FISH DETECTION OF CHROMOSOME 14Q32 IGH TRANSLOCATIONS - EVALUATION INFOLLICULAR LYMPHOMA/

A FISH strategy capable of detecting chromosome 14q32 rearrangements i nvolving the IgH locus, including in interphase nuclei, was developed using Ig variable and constant region cosmids from the extremities of the locus in a dual hybridization approach, using signal splitting as evidence of rearrangement. The large size of the locus (1.3 Mb) and th e propensity for internal deletion due to physiological VDJ recombinat ion and isotype switching complicate analysis of this locus. We used t he Ig10 cosmid, which hybridizes to C epsilon and C alpha 2 at the 3' end of the constant region, in order to minimize deletion and/or split ting of the constant region probe. Cos Ig10 and the IgV18 VH probes we re compared with a specific IgH-BCL2 FISH dual hybridization approach in follicular lymphoma (FL). Both were capable of detecting the t(14:1 8) in interphase nuclei, including in cases with no apparent abnormali ty by classic karyotype analysis, although the sensitivity of the IgH approach was slightly lower. We have also successfully applied these p robes to whole cell cytospin preparations, rendering analysis of cryop reserved material possible, although interpretation should be limited to frequent events, particularly following cell manipulation Analysis of flow cytometric sorted bone marrow fractions from three FL patients by FISH and FICTION showed that the t(14;18) was present in a much lo wer proportion of CD34 positive than negative cells but that the highe r level of background hybridization limits use of these techniques for the reliable quantification of rare events.