Single-Cell Analysis and Next-Generation Immuno-Sequencing Show That Multiple Clones Persist in Patients with Chronic Lymphocytic Leukemia

The immunoglobulin heavy chain (IGH) gene rearrangement in chronic lymphocytic leukemia (CLL) provides a unique molecular signature; however, we demonstrate that 26/198 CLL patients (13%) had more than one IGH rearrangement, indicating the power of molecular technology over phenotypic analysis. Single-cell PCR analysis and next-generation immuno-sequencing identified IGH-defined clones. In 23% (18/79) of cases whose clones carried unmutated immunoglobulin heavy chain variable (IGHV) genes (U-CLL), IGH rearrangements were bialleic with one productive (P) and one non-productive (NP) allele. Two U-CLL were biclonal, each clone being monoallelic (P). In 119 IGHV-mutated (M-CLL) cases, one had biallelic rearrangements in their CLL (P/NP) and five had 2–4 distinct clones. Allelic exclusion was maintained in all B-clones analyzed. Based on single-cell PCR analysis, 5/11 partner clones (45%) reached levels of >5x10⁹ cells/L, suggesting second CLL clones. Partner clones persisted over years. Conventional IGH characterization and next-generation sequencing of 13 CLL, 3 multiple myeloma, 2 Waldenstrom’s macroglobulinemia and 3 age-matched healthy donors consistently identified the same rearranged IGH sequences. Most multiple clones occurred in M-CLL, perhaps indicative of weak clonal dominance, thereby associating with a good prognosis. In contrast, biallelic CLL occurred primarily in U-CLL thus being associated with poor prognosis. Extending beyond intra-clonal diversity, molecular analysis of clonal evolution and apparent subclones in CLL may also reflect inter-clonal diversity.

Models for antigen receptor gene rearrangement: CDR3 length

Despite the various processing steps involved in V(D)J recombination, which could potentially introduce many biases in the length distribution of complementarity determining region 3 (CDR3) segments, the observed CDR3 length distributions for complete repertoires are very close to a normal-like distribution. This raises the question of whether this distribution is simply a result of the random steps included in the process of gene rearrangement, or has been optimized during evolution. We have addressed this issue by constructing a simulation of gene rearrangement, which takes into account the DNA modification steps included in the process, namely hairpin opening, nucleotide additions, and nucleotide deletions. We found that the near-Gaussian- shape of CDR3 length distribution can only be obtained under a relatively narrow set of parameter values, and thus our model suggests that specific biases govern the rearrangement process. In both B-cell receptor (BCR) heavy chain and T-cell receptor beta chain, we obtained a Gaussian distribution using identical parameters, despite the difference in the number and the lengths of the D segments. Hence our results suggest that these parameters most likely reflect the optimal conditions under which the rearrangement process occurs. We have subsequently used the insights gained in this study to estimate the probability of occurrence of two exactly identical BCRs over the course of a human lifetime. Whereas identical rearrangements of the heavy chain are highly unlikely to occur within one human lifetime, for the light chain we found that this probability is not negligible, and hence the light chain CDR3 alone cannot serve as an indicator of B-cell clonality.

Spontaneous regression of intraoral mucosa-associated lymphoid tissue lymphoma: molecular study of a case

Mucosa-associated lymphoid tissue (MALT) lymphoma presentation in the oral cavity is very rare. Reported herein is a case of intraoral MALT lymphoma of the minor salivary gland in a 70-year-old woman with Sjogren's syndrome. Unexpectedly, a spontaneous clinically and histologically confirmed regression occurred 1 month after the tumor biopsy for diagnosis. Considering that salivary MALT lymphoma is associated with Sjogren's syndrome and that the chronic inflammation caused by Sjogren's syndrome persisted, it is hypothesized that the tumor clone might be present in the regressed lesion. Minimal residual tumor clone identical with the primary lesion was detected using the polymerase chain reaction (PCR) clonality assay for immunoglobulin heavy chain gene (IgH) rearrangement. No recurrence was clinically evident 38 months after the diagnosis. Spontaneous regression of MALT lymphoma should be examined at the molecular level in addition to clinical and histological evaluations. When minimal residual disease is detected, close follow up is necessary for early detection of the tumor relapse.

The origin of B-cell chronic lymphocytic leukemia

An immunobiologic approach has led to substantial changes in our current view of chronic lymphocytic leukemia (CLL). Several questions remain unsolved and the definition of the cell origin of CLL is still prominent. The presence of somatic mutations of IGHV genes indicates that, at least in a portion of cases, CLL cells had encountered an antigen during the natural history of the disease. Unmutated (UM) cases show a remarkable skewing in IGHV gene usage. In addition, all CLL cases, both mutated (M) and UM, show a common surface phenotype which is significantly activated and similar to the surface phenotype of antigen (Ag)-experienced B cells. The properties of CLL B-cell receptors (BCR) resemble those observed in normal B cells upon Ag interaction, and gene profiling analyses revealed that both subsets share striking similarities with the so-called memory B cells. The detailed analyses of the complementary determining region 3 (CDR3) sequences of the leukemic immunoglobulin (Ig) receptors showed that unrelated patients in different parts of the world express very similar if not identical BCR. Remarkably, similar V(H)DJ(H) rearrangements have been identified in both UM- and M-CLL, suggesting an antigenic selection in both subsets of the disease. From all this evidence, the concept has arisen that the cell of origin, regardless its mutational status, has to be "an Ag-experienced" B cell that gives rise to a malignant clone that appears to be more dynamic than previously appreciated and whose progression is favored by a number of molecular and cellular interactions that occur in tissues.

An antibody VH gene that promotes marginal zone B cell development and heavy chain allelic inclusion

The Ig heavy (H) chain plays a pivotal role in the regulation of primary B cell development through its association with a variety of other proteins including Igalpha and Igbeta, the surrogate light chain components and bona fide L chains, to form transmembrane signaling complexes. Little is known about how alterations in the structure of the H chain variable region influence association with these proteins, or the signaling capacity of the complexes that form. Here we describe a line of VH 'knockin' mice in which the transgene-encoded VH region differs by eight amino acid residues from the VH region in a VH knockin line we previously constructed and characterized. The transgenic H chain locus in the line of mice we characterized earlier efficiently promotes H chain allelic exclusion and all phases of primary B cell development, resulting in the generation of mature B1, marginal zone (MZ) and follicular (FO) B cell compartments. In contrast, the transgenic H chain locus in the new line fails to enforce allelic exclusion, as evidenced by the majority of peripheral B cells expressing two H chains on their surfaces. Moreover, this locus inefficiently drives bone marrow B lymphopoiesis and FO B cell development. However, this H chain locus does promote MZ B cell development, from precursors that appear to be generated during fetal and neonatal life. We discuss these data in the context of previous findings on the influence of Ig H chain structure on primary B cell development.

Absence of immunoglobulin class switch in primary lymphomas of the central nervous system

Primary lymphomas of the central nervous system (PCNSLs) were investigated for their capacity to perform further maturation steps. We studied a series of 11 PCNSLs derived from immunocompetent patients for immunoglobulin (Ig) class switch recombination (CSR) by performing reverse transcriptase-polymerase chain reaction (RT-PCR) for transcripts of Ig constant region gene segments (IGHC). This analysis revealed exclusive transcription of IgM and IgD mRNA in the absence of IgG, IgA, or IgE transcription. This finding was corroborated at the protein level by the immunohistochemical demonstration of IgM on the surface of the tumor cells. The unexpected lack of CSR may be due to internal switch mu region deletions, which were detected in 7 of 11 cases. We also found that expression of activation-induced cytidine deaminase (AID), which is required for CSR and somatic hypermutation, was detectable by RT-PCR in 4 of 10 cases and by immunohistochemistry in one of three cases analyzed. This may indicate that ongoing somatic mutation, which is often observed in PCNSL, could be due to sustained AID expression in a fraction of cases and that intraclonal V gene diversity may occur in other cases at an earlier phase of tumor clone expansion, when AID may have been expressed.

Selection of stereotyped VH81X-{micro}H chains via pre-B cell receptor early in ontogeny and their conservation in adults by marginal zone B cells

The pre-B cell receptor (preBCR) plays critical roles in early B cell differentiation. It has been shown that not all muH chains are capable of pairing with surrogate light (SL) chains to form preBCR. Here, we established a novel system to differentially identify two types of early pre-B cell populations in bone marrow and fetal liver of mice, one producing SL-pairing muH chains and the other producing SL-non-pairing muH chains. The former population accounted for 80% of all the early pre-B cells in adult bone marrow, while it accounted for only 20% of those in fetal liver. Comparison of the two types of pre-B cell populations in fetal liver revealed the structural difference between SL-pairing and -non-pairing muH chains encoded by the V(H)81X segment that was most frequently utilized in fetal liver pre-B cells but rarely expressed by B cells generated in adults. PreBCR played an important role in the positive selection of V(H)81X-muH chains carrying the characteristic sequences of the complementarity-determining region 3 with little or no nibbling or N nucleotide addition, leading to their predominance in neonatal splenic B cells. These fetal-type V(H)81X-muH chains were also detected in adult spleen, but almost exclusively in marginal zone (MZ) B cells in contrast to the adult-type V(H)81X-muH chains. This strongly suggests that neonatally generated and selected B cells expressing the stereotyped V(H)81X-muH chains are maintained in the adult MZ and could function as innate-like lymphocytes.

The CD5+ B-cell

In the last two decades, many efforts have been made to better understand the biology of B-lymphoproliferative disorders through the knowledge of physiology and function of the postulated normal counterpart. The follicular mantle B-cells express a typical CD23+ IgM+ IgD+ phenotype and surround the germinal center area in secondary lymphoid organs. CD5+ B-cells with FM phenotype can be isolated from different sources and all share similar morphologic, phenotypic and functional features (small cells, scanty nucleus/cytoplasm ratio, unmutated VH genes, response to polyclonal activators but not to T independent antigens, production of "natural" antibodies). While the CD5+ B-cells predominate in fetal life, their number decreases with age. However, the CD5+ B-cells have been demonstrated to increase again in elderly both in man and mouse. This finding may explain the incidence of B-CLL and of MCL that are believed to represent the malignant transformation of the normal CD5+ B-cells, among elderly and middle aged individuals, respectively.

Locus 'decontraction' and centromeric recruitment contribute to allelic exclusion of the immunoglobulin heavy-chain gene

Allelic exclusion of immunoglobulin genes ensures the expression of a single antibody molecule in B cells through mostly unknown mechanisms. Large-scale contraction of the immunoglobulin heavy-chain (Igh) locus facilitates rearrangements between Igh variable (V(H)) and diversity gene segments in pro-B cells. Here we show that these long-range interactions are mediated by 'looping' of individual Igh subdomains. The Igk locus also underwent contraction by looping in small pre-B and immature B cells, demonstrating that immunoglobulin loci are in a contracted state in rearranging cells. Successful Igh recombination induced the rapid reversal of locus contraction in response to pre-B cell receptor signaling, which physically separated the distal V(H) genes from the proximal Igh domain, thus preventing further rearrangements. In the absence of locus contraction, only the four most proximal V(H) genes escaped allelic exclusion in immature mu-transgenic B lymphocytes. Pre-B cell receptor signaling also led to rapid repositioning of one Igh allele to repressive centromeric domains in response to downregulation of interleukin 7 signaling. These data link both locus 'decontraction' and centromeric recruitment to the establishment of allelic exclusion at the Igh locus.

Subsets with restricted immunoglobulin gene rearrangement features indicate a role for antigen selection in the development of chronic lymphocytic leukemia

We recently identified a chronic lymphocytic leukemia (CLL) subgroup using the immunoglobulin variable heavy-chain (V(H)) gene V(H)3-21 with almost identical heavy-chain complementarity determining region 3s (HCDR3s) and preferential variable light-chain (V(L)) gene usage, suggesting recognition of a common antigen epitope in this subset. To further explore the B-cell receptors (BCRs) in CLL, we characterized 407 V(H) rearrangements amplified from 346 CLLs regarding V(H), diversity (D), and joining (J(H)) gene usage and performed multiple alignment of the HCDR3 sequences. These analyses revealed 3 small subsets (2 V(H)1-69 groups, 7 cases; and 1 V(H)1-2 group, 5 cases) with highly restricted HCDR3 features including identical V(H)/D/J(H) usage, HCDR3 lengths, and shared N-sequences, in addition to the V(H)3-21 group (22 cases). Furthermore, another 3 groups (9 V(H)1-3(+) cases, 3 V(H)1-18(+) cases, and 5 V(H)4-39(+) cases) had essentially identical V(H)/D/J(H) use and similar HCDR3 lengths but less conserved N-regions. Analysis in all 6 of these subgroups showed restriction in V(L) gene use, whereas no association between V(H) and V(L) usage was found in cases without HCDR3 similarities. Altogether, structurally similar HCDR3s associated with preferential V(L) gene usage implies selection of BCRs, especially in subsets showing high HCDR3 similarities, thus pointing to restricted antigen recognition sites and possibly involvement of specific antigens in CLL development.

Immunoglobulin heavy-chain receptor editing is observed in the NOD/SCID model of human B-cell development

Receptor editing and receptor revision are the two mechanisms of antibody diversity that result in either complete V-gene replacement or the formation of hybrid V genes. We do not yet understand how this process unfolds, because they are rare and difficult to study in vivo. In this study, we describe a family of VH4-34:VH4-61 hybrids isolated from a human B-cell chimeric non-obese diabetic/severe combined immunodeficient mouse. The observation of hybrid immunoglobulin sequences in human B cells that developed in this model system makes it useful for the study of this mechanism of diversification and tolerance.

Induction of somatic hypermutation by antigen-specific B cell receptors in the human BL2 cell line

The role of the B cell antigen receptor in the induction of somatic hypermutation is presently unclear. We established stable transfectants of the human BL2 cell line expressing hen-egg lysozyme-specific IgM or IgA and compared their ability to induce somatic hypermutation of the endogenous rearranged heavy-chain gene. We found that IgM and IgA were both able to induce somatic hypermutation in an antigen dose-independent manner. The mutations displayed most of the characteristics of somatic hypermutation in vivo. Notably, some replacements introduced stop codons in the coding region. Our data suggest that class-switched memory B cells may undergo somatic hypermutation. They also suggest that the transmembrane/cytoplasmic domains of the class-switched isotypes modulate the signaling and down-modulation activities of the BCR in an antigen dose-dependent manner.

Regulation of E2A gene expression in B-lymphocyte development

Biochemical and genetic studies have demonstrated that transcription factors encoded by the E2A gene are essential in regulating B lineage specific gene expression and B lineage commitment. However, the mechanism by which E2A regulates B lineage commitment is not known. It has been reported that E2A controls B lineage commitment in a dosage dependent manner. To further investigate this gene dosage effect, we analyzed E2A expression during normal B cell development in mice carrying a functional E2AGFP knockin allele. Mice carrying this fusion allele were examined for E2A gene expression during bone marrow B cell development. A dramatic upregulation of E2A is observed concomitant with the initiation of immunoglobulin heavy chain D-J rearrangement and the induction of Early B cell Factor (EBF) gene expression. We also show that this E2A upregulation does not occur in the absence of the EBF gene. These results indicate that E2A upregulation is a critical step in regulating B-lineage commitment. It further suggests that E2A gene dosage may be determined by a cross regulation between E2A and EBF during B lineage commitment.

Non-functional immunoglobulin G transcripts in a case of hyper-immunoglobulin M syndrome similar to type 4

Summary 86% of immunoglobulin G (IgG) heavy-chain gene transcripts were found to be non-functional in the peripheral blood B cells of a patient initially diagnosed with common variable immunodeficiency, who later developed raised IgM, whereas no non-functionally rearranged transcripts were found in the cells of seven healthy control subjects. All the patient's IgM heavy-chain and kappa light-chain transcripts were functional, suggesting that either non-functional rearrangements were being selectively class-switched to IgG, or that receptor editing was rendering genes non-functional after class-switching. The functional gamma-chain sequences showed a normal rate of somatic hypermutation while non-functional sequences contained few somatic mutations, suggesting that most came from cells that had no functional gene and therefore were not receiving signals for hypermutation. However, apoptosis of peripheral blood lymphocytes was not impaired. No defects have been found in any of the genes currently known to be responsible for hyper-IgM syndrome but the phenotype fits best to type 4.

Characterization of B lymphopoiesis in mouse bone marrow and spleen

This chapter provides information on the application of flow cytometry for analysis of B-cell development, describing in detail the particular surface proteins that can serve as markers for recognizing distinct stages in this process. These cell fractions range from just prior to initial heavy chain rearrangement, the germline pro-B stage, through D-J rearranged pro-B and heavy chain expressing pre-B stages, to the maturing surface BCR positive B-cell stages. It also outlines assays for the characterization of these cells, including procedures for testing functional lineage restriction, determination of rearrangement status, analyses of gene expression at the ribonucleic acid (RNA) and protein level, and assessment of cell cycle state.

Molecular single-cell PCR analysis of rearranged immunoglobulin genes as a tool to determine the clonal composition of normal and malignant human B cells

Owing to the nearly limitless diversity of immunoglobulin (Ig) variable-region gene rearrangements, such rearrangements represent ideal clonal markers for B-lineage cells. This chapter describes an approach to isolate single cells from frozen tissue sections by microdissection using a hydraulic micromanipulator and the subsequent amplification of rearranged IgH and Igkappa genes from the cells in a seminested polymerase chain reaction (PCR) approach. The amplification of a priori unknown V-gene rearrangements is made possible by the usage of a collection of V-gene family-specific primers recognizing nearly all V-gene segments together with primer mixes for the J-gene segments. By sequence comparison of V-gene amplificates from distinct cells, the clonal relationship of the B-lineage cells can unequivocally be determined. As a large part of the V-gene rearrangements is amplified, the approach is also useful to address additional issues, such as V-, D-, and J-gene usage and the presence and pattern of somatic mutations.

The nonimmunoglobulin portion of lambda5 mediates cell-autonomous pre-B cell receptor signaling

The pre-B cell receptor (preBCR), composed of mu immunoglobulin (Ig) and surrogate light chains, signals large 'preB-II' cells to proliferate in the apparent absence of ligands or cooperating cells. We deleted the N-terminal, nonimmunoglobulin (nonlg) portion of lambda5, or mutated seven arginine residues in it to serine residues. PreBCRs with such mutant lambda5 proteins showed increased cell surface representation and a diminished rate of aggregation and internalization. Tyrosine phosphorylation of preBCR complexes containing mutant lambda5 proteins was abolished. These results indicate that the nonIg portion of lambda5, and the seven arginine residues in it, are needed for signal transduction, and that signaling could be cell autonomous. We propose two models to explain the apparently constitutive, ligand-independent signal-transducing capacity of the preBCR.

The "dispensable" portion of RAG2 is necessary for efficient V-to-DJ rearrangement during B and T cell development

Previous in vitro studies defined the minimal regions of RAG1 and RAG2 essential for V(D)J recombination. In order to characterize the role of the C-terminal "dispensable" portion of RAG2, we generated core-RAG2 knock-in mice. We found that the core-RAG2-containing recombinase complex is selectively defective in catalyzing V-to-DJ rearrangement at the IgH and TCRbeta loci, resulting in partial developmental blocks in B and T lymphopoiesis. Analysis of recombination intermediates showed defects at the cleavage phase of the reaction. We also observed a reduction in overall recombinase activity in core-RAG2-expressing thymocytes, leading us to suggest that the interaction of a defective recombinase with RSS sequences unique to VH and Vbeta gene segments may underlie the specific V-to-DJ rearrangement defect in core-RAG2 mice.

Immunglobulin repertoire analysis provides new insights into the immunopathogenesis of Sjögren's syndrome

This review focuses on the use of immunglobulin (Ig) variable region genes by B cells from patients with primary Sjögren's syndrome (pSS) and the biologic insights that this provides. Comparison of the Ig repertoire from the blood and parotid gland of pSS patients with that of normal donors suggests that there are typical disturbances of B cell homeostasis with depletion of memory B cells from the peripheral blood and accumulation/retention of these antigen-experienced B cells in the inflamed tissue. Although there are clonally expanded B cells in the parotid gland, generalized abnormalities in the B cell repertoire are also found in pSS patients. The vast majority of the current data indicate that there is no major molecular abnormality in generating the IgV chain repertoire in patients with pSS. In contrast, disordered selection leads to considerable differences in the V(L) gene usage and V(H) CDR3 length of the B cell Ig repertoire in pSS patients. The nature of the influences that lead to disordered selection in pSS remains to be determined, but should provide important clues to the etiology of this autoimmune inflammatory disorder.

Unequal VH gene rearrangement frequency within the large VH7183 gene family is not due to recombination signal sequence variation, and mapping of the genes shows a bias of rearrangement based on chromosomal location

Much of the nonrandom usage of V, D, and J genes in the Ab repertoire is due to different frequencies with which gene segments undergo V(D)J rearrangement. The recombination signal sequences flanking each segment are seldom identical with consensus sequences, and this natural variation in recombination signal sequence (RSS) accounts for some differences in rearrangement frequencies in vivo. Here, we have sequenced the RSS of 19 individual V(H)7183 genes, revealing that the majority have one of two closely related RSS. One group has a consensus heptamer, and the other has a nonconsensus heptamer. In vitro recombination substrate studies show that the RSS with the nonconsensus heptamer, which include the frequently rearranging 81X, rearrange less well than the RSS with the consensus heptamer. Although 81X differs from the other 7183-I genes at three positions in the spacer, this does not significantly increase its recombination potency in vitro. The rearrangement frequency of all members of the family was determined in microMT mice, and there was no correlation between the in vitro recombination potential and V(H) gene rearrangement frequency in vivo. Furthermore, genes with identical RSS rearrange at different frequencies in vivo. This demonstrates that other factors can override differences in RSS potency in vivo. We have also determined the gene order of all V(H)7183 genes in a bacterial artificial chromosome contig and show that most of the frequently rearranging genes are in the 3' half of the region. This suggests that chromosomal location plays an important role in nonrandom rearrangement of the V(H)7183 genes.

Rearrangement of the human heavy chain variable region gene V3-23 in transgenic mice generates antibodies reactive with a range of antigens on the basis of VHCDR3 and residues intrinsic to the heavy chain variable region

To formulate a 'logic' for how a single immunoglobulin variable region gene generates antibodies with different antigen specificity and polyreactivity, we analysed chimeric antibodies produced in transgenic mice carrying the germ-line human V3-23 gene, multiple diversity (D) and joining (J) gene segments. Hybridomas producing antibodies encoded by the V3-23 gene in combination with different mouse Vkappa genes were obtained by fusion of splenocytes from transgenic mice. All antibodies had human mu-chains and mouse light chains, were multimeric in structure and expressed the human V3-23 gene. Nucleotide sequence analyses of genes encoding the heavy and light chains of 12 antibodies in relation to antigen specificity highlighted the importance of heavy chain variable region CDR3 in determining reactivity with different antigens. However, the results also suggest that non-CDR3 sequences intrinsic to the V3-23 gene itself may be involved in, or determine, the binding of the chimeric antibodies to some of the antigens tested in the current study.

Epstein-Barr virus-associated high-grade B-cell lymphoma of mucosal-associated lymphoid tissue in a 9-year-old Boy

We report an unusual case of Epstein-Barr virus (EBV)-associated mucosal-associated lymphoid tissue (MALT) lymphoma involving the lungs, kidneys, and axillary lymph nodes in a child with congenital hypoadrenalism and panhypopituitarism. The patient presented with an aggressive clinical course and histologic evolution. Initial biopsies (1994) of the lung and kidney revealed histologic features of low-grade B-cell MALT lymphoma with lymphoepithelial lesions within the renal tubules and bronchial epithelium. Subsequent biopsies (1996, 1997, and 1999) revealed progressively greater cytologic atypia, polymorphism, and necrosis; an increased mitotic rate; and a preponderance of large cells, indicative of progression from a low-grade to a high-grade MALT lymphoma. Immunophenotyping of the lung and lymph node lesions revealed identical surface marker profiles: cells were CD19(+), CD20(+), immunoglobulin (Ig) G(+), kappa(+), lambda(-), CD5(-), CD10(-), CD23(-), and IgM(-), and also negative for T-cell markers. Genotypic analysis demonstrated the presence of immunoglobulin heavy chain rearrangement and monoclonality of EBV in the lung lesion by Southern blot hybridization and polymerase chain re()action (PCR). The clinicopathologic features suggest that these lesions might represent an immunosupression-related continuum of low-grade to high-grade MALT lymphomas. Infection with EBV may have contributed to this tumor's aggressive clinical and histologic evolution.

Optimized multiplex IgH/ras PCR: a tool for quantitative monitoring of B-lymphoproliferative disorders

The use of quantitative PCR is recommended to monitor the level of residual hematological malignancies. The proposed multiplex IgH/ras PCR uses a co-amplification of the clonal CDR3 rearrangement of the immunoglobulin heavy chain gene (IgH) as a disease marker and a segment of the Hras 1 gene containing codon 61 (ras) as a control gene. Serial dilutions of stored diagnostic DNAs are examined together in the same PCR at a sub-plateau phase and, after analysis by densitometry, the amount of CDR3 product is related to the ras product. An increase of this ratio at comparable amounts of DNA is viewed as an increase of malignant cells. This endpoint PCR quantifying approach appears to be applicable in monitoring B-lymphoproliferative disorders as was shown to be true in B-cell non-Hodgkin's lymphoma and may provide information on disease activity and treatment outcome.

Distinct signals mediate maturation and allelic exclusion in lymphocyte progenitors

Successful in-frame rearrangement of immunoglobulin heavy chain genes or T cell antigen receptor (TCR) beta chain genes in lymphocyte progenitors results in formation of pre-BCR and pre-TCR complexes. These complexes signal progenitor cells to mature, expand in cell number, and suppress further rearrangements at the immunoglobulin heavy chain or TCRbeta chain loci, thereby ensuring allelic exclusion. We used transgenic expression of a constitutively active form of c-Raf-1 (Raf-CAAX) to demonstrate that activation of the Map kinase pathway can stimulate both maturation and expansion of B and T lymphocytes, even in the absence of pre-TCR or pre-BCR formation. However, the same Raf signal did not mediate allelic exclusion. We conclude that maturation of lymphocyte progenitors and allelic exclusion require distinct signals.

Herpes virus type 8-negative primary effusion lymphoma associated with PAX-5 gene rearrangement and hepatitis C virus: a case report and review of the literature

At present, there is no case report of HHV8- primary effusion lymphoma (PEL) with t(9;14)(p13;q32) involving both PAX-5 and immunoglobulin heavy chain gene rearrangement, which is a rare translocation in B-cell non-Hodgkin's lymphoma, in an HIV- patient. We examined an HIV-seronegative 63-year-old Japanese man with hepatitis C virus-associated liver cirrhosis and hepatocellular carcinoma manifesting peritoneal lymphomatous effusion without tumor mass at any body site. The lymphoma cells were examined twice by light microscopy, immunohistochemistry, three-color flow cytometry, cytogenetics, and molecular analyses. The nuclear morphology of lymphoma cells was similar to that of large noncleaved cells, although the lymphoma cell size was a little smaller that of the usual large-cell lymphoma. Immunophenotyping of lymphoma cells in the ascitic fluid revealed a mature peripheral B-cell phenotype (CD5- CD10- CD19+ CD20+ CD22+ Ig G+ lambda+). Cytogenetics showed a clonal population: 45,X,-Y, der(2) t(2;6)(q31;p21.3), t(4;8)(q21;q11.2), der(6) t(2;6)(q31;p21.3) add(6)(q15), t(9;14)(p13;q32.3) [10]/47, idem, +der(6) t(2;6), +16[10]. Southern blot analysis revealed rearranged fragments with a probe for immunoglobulin heavy chain, some of which were a size similar to those with a PAX-5 gene probe. Polymorphism, not rearrangement, of the c-MYC gene, was also found. HHV8 and the Epstein-Barr virus were not detected by polymerase chain reaction. This case is the first report of an HHV8- PEL with t(9;14) involving a PAX-5 gene rearrangement in an HIV-seronegative patient. This primary effusion lymphoma manifested spontaneous regression without any therapy. These findings suggest that there may be an additional subcategory of primary effusion lymphoma that is not associated with HHV8 nor c-MYC(R) but is pathogenetically associated with the PAX-5 gene or hepatitis C virus.