Epstein-Barr virus-transformed human precursor B cell lines: altered growth phenotype of lines with germ-line or rearranged but nonexpressed heavy chain genes

miR-488-3p sponged by circ-0000495 and mediated upregulation of TROP2 in head and neck squamous cell carcinoma development

TROP2 (trophoblast cell surface antigen 2) overexpression has been reported in many human cancers. The correlation between TROP2 and tumor aggressiveness has implied it could be a prognostic indicator. However, the roles of TROP2 and their underlying mechanisms remain of great interest in head and neck squamous cell carcinoma (HNSCC) biology. In the current study, the prognostic significance of TROP2 in HNSCC archival samples was determined using immunohistochemistry. Quantitative reverse transcriptase PCR (qRT-PCR) was used to measure the phenotypic effects of TROP2 knockdown, miR-488-3p re-expression, and circRNAs expression. Cell viability, migration/invasion as well as in vivo tumor formation assays were accessed. The interactions of miRNAs-TROP2 or circRNAs-miRNAs were determined by qRT-PCR, western blot analysis and luciferase assays. TROP2 was demonstrated overexpression in HNSCC patients and cancer cell lines. High expression of TROP2 was significantly associated with patient relapse. TROP2 promoted tumor cell proliferation, migration, invasion, and tumor growth, through AKT and MAPK pathways. Further investigation revealed that TROP2 is a direct target of miR-488-3p, while circ-0000495 bounds to miR-488-3p. Our study unraveled a novel mechanism by which down-regulation of miR-488-3p sponged by circ-0000495 releases its epigenetic silencing to TROP2. The increased TROP2 promotes tumor proliferation, therefore, providing evidence in support of targeting the circ-0000495/miR-488-3p/TROP2 axis in contributing to HNSCC therapy and preventing tumor metastasis.

Upregulation of the Chemokine Receptor CCR2B in Epstein‒Barr Virus-Positive Burkitt Lymphoma Cell Lines with the Latency III Program

CCR2 is the cognate receptor to the chemokine CCL2. CCR2–CCL2 signaling mediates cancer progression and metastasis dissemination. However, the role of CCR2–CCL2 signaling in pathogenesis of B-cell malignancies is not clear. Previously, we showed that CCR2B was upregulated in ex vivo peripheral blood B cells upon Epstein‒Barr virus (EBV) infection and in established lymphoblastoid cell lines with the EBV latency III program. EBV latency III is associated with B-cell lymphomas in immunosuppressed patients. The majority of EBV-positive Burkitt lymphoma (BL) tumors are characterized by latency I, but the BL cell lines drift towards latency III during in vitro culture. In this study, the CCR2A and CCR2B expression was assessed in the isogenic EBV-positive BL cell lines with latency I and III using RT-PCR, immunoblotting, and immunostaining analyses. We found that CCR2B is upregulated in the EBV-positive BL cells with latency III. Consequently, we detected the migration of latency III cells toward CCL2. Notably, the G190A mutation, corresponding to SNP CCR2-V64I, was found in one latency III cell line with a reduced migratory response to CCL2. The upregulation of CCR2B may contribute to the enhanced migration of malignant B cells into CCL2-rich compartments.

Epstein-Barr virus and Burkitt lymphoma

In 1964, a new herpesvirus, Epstein-Barr virus (EBV), was discovered in cultured tumor cells derived from a Burkitt lymphoma (BL) biopsy taken from an African patient. This was a momentous event that reinvigorated research into viruses as a possible cause of human cancers. Subsequent studies demonstrated that EBV was a potent growth-transforming agent for primary B cells, and that all cases of BL carried characteristic chromosomal translocations resulting in constitutive activation of the c-MYC oncogene. These results hinted at simple oncogenic mechanisms that would make Burkitt lymphoma paradigmatic for cancers with viral etiology. In reality, the pathogenesis of this tumor is rather complicated with regard to both the contribution of the virus and the involvement of cellular oncogenes. Here, we review the current understanding of the roles of EBV and c-MYC in the pathogenesis of BL and the implications for new therapeutic strategies to treat this lymphoma.

Circulating tumor cells in Hodgkin's lymphoma - a review of the spread of HL tumor cells or their putative precursors by lymphatic and hematogenous means, and their prognostic significance

About 15% of patients diagnosed with classical Hodgkin's lymphoma (cHL) are considered high risk with unfavorable prognosis. The biology of the disease bears a direct relationship to its clinical course. However, some aspects of the disease are still being debated. Related topics include origin of neoplastic cells as circulating precursor versus germinal center B cell, and disease metastasis via hematogenous routes and the effect of HL circulation on relapse potential and further spread of the disease. The terminally differentiated giant neoplastic Hodgkin Reed-Sternberg (HRS) cells (HRSC) have limited proliferation and lack mobility. Therefore, they are unable to penetrate epithelium. Thus, the clinical aggressiveness of HRSCs that disseminate via both lymphatic and hematogenous may be determined by their molecular composition. This review discusses in detail the historical perspectives on scientific and clinical evidences of precursors of circulating HL cells and the prognostic importance of these circulating cells for predicting outcome.

Epstein-Barr virus infection of naïve B cells in vitro frequently selects clones with mutated immunoglobulin genotypes: implications for virus biology

Epstein-Barr virus (EBV), a lymphomagenic human herpesvirus, colonises the host through polyclonal B cell-growth-transforming infections yet establishes persistence only in IgD⁺ CD27⁺ non-switched memory (NSM) and IgD⁻ CD27⁺ switched memory (SM) B cells, not in IgD⁺ CD27⁻ naïve (N) cells. How this selectivity is achieved remains poorly understood. Here we show that purified N, NSM and SM cell preparations are equally transformable in vitro to lymphoblastoid cells lines (LCLs) that, despite upregulating the activation-induced cytidine deaminase (AID) enzyme necessary for Ig isotype switching and Ig gene hypermutation, still retain the surface Ig phenotype of their parental cells. However, both N- and NSM-derived lines remain inducible to Ig isotype switching by surrogate T cell signals. More importantly, IgH gene analysis of N cell infections revealed two features quite distinct from parallel mitogen-activated cultures. Firstly, following 4 weeks of EBV-driven polyclonal proliferation, individual clonotypes then become increasingly dominant; secondly, in around 35% cases these clonotypes carry Ig gene mutations which both resemble AID products and, when analysed in prospectively-harvested cultures, appear to have arisen by sequence diversification in vitro. Thus EBV infection per se can drive at least some naïve B cells to acquire Ig memory genotypes; furthermore, such cells are often favoured during an LCL's evolution to monoclonality. Extrapolating to viral infections in vivo, these findings could help to explain how EBV-infected cells become restricted to memory B cell subsets and why EBV-driven lymphoproliferative lesions, in primary infection and/or immunocompromised settings, so frequently involve clones with memory genotypes.

Epstein-Barr virus (EBV), a growth-transforming virus linked to several B cell lymphomas in man, is usually carried as an asymptomatic latent infection in B lymphocytes. Such virus carriage selectively involves memory, but not naive, B cells. How this selectivity is achieved is poorly understood since we find that naive and memory cell types are equally susceptible to infection and growth transformation to lymphoblastoid cell lines in vitro. Here we ask if EBV-transformation of purified naïve B cells can induce key features of memory cells, namely immunoglobulin (Ig) class switching and Ig gene mutation. We find that EBV does not induce Ig class switching (though the infected cells remain responsive to exogenous switch signals) but can induce Ig gene mutation. Thus, within 4 weeks of infecting naive B cell preparations, one can often detect cells carrying Ig mutations which appear to have arisen by somatic hypermutation in vitro. Furthermore, in many cases such cells become dominant during clonal evolution of the emergent EBV-transformed cell line. Overall these findings suggest a possible explanation as to why EBV is selectively found in memory B cell populations in vivo and why EBV-positive lymphoproliferative lesions/lymphomas so frequently involve clones with mutated Ig genotypes.

Restricted expression of Epstein-Barr virus latent genes in murine B cells derived from embryonic stem cells

Background

Several human malignancies are associated with Epstein-Barr virus (EBV) and more than 95% of the adult human population carries this virus lifelong. EBV efficiently infects human B cells and persists in this cellular compartment latently. EBV-infected B cells become activated and growth transformed, express a characteristic set of viral latent genes, and acquire the status of proliferating lymphoblastoid cell lines in vitro. Because EBV infects only primate cells, it has not been possible to establish a model of infection in immunocompetent rodents. Such a model would be most desirable in order to study EBV's pathogenesis and latency in a suitable and amenable host.

Methodology/Principal Findings

We stably introduced recombinant EBV genomes into mouse embryonic stem cells and induced their differentiation to B cells in vitro to develop the desired model. In vitro differentiated murine B cells maintained the EBV genomes but expression of viral genes was restricted to the latent membrane proteins (LMPs). In contrast to human B cells, EBV's nuclear antigens (EBNAs) were not expressed detectably and growth transformed murine B cells did not arise in vitro. Aberrant splicing and premature termination of EBNA mRNAs most likely prevented the expression of EBNA genes required for B-cell transformation.

Conclusions/Significance

Our findings indicate that fundamental differences in gene regulation between mouse and man might block the route towards a tractable murine model for EBV.

Rescue of "crippled" germinal center B cells from apoptosis by Epstein-Barr virus

Epstein-Barr virus (EBV) is associated with B-cell lymphomas such as Hodgkin lymphoma, Burkitt lymphoma, and post-transplantation lymphoma, which originate from clonal germinal center (GC) B cells. During the process of somatic hypermutation, GC B cells can acquire deleterious or nonsense mutations in the heavy and light immunoglobulin genes. Such mutations abrogate the cell surface expression of the B-cell receptor (BCR), which results in the elimination of these nonfunctional B cells by immediate apoptosis. EBV encodes several latent genes, among them latent membrane protein 1 (LMP1) and LMP2A, which are regularly expressed in EBV-positive Hodgkin lymphoma and posttransplantation lymphomas. Since LMP1 and LMP2A mimic the function of 2 key receptors on B cells, CD40 and BCR, respectively, we wanted to learn whether EBV infection can rescue proapoptotic GC B cells with crippling mutations in the heavy chain immunoglobulin locus from apoptosis. We show here that BCR-negative GC B cells readily enter the cell cycle upon infection with EBV in vitro and yield clonal lymphoblastoid cell lines that are incapable of expressing a functional BCR because the rearranged and formerly functional heavy chain immunoglobulin alleles carry deleterious mutations. Our findings imply an important role for EBV in the process of lymphomagenesis in certain cases of Hodgkin lymphoma and posttransplantation lymphomas.

Distribution and phenotype of Epstein-Barr virus-infected cells in human pharyngeal tonsils

Although Epstein-Barr virus (EBV) is often found in human tonsils, it remains to be precisely determined in what cells and microenvironment the virus is present. Although generally regarded as a B lymphotropic virus, EBV is associated with non-B-cell tumors, for example, NK/T-cell lymphoma, carcinoma, and leiomyosarcoma. To provide a basis for understanding the origin and biology of EBV-infected non-B cells, the immunophenotype of all EBV-infected cells in reactive human tonsils was determined by subjecting tonsil sections to dual/triple EBER in situ hybridization and immunohistochemistry with monoclonal antibodies to T cells (CD3, CD4, CD8, CCR3), B cells (CD20), plasma cells (CD138), natural killer (NK) cells (PEN5), and epithelial cells (cytokeratin), as well as frozen section immunostaining with antibodies to EBV latent proteins EBNA1, EBNA2, LMP1, and EBV early protein BZLF1. Most tonsils contained nearly equal numbers of EBNA1- and LMP1-positive cells (latency program) while only a few contained EBNA2-positive cells (growth program). More than 1000 EBER-positive cells from six tonsils were detected in the interfollicular zone (59%), tonsillar crypts (26%), and follicles (15%). Most (82%) EBER-positive cells are CD20-positive B cells, 7% are CD3-positive T cells, and 11% are cells of indeterminate lineage, often with plasmacytoid morphology. However, no EBER-positive plasma cells were identified. Rare EBER-positive NK cells and EBER/BZLF1-positive epithelial cells were identified. The direct demonstration of EBV within rare T cells, NK cells, and epithelial cells in reactive human tonsils provide a basis for further understanding of the origin of EBV-associated tumors of non-B-cell type.

Role of cytotoxic T lymphocytes in Epstein-Barr virus-associated diseases

Adaptation of persistent infection within the cells of the immune system is a unique characteristic of gamma herpes viruses. A classic example of this is Epstein-Barr virus (EBV), which may have co-evolved with Homo sapiens over millions of years, thus achieving a balance between viral persistence and immune control. In this review, we present an overview of virus and the host immune system interactions that regulate the life-long host-virus relationship in healthy virus carriers and EBV-associated diseases. Extensive analysis of cytotoxic T lymphocyte-mediated immune responses in healthy virus carriers has revealed unique mechanisms used by EBV to maintain a benign persistent state in vivo. On the other hand, this relationship in EBV-associated diseases favors the escape of the virus from the hostile effects of the immune response. This escape is achieved by either down-regulating the expression of highly immunogenic antigens of the virus or by direct modulation of the host cytotoxic T lymphocyte response by virus-encoded proteins.

Immortalization of immunologically committed Epstein-Barr virus-transformed human B-lymphoblastoid cell lines accompanied by a strong telomerase activity

The immunological characteristics and immortalization processes of three EBV-transformed human B-lymphoblastoid cell lines, N0003, N0005 and N6803, with strong telomerase and infinitively proliferating activities are described. The three cell lines were apparently immortalized: they developed a strong telomerase activity at the population doubling levels (PDLs) between 11 and 135, and continued proliferation over 250 PDLs. All the cell lines expressed CD22, CD19 and CD20 antigens. They were uniformly stained with IgM (N0005), IgG (N6803) or IgA (N0003) at early PDLs between 17 and 20, and they secreted the corresponding class of Ig into the medium; the N6803 and N0003 cell lines continued to secrete each class of Ig at decreased levels while the N0005 cell line expressed or secreted virtually no Ig after immortalization. Karyotype analysis of the immortalized cell lines showed that they were derived from a single cell because they shared a set of abnormal chromosomes within each cell population, and two of the cell lines attained clonal characteristics before they developed a strong telomerase activity. These results indicate that the three immortalized cell lines with a strong telomerase activity correspond to the intermediate stages of B-cell differentiation naturally committed to a specific Ig class, and suggest that they were derived from a B-lymphoblastoid cell committed to a specific class of Ig with poor telomerase activity, rather than from a strongly telomerase-positive B-lymphoblastoid cell either committed or multipotential.

Reappraisal of the relationship between immunoglobulin heavy chain gene rearrangement and Epstein-Barr virus infection in Reed-Sternberg cells of Hodgkin's disease

We investigated 44 cases of Hodgkin's disease for Epstein-Barr virus genome with EBER-1 in situ hybridization. Twenty of 44 (45.5%) were positive for EBV. Simultaneously, immunoglobulin gene rearrangements were assessed in 32 of these 44 cases with PCR on DNA extracted from Reed-Sternberg cell (RS-cell) -rich areas microdissected from paraffin sections. Clonally rearranged immunoglobulin (IgH) gene was observed in 15 cases (46.9%). EBV-negative cases showed more frequent IgH rearrangement than EBV-positive cases (10 and 5 cases, respectively). In 9 cases, the RS cells were CD20-positive immunohistochemically and these were all EBV negative and the IgH gene was rearranged in all except one. These findings may suggest that EBV infection has occurred before the immunoglobulin gene rearrangement or that EBV infection has influenced the rearrangement of the immunoglobulin gene. The results may also hint towards the obscure B-cell nature of the RS cells.

Ig DH Gene Segment Transcription and Rearrangement Before Surface Expression of the Pan-B–Cell Marker CD19 in Normal Human Bone Marrow

The onset of IgH transcription and rearrangement is a defining characteristic of the progenitor population in which B-lineage commitment occurs. These features were used to better define the earliest stage of B-cell commitment in humans and to determine if these stages differ as a function of human ontogeny. Fetal and adult bone marrow mononuclear cells were sorted into B-lineage subpopulations on the basis of surface expression of the stem cell marker CD34, the pan-B–cell marker CD19, and IgM and analyzed for transcription and rearrangement of the IgH locus. The locus was found to be transcriptionally active before surface expression of CD19, as indicated by the presence of germline Iμ, Cμ, and DHQ52 transcripts in the CD34+ CD19− subpopulation. Transcripts from IgH alleles that had undergone DJCμ rearrangements were also detected in the CD34+ CD19− subpopulation. Within this subpopulation, low levels of DXP-containing DJCμ transcripts were detected in both fetal and adult cells. Although DHQ52 DJCμ transcripts were abundant in fetal CD34+ CD19− cells, they were not detected in cells of the same phenotype derived from adult bone marrow. In both fetus and adult, VH3-and VH6-containing VDJCμ transcripts were detected only in the CD19+ subpopulations. These data indicate that transcription of DHQ52-JH and DXP-JH rearrangements differs during fetal and adult B lymphopoiesis. Moreover, in both fetus and adult, transcription of unrearranged components of the IgH locus and DJ rearrangements can proceed before the surface expression of CD19.

Ig DH Gene Segment Transcription and Rearrangement Before Surface Expression of the Pan-B–Cell Marker CD19 in Normal Human Bone Marrow

The onset of IgH transcription and rearrangement is a defining characteristic of the progenitor population in which B-lineage commitment occurs. These features were used to better define the earliest stage of B-cell commitment in humans and to determine if these stages differ as a function of human ontogeny. Fetal and adult bone marrow mononuclear cells were sorted into B-lineage subpopulations on the basis of surface expression of the stem cell marker CD34, the pan-B–cell marker CD19, and IgM and analyzed for transcription and rearrangement of the IgH locus. The locus was found to be transcriptionally active before surface expression of CD19, as indicated by the presence of germline Iμ, Cμ, and DHQ52 transcripts in the CD34+ CD19− subpopulation. Transcripts from IgH alleles that had undergone DJCμ rearrangements were also detected in the CD34+ CD19− subpopulation. Within this subpopulation, low levels of DXP-containing DJCμ transcripts were detected in both fetal and adult cells. Although DHQ52 DJCμ transcripts were abundant in fetal CD34+ CD19− cells, they were not detected in cells of the same phenotype derived from adult bone marrow. In both fetus and adult, VH3-and VH6-containing VDJCμ transcripts were detected only in the CD19+ subpopulations. These data indicate that transcription of DHQ52-JH and DXP-JH rearrangements differs during fetal and adult B lymphopoiesis. Moreover, in both fetus and adult, transcription of unrearranged components of the IgH locus and DJ rearrangements can proceed before the surface expression of CD19.

IgH and TcR-gamma gene rearrangements identified in Hodgkin's disease by PCR demonstrate lack of correlation between genotype, phenotype, and Epstein-Barr virus status

Analysis of IgH and TcR-gamma genes using consensus primers identifying junctional regions of rearranged genes by polymerase chain reaction (PCR) was performed on tissues involved by Hodgkin's disease (HD) in 90 cases and was correlated with the immunophenotype of Hodgkin and Reed-Sternberg (HRS) cells and the presence of Epstein-Barr virus (EBV) within these cells. Clonal IgH gene rearrangements were found in 1/5 cases of lymphocyte predominance (LP) subtype and none was positive for EBV. In 85 cases of classic HD, no IgH or TcR-gamma gene rearrangements were found in 51 (60 per cent) cases. A similar percentage, but not the same cases, were of null (non-B, non-T) phenotype. Of 30 cases where a B phenotype was assigned to HRS cells, nine had IgH gene rearrangements, three had TcR-gamma gene rearrangements, and two had both genes rearranged. None of the five cases assigned to T phenotype of HRS cells showed rearrangement of TcR-gamma genes, but two cases showed rearranged IgH genes. Among 41 cases of null phenotype, ten had IgH gene rearrangements, five had TcR-gamma gene rearrangements, and three cases had both genes rearranged. Whereas EBV was detectable in HRS cells in 17/43 classic HD cases of assigned B phenotype, EBV was also detectable in 2/5 cases of assigned T phenotype and in 21 cases with the null phenotype. Furthermore, there was no correlation of EBV with the presence or lack or IgH or TCR-gamma gene rearrangements. Of the remainder, half (30 per cent) expressed antigens associated with lymphocytes without an appropriate genotype. The results confirm lymphocyte-lineage committed cells at the origin of HRS cells in 40 per cent of cases. Any hypothesis of a non-lymphocytic origin of HRS cells will require the inducibility of CD30 on candidate precursors and the methodology for probing genetic events in such cells to be addressed.

Pyothorax-associated lymphoma. An unusual case with biphenotypic character of T and B cells

Pyothorax-associated lymphoma is known to develop in patients who received an artificial pneumothorax for pulmonary tuberculosis some 30 to 40 years previously. Such patients exhibit large, immunoblastic lymphoma cells and often have a B-cell phenotype. We present a patient with an artificial pneumothorax and such a late developing lymphoma but with the unique finding of aberrant T- and B-cell phenotypes. Southern blot hybridization using immunoglobulin gene JH and T-cell receptor beta chain receptors revealed germline configurations. Lymphomas developing in immunocompromised patients, such as those with acquired immunodeficiency syndrome, may show such unusual phenotypes. The unusual phenotypes found in this patient provide evidence that his pyothorax-associated lymphoma was related to an immunocompromised state.

Hodgkin's Disease and Anaplastic Large Cell Lymphoma Revisited. ii. from cytokines to cell lineage

The true identity of Hodgkin's mononuclear cells and Reed-Sternberg (H-RS) cells has been a subject of controversy for decades. Those who believe that Hodgkin's disease (HD) is a heterogeneous disease may consider it to constitute lymphomas of various origins. However, this theory seems incompatible with the finding of similar phenotypic, biologic, and immunologic properties among most HD. We believe that, in the majority of cases, HD, except for LP and some LD-type HD, is a homogeneous disease despite differences in the degree of fibrosis and/or cellular reaction. The heterogeneity in cellular reactions is a result of secretion of various cytokines by H-RS cells, which may or may not be influenced by the presence of EBV. H-RS cells, and anaplastic large cell lymphoma (ALCL) cells as well, can express a combination of cytokines and cytokine receptors that is not seen in other types of lymphomas. The unique cytokine/receptor profile (e.g. the expression of c-kit-R/CD117), along with various properties associated with H-RS/ALCL cells, leads to a hypothesis that H-RS/ALCL cells are related to similar lymphohematopoietic progenitor cells with different etiologies and somewhat limited differentiation capacity. A number of H-RS cells may differentiate with limited capacity along the B-cell pathway and may be infected by EBV, which further complicates the biologic and immunologic properties of these cells. The majority of H-RS cells may also, however, differentiate along the antigen-presenting dendritic cell pathway, as indicated by the abundant expression of restin, CD15, CD40, CD54, CD58, CD80, and CD86. The majority of ALCL cells clearly differentiate to T cells, but some may acquire B-cell or histiocyte phenotypes. The progenitor cell hypothesis may explain (1) the variable expression of CD117, CD43, and CD34 as well as the absence of CD27, CD45 and CD45RA in H-RS cells; (2) the inconsistent and irregular patterns of phenotype and genotype and the various, often very limited, degrees of differentiation among these two types of lymphoma cells; (3) the existence of secondary HD or ALCL associated with rare types of lymphomas or leukemias, or vice versa; (4) the absence of recombinase and of the B-specific transcription factors BSAP; and (5) the frequent expression of IL-7 and IL-9 in H-RS cells. Copyright 1996 S. Karger AG, Basel

The role of Epstein-Barr virus in the pathogenesis of Hodgkin's disease

Hodgkin's disease represents a phenotypically and genotypically heterogeneous lymphoma of CD30-positive tumour cells. Infection of the putative tumour cell population with Epstein-Barr virus (EBV) represents the most common genetic abnormality detectable in HD, yet the role of EBV in the pathogenesis of HD is only poorly understood. In virus-associated HD cases, monoclonal EBV genomes are detectable in all Hodgkin and Reed-Sternberg (HRS) cells, indicating that EBV infection takes place before expansion of the HRS cell population and, by implication, supporting the concept of a monoclonal origin of HRS cells. EBV infection does not define a distinct subgroup of HD but is detectable in different histotypes and in HRS cells expressing lymphocyte differentiation antigens of different cell lineages. Through the EBV-encoded protein, LMP1, the virus may superimpose an activated phenotype on genotypically immature lymphocytes. EBV-induced modulation of the cytokine expression pattern of HRS cells may contribute to the local inhibition of EBV-specific immunity observed in EBV-positive cases.

Molecular genetic analysis demonstrates that multiple posttransplantation lymphoproliferative disorders occurring in one anatomic site in a single patient represent distinct primary lymphoid neoplasms

BACKGROUND

Posttransplantation lymphoproliferative disorders (PT-LPDs) are a clinicopathologically heterogeneous group of lymphoid proliferations of varied clonal composition, the majority of which are associated with Epstein-Barr virus (EBV) infection. The clonal content and clonal relatedness of 24 separate PT-LPD lesions occurring synchronously in one organ in a single patient were investigated.

METHODS

Twenty-four separate PT-LPD lesions from the colon and mesentery of a 15-year-old male, developing 4 months after cardiac transplantation, were studied for clonality based on immunoglobulin heavy chain (IgH) gene rearrangements for the presence, clonality, and type of EBV infection and for the presence of c-myc, ras, and p53 gene alterations. Southern blot hybridization, polymerase chain reaction, and single strand conformation polymorphism assays were employed.

RESULTS

All 24 lesions were histologically similar (polymorphic B-cell lymphomas) but exhibited varied clonality and were clonally distinct with respect to both IgH gene rearrangements and EBV infection. All lesions were infected with EBV type A. Structural alterations of oncogenes or tumor suppressor genes were not identified.

CONCLUSIONS

Separate PT-LPD lesions occurring synchronously in a single organ or patient may be clonally distinct, suggesting that they represent multiple distinct primary lymphoid proliferations rather than metastatic disease as in conventional malignant lymphomas. This may explain partially the rapid development in some patients of a large PT-LPD tumor burden that may regress rapidly after reduction of immunosuppression.

The gene loci for immunoglobulin heavy chains in precursor B cell lines from a patient with severe combined immunodeficiency appear able to participate in DNA rearrangement but have a germ-line configuration

In a previous study (Immunogenetics 1988. 27:330) with Epstein-Barr virus, we established lines of precursor B cells from bone marrow cells of a patient with severe combined immunodeficiency in whom the numbers of B cells and T cells were markedly reduced. Although based on their surface markers these cell lines appeared to be at an early stage of B cell differentiation, the gene loci for immunoglobulin heavy chains (IgH) retained the germ-line configuration on both chromosomes in almost all the transformants. In this study, we found that the enhancer sequence, located between the JH and mu genes, was hypomethylated and an abundance of the germ-line Cmu transcript was detected in these cell lines by Northern hybridization. These results suggest that the chromatin structure of the IgH gene locus in these cell lines is accessible to VDJ recombinase and is able to participate fully in DNA rearrangement. By contrast, we did not detect transcripts of the RAG-1 and RAG-2 genes, which are required for V(D)J recombination at gene loci for immunoglobulin and T cell receptors. Thus, it seems likely that these cell lines fail to initiate the V(D)J recombination process because of some deficiency in the formation of VDJ recombinase, which includes the inability to express RAG genes.

Direct BRLF1 binding is required for cooperative BZLF1/BRLF1 activation of the Epstein-Barr virus early promoter, BMRF1

Disruption of Epstein-Barr virus (EBV) latency is mediated through the activation of the viral immediate-early proteins, BZLF1 (Z) and BRLF1 (R).i.; (Chevallier-Greco, A., et al., (1986) EMBO J., 5, 3243-9; Countryman, and Miller, G. (1985) Proc. Natl. Acad. Sci. USA, 82, 4085-4089). We have previously demonstrated that these proteins cooperatively activate the EBV early promoter BMRF1 in lymphoid cells but not in epithelial cells. Although cooperative transactivation by these proteins has been demonstrated with a number of EBV promoters, the mechanism of this interaction is not well understood. We now show that the cooperative activation of the BMRF1 promoter by Z-plus-R requires an intact R binding site and at least one functional Z response element (ZRE). Despite the presence of an R binding site, the BMRF1 promoter is only moderately responsive to R alone in either HeLa or Jurkat cells. Efficient activation of the BMRF1 promoter by Z alone in HeLa cells requires two ZREs (located at -59 and -106), whereas two additional Z binding sites (located at -42 and -170) contribute very little to Z-induced activation. In the absence of ZREs, Z acted as a repressor of R-induced transactivation. These observations, along with observations made by other investigators (Giot, J.F. et al., (1991) Nucleic Acids Res., 19, 1251-8), suggest that Z-plus-R cooperative activation is dependent upon 1) direct binding by R and Z to responsive promoter elements and 2) contributions by cell-specific factors.

Gene rearrangement and B-cell development

The differentiation of B lymphocytes from their progenitors progresses through a series of successive stages that are defined by sequential rearrangement of Ig loci and surface expression of various stage-specific markers, including Ig heavy and light chain proteins. Considerable evidence suggests that the appearance of cells with an orderly progression of Ig gene rearrangements is linked to the expression of the rearranged Ig gene products. Recent experiments have clarified our understanding of mechanisms by which rearrangement of Ig gene segments is controlled and how Ig gene products participate in the regulation of the B-cell differentiation program.

Significance of the detection of Epstein-Barr virus DNA in lymph nodes in patients with Hodgkin's disease

Epstein-Barr virus (EBV) DNA is frequently identified in benign and malignant lymphoproliferative conditions. As shown by in situ hybridization studies viral DNA is localized within malignant cells as well as benign lymphocytes. Clonal and nonclonal EBV genomes are present in Hodgkin's disease (HD), lymphomas of the immunocompromised host and reactive lymph node hyperplasia. Lytic infection with formation of linear genomes is observed in the same conditions but appears to be infrequent in HD as shown by quantitation of mRNA coding for viral capsid antigen. Expression of the oncogene LMP (latent membrane protein) is seen in Sternberg-Reed (SR) cells and immunoblasts of AIDS-related lymphoma and infectious mononucleosis (IM). In HD, the region of the BNLF1 oncogene coding for the amino terminal and transmembrane domains (associated with oncogenic function) of LMP appears to be homogeneous whereas the region coding for the intracytoplasmic (carboxy terminal) domain of LMP is heterogeneous. Cytological similarities between SR cells and immunoblasts of IM and AIDS-related lymphomas are consistent with the hypothesis that the BNLF1 oncogene is one possible inducer of morphological features of SR cells. Whether chromosomal integration of EBV DNA is an important factor in activation of such a transforming activity remains to be elucidated. EBV DNA positive and negative HD cases with numerous SR cells lack significant mRNA expression of the two recombinase activating genes (RAG-1 and RAG-2). Therefore the SR cells appear to be derived from lymphocytes beyond the pre-B-cell or common thymocyte stage which may or may not subsequently become infected by EBV.

Recent results on the biology of Hodgkin and Reed-Sternberg cells. I. Biopsy material

The most recent sophisticated investigations have provided new and revealing, but also contradictory and controversial information on the biological nature and the cellular origin of Hodgkin and Reed-Sternberg cells (H-RS). Immunophenotypic analyses have shown variable phenotypic antigen expression; but, on balance the data suggest a lymphoid cell expressing T- and/or B-cell-associated markers and certain activation antigens while lacking immunological features of monocytes-macrophages or other lineages. Molecular genetic studies have demonstrated heterogenous findings with respect to rearrangements of T-cell receptor and immunoglobulin genes. Only a small percentage of the cases has rearrangements; this might be due to the threshold of sensitivity of the method combined with the scarcity of the malignant cells. Epstein-Barr virus (EBV) genomes are clonally integrated in the H-RS cells of about half the cases. The significance of these findings--whether EBV is a causative agent or an epiphenomenon--remains to be elucidated. H-RS cells express mRNA and proteins of various cytokines and cytokine receptors implying a predominant role for cytokines in the pathophysiology of HD. The mononuclear and polynuclear H-RS cells are capable of DNA synthesis and nuclear division; the lack of cellular division leads to multinuclearity through the process of endomitosis. Mutations and expression of only a limited number of oncogenes have been tested thus far. Whether the bcl-2 oncogene is involved in HD remains a matter of debate. Aneuploidy and non-random chromosomal abnormalities are the results of cytogenetic analyses of H-RS cells. However, no chromosomal marker specific for HD has yet been found. Thus, while studies of EBV involvement, growth factor production, oncogene expression and chromosomal abnormalities contributed a fair amount of new data on the nature of H-RS cells, only immunophenotyping and genotyping provided some indication of the cellular derivation: an activated lymphoid cell that possibly expresses oncogenes, that probably is infected with EBV, that most likely produces cytokines, that certainly has multiple karyotypic abnormalities.

The cellular oncogene c-myb can interact synergistically with the Epstein-Barr virus BZLF1 transactivator in lymphoid cells

Regulation of replicative functions in the Epstein-Barr virus (EBV) genome is mediated through activation of a virally encoded transcription factor, Z (BZLF1). We have shown that the Z gene product, which binds to AP-1 sites as a homodimer and has sequence similarity to c-Fos, can efficiently activate the EBV early promoter, BMRF1, in certain cell types (i.e., HeLa cells) but not others (i.e., Jurkat cells). Here we demonstrate that the c-myb proto-oncogene product, which is itself a DNA-binding protein and transcriptional transactivator, can interact synergistically with Z in activating the BMRF1 promoter in Jurkat cells (a T-cell line) or Raji cells (an EBV-positive B-cell), whereas the c-myb gene product by itself has little effect. The simian virus 40 early promoter is also synergistically activated by the Z/c-myb combination. Synergistic transactivation of the BMRF1 promoter by the Z/c-myb combination appears to involve direct binding by the Z protein but not the c-myb protein. A 30-bp sequence in the BMRF1 promoter which contains a Z binding site (a consensus AP-1 site) is sufficient to transfer high-level lymphoid-specific responsiveness to the Z/c-myb combination to a heterologous promoter. That the c-myb oncogene product can interact synergistically with an EBV-encoded member of the leucine zipper protein family suggests c-myb is likely to engage in similar interactions with cellularly encoded transcription factors.

Local growth of a Burkitt's lymphoma versus disseminated invasive growth of the autologous EBV-immortalized lymphoblastoid cells and their somatic cell hybrids in SCID mice

Specific host-graft interactions, as well as intrinsic properties of transferred cell, determine tumorigenicity in xenogeneic systems. We compared the growth characteristics of human B-lymphoid cell lines in SCID mice with the well characterized growth pattern in nude mice and observed striking differences in malignancy in the respective hosts. Two cell lines derived from the same individual, the Epstein-Barr-virus(EBV)-positive Burkitt's lymphoma BL 60 (BL) and the autologous EBV-immortalized lymphoblastoid cell line IARC 277 (LCL) were used. In addition, we tested somatic cell hybrids (HYB) of both cell lines, which despite the LCL-like differentiation phenotype show the de-regulated c-myc expression pattern of the parental BL line, assumed to be a critical factor in BL pathogenesis. Subcutaneously (s.c.) injected BL cells produced local progressively growing tumor masses at the injection site without distant metastases in both nude and SCID mice. Although both mouse strains possess the same genetic background (BALB/c) and differ only in the B-cell sub-set, the growth patterns of the LCL and hybrids were completely different. In contrast to the regressive behaviour of LCL and hybrids in nude mice, these lines show invasive and disseminated progressive growth in SCID mice. Peripheral lymph nodes an thymic tissue were preferentially colonized, whereas mucosal-associated lymphoid tissue (Peyer's patches and appendix) and spleen were not infiltrated. The preferential migration of lymphocytes to certain tissues is termed homing in a syngeneic system and mediated by homing receptors and vascular addressins. The "homing" of LCL and hybrids into lymphoid SCID mouse tissue suggests a strong interaction with the endothelial cells of the host. Detailed phenotypic analysis of BL, LCL and 3 different hybrids was performed using an antibody panel against differentiation and adhesion markers. Overall dominance of the LCL phenotype was observed in the hybrids, as indicated by cytology, tumor growth, dissemination and the pattern of surface-marker expression. The c-myc activation in hybrids does not appear to influence growth behavior.

The cellular oncogene c-myb can interact synergistically with the Epstein-Barr virus BZLF1 transactivator in lymphoid cells

Regulation of replicative functions in the Epstein-Barr virus (EBV) genome is mediated through activation of a virally encoded transcription factor, Z (BZLF1). We have shown that the Z gene product, which binds to AP-1 sites as a homodimer and has sequence similarity to c-Fos, can efficiently activate the EBV early promoter, BMRF1, in certain cell types (i.e., HeLa cells) but not others (i.e., Jurkat cells). Here we demonstrate that the c-myb proto-oncogene product, which is itself a DNA-binding protein and transcriptional transactivator, can interact synergistically with Z in activating the BMRF1 promoter in Jurkat cells (a T-cell line) or Raji cells (an EBV-positive B-cell), whereas the c-myb gene product by itself has little effect. The simian virus 40 early promoter is also synergistically activated by the Z/c-myb combination. Synergistic transactivation of the BMRF1 promoter by the Z/c-myb combination appears to involve direct binding by the Z protein but not the c-myb protein. A 30-bp sequence in the BMRF1 promoter which contains a Z binding site (a consensus AP-1 site) is sufficient to transfer high-level lymphoid-specific responsiveness to the Z/c-myb combination to a heterologous promoter. That the c-myb oncogene product can interact synergistically with an EBV-encoded member of the leucine zipper protein family suggests c-myb is likely to engage in similar interactions with cellularly encoded transcription factors.

Hodgkin's disease

The epidemiological features of Hodgkin's disease (HD) suggest that it is a heterogeneous condition which may have different aetiologies in different age groups. The risk factors for the development of HD in young adults suggest that delayed exposure to a common infectious agent may be involved in this age group. Seroepidemiological studies have shown that HD patients have elevated antibody titres to Epstein-Barr virus (EBV) and the elevated titres have been shown to precede the diagnosis of HD. Recent molecular studies provide support for the idea that EBV is involved in the pathogenesis of HD. EBV genomes are consistently found in a proportion of tumour biopsies, the EBV-infected cells are clonal and the EBV genomes have been localized to Reed-Sternberg cells. Furthermore, EBV latent gene products are expressed by the Reed-Sternberg cells. The majority of HD samples from patients aged greater than 50 years and less than 15 years are EBV positive, whereas the minority (less than 15%) of samples from young adults contain detectable EBV DNA. The results suggest that EBV plays a role in HD in children and older adults but that other agents, possibly other viruses, are involved in young adults.

The Epstein-Barr virus nuclear protein encoded by the leader of the EBNA RNAs is important in B-lymphocyte transformation

These experiments evaluate the role of the Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) in B-lymphocyte growth transformation by using a recombinant EBV molecular genetic approach. Recombinant viruses encoding for a mutant EBNA-LP lacking the carboxy-terminal 45 amino acids were markedly impaired in their ability to transform primary B lymphocytes compared with EBNA-LP wild-type but otherwise isogenic recombinant viruses. This impairment was particularly evident when primary B lymphocytes were infected under conditions of limiting virus dilution. The impairment could be partially corrected by growth of the infected lymphocytes with fibroblast feeder layers or by cocultivation of primary B lymphocytes with relatively highly permissive mutant virus-infected cells. One of the five mutant recombinants recovered by growth of infected cells on fibroblast feeder cultures was a partial revertant which had a normal transforming phenotype. Several lymphoblastoid cell lines infected with the EBNA-LP mutant recombinant viruses had a high percentage of cells with bright cytoplasmic immunoglobulin staining, as is characteristic of cells undergoing plasmacytoid differentiation. Expression of the other EBV latent or lytic proteins and viral replication were not affected by the EBNA-LP mutations. Thus, the EBNA-LP mutant phenotype is not mediated by an effect on expression of another EBV gene. These data are most compatible with the hypothesis that EBNA-LP affects expression of a B-lymphocyte gene which is a mediator of cell growth or differentiation.

Viral involvement in Hodgkin's disease: detection of clonal type A Epstein-Barr virus genomes in tumour samples

Thirty-five cases of Hodgkin's disease (HD) were analysed for the presence of Epstein-Barr virus (EBV) and human herpesvirus-6 (HHV-6) DNA. EBV genomes were detected in 11/35 cases while none of the cases was positive for HHV-6. Ten of the EBV-positive cases were subsequently analysed using a probe for the terminal region of the virus; the results suggested that the EBV-infected cells were clonally expanded. EBV subtypes specific DNA amplification was used to demonstrate that EBV subtype A, and not subtype B was present in the EBV-positive cases. The age distribution of the EBV-positive cases indicated a statistically significant trend for an increase in positivity with increasing age. This is the first indication that EBV is significantly associated with any subset of HD patients.

Antibody specificity and immunoglobulin VH gene utilization of human monoclonal CD5+ B cell lines

Human B lymphocytes that bear the CD5 antigen are relatively abundant in early ontogeny and comprise a small fraction of the B cell population in adults. The CD5 B cell subset has attracted much attention because of its possible involvement in autoimmune disease and certain B cell malignancies. To begin to understand the role of CD5 B cells in disease processes, we have generated a panel of ten human monoclonal B cell lines selected for expression of the CD5 antigen. These cell lines were obtained by Epstein-Barr virus transformation of B lymphocytes isolated from the spleen, liver and bone marrow of a 19-week-old fetus, from cord blood and from peripheral blood of healthy volunteers. In addition, one cell line was isolated from the spleen of a patient with chronic lymphocytic leukemia. Here, we describe the antibody and immunoglobulin VH gene repertoire of this panel of CD5 B cell lines. The results of these experiments show that (a) some but not all CD5 B cell lines secrete polyreactive antibodies that bind to a variety of self- and xenoantigens and (b) members of the small VH4, VH5 and VH6 gene families are overrepresented in this panel of cell lines. Nucleotide sequence analysis revealed the expression of VH gene elements that have been previously reported in the preimmune B cell repertoire, in CD5 B cell tumors and in polyreactive antibodies.

Clinical characteristics of high-grade lymphomas with immune genes in germline configuration

In a prospective study of 42 high-grade lymphomas which were categorized according to the Kiel classification, the clinical significance of immune genotyping was studied. Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements were investigated. In 33 cases the immune genotype confirmed the phenotype. In one case with equivocal phenotype a TCR beta-chain rearrangement proved the T-cell origin of the lymphoma. None of the cases showed a bigenotype. There were eight lymphomas with immunoglobulin and TCR beta-chain and gamma-chain genes in germline configuration, which were divided into a group of immature lymphomas and a group of lymphomas with a more mature phenotype. The immature lymphomas had widespread disease, rapid progression, and favorable prognosis after intensive chemotherapy. The group of T-cell and Ki-1 lymphomas with null-cell genotype was clinically heterogeneous. Three of four cases were secondary lymphomas after lymphomatoid papulosis, lymphomatoid granulomatosis, or Hodgkin's disease. All cases presented with extranodal involvement. Only one of these patients is in continuous remission. In conclusion, the lack of immunoglobulin and TCR beta-chain and gamma-chain gene rearrangements does not exclude the diagnosis of high-grade malignant lymphoma, especially in cases with unusual extranodal involvement. However, the DNA analysis identifies a null-cell genotype subset of high-grade lymphomas which may have clinical significance.

The nature of Hodgkin and Reed-Sternberg cells, their association with EBV, and their relationship to anaplastic large-cell lymphoma

This review focuses on the cellular origin of Hodgkin and Reed-Sternberg (HRS) cells, their association with the Epstein-Barr virus (EBV), and their relation to Ki-1+ anaplastic large-cell (ALC) lymphoma. The tingibility of HRS cells in paraffin sections for polyclonal immunoglobulin represents a staining artifact and thus can no longer serve as an argument for the histiocytic nature of HRS cells. Immunolabeling studies do not support the putative relationship of HRS cells to cell types such as macrophages or interdigitating reticulum cells, but instead suggest: a) that lymphocyte-predominant (LP) Hodgkin's disease (HD) represents a B-cell neoplasm which is distinct from non-LP HD, and b) that non-LP HD constitutes a syndrome rather than a disease entity, with the existence of T-cell types and B-cell types. HRS cells (and the tumor cells in ALC lymphomas) frequently display an immature genotype in association with late activation markers, leading to the assumption that the tumor cells in many cases of HD (and some cases of ALC lymphoma) may be derived from immature lymphoid cells that are infected by a virus that superimposes characteristics of mature activated lymphocytes on these cells. Southern blotting, in situ hybridization, and polymerase chain reaction (PCR) experiments revealed an association of EBV with HRS cells in a significant proportion of HD cases, suggesting that EBV may be responsible for the dissociation between genotype and phenotype in HRS cells, because EBV is a strong inducer of the activation antigens CD30 and CDw70.(ABSTRACT TRUNCATED AT 250 WORDS)

Isotype commitment of human B cells that are transformed by Epstein-Barr virus

Epstein-Barr virus (EBV) can transform a subpopulation of preactivated B cells thus promoting their growth and differentiation into plasma cells. In EBV-transformed clones of IgM-producing cells, the heavy chain constant region (CH) genes on the productive allele are fixed in germ-line configuration, whereas in isotype-switched clones the CH genes proximal to the expressed CH gene are deleted. In order to define more precisely the EBV-susceptible B cells, we sorted subpopulations of B cells on the basis of their cell surface Ig (sIg) isotypes, infected them with EBV, and determined which isotypes they could produce following transformation. Most precursors of IgM-producing plasma cells expressed both IgM and IgD on their surface, while a minority expressed IgM alone. Some B cell precursors of IgG- and IgA-producing cells also expressed sIgM, but surprisingly none expressed IgD. Those precursors of IgG and IgA producers, which bore sIgM, expressed it in relatively low levels, whereas B cells expressing high levels of sIgM were incapable of generating IgG and IgA producers. All of the precursors of IgG and IgA plasma cells expressed these isotypes on their cell surface. Interestingly, precursor B cells capable of producing the IgG3 and IgA2 subclasses could be respectively enriched on the basis of the presence or absence of cell sIgM. These results demonstrate the isotype precommitment of EBV-transformable B cells. They further suggest that residual IgM is transiently expressed on the surface of the IgG- and IgA-committed B cell precursors, whereas sIgD expression is extinguished earlier in the process of isotype switching via CH gene deletion.

Immunohistochemical, molecular, and cytogenetic analysis of a consecutive series of 20 peripheral T-cell lymphomas and lymphomas of uncertain lineage, including 12 Ki-1 positive lymphomas

Although several independent series of non-Hodgkin's lymphomas (NHLs) have been subjected to cytogenetic studies or analyses of lineages by assaying for clonal immunophenotypes and clonal rearrangements affecting immunoglobulin (IG) and T-cell receptor (TCR) genes, no published reports exist of series of non-B-cell NHLs on which cytogenetic, immunohistochemical, and IG and TCR gene rearrangement studies have been undertaken together. Among 343 NHLs ascertained prospectively between January 1984 and December 1988 at the Memorial Sloan-Kettering Cancer Center, 278 cases with clonal chromosome abnormalities were identified. Of the latter, 20 were non-B-cell NHLs, which in turn comprised 15 peripheral T-cell lymphomas (PTCLs) and 5 lymphomas of uncertain lineage (LULs). The LULs either were biogenotypic, had discordant immunophenotype and immunogenotype, or showed no evidence of B-cell, T-cell, or histiocytic derivation. Of the 15 PTCLs, eight expressed the Ki-1 antigen and four of these had translocations involving the band 5q35 [t(5q35)]. Of the five LULs, four expressed the Ki-1 antigen and one of these had a translocation involving band 5q35. Previous studies have associated t(5q35) with Ki-1 positive NHLs characterized histologically by a pleomorphic diffuse large cell morphology. In our series of 12 Ki-positive non-B-cell NHLs, five (42%) had a 5q35 translocation. They were histologically indistinguishable from the subset without the translocation. The frequent lineage uncertainty exhibited by Ki-1 positive NHLs of similar histology and cytogenetic abnormalities suggests their derivation from an early uncommitted lymphoid cells.

Recurrent mutation of immunoglobulin and c-myc genes and differential expression of cell surface antigens occur in variant cell lines derived from a Burkitt lymphoma

The phenotypic and molecular genetic characteristics of 4 variant sublines of the Burkitt lymphoma cell line Namalwa have been examined. The sublines are DNA-fingerprint-identical and derived from a monoclonal tumour, as shown by a rearrangement of the T-cell-receptor beta-chain gene common to the 4 sublines. There is non-co-ordinate expression of MHC class-I MHC class-II, surface immunoglobulin and a number of antigens recognized by CD MAbs on the different sublines. These different phenotypes of the cells are reminiscent of B cells arrested in varying states of cellular maturity. On Southern blots there are different patterns of restriction fragments hybridizing with Ig heavy- and light-chain gene probes among the sublines, indicating that multiple rearrangements or mutations of Ig genes have occurred in the cells. Different patterns of hybridizing fragments among the sublines were also found by using c-myc probes, implying the existence of different mutations of the c-myc locus. The c-myc mutation found in one of the sublines mapped to the 5' flanking sequence and in another 3' to the c-myc locus. Using the J17BS8 probe, which detects a restriction fragment length polymorphism in the 3' flanking region of the c-myc gene, a 4-fold variation in the gene copy number among the subline was found and one of the sublines was shown to be hemizygous for c-myc. Examination of DNA from early cultures of Namalwa cells showed that the alternations in Ig and c-myc structure had occurred on prolonged culture of the cells.

Growing human B-cell precursors in vitro: the continuing challenge

Methods for propagating murine B-cell precursors in vitro have been instrumental in unraveling the cells and molecules regulating murine B-cell ontogeny. However, similar methods are not available for studying human B-cell ontogeny. Here, Tucker LeBien discusses why efforts to grow human B-cell precursors in vitro have been largely unsuccessful and proposes alternative strategies that may prove useful.

Predilection of a nasopharyngeal carcinoma-derived isolate of Epstein-Barr virus for infection of specific subsets of B lymphocytes

It is important to know whether there are variants of Epstein-Barr virus (EBV) with biological properties that are different from the prototype viruses that have been studied in detail, such as P3HR-1 and B95-8. We have studied an EBV isolate derived from a nasopharyngeal carcinoma (NPC) tumor, designated NPC-EBV. We have examined the target B lymphocytes infected and growth-transformed with NPC-EBV as compared with two common EBV isolates, B95-8 and AG876 EBV, for stage of maturation using antibodies to several immunoglobulin chains. Typing of the NPC-EBV transformed lymphoblastoid cell lines revealed the predilection of the NPC-EBV isolate to infect immature B lymphocytes. This was not the case for the B95-8 and AG876 isolates. The reason for the predilection of NPC-EBV for immature B lymphocytes remains to be explored further. However, these results may be important in understanding the pathophysiology of EBV-associated diseases.

Epstein-Barr virus-transformed pro-B cells are prone to illegitimate recombination between the switch region of the mu chain gene and other chromosomes

Six independently maintained sublines of FLEB 14, a fetal-liver-derived Epstein-Barr virus-transformed pro-B cell line that has not yet rearranged its immunoglobulin genes, were examined after in vitro propagation during 19-36 months. Two lines showed no immunoglobulin heavy chain gene rearrangement, whereas one allele was rearranged with breakpoints inside the switch region of the mu chain gene in the remaining four. These rearrangements had been generated by the translocation of different chromosome fragments to the immunoglobulin heavy chain gene cluster-carrying 14q32 band in each of the four lines. Previously, a similar rearrangement was found in a fifth subline concurrently with a reciprocal 6;14 translocation. The transposed pieces have been derived from chromosomes 16 and 18 in two of the more recently rearranged lines. Their origins could not be determined in the remaining two lines, but they were different from each other and the other three 14q+ markers. The 14q+ marker-carrying variant has replaced its diploid progenitor suggesting that the translocation has conveyed some in vitro growth advantage on its carrier. This was also supported by the duplication of the 14q+ marker and the loss of its normal chromosome 14 homologue in one subline during serial culturing. The vulnerability of the switch region of the mu chain gene to illegitimate recombination at the pro-B stage and the possible relevance of this finding for the origin of the Burkitt lymphoma-associated 8;14 (immunoglobulin heavy chain gene cluster/MYC) translocation is discussed.

'Fetal-type' B and T lymphocytes in rheumatoid arthritis and primary Sjögren's syndrome

B lymphocytes expressing CD5 (CD5+B cells) and T lymphocytes using the gamma and delta chains to form their antigen receptor (gamma delta +T cells) are major populations in developing fetuses, but become relatively minor in normal adults. However, both subsets are expanded in the peripheral blood of more than 50% of patients with rheumatoid arthritis and primary Sjögren's syndrome. We have examined the surface phenotype of these subsets using flow cytometry and have studied the frequency of IgM-producing lines after EBV-transformation of sorted CD5+B and CD5-B cells isolated from neonatal umbilical vein and RA peripheral blood. The intensity of CD5 expression on B cells was at least 10 times 'duller' than on T cells, CD5 'dull' cells were CD3 negative, and T cells bearing the gamma delta antigen receptor did not express either CD4 or CD8 on their surface. In vitro stimulation by Staphylococcus aureus Cowan I or transformation by Epstein-Barr virus of CD5+B cells resulted in loss of CD5 antigen from the surface of B cells. EBV-transformation of sorted CD5+B and CD5-B lymphocytes from neonatal blood gave rise to IgM-secretion in 100% of the Ig-secreting lines. CD5+B fraction isolated from RA blood also generated 100% IgM-secreting lines, whereas 29% of the Ig-secreting lines obtained from RA CD5-B fraction did not secrete IgM. The function of these 'fetal-type' T and B lymphocytes is unknown, however their expansion in rheumatoid arthritis and primary Sjögren's Syndrome suggests that they may play a role in autoimmune diseases.

Clonal diversity in the B cell repertoire of patients with X-linked agammaglobulinemia

Ig protein and mRNA expression was examined in a collection of 18 monoclonal EBV-transformed B cell lines derived from five patients with X-linked agammaglobulinemia (XLA). A diversity of H and L chain isotypes were synthesized by these lines: the majority (12 lines) expressed mu kappa chains, while mu lambda (two lines), gamma kappa (one), gamma lambda (one), delta lambda (one), and alpha kappa (one) isotype expression was also observed. For all the mu kappa-producing XLA B cell lines, the mu and kappa mRNA transcripts were of native size, and sequence analysis across the regions of VHDJH and V kappa J kappa gene joining showed that Ig gene rearrangements occurred in a typical manner. A variety of VHDJH and V kappa J kappa gene rearrangements were observed, not only within the set of mu kappa+ XLA B cells as a whole, but also among the cell lines derived from single patients. Southern blot analysis for genomic Ig H chain gene rearrangements was done to fully assess the extent of clonal heterogeneity among multiple mu kappa+ XLA B cell lines derived from two patients; all the B cell lines possessed distinct gene rearrangement patterns demonstrating their clonal unrelatedness. Our findings indicate that the B cell repertoire in individual XLA patients is clonally diverse and that it is unlikely that the defect in B cell differentiation in XLA is the result of inefficient or ineffective rearrangement of Ig H or L chain genes. Rather, this study provides support for the idea that the XLA defect relates to a more generalized cellular function, such as regulating the proliferation and/or clonal expansion of cells of the B lymphoid lineage.

Early human IgH gene assembly in Epstein-Barr virus-transformed fetal B cell lines. Preferential utilization of the most JH-proximal D segment (DQ52) and two unusual VH-related rearrangements

We have analyzed the phenotypic characteristics and IgH gene rearrangements in a panel of EBV-transformed B lineage cell lines from human fetal liver and bone marrow. Some lines contained only populations of immature, Ig- Be cells, while others contained mixed populations of mature and immature B cells. The majority of identifiable IgH rearrangements involved joining of the most JH-proximal D segment, DQ52, to various JH segments, implying that DQ52 is a preferred target for initial DJH rearrangements. Three other rearrangements involving VH-related sequences were also characterized. Two involved VHDJH joining using VH3 genes, although one of these had a very unusual DJH structure. The third consisted of inverted 3' signal sequences and flanking regions of a VH4 gene appended to a JH. The mechanisms by which the later rearrangement could have occurred and its potential physiological significance are discussed.

Light-chain gene expression before heavy-chain gene rearrangement in pre-B cells transformed by Epstein-Barr virus

Epstein-Barr virus transformation of B-cell-depleted bone marrow cells from human fetuses allowed us to identify novel cell types characterized by the expression of immunoglobulin kappa or lambda light chain without heavy chains. Four kappa-only clones with normal karyotype were obtained and examined for their immunoglobulin gene configurations and expression. All four clones had kappa-chain gene rearrangements at either one or both alleles, but the heavy-chain gene loci in these clones either were in germ-line context or had undergone only D-JH rearrangements (D and JH represent diversity and joining gene segments). All clones contained kappa mRNA of normal size at levels consistent with the protein level, except for one clone that no longer produced kappa protein. No mu mRNA or immunoglobulin heavy-chain molecules were detected in any of the kappa+ clones. The results suggest that the mu heavy-chain protein is not an obligatory prerequisite for light-chain gene rearrangements.

Immunoglobulin and T-cell receptor gene rearrangements in Hodgkin's disease and Ki-1-positive anaplastic large cell lymphoma: dissociation between phenotype and genotype

We have determined the tumor cell immunophenotype and the rearrangement configuration of immunoglobulin and T-cell receptor genes in 39 cases of Hodgkin's disease (HD), six HD-derived cell lines and 22 cases of Ki-1-positive anaplastic large cell lymphomas (Ki-1-ALC). Rearrangements were observed in 11/39 HD cases, 15/22 Ki-1-ALC, and all cell lines. Epstein-Barr virus DNA was found in five HD cases, one cell line, and one Ki-1-ALC. Both HD and Ki-1-ALC frequently displayed a dissociated genotypic and phenotypic maturation status, i.e. an immature genotype in association with late activation markers. We postulate that the tumor cells in many cases of HD and some cases of Ki-1-ALC may be derived from immature lymphoid cells by a transformation process that superimposes characteristics of mature activated lymphocytes on these cells.