Characterization of the Immunoglobulin Heavy- and Light-Chain Repertoires in a Single Reaction

Background

B cell repertoire analysis by next-generation sequencing (NGS) has shown particular utility in the field of hematological oncology research. Some advantages provided by NGS-based techniques include a lower limit-of-detection and simpler paths to standardization compared to flow-based methods, and the elimination of specifically designed primers often required for qPCR-based methods. Owing to primer-primer interactions and incompatibility of reaction conditions, current multiplex PCR assays require separate PCR reactions to survey each immunoglobulin chain (IGH, IGK, IGL), often leading to a longer time-to-answer for samples in which no marker is initially detected. We have developed an assay for receptor analysis based on Ion AmpliSeq technology to circumvent these issues, allowing the effective use of up to thousands of primers in a single reaction. The highly multiplexed, pan-clonality NGS assay provides for efficient detection of IGH, IGK, and IGL chain rearrangements in a single reaction.

Methods

We developed a single primer panel targeting the framework 3 (FR3) portion of the variable gene and the joining gene region of heavy- and light-chain loci (IGH, IGK, IGL) for all alleles found within the IMGT database, enabling readout of the complementary-determining region 3 (CDR3) sequence of each immunoglobulin chain. To maximize sensitivity, we included primers to amplify IGK loci rearrangements involving Kappa deletion and C intron elements. To evaluate performance, we conducted clonality assessment and limit-of-detection testing used gDNA from a total of 45 research samples representing common B cell malignancies. We included samples derived from peripheral blood, bone marrow, and FFPE-preserved tissues at input levels ranging from 100ng to 2µg. Finally, we further characterized the samples via a separate AmpliSeq-based multiplex PCR assay targeting rearranged TCRB and TCRG chains. Sequencing and clonality analysis was performed using the Ion GeneStudio S5 System and Ion Reporter 5.16.

Results

Clonality assessments carried out using gDNA collected from both cell line and clinical research samples (CLL, B-ALL, Multiple Myeloma, Burkitt's Lymphoma, NHL, and DLBCL) show a >90% overall positive detection rate. Assessment of linearity-of-response and limit-of-detection was carried out using cell lines diluted in PBL to between 10^-3 and 10^-6 by mass. The multi-receptor assay performs as expected, with linear response to the cell line frequency across the range tested, including the ability to detect clones of interest at 10^-6.

Conclusions

These results demonstrate the robustness of our newly developed Ion AmpliSeq-assay for B cell receptor heavy and light chains. We expect this assay to simplify the workflow for clonality assessment and rare clone detection in B cell malignancy research.

For research use only.