Prevalence of resistance-associated substitutions and retreatment of patients failing a glecaprevir/pibrentasvir regimen

OBJECTIVES

To investigate resistance-associated substitutions (RASs) as well as retreatment efficacies in a large cohort of European patients with failure of glecaprevir/pibrentasvir.

METHODS

Patients were identified from three European Resistance Reference centres in Spain, Italy and Germany. Sequencing of NS3, NS5A and NS5B was conducted and substitutions associated with resistance to direct antiviral agents were analysed. Clinical and virological parameters were documented retrospectively and retreatment efficacies were evaluated.

RESULTS

We evaluated 90 glecaprevir/pibrentasvir failures [3a (n = 36), 1a (n = 23), 2a/2c (n = 20), 1b (n = 10) and 4d (n = 1)]. Ten patients were cirrhotic, two had previous exposure to PEG-interferon and seven were coinfected with HIV; 80 had been treated for 8 weeks. Overall, 31 patients (34.4%) failed glecaprevir/pibrentasvir without any NS3 or NS5A RASs, 62.4% (53/85) showed RASs in NS5A, 15.6% (13/83) in NS3 and 10% (9/90) in both NS5A and NS3. Infection with HCV genotypes 1a and 3a was associated with a higher prevalence of NS5A RASs. Patients harbouring two (n = 34) or more (n = 8) RASs in NS5A were frequent. Retreatment was initiated in 56 patients, almost all (n = 52) with sofosbuvir/velpatasvir/voxilaprevir. The overall sustained virological response rate was 97.8% in patients with end-of-follow-up data available.

CONCLUSIONS

One-third of patients failed glecaprevir/pibrentasvir without resistance. RASs in NS5A were more prevalent than in NS3 and were frequently observed as dual and triple combination patterns, with a high impact on NS5A inhibitor activity, particularly in genotypes 1a and 3a. Retreatment of glecaprevir/pibrentasvir failures with sofosbuvir/velpatasvir/voxilaprevir achieved viral suppression across all genotypes.

Prevalence of resistance-associated substitutions to NS3, NS5A and NS5B inhibitors at DAA-failure in hepatitis C virus in Italy from 2015 to 2019

Despite the high efficacy of direct-acting antivirals (DAAs), the selection of resistance-associated substitutions (RASs) after virological failure of hepatitis C virus (HCV) DAAs can impair the cure of chronic HCV. The aim of the study was to characterize RASs after virological failure of DAAs in Italy over the years. Within the Italian network VIRONET-C, the change in prevalence of NS3/4A-NS5A-NS5B RASs was retrospectively evaluated in patients who failed a DAA regimen over the years 2015-2019. NS3, NS5A and NS5B Sanger sequencing was performed using homemade protocols and the geno2pheno system was used to define HCV-genotype/subtype and predict drug resistance. The changes in the prevalence of RASs over time were evaluated using the chi-square test for trend. Predictors of RASs at failure were analysed by logistic regression. Among 468 HCV-infected patients, HCV genotype 1 was the most prevalent (1b in 154, 33% and 1a in 109, 23%). DAA regimens were: ledipasvir (LDV)/sofosbuvir (SOF) in 131 patients (28%), daclatasvir (DCV)/SOF in 109 (23%), ombitasvir/paritaprevir/ritonavir+dasabuvir (3D) in 89 (19%), elbasvir (EBR)/grazoprevir (GRZ) in 52 (10.5%), velpatasvir (VEL)/SOF in 53 (11%), glecaprevir (GLE)/pibrentasvir (PIB) in 27 (6%) and ombitasvir/paritaprevir/ritonavir (2D) in 7 (1.5%); ribavirin was administered in 133 (28%). The NS5A fasta sequence was available for all patients, NS5B and NS3/4A both for 93%. The prevalence of NS5A and NS3/4A RASs significantly declined from 2015 to 2019; NS5B RAS remained stable. Independent predictors of any RASs included older age and genotype 1a (vs G2 and vs G4). Notably, at least partial susceptibility to all the agents included in the GLE/PIB and VEL/SOF/Voxilaprevir (VOX) combinations was predicted in >95% of cases. As RASs remain common at the failure of DAAs, their identification could play a crucial role in optimizing re-treatment strategies. In Italy RAS prevalence has been decreasing over the years and susceptibility to the latest developed drug combinations is maintained in most cases.

Analysis of genetic and viral determinants of HBsAg levels in patients with chronic HBV infection

Single nucleotide polymorphisms (SNPs) in the interleukin 28B (IL28B) gene can influence the course of treated and untreated HBV infection. However, the correlation between different IL28B-SNPs and HBVDNA and quantitative HBsAg (qHBsAg) in chronic HBV infection remains to be fully elucidated. Patients with chronic HBV infection were analysed for qHBsAg, HBVDNA, HBV genotype and six IL28B-SNPs (rs12980275, rs8105790, rs8099917, rs7248668, rs12979860, rs10853728). Seventy patients were recruited: 80% Caucasian, 56% genotype D, 44% treated with nucleos(t)ide analogues, 11% cirrhotic, 37% inactive carriers (IC). Median (IQR) qHBsAg and HBVDNA were 3.2 log10 IU/ml (2.2-3.9) and 2.2 log10 IU/ml (0.3-3.3), respectively. Lower levels of qHBsAg were associated in the whole study population with rs12979860 CC vs. CT (p=0.05), rs12980275 AA vs. AG (p=0.04), rs8105790 TT vs. CT (p=0.05) and genotype D vs. A+E (p=0.01). rs8105790 TT was present in 81% of IC vs. 46% non-IC (p=0.005). These data were also confirmed in the untreated patients' subgroup. In multivariate analysis, IL28B-SNP haplogroups were associated with lower qHBsAg: CC/AA at rs12979860/rs12980275 (-0.70 log IU/mL, 95% CI -1.26;-0.14; p=0.01), CC/TT at rs12979860/rs8105790 (-0.78 log IU/mL, 95% CI -1.33;-0.23; p=0.006) and AA/TT at rs12980275/rs8105790 (-0.71 log IU/mL, 95% CI -1.27;-0.17; p=0.01) both in the whole population and in the untreated subgroup. Specific IL28-SNP haplogroups might be associated with lower qHBsAg.

Hepatitis C Genotype 4 Virus Nonstructural 3 and Nonstructural 5A Resistance-associated Substitutions in a 16-year-old Adolescent Failing Ombitasvir/Paritaprevir/Ritonavir Plus Ribavirin

Preexistence and appearance of resistance-associated substitutions limit the efficacy of direct-acting antivirals in treatment of hepatitis C. This is the first case report of an adolescent with chronic hepatitis C virus genotype 4 infection and cirrhosis who failed treatment with ombitasvir/paritaprevir/ritonavir and ribavirin. Resistance analysis showed baseline resistance-associated substitutions M28V and Y93C and emergent D168H.

Natural NS5A inhibitor resistance associated substitutions in hepatitis C virus genotype 1 infected patients from Italy

OBJECTIVES

Genetic variability in NS5A is associated with different levels of resistance to the currently licensed NS5A inhibitors. The aim of this study was to detect NS5A inhibitor resistance associated substitutions (RASs) in hepatitis C virus (HCV) genotype 1 (GT1) patients who are naive to direct-acting HCV antivirals.

METHODS

Amplification, Sanger sequencing and phylogenetic analysis of the HCV NS5A region were performed on plasma obtained from 122 consecutive patients with HCV chronic infection attending four different clinics in Italy.

RESULTS

NS5A inhibitor RASs were detected in 14/61 (23.0%) HCV GT1b and 3/61 (4.9%) HCV GT1a infected patients (p 0.007). The pan-genotypic RAS Y93H was detected in 1 (1.6%) GT1a and 4 (6.6%) GT1b patients. GT1a sequences clustered into two different clades with RASs detected in 1/34 (2.9%) clade I and 2/27 (7.4%) clade II sequences.

CONCLUSIONS

Although the impact of naturally occurring NS5A RASs might be limited with upcoming pan-genotypic treatment regimens, this information is still useful to map naturally occurring HCV variants in different geographic areas in the context of current HCV therapy.

Two Distinct Hepatitis C Virus Genotype 1a Clades Have Different Geographical Distribution and Association With Natural Resistance to NS3 Protease Inhibitors

Background.  Hepatitis C virus (HCV) genotype 1 is the most prevalent worldwide. Subtype 1a, compared with 1b, shows lower response rates and higher propensity to select for drug resistance to NS3 and selected NS5A and nonnucleoside NS5B inhibitors. Two distinct clades of subtype 1a have been described. Methods.  Using Bayesian methodology, we performed a time-scaled phylogeny reconstruction of clade separation and characterized the geographic distribution, phylodynamics, and association with natural resistance variants of NS3 sequences from 362 patients carrying subtype 1a HCV. Results.  All sequences segregated in 2 clearly distinct clades. Clade I showed an earlier origin from the common ancestor compared with clade II. Clade I virus was more prevalent in non-European countries, represented mostly by United States, compared with European (75.7% vs 49.3%; P < .001). The prevalence of the natural NS3 variant Q80K, associated with resistance to the macrocyclic protease inhibitor simeprevir, was detected in 51.6% of clade I and 0% of clade II (P < .001); clade I showed a lower genetic barrier for Q80K, whereas no sign of selective pressure at any protease inhibitor resistance-associated codon was detected. Conclusions.  Hepatitis C virus subtype 1a clades have a clearly different distribution in Europe and the United States, and the natural resistance mutation Q80K is exclusively associated with clade I.

Stability of unfrozen whole blood DNA for remote genotypic analysis of HIV-1 coreceptor tropism

Background

Maraviroc is an HIV-1 coreceptor antagonist that has shown good efficacy and tolerability in treatment-naive and treatment-experienced patients harboring CCR5-tropic virus. The use of Maraviroc in treatment simplification in patients with suppressed plasma HIV-1 RNA requires analysis of HIV-1 DNA. Coreceptor tropism testing is often performed remotely at reference laboratories. In this study paired whole blood stored at + 4°C and at−20°C were compared as a source for genotypic coreceptor tropism testing.

Methods

Two hundred paired whole blood samples from different patients were analysed. Each sample was stored in two different conditions: one aliquot was stored at−20°C until spin column DNA extraction (WB20) and one aliquot was stored at +4°C for two weeks and then placed at room temperature (22-24°C) for two days before DNA extraction (WB4). Subsequently, a fragment encompassing the HIV-1 gp120 V3 domain was amplified by a singlicate nested PCR followed by triplicate nested PCR in the negative samples. A randomly selected panel of 20 paired WB4 and WB20 duplicate amplification products were sequenced and coreceptor tropism was inferred by geno2pheno [coreceptor].

Results

WB20 yielded a higher amount of DNA than WB4 (median [IQR] values 332.5 ng/μl [117.5-401] and 107 ng/μl [56.6-318], respectively; P < 0.001). However, the DNA purity was higher for WB4 than for WB20 (median distance from the optimal OD_260/280 ratio, 0.14 [0.07-0.79] and 0.96 [0.36-1.10], respectively; P < 0.0001). The number of samples successfully amplified was 152 (76.0%) for WB20 and 155 (77.5%) for WB4 with the first PCR and 179 (89.5%) for WB20 and 181 (90.5%) for WB4 (P = ns) following subsequent triplicate analysis. The inferred coreceptor tropism was concordant in 18 out of 20 paired WB4 and WB20 samples. Two samples yielded discordant results, consistent with the discordance rate within duplicates from the same sample source (2/20 with WB4 and 1/20 with WB20) due to the inherent gp120 V3 variability.

Conclusions

Storing whole blood at +4°C for up to two weeks and shipping at room temperature is a convenient method for obtaining HIV-1 gp120 V3 sequence information via testing at a remote laboratory in patients with suppressed viremia.

Naturally occurring hepatitis C virus (HCV) NS3/4A protease inhibitor resistance-related mutations in HCV genotype 1-infected subjects in Italy

OBJECTIVES

To assess the prevalence of hepatitis C virus (HCV) NS3/4A protease inhibitor (PI) resistance mutations in HCV genotype 1-infected PI-naive individuals in Italy.

PATIENTS AND METHODS

One hundred and twelve patients infected with HCV genotype 1a or 1b (based on Versant HCV Genotype 2.0 or 5'UTR/core sequencing) and never treated with any HCV PI were evaluated. The whole NS3 region was analysed by population sequencing and mutations related to resistance to linear and macrocyclic PIs were recorded.

RESULTS

Forty-six HCV-monoinfected and 66 HCV/HIV-coinfected subjects were studied. Complete NS3 sequence information was obtained for 109 (97.3%) samples: 67 subtype 1a and 42 subtype 1b. Subtype assignment by NS3 sequencing was concordant in 100.0% and 83.9% of cases with the original 5'UTR sequencing and Versant result, respectively. At least one mutation related to PI resistance was detected in 21 (19.3%) isolates. However, 11 of these had only Q80K, expected to confer resistance to one investigational macrocyclic compound, and were detected only in subtype 1a. Boceprevir and telaprevir resistance-related mutations were detected in 10 (9.2%) isolates and included V36L, T54S and V55A. Only one isolate harboured two mutations (V36L and T54S). There was no association between HCV PI resistance and HIV coinfection or exposure to HIV PIs.

CONCLUSIONS

A minority of untreated HCV genotype 1 patients in Italy harbour a virus population carrying HCV PI resistance-related mutations. The clinical implications of this finding warrant further analysis.

Structurally Driven Selection of Human Hepatitis C Virus Mimotopes

A structural genomics approach is proposed for the development of new diagnostic kits. It combines molecular modelling, peptide synthesis and immunological tests. The preliminary step is the development of a reliable three-dimensional structure of an immunodominant protein of the target pathogenic organism using the various bioinformatic strategies that are now available to structural biologists. Once the protein structure is obtained, the most surface-exposed fragments with minimal sequence variability among the different strains reported in the genomic data bank are reproduced synthetically as linear peptides. These peptides are then tested for immunoreactivity with the plasma of infected patients to determine whether the synthetic molecules have antigenic activity and can therefore be used to detect infecting agents. This structurally driven selection of mimotopes was successfully performed for the human hepatitis C virus, as five peptides that specifically interact with the plasma of HCV-infected patients were identified solely on the basis of the three-dimensional structure predicted for the E2 homodimer of the 1a viral subtype. A similar approach could easily be extended to a large variety of immunogenic proteins from other pathogenic organisms.

Prevalence of skin allograft discards as a result of serological and molecular microbiological screening in a regional skin bank in Italy

BACKGROUND

Postmortem skin is widely used in the treatment of patients with severe burns. Skin specimens must be screened for transmissible agents including human immunodeficiency virus (HIV), hepatitis B (HBV) and C (HCV) virus, human T-cell lymphotropic virus (HTLV), cytomegalovirus (CMV) and Treponema pallidum.

METHODS

Four hundred and sixty-one cadaveric donors underwent serological and molecular microbiological (polymerase chain reaction, PCR) screening at Siena Skin Bank between 2000 and 2004.

RESULTS

74/461 donors (16.1%) were found ineligible under current regulations.

CONCLUSIONS

These results are interesting in a local context and underline the importance of screening involving both routine serological procedures and molecular microbiological investigation. The latter has not been uniformly introduced in many countries and very limited data is available to assess its cost-benefit ratio in the field of skin donor screening.

Structurally driven selection of human hepatitis C virus mimotopes

A structural genomics approach is proposed for the development of new diagnostic kits. It combines molecular modelling, peptide synthesis and immunological tests. The preliminary step is the development of a reliable three-dimensional structure of an immunodominant protein of the target pathogenic organism using the various bioinformatic strategies that are now available to structural biologists. Once the protein structure is obtained, the most surface-exposed fragments with minimal sequence variability among the different strains reported in the genomic data bank are reproduced synthetically as linear peptides. These peptides are then tested for immunoreactivity with the plasma of infected patients to determine whether the synthetic molecules have antigenic activity and can therefore be used to detect infecting agents. This structurally driven selection of mimotopes was successfully performed for the human hepatitis C virus, as five peptides that specifically interact with the plasma of HCV-infected patients were identified solely on the basis of the three-dimensional structure predicted for the E2 homodimer of the la viral subtype. A similar approach could easily be extended to a large variety of immunogenic proteins from other pathogenic organisms.

Longitudinal study in HIV/HCV-coinfected HAART-naive patients and role of HCV genotype

To evaluate the impact of highly active antiretroviral therapy (HAART) on the course of hepatitis C (HCV) infection, we studied the biological and virological characteristics of 23 HCV/HIV-coinfected HAART-naive patients. The HCV genotype, HCV and HIV viral loads, serum alanine aminotransferase, CD4+ and CD8+ cell/mm3 were determined at baseline, 1 month, 6 months and 12 months after initiation of HAART. Results were analyzed both in terms of total population and of HCV genotype. The study of the total population suggests that this therapy did not determine a significant alteration of HCV viremia and levels of ALT, while a significant decrease in HIV viremia (-1.7log10 at one year from the start of HAART) and increase in CD4+ counts was observed (P < 0.005). The biological and virological parameters of HCV/HIV coinfection differed according to the HCV genotype. In particular, only genotype 4 showed a significant inverse correlation between HCV and HIV viral loads.

Association of extrahepatic manifestations with HLA class II alleles and with virus genotype in HCV infected patients

It has been postulated that host factors, such as the human leucocyte antigen (HLA) system, may play a predominant role in the pathogenesis of HCV-related extra-hepatic manifestations. This study was performed to investigate the role of HLA- DR and DQ alleles in a group of Italian patients, with HCV infection and associated extrahepatic manifestations and to test whether an association between HCV genotype, HLA locus and clinical or serological manifestations can be demonstrated. Thirty unrelated patients affected by HCV infection with extra-hepatic manifestations were consecutively included in the study. One hundred and sixty-three HCV patients without extrahepatic manifestations were tested as controls for the prevalence of HCV genotypes, and 283 healthy donors were used as controls for HLA class II alleles distribution. HCV-RNA was quantified by an reverse transcription-PCR. HLA class II alleles typing was performed using a standard microlymphocytotoxicity assay on B lymphocyte purified. HCV 2c genotype was found in 53.3% compared to 18.4% of controls (p=0.00001; OR=5.1). Cryoglobulins were detected in 72.7% DR6+ patients and in 31.6% DR6- patients (p=0.05; OR=3.21). Rheumatoid factor was found in 90.9% of DR6+ patients and in 42.1% DR6- patients (p=0.018; OR 13.7). Only two DR5+ patients (20%) had cryoglobulinemia, while 6 patients (30%) in the DR5- group had cryoglobulinemia (p=0.02; OR=0.07). Associations were found between DR7 and ANA (OR=1.74) and between DQ2 and ANA (OR=1.97). According to our findings HLA-DR6 might play an important role in developing extra-hepatic manifestations and genotype 2c could be considered as a risk factor for their onset.

Vertical transmission of the hepatitis C virus to infants of anti-human immunodeficiency virus-negative mothers: molecular evolution of hypervariable region 1 in prenatal and perinatal or postnatal infections

In a prospective study of 33 infants born to hepatitis C virus (HCV)-positive human immunodeficiency virus-negative mothers the vertical transmission of HCV occurred in 6.8%. The evolution of HCV infection in two babies was studied from birth up to 5 or 6 years of age, and the sequencing of the hypervariable region (HVR) of the putative envelope-encoding E2 region of the HCV genome was performed. The HVR1 sequence variability and the different serological profiles during follow-up could reflect the differences in HCV transmission routes, HCV genotypes, and clinical evolution of infection.

Hepatitis C virus infection and myositis: a polymerase chain reaction study

Muscle biopsy tissue from a patient with chronic hepatitis, who was hepatitis C virus (HCV) positive and showed slight weakness of the right arm and leg associated with increased serum creatine kinase levels, was studied using immunocytochemical and polymerase chain reaction (PCR) techniques. Muscle biopsy showed changes compatible with an inflammatory myopathy. Immunohistochemical studies included the use of monoclonal antibodies against human T lymphocytes, macrophages, immunoglobulins, major histocompatibility complex class I molecules (MHC-I), and the neoantigens of the terminal C5b-9 complement membrane attack complex (MAC). In addition to confirming the potential importance of cytotoxic T cells and MHC-I antigen expression in inducing muscle pathology, we demonstrated MAC deposition and the presence of HCV-RNA in the muscle of our patient, suggesting that direct involvement of the virus leading to complement activation might be important in inducing muscle damage.

Typing of hepatitis C virus by a new method based on restriction fragment length polymorphism

A new restriction fragment length polymorphism (RFLP) analysis has been developed for hepatitis C virus (HCV) typing in the viral 5' non-coding region and contiguous core region. These genomic sequences were chosen for the relative nucleotide homology among different genotypes and for the presence of polymorphic sites. By employing two endonucleases (AccI and MboI) and, in some instances, a third one (EcoRII), we can unambiguously and reproducibly distinguish between genotypes and subtypes 1a, 1b, 1c, 2a, 2c, 2b, 3a, 3b, 4a, 5a and 6a. The method was applied for diagnosing two Italian groups of HCV-infected individuals reflecting a randomly collected population and a group of intravenous drug users. The accuracy of this method has been validated by comparison with INNOLiPA and by sequencing. Our approach represents an improvement over previous RFLP methods, since typing is accurate and simpler.

Antibody testing and RT-PCR results in hepatitis C virus (HCV) infection: HCV-RNA detection in PBMC of plasma viremia-negative HCV-seropositive persons

To evaluate the concordance between viremia and antibody testing in hepatitis C virus (HCV) diagnosis, 682 serum or plasma samples collected from patients with known or suspected HCV infection were tested. An overall concordance of 77% between serological and PCR results was found, 5% was RNA positive/antibody negative and 18% antibody positive/RNA negative. The relationship between HCV infection, risk group and clinical diagnosis was studied in 116 patients: the presence of anti-HCV antibody without viremia was shown in 72.7% of asymptomatic subjects and 17.6% of chronic hepatitis subjects without interferon treatment. However, the detection of HCV-RNA in peripheral blood mononuclear cells (PBMC) in four out of 38 plasma viremia-negative HCV-seropositive subjects (10.5%), showed that HCV-RNA could persist in PBMC and could begin the viral replication again at different times. The detection of HCV-RNA in PBMC in anti-HCV-positive subjects without viremia could reduce false-negative results of HCV-RNA testing by RT-PCR in serum or plasma.

Detection of HCV and GBV-C/HGV infection by multiplex PCR in plasma samples of transfused subjects

A multiplex polymerase chain reaction (PCR) was applied to clinical samples for simultaneous detection of hepatitis C virus (HCV) and GBV-C/HGV genome. With both RNA viruses, the amplification was performed with primers of the 5' UTR region starting from the single viral RNA reverse transcripted (cDNA) with random hexanucleotide primer mix. GBV-C/HGV RNA was detected in plasma sample of seven out of 50 transfused patients (14%). The multiplex PCR demonstrated a sensitivity up to 7.8 x 10(2) copies/ml respectively for GBV-C/HGV and HCV RNA in plasma samples of 5/50 patients with GBV-C/HGV/HCV co-infection and in patients with HCV (27/50) or GBV-C/HGV infection alone (2/50).

The potential role of hepatitis C virus in the pathogenesis of the neurological syndrome in chronic hepatitis C

A 72-year-old man developed chronic sensory neuropathy (CSN) during chronic hepatitis C (HCV) infection. Neurological symptoms began one year after acute HCV hepatitis and slowly worsened over three years. No conventional cause for CSN was found. Circulating antinervous tissue antibodies (including anti-Hu) and inflammatory infiltrates in sural nerve biopsy specimens were absent. However, the presence of anti-HCV antibody and HCV-RNA in cerebrospinal fluid indicated that HCV had reached the intrathecal compartment, suggesting the direct viral involvement in the pathogenesis of CSN.

Nuclear magnetic resonance investigation of virus-lymphomonocyte interactions

The water protein spin-lattice relaxation time (T1) was measured in suspensions of human peripheral blood mononuclear cells (PBMC), uninfected or infected with type 1 herpes simplex virus, human cytomegalovirus and rubella virus. In the infected samples, T1 enhancements, which linearly depend on virus concentration, were observed. This T1 increase can be related to the early changes induced by the virus adsorption of the cells, not always confirmed by virus-induced cytopathic effect (CPE) in cocultures of infected PBMC and other sensitive cells. Compared with other conventional virological techniques, this NMR method seems to be rapid and sensitive. The NMR response was reproducible and specific, since neutralization of the viral infection by homologous antisera consistently matched the neutralization of the virus-induced NMR effects. These observations suggest that fast and sensitive 1H-NMR relaxation techniques can be implemented in virological diagnosis directly on pathological materials.

Characterization of immunoreactive octapeptides of human-cytomegalovirus gp58

We have mapped continuous epitopes, for positions 591-673 of the human cytomegalovirus 58-kDa glycoprotein using overlapping synthetic peptides and human sera. This region contains a fragment previously described as including the dominant site for induction of human-cytomegalovirus antibodies. Since the selected sequence is highly conserved among herpes viruses, we have considered the possible presence of antigenic cross-reactivity, particularly with the Epstein-Barr virus. Several peptides in the studied region were antigenic and two main continuous epitopes have been identified. Serological cross-reactions observed with Epstein-Barr virus are discussed, focusing on the possible implications of structural features and sequence similarity between human-cytomegalovirus and Epstein-Barr-virus glycoproteins.