Liquid-Phase Capture AAV Integration Site Analysis

Liquid-Phase Capture AAV Integration Site Analysis

1. Background

The gene therapy field has witnessed rapid development in recent years. Adeno-associated virus (AAV) vectors have become the dominant delivery system for CRISPR-based gene editing and gene replacement therapies owing to their natural tissue tropism, low immunogenicity, and capacity for long-term transgene expression. As of 2023–2024, four AAV-based gene therapy products have received global marketing approval, with more than 650 clinical trials underway, signaling that AAV-based gene therapy has entered an accelerated phase of commercialization.[1]

Although AAV vectors are generally regarded as non-integrating, high-depth NGS analyses have revealed that approximately 0.1%–0.5% of AAV genomes can integrate into host DNA via non-canonical mechanisms. These low-frequency yet biologically significant genomic integration events may lead to insertional mutagenesis, disruption of transcriptional regulatory networks, or chromosomal structural rearrangements—representing a key long-term safety challenge that must be addressed in the field of gene therapy.[4]

In response to this safety concern, the regulatory landscape continues to evolve. Recent domestic regulatory developments include: in May 2022, the NMPA Technical Guidelines for Pharmacological Research and Evaluation of In Vivo Gene Therapy Products formally incorporated "integration site distribution trends and mutational risk assessment" as mandatory evaluation indicators; in July 2024, the NMPA-CDE Technical Guidelines for Non-Clinical Research of AAV Vector-Based Gene Therapy Products explicitly stated that "the genomic integration characteristics of AAV vector products may differ from wild-type AAV," requiring "systematic genomic integration analysis" to be conducted.[1,2]

Conventional integration site detection methods such as nrLAM-PCR and LM-PCR perform well for lentiviral and transposon vectors, but are not well suited for comprehensive detection of AAV integration sites due to the unique characteristics of the AAV integration mechanism, making it difficult to meet increasingly stringent regulatory requirements. To address this industry pain point, ZhuHai GeneRulor has developed a high-precision AAV integration site analysis technology based on liquid-phase hybrid capture, providing a reliable solution for the integration safety evaluation of AAV gene therapy products.

2. Principle of Liquid-Phase Hybrid Capture

The fundamental principle of liquid-phase hybrid capture detection technology is based on nucleic acid base complementary pairing. A panel of biotinylated capture probes designed to cover the full length of the AAV plasmid sequence is used to enrich and detect AAV integration events. When the AAV plasmid integrates into the host genome, it forms a chimeric DNA molecule containing both the exogenous plasmid sequence and the host genomic sequence at the integration site. After shearing the extracted genomic DNA into fragments, hybridization with the probes followed by streptavidin–magnetic bead capture enables specific enrichment of DNA fragments containing plasmid sequences.

The detection workflow is as follows: the DNA sample to be analyzed is first subjected to library construction including end repair, dA-tailing, and adapter ligation; full-length strand-specific probes are then custom-synthesized based on the AAV plasmid sequence provided by the client, and the library is hybridized with the probes followed by streptavidin–magnetic bead capture to enrich integration-positive fragments containing both plasmid and host genomic sequences; finally, integration site signals are amplified by PCR and a sequencing library is constructed. Compared to conventional methods that rely on ITR region-specific primers, the liquid-phase hybrid capture approach enables more comprehensive capture of all AAV integration events, significantly improving the accuracy, comprehensiveness, and sensitivity of AAV integration site detection.

Figure 1. Schematic Diagram of the Liquid-Phase Hybrid Capture Workflow for AAV Vector Integration Detection

3. Technical Innovations and Advantages of Liquid-Phase Hybrid Capture for AAV Vector Integration Site Detection

3.1 Core Technical Innovations

3.1.1 Full-Length Probe Design Strategy

Probes are designed based on the full-length AAV vector sequence. Compared to conventional methods:

Comprehensive coverage of ITR regions, transgene single-unit regions, and vector backbone regions, eliminating the detection blind spots of conventional methods;

Capability to detect all types and forms of integration events, including complete integrations and truncated integrations.

3.1.2 Liquid-Phase Hybrid Capture Efficient Enrichment

Optimized hybridization conditions and magnetic bead purification workflows are employed to build a highly efficient enrichment system:

Long-duration hybridization in a liquid-phase environment substantially improves probe sequence capture efficiency;

Stringent washing steps effectively remove non-specific binding, reducing background noise;

Supports parallel processing of multiple samples, improving throughput and experimental efficiency.

3.1.3 Multi-Dimensional Bioinformatic Analysis

A comprehensive professional bioinformatic analysis pipeline is integrated to achieve:

Precise characterization of the chromosomal coordinates and functional features of integration sites;

Genomic functional element annotation, oncogenic risk assessment, and multi-sample comparative analysis;

Multi-dimensional visualization of integration events, supporting in-depth interpretation.

3.2 Method Validation and Performance Metrics

ZhuHai GeneRulor has conducted a comprehensive systematic validation. Comparative validation results across WGS, nrLAM-PCR, LM-PCR, and liquid-phase hybrid capture demonstrate that liquid-phase hybrid capture performs optimally across all technical metrics:

4. Application Scenarios and Service Advantages

4.1 Application Scenarios

Liquid-phase hybrid capture technology has broad applications in AAV gene therapy product research, development, and regulatory processes:

AAV gene therapy product safety assessment: precise detection of integration site distribution of AAV vectors in in vivo or ex vivo settings, evaluation of insertional mutagenesis risk;

IND application support for gene therapy products: provision of integration site analysis and method validation reports compliant with regulatory requirements;

Pre-clinical research data support: assistance in evaluating integration characteristic differences among AAV vectors of different serotypes;

Clinical sample analysis: support for integration site detection in clinical trial samples, providing safety data;

Post-marketing surveillance: support for long-term post-marketing safety monitoring and evaluation of gene therapy products.

4.2 Service Advantages

Technical leadership: ZhuHai GeneRulor's proprietary liquid-phase hybrid capture technology overcomes the limitations of conventional methods, providing more accurate and comprehensive integration site analysis;

Certified quality management: the laboratory operates concurrently under an ISO 9001 quality management system and meets ISO/IEC 17025 testing and calibration laboratory competency accreditation standards, ensuring data reliability and complete traceability;

Comprehensive method validation: full method validation encompassing sensitivity, specificity, accuracy, and precision has been completed; validation reports can directly support IND submissions;

Standardized reporting system: integration site analysis reports conforming to the latest CDE and FDA guidance requirements, fully supporting drug review and regulatory inspection;

Extensive track record: ZhuHai GeneRulor has assisted numerous pioneering companies in completing AAV product integration safety assessments, accumulating rich project experience.

5. Liquid-Phase Hybrid Capture AAV Integration Site Analysis — Sample Report

ZhuHai GeneRulor provides comprehensive AAV integration site analysis reports that meet regulatory requirements, including detailed sequencing data quality assessment, per-sample sequencing depth statistics, reference genome alignment analysis, vector sequence variant analysis, and integration site count statistics as foundational information. In addition, the report includes the following core content:

(1) Integration Site Detection Results and Genomic Distribution Analysis: Precise chromosomal coordinates, gene annotations, reads support counts, and other detailed information are provided for each integration site. The system displays the chromosomal location of each detected integration site, the associated gene names, genomic functional regions (such as UTR5, intergenic, intronic, etc.), as well as the positional information of the exogenous sequence within the vector. Circos circular plots are simultaneously employed to intuitively visualize the distribution pattern of integration sites across chromosomes, enabling visualization of the association between the vector and host genome.

Figure 2. AAV Integration Site Detection Results by Liquid-Phase Hybrid Capture

(2) Vector–Host Junction Sequence Validation Analysis: The precise junction information between viral sequences and host genomic sequences at each integration site is displayed in detail. The exogenous sequence fragment and corresponding host sequence fragment at each integration site are provided, enabling authenticity and accuracy verification of integration events through sequence alignment, furnishing critical sequence-level evidence for molecular mechanism analysis and safety assessment of integration sites.

Figure 3. Vector–Host Junction Sequence Validation Results for AAV Integration Sites Detected by Liquid-Phase Hybrid Capture

(3) Oncogene Annotation: Integration events associated with tumor-related genes are screened based on ONCOGENE and TSG databases, with integration sites related to proto-oncogenes and tumor suppressor genes specifically highlighted and labeled, and safety risk assessment provided.

Figure 4. Oncogene Risk Assessment Annotation Table for AAV Integration Sites Detected by Liquid-Phase Hybrid Capture

(4) Integration Site Diversity Analysis: Statistical indices including Chao Index, Shannon Index, and Pielou's Index are employed to quantitatively assess integration site distribution characteristics, identify integration hotspots and clonal dominance phenomena, and evaluate the randomness of AAV vector integration.

Figure 5. Integration Site Diversity Statistical Analysis Table for AAV Integration Sites Detected by Liquid-Phase Hybrid Capture

(5) Gene Functional Analysis: GO functional enrichment and KEGG pathway analysis are performed on genes harboring integration events, evaluating the potential impact of integration events on cellular biological processes and signaling pathways, and providing scientific evidence for risk control strategies.

Figure 6. GO and KEGG Pathway Enrichment Analysis (Example)

6. Liquid-Phase Hybrid Capture AAV Integration Site Detection Service Contents

*Standard service turnaround: 20–30 business days

7. Sample Requirements

*Notes: ① All samples must comply with the above standards to ensure the accuracy and reliability of detection results; ② Clients may also submit tissue or cell samples for DNA extraction, with a tissue requirement of > 50 mg and a cell requirement of > 2×10⁷ cells per site; ③ For special sample types, please contact ZhuHai GeneRulor's technical team in advance (Tel: 400-6309596; Product Orders/Technical Support: service@generulor.com).

8. References

[1] Center for Drug Evaluation, NMPA. (2022). Technical Guidelines for Pharmacological Research and Evaluation of In Vivo Gene Therapy Products (Trial). Center for Drug Evaluation, NMPA.

[2] Center for Drug Evaluation, NMPA. (2024). Technical Guidelines for Non-Clinical Research of AAV Vector-Based Gene Therapy Products. Center for Drug Evaluation, NMPA.

[3] Center for Drug Evaluation, NMPA. (2024). Technical Guidelines for Non-Clinical Research of AAV Vector-Based Gene Therapy Products (Draft for Comment). Center for Drug Evaluation, NMPA.

[4] Bijlani, S., et al. (2022). The role of recombinant AAV in precise genome editing. Frontiers in Genome Editing, 3, 799722.

[5] Corre, G., et al. (2023). Evaluation of diversity indices to estimate clonal dominance in gene therapy studies. Molecular Therapy Methods & Clinical Development, 29, 418–425.