CMV gB
Description
Genotypic Variability
Four gB genotypes (gB1-gB4) show distinct clinical distributions :
Table 1: gB Genotype Prevalence in Clinical Specimens
| Specimen Type | gB1 (%) | gB2 (%) | gB3 (%) | gB4 (%) | Mixed Infections (%) |
|---|---|---|---|---|---|
| Serum (n=40) | 12.5 | 2.5 | 42.5 | 2.5 | 40 |
| CSF (n=26) | 11.5 | 38.5 | 30.8 | 7.7 | 11.5 |
Key findings:
gB/MF59 Vaccine
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Efficacy: 50% reduction in maternal CMV infection (Phase 2 trial, NCT00299260)
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Immune Response: Induces antibodies against novel antigenic domain AD-6 (aa 648-697), correlating with reduced cell-to-cell spread
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Limitations: Weak neutralization against canonical ADs (AD1-5)
Next-Generation Vaccines
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mRNA-1647: Combines gB with pentameric complex (PC), showing 6.4-fold higher neutralizing titers than gB/MF59
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Prefusion-stabilized gB: Engineered mutants (e.g., gB-5mut) enhance complement-dependent neutralization by 3.6x
Functional Insights
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Fusion Mechanism: Irreversible transition from prefusion to postfusion states, unlike pH-dependent VSV-G
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Cell-to-Cell Spread: Antibodies targeting the cytoplasmic domain reduce viral replication by 78% in epithelial cells
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Receptor Interaction: Binds heparin sulfate glycosaminoglycans and integrins (αVβ3, α6β1)
Clinical Implications
Product Specs
Q&A
Here’s a structured collection of research-focused FAQs addressing CMV gB, synthesized from peer-reviewed studies and optimized for academic inquiry:
What molecular techniques are used to genotype CMV gB in clinical specimens?
Methodological Answer:
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Multiplex nested PCR (M-nPCR) is the gold standard for genotyping CMV gB directly from clinical samples. Primers target conserved regions (gB/gpUL55) for primary amplification, followed by genotype-specific nested primers to generate size-distinct amplicons (e.g., 180–400 bp) resolved via agarose gel electrophoresis .
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Example Workflow:
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Extract CMV DNA from serum/cerebrospinal fluid (CSF).
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Primary PCR with universal primers.
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Secondary PCR with genotype-specific primers (gB1–gB4).
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Analyze band patterns (e.g., gB2 = 220 bp, gB3 = 280 bp).
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How is CMV gB structurally analyzed to inform vaccine design?
Methodological Answer:
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Cryo-EM and X-ray crystallography resolve prefusion (2.8 Å cryo-EM) and postfusion (5CXF, 5C6T PDB IDs) conformations.
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Key domains mapped:
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Design strategies: Disulfide bonds, cavity-filling substitutions, and proline mutations stabilize prefusion conformations .
How do contradictory findings about prefusion gB’s immunogenicity impact vaccine development?
Critical Analysis:
While prefusion-stabilized class I viral proteins (e.g., SARS-CoV-2 spike) enhance neutralizing antibody responses, CMV gB prefusion variants fail to outperform postfusion gB in murine models .
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Hypotheses:
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Experimental Validation:
What explains tissue-specific CMV gB genotype distributions?
Data-Driven Insights:
A study of 66 AIDS patients revealed divergent gB genotype prevalence in serum vs. CSF :
| Specimen | gB1 | gB2 | gB3 | gB4 | Mixed Infections |
|---|---|---|---|---|---|
| Serum | 12.5% | 2.5% | 42.5% | 2.5% | 40% |
| CSF | 11.5% | 38.5% | 30.8% | 7.7% | 11.5% |
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Mechanistic Insight: gB2’s prevalence in CSF (38.5%, P = 0.005) suggests neural tropism, potentially due to enhanced blood-brain barrier penetration .
How do multi-glycoprotein interactions (gB/gH/gL) affect neutralizing antibody responses?
Methodological Approach:
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Epitope Mapping: Identify overlapping binding sites using monoclonal antibodies (e.g., SM5-1 FAb blocks gH/gL binding to gB) .
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Structural Analysis: Cryo-ET of virion-embedded gB/gH/gL complexes reveals conformational dependencies .
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Functional Assays: Measure neutralization potency against gB/gH/gL pseudotyped viruses in ARPE-19 epithelial cells .
Why do glycoprotein genotypes (gB/gH/gN) inconsistently correlate with clinical outcomes?
Analysis Framework:
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Study Design: Retrospective cohort of 120 symptomatic congenital CMV cases found no association between gB/gH/gN genotypes and hearing loss/neurodevelopmental outcomes .
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Confounders: Host immune status, viral load heterogeneity, and epistatic interactions between glycoproteins.
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Mitigation: Use multivariate regression adjusting for covariates (e.g., CD4+ counts in AIDS patients) .
How reliable are in vitro neutralization assays for predicting gB vaccine efficacy?
Validation Strategy:
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Fibroblast vs. Epithelial Models: Anti-gB antibodies show higher neutralization potency in fibroblasts (70% of total response) , but epithelial entry (via gH/gL) requires complementary assays.
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Correlates of Protection: Phase II trials link AD-1/AD-2 epitope-specific IgG3 to reduced congenital transmission (OR = 0.32, P < 0.01) .
Technical Recommendations
Product Science Overview
Human Cytomegalovirus (HCMV) is a widespread pathogen that infects human populations globally. It is an enveloped double-stranded DNA virus and the largest member of the Herpesviridae family, which also includes other significant pathogens such as HSV-1, HSV-2, Epstein-Barr virus (EBV), and varicella-zoster virus (VZV) . HCMV can infect a wide range of cells, including endothelial cells, epithelial cells, fibroblasts, smooth muscle cells, leukocytes, and dendritic cells .
HCMV is primarily transmitted through body fluids such as saliva, blood, urine, and breast milk, leading to contact with mucosal surfaces . While primary infection and reactivation from latency are often asymptomatic in immunocompetent individuals, HCMV poses a significant threat to immunocompromised individuals, including AIDS patients and transplant recipients . Additionally, congenital HCMV infection can lead to severe complications such as hearing loss and neurological developmental defects .
Glycoprotein B (gB) is a crucial component of the HCMV envelope and plays a significant role in the virus’s ability to infect host cells. It is involved in the initial attachment and fusion of the virus with the host cell membrane . Due to its essential role in viral entry, gB is a primary target for vaccine development and therapeutic interventions .
Recombinant gB has been a focal point in the development of HCMV vaccines. The most effective vaccine tested to date, which achieved a 50% reduction in the acquisition of HCMV, comprised the glycoprotein B protein given with an oil-in-water emulsion adjuvant MF59 . Vaccination with recombinant gB elicits a specific monoclonal antibody repertoire distinct from natural infection, providing a promising approach to preventing HCMV infection .
The development of a recombinant gB subunit vaccine for HCMV remains a high priority due to the significant complications associated with HCMV infection in immunocompromised individuals and congenitally infected neonates . Ongoing research and clinical trials continue to explore the potential of gB-based vaccines to provide effective protection against HCMV .
