Targeted RNA-Sequencing Enables Detection of Relevant Translocations and Single Nucleotide Variants and Provides a Method for Classification of Hematological Malignancies-RANKING.

BACKGROUND: Patients with hematological malignancies (HMs) carry a wide range of chromosomal and molecular abnormalities that impact their prognosis and treatment. Since no current technique can detect all relevant abnormalities, technique(s) are chosen depending on the reason for referral, and abnormalities can be missed. We tested targeted transcriptome sequencing as a single platform to detect all relevant abnormalities and compared it to current techniques. MATERIAL AND METHODS: We performed RNA-sequencing of 1385 genes (TruSight RNA Pan-Cancer, Illumina) in bone marrow from 136 patients with a primary diagnosis of HM. We then applied machine learning to expression profile data to perform leukemia classification, a method we named RANKING. Gene fusions for all the genes in the panel were detected, and overexpression of the genes EVI1, CCND1, and BCL2 was quantified. Single nucleotide variants/indels were analyzed in acute myeloid leukemia (AML), myelodysplastic syndrome and patients with acute lymphoblastic leukemia (ALL) using a virtual myeloid (54 genes) or lymphoid panel (72 genes). RESULTS: RANKING correctly predicted the leukemia classification of all AML and ALL samples and improved classification in 3 patients. Compared to current methods, only one variant was missed, c.2447A>T in KIT (RT-PCR at 10-4), and BCL2 overexpression was not seen due to a t(14; 18)(q32; q21) in 2% of the cells. Our RNA-sequencing method also identified 6 additional fusion genes and overexpression of CCND1 due to a t(11; 14)(q13; q32) in 2 samples. CONCLUSIONS: Our combination of targeted RNA-sequencing and data analysis workflow can improve the detection of relevant variants, and expression patterns can assist in establishing HM classification.

Genetic Screening Test to Detect Translocations in Acute Leukemias by Use of Targeted Locus Amplification.

BACKGROUND: Over 500 translocations have been identified in acute leukemia. To detect them, most diagnostic laboratories use karyotyping, fluorescent in situ hybridization, and reverse transcription PCR. Targeted locus amplification (TLA), a technique using next-generation sequencing, now allows detection of the translocation partner of a specific gene, regardless of its chromosomal origin. We present a TLA multiplex assay as a potential first-tier screening test for detecting translocations in leukemia diagnostics. METHODS: The panel includes 17 genes involved in many translocations present in acute leukemias. Procedures were optimized by using a training set of cell line dilutions and 17 leukemia patient bone marrow samples and validated by using a test set of cell line dilutions and a further 19 patient bone marrow samples. Per gene, we determined if its region was involved in a translocation and, if so, the translocation partner. To balance sensitivity and specificity, we introduced a gray zone showing indeterminate translocation calls needing confirmation. We benchmarked our method against results from the 3 standard diagnostic tests. RESULTS: In patient samples passing QC, we achieved a concordance with benchmarking tests of 81% in the training set and 100% in the test set, after confirmation of 4 and nullification of 3 gray zone calls (in total). In cell line dilutions, we detected translocations in 10% aberrant cells at several genetic loci. CONCLUSIONS: Multiplex TLA shows promising results as an acute leukemia screening test. It can detect cryptic and other translocations in selected genes. Further optimization may make this assay suitable for diagnostic use.

BCL6 alternative breakpoint region break and homozygous deletion of 17q24 in the nodular lymphocyte predominance type of Hodgkin's lymphoma-derived cell line DEV.

DEV is the only cell line derived from nodular lymphocyte predominance type of Hodgkin's lymphoma (NLPHL); however, a comprehensive report about the genetic and immunophenotypic profile of this unique cell line is lacking. We analyzed DEV with respect to immunophenotype and genetic aberrations. The immunostaining revealed positivity for CD45, CD20, CD22, CD79a, IgA2, CD80, CD86, CD74, and BCL6. Cytogenetically, DEV has complex chromosome 3 translocations involving chromosomes 7, 14, and 22. A detailed analysis of the 3q27 breakpoint of the der(3)t(3;14)(p14;q32)t(3;22)(q27;q11.2) revealed a break in the BCL6 alternative breakpoint region. Using array comparative genomic hybridization, a 3-megabase homozygous deletion at 17q24.1-24.2 was identified. Fluorescence in situ hybridization indicated the presence of 2 chromosome 17 homologues, each of which carried a small interstitial deletion. Eight microsatellite markers flanking the homozygously deleted region all showed a homozygous pattern suggesting loss of one of the parental alleles. D17S1809 and D17S1816 could not be amplified using DEV DNA, in keeping with a location within the homozygously deleted segment. In conclusion, DEV has an immunophenotype that is consistent with the neoplastic cells of NLPHL cases, the lymphocytic and histiocytic cells. We demonstrated involvement of the BCL6 gene based on the presence of a breakpoint in the alternative breakpoint region and nuclear staining for BCL6 protein and identified a homozygously deleted region at 17q24.