA-RhUL128C. Coimmunoprecipitation confirmed the interaction of RhgH with the other 4 RhCMV subunits of the pentameric complex. All 8 RhCMV-naïve rhesus macaques (RM) vaccinated with MVA-RhUL128C developed NAb that blocked infection of monkey kidney epithelial cells (MKE) and rhesus fibroblasts. NAb titers induced by MVA-RhUL128C measured on both cell types at 2 to 6 weeks postvaccination were comparable to levels observed in naturally infected RM. In contrast, MVA expressing a subset of RhUL128C proteins or RhgB glycoprotein only minimally stimulated NAb that inhibited infection of MKE. In addition, following subcutaneous RhCMV challenge at 8 weeks postvaccination, animals vaccinated with MVA-RhUL128C showed reduced plasma viral loads. These results indicate that MVA expressing the RhUL128C induces NAb inhibiting RhCMV entry into both Epi/EC and fibroblasts and limits RhCMV replication in RM. This novel approach is the first step in developing a prophylactic HCMV vaccine designed to interfere with virus entry into major cell types permissive for viral replication, a required property of an effective vaccine.

Antibodies Against Neutralization Epitopes of Human Cytomegalovirus gH/gL/pUL128-130-131 Complex and Virus Spreading May Correlate with Virus Control In Vivo

Recently, human cytomegalovirus (HCMV) UL128-131 locus gene products have been found to be associated with glycoprotein H (gH) and glycoprotein L (gL) to form a pentameric glycoprotein complex gH/gL/pUL128-130-131, which is present in the virus envelope and elicits production of neutralizing antibodies. Purpose of this study was to verify whether in vitro activities of these antibodies may correlate with protection in vivo. By using potently neutralizing human monoclonal antibodies (mAbs) targeting 10 different epitopes of the pentameric complex, a competitive ELISA assay was developed, in which the pentamer bound to the solid-phase was reacted competitively with human sera and murinized human mAbs. In addition, inhibition of virus spreading (plaque formation and leukocyte transfer) by neutralizing human mAbs and sera was investigated. In the absence of any reactivity of sera from HCMV-seronegative subjects, antibodies to all 10 epitopes were detected in HCMV-seropositive individuals. During primary HCMV infection in pregnancy antibodies to some epitopes showed a trend towards an earlier appearance in mothers not transmitting the virus to the fetus as compared to transmitting mothers. In addition, the activity of neutralizing human mAbs and sera in blocking virus cell-to-cell spreading and virus transfer to leukocytes from infected endothelial cells was shown to develop during the convalescent phase of primary infection. Dissection of the neutralizing/inhibiting activities of human sera may be helpful in the study of their protective role in vivo. In particular, neutralizing antibodies to the pentamer may be a surrogate marker of protection in vivo.