Preferential IgH V4-34 gene segment usage in particular subtypes of B-cell lymphoma detected by antibody 9G4

Primary vitreoretinal lymphomas display a remarkably restricted immunoglobulin gene repertoire

Primary vitreoretinal lymphoma (PVRL) is a high-grade lymphoma affecting the vitreous and/or the retina. The vast majority of cases are histopathologically classified as diffuse large B-cell lymphoma (DLBCL) and considered a subtype of primary central nervous system lymphoma (PCNSL). To obtain more insight into the ontogenetic relationship between PVRL and PCNSL, we adopted an immunogenetic perspective and explored the respective immunoglobulin gene repertoire profiles from 55 PVRL cases and 48 PCNSL cases. In addition, considering that both entities are predominantly related to activated B-cell (ABC) DLBCL, we compared their repertoire with that of publicly available 262 immunoglobulin heavy variable domain gene rearrangement sequences from systemic ABC-type DLBCLs. PVRL displayed a strikingly biased repertoire, with the IGHV4-34 gene being used in 63.6% of cases, which was significantly higher than in PCNSL (34.7%) or in DLBCL (30.2%). Further repertoire bias was evident by (1) restricted associations of IGHV4-34 expressing heavy chains, with κ light chains utilizing the IGKV3-20/IGKJ1 gene pair, including 5 cases with quasi-identical sequences, and (2) the presence of a subset of stereotyped IGHV3-7 rearrangements. All PVRL IGHV sequences were highly mutated, with evidence of antigen selection and ongoing mutations. Finally, half of PVRL and PCNSL cases carried the MYD88 L265P mutation, which was present in all 4 PVRL cases with stereotyped IGHV3-7 rearrangements. In conclusion, the massive bias in the immunoglobulin gene repertoire of PVRL delineates it from PCNSL and points to antigen selection as a major driving force in their development.

Primary cystic lung light chain deposition disease: a clinicopathologic entity derived from unmutated B cells with a stereotyped IGHV4-34/IGKV1 receptor

We have recently described a new form of light chain deposition disease (LCDD) presenting as a severe cystic lung disorder requiring lung transplantation. There was no bone marrow plasma cell proliferation. Because of the absence of disease recurrence after bilateral lung transplantation and of serum-free light chain ratio normalization after the procedure, we hypothesized that monoclonal light chain synthesis occurred within the lung. The aim of this study was to look for the monoclonal B-cell component in 3 patients with cystic lung LCDD. Histologic examination of the explanted lungs showed diffuse nonamyloid kappa light chain deposits associated with a mild lymphoid infiltrate composed of aggregates of small CD20(+), CD5(-), CD10(-) B lymphocytes reminiscent of bronchus-associated lymphoid tissue. Using polymerase chain reaction (PCR), we identified a dominant B-cell clone in the lung in the 3 studied patients. The clonal expansion of each patient shared an unmutated antigen receptor variable region sequence characterized by the use of IGHV4-34 and IGKV1 subgroups with heavy and light chain CDR3 sequences of more than 80% amino acid identity, a feature evocative of an antigen-driven process. Combined with clinical and biologic data, our results strongly argue for a new antigen-driven primary pulmonary lymphoproliferative disorder.

Over 20% of patients with chronic lymphocytic leukemia carry stereotyped receptors: Pathogenetic implications and clinical correlations

The chronic lymphocytic leukemia (CLL) immunoglobulin repertoire is biased and characterized by the existence of subsets of cases with closely homologous ("stereotyped") complementarity-determining region 3 (CDR3) sequences. In the present series, 201 (21.9%) of 916 patients with CLL expressed IGHV genes that belonged to 1 of 48 different subsets of sequences with stereotyped heavy chain (H) CDR3. Twenty-six subsets comprised 3 or more sequences and were considered "confirmed." The remaining subsets comprised pairs of sequences and were considered "potential"; public database CLL sequences were found to be members of 9 of 22 "potential" subsets, thereby allowing us to consider them also "confirmed." The chance of belonging to a subset exceeded 35% for unmutated or selected IGHV genes (eg, IGHV1-69/3-21/4-39). Comparison to non-CLL public database sequences showed that HCDR3 restriction is "CLL-related." CLL cases with selected stereotyped immunoglobulins (IGs) were also found to share unique biologic and clinical features. In particular, cases expressing stereotyped IGHV4-39/IGKV1-39-1D-39 and IGHV4-34/IGKV2-30 were always IgG-switched. In addition, IGHV4-34/IGKV2-30 patients were younger and followed a strikingly indolent disease, contrasting other patients (eg, those expressing IGHV3-21/IGLV3-21) who experienced an aggressive disease, regardless of IGHV mutations. These findings suggest that a particular antigen-binding site can be critical in determining the clinical features and outcome for at least some CLL patients.

Somatic hypermutation and V(H) gene usage in mantle cell lymphoma

Mantle cell lymphoma (MCL) is considered to derive from naïve, pregerminal center (GC) CD5+ B-cells. However, the cell of origin has been questioned in recent studies that showed somatic hypermutations in the immunoglobulin (Ig) variable heavy chain (V(H)) genes in subsets of MCL. To clarify this issue, we analyzed the IgV(H) genes for the presence of somatic hypermutations in 51 MCL cases. Twenty percent of the MCL cases displayed somatically mutated V(H) genes (defined as >2% mutated), whereas 80% showed unmutated V(H) genes. This finding suggests that MCL is a genetically heterogeneous disease, with the majority of cases originating from unmutated pre-GC B-cells and a subset deriving from more mature B-cells which have been exposed to the GC environment and have undergone somatic hypermutation. A biased V(H) gene usage has been demonstrated in several B-cell malignancies; however, this has not yet been investigated in MCL, although V(H)4-34 overusage has been indicated by small studies. Interestingly, we found a restricted usage of three individual V(H) genes in our MCL material; V(H)4-34 (22%), V(H)3-21 (16%) and V(H)5-51 (12%). This novel finding of preferential V(H) gene usage in half of the MCL cases may suggest an antigen driven process occurring in B-cells expressing specific VH genes, thus implicating that Ig specificity could be involved in mantle cell lymphoma development.

Isotype-switched immunoglobulin genes with a high load of somatic hypermutation and lack of ongoing mutational activity are prevalent in mediastinal B-cell lymphoma

Primary mediastinal B-cell lymphoma (PMBL) is a subentity of diffuse large B-cell lymphoma with characteristic clinical, histomorphologic, immunophenotypical, and genetic features. Unlike other B-cell lymphomas, PMBL has not yet been the subject of comprehensive molecular studies on the rearranged immunoglobulin (Ig) gene. Such investigations have proved essential to obtaining information about the differentiation stage of the lymphomagenic B cell. In the present study, the clonally rearranged immunoglobulin heavy-chain gene of 13 PMBL cases is analyzed by polymerase chain reaction (PCR) in conjunction with cloning and DNA sequencing. Twelve of 13 rearrangements were potentially functional. All clonally rearranged immunoglobulin genes bore a high load of somatic mutations (average, 13.0%), which appeared to be selected for a functional antibody in the majority of cases. The comparison of cloned PCR products revealed no evidence of ongoing mutation of the immunoglobulin variable gene. By means of reverse-transcriptase PCR, lymphoma-specific immunoglobulin transcripts were detected in 8 of 13 cases, all of which were of the postswitched type, whereas immunoglobulin protein expression was undetectable except for 1 case. A PMBL cell line, MedB-1, generated from an IgG(-) parental tumor, constitutively expressed IgG protein in a subset of cells, which was moderately suppressed by interleukin-4 and up-regulated in the presence of dexamethasone. PMBL is thus characterized by a heavily mutated, class-switched immunoglobulin gene without evidence of ongoing mutational activity. Moreover, our data indirectly suggest that regulation by extrinsic signals contributes to the immunoglobulin-negative phenotype of PMBL.

Clinical relevance of immunoglobulin mutation analysis

The precise diagnosis of malignant B-cell lymphoproliferations is essential for their appropriate clinical management. Histologic and immunophenotypical features alone are often insufficient in discriminating between various lymphoma entities and subtypes. The analysis of clonally rearranged immunoglobulin chain genes of the tumor cells was therefore suggested as an additional parameter. This article reviews current knowledge and describes which conclusions can be drawn for lymphoma diagnosis based on the type of immunoglobulin chain gene rearrangement, as well as on the number and distribution of somatic immunoglobulin mutations. Although there are striking correlations between the clinical outcome and the immunoglobulin mutations in some entities, many additional studies are required in order to draw final conclusions for most types of lymphoma.

Molecular analysis of immunoglobulin genes in diffuse large B-cell lymphomas

Diffuse large B-cell lymphoma (DLBCL) is a common type of non-Hodgkin's lymphoma (NHL) that is highly heterogeneous from both clinical and histopathologic viewpoints. The immunoglobulin (Ig) heavy (H) chain variable region genes were examined in 71 patients with untreated primary DLBCL. Fifty-eight potentially functional VH genes were detected in 53 DLBCL cases; VHgenes were nonfunctional in 9 cases and were not detected in an additional 9 cases. The use of VH gene families by DLBCL tumors was unbiased without overrepresentation of any particular VH gene or gene family. Analysis of Ig mutations in comparison to the most closely related germline gene disclosed mutated VH genes in all but 1 DLBCL case. More than 2% difference from the most similar germline sequence was detected in 52 potentially functional and the 8 nonfunctional VH gene sequences, whereas less than 2% difference from the germline sequence was observed in 3 VH gene isolates. Only 3 VH gene isolates were unmutated. No correlation was found between VH gene use, mutation level, and International Prognostic Index (IPI) or survival. Six of 8 tested tumors showed evidence of ongoing somatic mutations. Evidence for positive or negative antigen selection pressure was observed in 65% of mutated DLBCL cases. Our findings indicate that the etiology and the driving forces for clonal expansion are heterogeneous, which may explain the well-known clinical and pathologic heterogeneity of DLBCL.

Primary central nervous system lymphomas are derived from germinal-center B cells and show a preferential usage of the V4-34 gene segment

Primary central nervous system lymphomas (PCNSLs) have recently received considerable clinical attention due to their increasing incidence. To clarify the histogenetic origin of these intriguing neoplasms, PCNSLs from 10 HIV-negative patients were analyzed for immunoglobulin (Ig) gene rearrangements. All tumors exhibited clonal IgH gene rearrangements. Of the 10 cases, 5 used the V4-34 gene segment, and all of these lymphomas shared an amino acid exchange from glycine to aspartate due to a mutation in the first codon of the complementarity-determining region 1. No preferential usage of D(H), J(H), V(kappa), J(kappa), V(lambda), or J(lambda) gene segments was observed. All potentially functional rearrangements exhibited somatic mutations. The pattern of somatic mutations indicated selection of the tumor cells (or their precursors) for expression of a functional antibody. Mean mutation frequencies of 13. 2% and 8.3% were detected for the heavy and light chains, respectively, thereby exceeding other lymphoma entities. Cloning experiments of three tumors showed ongoing mutation in at least one case. These data suggest that PCNSLs are derived from highly mutated germinal-center B cells. The frequent usage of the V4-34 gene and the presence of a shared replacement mutation may indicate that the tumor precursors recognized a shared (super) antigen.

VH Gene Sequences From Primary Central Nervous System Lymphomas Indicate Derivation From Highly Mutated Germinal Center B Cells With Ongoing Mutational Activity

Primary central nervous system lymphoma (PCNSL) represents 1% to 3% intracranial tumors. Most PCNSL are located in the brain, and 75% are large B-cell lymphomas. The largest subgroup of these tumors contains cells that resemble centroblasts and has been labelled diffuse centroblastic (polymorphous) lymphoma. To investigate the cell of origin and the clonal history of these tumors, we have analyzed VH gene of 5 cases of PCNSL, all confirmed by histological studies to be Epstein-Barr virus (EBV)-negative, high-grade diffuse B-cell lymphomas. The V4-34 gene of the VH4 family was used in 4 of 5 cases. All VHgenes were found to have accumulated very high levels of somatic mutation (14% to 25%). In 3 of 5 cases, intraclonal nucleotide heterogeneity, including codon deletion in some clones in 1 case, was observed, indicating that the VH genes were still under the influence of the somatic hypermutation mechanism. Analysis of the distribution of silent and replacement mutations showed evidence for preservation of immunoglobulin structure in all cases. These results suggest that, although there is no evidence for germinal center formation in the brain tissue, PCNSL is derived from a B cell with features associated with location in a germinal center environment.

VH Gene Sequences From Primary Central Nervous System Lymphomas Indicate Derivation From Highly Mutated Germinal Center B Cells With Ongoing Mutational Activity

Primary central nervous system lymphoma (PCNSL) represents 1% to 3% intracranial tumors. Most PCNSL are located in the brain, and 75% are large B-cell lymphomas. The largest subgroup of these tumors contains cells that resemble centroblasts and has been labelled diffuse centroblastic (polymorphous) lymphoma. To investigate the cell of origin and the clonal history of these tumors, we have analyzed VH gene of 5 cases of PCNSL, all confirmed by histological studies to be Epstein-Barr virus (EBV)-negative, high-grade diffuse B-cell lymphomas. The V4-34 gene of the VH4 family was used in 4 of 5 cases. All VHgenes were found to have accumulated very high levels of somatic mutation (14% to 25%). In 3 of 5 cases, intraclonal nucleotide heterogeneity, including codon deletion in some clones in 1 case, was observed, indicating that the VH genes were still under the influence of the somatic hypermutation mechanism. Analysis of the distribution of silent and replacement mutations showed evidence for preservation of immunoglobulin structure in all cases. These results suggest that, although there is no evidence for germinal center formation in the brain tissue, PCNSL is derived from a B cell with features associated with location in a germinal center environment.