Detection of PAX5 Overexpression By RNA-Seq for B-Cell Lineage Detection in Acute Lymphocytic Leukemia

Background: Paired-box Pax gene family protein 5 (PAX5)/B-cell specific activator protein (BSAP) is a transcription factor encoded by the PAX5 gene and has an essential role in B-cell differentiation and maturation. High PAX5 expression is detected ensures commitment to B-cell lineage. PAX5 is normally downregulated at the plasma cell stage of B-cell development. Complete or partial deletion of the PAX5 gene has been found as secondary event associated with BCR-ABL1 or TCF3-PBX1 fusions in Acute Lymphocytic Leukemia (ALL) cases. PAX5 expression is a diagnostic marker for B-cell lineage and may help quantify minimal residual disease in B-ALL. Lineage determination of leukemic blasts is most often performed by flow cytometry, but also by immunohistochemistry (IHC). Evaluation of PAX5 is most commonly available by IHC and is not widely performed by flow cytometry. In cases with limited specimen for evaluation or aberrant loss of some B-cell markers, determining quantitative levels of RNA from lineage-specific genes, such as PAX5, could be a valuable clinical diagnostic tool for ALL patients. Our existing single tube NGS based assay for simultaneous detection of DNA alterations and RNA fusions in heme malignancies from Total Nucleic Acid (TNA), can also be used to detect PAX5 gene expression through select exons enrichment along with a total of 213 genes. However, one of the current challenges for NGS-based gene expression profiling is to setup a threshold for overexpression. Here we developed a cutoff criterion for PAX5 overexpression and evaluated the performance of PAX5 gene expression analysis using the in-use heme assay and its potential use in clinical laboratory for cell lineage detection. Methods: RNA sequencing was performed on TNA extracted from ALL samples and from 32 healthy donors using partial anchored amplicon based (Qiagen, inc) heme NGS assay. PAX5 RNA expression was calculated by TPM (transcript per million) counts normalized to TPM of the house-keeping gene GUSB. A commercially available qRT-PCR assay was used as orthogonal method to confirm the gene expression. The expression call by NGS based on the normalized value was confirmed by a commercial qRT-PCR assay in house validated through serial dilutions of template for six log scale. The analytical cutoff was determined from normalized TPM calculation from 32 healthy volunteers following CLSI guideline (CLSI_EP17-A2) and evaluated the outcome with IHC positive /negative clinical samples (a CLIA validated assay). Further, we used the established cutoff to evaluate the sensitivity or specificity in cohort of ALL samples. Results: In this study we established the cutoff for PAX5 gene over-expression using the currently in-use heme NGS assay. First, a cutoff was established following the method in the CLSI guidelines and tested for sensitivity and specificity in the ALL sample cohort. PAX5 TPM normalization to GUSB or to the geometric mean of four house keeping genes (GUSB, PGD, RPL5 and RPL19) showed a strong correlation (R2>0.95), and GUSB was selected for further normalization since GUSB TPM values were most conserved across all the samples. Independent in-house evaluation for commercial qRT-PCR assay showed efficiency at 94.3 and 96% for GUSB and PAX5, respectively (with linearity R2>0.95), and been used to compare the NGS and IHC data as independent orthogonal assay. When a cohort of samples for Pax5 by IHC (positive and negative), a sensitivity at 67% and specificity at 100% were observed for the NGS based Pax5 detection. NGS results on the discordant samples were confirmed by qRT-PCR to have low RNA expression. Notably the discordant, IHC positive samples contained very low numbers of B cells. Alongside with other possible mechanisms of increased protein levels such as increased protein translation/increased protein stability could explain the discordance between RNA expression and the protein detection by IHC. Conclusions: In this study we demonstrate that NeoGenomics's (heme) NGS assay can be used for PAX5 gene over-expression analysis on ALL. The heme NGS is inexpensive and is already integrated in the benchwork workflow without adding extra burden and can be used as an objective quantification of PAX5 levels overcoming the challenges associated with the relative signal intensity biases in IHC testing. This type of RNA testing can be useful especially with specimens having limited material. Disclosures Ghosal: NeoGenomics Laboratories: Current Employment. Alarcon: NeoGenomics Laboratories: Current Employment. Koo: Neo Genomics Laboratories: Current Employment. Kang: Neo Genomics Laboratories: Current Employment. Ramesh: Neo Genomics Laboratories: Current Employment. Gyuris: Neo Genomics Laboratories: Current Employment. Jung: NeoGenomics Laboratories, Inc.: Current Employment. Thomas: NeoGenomics Laboratories, Inc.: Current Employment. Fabunan: NeoGenomics Laboratories, Inc.: Current Employment. Magnan: NeoGenomics Laboratories, Inc.: Current Employment. Nam: NeoGenomics Laboratories, Inc.: Current Employment. Petersen: Neo Genomics Laboratories: Current Employment. Lopez-Diaz: NeoGenomics Laboratories, Inc.: Current Employment. Bender: NeoGenomics Laboratories, Inc.: Current Employment. Agersborg: NeoGenomics Laboratories, Inc.: Current Employment. Ye: Neo Genomics Laboratories: Current Employment. Funari: NeoGenomics Laboratories, Inc.: Current Employment.

Genome-Wide Analysis of Allele-Specific Expression Genes in Pediatric B-Cell Precursor Acute Lymphoblastic Leukemia

Introduction. Pediatric B-cell precursor acute lymphoblastic leukemia (BCP ALL) is the most common pediatric hematological malignancy and it remains an important cause of morbidity and mortality in children. In this study, we performed an allele-specific expression (ASE) analysis of pediatric BCP ALL with the aim to investigate the relationship between cis-regulatory mutations and gene expression patterns. Materials and methods. Twenty-two high hyperdiploid ALL, twenty ETV6/RUNX1-positive ALL, seven TCF3/PBX1-positive ALL and twenty-eight genetically unclassified BCP ALL ("B-other") were subjected to whole genome sequencing, SNP array analysis and RNA sequencing. The binomial test was applied to estimate the allelic bias of heterozygous exonic single nucleotide variants (SNVs) in the RNA sequencing data against the genomic data. Allelic ratios >2 or <0.5, and P values <0.05 were used to identify allele-specific expression protein-coding genes. Results. We identified 12,693 expressed genes, of which 9,672 (76%) had heterozygous exonic SNVs (informative genes), in multiple BCP ALL samples (n>2) in 77 of the investigated samples. Genes with ASE were distributed evenly across the autosomal chromosomes in the different subtypes with a range of 30 - 165 ASE genes per case (median number, 86). We found that 630 (6.5%) genes displayed ASE in multiple BCP ALL samples (n>2), of which only eight autosomal genes had monoallelic expression in more than two investigated samples. This suggests that ASE and monoallelic expression are relatively rare in BCP ALL. Gene enrichment analyses showed that pathways involving negative regulation of natural killer cell-mediated cytotoxicity and cell proliferation were enriched, indicating that ASE events possibly were associated with the cell proliferation and leukemia progression in BCP ALL. Furthermore, the hematopoiesis pathway was also enriched in ASE genes that showed high allelic expression bias (allelic ratios >2.5), suggesting that ASE genes might be associated with leukemia development. Somatic genomic aberrations that could cause ASE were also investigated in this study. All informative cases with TCF3/PBX1 rearrangement (n=4) showed monoallelic expression of the PBX1 gene, likely associated with the PBX1 truncation caused by the fusion. Additionally, CHP1, located in 15q15.1, displayed ASE in one case with an inversion involving that chromosome band, indicating a potential cis-acting element in the inversion region that regulated the CHP1 gene expression. Notably, PAX5 displayed various patterns of ASE in BCP ALL. One of three cases with PAX5/ZCCHC7 gene rearrangements displayed PAX5 ASE while the other two did not, indicating a potential uncovered cis-regulatory element around the PAX5/ZCCHC7 breakpoints. Furthermore, two cases with no PAX5 gene rearrangement displayed monoallelic expression of the PAX5 gene, suggesting that there are additional epigenetic alterations were also involved in the regulation of PAX5 gene expression in BCP ALL. Conclusions. In this study, we have characterized genes displaying ASE in childhood BCP ALL. Our data provide new insight into pathogenesis of BCP ALL and may be used to identify novel targets for treatment. Disclosures No relevant conflicts of interest to declare.

Expression Rate and PAX5 Gene Methylation in the Blood of People Suffering from Gastric Cancer

BACKGROUND: Gastric cancer is one of the most important health issues in the world. Considering the lack of plenty of pre-awarenesses, the survival of gastric cancer is still quite disappointing. Methylation of PAX5 gene promoter is observed in most cancer cells of a human. A study has shown that PAX5 is a new tumoral suppressor in gastric cancer and methylation of the PAX5 promoter is associated with the survival rate of gastric cancer. AIM: The present research seeks to study the expression rate and methylation of the PAX5 gene in the blood of patients who have gastric cancer to be used as a biomarker in this type of cancer. MATERIAL AND METHODS: Real-time PCR technique was used to assess expression of PAX5 gene, while the methylation status of PAX5 gene promoter in the blood samples of people who have gastric cancer versus blood samples obtained from normal Iranian population was studied using MS PCR technique. RESULTS: The final results pointed to the fact that expression of PAX5 in blood samples obtained from those who have gastric cancer is much less than what is observed in normal blood samples. A significant correlation was also observed between expression of this gene and age and promoter methylation rate. The results of methylation also indicated that 28% of PAX5 gene promoters among patients were methylated, while all normal samples were non-methylated. CONCLUSION: Studying the decrease observed in PAX5 gene expression and the rise in promoter methylation can be utilised as a biomarker to enhance pre-awareness of gastric cancer.