Risk of follicular lymphoma associated with BCL2 translocations in peripheral blood

The clinical and molecular taxonomy of t(14;18)-negative follicular lymphomas

Follicular lymphoma (FL) is a neoplasm derived from germinal center B cells, composed of centrocytes and centroblasts, with at least a focal follicular growth pattern. The t(14;18) translocation together with epigenetic deregulation through recurrent genetic alterations are now recognized as the hallmark of FL. Nevertheless, FL is a heterogeneous disease, clinically, morphologically, and biologically. The existence of FL lacking the t(14;18) chromosomal alteration highlights the complex pathogenesis of FL, and indicates that there are alternative pathogenetic mechanisms that can induce a neoplasm with follicular center B-cell phenotype. Based on their clinical presentation, t(14;18)-negative FLs can be divided into 3 broad groups: nodal presentation, extranodal presentation, and those affecting predominantly children and young adults. Recent studies have shed some light into the genetic alterations of t(14;18)-negative FL. Within the group of t(14;18)-negative FL with nodal presentation, cases with STAT6 mutations are increasingly recognized as a distinctive molecular subgroup, often cooccurring with CREBBP and/or TNFRSF14 mutations. FL with BCL6 rearrangement shows clinicopathological similarities to its t(14;18)-positive counterpart. In contrast, t(14;18)-negative FL in extranodal sites is characterized mainly by TNFRSF14 mutations in the absence of chromatin modifying gene mutations. FL in children have a unique molecular landscape when compared with those in adults. Pediatric-type FL (PTFL) is characterized by MAP2K1, TNFRSF14, and/or IRF8 mutations, whereas large B-cell lymphoma with IRF4 rearrangement is now recognized as a distinct entity, different from PTFL. Ultimately, a better understanding of FL biology and heterogeneity should help to understand the clinical differences and help guide patient management and treatment decisions.

Tracing Founder Mutations in Circulating and Tissue-Resident Follicular Lymphoma Precursors

Follicular lymphomas (FL) are characterized by BCL2 translocations, often detectable in blood years before FL diagnosis, but also observed in aging healthy individuals, suggesting additional lesions are required for lymphomagenesis. We directly characterized early cooperating mutations by ultradeep sequencing of prediagnostic blood and tissue specimens from 48 subjects who ultimately developed FL. Strikingly, CREBBP lysine acetyltransferase (KAT) domain mutations were the most commonly observed precursor lesions, and largely distinguished patients developing FL (14/48, 29%) from healthy adults with or without detected BCL2 rearrangements (0/13, P = 0.03 and 0/20, P = 0.007, respectively). CREBBP variants were detectable a median of 5.8 years before FL diagnosis, were clonally selected in FL tumors, and appeared restricted to the committed B-cell lineage. These results suggest that mutations affecting the CREBBP KAT domain are common lesions in FL cancer precursor cells (CPC), with the potential for discriminating subjects at risk of developing FL or monitoring residual disease.

SIGNIFICANCE

Our study provides direct evidence for recurrent genetic aberrations preceding FL diagnosis, revealing the combination of BCL2 translocation with CREBBP KAT domain mutations as characteristic committed lesions of FL CPCs. Such prediagnostic mutations are detectable years before clinical diagnosis and may help discriminate individuals at risk for lymphoma development. This article is highlighted in the In This Issue feature, p. 1275.

Lymphoid clonal hematopoiesis: implications for malignancy, immunity, and treatment

Clonal hematopoiesis (CH) is the age-related expansion of hematopoietic stem cell clones caused by the acquisition of somatic point mutations or mosaic chromosomal alterations (mCAs). Clonal hematopoiesis caused by somatic mutations has primarily been associated with increased risk of myeloid malignancies, while mCAs have been associated with increased risk of lymphoid malignancies. A recent study by Niroula et al. challenged this paradigm by finding a distinct subset of somatic mutations and mCAs that are associated with increased risk of lymphoid malignancy. CH driven by these mutations is termed lymphoid clonal hematopoiesis (L-CH). Unlike myeloid clonal hematopoiesis (M-CH), L-CH has the potential to originate at both stem cells and partially or fully differentiated progeny stages of maturation. In this review, we explore the definition of L-CH in the context of lymphocyte maturation and lymphoid malignancy precursor disorders, the evidence for L-CH in late-onset autoimmunity and immunodeficiency, and the development of therapy-related L-CH following chemotherapy or hematopoietic stem cell transplantation.

Follicular lymphoma dynamics

Follicular lymphoma (FL) is an indolent yet challenging disease. Despite a generally favorable response to immunochemotherapy regimens, a fraction of patients does not respond or relapses early with unfavorable prognosis. For the vast majority of those who initially respond, relapses will repeatedly occur with increasing refractoriness to available treatments. Addressing the clinical challenges in FL warrants deep understanding of the nature of treatment-resistant FL cells seeding relapses, and of the biological basis of early disease progression. Great progress has been made in the last decade in the description and interrogation of the (epi)genomic landscape of FL cells, of their major dependency to the tumor microenvironment (TME), and of the stepwise lymphomagenesis process, from healthy to subclinical disease and to overt FL. A new picture is emerging, in which an ever-evolving tumor-TME duo sparks a complex and multilayered clonal and functional heterogeneity, blurring the discovery of prognostic biomarkers, patient stratification and reliable designs of risk-adapted treatments. Novel technological approaches allowing to decipher both tumor and TME heterogeneity at the single-cell level are beginning to unravel unsuspected cell dynamics and plasticity of FL cells. The upcoming drawing of a comprehensive functional picture of FL within its ecosystem holds great promise to address the unmet medical needs of this complex lymphoma.

Early stages in the ontogeny of small B-cell lymphomas: genetics and microenvironment

In this review, we focus on the mechanisms underlying lymphomagenesis in chronic lymphocytic leukaemia, follicular lymphoma, mantle cell lymphoma and splenic marginal zone lymphoma. The cells of origin of these small B-cell lymphomas are distinct, as are the characteristic chromosomal lesions and clinical courses. One shared feature is retention of expression of surface immunoglobulin. Analysis of this critical receptor reveals the point of differentiation reached by the cell of origin. Additionally, the sequence patterns of the immunoglobulin-variable domains can indicate a role for stimulants of the B-cell receptor before, during and after malignant transformation. The pathways driven via the B-cell receptor are now being targeted by specific kinase inhibitors with exciting clinical effects. To consider routes to pathogenesis, potentially offering earlier intervention, or to identify causative factors, genetic tools are being used to track pretransformation events and the early phases in lymphomagenesis. These methods are revealing that chromosomal changes are only one of the many steps involved, and that the influence of surrounding cells, probably multiple and variable according to tissue location, is required, both to establish tumours and to maintain growth and survival. Similarly, the influence of the tumour microenvironment may protect malignant cells from eradication by treatment, and the resulting minimal residual disease will eventually give rise to relapse. The common and different features of the four lymphomas will be summarized to show how normal B lymphocytes can be subverted to generate tumours, how these tumours evolve and how their weaknesses can be attacked by targeted therapies.

Digital PCR using micropatterned superporous absorbent array chips

Digital PCR (dPCR) is an emerging technology for genetic analysis and clinical diagnostics. To facilitate the widespread application of dPCR, here we developed a new micropatterned superporous absorbent array chip (μSAAC) which consists of an array of microwells packed with highly porous agarose microbeads. The packed beads construct a hierarchically porous microgel which confers superior water adsorption capacity to enable spontaneous filling of PDMS microwells for fluid compartmentalization without the need of sophisticated microfluidic equipment and operation expertise. Using large λ-DNA as the model template, we validated the μSAAC for stochastic partitioning and quantitative digital detection of DNA molecules. Furthermore, as a proof-of-concept, we conducted dPCR detection and single-molecule sequencing of a mutation prevalent in blood cancer, the chromosomal translocation t(14;18), demonstrating the feasibility of the μSAAC for analysis of disease-associated mutations. These experiments were carried out using the standard molecular biology techniques and instruments. Because of its low cost, ease of fabrication, and equipment-free liquid partitioning, the μSAAC is readily adaptable to general lab settings, which could significantly facilitate the widespread application of dPCR technology in basic research and clinical practice.