105 research outputs found
Follicular lymphoma-like B cells in healthy individuals: a novel intermediate step in early lymphomagenesis
Follicular lymphoma is one of the most common adult lymphoma, and remains virtually incurable despite its relatively indolent nature. t(14;18)(q32;q21) translocation, the genetic hallmark and early initiating event of follicular lymphoma (FL) pathogenesis, is also present at low frequency in the peripheral blood of healthy individuals. It has long been assumed that in healthy individuals t(14;18) is carried by circulating quiescent naive B cells, where its oncogenic potential would be restrained. Here, we question this current view and demonstrate that in healthy individuals, t(14;18) is actually carried by an expanding population of atypical B cells issued from germinal centers, displaying genotypic and phenotypic features of FL, and prone to constitute potent premalignant FL niches. These findings strongly impact both on the current understanding of disease progression and on the proper handling of t(14;18) frequency in blood as a potential early biomarker for lymphoma
Contiguous follicular lymphoma and follicular lymphoma in situ harboring N-glycosylated sites
International audienceFollicular lymphoma in situ (FLIS) is composed of a clonal B-cell population harboring the typical t(14;18) hallmark of follicular lymphoma (FL), forming unconventional BCL2 Bright CD10 + cell foci in an otherwise normal reactive lymph node (LN). The diagnosis of FLIS is made on the fortuitous discovery of unconventional BCL2 Bright CD10 + cell foci. 1 Several studies recently demonstrated that FLIS are already advanced precursors in follicular lymphomagene-sis, but not necessarily committed to malignant transformation. 2,3 However, the relationship between FLIS and FL still remains unclear, as only a minority (<5%) of FLIS patients eventually develop FL. This is in line with the usually indolent progression of the disease, and the genomic instability observed in FLIS cells, which can engage FL precursor cells either in an evolutionary malignant process, or to an evolutionary dead end. 4 We report the case of a 35-year old male patient who presented with a cervical adenopathy. Histological examination of the excised LN displayed an altered architecture suggestive of FL, consisting of high number of monomorphic large follicles, uniformly spread in the cortical and medullary areas. Most follicles contained a predominant population of small cleaved cells with scant macrophages and mitoses. The mantle zone was reduced or absent. However, in a minor cortical area, a few follicles showed features mimicking residual classical germ cells (GC), including a smaller size, higher cell polymorphism, and a preserved mantle zone (Figure 1A). The BCL2 immunostaining (clone 100) was negative in follicles displaying a typical FL pattern. In contrast, follicles located in the pseudo-residual area were BCL2bright, i.e. more strongly stained than the surrounding mantle zone and reactive T cells (Figure 1B). Most follicles were only slightly positive for Ki67 (Online Supplementary Figure S1A). Both BCL2 – and BCL2 + follicles were CD10 positive (Online Supplementary Figure S1B) and contained a BCL2/JH break-point evidenced by fluorescence in situ hybridization (FISH) (Figure 1C). Taken together these results suggested the diagnosis of simultaneous occurrence of BCL2 – FL (grade I/II) and of BCL2 + FLIS in the same LN. We decided to further analyze those two lesions independently, and performed macrodissection in order to proceed with individual molecular analyses when required. Sanger sequenc-ing revealed that both FLIS and FL shared the same BCL2/JH sequence at the t(14;18)+ breakpoint, and thus originated from the same clone (Figure 1D). We tested two other anti-BCL2 antibodies (E17, SP66) directed against other epitopes, but the staining remained BCL2-in the FL area of the LN, similar to the anti-BCL2 antibody (clone 100) staining (Figure 1E and F). We thus sequenced exons 1 to 3 of the BCL2 gene (B-cell CLL/lym-phoma 2, NG_009361.1). Punctual mutations, resulting in amino acid substitutions, were found in the FL component (Online Supplementary Table S1), and were indeed located in the targeted aa41 to aa54 epitope of clone 100 (mutation
In Vivo Reinsertion of Excised Episomes by the V(D)J Recombinase: A Potential Threat to Genomic Stability
It has long been thought that signal joints, the byproducts of V(D)J recombination, are not involved in the dynamics of the rearrangement process. Evidence has now started to accumulate that this is not the case, and that signal joints play unsuspected roles in events that might compromise genomic integrity. Here we show both ex vivo and in vivo that the episomal circles excised during the normal process of receptor gene rearrangement may be reintegrated into the genome through trans-V(D)J recombination occurring between the episomal signal joint and an immunoglobulin/T-cell receptor target. We further demonstrate that cryptic recombination sites involved in T-cell acute lymphoblastic leukemia–associated chromosomal translocations constitute hotspots of insertion. Eventually, the identification of two in vivo cases associating episomal reintegration and chromosomal translocation suggests that reintegration events are linked to genomic instability. Altogether, our data suggest that V(D)J-mediated reintegration of episomal circles, an event likely eluding classical cytogenetic screenings, might represent an additional potent source of genomic instability and lymphoid cancer
V(D)J-mediated Translocations in Lymphoid Neoplasms: A Functional Assessment of Genomic Instability by Cryptic Sites
Most lymphoid malignancies are initiated by specific chromosomal translocations between
immunoglobulin (Ig)/T cell receptor (TCR) gene segments and cellular proto-oncogenes. In
many cases, illegitimate V(D)J recombination has been proposed to be involved in the
translocation process, but this has never been functionally established. Using
extra-chromosomal recombination assays, we determined the ability of several
proto-oncogenes to target V(D)J recombination, and assessed the impact of their
recombinogenic potential on translocation rates in vivo. Our data support the involvement
of 2 distinct mechanisms: translocations involving LMO2, TAL2, and TAL1 in T cell acute
lymphoblastic leukemia (T-ALL), are compatible with illegitimate V(D)J recombination
between a TCR locus and a proto-oncogene locus bearing a fortuitous but functional
recombination site (type 1); in contrast, translocations involving BCL1 and BCL2 in B cell
non-Hodgkin's lymphomas (B-NHL), are compatible with a process in which only the IgH
locus breaks are mediated by V(D)J recombination (type 2). Most importantly, we show that
the t(11;14)(p13;q32) translocation involving LMO2 is present at strikingly high frequency
in normal human thymus, and that the recombinogenic potential conferred by the LMO2
cryptic site is directly predictive of the in vivo level of translocation at that locus.
These findings provide new insights into the regulation forces acting upon genomic
instability in B and T cell tumorigenesis
Unraveling the consecutive recombination events in the human IGK locus
In addition to the classical Vkappa-Jkappa, Vkappa-kappa deleting element
(Kde), and intron-Kde gene rearrangements, atypical recombinations
involving Jkappa recombination signal sequence (RSS) or intronRSS elements
can occur in the Igkappa (IGK) locus, as observed in human B cell
malignancies. In-depth analysis revealed that atypical
JkappaRSS-intronRSS, Vkappa-intronRSS, and JkappaRSS-Kde recombinations
not only occur in B cell malignancies, but rather reflect physiological
gene rearrangements present in normal human B cells as well. Excision
circle analysis and recombination substrate assays can discriminate
between single-step vs multistep rearrangements. Using this combined
approach, we unraveled that the atypical Vkappa-intronRSS and
JkappaRSS-Kde pseudohybrid joints most probably result from ongoing
recombination following an initial aberrant JkappaRSS-intronRSS signal
joint formation. Based on our observations in normal and malignant human B
cells, a model is presented to describe the sequential (classical and
atypical) recombination events in the human IGK locus and their estimated
relative frequencies (0.2-1.0 vs < 0.03). The initial JkappaRSS-intronRSS
signal joint formation (except for Jkappa1RSS-intronRSS) might be a side
event of an active V(D)J recombination mechanism, but the subsequent
formation of Vkappa-intronRSS and JkappaRSS-Kde pseudohybrid joints can
represent an alternative pathway for IGK allele inactivation and allelic
exclusion, in addition to classical Ckappa deletions. Although usage of
this alternative pathway is limited, it seems essential for inactivation
of those IGK alleles that have undergone initial aberrant recombinations,
which might otherwise hamper selection of functional Ig L chain proteins
Agricultural pesticide exposure and the molecular connection to lymphomagenesis
The t(14;18) translocation constitutes the initiating event of a causative cascade leading to follicular lymphoma (FL). t(14;18) translocations are present in blood from healthy individuals, but there is a trend of increased prevalence in farmers exposed to pesticides, a group recently associated with higher risk of t(14;18)+ non-Hodgkin's lymphoma development. A direct connection between agricultural pesticide use, t(14;18) in blood, and malignant progression, however, has not yet been demonstrated. We followed t(14;18) clonal evolution over 9 yr in a cohort of farmers exposed to pesticides. We show that exposed individuals bear particularly high t(14;18) frequencies in blood because of a dramatic clonal expansion of activated t(14;18)+ B cells. We further demonstrate that such t(14;18)+ clones recapitulate the hallmark features of developmentally blocked FL cells, with some displaying aberrant activation-induced cytidine deaminase activity linked to malignant progression. Collectively, our data establish that expanded t(14;18)+ clones constitute bona fide precursors at various stages of FL development, and provide a molecular connection between agricultural pesticide exposure, t(14;18) frequency in blood, and clonal progression
A new mouse model for the trisomy of the Abcg1–U2af1 region reveals the complexity of the combinatorial genetic code of down syndrome
Mental retardation in Down syndrome (DS), the most frequent trisomy in humans, varies from moderate to severe. Several studies both in human and based on mouse models identified some regions of human chromosome 21 (Hsa21) as linked to cognitive deficits. However, other intervals such as the telomeric region of Hsa21 may contribute to the DS phenotype but their role has not yet been investigated in detail. Here we show that the trisomy of the 12 genes, found in the 0.59 Mb (Abcg1–U2af1) Hsa21 sub-telomeric region, in mice (Ts1Yah) produced defects in novel object recognition, open-field and Y-maze tests, similar to other DS models, but induces an improvement of the hippocampal-dependent spatial memory in the Morris water maze along with enhanced and longer lasting long-term potentiation in vivo in the hippocampus. Overall, we demonstrate the contribution of the Abcg1–U2af1 genetic region to cognitive defect in working and short-term recognition memory in DS models. Increase in copy number of the Abcg1–U2af1 interval leads to an unexpected gain of cognitive function in spatial learning. Expression analysis pinpoints several genes, such as Ndufv3, Wdr4, Pknox1 and Cbs, as candidates whose overexpression in the hippocampus might facilitate learning and memory in Ts1Yah mice. Our work unravels the complexity of combinatorial genetic code modulating different aspect of mental retardation in DS patients. It establishes definitely the contribution of the Abcg1–U2af1 orthologous region to the DS etiology and suggests new modulatory pathways for learning and memory
RUNX1-dependent RAG1 deposition instigates human TCR-δ locus rearrangement
V(D)J recombination of TCR loci is regulated by chromatin accessibility to RAG1/2 proteins, rendering RAG1/2 targeting a potentially important regulator of lymphoid differentiation. We show that within the human TCR-α/δ locus
- …