Whole Genome Copy Number Variation Analysis of Chronic Lymphocytic Leukemia (CLL) Cells From Early-Intermediate Stage, High Risk CLL Patients Prior to First Treatment Reveals New Loss of Heterozygosity and Duplication Events in the CLL Genome.

Abstract

Abstract 1265Poster Board I-287 IntroductionFluorescence in situ hybridization (FISH), in combination with other markers, is used as a prognostic tool for CLL patients at diagnosis. The presence or absence of trisomy 12 and deletions at 13q, 11q, and 17p helps to predict disease progression and to stratify patients for therapeutic decisions. We hypothesized that whole genome single nucleotide polymorphism (SNP)-based copy number variation (CNV) analysis would capture all of the information in current CLL FISH panels and would reveal new CNV features in the CLL genome. Patients and MethodsNineteen early-intermediate clinical stage, untreated CLL patients aged 29 to 77 were determined to be at high risk for disease progression by FISH, IgVH mutation status, ZAP-70, and CD38 prognostic markers. CLL cells and normal cells were separated by magnetic bead selection from patient peripheral blood samples with absolute lymphocyte counts that ranged from 7.4 to 162 × 109/L. CNV analysis was performed on purified genomic DNA from the CLL cells and from normal cells for each patient in order to distinguish acquired CNVs in malignant cells from polymorphic CNVs in the human genome. We used the Illumina human660w-quad beadchip, a SNP-based microarray for whole-genome genotyping and CNV analysis that contains more than 550,000 tag SNPs and approximately 100,000 additional markers that target regions of common CNV. CNV data was analyzed using CNV partition (Illumina Genome Studio software) and PennCNV. Results100% concordance is found between del(13q), del(11q), and del(17p) FISH abnormalities and loss of heterozygosity (LOH) at 13q, 11q, and 17p by CNV analysis. All three patients with trisomy 12 by FISH show copy number(CN)=3 of chromosome 12 by CNV analysis. Of 15 patients with del(13q) by FISH, 12 out of 15 have regions of hemizygous deletion on 13q that vary from ∼830 Kb to ∼38 Mb. The smallest region of LOH is located within 13q14.3. Three out of 15 patients show homozygous deletion within 13q14.3. One of these 3 patients has copy-neutral LOH of the entire 13q arm with an embedded 835 Kb segment of homozygous deletion at 13q14.3. Two patients have large discontinuous segments of LOH on 13q, indicating complex interstitial deletion events. Two out of 5 patients with del(13q) as a sole FISH abnormality show additional CNV events in the CLL genome. One of these patients has copy neutral LOH at 2q33.1-telomere(tel). One other patient with sole del(13q) FISH shows LOH events at 10q23.31-23.33 and at 15q15.1. Five out of six patients with del(11q) by FISH have either 13q LOH (n=4) or chromosome 12 CN=3 (n=1) without any other CNV events detected in the CLL genome. One patient with trisomy 12 and del(11q) by FISH has three additional acquired CNV abnormalities in the CLL genome: LOH at 7p15.2-tel, LOH at 11p13, and CN=3 at 3q24-tel. In contrast to patients with del(11q), del(13q), and trisomy 12, patients with del(17p) by FISH have numerous acquired CNV abnormalities in the CLL genome. These include LOH events at 1p34.3-p34.2, 2q34-q36.3, 3p21.31-tel, 4p13, 4p15.1-tel, 15q11.2-q14 and 15q14-q15.3, 16p13.3-tel, 16p13.11, 16p13.2, 18p11.21-tel, 20p11.21-tel, and 20q13.2-q13.31. CN=3 at 2p12-tel is detected in 2 out of 5 patients with 17p hemizygous deletion. One out of 5 patients with 17p hemizygous deletion shows CN=3 at 10q22.2-tel. One other patient also with 17p hemizygous deletion shows CN=3 at 22q12.2-tel. ConclusionsWhole genome CNV analysis by SNP-based microarrays greatly expands our ability to detect acquired genomic events in CLL cells. These events include hemizygous deletion, homozygous deletion, copy-neutral LOH, and CN=3 duplication. Detection of copy-neutral LOH is not possible by FISH or array comparative genomic hybridization technology. The current study reveals a high number of acquired CNV events in earlier stage, untreated CLL patients with 17p hemizygous deletion. This observation, indicative of genomic instability, is consistent with the known poor prognosis of del(17p) patients. The new somatic CNV abnormalities detected in CLL cells may help to discover additional genes or signaling pathways involved in CLL initiation and progression. In addition, the new CNV markers may be used in larger clinical studies to improve CLL prognosis and patient stratification for therapy. DisclosuresShanafelt:Genentech: Research Funding; Hospira: Membership on an entity's Board of Directors or advisory committees, Research Funding; Polyphenon E International: Research Funding; Celgene: Research Funding; Cephalon: Research Funding; Bayer Health Care Pharmaceuticals: Research Funding. Kay:Genentech, Celgene, Hospira, Polyphenon Pharma, Sanofi-Aventis: Research Funding; Biogenc-Idec, Celgene, Genentech, genmab: Membership on an entity's Board of Directors or advisory committees. Zent:Genentech, Bayer, Genzyme, Novartis: Research Funding.