Immune repertoire sequencing uses next-generation sequencing (NGS) to capture the highly variable complementarity-determining region 3 (CDR3) of immunoglobulin or TCR transcripts from a bulk population of lymphocytes. This process generates millions of paired heavy- and light-chain sequences, quantifying the clonal diversity and abundance of the antibody repertoire in a biological sample.
Glossary
Immune Repertoire Sequencing

What is Immune Repertoire Sequencing?
Immune repertoire sequencing is a high-throughput molecular technique that profiles the vast diversity of B-cell receptors (BCRs) or T-cell receptors (TCRs) within an individual, providing a comprehensive snapshot of the adaptive immune system's specificity.
The resulting massive sequence datasets serve as a foundational input for AI-driven antibody discovery, enabling the identification of rare, potent neutralizing antibodies from convalescent donors or vaccinated subjects. By applying machine learning to repertoire features—such as clonal expansion, somatic hypermutation patterns, and convergence—researchers can computationally mine natural immune responses to guide de novo therapeutic design.
Key Features of Rep-seq Data
Rep-seq data provides a high-dimensional snapshot of the adaptive immune system, capturing the diversity and clonal architecture of B-cell and T-cell receptor repertoires. Understanding these features is critical for leveraging AI in antibody discovery.
Massive Sequence Diversity
A single human blood sample can contain 10^6 to 10^8 unique B-cell receptor (BCR) heavy-chain sequences. This vast diversity arises from V(D)J recombination, a somatic process that randomly combines Variable (V), Diversity (D), and Joining (J) gene segments.
- Combinatorial Diversity: The random selection and pairing of V, D, and J segments.
- Junctional Diversity: The addition and deletion of non-templated (N) and palindromic (P) nucleotides at segment junctions, creating the hypervariable CDR3 region. This makes the CDR3 a unique molecular barcode for each B-cell clone.
Clonal Grouping and Lineage Trees
Sequences are not isolated; they are grouped into clonal families that descend from a common naive B-cell ancestor. Computational tools cluster sequences by V-gene, J-gene usage, and CDR3 sequence similarity.
- Clonal Expansion: The frequency of identical sequences indicates an active immune response, with expanded clones being prime candidates for therapeutic antibody discovery.
- Phylogenetic Trees: Somatic hypermutation (SHM) patterns allow the reconstruction of B-cell lineage trees, tracing the evolutionary path of an antibody's affinity maturation.
- Key Insight: Lineage analysis reveals intermediate ancestors that may have superior properties to the terminal, affinity-matured variant.
Paired Heavy and Light Chains
A functional antibody requires both a heavy chain (VH) and a light chain (VL). Single-cell sequencing technologies capture the cognate VH:VL pair from individual B cells, preserving the native pairing information.
- Native Pairing: Critical for maintaining the antibody's original paratope structure and antigen specificity.
- Bulk vs. Single-Cell: Bulk Rep-seq loses pairing information, requiring computational pairing algorithms. Single-cell data provides a ground-truth dataset for training AI models to predict functional VH:VL pairing.
- Data Structure: Each record represents a single cell, with fields for VH sequence, VL sequence, and associated metadata.
Somatic Hypermutation (SHM) Profiles
SHM introduces point mutations into the variable region at a rate of ~10^-3 per base pair per cell division. Rep-seq data captures the resulting mutation landscape.
- Mutation Frequency: The number of nucleotide mutations relative to the germline V-gene sequence indicates the degree of affinity maturation.
- Hotspot Motifs: Mutations are not random; they cluster in specific DNA motifs (e.g., WRCY/RGYW) targeted by Activation-Induced Cytidine Deaminase (AID).
- Replacement/Silent (R/S) Ratio: A high R/S ratio in the CDRs indicates antigen-driven positive selection, a key filter for identifying functionally relevant antibodies.
Isotype and Subclass Distribution
Rep-seq data identifies the constant region gene usage, revealing the isotype (e.g., IgM, IgG, IgA, IgE) and subclass (e.g., IgG1, IgG2) of each BCR sequence.
- Class-Switch Recombination (CSR): The biological process by which a B cell changes its isotype from IgM to IgG, IgA, or IgE, altering effector function without changing antigen specificity.
- Functional Relevance: IgG1 and IgG3 are potent for antibody-dependent cellular cytotoxicity (ADCC), while IgG2 is preferred for targeting bacterial polysaccharides.
- AI Application: Isotype distribution data helps train models to predict the developability profile of a candidate antibody based on its Fc-mediated effector functions.
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Frequently Asked Questions
Clear, technically precise answers to the most common questions about profiling B-cell and T-cell receptor diversity using next-generation sequencing for AI-driven antibody discovery.
Immune repertoire sequencing (Rep-seq) is a high-throughput molecular technique that uses next-generation sequencing (NGS) to profile the vast diversity of B-cell receptors (BCRs) or T-cell receptors (TCRs) within a biological sample. The process begins with extracting RNA or genomic DNA from a population of lymphocytes. For BCRs, the workflow typically targets the variable (V), diversity (D), and joining (J) gene segments of the immunoglobulin heavy and light chains. After reverse transcription, the complementarity-determining region 3 (CDR3)—the most hypervariable region responsible for antigen binding—is amplified using multiplex PCR with primers targeting the conserved framework regions. The resulting amplicon libraries are sequenced at high depth, generating millions of paired-end reads. Bioinformatic pipelines then perform V(D)J gene segment alignment, clonotype clustering, and somatic hypermutation analysis to reconstruct the repertoire's composition, diversity metrics, and clonal expansion patterns.
Related Terms
Core concepts and technologies that intersect with high-throughput profiling of B-cell and T-cell receptor diversity for AI-driven antibody discovery.

About the author
Prasad Kumkar
CEO & MD, Inference Systems
Prasad Kumkar is the CEO & MD of Inference Systems and writes about AI systems architecture, LLM infrastructure, model serving, evaluation, and production deployment. Over 5+ years, he has worked across computer vision models, L5 autonomous vehicle systems, and LLM research, with a focus on taking complex AI ideas into real-world engineering systems.
His work and writing cover AI systems, large language models, AI agents, multimodal systems, autonomous systems, inference optimization, RAG, evaluation, and production AI engineering.
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