TCR 5'RACE Full-Length Sequencing

TCR 5'RACE Full-Length Sequencing

1. Background

T cell receptors (TCRs) generate enormous clonotypic diversity through the random recombination of V(D)J gene segments combined with nucleotide insertions and deletions at the junctional regions, forming the molecular basis by which adaptive immunity recognizes tumor antigens, pathogens, and self-antigens. The complete V(D)J sequence of the TCR α/β chain carries all the information that defines clonal recognition specificity—including the CDR3 that determines antigen recognition, the CDR1/CDR2 that mediate auxiliary contacts, and the framework regions (FR1–FR4). It is therefore an indispensable data foundation for high-resolution immune repertoire profiling, antigen-specific clone discovery, and TCR engineering.

The RNA-based 5'RACE (Rapid Amplification of cDNA Ends) strategy employs SMART template switching to introduce a universal adapter at the 5' end of the cDNA, enabling a single primer pair to amplify the full-length variable region across all V gene families. This fundamentally avoids the amplification bias arising from efficiency differences among the dozens to hundreds of V/J primers used in multiplex PCR systems. In combination with unique molecular identifiers (UMIs), it enables PCR-duplicate removal and sequencing-error correction, bringing clonal-abundance quantification closer to true molecular counts.

At the regulatory and industry level, the FDA's Hematologic Malignancies: Regulatory Considerations for Use of Minimal Residual Disease in Development of Drug and Biological Products for Treatment (2020) lists NGS-based Ig/TCR rearrangement detection as one of the accepted methods for MRD assessment; the FDA's Considerations for the Development of CAR T Cell Products (2024) and Long-Term Follow-Up After Administration of Human Gene Therapy Products (2020) set explicit requirements regarding the clonal composition, delayed risks, and long-term follow-up of TCR-T/CAR-T therapies; and China's CDE Technical Guidelines for the Pharmaceutical Research and Evaluation of Immune Cell Therapy Products (Trial) (Announcement No. 30, 2022) likewise emphasizes TCR repertoire characterization. Building on the BIOMED-2 primer system, the EuroClonality-NGS consortium has established a standardized protocol for NGS-based TR rearrangement analysis. The RNA-based full-length V(D)J + UMI approach provides high-resolution, reproducible clonotype data to support all of the above.

ZhuHai GeneRulor offers an end-to-end service spanning sample QC, cDNA synthesis and library construction, high-throughput sequencing, and systematic immune repertoire bioinformatics, helping customers precisely characterize TCR clonal dynamics and functional evolution trajectories at full-length resolution.

2. Technical Principle

This service is based on SMART template switching and the 5'RACE strategy. Starting from total RNA, full-length TCR V(D)J sequences are enriched by semi-nested PCR, with a 12-nt UMI introduced early in library construction to enable single-molecule quantification. The core steps are as follows:

（1）RNA Input and Reverse Transcription

Using high-quality total RNA (RIN ≥ 7) as the template, oligo-dT-primed reverse transcription synthesizes first-strand cDNA, capturing poly(A)-tailed TCR transcripts.

（2）SMART Template Switching and UMI Incorporation

Template switching occurs at the 5' end of the cDNA during reverse transcription, introducing a universal adapter sequence containing a 12-nt UMI. Each original mRNA molecule thereby acquires a unique molecular tag, laying the foundation for downstream deduplication and error correction.

（3）Semi-nested PCR Enrichment and Indexing

PCR1 performs selective amplification using the universal 5' adapter together with a TCR constant-region–specific primer; PCR2 adds dual-index (UDI) sample barcodes and Illumina sequencing adapters at both ends, generating a full-length library of approximately 600–900 bp.

（4）High-throughput Sequencing and Data Analysis

Illumina 2×300 bp paired-end sequencing covers the full-length V(D)J. Following UMI deduplication, error correction, and IMGT/MiXCR alignment, TCR α/β clonotype reconstruction, clonal-frequency quantification, and multidimensional systematic immune repertoire analysis are performed (see Section 5).

Figure 1. Workflow of TCR 5'RACE Full-Length Sequencing

3. Technical Features and Advantages

（1）Unbiased Full-length Amplification

A single primer pair covers all TRAV/TRBV gene families, fundamentally eliminating the primer bias inherent to multiplex PCR and bringing clonal abundance closer to true molecular proportions. It fully covers all variable regions (FR1–FR4 + CDR1–CDR3), outperforming short-fragment approaches that cover only CDR3.

（2）Precise UMI-based Quantification and Error Correction

The 12-nt UMI provides approximately 17 million molecular-tag combinations, systematically correcting PCR amplification bias and sequencing errors. This prevents erroneous reads from being misinterpreted as novel clones—which would artificially inflate diversity—and achieves precise quantification based on original molecule counts.

（3）Optional α/β Chain Detection

TCRα and TCRβ can be detected separately or simultaneously, flexibly accommodating different research objectives. For native α–β pairing at single-cell resolution, a single-cell TCR sequencing solution is available.

（4）Low-input Friendly

Supports starting inputs as low as 10 ng of PBL total RNA and is applicable to diverse sample types, including peripheral blood, tissue, and sorted T cells, making it feasible even for precious samples.

（5）Standardized Analysis Pipeline

A standardized pipeline has been established—from raw-data QC, UMI deduplication, and clonotype reconstruction (MiXCR/IMGT) through diversity-index calculation, clonal-dynamics tracking, and visualization output—ensuring comparability across samples and batches. Raw FASTQ files are delivered in full, supporting secondary in-depth mining.

Scope of application: This service uses RNA as the starting template and requires high-quality total RNA with RIN ≥ 7. It is not suitable for FFPE samples, pure gDNA, or severely degraded RNA. For gDNA or FFPE samples, a TCR multiplex PCR sequencing solution is recommended.

4. Applications

Tumor Immunology and Cell Therapy: Monitoring T cell clonal dynamics before and after infusion of adoptive cell therapy products such as CAR-T/TCR-T, assessing expansion persistence, and profiling the accompanying T cell clonal composition—supporting product characterization and long-term follow-up studies.

Antigen-specific T cell Research: Combined with strategies such as tetramer (multimer) enrichment and TCR-stimulated expansion, full-length resolution of the TCR α/β sequences of antigen-specific T cell clones provides complete variable-region information for TCR-T candidate clone screening.

Autoimmunity and Infectious Immunity: Identifying and tracking pathogenic or protective T cell clones, resolving disease-associated TCR motifs and public clones, and supporting vaccine immunogenicity assessment and the dynamic characterization of immune responses.

Transplant Immunology and Immune Reconstitution: Resolving changes in the T cell repertoire before and after hematopoietic stem cell transplantation or organ transplantation, and monitoring rejection-associated clonal expansion and immune reconstitution trajectories.

Longitudinal Tracking of Clonal Dynamics: Precise quantitative comparison of clonal expansion/contraction dynamics and shared clones across samples collected before and after treatment, at different time points, or from different tissue sources.

5. Report and Deliverables

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

·Sequencing data QC and UMI deduplication statistics (read quality, mapping rate, UMI distribution, effective molecule counts)

·Clonotype identification and quantification (UMI-corrected TCR α/β clonotype tables and frequency distributions)

·Clonal diversity and clonality metrics (Shannon entropy, Simpson index, Chao1, Gini coefficient, etc.)

·V/D/J gene usage frequency analysis (TRAV/TRAJ, TRBV/TRBD/TRBJ frequencies and gene-pairing patterns)

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

·Top dominant clone ranking and complete clonotype sequence information

·Inter-sample shared-clone analysis and time-course clonal-dynamics tracking (for multi-sample projects)

·(Optional) Comparison of public clones against databases such as IMGT, plus customized visualization analysis

Deliverables: An illustrated analysis report (PDF) + a detailed clonotype information table (Excel/CSV, including V/D/J gene annotation, CDR3 nucleotide/amino acid sequences, UMI counts, and clonal frequencies) + raw sequencing data (FASTQ).

Figure 2. Schematic of Multidimensional TCR Immune Repertoire Analysis Results

6. Service Workflow

7. Sample Requirements

*Note: RNA must be dissolved in nuclease-free water and must not contain poly(A) carrier; do not use heparin as an anticoagulant during blood collection; cells should be washed ≥ 2 times with Ca²⁺/Mg²⁺-free PBS, and fixed cells must not be used; avoid repeated freeze-thaw cycles, and submit 2–3× the required amount; ship frozen on dry ice throughout transport. Specific requirements are subject to the latest Sample Submission Form; please schedule and confirm the plan before shipping. This service is not suitable for FFPE samples, pure gDNA, or severely degraded RNA.

8. Technical Specifications

9. References

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

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

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

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

[5] Knecht H, et al. Quality control and quantification in IG/TR next-generation sequencing marker identification: protocols and bioinformatic functionalities by EuroClonality-NGS. Leukemia. 2019.