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

Development of Central Nervous System Vasculitis in a Patient with Waldenstrom Macroglobulinemia: A Rare Presentation with Poor Prognosis

Waldenstrom macroglobulinemia (WM) is a rare lymphoproliferative disorder characterized by the presence of monoclonal immunoglobulin M in serum. WM may present with neurologic complications involving the peripheral and central nervous systems (CNS) though CNS complications associated with WM are rare. We present a case of a 72-year-old male with an 18-month history of WM who experienced neurologic and constitutional symptoms indicative of WM progression over a three-week period while on rituximab maintenance therapy. The patient’s symptoms were initially attributed to rituximab-induced asthenia though his clinical condition did not improve with rituximab discontinuation. Due to progressively worsening neurologic symptoms, the patient was re-evaluated and found to have multiple cerebral infarcts and increased serum cryoglobulin levels indicative of cryoglobulinema. The patient was promptly initiated on a combination regimen of high dose steroids, intravenous immunoglobulin (IVIG), and plasmapheresis but had a poor response. Brain biopsy revealed necrotizing vasculitis with dense intra- and peri-vascular CD3 positive T-cell infiltrates with mural necrosis. This is a unique case of WM complicated by type 1 cryoglobulinemia associated with CNS vasculitis that was unresponsive to active rituximab therapy; this case illustrates a poor prognosis of patients with CNS involvement in WM.

Lymphoplasmacytic lymphoma and other non-marginal zone lymphomas with plasmacytic differentiation

Small B-cell lymphomas with plasmacytic differentiation frequently present diagnostic challenges. Session 3 of the 2009 Society for Hematopathology/European Association for Haematopathology Workshop focused on lymphoplasmacytic lymphoma (LPL). The submitted cases illustrated classic examples of bone marrow-based and nodal LPL and cases with atypical features, including unusual phenotypes or involvement of extranodal sites. Several cases showed varying degrees of overlap with marginal zone lymphoma, and, as acknowledged in the 2008 World Health Organization classification, a definitive distinction between these 2 possibilities cannot always be established. Session 6 of the workshop focused on other non-marginal zone lymphomas that may display plasmacytic differentiation. This session highlights the wide variety of neoplasms that enter into the differential diagnosis of small B-cell lymphomas with plasmacytic differentiation and demonstrates the use of clinical features and ancillary studies in establishing an appropriate diagnosis by 2008 World Health Organization criteria.

Chronic lymphocytic leukemia in a Japanese population: varied immunophenotypic profile, distinctive usage of frequently mutated IGH gene, and indolent clinical behavior

Chronic lymphocytic leukemia (CLL) is relatively rare in Japan. Among 46 cases of mature B-cell leukemia, we identified 28 Japanese patients with CLL, including prolymphocytoid and lymphoplasmacytoid morphological variants. Compared with Western patients with CLL, only 52.0% of cases showed the typical immunophenotypic profile. IgG-bearing (15.4%) and clearly CD20-expressing (71.4%) cases were frequently observed. Most cases harbored a mutated immunoglobulin heavy-chain (VH) gene (88.5%) and commonly used a VH3 family member (61.5%) other than VH3-21. During the median follow-up period of 64 months, 20 cases (71.4%) showed an indolent clinical course without any treatment, and six cases (21.4%) were accompanied by other malignancies. Binet A stage (p = 0.003), low-risk category according to the modified Rai classification (p = 0.016), and ≤ 15 U/mL level of serum thymidine kinase activity (p = 0.016) were associated with prolongation of treatment-free status. Although Japanese cases of CLL showed heterogeneity in morphology and immunophenotype, most cases arose from post-antigen-selected B cells and presented with indolent clinical behavior.

IgG-Secreting B-Cell Lymphoplasmocytoid Leukaemia : Molecular Characterization of Igh Rearrangements

Purpose : Elevated serum M component of IgG isotype is typically associated with multiple myeloma (MM). However, our group has previously reported cases with an elevated serum monoclonal IgG and a leukaemic B-cell lymphoplasmocytoid lymphoma (LPL) similar to Waldenstrom’s macroglobulinaemia (WM). The aim of this study was to extend analysis of IgH locus events in a larger series of IgG-secreting LPL.

Patients and Methods : We investigated 20 patients with an elevated serum monoclonal IgG (>20g/l) and LPL (IgG-LPL). Morphological classification and immunophenotyping analysis were performed at diagnosis (serum IgG>4 g/l, CD19+ cells >30%, presence of lymphoplasmocytoid cells in blood and/or bone marrow). Histological classification and FISH analysis were performed when possible to further characterize those cases. Analysis of VH genes was carried out from RNA with VHLeader and CH primers. 14 patients were examined for both IgG and IgM transcripts; VH-Cμ and VH-Cg transcripts could be compared in 9 patients.

Results : Of 25 Ig VH rearrangement sequences, 23 were functional and expressed in each case. VH3 family members appeared to be over-represented (19/21 patients (90.5%) as compared to 40/71 (56.3%) in normal B-cell repertoire (1). VH3-23 was the most frequently used segment (10/21 patients) and is frequently utilized in normal B-cells. IgG-LPL JH family use resembled the normal B-cell repertoire (predominance of JH4 and JH6 segments). The median CDR3 length was 10 amino acids [5–19]. However, and in contrast with features seen in other leukaemia, there was no evidence of homologous CDR3 motifs. All VH genes revealed highly somatically mutated sequences, with a median mutation rate 8.8% [0.7 – 11.1%] (IMGT database(2)). We compared pre (VH-Cμ) and post-switch (VH-Cg) transcripts, and 4/9 patients had identical clonally-derived sequences, and two 2/9 had divergent sequences.

Interpretation and conclusion : This intended study of IgG-LPL reveals consistent features that argue for common origins of IgG-LPL with Waldenstrom’s macroglobulinemia. One feature is extensive somatic mutations in VH genes, suggesting origins from a cell that may have undergone successive rounds of mutation. Patterns of mutations in pre-and post-switched clonally derived sequences suggest that the final neoplastic event has occurred in a IgM+ memory cell undergoing isotype switch. However, no aberrant chromosomal translocation accrue at the IgH locus, as apparent from FISH data. This indicates that, unlike in typical MM, switch activity does not generate 14q32 abnormalities nor that such lesions play a role in the pathogenesis of LPL. Extensive mutations are also seen in VH genes in WM, and there is evidence that WM cells can undergo class switch events in vivo. In this tumor, switching occurs at a low subclonal level in some cells, which in rare cases can lead to the emergence of a dual population of clonally identical IgM and IgG expressing WM tumor cells at a later stage of disease (7). In typical WM, 14q32 abnormalities are also generally not seen. These data suggest that IgG-LPL and WM could be two variants of the same entity, with IgG-LPL exposed to persistent switch stimuli following transformation.

Functional class switch recombination may occur ‘in vivo’ in Waldenström macroglobulinaemia

Waldenström macroglobulinaemia (WM) malignant cells have been considered incapable of undergoing class switch recombination (CSR). However, we report a WM patient who developed an IgG M-component 4 years after diagnosis. When the second monoclonal component appeared, reverse transcription-polymerase chain reaction showed the presence of pre (Cmu) and postswitch (Cgamma) clonotypic isotypes; sequencing of these isotypes demonstrated that both corresponded to the single clone amplified at diagnosis, including the same complementarity-determining region 3 and somatic mutation pattern. This proves that WM cells can undergo a functional in vivo CSR.

AH Amyloidosis Associated With Lymphoplasmacytic Lymphoma Secreting a Monoclonal γ Heavy Chain Carrying an Unusual Truncated D Segment

To date, the presence of amyloidosis associated with immunoglobulin heavy chain (AH amyloidosis) was reported in only 7 cases. Although AH amyloidosis is caused mainly by plasma cell dyscrasia, as in AL amyloidosis, we report a 61-year-old patient who presented with nephrotic syndrome caused by AH amyloidosis associated with lymphoplasmacytic lymphoma. Biochemical and molecular analyses of the deposited amyloid fibrils and heavy-chain genes of lymphocytes showed that proliferative lymphoma cells produced a gamma heavy chain, not a mu heavy chain, which carried an unusual truncated diversity (D) segment of the variable region. Our results indicate that production of the abnormal heavy chain caused by the partially deleted D segment gene is responsible for gamma heavy-chain-related amyloid fibril formation in this patient.

B cell chronic lymphocytic leukemia: lessons learned from studies of the B cell antigen receptor

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

Translocation t(11;14)(q13;q32) is the hallmark of IgM, IgE, and nonsecretory multiple myeloma variants

In an attempt to address the issue of cytogenetic features of multiple myeloma (MM) variants, we have analyzed a series of 8 IgM, 9 IgD, 2 IgE, and 14 nonsecretory (NS) MM cases using fluorescence in situ hybridization. A very high incidence (83%) of t(11;14)(q13;q32) was detected in the IgM (7 of 8), IgE (2 of 2), and NS (11 of 14) MM cases, but not in the IgD cases (2 of 9). Of note, no t(4;14) was observed in this cohort of patients. This increased incidence of t(11;14) was associated with 2 dominant features in these variants, namely, a "lymphoplasmacytic" presentation mainly in IgM MM and a lower secreting capacity in the others, 2 features previously associated with t(11;14). Of major interest, t(11;14) was never observed in Waldenström macroglobulinemia or in IgG/IgA "lymphoplasmacytic" lymphomas. Thus, for unknown reasons, t(11;14) is the hallmark of IgM, IgE, and NS MM, (but not IgD MM), with a 5-fold increase of its incidence compared to that of IgG and IgA MM.

Chronic lymphocytic leukemia B cells can undergo somatic hypermutation and intraclonal immunoglobulin V(H)DJ(H) gene diversification

Chronic lymphocytic leukemia (CLL) arises from the clonal expansion of a CD5(+) B lymphocyte that is thought not to undergo intraclonal diversification. Using V(H)DJ(H) cDNA single strand conformation polymorphism analyses, we detected intraclonal mobility variants in 11 of 18 CLL cases. cDNA sequence analyses indicated that these variants represented unique point-mutations (1-35/patient). In nine cases, these mutations were unique to individual submembers of the CLL clone, although in two cases they occurred in a large percentage of the clonal submembers and genealogical trees could be identified. The diversification process responsible for these changes led to single nucleotide changes that favored transitions over transversions, but did not target A nucleotides and did not have the replacement/silent nucleotide change characteristics of antigen-selected B cells. Intraclonal diversification did not correlate with the original mutational load of an individual CLL case in that diversification was as frequent in CLL cells with little or no somatic mutations as in those with considerable mutations. Finally, CLL B cells that did not exhibit intraclonal diversification in vivo could be induced to mutate their V(H)DJ(H) genes in vitro after stimulation. These data indicate that a somatic mutation mechanism remains functional in CLL cells and could play a role in the evolution of the clone.

Frequent discordance of the light-chain isotypes expressed by serum monoclonal components and leukaemic B-cells

In B-cell malignancies, it is generally held that the monoclonal components (MC) are produced by the malignant clones. Genetic relatedness implies the concordant expression of light-chain (LC) isotypes in the MC and at the surface of the malignant lymphocytes. We reviewed a series of 91 B-cell leukaemias, immunophenotyped by flow cytometry in our laboratory. A serum MC had been sought in 75 of these patients, and had been found in 23 (31%). Biclonal serum components were detected in three cases. LC concordance could not be assessed in three cases of surface LC-null lymphocytes. Of the 23 MC studied in 20 patients, light-chains were discordant in 39%, mostly due to kappa MC in lambda leukaemias. The origin of LC discordance remains speculative. It could be due to the emergence of subclones with the same primal VDJ gene rearrangement or, alternatively, to the development of new B-cell clones escaping immune surveillance from deregulated T-cells.