Resolution and characterization of pro-B and pre-pro-B cell stages in normal mouse bone marrow

We have resolved B220+ IgM- B-lineage cells in mouse bone marrow into four fractions based on differential cell surface expression of determinants recognized by S7 (leukosialin, CD43), BP-1, and 30F1 (heat stable antigen). Functional differences among these fractions can be correlated with Ig gene rearrangement status. The largest fraction, lacking S7, consists of pre-B cells whereas the others, expressing S7, include B lineage cells before pre-B. These S7+ fractions, provisionally termed Fr. A, Fr. B, and Fr. C, can differentiate in a stromal layer culture system. Phenotypic alteration during such culture suggests an ordering of these stages from Fr. A to Fr. B to Fr. C and thence to S7- pre-B cells. Using polymerase chain reaction amplification with pairs of oligonucleotide primers for regions 5' of JH1, DFL16.1, and Jk1, we find that the Ig genes of Fr. A are in germline configuration, whereas Fr. B and C are pro-B cell stages with increasing D-J rearrangement, but no V-D-J. Finally, functional analysis demonstrates that the proliferative response to IL-7, an early B lineage growth factor, is restricted to S7+ stages and, furthermore, that an additional, cell contact-mediated signal is essential for survival of Fr. A.

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.

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.

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.

Clonal B-cell expansions in peripheral blood of HCV-infected patients

Clonal expansions of IgM-producing B cells were investigated in 38 patients with a chronic hepatitis C virus infection. Eight patients were affected with type II mixed cryoglobulinaemia (two of whom also had non-Hodgkin's lymphoma and one had Waldenström's disease), one with type III mixed cryoglobulinaemia, one with Waldenström's disease, and 28 with chronic liver disease. To detect the clonal B-cell expansions we used a RT/PCR procedure in which the CDR3/FW4 regions of the IgM heavy chain mRNAs were amplified and resolved in sequencing polyacrylamide gels. Clonal Ig gene rearrangements were detected in all patients with type II mixed cryoglobulinaemia and also at a high frequency (24%) in the HCV-infected patients without cryoglobulinaemia. A polyclonal pattern was present in the patient with type III mixed cryoglobulinaemia and in the 15 normal individuals and 16 age-related patients with HCV-negative alcoholic liver disease which were investigated as controls. No association was found between the presence of a clonal B-cell expansion and age, sex, liver histology, or levels of serum aminotransferase. The serum levels of rheumatoid factor were increased in all patients with a clonal expansion, suggesting that the expanded B-cell clones belong to the rheumatoid factor producing B-cell subset.

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.

Clonal deletion of autospecific B lymphocytes

Using mice transgenic for functional, rearranged immunoglobulin heavy and light chain genes, it can be demonstrated that B lymphocytes reactive with cell surface-bound class I MHC antigen can be controlled by clonal elimination. Even low-affinity cell-bound ligands can induce deletion. Deletion can occur in the pre-B to B cell transitional stage or after the B cells exist the bone marrow, depending on where the cells first encounter autoantigen. IgD appears to play no role in protecting cells from deletion. It is argued that defects in B-cell tolerance alone may be sufficient to lead to systemic autoimmunity.

Use of a single VH family and long CDR3s in the variable region of cattle Ig heavy chains

We have analyzed transcripts encoding the variable regions of Ig heavy chains from adult and fetal bovine splenocytes and bovine x mouse heterohybridomas. The 13 adult, seven fetal and two heterohybridomas transcripts as well as the six genes that were sequenced had > 83% identity to each other in the VH-encoded regions (FRs 1-3 and CDRs 1 and 2). By this criterion, all the bovine sequences were assigned to one family, which corresponds to the bovine homolog of the murine Q52 family. Southern blot analysis of genomic DNA demonstrated that homologs of other murine VH families such as 7183, S107 and 36-60 were present in the genome, but transcripts from these families were not detected in rapid amplification of cDNA ends (RACE)-PCR amplified products or in individual clones. The sequences of the adult transcripts using the mu isotype showed extensive somatic mutation indicating that the process of somatic hypermutation begins earlier in development of the bovine B cell. The length of CDR3 from V(D)J rearrangements averaged 21 amino acids, which is larger than other mammalian CDR3s. Analysis of CDR3s from 23 fetal transcripts revealed a preference for a reading frame in the putative D genes which is rich in glycine and tyrosine, and is also extensively mutated in adults. The bovine immune system appears to utilize Ig VH genes of a single family, but generates antibody diversity by extensive somatic mutation and long CDR3s which are subsequently hypermutated.

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.

Expression of IL-4, Cepsilon RNA, and Iepsilon RNA in the nasal mucosa of patients with seasonal rhinitis: effect of topical corticosteroids

BACKGROUND

Nasal allergen provocation has demonstrated that allergen-induced rhinitis is associated with an increase in local IL-4 mRNA and IgE heavy chain (Cepsilon) and IgE heavy chain promoter (Iepsilon) RNA and that pretreatment with topical glucocorticosteroids inhibits the increase in these transcripts.

OBJECTIVE

This study was undertaken to determine whether observations made after acute allergen provocation can be extended to the case of chronic exposure experienced during the pollen season.

METHODS

Biopsy specimens were obtained from the inferior turbinate of 33 pollen-sensitive subjects with allergic rhinitis before and during pollen season. Patients were randomized in a double-blind fashion and treated with either topical steroids (200 microg fluticasone propionate twice daily; n = 16) or matched placebo nasal spray (n = 17) before the pollen season. Alkaline phosphatase anti-alkaline phosphatase immunocytochemistry was used to identify B cells (CD20+), and in situ hybridization was used to detect IL-4, Cepsilon, and Iepsilon RNA+ cells.

RESULTS

Baseline examination revealed IL-4 and Cepsilon RNA but virtually no Iepsilon RNA+ cells in the nasal mucosa. Analysis revealed a significant difference in the expression of Cepsilon and Iepsilon RNA+ cells (p < 0.001). Biopsy specimens taken after antigen exposure exhibited highly significant increases in placebo-treated (p < 0.001) but not steroid-treated patients. In both groups, the number of CD20+ cells was unchanged when preexposure and postexposure biopsy specimens were compared.

CONCLUSIONS

These results show strong support for the hypothesis that IgE class switching occurs locally within the nasal mucosa of subjects with seasonal allergic rhinitis and that this response can be inhibited through strategies directed against local IgE production.

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.

T-cell-rich B large-cell lymphoma simulating lymphocyte-rich Hodgkin's disease

Immunophenotypic analysis of 50 cases fulfilling the histologic criteria for mixed cellularity Hodgkin's disease disclosed nine cases with a B-cell, non-Hodgkin's phenotype (CD20+, CD15-, CD30-, EMA-). The cases were characterized by a diffuse small lymphocytic milieu, interspersed atypical large cells including classic Reed-Sternberg cells, and infrequent plasma cells, eosinophils, and L&H cells. The male:female ratio was 7:2 (aged 22-65 years, median 39 years). Three patients were Ann Arbor stage II, two stage III, and four stage IV. The patients presented with generalized lymphadenopathy (four), mesenteric lymph node involvement (two), splenomegaly (four), and bone marrow involvement (three). Four patients were treated with standard Hodgkin's disease protocols. Two attained a complete response and two a partial response; all relapsed and died. Four of five patients treated for large-cell lymphoma achieved a complete response and are currently alive without evidence of disease. The one patient with an initial partial response relapsed and died. We conclude that immunophenotypic analysis is essential in cases of histologic mixed cellularity Hodgkin's disease, especially in those with lymphocyte-rich morphology. Cases with a B-cell phenotype should be diagnosed and treated as T-cell-rich B large-cell lymphoma.

Frequent occurrence of identical heavy and light chain Ig rearrangements

Single-cell PCR analyses of expressed Ig H and L chain sequences presented here show that certain rearrangements occur repeatedly and account for a major segment of the well-studied repertoire of B-1 cell autoantibodies that mediate the lysis of bromelain-treated mouse erythrocytes, i.e. antibodies reactive with phosphatldyicholine (PtC). We repeatedly isolated at least 10 different types of VH region rearrangements, involving three distinct germline genes, among FACS-sorted PtC-binding B-1 cells from three strains of mice (C57BL/6J, BALB/c and C.B-17). The predominant rearrangement, VH11-DSP-JH1 (VH11 type 1), has been previously found in anti-PtC hybridomas in several studies. We show that within each of six mice from two strains (C57BL/6J and BALB/c), unique instances of IgH/IgL pairing arose either from different B cell progenitors prior to IgH rearrangement or from pre-B cells which expanded after IgH rearrangement but prior to IgL rearrangement. Together with other recurrent rearrangements described here, our findings demonstrate that clonal expansion of mature B cells cannot account for all repeated rearrangements. As suggested by initial studies of dominant idiotype expression, these findings confirm that clonal expansion is only one of the mechanisms contributing to the establishment of recurrent rearrangements.

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.

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.

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.

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.

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.

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.

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.

Expansion of B lymphocytes with an unusual immunoglobulin rearrangement associated with atypical lymphocytosis and cigarette smoking

Persistent polyclonal lymphocytosis has been described in a group of female patients who all have the HLA-DR7 antigen in common and who are all heavy cigarette smokers. Immunoglobulin heavy chain gene rearrangement was analyzed by hybridization with specific immunoglobulin heavy chain genes to restriction enzyme-digested genomic DNA samples. The results in two of these patients showed that the lymphocytosis was associated with an expanded subpopulation of B-lineage cells represented by the presence of an unusual immunoglobulin gene rearrangement pattern. Expansion of this subpopulation of B cells appeared to be linked to cigarette smoking since the intensity of the cell population harboring the rearranged gene was much stronger in patients who were smoking heavily compared with the same patients who were temporarily not smoking.

The role of recombination signal sequences in the preferential joining by deletion in DH-JH recombination and in the ordered rearrangement of the IgH locus

The bias favoring deletion over inversion in DH-JH rearrangement has been known for years, but the underlying mechanism has yet to be fully defined. It has been suggested that the ratio of deletion/inversion is determined by the combined effect of two factors: (i) the relative strengths of 5' and 3' recombination signal sequences (RSS) of a DH segment, and (ii) the efficiency with which the deletional product (one joint) forms relative to the inversional product (two joints). In this study, we analyzed for the first time the effect of factor 1 alone on the biased 3' RSS utilization in DH-JH joining by using deletional plasmids in an extrachromosomal substrate V(D)J recombination assay. It was found that the 3' RSS and associated coding end (12 bp) mediate recombination more efficiently than the 5' RSS/coding end DH-JH plasmids. These results demonstrate that the effect of the RSS/coding end alone can account, at least partially, for the predominant deletion in DH-JH recombination. The potential effect of the relative strength of RSS and associated coding end on the ordered rearrangement of DH-JH followed by VH to DH-JH was also assessed. When recombination frequencies of D-->J (3' DH to J3) were compared with frequencies of V-->D (VHPJ14 to 3' DH or VHOX2 to 3' DH), it was found that V-->D joining was, if anything, more efficient than D-->J joining. Therefore, if all three segments were accessible, RSS/coding end effects would not contribute to the ordered rearrangement of the IgH locus.

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.

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.