GENOMIC COPY NUMBER ALTERATIONS IN HIGH-RISK CLL PATIENTS HARBORING TP53 DEFECTS: INSIGHTS FROM CONSECUTIVE INVESTIGATIONS

Sborník

Background. In chronic lymphocytic leukemia (CLL), recurrent copy number alterations (CNAs) have been described (deletions of 13q14, 17p13 and 11q22, and trisomy 12), that are typically present in variable proportions of leukemic cells. Significantly, genomic lesions can accumulate during the disease course, which is evident when pre-treatment and relapse samples are compared. Among them, TP53 defects (mutations/deletions), that are in general associated with genomic instability, are selected in approximately one-fifth of treated CLL patients with an originally intact gene. Taken together, these phenomena likely contribute to the chronic relapsing course of CLL and the development of chemotherapy resistance. Aims. Our study aimed to describe specific CNAs accompanying selection of TP53 defects by therapy in CLL patients, and compare them to those present in patients having either wild-type (wt) TP53, or mutant (mut) TP53 in all subsequent samples. Methods. Consecutive peripheral blood samples from 22 well characterized CLL patients (unmutated IGHV in 18/22 cases) were collected. Since therapy administration can facilitate expansion of more aggressive subclones in the disease relapse, samples separated by therapy were preferentially selected for the study. TP53 mutations were identified by FASAY and direct sequencing. Genomic DNA (gDNA) was isolated from separated CD19+ or mononuclear cells and analyzed using Cytogenetics 2.7M Array (Affymetrix). Further data parsing, filtering, and mining were performed with in-house computer programming. Array results were compared to results of I-FISH and metaphase cytogenetics with CpG/IL-2 stimulation. Results. In total, 46 gDNA samples were analyzed (two or three consecutive samples in 20/22 and 2/22 patients, respectively). Median interval between the samplings was 24 months (range 9-55 months). Altogether, 18 wt-TP53 and 28 mut-TP53 samples were analyzed. Concerning a simple number of CNAs, no significant differences between wt- and mut-TP53 samples were observed. It might be explained by the fact that majority of patients belonged to the highrisk CLL and, more importantly, that accumulation, but also elimination of CNAs was observed during the disease course. The original and follow-up TP53 status was used to divide the patients into three groups: group A with wt-TP53 in consecutive samples (3/22 patients), group B with mut-TP53 in consecutive samples (8/22), and group C with selection of new TP53 mutations after CLL therapy (11/22). Group C exhibited the most dramatic genomic changes. Specifically, del(17p) leading to complete inactivation of TP53, as well as del(4p), del(4q), del(6q), and del(13q) (including miR-15-1/16a and RB1 genes) occurred frequently in this group. Interestingly, in this group we also noted recurrent vanishing of del(11q); the subclone was likely replaced by the one harboring TP53 defect. In group B, only del(15q) appeared recurrently. Summary. Our gradual analysis catalogues the appearance, but also disapperance of recurrent CNAs during the disease course of CLL. In particular, selection of TP53 defects after therapy seems to be accompanied by accumulation of specific CNAs in our patients. We assume that these CNAs potentially drive disease aggressiveness, whereas CNAs which appear as well as diminish likely do not play role in disease progression. Supported by CZ.1.05/1.1.00/02.0068, CZ.1.07/2.3.00/20.0045, CZ.1.07/2.4.00/17.0042, MSM0021622430, MUNI/A/ 0784/2011, GACR204/09/H058

Haematologica, 2012; 97(s1):  291