YMR194C-A Antibody

How are human monoclonal antibodies isolated from immune subjects?

Human monoclonal antibodies can be isolated through several methodological approaches, with B cell hybridoma technology being particularly effective. This process involves:

• Collection of peripheral blood mononuclear cells (PBMCs) from vaccinated or naturally infected individuals

• Transformation of memory B cells with Epstein-Barr virus (EBV) to establish stable antibody-producing lines

• Screening of cell culture supernatants for binding to target antigens using enzyme-linked immunosorbent assay (ELISA) and/or flow cytometry against infected cells

• Fusion of positive clones with myeloma partner cells to generate hybridoma lines

• Cloning by flow cytometric cell sorting to establish monoclonal populations

• Purification of antibodies from serum-free hybridoma supernatants using affinity chromatography

This approach was successfully employed to isolate 15 monoclonal antibodies from four YFV-immune subjects, yielding antibodies with varying binding affinities to the YFV envelope (E) protein . The process ensures native heavy and light chain pairing, making it preferable for identifying therapeutic candidates compared to other technologies like phage display.

What methods are used to evaluate antibody binding characteristics?

Researchers employ multiple complementary techniques to comprehensively characterize antibody binding:

• ELISA for quantitative assessment of binding affinity to recombinant proteins

• Flow cytometry to assess binding to native viral proteins on infected cells

• Western blotting to confirm recognition of denatured or native protein targets

• Immunofluorescence microscopy to visualize binding patterns and cellular localization

• Competition binding assays to map antigenic sites and epitope relationships

For example, antibodies against YFV showed variable half-maximal effective concentrations (EC50s) for binding, ranging from 29 to 15,600 ng/mL when tested against recombinant E protein . Similarly, proper display of SARS-CoV-2 receptor-binding domain (RBD) variants on yeast surfaces was confirmed using both Western blotting analysis and immunofluorescence microscopy, which revealed distinct fluorescence patterns forming rings around the cell wall rather than intracellular signals .

How is neutralizing activity of antibodies measured in vitro?

Neutralizing activity is primarily assessed through cell-based assays that measure inhibition of viral infection:

• Focus Reduction Neutralization Test (FRNT): Measures the antibody concentration required to reduce viral infection foci by a specified percentage (usually 50%)

• Plaque Reduction Neutralization Test (PRNT): Similar to FRNT but measures reduction in plaque formation

• Pseudovirus neutralization assays: Uses reporter viruses expressing target viral proteins

• Competitive ELISA: Measures inhibition of virus binding to cellular receptors

In the YFV studies, FRNT in Vero cells identified YFV-136 as an exceptionally potent neutralizing antibody with an IC50 below 10 ng/mL, while YFV-121 showed moderate neutralization (IC50 of 202 ng/mL) . For SARS-CoV-2 research, competitive ELISA determined that antiserum from mice immunized with variant B.1.617.1 mRBD had neutralizing titers of 64 (20% inhibition rate) against wild-type RBD .

How do researchers map antibody binding epitopes on target proteins?

Epitope mapping employs sophisticated techniques to precisely identify antibody binding sites:

• Competition binding assays: Determine if antibodies compete for binding, suggesting overlapping epitopes

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS): Identifies regions of altered solvent accessibility upon antibody binding

• Neutralization escape mutant selection: Identifies viral mutations that confer resistance to antibody neutralization

• Site-directed mutagenesis: Systematically alters amino acids to determine their contribution to binding

• Structural analysis: Uses X-ray crystallography or cryo-EM to visualize antibody-antigen complexes at atomic resolution

These approaches revealed that neutralizing antibodies YFV-121 and YFV-136 targeted an overlapping antigenic site on the YFV E protein, specifically in domain II (DII). Interestingly, YFV-65 competed for binding at the same site but did not neutralize the virus, suggesting that precise epitope recognition is crucial for neutralization activity . For SARS-CoV-2, mutations at position E484 in variants B.1.351 and B.1.617.1 significantly reduced binding of antibodies raised against wild-type RBD, highlighting this position as a critical epitope component .

What factors influence cross-reactivity of antibodies against variant proteins?

Several factors determine whether antibodies can cross-react with variant proteins:

• Conservation of key epitope residues across variants

• Structural similarity in antigenic regions

• Binding affinity to the primary target

• Epitope accessibility in different conformational states

• Post-translational modifications of target proteins

Cross-reactivity analysis of sera from mice immunized with SARS-CoV-2 variant B.1.617.1 mRBD demonstrated robust binding to not only its cognate antigen but also to wild-type RBD and variants B.1.351 and B.1.1.7 . This broad reactivity suggests that B.1.617.1 induced antibodies targeting conserved epitopes. In contrast, fluorescence intensity measurements showed that antibodies against wild-type RBD had reduced binding to variants B.1.351 and B.1.617.1, which both contain mutations at position E484, highlighting how specific mutations can affect cross-reactivity .

How do glycosylation patterns affect antibody-antigen interactions?

Glycosylation significantly impacts antibody-antigen interactions through multiple mechanisms:

• Shielding of potential epitopes from antibody recognition

• Creating novel antigenic determinants through the glycan structures themselves

• Altering protein conformation and stability

• Influencing receptor binding affinity

• Affecting neutralization sensitivity

Studies with deglycosylated SARS-CoV-2 RBD variants demonstrated that glycosylation at specific sites is essential for protein function. Double deglycosylation mutants (N331Q and N343Q) showed markedly reduced binding affinity to the ACE2 receptor and escaped antibody neutralization . This finding demonstrates how glycosylation contributes to both the functional activity of viral proteins and their recognition by antibodies, making glycosylation analysis a critical component of comprehensive epitope mapping.

What approaches are used to evaluate therapeutic potential of monoclonal antibodies?

Evaluation of therapeutic potential follows a systematic progression:

• In vitro neutralization: Initial screening for neutralizing activity

• Binding kinetics: Assessing affinity and stability of binding

• Mechanism of action studies: Determining how antibodies inhibit infection (pre-attachment vs. post-attachment)

• Small animal efficacy models: Testing protection in immunocompetent or immunocompromised rodents

• Humanized liver mouse models: Evaluating efficacy in mice engrafted with human hepatocytes

• Non-human primate studies: Assessing efficacy in physiologically relevant models

• Phase 1 clinical trials: Evaluating safety and pharmacokinetics in humans

The YFV-136 antibody demonstrated therapeutic protection in multiple animal models, including Syrian golden hamsters and immunocompromised mice engrafted with human hepatocytes . Mechanistic studies revealed that YFV-136 inhibited infection at a post-attachment step in the virus replication cycle, providing insight into its mode of action. Similarly, the SC27 antibody against SARS-CoV-2 was discovered to neutralize all known variants, creating potential for broad therapeutic application .

How can yeast surface display technology advance antibody and antigen research?

Yeast surface display offers several advantages for antibody and antigen research:

• Rapid expression of recombinant proteins without expensive inducers

• Proper protein folding and post-translational modifications

• Direct display of antigens in their native conformation

• Easy visualization and quantification of binding interactions

• Potential for high-throughput screening of antibody libraries

• Cost-effective production at laboratory scale

Researchers successfully displayed the receptor-binding domains (RBDs) of SARS-CoV-2 Spike protein and its variants on the surface of Saccharomyces cerevisiae by fusing them to the C-terminus of the yeast Aga2 protein . To optimize the system, they knocked out the gal80 gene, enabling rapid expression using glucose rather than expensive galactose, and reducing culture time from 72 to 24 hours. This approach facilitated immunization studies that revealed the B.1.617.1 variant induced robust humoral and cellular immune responses in mice, with cross-reactivity against other variants .