Characterization of Secondary Alterations in Mantle Cell Lymphomas Using Matrix-/Array CGH.

Overexpression of Cyclin D1 due to the chromosomal translocation t(11;14)(q13;q32) alone is not sufficient to induce the development of mantle cell lymphoma (MCL). Therefore, secondary genetic alterations seem to be necessary for the malignant transformation and may determine the clinical course of the disease. In order to define chromosomal imbalances more precisely, we analyzed six t(11;14)-positive mantle cell lymphoma cell lines (Granta-519, NCEB1, JeKo-1, Rec-1, SP-53 and HBL-2) by means of matrix-/array-based comparative genomic hybridization (array-CGH), a new molecular tool that allows the genome-wide screening of chromosomal imbalances. The microarray used contains 6251 individual BAC/PAC clones. Clones were selected to reach a genome-wide resolution of 1 Mb and an even higher resolution of up to 100kb in recurrently aberrant regions of MCL. In addition, regions containing known tumor suppressor genes and oncogenes were covered by a high density of clones. The hybridization of tumor DNA against normal control DNA and the subsequent washing steps were carried out using the automated slide processor Lucidea (Amersham-Pharmacia Biotech). Based on the normalized fluorescence ratios computed as log₂ values, we were able to detect amplifications as well as single gains and losses. The most frequent alterations were losses in 9p21.3, 2p11.2, 22q11.22, 1p21.1-p31.2, 13q14, 11q22, 6q21, 6q27, 17p13 and gains in 7p14.1, 7q11.2, 2q37.1, 8q24, 12q13 and 18q21. These results are in agreement with the recently published data from deLeeuw et al. (HMG Advance Access June 30, 2004). Up to now, losses of 2p11.22 (all cell lines except for JeKo-1) and 22q11.22 (all cell lines except for Rec-1) have not been known as recurrent aberrations of MCL. Selected chromosomal losses (p16, p53) and the amplification of BCL2 in Granta-519 were confirmed by means of fluorescence in situ hybridization using commercially available probes (Abbott Diagnostics, Wiesbaden, Germany). Matrix-/array CGH analyses enabled us to further delineate important regions of gain and loss like 13q14. In conclusion, the cell lines are excellent model systems which will facilitate the identification and characterization of novel genes which play important roles in the pathobiology of MCL.