MicroRNA Profiling in Patients with CLL B Cells Expressing the Unmutated IGHV1-69 Gene

Abstract 2846

The immunoglobulin heavy chain variable (IGHV) 1-69 gene, is rearranged in chronic lymphocytic leukemia (CLL) B cells in approximately 20% of the patients, is typically found without somatic mutations, and its expression is often associated with an aggressive clinical course. Unique microRNA (miRs) signatures have been found to be associated with various CLL prognostic markers such as: IGHV mutation status, ZAP-70 expression, and chromosomal aberrations. A karyotype specific signature of some of these miRs has emerged that can differentially segregate patients with adverse clinical behavior and can predict the time from diagnosis to initial treatment.

We had interphase FISH available on 281 of the 452 IGHV1-69 cases analyzed in our companion study. We investigated the miRs signature of 53 of these cases that had CLL cells with a sole cytogenetic lesion. All of these cases expressed unmutated (UM) IGHV1-69. These samples included: 18 that had isolated del 11q, 14 that had trisomy 12, 10 that had del 17p and 11 had no detectable chromosomal abnormalities. We did not include any cases that had del 13q. Expression data of the miRs were analyzed by the multiclass comparison within BRB Array Tools to identify a specific set of miRs differentially expressed among the various cytogenetic classes (p=0.05). The data were normalized using the quantiles method. We compared the miRs profiles of CLL cells having defined cytogenetic aberrations with those described in a previously published cohort of 61 CLL patients not selected for IGHV use (Visone et al. Blood 2009).

In our cohort of 53 IGHV1-69 cases, we observed significant differences in the expression level of 33 miRs between CLL cells of patients that had no detectable chromosomal aberrations and those of patients with cytogenetic lesions. Of these 2 miRs (miR-543 and miR-769-3p) were published in the cohort of 61 CLL patients. We identified significant differences in the miR expression level of 91 miRs between CLL cells with trisomy 12 and those with other chromosomal aberrations or not. Of these 6 (miR-125b-2*, miR-103, miR-155, miR-107, miR-340 and miR-222) had been previously described in the 61 CLL cohort. We found significant differences in the miR expression level of 26 miRs between CLL cells with the 11q deletion and those with other chromosomal aberrations or not, none of these was previously identified in the 61 CLL cohort. We observed significant differences in the miR expression level of 20 miRs between CLL cells with the 17p deletion and those with other chromosomal aberrations or not, of these only 1 (miR-618) had already been described in the 61 CLL cohort.

Since in our companion study on 452 IGHV1-69 cases we found that ZAP-70 expression was a strong predictor of time to first treatment (TFS). We investigated whether CLL expression of ZAP-70 was associated with the peculiar expression of particular miRs in this cohort. Of these 53 patients, 33 (62%) cases had CLL cells that were ZAP-70 positive and had a median TFS of 2.4 years, whereas the 20/53 patients with CLL cells lacking ZAP-70 had a median TFS of 4.0 years.

We found that miR-618 and miR-639 were commonly overexpressed in patients with CLL B cells carrying the 11q or 17p deletions and lacking ZAP-70 whereas miR-22 was down-regulated in CLL cells from patients carrying the trisomy 12 or no chromosomal aberrations and lacking ZAP-70. There was a significant difference in miR-618 expression between patients with CLL cells carrying the 11q or 17p chromosomal aberrations with or without ZAP-70 (9.6 vs 10.8, respectively p<0.0001). In this initial investigation we conclude that in patients with CLL cells expressing the UM IGHV1-69 gene mir-618 appears to be associated with ZAP-70 expression, most apparent in cases with CLL cells carrying 11q or 17p deletions. Mir-618 is known to target the histone deacetylase 4 (HDAC4) which may be involved in the regulation of ZAP-70 expression. Further work needs to be performed to establish the miR-618 prognostic value in CLL.