Single-Cell BCR Immune Repertoire Sequencing

Single-Cell BCR Immune Repertoire Sequencing

1. Background

B cell receptor (BCR) diversity is the molecular foundation of humoral immune responses. Its clonal composition, subtype distribution, affinity maturation status, and relationship with tumor immunology, autoimmune diseases, infectious diseases, and antibody drug research are of great significance. Antibodies are composed of heavy chains (IgH) paired with light chains (IgK/IgL). While conventional bulk BCR sequencing can characterize heavy- or light-chain clonal repertoires separately, it cannot determine the native heavy-light chain pairing within the same B cell, nor directly link clonotype to single-cell phenotype — limiting in-depth analysis of B cell functional heterogeneity and antibody discovery.

Single-cell BCR sequencing (single-cell BCR sequencing) is based on droplet microfluidics or microwell single-cell platforms. At single-cell resolution, each B cell is tagged with a unique cell barcode and UMI, enabling native-paired full-length V(D)J sequence capture of BCR heavy chains (IgH V-D-J rearrangement) and light chains (IgK/IgL V-J rearrangement), along with simultaneous profiling of antibody isotypes (IgM/IgG/IgA/IgD/IgE) and somatic hypermutation (SHM). Combined with single-cell transcriptome sequencing (scRNA-seq) on the same platform, clonotype information can be directly linked to cell phenotype, functional state, and differentiation trajectory, offering unprecedented resolution for B cell immune research.

In the cutting-edge fields of antibody drug development and cell therapy, the value of single-cell BCR sequencing has been widely recognized. The FDA Considerations for the Development of CAR T Cell Products (2024) and China's CDE Technical Guidelines for Pharmaceutical Research and Evaluation of Immune Cell Therapy Products (Trial) (Announcement No. 30 of 2022) have set explicit requirements for clonal composition and receptor chain pairing characterization of cell therapy products. The FDA Long-Term Follow-Up After Administration of Human Gene Therapy Products (2020) also emphasizes refined monitoring of risks such as clonal expansion. Native VH-VL paired sequences can directly serve as the starting sequences for therapeutic antibody discovery, making them an essential tool in antibody drug R&D.

ZhuHai GeneRulor provides end-to-end services — from sample QC, single-cell capture and library construction, high-throughput sequencing, to systematic bioinformatics analysis — empowering clients to precisely resolve B cell clonal dynamics, subtype differentiation, and antibody sequence information at single-cell resolution.

2. Technical Principle

Single-cell BCR sequencing is based on a 5′ V(D)J capture strategy. Through droplet microfluidics or microwell single-cell platforms, it achieves high-efficiency amplification and native-paired sequencing of full-length BCR V(D)J sequences at the single-cell level. The technical workflow consists of the following core steps:

（1）Single-Cell Suspension Preparation and Capture

A highly viable single-cell suspension is prepared and individual B cells are captured via droplet or microwell platforms. Each cell is loaded with a unique cell barcode and UMI, ensuring downstream deduplication and precise single-cell traceability.

（2）Reverse Transcription and V(D)J Targeted Library Construction

Reverse transcription is performed using a 5′ template-switching strategy, followed by targeted enrichment of BCR V(D)J sequences — covering full-length variable regions of both heavy chains (IgH V-D-J) and light chains (IgK/IgL V-J), with simultaneous profiling of antibody isotype information and SHM sites. An scRNA-seq library can be co-constructed to enable simultaneous capture of clonotype and transcriptome data. Library preparation is completed following indexing.

（3）High-Throughput Sequencing and Data Analysis

Sequencing is performed on the Illumina platform. After quality filtering, UMI deduplication, and VDJ alignment (against the IMGT database), BCR heavy/light chain sequence reconstruction and clonotype annotation are completed. The native-paired BCR information for each cell is output, and isotype distribution, SHM frequency, and clonal lineage relationships are analyzed, followed by systematic multi-dimensional immune repertoire analysis (see Section 5 for details).

Figure 1. Single-Cell BCR Sequencing Technical Workflow

3. Technical Features and Advantages

（1）Native VH-VL Pairing

At single-cell resolution, the native-paired heavy- and light-chain sequences of each B cell are accurately captured, overcoming the fundamental limitation of bulk BCR-seq in determining heavy-light chain native pairing, and providing a precise molecular foundation for antibody specificity validation, functional studies, and engineering optimization.

（2）Full-Length V(D)J Sequence Coverage

Complete coverage of the BCR variable region (IgH V-D-J, IgK/IgL V-J), including full CDR1–CDR3 information, with simultaneous capture of antibody isotypes (IgM/IgG/IgA, etc.) and somatic hypermutation (SHM) data. This is superior to short-read CDR3-only approaches, facilitating sequence reconstruction, database alignment, and downstream functional validation.

（3）Clonal Lineage and Affinity Maturation Analysis

Clonal family phylogenetic trees are reconstructed at single-cell resolution to trace mutation accumulation and affinity maturation processes in clonally related cells, revealing clonal evolution patterns and class-switching pathways of B cells during immune responses.

（4）Integrated Clonotype–Phenotype Analysis

Compatible with simultaneous scRNA-seq library analysis on the same platform, BCR clonotype information is directly mapped to cell phenotypes (e.g., naïve B cells, memory B cells, plasma cell subsets), enabling multi-dimensional integrated analysis of "clonotype–subtype–phenotype–function."

（5）High-Resolution Clonal Dynamic Tracking

With UMI correction and single-cell-level resolution, quantitative comparison of clonal expansion dynamics across different time points and tissue sources is supported, suitable for longitudinal analysis of clonal changes before and after treatment and during immune responses.

（6）Standardized Analysis Workflow with Reproducible Results

A standardized pipeline covering upstream data processing (Cell Ranger VDJ) through downstream immune repertoire analysis (scRepertoire and other mainstream tools) is established, with unified diversity index calculation methods and visualization output standards to ensure cross-sample and cross-batch comparability.

Scope of Application: This service requires highly viable single-cell suspensions (viability ≥80%, fresh or properly cryopreserved). It is not suitable for FFPE samples, degraded RNA, genomic DNA (gDNA), or fixed cells. Throughput ranges from several thousand to tens of thousands of cells per sample; rare clonotype detection depends on the number of cells loaded. For large-scale, cost-effective comprehensive BCR repertoire profiling without single-cell pairing, Bulk BCR-seq is recommended. For unbiased repertoire diversity analysis without single-cell pairing, the BCR 5′RACE full-length sequencing approach may be considered.

4. Application Scenarios

Antibody Drug Discovery: Native-paired VH-VL sequences obtained at single-cell resolution serve directly as starting sequences for therapeutic/neutralizing antibody clones and expression validation, representing a core data source for antibody drug R&D.

Vaccine Immune Response Research: Profiling the expansion patterns, affinity maturation trajectories, and isotype switching of antigen-specific B cell clones following immunization or infection, to assist in neutralizing antibody clone identification and vaccine immunomechanism research.

B Cell Tumor Analysis: Combined with transcriptome data, analyzing the correspondence between clonal expansion degree and functional states (activation, exhaustion, regulatory subsets) of tumor-infiltrating B cells (TIL-B), to support tumor immune microenvironment and immune checkpoint therapy mechanism exploration.

Autoimmune and Infectious Disease Immunology Research: Characterizing the expansion patterns and disease-specific BCR sequences of disease-associated B cell clones, supporting pathogenic clone identification and vaccine/therapeutic response assessment.

Cell Therapy Product Characterization (Research): For B cell-directed CAR-T and other cell therapy products, confirming the chain-pairing integrity of sequences introduced into recipient cells at single-cell resolution, profiling co-introduced B cell clonal composition and phenotype distribution, and supporting the establishment of regulatory-compliant product characterization datasets.

Clonal Monitoring and Long-Term Follow-Up: In long-term follow-up settings following cell therapy or gene therapy product administration, tracking dynamic changes in specific B cell clones to provide refined data for clonal expansion risk assessment.

5. Reports and Deliverables

The report covers the complete content from sequencing quality control to systematic immune repertoire analysis. Core analysis modules include:

· Sequencing quality control and cell filtering statistics (UMI distribution, valid cell count, heavy/light chain pairing rate)

· Paired clonotype (VH-VL) identification, enumeration, and frequency statistics

· Clonal diversity indices (Shannon entropy, Gini coefficient, clonal expansion index, etc.)

· V/D/J gene usage frequency analysis (frequency distribution and gene combination patterns)

· CDR3 sequence characterization (length distribution, amino acid composition, and sequence motifs)

· Antibody isotype distribution (IgM/IgG/IgA/IgD/IgE) and class-switching analysis

· Somatic hypermutation (SHM) frequency distribution and hotspot analysis

· Clonal lineage tree construction (phylogenetic relationships and mutation accumulation among clonally related cells)

· Clonal expansion landscape, top highly expanded clone list, and sequence information

· Inter-sample shared clone analysis and longitudinal clone tracking (applicable for multi-sample studies)

· (Optional) Clonotype–phenotype integrated analysis: integration with scRNA-seq data, overlaying clonotype information onto cell subset UMAP projections

· (Optional) Candidate antibody sequence output: paired VH-VL sequence list for downstream antibody clone expression and validation

Deliverables: Graphical analysis report (PDF) + clonotype detail table (Excel/CSV, containing native-paired BCR sequences, V/D/J gene annotations, isotype, SHM frequency, and clonal frequency for each cell) + raw sequencing data (FASTQ).

Figure 2. Overview of Representative Analysis Output Examples

6. Service Workflow

*Service turnaround: Standard workflow 25–30 business days

7. Sample Requirements

*Note: Specific viability requirements, target cell counts, and shipping requirements are subject to the latest Sample Submission Form. Live cell samples are time-sensitive — please schedule in advance and confirm the protocol. If concurrent flow cytometry sorting, antigen-specific enrichment, or cell stimulation pre-processing is required, flexible combinations can be arranged based on project needs.

8. References

[1] U.S. Food and Drug Administration. Considerations for the Development of CAR T Cell Products; Draft Guidance. 2024.

[2] National Medical Products Administration, Center for Drug Evaluation. Technical Guidelines for Pharmaceutical Research and Evaluation of Immune Cell Therapy Products (Trial). Announcement No. 30, 2022.

[3] U.S. Food and Drug Administration. Long-Term Follow-Up After Administration of Human Gene Therapy Products; Guidance for Industry. 2020.

[4] U.S. Food and Drug Administration. Hematological Malignancies: Regulatory Considerations for Use of Minimal Residual Disease in Development of Drug and Biological Products for Treatment; Guidance for Industry. 2020.