About Us

Nebulabio is a specialized antibody discovery contract research organization (CRO) with a proven track record in successfully screening Fab phage display libraries. Our team of scientists possesses deep expertise in immunology, protein engineering, and molecular biology, specifically optimized for the unique challenges and advantages of the Fab format. We have partnered with leading biotech and pharmaceutical companies to discover high-affinity, functional leads against a diverse spectrum of targets, including complex membrane proteins, soluble cytokines, and viral antigens. Our service is designed to translate your Fab library—whether naïve, immune, or synthetic—into a shortlist of validated, developable candidates with speed and precision.

☞Types of Fab Libraries

The success of a screening campaign begins with understanding the library's origin. Nebulabio offer expert screening services for all major types of Fab libraries:

• Naïve Fab Libraries: Constructed from the natural, non-immunized B-cell repertoires of humans or other species. These libraries offer broad, unbiased diversity against virtually any antigen. Screening these libraries is ideal for novel targets or when immunization is not feasible. Initial hits may have moderate affinity, often followed by an in vitro affinity maturation step.

• Immune Fab Libraries: Generated from hosts (animals or humans) immunized with a specific antigen or antigen family. These libraries are pre-enriched for specificity and higher affinity, significantly increasing the frequency of positive clones. Screening immune libraries typically yields high-affinity leads (nanomolar to picomolar range) more rapidly and is the preferred route for well-defined targets.

• Synthetic Fab Libraries: Built de novo using designed gene fragments. Diversity is introduced into the Complementarity-Determining Regions (CDRs) of one or more optimized human frameworks. Screening these libraries provides fully humanized leads from the start and allows for tailored diversity focused on specific paratope properties or developability features.

☞Principle of Fab Phage Display Screening

Fab phage display is a cornerstone technology in modern antibody discovery. The core principle involves genetically fusing the Fab's heavy chain (Fd fragment) to a minor coat protein (pIII) of the M13 bacteriophage within a phagemid vector, while the light chain is co-expressed. During phage assembly in E. coli, the chains fold and assemble via a disulfide bond, forming a functional Fab displayed on the phage surface, with the phage particle encapsulating the genes for both chains.

This elegant system creates a direct physical link between the Fab's binding function (phenotype) and its genetic blueprint (genotype). The screening process, biopanning, exploits this link through iterative rounds of binding, washing, elution, and amplification to isolate the highest-affinity clones from libraries containing billions of variants.

Scientific and Translational Value:

Beyond lead isolation, Fab libraries are invaluable scientific tools. They serve as a means to immortalize and propagate antibody genes from a specific immune response, enabling detailed analysis of structural features, V-gene usage, and the nature of the immune response in an individual. Furthermore, the isolated Fabs provide direct tools to evaluate immunogenic epitopes on the target antigen. This contributes significantly to the fundamental understanding of antibody-antigen interactions and the in vivo immune response, while simultaneously generating potentially useful diagnostic or therapeutic agents.

☞Applications of Fab Library Screening

Nebulabio’s Fab screening service is a cornerstone technology for critical applications in biotechnology and drug development:

• Therapeutic Antibody Discovery: The primary application. Screening yields lead Fabs that can be directly reformatted into full-length IgGs, providing a seamless path to therapeutic candidate development, especially for targets requiring native domain interactions.

• Diagnostic & Assay Reagent Development: Identifying highly specific, matched Fab pairs for sandwich ELISA, lateral flow tests, and clinical diagnostics, where the bivalent nature of the derived IgG is advantageous.

• Antibody Humanization & Affinity Maturation: Screening focused libraries to improve the affinity or humanize non-human antibodies while maintaining the Fab's stable architecture.

• Epitope Mapping & Binning: Using panels of selected Fabs to characterize antigen binding sites, which is crucial for intellectual property strategies and understanding biological mechanisms.

• Bispecific Antibody Development: Fab arms are fundamental modules in many bispecific platforms. Screening provides the optimal binding "arms" for constructing novel multi-specific therapeutics.

☞Fab Library Screening Process

Nebulabio execute a comprehensive, multi-stage screening campaign designed for maximum efficiency and success.

 Stage 1: Project Initiation & Antigen Preparation 

• Consultation: Define screening objectives, stringency, and library specifics.

• Antigen QC & Immobilization: We prepare your antigen in the optimal format—direct coating, biotinylation, or cell-surface presentation.

 Stage 2: Pre-Panning Library Assessment 

• Library Titration: Determine the functional phage titer.

• Diversity Check: Optional sequencing to confirm library status before screening.

 Stage 3: Iterative Biopanning (The Core Selection Engine) 

We perform 3-5 rounds of panning, each round comprising:

• Binding: Incubation of Fab-phage library with target.

• Stringent Washing: Gradual increase in wash rigor to favor strong binders.

• Elution: Recovery of specific binders using pH shift or competitive elution.

• Amplification: Infection of E. coli with eluted phage to produce an enriched output for the next round.

 Stage 4: Monoclonal Analysis & Hit Identification 

• Clone Isolation: Individual bacterial colonies are picked from the final enriched output.

• Monoclonal Phage ELISA: Each clone is screened for antigen binding.

• DNA Sequencing & Clustering: All positive clones are sequenced. Bioinformatics analysis groups them into families based on CDR homology to identify unique leads.

 Stage 5: Soluble Fab Expression & Primary Validation 

• Subcloning & Expression: Unique Fab genes are transferred to an expression vector for soluble production in E. coli.

• Purification: Fabs are purified via affinity chromatography (e.g., Protein L or CaptureSelect).

• Primary Characterization:

1. Binding Confirmation: ELISA.

2. Affinity Measurement: Preliminary kinetics via Octet BLI (Biolayer Interferometry).

3. Specificity Assessment: Cross-reactivity testing.

 Stage 6: Reporting & Delivery 

You receive a complete project report with all data (enrichment curves, ELISA results, sequences, affinity data) and deliverables including expression plasmids, sequences, and purified Fab samples.

 Screening Process Flowchart: 

☞Why Choose Us for Your Fab Screening?

• Fab Format Specialization: Our protocols are specifically optimized for the expression, folding, and stability of the heterodimeric Fab format in E. coli, leading to higher recovery of functional clones.

• Proven Expertise with Challenging Targets: We have a demonstrated history of successfully isolating Fabs against difficult target classes such as GPCRs, ion channels, and other multi-pass membrane proteins using specialized cell-surface panning techniques.

• Customized Panning Strategies: We design bespoke screening campaigns. This includes choosing between solid-phase, solution-phase (biotinylated antigen), or whole-cell panning, and implementing negative selection steps to enhance specificity.

• Integrated Bioinformatics Pipeline: Our in-house bioinformatics team provides deep sequence analysis, identifying true unique leads, assessing VH/VL pairing patterns, and screening for early developability flags.

• Focus on Developable Leads: We prioritize leads not only for affinity but also for favorable biophysical characteristics (expression yield, solubility, thermal stability), saving you time in downstream development.

• End-to-End Project Management: You are assigned a dedicated PhD-level project manager who provides regular updates, expert interpretation of data, and seamless communication throughout the entire process.

• Speed, Confidentiality & IP Security: We deliver high-quality data within a transparent 10-14 week timeline, operating under strict confidentiality agreements with clear IP assignment to you.

Accelerate your therapeutic or diagnostic pipeline with Nebulabio’s specialized Fab screening expertise. Contact us to discuss your target and design a winning screening strategy.