Julie Bruneau

Loss of p19Arf in a Rag1 -/- B-cell precursor population initiates acute B-lymphoblastic leukemia

In human B-acute lymphoblastic leukemia (B-ALL), RAG1-induced genomic alterations are important for disease progression. However, given that biallelic loss of the RAG1 locus is observed in a subset of cases, RAG1s role in the development of B-ALL remains unclear. We chose a p19Arf(-/-)Rag1(-/-) mouse model to confirm the previously published results concerning the contribution of CDKN2A (p19ARF /INK4a) and RAG1 copy number alterations in precursor B cells to the initiation and/or progression to B-acute lymphoblastic leukemia (B-ALL). In this murine model, we identified a new, Rag1-independent leukemia-initiating mechanism originating from a Sca1(+)CD19(+) precursor cell population and showed that Notch1 expression accelerates the cells self-renewal capacity in vitro. In human RAG1-deficient BM, a similar CD34(+)CD19(+) population expressed p19ARF. These findings suggest that combined loss of p19Arf and Rag1 results in B-cell precursor leukemia in mice and may contribute to the progression of precursor B-ALL in humans.

Decreased somatic hypermutation induces an impaired peripheral B cell tolerance checkpoint

Patients with mutations in AICDA, which encodes activation-induced cytidine deaminase (AID), display an impaired peripheral B cell tolerance. AID mediates class-switch recombination (CSR) and somatic hypermutation (SHM) in B cells, but the mechanism by which AID prevents the accumulation of autoreactive B cells in blood is unclear. Here, we analyzed B cell tolerance in AID-deficient patients, patients with autosomal dominant AID mutations (AD-AID), asymptomatic AICDA heterozygotes (AID+/-), and patients with uracil N-glycosylase (UNG) deficiency, which impairs CSR but not SHM. The low frequency of autoreactive mature naive B cells in UNG-deficient patients resembled that of healthy subjects, revealing that impaired CSR does not interfere with the peripheral B cell tolerance checkpoint. In contrast, we observed decreased frequencies of SHM in memory B cells from AD-AID patients and AID+/- subjects, who were unable to prevent the accumulation of autoreactive mature naive B cells. In addition, the individuals with AICDA mutations, but not UNG-deficient patients, displayed Tregs with defective suppressive capacity that correlated with increases in circulating T follicular helper cells and enhanced cytokine production. We conclude that SHM, but not CSR, regulates peripheral B cell tolerance through the production of mutated antibodies that clear antigens and prevent sustained interleukin secretions that interfere with Treg function.

Adult T cell leukemia aggressivenness correlates with loss of both 5-hydroxymethylcytosine and TET2 expression

Mutations in TET2, encoding one of the TET members responsible for the conversion of DNA cytosine methylation to hydroxymethylation (5-hmc), have been recently described in Human T-lymphotropic virus type 1-associated adult T-cell leukemia/lymphoma (ATLL). However, neither the amount of genomic 5-hmc in ATLL tumor cells nor TET2 expression has been studied yet. In this study, we analyzed these two parameters as well as the mutational status of TET2 in ATLL patients. By employing a direct in situ approach, we documented that tumor T cells infiltrating lymph nodes exhibit low level of 5-hmc compared to residual normal T cells. Furthermore, this 5-hmc defect was more pronounced in tumor T cells from acute patients than from chronic ones and correlated with reduced expression of TET2 protein. TET2 variations were found in 14 patients (20%), including 13 with aggressive forms. Strikingly, 9 of the 14 patients showed the same variation (SNP rs72963007), whose frequency in ATLL patients was significantly higher than that of an ethnically matched control population (13% vs. 5%). However, no reduction of 5-hmc was found in PBMC from individuals possessing the variant rs72963007 TET2 allele, as compared to wild-type individuals. In contrast, a robust correlation was observed between 5-hmc and the levels of TET2 mRNA. Finally, loss of 5-hmc and TET2 downregulation both correlated with poor survival. These findings demonstrate that ATLL progression coincides with loss of genomic 5-hmc and indicate that downregulation of TET2, rather than TET2 mutations, is the key mechanism involved in 5-hmc modulation during ATLL progression.Mutations in TET2, encoding one of the TET members responsible for the conversion of DNA cytosine methylation to hydroxymethylation (5-hmc), have been recently described in Human T-lymphotropic virus type 1-associated adult T-cell leukemia/lymphoma (ATLL). However, neither the amount of genomic 5-hmc in ATLL tumor cells nor TET2 expression has been studied yet. In this study, we analyzed these two parameters as well as the mutational status of TET2 in ATLL patients. By employing a direct in situ approach, we documented that tumor T cells infiltrating lymph nodes exhibit low level of 5-hmc compared to residual normal T cells. Furthermore, this 5-hmc defect was more pronounced in tumor T cells from acute patients than from chronic ones and correlated with reduced expression of TET2 protein. TET2 variations were found in 14 patients (20%), including 13 with aggressive forms. Strikingly, 9 of the 14 patients showed the same variation (SNP rs72963007), whose frequency in ATLL patients was significantly higher than that of an ethnically matched control population (13% vs. 5%). However, no reduction of 5-hmc was found in PBMC from individuals possessing the variant rs72963007 TET2 allele, as compared to wild-type individuals. In contrast, a robust correlation was observed between 5-hmc and the levels of TET2 mRNA. Finally, loss of 5-hmc and TET2 downregulation both correlated with poor survival. These findings demonstrate that ATLL progression coincides with loss of genomic 5-hmc and indicate that downregulation of TET2, rather than TET2 mutations, is the key mechanism involved in 5-hmc modulation during ATLL progression.

Corrigendum: Evidence of innate lymphoid cell redundancy in humans.

Frédéric Vély, Vincent Barlogis, Blandine Vallentin, Bénédicte Neven, Christelle Piperoglou, Thibaut Perchet, Maxime Petit, Nadia Yessaad, Fabien Touzot, Julie Bruneau, Nizar Mahlaoui, Nicolas Zucchini, Catherine Farnarier, Gérard Michel, Despina Moshous, Stéphane Blanche, Arnaud Dujardin, Hergen Spits, Jörg H W Distler, Andreas Ramming, Capucine Picard, Rachel Golub, Alain Fischer & Eric Vivier Nat. Immunol. 17, 1291–1299 (2016); published online 12 September 2016; corrected after print 19 October 2016

Traitement d’un lymphome agressif chez un babouin naturellement infecté par STLV-1

L’infection par le virus T Lymphotrope Humain de Type 1 (HTLV-1) est associee a une lymphoproliferation maligne nommee Leucemie/Lymphome T de l’adulte (ATLL). STLV-1 est l’homologue simien de HTLV-1 et cause aussi des ATLL chez les primates non humains. Au cours du controle sanitaire annuel dans notre colonie de Papio anubis naturellement infectes par STLV-1 (n=45), une femelle de 9 ans fut identifiee comme presentant des troubles respiratoires, un amaigrissement prononce, un nombre de lymphocytes superieur a 1010/L, des metastases pulmonaires et des lesions de la peau, similaires a celles qui sont observees chez les patients souffrant d’ATLL. Ces symptomes etaient donc evocateurs d’une maladie hematologique provoquee par l’infection a STLV-1. Ce diagnostic fut confirme par la presence d’une lymphoproliferation massive dans la biopsie d’un ganglion inguinal et par la presence de lymphocytes presentant un noyau typique en trefle, caracteristique des cellules ATL, dans les frottis sanguins. Comme chez les patients souffrant d’ATLL, l’animal a recu une combinaison d’AZT (Combivir) et d’interferon alpha (viraferon, 50 μg/semaine) pendant quatre mois. La charge provirale (PVL) fut mesuree de maniere hebdomadaire. En l’absence d’amelioration des symptomes cliniques, et puisque seule une tres faible diminution de la charge provirale etait observee, l’animal fut euthanasie. Des analyses histologiques furent realisees et la charge provirale mesuree dans 25 organes differents. Tous les organes lymphoides montraient des infiltrats lymphocytairesxa0CD3+, CD25+. D’autre part, des cellules anormales furent trouvees dans les poumons et le foie. Grâce a des techniques d’immunohistochimie, nous avons detecte des cellules positives pour le transactivateur viral Tax dans la rate, les poumons, les ganglions mesenteriques, axillaires, inguinaux et lymphatiques. Tous les organes testes en PCR etaient positifs pour le virus. La PVL la plus elevee fut mesuree dans les ganglions lymphatiques, la rate et les poumons. Enfin, l’indice d’oligoclonalite et la diversite clonale ont ete analyses dans les cellules mononucleees du sang peripherique au cours du traitement, et dans differents organes obtenus apres autopsie. En conclusion, les primates non-humains infectes naturellement par STLV-1 representent un modele unique permettant d’etudier la pathogenese retrovirale et l’evaluation de nouveaux traitements.Nous remercions l’INSERM, l’Ecole Normale Superieure de Lyon, la Ligue Contre le Cancer (programme «u2009equipe labelliseeu2009»), l’Association pour la Recherche sur le Cancer et la region Rhone Alpes programme ARC1.