Early steps in follicular lymphomagenesis

L'incidence des Lymphomes non-Hodgkiniens a connu un essor fulgurant ces dernières années en dépit d'indiscutables progrès thérapeutiques. Cette progression reste encore inexpliquée et l'identification de facteurs de risque et mécanismes sous-jacents constituent un enjeu majeur de santé publique. Ma thèse s'inscrit dans cette démarche et a visé à mieux comprendre 1) l'étiologie et 2) le développement de ces hémopathies. Les translocations chromosomiques impliquant des loci immuns sont à la fois initiatrices et signatures des hémopathies et peuvent résulter d'un défaut de la recombinaison VDJ à l'exemple de la t(14;18) et t(11;14) dans les lymphomes folliculaire (LF) ou du manteau et t(10;14) dans les leucémies T. Cependant les facteurs à l'origine des cassures oncogéniques restent méconnus et leur exploration a constitué le 1er objectif de ma thèse. Le 2nd axe de ma thèse a porté sur l'étiologie du processus de transformation d'une cellule prétumorale avec comme modèle le LF. La t(14 ;18) est nécessaire mais insuffisante à la pathogenèse du FL et la preuve en est que des cellules t(14;18)+ sont décrites à taux variables (~10-6) dans le sang d'individus sains(IS). Ces cellules "LF-Like" portent un ensemble d'anomalies génomiques typiques du LF pouvant bien représenter des précurseurs du LF à différents stades d'évolution. Leur persistance et évolution clonale chez l'IS suggèrent l'existence de niches prétumorales, possiblement dans les organes lymphoïdes (rate/ganglions/moelle osseuse). Je me suis donc intéressée à l'identification de ces niches prétumorales et à la capacité des "LF-like" à disséminer et acquérir des hits secondaires clé de leur évolution vers le LFNon Hodgkin Lymphomas have shown an increasing incidence in western countries over the last decades. As etiologic factors still remain elusive, it is clearly of critical importance to better define risk factors and early steps of lymphomagenesis and progression. Chromosomal translocations juxtaposing oncogenes to immune locus thereby deregulating oncogenic expression are hallmarks of lymphoid neoplasms; examples are t(14;18) and t(11;14) in Follicular (FL) and Mantle Cell lymphomas and t(10;14) in T Leukemias. Though it is assumed that the break at the immune locus is due to physiological VDJ recombination, the origin of the break at the oncogene remains unknown. In line with this, my 1st aim was to identify factors involved in the initiation of breaks at the oncogenic locus. My 2nd aim concerned the mechanisms governing evolution of a pre-malignant cell clone into the multiple steps of lymphomagenesis with FL, a B-cell neoplasm as model. T(14;18) translocation is a critical early event in the natural history of FL. However it is now clear that t(14;18) alone is not sufficient and that acquisition of synergistic oncogenic hits are required for malignant transformation. Indeed, it has been reported that t(14;18) cells are present at variable rates in blood of healthy individuals (HI) with yet uncertain significance. We recently demonstrated that in HI t(14;18) cells constitute an expanding population of atypical B-cells displaying geno/phenotypic features of FL suggesting that those cells could be bona-fide FL precursors prone to constitute potent premalignant niches. In the 2nd part of my PhD, I questioned the ability of these so-called "FL-Like" cells to seed pretumoral niches in lymphoid organs (spleen/lymph nodes/bone marrow) and to disseminate and acquire secondary transforming hits as their FL counterparts

Early steps in follicular lymphomagenesis

L'incidence des Lymphomes non-Hodgkiniens a connu un essor fulgurant ces dernières années en dépit d'indiscutables progrès thérapeutiques. Cette progression reste encore inexpliquée et l'identification de facteurs de risque et mécanismes sous-jacents constituent un enjeu majeur de santé publique. Ma thèse s'inscrit dans cette démarche et a visé à mieux comprendre 1) l'étiologie et 2) le développement de ces hémopathies. Les translocations chromosomiques impliquant des loci immuns sont à la fois initiatrices et signatures des hémopathies et peuvent résulter d'un défaut de la recombinaison VDJ à l'exemple de la t(14;18) et t(11;14) dans les lymphomes folliculaire (LF) ou du manteau et t(10;14) dans les leucémies T. Cependant les facteurs à l'origine des cassures oncogéniques restent méconnus et leur exploration a constitué le 1er objectif de ma thèse. Le 2nd axe de ma thèse a porté sur l'étiologie du processus de transformation d'une cellule prétumorale avec comme modèle le LF. La t(14 ;18) est nécessaire mais insuffisante à la pathogenèse du FL et la preuve en est que des cellules t(14;18)+ sont décrites à taux variables (~10-6) dans le sang d'individus sains(IS). Ces cellules "LF-Like" portent un ensemble d'anomalies génomiques typiques du LF pouvant bien représenter des précurseurs du LF à différents stades d'évolution. Leur persistance et évolution clonale chez l'IS suggèrent l'existence de niches prétumorales, possiblement dans les organes lymphoïdes (rate/ganglions/moelle osseuse). Je me suis donc intéressée à l'identification de ces niches prétumorales et à la capacité des "LF-like" à disséminer et acquérir des hits secondaires clé de leur évolution vers le LFNon Hodgkin Lymphomas have shown an increasing incidence in western countries over the last decades. As etiologic factors still remain elusive, it is clearly of critical importance to better define risk factors and early steps of lymphomagenesis and progression. Chromosomal translocations juxtaposing oncogenes to immune locus thereby deregulating oncogenic expression are hallmarks of lymphoid neoplasms; examples are t(14;18) and t(11;14) in Follicular (FL) and Mantle Cell lymphomas and t(10;14) in T Leukemias. Though it is assumed that the break at the immune locus is due to physiological VDJ recombination, the origin of the break at the oncogene remains unknown. In line with this, my 1st aim was to identify factors involved in the initiation of breaks at the oncogenic locus. My 2nd aim concerned the mechanisms governing evolution of a pre-malignant cell clone into the multiple steps of lymphomagenesis with FL, a B-cell neoplasm as model. T(14;18) translocation is a critical early event in the natural history of FL. However it is now clear that t(14;18) alone is not sufficient and that acquisition of synergistic oncogenic hits are required for malignant transformation. Indeed, it has been reported that t(14;18) cells are present at variable rates in blood of healthy individuals (HI) with yet uncertain significance. We recently demonstrated that in HI t(14;18) cells constitute an expanding population of atypical B-cells displaying geno/phenotypic features of FL suggesting that those cells could be bona-fide FL precursors prone to constitute potent premalignant niches. In the 2nd part of my PhD, I questioned the ability of these so-called "FL-Like" cells to seed pretumoral niches in lymphoid organs (spleen/lymph nodes/bone marrow) and to disseminate and acquire secondary transforming hits as their FL counterparts.AIX-MARSEILLE2-Bib.electronique (130559901) / SudocSudocFranceF

Early steps of follicular lymphoma pathogenesis.

International audienceFollicular lymphoma (FL) pathogenesis is a complex and fascinating multi-hit process, escalating along successive derailments of the distinctive molecular and cellular mechanisms paving B-cell differentiation and activation. This progressive subversion of B-cell receptor diversification mechanisms and B-cell homeostasis likely occurs during a protracted preclinical phase of asymptomatic growth, in which premalignant clones already disseminate and establish "niches" in secondary lymphoid organs. Following FL diagnosis, a parallel indolent behavior is observed in most patients, slowly progressing over a period of many years, to eventually generate a highly refractory (and in some case transform into an aggressive subtype of) lymphoma. Novel insights in human germinal center B-cell biology recently allowed a more comprehensive understanding of the various illegitimate events sequentially involved in the premalignant progression phases. In this review, we will discuss how these new data have modified our perception of early FL pathogenesis, the new questions and challenges it opened up, and how this knowledge could impact on innovative programs of early detection, follow-up, and patient management

Germinal center reentries of BCL2-overexpressing B cells drive follicular lymphoma progression

International audienceIt has recently been demonstrated that memory B cells can reenter and reengage germinal center (GC) reactions, opening the possibility that multi-hit lymphomagenesis gradually occurs throughout life during successive immunological challenges. Here, we investigated this scenario in follicular lymphoma (FL), an indolent GC-derived malignancy. We developed a mouse model that recapitulates the FL hallmark t(14;18) translocation, which results in constitutive activation of antiapoptotic protein B cell lymphoma 2 (BCL2) in a subset of B cells, and applied a combination of molecular and immunofluorescence approaches to track normal and t(14;18)(+) memory B cells in human and BCL2-overexpressing B cells in murine lymphoid tissues. BCL2-overexpressing B cells required multiple GC transits before acquiring FL-associated developmental arrest and presenting as GC B cells with constitutive activation-induced cytidine deaminase (AID) mutator activity. Moreover, multiple reentries into the GC were necessary for the progression to advanced precursor stages of FL. Together, our results demonstrate that protracted subversion of immune dynamics contributes to early dissemination and progression of t(14;18)(+) precursors and shapes the systemic presentation of FL patients

Determinants of the t(14;18) translocation and their role in t(14;18)-positive follicular lymphoma

PURPOSE: The strong association between t(14;18) translocation and follicular lymphoma (FL) is well known. However, the determinants of this chromosomal aberration and their role in t(14;18) associated FL remain to be established. METHODS: t(14;18) frequency within the B cell lymphoma 2 major breakpoint region was determined for 135 incident FL cases and 251 healthy controls as part of a nested case-control study within the European Prospective Investigation into Cancer cohort. Quantitative real-time PCR was performed in DNA extracted from blood samples taken at recruitment. The relationship between prevalence and frequency of the translocation with baseline anthropometric, lifestyle, and dietary factors in cases and controls was determined. Unconditional logistic regression was used to explore whether the risk of FL associated with these factors differed in t(14;18)(+) as compared to t(14;18)(-) cases. RESULTS: Among incident FL cases, educational level (χ (2) p = 0.021) and height (χ (2) p = 0.025) were positively associated with t(14;18) prevalence, and cases with high frequencies [t(14;18)(HF)] were significantly taller (t test p value = 0.006). These findings were not replicated in the control population, although there were a number of significant associations with dietary variables. Further analyses revealed that height was a significant risk factor for t(14;18)(+) FL [OR 6.31 (95 % CI 2.11, 18.9) in the tallest versus the shortest quartile], but not t(14;18)(-) cases. CONCLUSIONS: These findings suggest a potential role for lifestyle factors in the prevalence and frequency of the t(14;18) translocation. The observation that the etiology of FL may differ by t(14;18) status, particularly with regard to height, supports the subdivision of FL by translocation status

Alterations of microRNA and microRNA-regulated messenger RNA expression in germinal center B-cell lymphomas determined by integrative sequencing analysis

MicroRNA are well-established players in post-transcriptional gene regulation. However, information on the effects of microRNA deregulation mainly relies on bioinformatic prediction of potential targets, whereas proof of the direct physical microRNA/target messenger RNA interaction is mostly lacking. Within the International Cancer Genome Consortium Project “Determining Molecular Mechanisms in Malignant Lymphoma by Sequencing”, we performed miRnome sequencing from 16 Burkitt lymphomas, 19 diffuse large B-cell lymphomas, and 21 follicular lymphomas. Twentytwo miRNA separated Burkitt lymphomas from diffuse large B-cell lymphomas/follicular lymphomas, of which 13 have shown regulation by MYC. Moreover, we found expression of three hitherto unreported microRNA. Additionally, we detected recurrent mutations of hsa-miR-142 in diffuse large B-cell lymphomas and follicular lymphomas, and editing of the hsa-miR-376 cluster, providing evidence for microRNA editing in lymphomagenesis. To interrogate the direct physical interactions of microRNA with messenger RNA, we performed Argonaute-2 photoactivatable ribonucleoside-enhanced cross-linking and immunoprecipitation experiments. MicroRNA directly targeted 208 messsenger RNA in the Burkitt lymphomas and 328 messenger RNA in the non-Burkitt lymphoma models. This integrative analysis discovered several regulatory pathways of relevance in lymphomagenesis including Ras, PI3KAkt and MAPK signaling pathways, also recurrently deregulated in lymphomas by mutations. Our dataset reveals that messenger RNA deregulation through microRNA is a highly relevant mechanism in lymphomagenesis

Alterations of microRNA and microRNA-regulated messenger RNA expression in germinal center B-cell lymphomas determined by integrative sequencing analysis

MicroRNAs are well-established players in posttranscriptional gene regulation. However, information on the effects of microRNA deregulation mainly relies on bioinformatic prediction of potential targets, whereas proof of the direct physical microRNAs/target mRNAs interaction is mostly lacking. Within the International Cancer Genome Consortium Project Determining Molecular Mechanisms in Malignant Lymphoma by Sequencing (ICGC MMML-Seq), we performed miRnome sequencing from 16 Burkitt lymphomas, 19 diffuse large B-cell lymphomas, and 21 follicular lymphomas. Twenty-two miRNAs separated Burkitt lymphomas from diffuse large B-cell lymphomas/follicular lymphomas, of which 13 have shown regulation by MYC. Moreover, we show expression of three hitherto unreported microRNAs. Additionally, we detect recurrent mutations of hsa-miR-142 in diffuse large B-cell lymphomas and follicular lymphomas, and editing of the hsa-miR-376 cluster, providing evidence for microRNA editing in lymphomagenesis. To interrogate the direct physical interactions of microRNAs with mRNAs, we performed Argonaute-2 photoactivatable ribonucleoside-enhanced cross-linking and immunoprecipitation experiments. MicroRNAs directly targeted 208 mRNAs in the Burkitt lymphomas and 328 mRNAs in the non-Burkitt lymphoma models. This integrative analysis discovered several regulatory pathways of relevance in lymphomagenesis including Ras, PI3K-Akt and MAPK signaling pathways, also recurrently deregulated in lymphomas by mutations. Our dataset uncovers in detail the mRNA deregulation through microRNAs as a highly relevant mechanism in lymphomagenesis

t(14;18) Translocation : A predictive blood biomarker for follicular lymphoma

PURPOSE: The (14;18) translocation constitutes both a genetic hallmark and critical early event in the natural history of follicular lymphoma (FL). However, t(14;18) is also detectable in the blood of otherwise healthy persons, and its relationship with progression to disease remains unclear. Here we sought to determine whether t(14;18)-positive cells in healthy individuals represent tumor precursors and whether their detection could be used as an early predictor for FL. PARTICIPANTS AND METHODS: Among 520,000 healthy participants enrolled onto the EPIC (European Prospective Investigation Into Cancer and Nutrition) cohort, we identified 100 who developed FL 2 to 161 months after enrollment. Prediagnostic blood from these and 218 controls were screened for t(14;18) using sensitive polymerase chain reaction-based assays. Results were subsequently validated in an independent cohort (65 case participants; 128 controls). Clonal relationships between t(14;18) cells and FL were also assessed by molecular backtracking of paired prediagnostic blood and tumor samples. RESULTS: Clonal analysis of t(14;18) junctions in paired prediagnostic blood versus tumor samples demonstrated that progression to FL occurred from t(14;18)-positive committed precursors. Furthermore, healthy participants at enrollment who developed FL up to 15 years later showed a markedly higher t(14;18) prevalence and frequency than controls (P 10(-4) (odds ratio, 23.17; 95% CI, 9.98 to 67.31; P < .001). Remarkably, risk estimates remained high and significant up to 15 years before diagnosis. CONCLUSION: High t(14;18) frequency in blood from healthy individuals defines the first predictive biomarker for FL, effective years before diagnosis