About Us

Nebulabio is a premier contract research organization (CRO) specializing in antibody discovery, with deep-seated expertise in the Fab (Fragment antigen-binding) phage display platform. Our platform is engineered to bridge the critical gap between in vitro library screening and downstream therapeutic development. Unlike single-chain systems, our focus on the Fab format ensures the discovery of leads that inherently possess the stability, folding efficiency, and structural fidelity of a natural antibody. We partner with global biopharmaceutical companies to tackle high-value, challenging targets—from complex multi-pass membrane proteins like GPCRs to soluble disease mediators. Our integrated service, combining custom library construction, high-stringency screening, and lead characterization, is designed to deliver functional, developable candidates primed for seamless conversion into full-length monoclonal antibodies. Our team’s proven track record is built on a foundation of scientific rigor and a commitment to project success.

☞Principle of Fab Phage Display Technology

■ Technical Foundation

The Fab phage display platform is a sophisticated evolution of the classic phage display system, specifically designed to handle the heterodimeric nature of the Fab fragment. A Fab consists of the entire antigen-binding portion of an antibody: the variable heavy (VH) and constant heavy 1 (CH1) domains (together called the Fd fragment) linked via a disulfide bond to the variable light (VL) and constant light (CL) domains.

In our platform, the genes encoding the Fd fragment and the light chain are cloned into a single phagemid vector. The Fd fragment is genetically fused to the gene encoding the minor coat protein pIII of the M13 bacteriophage, while the light chain is expressed in tandem. Upon transformation into E. coli and superinfection with helper phage, both chains are co-expressed in the bacterial periplasm. Here, in an oxidative environment, they fold independently, assemble through their natural inter-chain disulfide bond, and the resulting functional Fab-pIII fusion is incorporated onto the phage surface. This preserves the native antibody architecture and ensures that selected binders are compatible with subsequent IgG reformatting.

■ Immortalizing Immune Responses: The Value of Fab Libraries

Fab libraries are more than just discovery tools; they are a means to immortalize and dissect immune responses. As documented in scientific literature, immune Fab libraries constructed from individuals who have mounted a specific response—due to disease, vaccination, or immunization—have been instrumental in recovering Fabs against high-value clinical targets such as c-erbB-2 (HER2) and p53. This approach not only yields potential therapeutic or diagnostic agents but also enables detailed analysis of V-gene usage, somatic hypermutation, and epitope immunogenicity, providing invaluable insights into the underlying biology.

■ Classification of Fab Libraries

Nebulabio’s platform supports the construction and screening of three strategic library types:

• Immune Fab Libraries: Derived from immunized hosts, these libraries are pre-enriched for high-affinity, antigen-specific binders, offering the most direct path to potent leads against a defined target.

• Naïve Fab Libraries: Sourced from the natural, non-immunized B-cell repertoires (e.g., human donors). They offer vast, unbiased diversity for novel antigen discovery or against targets where immunization is impractical.

• Synthetic Fab Libraries: Built de novo with designed diversity in the CDRs of chosen human frameworks. These libraries provide full humanization from the start and allow for control over structural and physicochemical properties.

☞Core Technology: Construction & Screening Process

Our platform operates on a refined, two-pillar process that ensures quality at every step.

 Pillar I: Fab Phage Library Construction 

• Genetic Material Acquisition: RNA is isolated from B-cell sources (spleen, PBMCs) for immune/naïve libraries, or gene fragments are synthesized for synthetic libraries.

• Separate Amplification: The Fd (VH+CH1) and Light Chain (VL+CL) genes are PCR-amplified independently using optimized primer sets.

• Combinatorial Cloning: Both gene pools are ligated into a phagemid vector, allowing for random pairing of heavy and light chains—a process that mimics natural antibody diversity.

• Library Transformation & Rescue: The ligated DNA is electroporated into E. coli, creating a primary bacterial library. Helper phage infection then produces the Fab-displaying phage particle library for screening.

 Pillar II: Fab Library Screening (Biopanning) 

• Antigen Immobilization: The target is prepared in the most relevant format: coated on plates, biotinylated for solution-phase capture, or presented on live cells.

• Iterative Panning Rounds (3-5 cycles): The phage library undergoes repeated cycles of Binding → Stringent Washing → Specific Elution → Amplification. Conditions are tuned to progressively favor high-affinity, specific interactions.

• Hit Deconvolution: Single clones from enriched outputs are screened via monoclonal phage ELISA.

• Lead Characterization: Positive clones are sequenced, and unique Fabs are expressed in soluble form for validation of binding, affinity (using BLI or SPR), and epitope specificity.

Figure1.Fab HC library construction and characterization.

☞Nebulabio Integrated Service Workflow

We provide a seamless, collaborative, and transparent project journey from conception to deliverable leads.

 Step 1: Project Scoping & Strategic Design 

Our scientists work with you to analyze the target, define critical success parameters (affinity, cross-reactivity, functional blocking), and select the optimal library strategy and panning approach.

 Step 2: Tailored Library Construction or Selection 

We execute custom library builds as per the chosen strategy or select a pre-validated, high-diversity naïve/synthetic Fab library from our in-house repertoire bank. All libraries undergo rigorous QC (titer, insert rate, NGS diversity analysis).

 Step 3: Advanced Panning Campaign 

Our screening specialists execute the panning protocol, employing techniques like negative selection against counter-targets and competitive elution to drive specificity. Enrichment is monitored via polyclonal phage ELISA after each round.

 Step 4: High-Throughput Screening & Bioinformatics 

Hundreds of individual clones are screened. NGS of the enriched pool combined with our bioinformatics pipeline performs sequence clustering, identifying all unique Fab families and providing insights into the selected immune repertoire.

Step 5: Soluble Expression & Multi-Parameter Validation

Lead Fabs are expressed in E. coli periplasm, purified, and characterized through a tiered cascade:

• Tier 1: Binding Confirmation (ELISA, FACS if applicable).

• Tier 2: Affinity & Kinetics (Biolayer Interferometry on an Octet system).

• Tier 3: Specificity & Developability Assessment (cross-reactivity panels, thermal shift assay for stability).

 Step 6: Comprehensive Delivery 

You receive a final project report with all data, a digital sequence database, physical materials (expression plasmids, glycerol stocks, purified Fabs), and strategic recommendations for downstream development.

 Our Service Flowchart: 

☞Applications of the Fab Phage Display Platform

Our platform is a versatile engine for discovery and development across multiple domains:

• Therapeutic Antibody Lead Discovery: The premier application. Selected Fabs are the direct precursor to full IgGs, ensuring a smooth transition into therapeutic development, particularly for targets where correct domain folding and disulfide bonding are critical (e.g., receptor-ligand systems).

• Diagnostic & Assay Reagent Development: Isolation of matched, high-specificity Fab pairs for superior sandwich immunoassays (ELISA, Luminex) and point-of-care diagnostics.

• Immune Repertoire Mining & Epitope Mapping: As highlighted in research, the platform is invaluable for studying antigen-specific immune responses, identifying immunodominant epitopes, and supporting vaccine design.

• Antibody Humanization & Affinity Maturation: Ideal scaffold for improving antibody properties, as modifications are made in the context of the native Fab structure.

• Bispecific Antibody Engineering: Fabs serve as the standard, stable "building block" arms in many bispecific antibody platforms (e.g., Knob-into-Hole, DuoBody®).

• Membrane Protein Targeting: Effective discovery of binders against complex cell-surface targets like ion channels and GPCRs using whole-cell panning strategies.

☞Why Choose Nebulabio’s Fab Platform?

• Dual-Chain System Expertise: We have specialized protocols for the efficient expression, folding, and periplasmic assembly of the two-chain Fab system, maximizing the yield of functional, disulfide-bonded clones—a key differentiator from single-chain platforms.

• Focus on Therapeutic Relevance: Our platform is designed with the final therapeutic antibody in mind. By working in the Fab format, we prioritize leads with superior developability profiles (expression, stability, solubility), de-risking downstream development.

• Proven Success with High-Value Targets: We have a documented history of isolating high-affinity Fabs against clinically significant and technically challenging targets, including those referenced in foundational literature.

• Integrated NGS & Bioinformatics: We don't just provide sequences; we deliver insights. Our analysis reveals clonal families, VH/VL pairing trends, and repertoire characteristics, adding significant intellectual value.

• End-to-End Project Partnership: You are assigned a dedicated project lead who ensures clear communication, provides expert data interpretation, and acts as a strategic partner throughout the discovery campaign.

• IP Security and Efficiency: We operate under robust confidentiality agreements with clear IP assignment to you, delivering high-quality lead candidates within a predictable 10-14 week timeline for a standard screening campaign.

Leverage the robustness and therapeutic relevance of the Fab format. Partner with Nebulabio’s expert team to advance your most promising targets with a platform engineered for success from discovery to development.