Cytogenetics and molecular cytogenetics in Hodgkin's disease

BCL2 and BCL3 are recurrent translocation partners of the IGH locus

Chromosomal translocations affecting the immunoglobulin heavy chain (IGH) locus in chromosomal band 14q32 are the most frequent cytogenetic changes in B-cell lymphomas. We studied the presence of IGH translocations in a consecutively ascertained series of 94 classical Hodgkin lymphomas (cHL) by combined immunofluorescence for CD30 and interphase cytogenetics (FICTION technique). The Hodgkin and Reed-Sternberg cells of a total of 11 of 87 evaluable cases (13%) showed signal patterns indicative of IGH translocations. To identify the translocation partners, these cases were further studied with probes for the MYC, BCL2, BCL6, BCL3, REL/BCL11A, JAK2/PDCD1LG2 (alias PDL2) C14orf43, and C2TA loci. The IGH translocation partner could be identified in four cHL and involved BCL2 and BCL3 in two cases each. Immunohistochemistry in cases with suitable material revealed that tumor cells of the two cHL with IGH/BCL2 fusion and the cHL with IGH/BCL3 fusion expressed the BCL2 and BCL3 protein, respectively. These data indicate that BCL2 or BCL3 are recurrent translocation partners of the IGH locus in cHL; however, most of the translocation partners of IGH translocations in cHL remain to be identified.

Segmental chromosomal aberrations and centrosome amplifications: pathogenetic mechanisms in Hodgkin and Reed–Sternberg cells of classical Hodgkin's lymphoma?

Tumor cell metaphases of classical Hodgkin's lymphoma (cHL) characteristically display highly rearranged karyotypes with chromosome numbers in the hyperploid range and marked intraclonal variability. The causes of this cytogenetic pattern remain largely unknown. An unusual type of chromosomal abnormality coined as segmental chromosomal aberration (SCA) has been recurrently observed in HL cell lines and was suggested to be associated with ribosomal DNA (rDNA) rearrangements. Moreover, centrosome abnormalities provoking deficient chromosome segregation have been reported in many solid tumors and also in cHL cell lines. Whether SCA, rDNA rearrangements or centrosome abnormalities also occur in primary cHL is not yet known. Thus, we performed extensive molecular cytogenetic and immunohistological studies in two cHL cases. Both cases presented SCA associated with genomic gains of the REL and JAK2 loci, respectively. The SCA involving JAK2 was associated with rDNA rearrangements. The absolute centrosome size of HRS cells in both cases was significantly larger than in non-HRS cells, but the relative centrosome size of HRS cells corrected for nuclear size was in the same range as that of the non-neoplastic cells. These findings demonstrate that the various mechanisms associated with chromosomal instability warrant a more detailed characterization in cHL.

Recurrent involvement of the REL and BCL11A loci in classical Hodgkin lymphoma

Comparative genomic hybridization studies have shown gains in chromosome region 2p as the most common imbalance in classical Hodgkin lymphoma (cHL). The minimal region of gain contained 2 candidate oncogenes, REL and BCL11A. This study examined the involvement of REL and BCL11A loci in 44 primary cases of cHL by combined immunophenotyping and interphase cytogenetics (FICTION). A median 2p13 copy number above the tetraploid range was detected in 24 (55%) cases. Adjustment for centromere 2 copy number indicated gains of 2p13 in 11 of 31 cHLs (35%) with 8 (26%) high-level amplifications. One cHL displayed selective amplification of the REL locus not affecting BCL11A; another case studied by FICTION and a cHL with cytogenetic 2p change investigated by fluorescence in situ hybridization showed signal patterns suggesting breakpoints in the region spanned by the REL probe. These data indicate that REL rather than BCL11A may be the target of the 2p13 alterations in cHL.

Molecular morphology of Hodgkin lymphoma

No other disease entity has provided greater impetus for the development of the concept of "molecular morphology" than Hodgkin lymphoma. Efforts to understand the etiology of this enigmatic disease have stimulated the application and refinement of almost every mode of biomedical scientific exploration. Notwithstanding the vast amount of data generated, much is still unknown about this remarkable disease, serving as an ongoing inducement to the development and application of new technologies for the analysis of cells and molecules in a morphologic environment.

Interaction between host T cells and Reed-Sternberg cells in Hodgkin lymphomas

Recent studies provide evidence that Reed-Sternberg (R-S) cells produce factors that may explain the characteristic inflammatory infiltrate in the affected tissues of Hodgkin lymphoma. The various chemokines and cytokines that are produced lead to a preferential influx of Th2-type T cells and suppress Th1-type immune responses. Overall, the immunophenotype of the lymphocytes surrounding the R-S cells is consistent with anergic and/or Th2-type T cells. Therefore, these cells do not support a cytotoxic anti-tumor response. Since the R-S cells are neoplastic B cells, the cytokines produced by these T cells may in fact help their growth and/or survival. The production and induction of various other cytokines may also explain the influx of eosinophils (IL-5, eotaxin) and plasma cells (IL-6). Differences in chemokine and cytokine production may be responsible for the differences between the histological subtypes.

Morphologically normal, CD30-negative B-lymphocytes with chromosome aberrations in classical Hodgkin's disease: the progenitor cell of the malignant clone?

A recent study observed that numerical chromosome abnormalities in Hodgkin's disease (HD) are detected not only in morphologically abnormal Hodgkin/Reed-Sternberg cells, but also in a fraction of morphologically normal cells. However, the phenotypic constitution of these genetically abnormal, morphologically normal cells and their relationship to the malignant Hodgkin/Reed-Sternberg cells could not be established in the earlier cases studied, because of the low frequency of these cells. The present study investigated two cases of classical Hodgkin's disease containing a relatively large population of such apparently normal cells with aberrant chromosome copy numbers. The phenotype and their position within the developmental route of the malignant compartment were examined by a combined in situ hybridization and immunocytochemistry approach. Numerical abnormalities for chromosome 1 in one case and for chromosomes X, Y, and 1 in the other case were observed not only in CD30-positive Hodgkin/Reed-Sternberg cells, but also in CD30-negative, morphologically normal cells. It was shown that these genetically aberrant cells expressed the B-cell antigen CD19, thus confirming their B-cell nature. These studies indicate a relationship between the genome aberrations in these genetically abnormal, morphologically normal B-cells and the Hodgkin/Reed-Sternberg cells, suggesting that they are progenitor cells of the malignant cell fraction.

Genetic analysis of sorted Hodgkin and Reed-Sternberg cells using comparative genomic hybridization

Hodgkin and Reed-Sternberg (H and RS) cells are generally considered to be the neoplastic cells of Hodgkin's disease (HD); however, such cells are found only in a minority of HD lesions. Very few data have so far been published on the cytogenetic abnormalities in HD. An analysis of unknown genetic aberrations has only recently become possible through the use of comparative genomic hybridization (CGH), which is based on the competitive binding of tumor and control DNA to metaphase chromosomes. In order to exclude the reaction of non-tumor cells, we used 100 sorted H-RS cells as the tumor DNA, then 100 sorted reactive T cells or B cells as the control DNA. We obtained the amplified DNA, using degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). In addition, to confirm whether or not the lymphocytes in the background were reactive, we performed CGH with 100 sorted B cells and 100 sorted T cells. CGH was thus performed on 9 HDs, including 6 cases of mixed-cellularity (MC) sub-type and 3 cases of nodular-sclerosis (NS) sub-type. CGH of the B and T cells showed no genetic changes in any cases. In contrast, CGH of H-RS cells revealed both gains and losses of DNA in all 9 cases, and multiple changes were also observed. In situ hybridization showed an Epstein-Barr-virus infection in 5 cases of MC; however, no definite relationship was observed between the EBV infection and genetic changes. The most commonly observed genetic aberrations were a loss on 16q11/21 in 6 cases, a gain on 1p13 in 5 cases, and a gain on 7q35/36 in 5 cases. The large number of chromosomal alterations in HD suggests, therefore, that an increased degree of genetic instability play a role in the formation of H-RS cells.