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Lymphoplasmacytic lymphoma (LPL) is not a sharply delineated lymphoma entity, either morphologically, phenotypically, or clinically. The diagnosis is often made by excluding other small cell lymphomas with plasmacytic differentiation, thus a genetic diagnostic marker would be of great benefit. Conventional cytogenetic techniques have previously demonstrated a deletion of 6q in a proportion of cases, varying from 7 to 55%. In this report, we apply array-based comparative genomic hybridization on 11 LPL samples. Genomic aberrations were detected in 9 of 11 cases, and included gains and losses. In general, the number of genetic aberrations was relatively low (two to three abnormalities per case). Recurrent aberrations detected were deletion of 6q (two cases), deletion of chromosome 17 (two cases), gain of 3q (two cases), and gain of chromosome 7 (two cases). This report not only confirms the reported loss of 6q in a proportion of cases but also highlights the genetic heterogeneity of LPL, in accordance with the known immunophenotypical, morphological, and clinical diversity of the disease.

Mature B-cell malignancies stem from B cells transformed at various developmental stages, accounting for the wide range of heterogeneous features observed in the different disease entities. Analysis of the immunoglobulin (Ig) genes can facilitate the identification of the normal B-cell counterpart of lymphomas and leukemias, as Ig genes acquire somatic hypermutation in germinal centers during the immune response to antigen. Therefore, lymphomas that derive from a naïve, pregerminal center B cell lack somatic hypermutation in the clonal Ig gene, whereas germinal center-derived lymphomas, such as diffuse large B-cell lymphoma and follicular lymphoma, display somatic hypermutation of their Ig genes. Furthermore, biases in the Ig variable heavy chain gene repertoire in B-cell malignancies can indicate a possible antigenic influence in pathogenesis. Much work has been accomplished in the past decade to characterize the Ig genes in different lymphoma entities, and the separation of chronic lymphocytic leukemia into two prognostic subgroups in the late 1990s based on the presence or absence of somatic hypermutation led to investigations of Ig genes in larger cohorts of previously uncharacterized entities, such as mantle cell lymphoma. This review will briefly discuss relevant aspects of normal B-cell development, and then focus on what can be ascertained from Ig studies of newly characterized entities, mantle cell lymphoma, hairy cell leukemia, lymphoplasmacytic lymphoma/ Waldenström's macroglobulinemia, and splenic marginal zone lymphoma, from the point of view of cellular origin and variable heavy chain gene restrictions as a sign of antigen involvement. Correlations with gene expression profiling data and the clinical implications of Ig gene studies, when relevant, will be mentioned. The recent evidence that an alternative pathway of gaining somatic hypermutation might exist is also considered, and the implications this has for understanding the cellular origin of B-cell malignancies.

B cell lymphomas and leukemias are heterogeneous tumors with different cellular origins. Analysis of immunoglobulin (Ig) genes enables insight into the B cell progenitor, as Ig somatic hypermutation correlates with antigen-related B cell transit through the germinal center (GC). Also, restricted Ig variable heavy chain (VH) gene repertoires in B cell malignancies could imply antigen selection during tumorigenesis. The length of telomeres has been shown to differ between GC B cells and pre/post-GC B cells, possibly representing an alternative angle to investigate B cell tumor origin.Mantle cell lymphoma (MCL), previously postulated to derive from a naive, pre-GC B cell, was shown to have an Ig-mutated subset (18/110 MCLs, 16%), suggestive of divergent cellular origin and GC exposure. Another subset of MCL (16/110, 15%), characterized by VH3-21/Vλ3-19 gene usage, alludes to a role for antigen(s) in pathogenesis, also possible for hairy cell leukemia (HCL) in which the VH3-30 gene (6/32, 19%) was overused. HCL consisted mainly of Ig-mutated cases (27/32, 84%) with low level intraclonal heterogeneity, contrasting with the proposed post-GC origin, for both Ig-mutated and Ig-unmutated HCLs. For MCL and HCL, derivation from naive or memory marginal zone B cells which may acquire mutations without GC transit are tempting speculations, but currently little is known about this alternative immunological pathway. Heavily mutated Ig genes without intraclonal heterogeneity were demonstrated in lymphoplasmacytic lymphoma/Waldenstrom’s macroglobulinemia (13/14, 93%), confirming that the precursor cell was transformed after GC affinity maturation. Telomere length analysis within 304 B cell tumors revealed variable lengths; shortest in the Ig-unmutated subset of chronic lymphocytic leukemia, longest in the GC-like subtype of diffuse large B cell lymphoma, and homogeneous in MCL regardless of Ig mutation status. However, telomere length is complex with regard to GC-related origin.In summary, this thesis has provided grounds for speculation that antigens play a role in MCL and HCL pathogenesis, although the potential antigens involved are currently unknown. It has also enabled a more informed postulation about the cellular origin of B cell tumors, which will ultimately enhance understanding of the biological background of the diseases.

Mantle cell lymphoma (MCL) is characterized by over-expression of cyclin Dl as a result of the characteristic t(11;14)(q13;q32). However, this translocation alone has proven not to be sufficient for lymphomagenesis, suggesting the involvement of additional alterations. We have characterized 35 cases of MCL by array comparative genomic hybridization with an average resolution of 0.97 Mb distributed over the complete human genome. The most common alterations were losses in 1p13.2–p31.1, 6q16.2–q27, 8p21.3, 9p13.2–p24.3, 9q13–q31.3, 11q14.3–q23.3, 13q14.13–q21.31, 13q33.1–q34, and 22q11.23–q13.33 and gains involving 3q21.2–q29, 7p12.1–p22.3, 8q24.13–q24.23, and 18q21.33–q22.3. Four homozygous deletions were identified in totally three patients; two overlapping at 1p32.3, and two adjacent at 13q32.3. The homozygous deletions at 1p32.3 cover the CDKN2C locus (coding for p18), while the region at 13q32.3 does not encompass any known tumor suppressor genes. A gain in 3q was significantly associated with shorter survival ( P = 0.047).

Lymphoplasmacytic lymphoma (LPL) is a rare lymphoma thought to originate from a B cell stimulated to differentiate to a plasma cell, and which is usually accompanied by clonal IgM secretion, defining the diagnosis of Waldenstrom's macroglobulinemia (WM). However, the immunoglobulin variable heavy chain (VH) gene usage and the somatic hypermutation status have not been widely investigated in LPL. LPL biopsies (CD19+/CD20+/CD22+/CD5-/CD10-/CD23-/kappa+) from 14 patients were included most of whom had a serum IgM component of variable magnitude (two cases with IgG). Highly mutated VH genes (mean mutation rate 8%) were revealed in 13 of 14 LPLs, whereas one case displayed a germline VH gene configuration. Cloning of the VH gene rearrangements in nine cases showed homogeneous sequences without intraclonal heterogeneity. Furthermore, no bias in the VH gene usage was shown, with VH3, VH4, and VH1 gene family members represented. These data confirm that the LPL precursor cell has been exposed to the germinal centre environment, as indicated by extensive hypermutation, but also that the transformation event occurred after affinity maturation, since there was a lack of intraclonal variation. Additionally, the VH gene repertoire was not skewed in LPL/WM as has been demonstrated in other B cell malignancies.

A preferential use of one particular immunoglobulin variable heavy chain gene, V(H)3-21, has recently been reported in mantle cell lymphoma, where almost all of these V(H)3-21+ mantle cell lymphomas showed usage of the same light chain Vlambda gene (Vlambda3-19) and also had a tendency towards improved prognosis. These findings suggested that V(H)3-21+ mantle cell lymphomas constitute a distinct subgroup, possibly with antigen stimulation involved in disease pathogenesis. In this study, we applied the comparative genomic hybridization (CGH) method on 37 mantle cell lymphoma tumors in order to investigate if the V(H)3-21+ tumors are different at the genomic level. Interestingly, V(H)3-21+ mantle cell lymphomas (n=14) showed significantly fewer genomic aberrations (mean 2.4) compared to non-V(H)3-21 mantle cell lymphomas (n=23) (mean 4.9). The chromosomal aberrations identified in our study were generally in accordance with previous CGH studies of mantle cell lymphoma; the most frequent aberration was complete or partial loss of chromosome 13, followed by recurrent losses within 6q, 9p, 9q and 11q and frequent gains in 3q, 7p, 8q and 15q. Deletions within 8p and 9p as well as gains in 7p and 15q were found exclusively in the non-V(H)3-21-utilizing tumors. In summary, V(H)3-21+ mantle cell lymphomas demonstrated both a lower number and a different spectrum of genomic aberrations than mantle cell lymphoma in general, thus supporting the hypothesis that V(H)3-21+ mantle cell lymphomas constitute a new subgroup. The findings presented in this report may explain the tendency for a better clinical outcome for patients whose tumors utilize V(H)3-21.

Hairy cell leukemia (HCL) is thought to arise from a post-germinal center (GC) B-cell, however the exact normal counterpart remains unclear. We performed VH gene analysis of 32 HCL cases, revealing somatically mutated VH genes (

Mantle cell lymphoma (MCL) is believed to originate from a naive B cell. However, we recently demonstrated that a subset of MCL displayed mutated V-H genes. We also reported restricted use of certain V-H genes. To assess the prognostic impact of these new findings, we performed V-H gene analysis of 110 patients, revealing that 18 (16%) patients had mutated and 92 (84%) patients had unmutated V-H genes. Because the mutation rate was low in the mutated group (2.2%-6.7%), further investigation of the germline V-H gene in T cells from 5 patients with mutated V-H genes was carried out; results showed that the unrearranged V-H gene was identical to the published sequence. These data confirm that the base pair substitutions within the rearranged V-H genes represent hyper-mutations, and indicate germinal center exposure. However, V-H gene mutation status did not correlate with prognosis because there was no difference in clinical outcome between the unmutated and mutated groups. The most frequently used V-H genes were V(H)3-21 (21 patients) and V(H)4-34 (19 patients). A novel finding was that V(H)3-21(+) MCL almost exclusively ex-pressed X light chains and displayed highly restricted use of the V(lambda)3-19 gene. V(H)3-21(+) patients had longer median survival than the remaining patients (53 vs 34 months; P = .03), but they tended to be younger at diagnosis. The combined use Of V(H)3-21/V(lambda)3-19 suggests a possible role for antigen(s) in the pathogenesis of these tumors and indicates that V(H)3-21(+) patients constitute a new MCL entity. (C) 2003 by The American Society of Hematology.