E mu N- and E mu L-myc cooperate with E mu pim-1 to generate lymphoid tumors at high frequency in double-transgenic mice.

Transgenic mice that contain the L-myc gene under the control of the immunoglobulin heavy-chain enhancer (E mu) express the transgene preferentially in T cells, develop thymic hyperplasia and are predisposed to T-cell lymphomas. An analogous E mu N-myc transgene is expressed preferentially in pre-B and B cells and provokes the development of B-cell neoplasias. Animals with an E mu pim-1 construct express the transgene in both B and T cells, but succumb to T-cell lymphomas. Complementation of the E mu N- and L-myc transgenic mice by breeding with E mu pim-1 animals leads to much more rapid development and a dramatically higher incidence of lymphoid malignancies, but the lineage specificity prescribed by the E mu N- and L-myc transgenes is maintained. The different oncogenic potential of myc genes is illustrated by the average latency period of tumor manifestation in double transgenics. Whereas c-myc/pim-1 animals develop pre-B-cell leukemia prenatally, the mean latency period for N-myc/pim-1 and L-myc/pim-1 mice is 36 and 94 days respectively. The N- and L-myc transgenes are expressed at high levels in tumors from double transgenic mice, but expression of the endogenous c- and N-myc genes is undetectable, directly implicating the myc transgenes in the tumor formation process.     

Carcinogen-induced lymphomagenesis in pim-1 transgenic mice: dose dependence and involvement of myc and ras

Transgenic mice overexpressing the pim-1 oncogene in their lymphoid compartments are predisposed to T-cell lymphomagenesis but only to the extent that approximately 10% of the transgenic mice develop lymphomas within 34 weeks after birth. Recently, we have shown that lymphomagenesis in pim-1 transgenic mice can be accelerated by infecting pim-1 transgenic mice with murine leukemia viruses or by treating the mice with a relatively low dose of 60 mg of the carcinogen N-ethyl-N-nitrosourea (ENU) per kg of body weight. Here we describe the incidence of tumors as a function of the dose of ENU. Either 200, 15, 4, 1, or 0.1 mg/kg ENU was injected into transgenic and control mice and the tumor incidence was monitored. T-cell lymphomas developed in 100 and 70% of the pim-1 transgenic mice treated with 200 and 15 mg/kg ENU, respectively. Approximately 20% of the Emu-pim-1 transgenic mice developed lymphomas after treatment with either 4, 1, or 0.1 mg/kg ENU. The nontransgenic mice developed lymphomas only after injection with 200 mg/kg (45%). The data show that Emu-pim-1 transgenic mice are approximately 25-fold more susceptible to ENU-induced lymphomagenesis than control mice. In most tumors the expression of c-myc was strongly elevated, probably as a direct or indirect effect of ENU. Analysis of the lymphomas for ras mutations revealed that approximately 10% of the lymphomas bear a ras mutation. The data indicate that at least some of these mutations are not the direct result of alkylation by ENU but rather represent spontaneous mutations that occurred later in the tumorigenic process.     

Deregulated expression of RasGRP1 initiates thymic lymphomagenesis independently of T-cell receptors

RasGRP1 is a Ras-specific exchange factor, which is activated by T-cell receptor (TCR) and promotes TCR-dependent positive selection of thymocytes. RasGRP1 is highly expressed on most T lymphocytic leukemias and is a common site of proviral insertion in retrovirus-induced murine T-cell lymphomas. We used RasGRP1 transgenic mice to determine if deregulated expression of RasGRP1 has a causative role in the development of T-cell malignancies. Thymic lymphomas occurred in three different RasGRP1 transgenic mouse lines. Thymocyte transformation correlated with high transgene expression in early stage lymphomas, indicating that deregulated RasGRP1 expression contributed to the initiation of lymphomagenesis. Expression of the positively selectable H-Y TCR accelerated lymphomagenesis in RasGRP1 transgenic mice. However, the transformed thymocytes lacked markers of positive selection and lymphomas occurred when positive selection was precluded by negative selection of the H-Y TCR. Therefore, initiation of lymphomagenesis via RasGRP1 was not associated with TCR-dependent positive selection of thymocytes. Thymic lymphomas occurred in RasGRP1 transgenic/Rag2-/- mice, demonstrating that neither TCR nor pre-TCR were required for RasGRP1-driven lymphomagenesis. The RasGRP1 transgene conferred pre-TCR-independent survival and proliferation of immature thymocytes, suggesting that deregulated expression of RasGRP1 promotes lymphomagenesis by expanding the pool of thymocytes which are susceptible to transformation.     

Lymphomagenesis in E mu-myc transgenic mice can involve ras mutations

Transgenic mice bearing c-myc driven by the immunoglobulin heavy chain enhancer (E mu) initially exhibit a preneoplastic lymphoproliferative syndrome from which clonal pre-B or B lymphomas develop at random. To investigate whether this transition involves the activation of oncogenes capable of transforming fibroblasts, we transfected DNA from 14 E mu-myc lymphomas into NIH3T3 cells and tested the tumorigenicity of the transfectants in nude mice. By this assay and subsequent direct analysis of the lymphoma mRNA by cDNA cloning or the polymerase chain reaction, two independent E mu-myc lymphomas were shown to contain an N-ras or a K-ras oncogene mutated at codon 61. When incorporated into a recombinant retrovirus, the mutant N-ras allele could collaborate with myc to transform preneoplastic E mu-myc bone marrow pre-B cells. These results indicate that spontaneous mutation of ras genes is one pathway to lymphomagenesis in E mu-myc mice but that many of the lymphomas arise in response to changes that do not register in fibroblasts.     

Downregulation of the p53 tumor suppressor gene and upregulation of the bcl-2 gene in retinoic acid receptor alpha-deficient transgenic mice

We recently demonstrated lymphoma development in transgenic mice deficient in retinoic acid receptor alpha (RARalpha). High incidence of lymphoma development in this transgenic mouse model system was similar to lymphoma development in p53 knockout mice. In an effort to understand the molecular basis of lymphomagenesis in RARalpha-deficient transgenic mice, we compared the levels of RARalpha to the levels of p53 mRNA, and Bcl-2, and Bax proteins in lymphoid and non-lymphoid tissues and in lymphomas derived from the RARalpha-deficient transgenic mice. The p53 mRNA levels were depleted in various tissues including spleen ( approximately 96%), thymus ( approximately 29%) and bone marrow ( approximately 62%) of RARalpha-deficient transgenic mice when compared with the normal littermates, and the reduction in p53 mRNA expression in the various tissues examined was proportional to the reduction in RARalpha expression. Bcl-2 to Bax ratios were highly increased in the lymphoid compartments (spleen >bone marrow >thymus) because of selective overexpression of Bcl-2 protein. In summary, RARalpha downmodulation in this transgenic mouse model system was accompanied by p53 downmodulation and deregulation of Bcl-2 to Bax ratios in the lymphoid compartments.     

Oncogene Rearrangement in Non-Hodgkin's Lymphoma with a 14q + Chromosome of Unknown Origin

Southern blot analysis was performed with a panel of DNA probes to detect rearrangements of c-myc, bcl-1, bcl-2 and bcl-1 in 14 cases of B-cell non-Hodgkin's lymphoma (NHL) with a clonal cytogenetic rearrangement involving the chromosome 14q32 locus and no known donor chromosome [t(14;?)(q32;?)]. In our experience, 21% of all chromosomal abnormalities involving the 14q32 locus in B-cell NHL are of this type. We found oncogene rearrangements in five of the 14 cases: bcl-1 rearrangement on one mantle zone lymphoma, bcl-2 rearrangements in two follicular lymphomas, and c-myc rearrangements in two small noncleaved cell lymphomas. We conclude that a 14q32 + abnormality of unknown origin is a relatively frequent karyotypic finding in B-cell NHL. In one third of the cases, known oncogenes that have been previously described in reciprocal translocations involving the immunoglobulin heavy chain locus were shown to be involved in the 14q32 + abnormality. The translocations in the other cases are likely to have involved one of the above oncogenes with breakpoints not revealed by the probes employed, other known oncogenes, or oncogenes that have not yet been identified.     

Block of T cell development in P53-deficient mice accelerates development of lymphomas with characteristic RAG-dependent cytogenetic alterations

Mice deficient in the DNA damage sensor P53 display normal T cell development but eventually succumb to thymic lymphomas. Here, we show that inactivation of the TCR beta gene enhancer (E beta) results in a block of T cell development at stages where recombination-activating genes (RAG) are expressed. Introduction of the E beta mutation into p53-/- mice dramatically accelerates the onset of lethal thymic lymphomas that harbor RAG-dependent aberrant rearrangements, chromosome 14 and 12 translocations, and amplification of the chromosomal region 9A1-A5.3. Phenotypic and genetic analyses suggest that lymphomas emerge through a normal thymocyte development pathway. These findings provide genetic evidence that block of lymphocyte development at stages with RAG endonuclease activity can provoke lymphomagenesis on a background with deficient DNA damage responses.     

Primary diffuse large B cell lymphoma of the stomach: analysis of somatic mutations in the rearranged immunoglobulin heavy chain variable genes indicates antigen selection.

Gastric low grade MALT lymphomas show a pattern of somatic mutations in their rearranged immunoglobulin genes, indicative of antigen selection. This provides evidence for antigen stimulation in the lymphomagenesis. Gastric diffuse large B cell lymphomas develop secondary to low grade MALT lymphoma or de novo. To study whether antigen-selection is also a feature of primary diffuse large B cell lymphomas, we analysed somatic mutations in the rearranged immunoglobulin heavy chain (IgH) variable genes (VH). The rearranged VH genes of six cases of gastric primary diffuse large B cell lymphoma were amplified from genomic or complementary DNA by a VH gene family-specific polymerase chain reaction method. The PCR products were directly sequenced and were compared to published germline sequences to analyse somatic mutations. Similarly to low grade MALT lymphomas 5/6 primary diffuse large B cell lymphomas show a pattern of somatic mutation in their rearranged VH genes, indicative of antigen selection and suggesting a role for antigens in lymphomagenesis. One case showed bi-allelic VH gene rearrangements, which were non-functional due to extensive deletions. Antigen selection could not be demonstrated or excluded. Antigen selection is a common feature in most analysed primary diffuse large B cell lymphomas, although some heterogeneity in the mechanisms involved in the lymphomagenesis of gastric primary diffuse large B cell lymphomas has not been excluded entirely (case 4).     

Notch and T cell malignancy

Notch signaling is required for normal T cell development. However, Notch expression must be precisely regulated as constitutive Notch signaling leads to T cell lymphomas. Recent evidence has provided insights into potential mechanisms of Notch-mediated lymphomagenesis and its relationship to T cell development. The evidence suggests that Notch likely interacts with several important cellular pathways and can cooperate with other oncogenes during lymphomagenesis. In particular, Notch appears to modulate pre-TCR signaling, inhibit the E2A pathway, and in murine leukemia models, frequently cooperates with Myc, E2A-PBX and dominant negative Ikaros dysregulation. This review will present current knowledge in these areas and explore theories on Notch-mediated T cell lymphomagenesis.     

Molecular pathogenesis of AIDS-associated non-Hodgkin's lymphoma

The pathogenesis of non-Hodgkin's lymphoma (NHL) in HIV-infected individuals is currently poorly understood; however, recent molecular studies have subdivided these lymphomas into distinct molecular pathologic entities. Similar to endemic and sporadic Burkitt's lymphoma, monoclonal B-lymphoma subsets were found to be infected with Epstein-Barr virus (EBV) or have c-myc gene rearrangements, suggesting a role for EBV infection or chromosomal translocation in a subset of AIDS NHLs. Similar to lymphomas that occur in immunosuppressed transplant patients, EBV-positive polyclonal lymphomas also have been described. Unique to HIV-infected patients, however, is the subset of polyclonal B-cell lymphoma with no evidence for EBV infection. Based on these molecular studies, it is apparent that the AIDS NHLs represent a heterogeneous set of diseases with a number of pathogenic processes involved in lymphomagenesis.     

B-cell lymphomagenesis in SIV-immunosuppressed cynomolgus monkeys

B-cell lymphomas developed frequently (approx. 40%) in SIVsm (SMM3) immunosuppressed monkeys and were mostly extranodal, aggressive and all associated with an EBV-related simian herpes virus operationally designated herpes virus Macoca fascicularis (HVMF-1). Lymphoma tissues from 21 monkeys were studied by PCR and DNA PAGE for mono/oligoclonality of the VDJ-rearranged IgH genes. Most lymphomas (n = 15) showed a monoclonal and approximately 1/3 (n = 6) an oligoclonal VDJ rearrangement pattern. The time after infection to tumor presentation was significantly shorter for oligoclonal than for monoclonal lymphomas, suggesting that oligoclonal selection frequently precedes the outgrowth of a single malignant clone. Comparison of the VDJ rearrangements in an established lymphoma cell line and the original, oligoclonal lymphoma tissue indicated in vitro selection of one HVMF-infected clone. Longitudinal studies of sequential lymph-node biopsies showed that the malignant lymphoma clone in 3 out of 8 lymphomas could be identified as a predominant clone in lymph nodes 2-12 months after SIV infection and 6-10 months before clinical presentation of the lymphomas. VDJ-rearranged DNA corresponding to that of the lymphomas was also detected in most sera at the time of lymphoma manifestation but not in corresponding PBL preparations. Clearly, the SIVsm AIDS model in cynomolgus monkeys represents a powerful tool for biological and clinical studies of herpes-virus-associated lymphomagenesis in immunosuppressed states. © 1995 Wiley-Liss, Inc.     

U-2940, a human B-cell line derived from a diffuse large cell lymphoma sequential to Hodgkin lymphoma

Several patterns of association between Hodgkin and non-Hodgkin lymphomas are recognized, some of which support a common cellular origin or shared transformation events for both malignancies. We describe the U-2940 cell line derived from a diffuse large B-cell lymphoma with some features consistent with mediastinal large B-cell lymphoma, clinically apparent 1 month after the initial course of chemotherapy for Hodgkin's disease, fulfilling the criteria for composite malignancies. U-2940 cells display a mature B phenotype with hypermutated IgH rearrangement typical of germinal/postgerminal center origin. The cell line is negative for Epstein-Barr virus and no evidence of t(14;18) was found. U-2940 cells display multiple chromosomal rearrangements similar to recurrent aberrations described in both Hodgkin and non-Hodgkin lymphomas, also partially shared by U-2932 derived from a B-cell lymphoma sequential to Hodgkin's disease. The original large B-cell lymphoma and the U-2940 cell line bear microsatellite instability, an abnormality associated with particular subtypes of non-Hodgkin lymphomas and found in tissues involved by Hodgkin lymphoma. Therefore, U-2940 cells bear several features known to occur in Hodgkin and in non-Hodgkin lymphomas, leading to the assumption that this cell line may constitute a useful tool to address elective pathways of lymphomagenesis and eventually the Hodgkin and non-Hodgkin lymphoma association.     

Early commitment to neoplasia in murine B- and T-cell lymphomas arising late in life

Lymphomas arise spontaneously in C57BL/10.H-2aH-4b (2a4b) mice greater than 1 year old. The purpose of this study was to determine when cells become committed to neoplasia and whether genes linked to H-2a or H-4b are a factor in predisposition to genesis of lymphoma. Following transplantation of a pool of spleen cells in large groups of mice, lymphoma incidence increased 1.8- to 2.1-fold and mean latent periods decreased, compared with those in controls. Lymphomas arising in mice that received the same pool of spleen cells often displayed identical rearrangements of genes for immunoglobulin and T-cell receptor. This finding indicates that the lymphomas were derived from expanding clones of cells present in the donor mice prior to transfer. The age of the donor mice determined the latency of lymphomas arising after spleen cell transfer. When donors were 3-4 months old at the time of spleen cell transfer, lymphomas were detected in the recipients 1 year later. When mice 1.5-2 years old were used as donors, tumors were observed 3 months after transfer. Almost all of these tumors were clonally related B-cell lymphomas. We conclude that the lymphomas seen late in life arise from premalignant clones of cells that have become committed to neoplasia in relatively young animals. These clones normally follow an indolent course and are manifested clinically only in old age. Neither H-2a nor H-4b alone appeared to alter susceptibility to the genesis of lymphoma in similar experiments with H-2a and H-4b congenic mice.     

Suppression of thymic lymphomas and increased nonthymic lymphomagenesis in Trp53-deficient mice lacking inducible nitric oxide synthase gene

Trp53-deficient mice spontaneously develop lymphomas, mainly of thymic origin, although the molecular mechanism remains largely unknown. As several interaction effects between p53 and iNOS have been reported, we hypothesized that iNOS activity in the thymus is causally linked to lymphomagenesis in Trp53-deficient mice. We therefore created mouse strains with different combinations of the Trp53 and iNOS genes. Western blot and histologic analyses showed that the iNOS protein was constitutively expressed in the thymus independently of Trp53 status and its expression was enhanced in Trp53+/- and Trp53-/- mice compared to Trp53+/+ mice. Homozygous disruption of iNOS decreased the incidence of thymic lymphomas by almost 40% (p=0.087) and 90% (p<0.05) in Trp53-/- and Trp53+/- mice, respectively, compared to the respective iNOS wild-type mice but significantly (p<0.05) increased the development of nonthymic lymphomas in Trp53-/- and Trp53+/- mice. Although iNOS gene disruption did not affect the phenotype of thymic lymphomas, absence of the iNOS gene shifted the spectrum of nonthymic lymphoma from the B-cell to the T-cell lineage. RT-PCR analysis revealed enhanced expression of IL-10, which could have a promoting effect on lymphomagenesis, even without any stimulation, in the spleen of aging mice with the gene combinations Trp53-/-iNOS-/- and Trp53+/-iNOS-/- but not Trp53-/-iNOS+/+ or Trp53+/-iNOS+/+. These results suggest that iNOS could increase the development of thymic lymphomas in Trp53-deficient mice. While iNOS may have protective effects against nonthymic lymphomagenesis, the regulation of cytokine production by iNOS may be involved in the underlying mechanism of antilymphomagenesis effects in the peripheral lymphoid organ.     

Lymphomas in patients with Sjögren's syndrome: review of the literature and physiopathologic hypothesis

The occurrence of non Hodgkin's lymphoma (NHL) is the most serious complication of Sj?gren's syndrome (SS). Taking the opportunity to study 16 patients with lymphoma and an underlying SS, we performed a review of literature concerning SS and lymphoma and made an hypothesis on the physiopathology of lymphoproliferation in patients with SS. Lymphomas occurring in patients with SS are in most cases low grade marginal zone lymphomas (MZL). They arise frequently in mucosal extranodal sites, not only in the salivary glands but also the stomach and the lung. These lymphomas are not associated with viruses including hepatitis C virus (HCV), Epstein-Barr virus, human herpes virus 8 or human T lymphotropic virus-I, known to be present in other types of lymphomas. Some of the translocations or mutations of oncogenes or anti-oncogenes described in other lymphomas are also detected in SS-associated lymphomas. Lymphomas complicating SS share a number of characteristics with lymphomas complicating HCV infection. We make the assumption that, in both diseases, the first event of lymphomagenesis is the chronic stimulation, on the site of the disease, of polyclonal B-cells secreting rheumatoid factor (RF). Then, these RF B-cells may become monoclonal and disseminate in other organs. The monoclonal secreted RF complexed with polyclonal IgG may cryoprecipitate. The following step would be a chromosomal abnormality (e.g. trisomy 3) which would confer to these cells a low grade B-cell lymphoma compartment. A last event (e.g. mutation of p53) could transform this low grade B-cell lymphoma into a high grade large B-cell lymphoma. If this hypothesis was correct, most of B-cell lymphomas associated with SS should have a surface immunoglobulin with RF activity and should grow through an auto-antigen driven process.