LymphoTrack^® IGK Assay - S5/PGM™

Product Details

• Summary and Explanation of the Test

  The human immunoglobulin kappa light chain (IGK) gene locus on chromosome 2 (2p11.2) includes many distinct Vϰ gene segments, grouped into seven Vϰ gene families as well as five Jϰ gene segments upstream of the Cϰ region.  The kappa deleting element (K_de), approximately 24 kb downstream of the Jϰ-Cϰ region can rearrange to Vϰ gene segments (Vϰ-K_de) but also to an isolated RSS in the Jϰ-Cϰ intron (INTR).  The resulting Vϰ-K_de and INTR-K_de rearrangements are a product of unsuccessful rearrangements retained by the B-cell.¹

  Lymphoid cells are different from the other somatic cells in the body.  During development, the antigen receptor genes in lymphoid cells undergo somatic gene rearrangement.²  For example, during B-cell development, genes encoding the IGK locus are assembled from multiple polymorphic gene segments that undergo rearrangements and selection, generating combinations that are unique in both length and sequence.  Since leukemias and lymphomas originate from the malignant transformation of individual lymphoid cells, all leukemias and lymphomas generally share one or more cell-specific or “clonal” antigen receptor gene rearrangements.  Therefore, tests that detect IGK clonal rearrangements can be useful in the study of B-cell malignancies.

  Initially, clonal rearrangements were identified using Restriction Fragment, Southern Blot Hybridization (RF-SBH) techniques.  However, these tests proved cumbersome, labor-intensive, required large amounts of DNA, and were not suitable for analysis of many of the less diverse antigen receptor loci.  During the last several decades, the use of RF-SBH assays has been supplanted by PCR-based clonality tests developed by Alexander Morley and are considered the current gold standard method. PCR-based assays identify clonality on the basis of over-representation of amplified V-J or D-J products following their separation using gel or capillary electrophoresis.³  Though sensitive and suitable for testing small amounts of DNA, these assays cannot readily differentiate between clonal populations and multiple rearrangements that might lie beneath a single-sized peak, and are also not designed to identify the specific V-J DNA sequence that is required to track clonal populations in subsequent analyses.  This second limitation can be of particular importance, as once the unique clone-specific DNA sequence is identified, this sequence can be used in subsequent tests to track and follow these clonal cell populations.

  This LymphoTrack IGK Assay – S5/PGM represents a significant improvement over existing clonality assays using fragment analysis as it efficiently detects the majority of IGK gene rearrangements using a single multiplex master mix.  At the same time, the assay identifies the DNA sequence specific for each clonal gene rearrangement.  Therefore, this assay has two important and complementary uses: it aids both in the detection of initial clonal populations, and it identifies sequence information required to track those clones in subsequent samples.

  Our single multiplex master mix for IGK targets the Vϰ-Jϰ, the Vϰ-K_de, and the INTR-K_de gene rearrangements described in lymphoid malignancies.  Primers included in the master mixes are designed with Thermo Fisher Scientific adapters and 12 different indices.  This assay allows for a one-step PCR reaction and pooling of amplicons from several different samples and targets (generated with other LymphoTrack Assays for the S5 or PGM, not included), onto one Ion S5 or PGM chip allowing for up to 12 samples per target to be analyzed in parallel in a single run.

  The associated LymphoTrack Software – S5/PGM provides a simple and streamlined method of analysis and visualization of data.

  Positive and negative controls for clonality are included in the kit.

  Note:  For a more thorough explanation of the locus and the targeted deep sequencing strategy, please refer to Principle of Immunoglobulin and B-Cell Receptor Gene Rearrangement.⁴

• Principles of the Procedure

  Polymerase Chain Reaction (PCR)

  PCR assays are routinely used for the identification of clonal B- and T-cell populations.  These assays amplify the DNA between primers that target the conserved framework (FR) of the V_H regions and the conserved J_H regions of antigen receptor genes.  Primers target these conserved regions which lie on either side of an area where programmed genetic rearrangements occur during the maturation of all B and T lymphocytes.  Different populations of the B and T lymphocytes arise as a result of these genetic rearrangements.

  The antigen receptor genes that undergo rearrangements are the immunoglobulin heavy chain (IGH) and light chains (IGK and IGL) in B-cells, and the T-cell receptor genes (TRA, TRB, TRG, and TRD) in T-cells.  Each B- and T-cell has a single productive V – J rearrangement that is unique in both length and sequence.  Therefore, when DNA from a normal or polyclonal population is amplified using DNA primers that flank the V-J region, amplicons that are unique in both sequence and length are generated, reflecting the heterogeneous population. In some cases, where lymphocyte DNA is not present, no amplicons will be generated. Samples containing TRG clonal populations yield  one or two prominent amplified products of the same length and sequence that are detected with significant frequency of occurrence, within a diminished polyclonal background amplified at a lower frequency.

  Amplicon Purification

  PCR amplicons are purified to remove excess primers, nucleotides, salts, and enzymes using the Agencourt^® AMPure^® XP system.  This method utilizes solid-phase reversible immobilization (SPRI) paramagnetic bead technology for high-throughput purification of PCR amplicons.  Using an optimized buffer, PCR amplicons that are 100 bp or larger are selectively bound to paramagnetic beads while contaminants such as excess primers, primer dimers, salts, and unincorporated dNTPs are washed away.  Amplicons can then be eluted and separated from the paramagnetic beads resulting in a more purified PCR product for downstream analysis and amplicon quantification.

  Amplicon Quantification

  Purified amplicons are quantified utilizing the Agilent Technologies 2100 Bioanalyzer or the Perkin Elmer LabChip^® GX.  These are electrophoretic methods that utilize the principles of traditional gel electrophoresis to separate and quantify DNA on a chip based platform.  Quantification is achieved by running a marker of known concentration alongside PCR amplicons and then extrapolating the concentration of the amplicons.  Calculating the concentration of PCR amplicons allows equal amplicon representation in the final pooled library that is loaded onto the Ion S5 or PGM for sequencing.

  Next-Generation Sequencing (NGS)

  Sanger sequencing methods represent the most popular in a range of ‘first-generation’ nucleic acid sequencing technologies.  Newer methods, which leverage massively parallel sequencing approaches, are often referred to as Next-Generation Sequencing (NGS).  NGS technologies can use various combination strategies of template preparation, sequencing, imaging, and bioinformatics for genome alignment and assembly.

  NGS technologies used in this product rely on the amplification of genetic sequences using a series of consensus forward and reverse primers that include adapter and index tags.  Amplicons generated with LymphoTrack master mixes are quantified, pooled, and loaded onto a chip for sequencing with a Thermo Fisher Scientific Ion S5 or Ion PGM platform.  The Ion PGM requires that the pooled library of DNA fragments be bound to individual beads prior to sequencing, (one unique sequence per bead) through a process known as emulsion PCR.  Once bound to the beads the DNA fragments are amplified until they cover the surface of the bead.  Beads are then loaded onto a semi-conductor chip, where they find their own well to occupy and where sequencing occurs.  Sequencing is conducted by flooding the chip with individual unincorporated nucleotides one base at a time (dATP, dCTP, dGTP, dTTP).  The Ion S5 or PGM instrument detects the addition of nucleotides when hydrogen ions are released during DNA polymerization and causes a change in pH of the wells, which can be measured as a change in voltage.  The voltage changes proportionally to the number of nucleotides added.  After nucleotides are incorporated, unincorporated nucleotides are washed away and the process begins again with a new dNTP.

  Multiplexing Amplicons

  These products were designed to allow for two different levels of multiplexing in order to reduce costs and time for laboratories.  The first level of multiplexing originates from the multiple indices that are provided with the assays, up to 12.  Each of these 12 indices can be considered to act as a unique barcode that allows amplicons from individual samples to be pooled together after PCR amplification to generate the sequencing library.  Later, the resulting sequences can be sorted by the bioinformatics software to identify those that originated from an individual sample.

  The second level of multiplexing originates from the ability of the accompanying software to sort sequencing data by both index and target.  This allows amplicons generated with targeted primers (even those tagged with the same index) to be pooled together to generate the library to be sequenced on a single sequencing chip.  An example would be to sequence products from several Invivoscribe LymphoTrack kits for the Ion S5 or PGM such as IGH FR1, IGH FR2, IGH FR3, IGK, and TRG together.  When multiplexing amplicons of different gene targets it is important to use the appropriate sequencing chemistry.  The number of sequencing cycles must be sufficient to sequence the largest amplicon in the multiplex.

  The number of samples that can be multiplexed onto a single sequencing chip is also dependent on the chip that is utilized.  Thermo Fisher Scientific Ion 316™ Chip v2 can generate 2-3 million reads so it is recommended to multiplex no more than three different gene targets together.  Up to five different gene targets can be multiplexed together on the Ion PGM Ion 318™ Chip v2 BC (4-5.5 million reads), Ion S5 Ion 520™Chip (3-6 million reads) and Ion S5 Ion 530™ Chip (15-20 million reads).  To determine the number of reads per sample, the total number of reads for the sequencing chip is divided by the number of samples that are multiplexed.

  Minimal Residual Disease Evaluation

  NGS-based minimal residual disease (MRD) testing is a proven tool that aids in the development of treatment strategies for hematologic malignancies.  The LymphoTrack Clonality Assays can be used with the LymphoTrack MRD Software (Catalog # 75000008) to objectively track up to five clonal rearrangements in longitudinal studies with up to 10^-6 sensitivity.  For more information on our bundled MRD solution email marketing@invivoscribe.com or visit www.invivoscribe.com/mrd-clonality.

• Specimen Requirements

  This RUO assay tests genomic DNA.  The minimum input quantity is 50 ng of high quality DNA.