Conventional PCR-based versus next-generation sequencing-based approach for T-cell receptor γ gene clonality...

Clonality assessment is currently the major molecular analysis utilized to support the diagnosis of suspicious lymphoid malignancies. Clonal rearrangements of the V-J segments of T-cell receptor G chain locus (TCRγ or TRG) have been observed in almost all types of T neoplasms, such as T-cell-related non-Hodgkin lymphomas and leukemias. At present, the gold standard for clonality evaluation is multiplex polymerase chain reaction (PCR), plus subsequent capillary electrophoresis/heteroduplex analyses, and/or Sanger sequencing. This approach overcomes the problem with the conventional Southern blot hybridization and is more efficient, simple, fast, and reproducible. In the recent years, the new next-generation sequencing (NGS) technologies provided alternative techniques for the analysis of antigen receptors genes, which presented several advantages, such as increased efficiency, specificity (SP), sensitivity (ST), resolution, and objectivity of the results, leading to a better classification, stratification, and monitoring of lymphoid malignancies. Nonetheless, these technologies are still far from being the new gold standard since further studies are warranted to prove their utility. The present study aimed to assess the diagnostic accuracy of these two methods by comparing a commercial NGS-based assay for the evaluation of TRG locus with the gold standard PCR-based one, to fulfill the requirements of a phase 3 diagnostic accuracy study.

We assessed the TRG gene rearrangements in 72 cases using the conventional and highly-validated PCR-based assay proposed by EuroClonality consortium, an alternative commercial PCR-based assay, namely, IdentiClone® TCR Gamma Gene Rearrangement Assay 2.0, and a commercial NGS-based assay, that is, Invivoscribe LymphoTrack® Dx MiSeq® (both by Invivoscribe Technologies Inc., San Diego, CA, USA), to determine the diagnostic accuracy of the latter, and compare them with reference diagnoses made based on observation of clinical manifestations, cytohistological, and immunohistochemical analyses. Statistical values were calculated using the Oxford CATmaker software package.

Using standardized criteria of interpretation, the obtained results showed a diagnostic accuracy of 90.3% (correspondence in 65 out of 72 cases) of the test under investigation, with a ST of 86%, a SP of 95%, a positive predicting value of 94%, and a negative predicting value of 88%, demonstrating that it had high efficiency and reliability in detecting clonal TRG gene rearrangements in T-cell non-Hodgkin lymphomas.

This diagnostic accuracy study yielded comparable results using a validated PCR-based approach and a new NGS-based one. Subsequent studies and cost-effectiveness evaluation are needed to put the NGS-based clonality assessment into routine diagnostic practice.