Molecular deregulation of signaling in lymphoid tumors

Clinical Utility of Targeted Next-Generation Sequencing in the Evaluation of Low-Grade Lymphoproliferative Disorders

OBJECTIVES

We investigated the usefulness of a custom-designed 31-gene next-generation sequencing (NGS) panel implemented on a routine basis for the evaluation of low-grade lymphoproliferative disorders (LPDs).

METHODS

In total, 147 blood, bone marrow, and tissue specimens were sequenced, including 81% B-cell, 15% T-cell, and 3% natural killer (NK)-cell neoplasms.

RESULTS

Of the cases, 92 (63%) of 147 displayed at least one pathogenic variant while 41 (28%) of 147 had two or more. Low mutation rates were noted in monoclonal B-cell lymphocytoses and samples with small T- and NK-cell clones of uncertain significance. Pathogenic molecular variants were described in specific disorders and classified according to their diagnostic, prognostic, and potential therapeutic value. Diagnostically, in addition to confirming the diagnosis of 15 of 15 lymphoplasmacytic lymphomas, 10 of 12 T large granular lymphocytic leukemias, and 2 of 2 hairy cell leukemias (HCLs), the panel helped resolve the diagnosis of 10 (62.5%) of 16 challenging cases lacking a specified diagnosis based on standard morphology, phenotype, and genetic analysis.

CONCLUSIONS

Overall, implementation of this targeted lymphoid NGS panel as part of regular hematopathology practice was found to be a beneficial adjunct in the evaluation of low-grade LPDs.

Coactivation of NF-κB and Notch signaling is sufficient to induce B-cell transformation and enables B-myeloid conversion

NF-κB and Notch signaling can be simultaneously activated in a variety of B-cell lymphomas. Patients with B-cell lymphoma occasionally develop clonally related myeloid tumors with poor prognosis. Whether concurrent activation of both pathways is sufficient to induce B-cell transformation and whether the signaling initiates B-myeloid conversion in a pathological context are largely unknown. Here, we provide genetic evidence that concurrent activation of NF-κB and Notch signaling in committed B cells is sufficient to induce B-cell lymphomatous transformation and primes common progenitor cells to convert to myeloid lineage through dedifferentiation, not transdifferentiation. Intriguingly, the converted myeloid cells can further transform, albeit at low frequency, into myeloid leukemia. Mechanistically, coactivation of NF-κB and Notch signaling endows committed B cells with the ability to self renew. Downregulation of BACH2, a lymphoma and myeloid gene suppressor, but not upregulation of CEBPα and/or downregulation of B-cell transcription factors, is an early event in both B-cell transformation and myeloid conversion. Interestingly, a DNA hypomethylating drug not only effectively eliminated the converted myeloid leukemia cells, but also restored the expression of green fluorescent protein, which had been lost in converted myeloid leukemia cells. Collectively, our results suggest that targeting NF-κB and Notch signaling will not only improve lymphoma treatment, but also prevent the lymphoma-to-myeloid tumor conversion. Importantly, DNA hypomethylating drugs might efficiently treat these converted myeloid neoplasms.

Lymphomagenic properties of a HIV p17 variant derived from a splenic marginal zone lymphoma occurred in a HIV-infected patient

Despite antiretroviral therapy, HIV+ individuals still have increased risk to develop lymphomas, including marginal zone lymphomas, suggesting that factors other than HIV-related immunosuppression are probably acting as lymphomagenic factors in the HIV setting. The possible pathogenic involvement of HIV p17 protein variants was investigated in a particularly informative case of HIV-related splenic marginal zone lymphoma, which was negative for oncogenic virus infections, thus allowing us to assess the possible direct contribution of these HIV-encoded proteins to lymphomagenesis. The presence of p17 protein was analyzed by immunohistochemistry in lymphoma tissue. Recombinant p17 protein derived from the dominant sequence detected in plasma and lymphoma biopsy was characterized for B-cell proliferation, clonogenicity in soft agar, in vitro tube formation and wound healing. Intracellular signaling was investigated by immunoblotting. HIV p17 protein was detected in reactive lymphoid follicles but not within lymphoma cells. An identical dominant variant p17 sequence, p17-Lyrm, carrying a 117 to 118 Ala-Ala insertion was detected in both plasma and lymphoma tissue. Recombinant p17-Lyrm enhanced B-cell proliferation and clonogenicity promoted the formation of capillary-like structures and enhanced endothelial cell migration. Unlike reference p17, the p17-Lyrm variant enhanced the activation of Akt and ERK, critical kinases in lymphomagenesis. p17-Lyrm clonogenic activity was dependent on the activation of Akt but not of ERK1/2. These results indicated that HIV p17 variants with distinct molecular signatures and functional properties may accumulate in lymphoid tissues of HIV-infected individuals where they may act as a local stimulus promoting the development of lymphomas.

Expression of T-cell receptor signalling pathway components in extranodal NK/T-cell lymphoma

AIMS

Although the neoplastic cells of extranodal natural killer (NK)/T-cell lymphoma (ENKTL) usually do not express T-cell antigens, the T-cell receptor (TCR) gene might be rearranged and TCR protein expressed. The aim is to elucidate the expression of the downstream TCR pathway components and their importance in ENKTL.

METHODS AND RESULTS

We used formalin-fixed paraffin-embedded tissues from 91 ENKTL samples to immunohistochemically characterise the expression of TCR pathway components. The following proteins were variably expressed: ZAP70 (94%; 83/88), GRAP2/GADS (68%; 60/88), DOK2 (42%; 38/90), LCK (35%; 31/88), and ITK (10%; 9/90). When these tumours were classified as being of T lineage (16%), NK lineage (45%), or indeterminate lineage (38%), the GRAP2/GADS expression rate was higher in T lineage tumours (versus NK, P = 0.0073; versus indeterminate, P = 0.00082). GRAP2/GADS-positive NK lineage tumours more frequently expressed DOK2 (P = 0.0073), and were more often confined to the nasal areas (P = 0.014). Furthermore, when these tumours were immunophenotypically classified into a T signature (42%) or NK signature (58%), the expression rates of GRAP2/GADS and ITK were higher in T signature tumours (P = 0.00074 and P = 0.067, respectively), whereas that of LCK was higher in NK-signature tumours (P = 0.10).

CONCLUSIONS

Although some ENTKL cases were polyclonal for TCR rearrangement and others lacked TCR expression, we speculate that the TCR pathway might be functioning in ENKTLs. A T signature versus a NK signature might be better for delineating the physiology of ENKTL than cellular lineage. Furthermore, ITK may represent a potential therapeutic target for patients with ITK-expressing tumours.

Expression patterns of the activator protein-1 (AP-1) family members in lymphoid neoplasms

The activator protein-1 (AP-1) is a dimeric transcription factor composed of proteins belonging to the Jun (c-Jun, JunB and JunD), Fos (c-Fos, FosB, Fra1 and Fra2) and activating transcription factor protein families. AP-1 is involved in various cellular events including differentiation, proliferation, survival and apoptosis. Deregulated expression of AP-1 transcription factors is implicated in the pathogenesis of various lymphomas such as classical Hodgkin lymphomas, anaplastic large cell lymphomas, diffuse large B cell lymphomas and adult T cell leukemia/lymphoma. The main purpose of this review is the analysis of the expression patterns of AP-1 transcription factors in order to gain insight into the histophysiology of lymphoid tissues and the pathology of lymphoid malignancies.

High prevalence of splenic marginal zone lymphoma among patients with acquired C1 inhibitor deficiency

Marginal zone lymphoma represents about 10% of all non-Hodgkin lymphomas (NHLs). 33% of patients with acquired angioedema (AAE) due to acquired C1-inhibitor (C1-INH) deficiency (C1-INH-AAE) have or will develop NHLs. C1-INH-AAE is a rare condition. We report the follow-up of 72 C1-INH-AAE patients, followed for a median of 15 years (range 1-24). Median age was 71 (range 64-79) years; median age at onset of angioedema symptoms was 57·5 (range 50-66) years and it was 63 [range 45-80) years at diagnosis]. Twenty patients were diagnosed with low-grade non-follicular B-cell lymphomas (75% were splenic MZL), one with follicular and three with high-grade lymphomas (two diffuse large B-cell lymphomas and one mantle cell lymphoma). Fifteen NHLs were diagnosed at onset of AAE or thereafter (3 months to 7 years), eight had already been diagnosed at onset of angioedema. Two of 24 patients remain on watchful wait. Thirthen of 24 received chemotherapy, two received rituximab. Three underwent splenectomy. All 18 patients receiving therapy for NHL experienced post-treatment reduction in AAE symptoms. Our study suggests that clonal B-cell proliferation is the pathology underlying AAE leading to production of C1-INH-neutralizing autoantibodies and to NHLs. The post-germinal centre origin of NHL suggests that immune stimulation may contribute to lymphomagenesis.