Ágota Szepesi

Richter's and prolymphocytic transformation of chronic lymphocytic leukemia are associated with high mRNA expression of activation-induced cytidine deaminase and aberrant somatic hypermutation

Chronic lymphocytic leukemia (CLL) is an indolent B-cell non-Hodgkins lymphoma that may transform into higher-grade lymphoma. The transformation involves an increased number of prolymphocytic cells, termed prolymphocytic transformation (PLT) or the development of diffuse large B-cell lymphoma (DLBL), also referred to as Richters transformation (RT). To analyze whether activation-induced cytidine deaminase (AID), which is essential for somatic hypermutation (SHM) of normal B-cells, and malfunction of SHM termed aberrant somatic hypermutation (ASHM) are associated with higher-grade transformation of CLL, AID mRNA expression and the mutation pattern of c-MYC, PAX-5 and RhoH genes were analyzed in eight cases of CLL without transformation and in 21 cases that showed RT or PLT. Chronic lymphocytic leukemia cases, which showed no transformation or eventually transformed into higher-grade lymphoma, showed low levels of AID mRNA expression and low frequency of mutations of c-MYC, PAX-5 and RhoH genes. In both RT and PLT, high-levels of AID mRNA expression and high-frequency mutations of c-MYC, PAX-5 and RhoH genes were detected. These results indicate that AID expression and ASHM are associated with higher-grade transformation of CLL and provide further evidences that AID expression and ASHM may be activated during the clonal history of B-cell lymphomas.

Microsatellite instability and hMLH1 promoter hypermethylation in Richter's transformation of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an indolent B cell non-Hodgkin lymphoma (NHL) that may transform into diffuse large B cell lymphoma (DLBL). This transformation is referred to as Richter’s syndrome or transformation. To analyze whether microsatellite instability (MSI) and DNA mismatch repair defects are associated with Richter’s transformation, we have performed microsatellite analysis, mutational analysis of hMLH1 and hMSH2 genes and methylation status analysis of CpG island of the hMLH1 promoter on serial biopsy specimens from 19 patients with CLL. Ten cases of CLL showed no histologic alteration in the second biopsy, and nine cases of CLL underwent morphologic transformation to DLBL in the second biopsy. Using eight microsatellite loci, high level of MSI was associated with Richter’s transformation in four cases of CLL, but none of the CLLs displayed this level of MSI without transformation. Mutations of the hMLH1 or hMSH2 genes were not detected in any of the lymphoma samples. In five cases of Richter’s transformation the hMLH1 promoter was hypermethylated in both CLL and DLBL samples. Hypermethylation of the hMLH1 promoter associated with high-level of MSI in four cases, and low-level of MSI in one case. These results suggest that in certain cases of Richter’s transformation the DNA mismatch-repair defect-initiated genetic instability may play a role in tumor progression.

Relationship between the mutational status of VH genes and pathogenesis of diffuse large B-cell lymphoma in Richter's syndrome.

Patients with chronic lymphocytic leukemia (CLL) may develop diffuse large B-cell lymphoma (DLBL), also known as Richters syndrome. Mutational status of immunoglobulin (Ig) heavy-chain variable region (VH) genes have prognostic impact in CLL. Patients with mutated VH genes have a stable disease, whereas patients with unmutated VH gene have more aggressive disease. The mutational status of CLLs that transform to DLBL is unknown. To reveal whether Richters syndrome occurs in CLLs with mutated or unmutated VH genes, we have performed mutational analysis on serial specimens from eight patients. CLL and DLBL tumorclones were identical in five cases and they were different in three cases. Six CLLs expressed unmutated and two cases expressed mutated VH genes. In five of the six unmutated CLLs, the DLBL clones evolved from CLL tumorclones and the VH genes expressed by DLBLs were also unmutated. In one unmutated and two mutated CLLs, the DLBLs expressed mutated VH genes, but in these three cases the DLBL tumorclones developed as independent secondary neoplasm. These results suggest that Richters syndrome may develop in both mutated or unmutated CLLs, but clonal transformation of CLL to DLBL occur only in the unmutated subgroup of CLL.

Thioacetamide-induced hepatic fibrosis in transforming growth factor beta-1 transgenic mice

Objective Transforming growth factor beta-1 (TGF-β1) is thought to be one of the most important factors affecting the development of fibrotic processes in the liver. Aim To discover whether endogenously higher TGF-β1 production influences the progression and reversibility of liver fibrosis in mice. Method We compared thioacetamide-induced liver fibrosis between wild-type and transgenic mice overexpressing active TGF-β1 in the liver. Hepatic fibrosis was detected on histological sections, and fibrotic areas were measured by means of morphometric analysis. We also performed Northern blot hybridisation and gelatine zymography to improve our understanding of the process. Results The fibrotic process was faster in the transgenic animals, and regression after the withdrawal of the fibrogenic agent was slower. Fibrosis did not disappear completely from the TGF-β1 overexpressing mice, even at the endpoint of the experiment. Conclusion Since the increased TGF-β1 production in the liver slowed down the regression of the liver fibrosis, the behaviour of these transgenic mice is more similar to the human situation, where cirrhosis is irreversible. We propose that this transgenic model is more suitable for investigating fibrotic liver diseases than the experiments done previously on wild-type rodents.

Aberrant somatic hypermutation and expression of activation-induced cytidine deaminase mRNA in mediastinal large B-cell lymphoma.

To determine the possible role of aberrant somatic hypermutation (ASHM) and activation‐induced cytidine deaminase (AID) expression in the pathogenesis of mediastinal large B‐cell lymphoma (MBL), the mutational status of genes affected by ASHM, including c‐MYC, PAX‐5 and RhoH, was analysed, and the expression level of AID mRNA in tumour specimens from six patients with MBL was determined. Mutations in one or more genes and high expression of AID mRNA were detected in all the six cases of MBL. These results suggest that ASHM and AID expression may have a role in the pathogenesis of MBL.

Clonal selection in the bone marrow involvement of follicular lymphoma

To characterize the pathways of bone marrow (BM) involvement of follicular lymphoma (FL), we performed morphological and immunophenotypical analysis of tumor cells from lymph nodes (LNs) and corresponding BMs in 21 patients with FL. In three cases, genealogical trees were constructed based on the immunoglobulin variable region heavy chain (IgVH) gene sequences of tumor clones from LNs and BMs. Results showed that FLs within the BMs display identical or lower cytological grades than in the LNs. In the majority of cases, different proportions of tumor cells expressed bcl-2, CD10 and Ki67 in LNs and BMs. Tumor cells in the BM showed ongoing somatic hypermutation of the IgVH genes; the distribution of these mutations was highly consistent with antigen selection. The topology of the genealogical trees revealed that different subclones populate the LN and BM and BM infiltration may occur at different points of the clonal evolution of FL. Early descendants of the original tumor clone and derivatives of diversified tumor clones may invade the BM. These results suggest that the BM involvement of FL is associated with intensive clonal selection of tumor cells, and the BM provides a microenvironment similar to the germinal centers of LNs, where tumor cells retain their biological nature.

High rate of neoplastic cells with genetic abnormalities in proliferation centers of chronic lymphocytic leukemia

In lymph nodes, chronic lymphocytic leukemia (CLL) cells (prolymphocytes and paraimmunoblasts) form proliferation centers (PCs), which are also known as pseudofollicles. To reveal whether PCs play a role in the accumulation of genetic alterations in CLL, we compared deletion at 11q22.3, 13q14.3, and 17p13.1 loci and trisomy 12 by the fluorescence in situ hybridization (FISH) technique in PCs versus surrounding small lymphocytes (SLs) in 12 formalin-fixed paraffin-embedded (FFPE) lymph nodes. The FFPE sections were stained with methylene blue and PCs were marked by laser beam. Subsequent FISH analysis was performed, relocalizing the previously defined regions. Loss of 11q was detected in five cases, loss of 13q in two cases, loss of 17p in two cases, and trisomy 12 in one case. In seven cases PCs contained a significantly higher ratio of cells with genetic alterations compared with the surrounding SLs. Our results show that CLL cells with genetic alterations tend to accumulate in PCs. The clonal expansion of the cell population carrying genetic alterations within PCs may contribute to CLL progression.

Folliculotropic mycosis fungoides: clinicopathological analysis of 17 patients

Folliculotropic mycosis fungoides (FMF) represents a variant of MF characterized by hair follicle invasion of mature, CD4‐positive small lymphoid cells with cerebriform nuclei. The disease displays resistance to standard treatment modalities and has an unfavourable course.

Expression of transforming growth factor‐α in hepatoblastoma

Transforming growth factor‐α (TGF‐α) is a potent stimulator of cell proliferation in the liver and in liver tumors; however, its significance and association with hepatocyte proliferation remains unclear.

Somatic hypermutation of IGVH genes and aberrant somatic hypermutation in follicular lymphoma without BCL-2 gene rearrangement and expression

The findings of this study suggest that follicular lymphoma with typical morphological and immunophenotypic features may develop even without the involvement of the BCL-2 gene. See related perspective article on page 1773. Background Follicular lymphoma is characterized by the t(14;18) translocation resulting in constitutive expression of BCL-2 protein; however approximately 10–15% of follicular lymphomas do not express BCL-2 protein, and a small fraction of these cases does not exhibit translocation of the BCL-2 gene either. It is highly debated whether cases of follicular lymphoma without BCL-2 gene rearrangement and expression represent a separate lymphoma entity with distinct biological characteristics, different from the BCL-2-positive cases. Design and Methods To further characterize follicular lymphomas without BCL-2 gene rearrangement and expression, we analyzed and compared the mutational status of IGVH genes as well as other genes (C-MYC, PAX-5 and RHOH) frequently involved in the specific type of genomic instability called aberrant somatic hypermutation in 11 cases of BCL-2-negative and 7 cases of BCL-2-positive follicular lymphomas. We also determined the levels of expression of activation-induced cytidine deaminase in these cases. Results The analyzed cases were grade 2 and grade 3A follicular lymphomas. Our findings demonstrate that follicular lymphomas without BCL-2 gene rearrangement and expression are associated with ongoing somatic hypermutation of the IGVH genes, low activity of aberrant somatic hypermutation and elevated activation-induced cytidine deaminase expression. These results were in concordance with the results found in the cases of BCL-2-positive follicular lymphoma. Conclusions Although, BCL-2 protein overexpression is considered to be a critical pathogenic event in the development of follicular lymphoma, our findings suggest that follicular lymphomas with the same morphology, immunophenotype, mutational pattern and activation-induced cytidine deaminase expression may develop without the involvement of BCL-2 gene. The present data support the hypothesis that BCL-2-positive and BCL-2-negative follicular lymphomas (grades 1-3A) represent a homogenous group with different initial but several common additional molecular pathways.