Burkitt's lymphoma - a human tumor model system for immunological studies.

Burkitt's lymphoma occurs mainly in parts of tropical Africa and has attracted the attention of experimental workers due to its epidemiological and clinical features, which indicate a viral etiology and a host immune response to the tumor. As a result of virological studies, Epstein-Barr virus (EBV) DNA has been demonstrated in almost all tested biopsies of African BL. This contrasts to the absence of EBV in all, or almost all, of the non-African Burkitt's lymphoma-like tumors, even though the number of tested tumors in this group is small, and to the lack of EBV in all other types of lymphoma or leukemia. Immunological studies have revealed the presence of antibodies to different EBV-associated antigens in all African patients with Burkitt's lymphoma. However the antibodies are not specific for Burkitt's lymphoma but are found in most adults all over the world, although at lower levels. They cannot therefore serve diagnostic purposes, but they can give prognostic information and occasionally give clues to the mechanisms behind late tumor recurrences, and possibly guide so-called immunotherapy. Burkitt's lymphoma patients contrast to appropriate control groups where some of the persons are anti-EBV seronegative, and this, together with the presence of EBV in Burkitt's lymphoma biopsies and the absence of EBV in other lymphomas, even though the cell type involved may be infectable by EBV in vitro and the tumor may arise in an EBV-carrying person, favors an etiological role in EBV in Burkitt's lymphoma and speaks against the "passenger" hypothesis, according to which EBV is picked up by the Burkitt's lymphoma cell which happens to be particularly suitable for EBV persistence. To explain the geographical distribution, a cofactor, such as certain forms of malaria, has been implied.     

A new translocation in Burkitt's tumor cells

Summary A t(8;22)(q24;q11) translocation was found in blood, bone marrow, and ascites cells from a European Burkitt's lymphoma. Cell surface markers were identified as monoclonal IgG. The relationship between these two unusual findings is questionable in this cytologically typical Burkitt's lymphoma.     

Epstein-Barr virus latent membrane protein: induction of B-cell activation antigens and membrane patch formation does not require vimentin.

The latent membrane protein (LMP) of Epstein-Barr virus (EBV) forms patches associated with the vimentin intermediate filament system in EBV-transformed lymphoblastoid cell lines, EBV-infected Burkitt's lymphoma cells, and LMP-transfected, EBV-negative Burkitt's lymphoma cells. By gene transfer, LMP induces the expression of vimentin and B-cell activation antigens in EBV-negative Burkitt's lymphoma cells. We have now expressed LMP in an EBV-positive Burkitt's lymphoma cell line, Daudi, which does not express any LMP or vimentin. In these Daudi transfectants, LMP still formed plasma membrane patches in the absence of vimentin. LMP did not resist nonionic detergent extraction in Daudi cells as it does in vimentin-expressing cells. LMP still retained functional activity as judged by induction of B-cell activation antigens. These data indicate that LMP can form plasma membrane patches and induce B-lymphocyte activation independent of vimentin association.     

Epstein-Barr nuclear antigen 1-specific CD4(+) Th1 cells kill Burkitt's lymphoma cells

The gamma-herpesvirus, EBV, is reliably found in a latent state in endemic Burkitt's lymphoma. A single EBV gene product, Epstein-Barr nuclear Ag 1 (EBNA1), is expressed at the protein level. Several mechanisms prevent immune recognition of these tumor cells, including a block in EBNA1 presentation to CD8(+) killer T cells. Therefore, no EBV-specific immune response has yet been found to target Burkitt's lymphoma. We now find that EBNA1-specific, Th1 CD4(+) cytotoxic T cells recognize Burkitt's lymphoma lines. CD4(+) T cell epitopes of EBNA1 are predominantly found in the C-terminal, episome-binding domain of EBNA1, and approximately 0.5% of peripheral blood CD4(+) T cells are specific for EBNA1. Therefore, adaptive immunity can be directed against Burkitt's lymphoma, and perhaps this role for CD4(+) Th1 cells extends to other tumors that escape MHC class I presentation.     

Proliferation inhibitory effect of human alpha interferon on primary explants of Burkitt lymphoma: inverse relationship to patient survival

Eleven biopsies from 9 patients with Burkitt's lymphoma were tested for their sensitivity to the cell multiplication inhibitory activity of interferon. Three were resistant to interferon while 8 were sensitive to various degrees. Different biopsies from the same patient did not differ in interferon sensitivity. These results indicate that Burkitt's lymphoma cells might be resistant to interferon already in vivo as previously shown for some derived cell lines tested in vitro. The results imply an inverse relationship between patient survival and interferon sensitivity of the tumor cells.     

Burkitt''s lymphoma: a pericardial presentation

Described herein is a case of childhood Burkitt's lymphoma initially presenting as a pericardial effusion. A cytological diagnosis was made from a Wright's-Giemsa stained cytospin preparation. Supporting diagnostic evidence was provided by immunological surface marker analysis and electron microscopy. To our knowledge, Burkitt's lymphoma has not hitherto been diagnosed initially from the morphology of cells in pericardial fluid.     

Epstein-Barr virus-associated lymphoproliferative disorders

Epstein-Barr virus (EBV) is a ubiquitous member of the herpesvirus family that is associated with a variety of lymphomas and lymphoproliferative diseases. It encodes a multitude of genes that drive proliferation or confer resistance to cell death. Among these are two key viral proteins which mimic the effects of the activated cellular signaling proteins. EBV-associated lymphomas include Burkitt's lymphoma; natural killer (NK)/T-cell lymphoma, lymphoma and lymphoproliferative diseases in immunocompromized populations, and Hodgkin's lymphoma. The character of the viral association differs among these entities with some consistently associated with EBV in all populations and all parts of the world, and others associated with the virus only in particular circumstances. An example of the former is nasal NK/T-cell lymphoma, while an example of the latter is Burkitt's lymphoma. The pattern of viral gene expression also varies among tumor types with different viral genes playing key roles in different tumors and conferring sensitivity to immune surveillance. Thus some of the post-transplant lymphoproliferative diseases are exquisitely sensitive to CD8 T-cell immunosurveillance, while other tumors such as Burkitt's lymphoma may be nearly impervious to such surveillance. Knowledge of the EBV association is not only important for understanding the pathogenesis of these tumors, but is increasingly important for diagnosis, monitoring and treatment.     

Genome of a mononucleosis Epstein-Barr virus contains DNA fragments previously regarded to be unique to Burkitt's lymphoma isolates

We wished to learn whether the genomes of strains of EMB isolated from patients with infectious mononucleosis are consistently distinguishable from those of strains from Burkitt's lymphoma. The genome of a new transforming strains (FF41) of EBV isolated from saliva of a patient with uncomplicated infectious mononucleosis was compared with the DNA of B95-8, the only other available virus from mononucleosis. It had been found previously that B95-8 has a deletion of about 8 Md in the region of the physical map represented by the Eco RI C, Hind III D, and Bam HI I fragments. The W91 and HR-1 isolates for Burkitt's lymphoma are not deleted in this region and it had been proposed that additional information was characteristic of EBV isolates from Burkitt's lymphoma. By means of restriction enzyme analysis, blot hybridization experiments and molecular cloning of FF41 DNA we demonstrate that the deletion found in B95-8 is not present in the new mononucleosis isolate. The FF41 genome contains an extra 8 Md of DNA, represented by Bam HI fragments B', W' and I', which are located in a larger Eco RI C fragment. Thus the genome of this salivary isolate contains DNA that had previously been regarded to be unique to strains from Burkitt's lymphoma. It is therefore unlikely that major insertions or deletions in the EBV genome account for differences in disease manifestation following EBV infection.     

Burkitt's lymphoma. Distinction of subgroups by morphometric analysis of the characteristics of 55 cell lines

In an attempt to clarify the controversy about the distinction between Burkitt's and non-Burkitt's small noncleaved lymphomas, 55 cell lines derived from 48 Burkitt's lymphoma patients were characterized by morphometry on plastic-embedded sections. The results of the measurements permitted the identification of five main cytologic types, with regard to nuclear size, nuclear area dispersion and irregularity of nuclear profiles. The presence of the Epstein-Barr virus (EBV) and the geographic origin of the tumors seemed to play essential roles in the determination of nuclear size, with a significantly larger size seen in EBV-positive cell lines, and especially in the African lines among these. Immunoglobulin profile and monoclonal antibody expression also correlated with the nuclear size. Two conclusions may be drawn from this analysis. An in vivo transformation of the cells of Burkitt's lymphoma can be postulated to explain the wide morphologic spectrum of lymphomas presenting a rearrangement of chromosome 8. The fact that typical and atypical Burkitt's lymphomas cannot be differentiated by study of their derived cell lines raises the question as to the validity of the distinction between the two subtypes of small noncleaved lymphomas.     

Is there a functional equivalence between abnormalities of the long arm of chromosome 1 and the presence of Epstein-Barr virus in continuous lines of Burkitt's lymphoma?

Chromosome 1 long arm abnormalities (translocations, partial of complete trisomies) are non-randomly but inconstantly associated with specific translocations involving chromosomes 8, and 2, 14 or 22 in Burkitt's lymphomas and leukemias. All nine Burkitt's lymphoma cell lines not associated with Epstein-Barr virus (EBV) were shown to exhibit a chromosome 1 long arm abnormality and were present in only 3 out of 18 EBV positive cell lines. Bands 1q23 - 1q24 were involved in EBV-negative cell lines. It was thus hypothesised that genetic information resembling that included in viral genome exists on chromosome 1 long arm. This hypothesis implies new possible aspects of relationship between Burkitt's cell line proliferation and EBV.     

Epstein-Barr virus-positive Burkitt's lymphoma in a German woman during pregnancy

A fatal case of a Burkitt's lymphoma which occurred in a 34-year-old German woman during pregnancy is described. Nearly all organs showed either diffuse or nodular infiltration by tumor cells. Placenta and fetus were free of detectable tumor tissue. The patient had extremely high antibody titers (1 : 2056), both against Epstein-Barr virus capsid antigen (VCA) and the early antigen complex (EA). Within the tumor cells the Epstein-Barr virus-specific nuclear antigen EBNA and viral DNA was detected. A cell line established from a tumor biopsy displayed a translocation involving chromosomes 2 and 8. The role of Epstein-Barr virus in the development of Burkitt's lymphoma is discussed.     

Three breakpoints of variant t(2;8) translocations in Burkitt''s lymphoma cells fall within a region 140 kilobases distal from c-myc.

The variant translocations t(2;8) in Burkitt's lymphoma cells join band q24 of chromosome 8, distal from c-myc, to the Igkappa locus, with considerable variation in the location of the breakpoints on chromosome 8. We report the cloning and molecular characterization of a chromosome 8 region, distal from the c-myc locus, which encompasses the breakpoints of the Burkitt's lymphoma cell lines BL64, BL21, and LY91 within 11 kilobase pairs, termed provisionally bvr-1 (Burkitt's variants' rearranging region 1). Using probes from the c-myc, the bvr-1, and the human pvt-1 loci obtained by chromosome walking coupled with pulsed-field gel electrophoresis, we have constructed a physical map of the region 3' of c-myc. We map bvr-1 and pvt-1 about 140 and 260 kilobase pairs, respectively, distal from c-myc.     

DNA degradation during radiation death of cultured cells

The method of flow cytofluorometry was used to study postirradiation changes in plasma membrane permeability and DNA content of the Burkitt's lymphoma cells (Raji line). At a dose of 10 Gy, the increase in membrane permeability preceded the appearance of cells with diminished DNA content. The synchronization of cells in phase G2 was associated with a virtually complete radiation arrest of mitoses. The postirradiation electrophoretic analysis of DNA of the Burkitt's lymphoma cells and of Syrian and Chinese hamster fibroblasts showed that the DNA degradation is unordered and results perhaps from activation of hydrolases in the dead cells.     

Effect of gangliosides on binding, internalization and cytotoxic activity of ricin

The only gangliosides in Burkitt's lymphoma EB-3 cells is GM3. Treatment of Burkitt's lymphoma EB-3 cells with gangliosides GM1 or GM3 results in their binding to and partial incorporation into the cell membrane. About 25% of cell-associated ganglioside GM1 can interact with the ricin. However, such an increase in the number of binding sites does not enhance but rather decreases the cytotoxic effect of ricin. A similar protective effect was observed when the cells were pretreated with ganglioside GM3. In contrast, the increase in ricin biding sites caused by pretreatment of the cells with neuraminidase was accompanied by increase in ricin cytotoxicity. These differences may be related to observed differences in the rate of ricin-endocytosis by native and ganglioside-treated cells.     

NF-kappa B sites function as positive regulators of expression of the translocated c-myc allele in Burkitt''s lymphoma.

An in vivo footprint over a potential NF-kappa B site in the first exon of the c-myc gene has been identified on the translocated allele in the Ramos Burkitt's lymphoma cell line. The potential NF-kappa B site in the 5' flanking sequence of c-myc was found to be occupied on the translocated allele in the Raji Burkitt's cell line. Electrophoretic mobility shift assays with each of these sequences demonstrated complexes with mobilities identical to those of the NF-kappa B site from the kappa light-chain gene. A supershift was obtained with anti-p50 antibody with the exon site. The upstream-site shift complex disappeared with the addition of anti-p50 antibody. Binding of NF-kappa B proteins to the c-myc exon and upstream sites was demonstrated by induction of binding upon differentiation of pre-B 70Z/3 cells to B cells. UV cross-linking experiments revealed that a protein with a molecular mass of 50 kDa bound to the exon and upstream sites. Transfection experiments with Raji cells demonstrated that both sites functioned as positive regulatory regions, with a drop in activity level when either site was mutated. Access to these sites is blocked in the silent normal c-myc allele in Burkitt's lymphoma cells, while Rel family proteins bind to these sites in the translocated allele. We conclude that the two NF-kappa B sites function as positive regulatory regions for the translocated c-myc gene in Burkitt's lymphoma.     

Immunotoxin-mediated elimination of clonogenic tumor cells in the presence of human bone marrow

An immunotoxin was synthesized with pokeweed antiviral protein and an IgG1 monoclonal antibody directed against human B and pre-B cells. The B43 murine monoclonal antibody does not react with normal human bone marrow precursor cells. The immunotoxin bound to all Burkitt's lymphoma cell lines that were tested but not to human peripheral blood T cells. The ability of antibody-toxin conjugate to inhibit human lymphoblast cell lines was checked in a clonogenic assay system. The immunotoxin in the presence of chloroquine elicited 5.8 logs of killing of Burkitt's lymphoma cells (B-ALL). The efficient inhibition of clonogenic growth of B-ALL cells was not affected by the presence of normal bone marrow cells. The immunotoxin was not very toxic to pluripotent stem cells; less than 50% of the stem cells were lost under conditions where 5.6 logs of clonogenic lymphoma cells were eliminated from a 100-fold excess of normal marrow cells. Further, when assayed by long-term human bone marrow cultures, immunotoxin treatment did not result in a significant loss of pluripotent precursor cells.