Haematologica 2004;89: supplement no. 6 - Supplements ...

VIII Congress of the Italian Society of Experimental Hematology, Pavia, September 14-16, 2004107PO-073EARLY AND LATE RECOMBINATIONS AT THE IMMUNOGLOBULINκ LIGHT CHAIN LOCUS OF MUTLIPLE MYELOMA: EVIDENCE OFRAG ACTIVITY IN GERMINAL CENTERSPerfetti V,° Colli Vignarelli M,° Palladini G,°Navazza V,° Giachino C, # Merlini G*°Department of Internal Medicine, Internal Medicineand Medical Oncology, and the *BiotechnologyResearch Laboratories, IRCCS Policlinico S. Matteo,Department of Biochemistry, University of Pavia, and#IRCCS Fondazione Maugeri, Pavia, ItalyB cells may undergo sequential rearrangements atthe light chain loci, despite already expressing lightchain receptors. This phenomenon, known as secondaryrearrangement, may occur during differentiationin the bone marrow (receptor editing) and in theperiphery, at some point of the germinal center reaction(receptor revision). To study light chain recombinationsthat preceded the development of a marrowplasma cell we used multiple myeloma as a singlecell-model and, taking advantage of the fact thatIg light chains usually rearrange before Ig ones, weused PCR to analyze the Ig locus of twenty-nine Igmyeloma cases. The results indicated that all Ig alleleswere inactivated via rearrangement of the κdeleting element, more frequently to a V segment(69%) than to the intronic recombination signalsequence (31%). Eighteen alleles (16 myelomaclones) had previous V-J attempts, and these revealedincreased utilization of distal V and J gene segments(J 56%), a marker of multiple sequential rearrangement.In-frame V-J rearrangements were found inapproximately 1/3 of available joints (5/18, with oneinvolving a V pseudogene), each one in differentmyeloma clones: 3 were identical to germline (i. e.compatible either with editing in the bone marrow orwith revision before the onset of somatic changes),while 1 had several nucleotide substitutions indicatinginactivation after the germinal center reactionhad been initiated. The present findings have relevancefor light chain genetics and support the viewthat developing B-cells may undergo both early andlate recombinations at the light chain locus. Sustainedactivity of recombination-activating genesmay contribute to immunoglobulin translocations inB-cell neoplasias.PO-074CHARACTERIZATION OF ONCOGENE DYSREGULATION IN MULTI-PLE MYELOMA BY COMBINED FISH AND DNA MICROARRAYANALYSESFabris S,* Agnelli l,* Mattioli M,* Baldini l,*Ronchetti D,* Morabito F, + Verdelli D,* Nobili l,*Intini D,* Callea V, + Stelitano C, + Maiolo AT,*Lombardi L,* Neri A**Laboratorio di Ematologia Sperimentale e GeneticaMolecolare, U. O. Ematologia 1, Dipartimento diScienze Mediche, Università degli Studi di Milano,Ospedale Maggiore IRCCS, Milan; + Divisione di Ematologiae Centro Trapianto di Midollo, Azienda Ospedaliera“Bianchi-Melacrinò-Morelli”, Reggio Calabria,ItalyMultiple myeloma (MM) is a neoplastic proliferationof plasma cells characterized by a marked biologicaland clinical heterogeneity. Dysregulation ofdistinct putative oncogenes, as a result of chromosomaltranslocations involving the IGH locus at14q32, occurs frequently in MM. Such oncogenicevents are thought to be linked with the transformationand clonal evolution of malignant plasmacells and may have a significance in the definition ofdifferent entities of the disease. In the present study,the expression profiles of FGFR3/MMSET, CCND1,CCND3, MAF and MAFB, involved respectively in thet(4;14)(p16.3;q32), t(11;14)(q13;q32), t(6;14)(p21;q32), t(16;14)(q23;q32), and t(14;20)(q32;q12),were investigated on purified plasma cell populationsfrom 39 MM and 6 plasma cell leukemia (PCL)patients by DNA microarray analysis and comparedwith the presence of translocations as assessed bydual-color FISH or RT-PCR. The t(4;14) was found in6 MM patients, the t(11;14) in 10 patients (9 MMand 1 PCL), the t(6;14) in one MM case, the t(14,16)in three cases (2 MM and 1 PCL), and the t(14;20) inone PCL. Traslocations were associated with spikedexpression of target genes in all cases. In addition,gene expression profiling allowed to the identificationof putative chromosomal translocations dysregulatingthe CCND1 (1 MM and 1 PCL) and MAFB (1MM and 1 PCL) without any apparent involvement ofimmunoglobulin loci. Notably, all of the translocationswere found to be mutually exclusive. Interestingly,marked increased levels of MMSET expressionhave been found in one MM case in which a 4p16.3allele was localized on an unidentified chromosome.Overall, our data support the notion that translocations(either or not involving the IGH locus) representthe mechanism of dysregulation of putative oncogenesprimarily involved in myelomagenesis and suggestthe importance of combined molecular cytogeneticsand gene expression approaches for the detectionof genetic aberrations in MM.haematologica vol. 89[suppl. n. 6]:september 2004