Background:
T-cell lymphomas account for approximately 15% of non-Hodgkin lymphomas and may pose a diagnostic challenge on the basis of histopathology alone and particularly in early stages of disease. The heterodimeric T-cell surface receptors, either alpha/beta (90% -95% of T cells) or gamma/delta (5% - 10% of T cells) are produced following somatic rearrangement of the T-cell receptor (TCR) genes (alpha, beta, delta, and gamma). This process is vital to proliferation of T-cells in normal immune function, but can be exploited to aid in the distinction between reactive (benign) versus neoplastic processes of T-cell proliferation. A reactive, benign T-cell proliferation is characterized by polyclonal expansion of T-cells whereas a malignant process is characterized by clonal expansion of one T-cell population. In conjunction with morphologic evaluation of lymph nodes, bone marrow and other tissue types the detection of a clonal T-cell gene rearrangement by polymerase chain reaction (PCR) can be used to aid a diagnosis of malignant T-cell lymphoma.
Clinical Utility:
PCR-based detection of rearranged T-cell receptor genes can be used to help establish a diagnosis of T-cell lymphoma, monitor for treatment response, and/or measure minimal residual disease (MRD).
Methodology:
For T-cell receptor gamma targets, extracted genomic DNA from blood, lymph node, bone marrow, or other tissue types are PCR amplified and subjected to next generation sequencing (NGS) library preparation with a combination of heterogeneous TCR-gamma V(variable) region and J-(joining) region primers to generate TCR-gamma receptor VJ-rearranged templates, which are then subjected to next-generation sequencing on a MiSeq instrument. The number and frequency of NGS sequencing reads from these rearranged VJ segment are then analyzed to assess the possible presence of a predominating clonal T-cell population. The analytical sensitivity limit for detecting low level T-cell clones with this NGS based method is approximately 6%. Clonal lymphocyte populations below this sensitivity threshold will not be detected. In addition, due to the great diversity of immune cell antigen receptor recombination breakpoints, only ~85% of all clonal T-cell populations will be identified with the primers utilized in this assay.
Clinical Sensitivity:
Approximately 85%
Clinical Specificity:
As cross-lineage TCR gene rearrangements have been reported in immature B-cell malignancies, interpretation of this test requires clinical, morphologic, and immunophenotypic correlation.
Specimen Requirements:
- 5-10 mL of blood or bone marrow — yellow (ACD) or purple (EDTA) tube. Store and ship refrigerated.
- Formalin-fixed paraffin-embedded (FFPE) tissue blocks or minimum 15 slides (5 microns). Store and ship at room temperature.
- Pathology report MUST accompany sample for interpretation of results.
DNA: 200g at a minimum of 10ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)
A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information.
Test Performed (Days):
Once per week
Turn Around Time:
7-10 days
Shipment Sensitivity Requirements:
- Keep specimen cold during transit, but do not ship on dry ice.
- Please use the cold pack provided in the KDL shipping kit.
- Ship the specimen overnight express, using the FedEx priority overnight label provided.
References:
- Van Dongen JJ, Langerak AW, Bruggemann M, et al. Design and standardization of PCR primers and protocols for detection of clonal immunoglobulin and T-cell receptor gene recombinations in suspect lymphoproliferations: report of the BIOMED-2 Concerted Action BMH4-CT98-3936. Leukemia 2003; 17(12):2257-2317.
- Langerak AW, Molina TJ, Lavender FL, et al. Polymerase chain reaction-based clonality testing in tissue samples with reactive lymphoproliferations: usefulness and pitfalls. Report of the BIOMED-2 Concerted Action BMH4-CT98-3936. Leukemia 2007; 21:222-229.
Additional Info: