The Humoral Immune Response against Human Cytomegalovirus Is Characterized by a Delayed Synthesis of Glycoprotein-Specific Antibodies

Human cytomegalovirus (HCMV) is an important, ubiquitous pathogen that causes severe clinical disease in immunocompromised individuals, such as organ transplant recipients and infants infected in utero. The envelope glycoprotein B (gB) of HCMV is a major antigen for the induction of virus-neutralizing antibodies. We have begun to define target structures within gB that are recognized by virus-neutralizing antibodies. Antigenic domain 5 (AD-5) of gB has been identified as an important target for neutralizing antibodies in studies using human monoclonal antibodies (MAbs). Anti-AD-5 MAbs share a target site on gB, despite originating from different, healthy, HCMV-infected donors. Mutational analysis of AD-5 identified tyrosine 280 in combination with other surface-exposed residues (the YNND epitope) as critical for antibody binding. The YNND epitope is strictly conserved among different HCMV strains. Recombinant viruses carrying YNND mutations in AD-5 were resistant to virus-neutralizing MAbs. Competition enzyme-linked immunosorbent assays (ELISAs) with human HCMV-convalescent-phase sera from unselected donors confirmed the conserved antibody response for the YNND epitope in HCMV-infected individuals and, because a significant fraction of the gB AD-5 response was directed against the YNND epitope, further argued that this epitope is a major target of anti-AD-5 antibody responses. In addition, affinity-purified polyclonal anti-AD-5 antibodies prepared from individual sera showed reactivity to AD-5 and neutralization activity toward gB mutant viruses that were similar to those of AD-5-specific MAbs. Taken together, our data indicate that the YNND epitope represents an important target for anti-gB antibody responses as well as for anti-AD-5 virus-neutralizing antibodies. IMPORTANCEHCMV is a major global health concern, and a vaccine to prevent HCMV disease is a widely recognized medical need. Glycoprotein B of HCMV is an important target for neutralizing antibodies and hence an interesting molecule for intervention strategies, e.g., vaccination. Mapping the target structures of neutralizing antibodies induced by naturally occurring HCMV infection can aid in defining the properties required for a protective capacity of vaccine antigens. The data presented here extend our knowledge of neutralizing epitopes within gB to include AD-5. Collectively, our data will contribute to optimal vaccine design and development of antibody-based therapies.H uman cytomegalovirus (HCMV) is an important, ubiquitously distributed human pathogen that is found throughout all geographic locations and socioeconomic groups. Initial infection with HCMV is followed by a lifelong persistence characterized by periodic reactivation episodes. While most infections occur subclinically in the immunocompetent host, HCMV can cause severe disease and death in immunocompromised patients and newborns infected in utero. HCMV is the most frequent viral cause of congenital infection and affects 0.5 to 2% of all live births worldwide (1). It is the lead...

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Identification of a Neutralizing Epitope within Antigenic Domain 5 of Glycoprotein B of Human Cytomegalovirus

Wiegers

Sticht

Winkler

et al. 2015

“…Administration of CMV-HIG has also been shown to be effective in preventing CMV disease in solid-organ transplant (SOT) patients (14,15,20). Many studies have shown that human sera can react with a broad spectrum of CMV proteins from either purified virus or virus-infected cells (1,2,10,13). However, binding to viral components does not necessarily confer protection.…”

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confidence: 99%

Antibodies against the gH/gL/UL128/UL130/UL131 Complex Comprise the Majority of the Anti-Cytomegalovirus (Anti-CMV) Neutralizing Antibody Response in CMV Hyperimmune Globulin

Fouts¹,

Chan²,

Stéphan³

et al. 2012

192

148

Anti-cytomegalovirus (anti-CMV) hyperimmune globulin (HIG) has demonstrated efficacy in preventing CMV disease in solidorgan transplant patients as well as congenital disease when administered to pregnant women. To identify the neutralizing component of cytomegalovirus hyperimmune globulin (CMV-HIG), we performed serial depletions of CMV-HIG on cell-surfaceexpressed CMV antigens as well as purified antigens. Using this approach, we demonstrate that the major neutralizing antibody response is directed at the gH/gL/UL128/UL130/UL131 complex, suggesting little role for anti-gB antibodies in CMV-HIG neutralization.

“…An important antibody target is glycoprotein B (gB). Antibodies directed against gB can be detected in all infected individuals (9,10). A major fraction of neutralizing antibodies in human sera seems to be directed against gB, and the overall in vitro neutralizing capacity in sera from HCMV-infected individuals correlates with anti-gB antibody titer (9,11).…”

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confidence: 99%

Characterization of a Discontinuous Neutralizing Epitope on Glycoprotein B of Human Cytomegalovirus

Spindler

Rücker

Pötzsch

et al. 2013

e Human cytomegalovirus (HCMV) is a ubiquitously distributed pathogen that causes severe disease in immunosuppressed patients and newborn infants infected in utero. The viral envelope glycoprotein B (gB) is an attractive molecule for active vaccination and passive immunoprophylaxis and therapy. Using human monoclonal antibodies (MAbs), we have recently identified antigenic region 4 (AD-4) on gB as an important target for neutralizing antibodies. AD-4 is formed by a discontinuous sequence comprising amino acids 121 to 132 and 344 to 438 of gB of HCMV strain AD169. To map epitopes for human antibodies on this protein domain, we used a three-dimensional (3D) model of HCMV gB to identify surface-exposed amino acids on AD-4 and selected juxtaposed residues for alanine scans. A tyrosine (Y) at position 364 and a lysine (K) at position 379 (the YK epitope), which are immediate neighbors on the AD-4 surface, were found to be essential for binding of the human MAbs. Recognition of AD-4 by sera from HCMV-infected individuals also was largely dependent on these two residues, indicating a general importance for the antibody response against AD-4. A panel of AD-4 recombinant viruses harboring mutations at the crucial antibody binding sites was generated. The viruses showed significantly reduced susceptibility to neutralization by AD-4-specific MAbs or polyclonal AD-4-specific antibodies, indicating that the YK epitope is dominant for the AD-4-specific neutralizing antibody response during infection. To our knowledge, this is the first molecular identification of a functional discontinuous epitope on HCMV gB. Induction of antibodies specific for this epitope may be a desirable goal following vaccination with gB.