Trans-chromosomal recombination within the Ig heavy chain switch region in B lymphocytes

Somatic DNA rearrangements in B lymphocytes, including V(D)J gene rearrangements and isotype switching, generally occur in cis, i. e., intrachromosomally. We showed previously, however, that 3 to 7% of IgA heavy chains have the V_H and Cα regions encoded in trans. To determine whether the trans-association of V_H and Cα occurred by trans-chromosomal recombination, by trans-splicing, or by trans-chromosomal gene conversion, we generated and analyzed eight IgA-secreting rabbit hybridomas with trans-associated V_H and Cα heavy chains. By ELISA and by nucleotide sequence analysis we found that the V_H and Cα regions were encoded by genes that were in trans in the germline. We cloned the rearranged VDJ-Cα gene from a fosmid library of one hybridoma and found that the expressed V_H and Cα genes were juxtaposed. Moreover, the juxtaposed V_H and Cα genes originated from different IgH alleles. From the same hybridoma, we also identified a fosmid clone with the other expected product of a trans-chromosomal recombination. The recombination breakpoint occurred within the Sμ/Sα region, indicating that the trans-association of V_H and Cα genes occurred by trans-chromosomal recombination during isotype switching. We conclude that trans-chromosomal recombination occurs at an unexpectedly high frequency (7%) within the IgH locus of B lymphocytes in normal animals, which may explain the high incidence of B-cell tumors that arise from oncogene translocation into the IgH locus.     

Splenic lymphoma with villous lymphocytes expressing chromosomal abnormalities]

An 88-year-old Japanese woman with splenomegaly, but without lymphadenopathy, was admitted because of epigastric distress. Laboratory data disclosed an RBC of 310 x 10(4)/microliter, Hb of 10.1 g/dl, Ht of 30.6%, Plt count of 9.8 x 10(4)/microliter, and WBC of 4,470/microliter with 38% abnormal lymphocytes. Peripheral blood films revealed lymphocytes with thin, short cytoplasmic villi, condensed nuclear chromatin, and small nucleoli. The lymphocytes stained negative for tartrate-resistant acid phosphatase. Also, immunophenotyping was positive for expression of the cell surface markers CD19, CD20, IgG, kappa and HLA-DR, but not for CD5, CD10, CD11c, CD23, CD25, CD38, or CD103 antigens. Chromosomal analysis of peripheral blood cells disclosed the 46, XX, del(7), (q32) aberration. A splenectomy was performed simultaneously with partial colon resection because of a mucinous carcinoma found in the transverse colon. Histologic examination of resected spleen tissues revealed a distinctive pattern of white pulp infiltration by lymphoma cells. The histologic findings and clinical data were consistent with the features of splenic lymphoma with circulating villous lymphocytes. Our patient exhibited a relatively benign clinical course, and was being followed on an outpatient basis with no additional therapy.     

Splenic lymphoma with circulating villous lymphocytes/splenic marginal-zone lymphoma.

Splenic lymphoma with villous lymphocytes (SLVL) represents a low-grade B-cell non-Hodgkin's lymphoma (NHL) that histologically is indistinguishable from splenic marginal-zone lymphoma (SMZL). Characteristic features of SLVL are splenomegaly, moderate lymphocytosis, nodular and intrasinusoidal pattern of bone marrow infiltration, serum monoclonal band, slow benign course, and response to splenectomy. The diagnosis is made by the morphology of the circulating villous cells and their immunophenotype, which is distinct from that of chronic lymphocytic leukemia (CLL) and hairy-cell leukemia (HCL), diseases with which SLVL may be confused. When treatment is indicated, splenectomy is the treatment of choice, but some patients may require additional chemotherapy to control progression. In those circumstances, fludarabine may be the agent of choice. Despite its unique features, which, compounded, suggest that SLVL is a clinicopathologic entity, there are no specific chromosome abnormalities and problems of differential diagnosis with other B-cell NHLs, chiefly mantle-cell lymphoma (MCL), remain in a minority of patients.     

Splenic lymphoma with villous lymphocytes: natural history and response to therapy in 50 cases

We studied the natural history and response to treatment in 50 patients with splenic lymphoma with villous lymphocytes followed for a minimum of 6 months and up to 15 years (median 3.7 years). The disease occurs in the elderly (median 68 years) and affects males more than females (M/F ratio 1.77). The median survival for the group was not reached but 82% were surviving at 3 years and 78% at 5 years. Twelve patients (24%) died, one-third of deaths were disease related (four patients) and one-half were due to cardiovascular disease or another malignancy (six patients). The outcome was worse for males (31% died) than females (11% died). Fourteen patients were not treated and 10 remain alive between 1 and 6 years from diagnosis. The remaining patients were treated by chemotherapy, splenic irradiation or splenectomy. The response to chemotherapy was poor and only eight of 22 (36%) patients treated achieved a good response. Splenic irradiation was employed in seven patients and three benefited from it. Splenectomy seems to be the treatment of choice, with significant improvement seen in 19 of 20 patients with one post-operative death. This response, lasting from 6 months to 7 years (median 4 years), was seen irrespective of whether splenectomy was the initial treatment or used later in management.     

Splenic lymphoma with circulating villous lymphocytes: Report of seven cases and review of the literature

Splenic lymphoma with villous lymphocytes (SLVL) is a relatively new entity with only a few reports published. We report seven cases of SLVL with detailed clinicopathologic and comprehensive immunophenotypic studies to further characterize this lymphoma, which is frequently confused with hairy cell leukemia and other low-grade B-cell lymphoid neoplasms. The diagnostic criteria we used include 1) prominent splenomegaly, 2) insignificant or no lymphadenopathy, 3) lymphocytosis without leukopenia, 4) presence of circulating villous lymphocytes, 5) characteristic cytologic and histologic features, and 6) specific phenotypic and cytochemical findings. Our studies show that SLVL does not represent a pure entity but rather a morphologically heterogeneous group of low-grade lymphomas with various cytologlc and histologic features. Although immunophenotyping is helpful in differential diagnosis, multiparameter studies are necessary to confirm the diagnosis. In our series, only two patients died of SLVL, who probably developed transformation to a higher-grade lymphoma. © 1994 Wiley-Liss, Inc.     

IgG-secreting lymphoplasmacytoid leukaemia: a B-cell disorder with extensively mutated VH genes undergoing Ig isotype-switching frequently associated with trisomy 12

We investigated 16 patients with elevated serum monoclonal IgG and a leukaemic B-cell lymphocytic disorder different from multiple myeloma. Their clinical history was that of a non-aggressive disease with dominant splenomegaly and long survival. Whereas abnormal blood and bone marrow cells were predominantly small lymphocytes with a few lymphoplasmacytoid cells, histopathological features included a lymphoplasmacytic infiltrate in eight cases. Most frequently, abnormal blood cells displayed a CD19+CD5-CD23+/- immunophenotype different from that of chronic lymphocytic leukaemia, except in two cases with a CD19+CD5+CD23+ phenotype. Interestingly, a coexistent serum monoclonal IgM and/or surface IgMG+ with identical light chain was identified in 10 patients, whereas in the remaining six patients only IgG expression was determined. VH gene analysis was performed in eight patients to investigate the clonal origins of tumour cells. All cases utilized the VH3 family, with evidence of extensive somatic mutations and intraclonal homogeneity in all cases. VH gene analysis indicated a clonal relationship between cells expressing IgM and IgG, with one case being biclonal. Cytogenetic evaluation showed a high incidence of trisomy 12 (60%) and 13q14 deletion (40%). In conclusion, we have described an unusual subset of low-grade lymphoma with high-serum IgG and frequent lymphoplasmacytoid features in which tumour cells derive from post-follicular memory B cells undergoing isotype switching with some cases arrested at both the IgM and IgG stage and others as IgG-positive cells only.     

Common clonal origin of lymphocytes and plasma cells in splenic lymphoma with villous lymphocytes

In two-thirds of patients with splenic lymphoma with villous lymphocytes (SLVL) a small amount of M-protein can be detected in association with the presence of plasma cells in the peripheral blood (PB) and/or bone marrow (BM). However, it is not known whether lymphoma cells and plasma cells originate from the same clone. In this report we describe a case of SLVL which was characterized by the presence of marked monoclonal gammopathy (IgG-κ 90 g/l) and increased plasma cells in the BM. In an attempt to elucidate the origin of lymphoma cells and plasma cells, we performed morphological, cytogenetic and molecular studies on PB mononuclear cells (PBMNC) without plasma cells and BMMNC containing 10% plasma cells from this patient.
Immunofluorescence showed that lymphoma cells and plasma cells were positive for cytoplasmic γ heavy and κ light chains. Well-developed endoplasmic reticulum was observed in the cytoplasmic organelles of PBMNC using an electron microscope. The mean IgG concentration in the 3 d supernatant cultures of PBMNC was 374±24μg/l. More than 50% PBMNC differentiated into plasmacytoid cells in 6 d of liquid culture with IL-3 and IL-6. Analysis by two-colour FISH revealed that karyotypic abnormalities of monosomy X and trisomy 17 existed simultaneously in both lymphoma cells and plasma cells. JH gene rearranged bands from PBMNC and BMMNC by Southern blot hybridization were identical, whereas DNAs from PBMNC failed to hybridize with the Cμ probe.
These observations strongly suggest that lymphoma cells and plasma cells originate from the same clone, and that plasma cells, as well as lymphoma cells, which have undergone class switch recombination, could produce IgG type M-protein in this case.     

Surface component of primate thymus-derived lymphocytes related to a heavy chain variable region.

In a study designed to determine whether T cells of man and higher primates express a surface component related to the variable region of immunoglobulin heavy chain (VH), chickens were immunized with the purified VH fragment of a monoclonal Waldenström macroglobulin. The antibody preparation reacted with a mu chain determinant contained in the Fd fragment and with individual determinants characteristic of the orginal Waldenström protein. As estimated by immunofluorescence analysis, a subpopulation of normal human peripheral T cells (approximately 30%) bound the anti-VH antibody. B-Cell lymphoma lines grown in vitro, as well as some T-cell leukemia lines of the cotton-topped marmoset (Sagiunus oedipus), also bound the anti-VH antibody. The VH-bearing component of the T-cell line 70-N-2 was labeled biosynthetically by incorporation of [3H]leucine and was precipitated specifically by anti-VH antibody. This component was characterized by an apparent mass of 70,000 daltons as assessed by polyacrylamide gel electrophoresis under reducing conditions in buffers containing sodium dodecyl sulfate. These data provide direct support for the hypothesis that some T cells express and synthesize a component related to immunoglobulin heavy chains.     

Cytogenetic studies in splenic lymphoma with villous lymphocytes

Summary. We report the cytogenetic findings on 31 cases of splenic lymphoma with villous lymphocytes (SLVL). TPA stimulated cells from peripheral blood (28 cases), spleen (two cases) and lymph node (one case) with SLVL have been analysed. A clonal chromosome abnormality was found in 27/31 patients (87%): this was identified as a simple abnormality in 12 cases and a complex one in 15. Four recurring abnormalities were seen: t(11:14) (q13:q32)in five patients, deletions or translocations involving 7q in seven patients. iso 17q in four patients and translocations involving 2p11 in four patients. The high frequency of clonal chromosome abnormalities in SLVL contrasts with the usually benign clinical course of this disease.
Abnormalities found frequently in patients with chronic lymphocytic leukaemia (CLL) such as trisosmy 12 and deletions or translocations involving 13q14 were each seen in only one patient. No case had the t(14:18) characteristic of follicular lymphoma.
Our findings demonstrate the high frequency of clonal and often complex chromosome abnormalities in SLVL. Although a unique chromosome rearrangement has not been identified, a pattern of four recurrent abnormalities has emerged. Our results suggest that SLVL is distinct on cytogenetic grounds from B-CLL and follicular lymphoma but shows similarity with mantle cell lymphoma, lymphoplasmacytic lymphoma and B-PLL.     

Structure and multiplicity of genes for the human immunoglobulin heavy chain variable region.

Several genes for the variable region of immunoglobulin heavy chains (VH genes) have been isolated from human fetal liver DNA by using a cDNA plasmid probe containing a mouse VH sequence. The detectable VH genes are separated by 12-16 kilobases of DNA, and hybridization experiments show about 23 hybridizing VH genes in DNA of three different individuals. The complete nucleotide sequence of one of these human VH genes shows that it belongs to the human VHIII subgroup. The VH gene appears to contain an intervening sequence (104 bases in length) within a precursor sequence, between residues -4 and -5. The precursor sequence is itself 19 codons in length. The 3' end of the V gene seems to be at codon 93 or 94, and this is followed by the conserved sequences C-A-C-A-G-T-G and G-A-C-A-C-A-A-A-C-C. The presence of these sequences suggests that similar enzymatic mechanisms are involved in the integration of V genes in both heavy and light chains.     

The histopathology of splenic lymphoma with villous lymphocytes

Whereas the hematologic, immunophenotypic, and molecular characteristics of splenic lymphoma with villous lymphocytes (SLVL) have been well documented, the histologic features of the spleen and lymph nodes remain uncharacterized. We have reviewed the histopathology of the spleen in 37 cases of SLVL and of involved splenic hilar lymph nodes in 6 cases. Tissue immunophenotyping was performed in 24 cases, 6 of which had frozen tissue available, and the results were compared with the membrane immunophenotype of the circulating villous lymphocytes and cells extracted from spleen and lymph nodes. In the spleen, SLVL is characterized by involvement of the white pulp follicles, which may be surrounded or replaced by the lymphoma cells. In the red pulp, the cells form small nodules and infiltrate diffusely with sinusoidal invasion. The cytologic appearance of the neoplastic cells varies from a resemblance to small mantle-zone--like lymphocytes to that of marginal-zone cells and there are scattered blast forms. In involved lymph nodes, the infiltrate again centers on the follicles that are usually replaced, but occasionally show preservation of follicle centers; sinuses are often preserved. The tissue immunophenotype is similar to that of marginal-zone B cells. Membrane immunophenotyping may give different results in some cases and may vary depending on the compartment from which the cells are obtained. SLVL in the peripheral blood is a histologically homogeneous entity identical to the condition previously characterised by histopathologists as splenic marginal-zone lymphoma.     

Polymorphisms of a human variable heavy chain gene show linkage with constant heavy chain genes.

In this study, restriction fragment length polymorphisms (RFLPs) were identified with an immunoglobulin variable heavy chain region (Ig VH) probe and the inheritance of the polymorphisms was analyzed in families. Linkage within the VHII gene cluster and between the VHII and Ig CH genes was investigated by lod (logarithm of odds) score analysis. In addition, the position of the VHII genes was determined in relation to another polymorphic locus--D14S1, which is tightly linked and centromeric to the CH genes. Genetic associations between genes in the CH and VH clusters were analyzed. These RFLPs represent genetically characterized VH region polymorphisms and it is hoped that they will facilitate the study of disease correlations as well as further the understanding of the genetics of the immunoglobulin heavy chain genes in humans.     

p53 abnormalities in splenic lymphoma with villous lymphocytes

The incidence and role of p53 abnormalities have not been reported in splenic lymphoma with villous lymphocytes (SLVL), the leukemic counterpart of splenic marginal zone lymphoma. Because p53 abnormalities correlate with progressive and refractory disease in cancer and isochromosome 17q has been described in SLVL, a low-grade lymphoma that behaves aggressively in a minority of patients, this study investigated p53 changes by molecular and immunophenotypic methods in samples from 59 patients. The p53 deletion was analyzed by fluorescence in situ hybridization, and p53 protein expression was assessed by immunocytochemistry in 35 of 59 cases and by flow cytometry in 20 of 35 patients. Ten patients (17%) had a monoallelic p53 loss, 3 (9%) of 35 nuclear protein expression by immunocytochemistry, and 2 (10%) of 20 by flow cytometry. Two patients had both deletion and protein expression. Direct sequencing of all p53 exons was used to delineate mutations in 9 of 11 patients with an identified abnormality. Mutations, both compromising p53 DNA binding, were identified in the 2 patients with deletion and protein accumulation. Kaplan-Meier analysis revealed a significantly worse survival for patients with p53 abnormalities. Although p53 abnormalities are infrequent in SLVL, they underlie a more aggressive disease course and poor prognosis. (Blood. 2001;97:3552-3558)     

Induction of Ig light chain gene rearrangement in heavy chain-deficient B cells by activated Ras

During B cell development, rearrangement and expression of Ig heavy chain (HC) genes promote development and expansion of pre-B cells accompanied by the onset of Ig light chain (LC) variable region gene assembly. To elucidate the signaling pathways that control these events, we have tested the ability of activated Ras expression to promote B cell differentiation to the stage of LC gene rearrangement in the absence of Ig HC gene expression. For this purpose, we introduced an activated Ras expression construct into JH-deleted embryonic stem cells that lack the ability to assemble HC variable region genes and assayed differentiation potential by recombination activating gene (RAG) 2-deficient blastocyst complementation. We found that activated Ras expression induces the progression of B lineage cells beyond the developmental checkpoint ordinarily controlled by mu HC. Such Ras/JH-deleted B cells accumulate in the periphery but continue to express markers associated with precursor B cells including RAG gene products. These peripheral Ras/JH-deleted B cell populations show extensive Ig LC gene rearrangement but maintain an extent of kappa LC gene rearrangement and a preference for kappa over lambda LC gene rearrangement similar to that of wild-type B cells. We discuss these findings in the context of potential mechanisms that may regulate Ig LC gene rearrangement.