THE SPECTRUM OF TP53, SF3B1, AND NOTCH1 MUTATIONS IN CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS EXPOSED TO IONIZING RADIATION DUE TO THE CHORNOBYL NPP ACCIDENT

IMMUNOPHENOTYPE OF LEUKEMIC CELLS IN CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS WITH NOTCH1 AND SF3B1 GENE MUTATIONS

BACKGROUND

The typical chronic lymphocytic leukemia (CLL) immunophenotype is vital for diagnosis, but the expression of some antigens varies and has prognostic value. There are data that reduced CD20 expression is associated with NOTCH1 and SF3B1 gene mutations.

AIM

To determine a high-risk group of CLL patients for prediction of unfavorable NOTCH1 and SF3B1 gene mutations based on immunophenotyping of leukemic cells.

MATERIALS AND METHODS

Flow cytometric and molecular-genetic analysis (mutations of NOTCH1, SF3B1, and TP53 genes using the polymerase chain reaction followed by direct sequencing) was performed in a group of 86 previously untreated CLL patients.

RESULTS

The immunophenotype of leukemic cells of all examined patients met the criteria of CLL diagnosis. NOTCH1 gene mutations were found in 21 patients (24.4%), and SF3B1 gene mutations - in 7 patients (8.1%). There were no TP53 gene mutations among the examined patients. A decreased number of CD20+CD5+ cells and a downward trend in the relative index of mean fluorescence intensity (iMFI) of CD20+ cells were found in patients with NOTCH1 and SF3B1 gene mutations. Based on the iMFI level (higher and/or lower than 3.0) and the number of CD20+CD5+ cells among all B-cells (higher and/or lower than 50%), we distinguished CLL cases with low and relatively high levels of CD20 antigen expression. Using ROC analysis and the parameter of low CD20 antigen expression, we could predict the presence of NOTCH1 and SF3B1 gene mutations in 73.3 ± 0.06% of patients (p = 0.001). The risk of NOTCH1 and SF3B1 gene mutations in cases with low CD20 antigen expression was 6.96 (95% CI = 2.53-19.18; p = 0.0001). The revealed regularities were statistically significant for patients in whom the diagnosis was established in all Binet - Rai stages except A0-AI.

CONCLUSION

Our data confirmed a reduced CD20 expression in CLL patients with NOTCH1 and SF3B1 mutations. In addition, an approach was proposed to identify high-risk CLL patients for prediction of such mutations: previously untreated CLL patients at advanced Binet - Rai stages (BII, CIII, CIV) with a reduced number of double-positive CD20+CD5+ cells in peripheral blood and/or low iMFI of CD20+ cells.

THE EXPRESSION OF THE MAIN AND ALTERNATIVE TRANSCRIPT (SORL1 Delta2) OF THE SORL1 GENE IN CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS AFFECTED BY THE CHORNOBYL ACCIDENT

OBJECTIVE

to study clinical-hematological data and expression of the main and alternative transcripts of SORL1 genein chronic lymphocytic leukemia (CLL) patients affected by the Chornobyl catastrophe.

METHODS

Analysis was performed in the main group of 34 CLL patients irradiated due to the Chornobyl NPP acci-dent (30 clean-up workers, and 4 evacuees) and in the control group of 27 non-irradiated CLL patients. Groups ofpatients were comparable by age, sex, stage of disease, mutational status of IGHV genes. Expression of the main andalternative transcripts of SORL1 gene was evaluated by Quantitative Real-time polymerase chain reaction (PCR). TheIGHV gene mutational status, TP53 and SF3B1 mutations were studied by PCR followed by direct sequencing. Data wereanalyzed with the SPSS software package, version 20.0.

RESULTS

Relative expression level of the main transcript of SORL1 gene was low (mean 1.71 ± 0.55, median 0.57),did not correlate with the IGHV gene mutational status, TP53 and SF3B1 mutations, stage of disease. The expressionof B transcript was not detected, F transcript was expressed at a very low level in 9 patients. The average relativeexpression level of SORL1-Δ2 transcript was 14.1 ± 6.04 (median 3.48; range 0.01-90.51). The expression of SORL1-Δ2transcript above the median was more frequent among patients on C stage (p = 0.001), and in patients with unmu-tated IGHV genes was associated with an extremely negative course of CLL (median of overall survival 9 months vs61 months at low expression). Relative expression levels of the main and alternative transcripts of SORL1 gene inpatients of the main and the control groups did not differ.

CONCLUSIONS

Our preliminary data suggest that increased expression of SORL1-Δ2 transcript in CLL patients withunmutated IGHV genes can be considered as a negative prognostic marker.

The signs of negative selection in IGHV framework regions are associated with worse overall survival of chronic lymphocytic leukemia patients

The mutational status of the variable region of the immunoglobulin heavy chain (IGHV) genes remains the most significant prognostic factor in chronic lymphocytic leukemia (CLL) patients. However, the groups of mutated (M) and unmutated (UM) patients are also heterogeneous, and additional markers are used for a more accurate prognosis. The aim of our work was to determine the prognostic value of the signs of antigen selection determined by BASELINe statistics in M IGHV sequences of CLL patients. Clinical data, IGHV gene configuration, TP53, NOTCH1, SF3B1 mutations were analyzed in 127 CLL patients with M IGHV sequences. The median OS of patients with negative selection in the framework regions (FWRs) of IGHV genes was 120 months compared to 202 month in other CLL patients (P = 0.016). In multivariate Cox regression analysis Binet stage C vs A + B (P < 0.0001), SF3B1 mutations (P < 0.0001), negative selection in the FWRs (HR P = 0.007), and age ≥65 years (P = 0.034) were powerful adverse prognostic factors for OS in CLL patients with M IGHV genes. These preliminary data suggest that the signs of antigen-driven selection may be used as a prognostic factor in CLL patients with M IGHV genes in combination with other markers.