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The volume of arrivals from third countries into the European Union has increased in recent decades. With the increase in the number of residents from outside the European Union, their mobility among member countries has also increased. In recent years the issue of intra-European mobility of non-EU nationals has become increasingly important due to the influx of refugees during so called Mediterranean crisis in 2015 and United Kingdom's exit from the EU. However, Intra-EU mobility of Third Country National (TCN) migrants is still under-studied. The objective of this report is to collect existing information and provide results from the available data to describe the main characteristics and dynamics of intra-EU mobility of TCN migrants. Mobility within Europe is a historical phenomenon, although traditionally intra-European migrations were carried out by Europeans themselves. It is only in the second half of 20th century that mobility to Europe from other parts of the world has gradually become a mass phenomenon and, consequently, a factor of social, economic, and demographic change. The increase in the volume of citizens from non-European countries has resulted in their greater mobility within the continent. Intra-European mobility has taken on a new dimension with the creation of European communities and the gradual process of European integration. Although the freedom of movement has become the axis of European construction, this right has been reserved to date only for European citizens. Residents of the European Union who do not have European citizenship do not enjoy full freedom of movement between the countries of the union and are subject to national regulations that vary according to their category. Available data reveal that intra-EU mobility of TCN migrants is characterised by a diversity of patterns and destinations. It is observed that some countries are particularly attractive to intra-European TCN migrants. It is also observed that mobility takes place mostly between neighbouring countries. In ...

© 2021 Diks, Khatri, Oosten, de Mooij, Groenland, Teodosio, Perez-Andres, Orfao, Berbers, Zwaginga, van Dongen and Berkowska. ; Antigen-specific serum immunoglobulin (Ag-specific Ig) levels are broadly used as correlates of protection. However, in several disease and vaccination models these fail to predict immunity. In these models, in-depth knowledge of cellular processes associated with protective versus poor responses may bring added value. We applied high-throughput multicolor flow cytometry to track over-time changes in circulating immune cells in 10 individuals following pertussis booster vaccination (Tdap, Boostrix®, GlaxoSmithKline). Next, we applied correlation network analysis to extensively investigate how changes in individual cell populations correlate with each other and with Ag-specific Ig levels. We further determined the most informative cell subsets and analysis time points for future studies. Expansion and maturation of total IgG1 plasma cells, which peaked at day 7 post-vaccination, was the most prominent cellular change. Although these cells preceded the increase in Ag-specific serum Ig levels, they did not correlate with the increase of Ig levels. In contrast, strong correlation was observed between Ag-specific IgGs and maximum expansion of total IgG1 and IgA1 memory B cells at days 7 to 28. Changes in circulating T cells were limited, implying the need for a more sensitive approach. Early changes in innate immune cells, i.e. expansion of neutrophils, and expansion and maturation of monocytes up to day 5, most likely reflected their responses to local damage and adjuvant. Here we show that simultaneous monitoring of multiple circulating immune subsets in blood by flow cytometry is feasible. B cells seem to be the best candidates for vaccine monitoring. ; K is supported by the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 707404. The here presented study is a pilot study for the Innovative Medicines Initiative (IMI) PERISCOPE program, a Joint Undertaking under grant agreement No 115910. This Joint Undertaking receives support from the European Union's Horizon 2020 Research and Innovation Programme, the European Federation of Pharmaceutical Industries and Associations (EFPIA), and the Bill and Melinda Gates Foundation (BMGF). The flow cytometric studies in this study were supported by the EuroFlow Consortium. The EuroFlow Consortium received support from the FP6-2004-LIFESCIHEALTH-5 program of the European Commission (grant LSHB-CT-2006-018708) as Specific Targeted Research Project (STREP).

This is an open-access paper. ; The B-cell compartment in which multiple myeloma stem cells reside remains unclear. We investigated the potential presence of mature, surface-membrane immunoglobulin-positive B lymphocytes clonally related to the tumor bone marrow plasma cells among different subsets of peripheral blood B cells from ten patients (7 with multiple myeloma and 3 with monoclonal gammopathies of undetermined significance). The presence of clonotypic immunoglobulin heavy chain gene rearrangements was determined in multiple highly-purified fractions of peripheral blood B-lymphocytes including surface-membrane IgM+ CD27- naïve B-lymphocytes, plus surface-membrane IgG+, IgA+ and IgM+ memory CD27+ B cells, and normal circulating plasma cells, in addition to (mono)clonal plasma cells, by a highly-specific and sensitive allele-specific oligonucleotide polymerase chain reaction directed to the CDR3 sequence of the rearranged IGH gene of tumor plasma cells from individual patients. Our results showed systematic absence of clonotypic rearrangements in all the different B-cell subsets analyzed, including M-compo-nent isotype-matched memory B-lymphocytes, at frequencies <0.03 cells/mL (range: 0.0003-0.08 cells/mL); the only exception were the myeloma plasma cells detected and purified from the peripheral blood of four of the seven myeloma patients. These results indicate that circulating B cells from patients with multiple myeloma and monoclonal gammopathies of undetermined significance are usually devoid of clonotypic B cells while the presence of immunophenotypically aberrant myeloma plasma cells in peripheral blood of myeloma patients is a relatively frequent finding. ; This work was supported by grants from European Union FP6 STREP MSCNet (N. E06005FF), Cooperative Research Thematic Network on Cancer (RTICs; RTICC RD06/0020/0035-FEDER, RD06/0020/0006, RD12/0036/0048, RD12/0036/0069 and G03/136), Instituto de Salud Carlos III/Subdirección General de Investigación Sanitaria Ministerio de Sanidad y Consumo (FIS: PI060339; 02/0905; 01/0089/01-02;PS09/01897, and PI06/0824-FEDER), Asociacion Española Contra el Cancer AECC (GCB120981SAN) and Gerencia Regional de Salud de Castilla y León; Ayuda de Excelencia de Castilla y León, Consejería de Educación (EDU/894/2009, GR37) Junta de Castilla y León, Valladolid, Spain. LST received a CAPES/Ministério da Educação scholarship from the Brazilian Government. ; Peer Reviewed

© 2019 by the authors. ; Despite recent therapeutic advances, systemic mastocytosis (SM) remains an incurable disease due to limited complete remission (CR) rates even after novel therapies. To date, no study has evaluated the expression on SM bone marrow mast cells (BMMC) of large panel of cell surface suitable for antibody-targeted therapy. In this study, we analyzed the expression profile of six cell-surface proteins for which antibody-based therapies are available, on BMMC from 166 SM patients vs. 40 controls. Overall, variable patterns of expression for the markers evaluated were observed among SM BMMC. Thus, CD22, CD30, and CD123, while expressed on BMMC from patients within every subtype of SM, showed highly variable patterns with a significant fraction of negative cases among advanced SM (aggressive SM (ASM), ASM with an associated clonal non-MC lineage disease (ASM-AHN) and MC leukemia (MCL)), 36%, 46%, and 39%, respectively. In turn, CD25 and FcεRI were found to be expressed in most cases (89% and 92%) in virtually all BMMC (median: 92% and 95%) from both indolent and advanced SM, but with lower/absent levels in a significant fraction of MC leukemia (MCL) and both in MCL and well-differentiated SM (WDSM) patients, respectively. In contrast, CD33 was the only marker expressed on all BMMC from every SM patient. Thus, CD33 emerges as the best potentially targetable cell-surface membrane marker in SM, particularly in advanced SM. ; This work was supported by the Fondo de Investigaciones Sanitarias (FIS) of the Instituto de Salud Carlos III (Ministerio de Economía y Competitividad, Madrid, Spain; grant number PI16/00642, FEDER), the Consejería de Educación (Regional Government of Castilla and León, Spain, grant number SA013U16), Biomedical Research Networking Center on Cancer (CIBERONC CB16/12/00400) of the Instituto de Salud Carlos III (Madrid, Spain) and grants from the Asociación Española de Mastocitosis y Enfermedades Relacionadas (AEDM 2017), Fondos de Investigación para Enfermedades Raras del Ministerio de Sanidad, Servicios Sociales e Igualdad, Ensayo clínico independiente del Ministerio de Salud y Política Social (EC11-287), Hospital Virgen de la Salud Biobank (BioB-HVS, grant PT13/0010/0007; Toledo, Spain). N D-F was supported by a grant from the Consejería de Educación (Junta de Castilla and León, Valladolid, Spain, ORDEN EDU/346/2013). A M was supported by a contract grant from the Biomedical Research Networking Center on Cancer (CIBERONC CB16/12/00400) (contract profile: 170504_CIBERONC_ORFAO_ONCG03/2017) of the Instituto de Salud Carlos III (Madrid, Spain), and JI M-G was supported by a grant from the Consejería de Educación (Junta de Castilla and León, Valladolid, Spain; ORDEN EDU/310/2015).

© 2021 by the authors. ; Monocyte/macrophages have been shown to be altered in monoclonal gammopathy of undetermined significance (MGUS), smoldering (SMM) and active multiple myeloma (MM), with an impact on the disruption of the homeostasis of the normal bone marrow (BM) microenvironment. ; This research was funded by the Biomedical Research Networking Center Consortium CIBER-CIBERONC (CB16/12/00400, CB16/12/00369 and CB16/12/00233-FEDER), PI13/01412- FEDER, from the Instituto de Salud Carlos III (ISCIII), Ministerio de Economía y Competitividad, Madrid, Spain; the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant agreement ERC-2015-AdG 695655 (TiMaScan); and the Black Swan Research Initiative of the International Myeloma Foundation (Los Angeles, CA, USA), (grant IMF13/IMF16)

© 2021 Rodríguez-Hernández, Casado-García, Isidro-Hernández, Picard, Raboso-Gallego, Alemán-Arteaga, Orfao, Blanco, Riesco, Prieto-Matos, García Criado, García Cenador, Hock, Enver, Sanchez-Garcia and Vicente-Dueñas. ; ETV6-RUNX1 is almost exclusively associated with childhood B-cell acute lymphoblastic leukemia (B-ALL), but the consequences of ETV6-RUNX1 expression on cell lineage decisions during B-cell leukemogenesis are completely unknown. Clinically silent ETV6-RUNX1 preleukemic clones are frequently found in neonatal cord blood, but few carriers develop B-ALL as a result of secondary genetic alterations. The understanding of the mechanisms underlying the first transforming steps could greatly advance the development of non-toxic prophylactic interventions. Using genetic lineage tracing, we examined the capacity of ETV6-RUNX1 to instruct a malignant phenotype in the hematopoietic lineage by cell-specific Cre-mediated activation of ETV6-RUNX1 from the endogenous Etv6 gene locus. Here we show that, while ETV6-RUNX1 has the propensity to trigger both T- and B-lymphoid malignancies, it is the second hit that determines tumor cell identity. To instigate leukemia, both oncogenic hits must place early in the development of hematopoietic/precursor cells, not in already committed B-cells. Depending on the nature of the second hit, the resulting B-ALLs presented distinct entities that were clearly separable based on their gene expression profiles. Our findings give a novel mechanistic insight into the early steps of ETV6-RUNX1+ B-ALL development and might have major implications for the potential development of ETV6-RUNX1+ B-ALL prevention strategies. ; Research in CV-D group has been funded by Instituto de Salud Carlos III through the project "PI17/00167" and by a "Miguel Servet Grant" (CPII19/00024—AES 2017–2020), co-funded by European Regional Development Fund/European Social Fund ("A way to make Europe"/"Investing in your future"). Research in the IS-G group is partially supported by FEDER and SAF2015-64420-R MINECO/FEDER, UE, RTI2018-093314-B-I00 MCIU/AEI/FEDER, UE, and by Junta de Castilla y León (UIC-017, CSI001U16, CSI234P18, and CSI144P20). The IS-G lab is a member of the EuroSyStem and the DECIDE Network funded by the European Union under the FP7 program. CV-D and IS-G have been supported by the German Federal Office for Radiation Protection (BfS)–Germany (FKZ: 3618S32274). IS-G has been supported by the Fundacion Unoentrecienmil (CUNINA project). HH was supported by a Hyundai Hope on Wheels scholar grant. GR-H was supported by FSE-Conserjería de Educación de la Junta de Castilla y León (CSI001-15). AC-G and MI-H are supported by FSE-Conserjería de Educación de la Junta de Castilla y León 2019 and 2020 (ESF—European Social Fund) fellowship, respectively (REF. CSI067-18 and CSI021-19). JR-G was supported by a scholarship from the University of Salamanca, co-financed by Banco Santander and ESF. SA-A was supported by RTI2018-093314-B-I00 MCIU/AEI/FEDER fellowship (PRE2019-088887).

This article is licensed under a Creative Commons Attribution-NoncommercialNo DerivativeWorks 3.0 Licence. ; Understanding the cellular origin of cancer can help to improve disease prevention and therapeutics. Human plasma cell neoplasias are thought to develop from either differentiated B cells or plasma cells. However, when the expression of Maf oncogenes (associated to human plasma cell neoplasias) is targeted to mouse B cells, the resulting animals fail to reproduce the human disease. Here, to explore early cellular changes that might take place in the development of plasma cell neoplasias, we engineered transgenic mice to express MafB in haematopoietic stem/progenitor cells (HS/PCs). Unexpectedly, we show that plasma cell neoplasias arise in the MafB-transgenic mice. Beyond their clinical resemblance to human disease, these neoplasias highly express genes that are known to be upregulated in human multiple myeloma. Moreover, gene expression profiling revealed that MafB-expressing HS/PCs were more similar to B cells and tumour plasma cells than to any other subset, including wild-type HS/PCs. Consistent with this, genome-scale DNA methylation profiling revealed that MafB imposes an epigenetic program in HS/PCs, and that this program is preserved in mature B cells of MafB-transgenic mice, demonstrating a novel molecular mechanism involved in tumour initiation. Our findings suggest that, mechanistically, the haematopoietic progenitor population can be the target for transformation in MafB-associated plasma cell neoplasias. © 2012 European Molecular Biology Organization | All Rights Reserved. ; MICINN (SAF2009-08803 to ISG); Junta de Castilla y León (REF. CSI007A11-2 and Proyecto Biomedicina 2009-2010 ); MEC OncoBIO Consolider-Ingenio 2010 (Ref. CSD2007-0017); Sandra Ibarra Foundation; Junta de Castilla y Leon; ARIMMORA project (FP7-ENV-2011, European Union Seventh Framework Program); Obra Social Kutxa; Conserjería de Sanidad de la Junta de Castilla y Leon ; Peer Reviewed

On behalf of the EuroFlow and PERISCOPE consortia. ; CD4+ T cells comprise multiple functionally distinct cell populations that play a key role in immunity. Despite blood monitoring of CD4+ T-cell subsets is of potential clinical utility, no standardized and validated approaches have been proposed so far. The aim of this study was to design and validate a single 14-color antibody combination for sensitive and reproducible flow cytometry monitoring of CD4+ T-cell populations in human blood to establish normal age-related reference values and evaluate the presence of potentially altered profiles in three distinct disease models—monoclonal B-cell lymphocytosis (MBL), systemic mastocytosis (SM), and common variable immunodeficiency (CVID). Overall, 145 blood samples from healthy donors were used to design and validate a 14-color antibody combination based on extensive reagent testing in multiple cycles of design–testing–evaluation–redesign, combined with in vitro functional studies, gene expression profiling, and multicentric evaluation of manual vs. automated gating. Fifteen cord blood and 98 blood samples from healthy donors (aged 0–89 years) were used to establish reference values, and another 25 blood samples were evaluated for detecting potentially altered CD4 T-cell subset profiles in MBL (n = 8), SM (n = 7), and CVID (n = 10). The 14-color tube can identify ≥89 different CD4+ T-cell populations in blood, as validated with high multicenter reproducibility, particularly when software-guided automated (vs. manual expert-based) gating was used. Furthermore, age-related reference values were established, which reflect different kinetics for distinct subsets: progressive increase of naïve T cells, T-helper (Th)1, Th17, follicular helper T (TFH) cells, and regulatory T cells (Tregs) from birth until 2 years, followed by a decrease of naïve T cells, Th2, and Tregs in older children and a subsequent increase in multiple Th-cell subsets toward late adulthood. Altered and unique CD4+ T-cell subset profiles were detected in two of the three disease models evaluated (SM and CVID). In summary, the EuroFlow immune monitoring TCD4 tube allows fast, automated, and reproducible identification of ≥89 subsets of CD4+ blood T cells, with different kinetics throughout life. These results set the basis for in-depth T-cell monitoring in different disease and therapeutic conditions. ; This work has been mainly supported by the PERISCOPE project, financed by the Innovative Medicines Initiative 2 Joint Undertaking (grant number 115910). This joint undertaking receives support from the European Union's Horizon 2020 Research and Innovation Programme, the European Federation of Pharmaceutical Industries and Associations (EFPIA), and The Bill and Melinda Gates Foundation (BMGF). The coordination and innovation processes of this study were supported by the EuroFlow Consortium. The EuroFlow Consortium received support from the FP6-2004-LIFESCIHEALTH-5 program of the European Commission (grant LSHB-CT-2006-018708) as Specific Targeted Research Project (STREP). Also, the study was partially supported by grants CB16/12/00400-FEDER [Biomedical Research Networking Center Consortium (CIBER-CIBERONC)], PI17/00399-FEDER, and PI19/01166-FEDER, Instituto de Salud Carlos III (ISCIII), Ministerio de Ciencia, Innovación y Universidades (Madrid, Spain), and a grant from Fundación Mutua Madrileña (Madrid, Spain). VB was supported by a grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (grant number 207555/2015-0; Ministério da Ciência, Tecnologia, Inovações e Comunicações, Brazil). AH-D was supported by a grant from the Agencia Estatal de Investigación (grant number DI-17-09591, Ministerio de Ciencia, Innovación y Universidades, Spain). ; Peer reviewed

The prerequisite to prevent childhood B-cell acute lymphoblastic leukemia (B-ALL) is to decipher its etiology. The current model suggests that infection triggers B-ALL development through induction of activation-induced cytidine deaminase (AID; also known as AICDA) in precursor B-cells. This evidence has been largely acquired through the use of ex vivo functional studies. However, whether this mechanism governs native non-transplant B-ALL development is unknown. Here we show that, surprisingly, AID genetic deletion does not affect B-ALL development in Pax5-haploinsufficient mice prone to B-ALL upon natural infection exposure. We next test the effect of premature AID expression from earliest pro-B-cell stages in B-cell transformation. The generation of AID off-target mutagenic activity in precursor B-cells does not promote B-ALL. Likewise, known drivers of human B-ALL are not preferentially targeted by AID. Overall these results suggest that infections promote B-ALL through AID-independent mechanisms, providing evidence for a new model of childhood B-ALL development. ; Research in CVD group is partially supported by FEDER, "Miguel Servet" Grant (CP14/00082 - AES 2013–2016) from the Instituto de Salud Carlos III (Ministerio de Economía y Competitividad), "Fondo de Investigaciones Sanitarias/Instituto de Salud Carlos III" (PI17/00167). J.H. has been supported by ERAPer Med, the German Cancer AID (Translational Oncology Program 70112951), the DKTK German Cancer Consortium Joint funding program "Targeting MYC" L*10, The German Jose Carreras Foundation (DJCLS 02R/2016), and the Kinderkrebsstiftung (2016/17). A.R.R. was supported by ERC StG BCLYM-207844, SAF2013-42767-R and SAF2016-75511-R grants and co-funding by Fondo Europeo de Desarrollo Regional (FEDER). P.D. was funded by the Asociación Española Contra el Cancer. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades (MCNU) and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). A.B. has been supported by the German Children's Cancer Foundation and the Federal Ministry of Education and Research, Bonn, Germany. Research in ISG group is partially supported by FEDER and by SAF2015-64420-R MINECO/FEDER, UE, RTI2018-093314-B-I00 MCIU/AEI/FEDER, UE, by Junta de Castilla y León (UIC-017, CSI001U16, and CSI234P18). I.S.G. lab is a member of the EuroSyStem and the DECIDE Network funded by the European Union under the FP7 program. A.B. and I.S.G. have been supported by the German Carreras Foundation (DJCLS R13/26) and by the German Federal Office for Radiation Protection (BfS)-Germany (FKZ: 3618S32274). G.R.H., A.C.-G and S.G.T.D. were supported by FSE-Conserjería de Educación de la Junta de Castilla y León (CSI001-15, CSI067-18 and CSI003-17, respectively). F.A. was supported by a Deutsche Forschungsgemeinschaft (DFG) fellowship (AU 525/1-1). ; Peer reviewed

© The Author(s). ; Recurrent deletions of the CDKN2A/ARF/CDKN2B genes encoded at chromosome 9p21 have been described in both pediatric and adult acute lymphoblastic leukemia (ALL), but their prognostic value remains controversial, with limited data on adult T-ALL. Here, we investigated the presence of homozygous and heterozygous deletions of the CDKN2A/ARF and CDKN2B genes in 64 adult T-ALL patients enrolled in two consecutive trials from the Spanish PETHEMA group. Alterations in CDKN2A/ARF/CDKN2B were detected in 35/64 patients (55%). Most of them consisted of 9p21 losses involving homozygous deletions of the CDKNA/ARF gene (26/64), as confirmed by single nucleotide polymorphism (SNP) arrays and interphase fluorescence in situ hybridization (iFISH). Deletions involving the CDKN2A/ARF/CDKN2B locus correlated with a higher frequency of cortical T cell phenotype and a better clearance of minimal residual disease (MRD) after induction therapy. Moreover, the combination of an altered copy-number-value (CNV) involving the CDKN2A/ARF/CDKN2B gene locus and undetectable MRD (≤ 0.01%) values allowed the identification of a subset of T-ALL with better overall survival in the absence of hematopoietic stem cell transplantation. ; This project was supported by the Asociación Española Contra el Cáncer, AECC (project ref.: GC16173697BIGA), by CERCA Program/Generalitat de Catalunya, the Catalan Government: 2014-SGR225 (GRE), Obra Social "La Caixa" and by Celgene Spain. E. Genescà is the recipient of agrant from the Spanish Health Ministry (ISCIII, CA12/00468) and an unrestricted grant from Gilead.A. Gonzalez-Perez is supported by a Ramon y Cajal fellowship (RYC-2013-14554) of the Educational Ministry (Madrid, Spain). This work was also partially supported by FEDER funds from the ISCIII (PT13/0010/0026, CIBERONC (CB16/12/00284 and CB16/12/00400), Madrid, Spain).

Recurrent deletions of the CDKN2A/ARF/CDKN2B genes encoded at chromosome 9p21 have been described in both pediatric and adult acute lymphoblastic leukemia (ALL), but their prognostic value remains controversial, with limited data on adult T-ALL. Here, we investigated the presence of homozygous and heterozygous deletions of the CDKN2A/ARF and CDKN2B genes in 64 adult T-ALL patients enrolled in two consecutive trials from the Spanish PETHEMA group. Alterations in CDKN2A/ARF/CDKN2B were detected in 35/64 patients (55%). Most of them consisted of 9p21 losses involving homozygous deletions of the CDKNA/ARF gene (26/64), as confirmed by single nucleotide polymorphism (SNP) arrays and interphase fluorescence in situ hybridization (iFISH). Deletions involving the CDKN2A/ARF/CDKN2B locus correlated with a higher frequency of cortical T cell phenotype and a better clearance of minimal residual disease (MRD) after induction therapy. Moreover, the combination of an altered copy-number-value (CNV) involving the CDKN2A/ARF/CDKN2B gene locus and undetectable MRD (≤ 0.01%) values allowed the identification of a subset of T-ALL with better overall survival in the absence of hematopoietic stem cell transplantation. ; We would like to thank Ernest Terribes for his advice and help in qPCR design andanalysisaswellasAlbaGarcíaandJes ús-María Hernández-Rivas for providing some DNA samples. We are grateful to Isabel Granada for her helpful advice regarding cytogenetic and FISH analyses. This project was supported by the Asociación Española C ontra el Cáncer, AECC (project ref.: GC16173697BIGA), by CERCA Program/Generalitat de Catalunya, the Catalan Government: 2014-SGR225 (GRE), Obra Social " La Caixa " and by Celgene Spain. E. Genescà is the recipient of agrant from the Spanish Health Ministry (ISCIII, CA12/00468) and an unrestricted grant from Gilead.A. Gonzalez-Perez is supported by a Ramon y Cajal fellowship (RYC-2013-14554) of the Educational Ministry (Madrid, Spain). This work was also partially supported by FEDER funds from the ...

The prerequisite to prevent childhood B-cell acute lymphoblastic leukemia (B-ALL) is to decipher its etiology. The current model suggests that infection triggers B-ALL development through induction of activation-induced cytidine deaminase (AID; also known as AICDA) in precursor B-cells. This evidence has been largely acquired through the use of ex vivo functional studies. However, whether this mechanism governs native non-transplant B-ALL development is unknown. Here we show that, surprisingly, AID genetic deletion does not affect B-ALL development in Pax5-haploinsufficient mice prone to B-ALL upon natural infection exposure. We next test the effect of premature AID expression from earliest pro-B-cell stages in B-cell transformation. The generation of AID off-target mutagenic activity in precursor B-cells does not promote B-ALL. Likewise, known drivers of human B-ALL are not preferentially targeted by AID. Overall these results suggest that infections promote B-ALL through AID-independent mechanisms, providing evidence for a new model of childhood B-ALL development. ; Research in CVD group is partially supported by FEDER, "Miguel Servet" Grant (CP14/00082 - AES 2013–2016) from the Instituto de Salud Carlos III (Ministerio de Economía y Competitividad), "Fondo de Investigaciones Sanitarias/Instituto de Salud Carlos III" (PI17/00167). J.H. has been supported by ERAPer Med, the German Cancer AID (Translational Oncology Program 70112951), the DKTK German Cancer Consortium Joint funding program "Targeting MYC" L*10, The German Jose Carreras Foundation (DJCLS 02R/2016), and the Kinderkrebsstiftung (2016/17). A.R.R. was supported by ERC StG BCLYM-207844, SAF2013-42767-R and SAF2016-75511-R grants and co-funding by Fondo Europeo de Desarrollo Regional (FEDER). P.D. was funded by the Asociación Española Contra el Cancer. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades (MCNU) and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). A.B. has been supported by the German Children's Cancer Foundation and the Federal Ministry of Education and Research, Bonn, Germany. Research in ISG group is partially supported by FEDER and by SAF2015-64420-R MINECO/FEDER, UE, RTI2018-093314-B-I00 MCIU/AEI/FEDER, UE, by Junta de Castilla y León (UIC-017, CSI001U16, and CSI234P18). I.S.G. lab is a member of the EuroSyStem and the DECIDE Network funded by the European Union under the FP7 program. A.B. and I.S.G. have been supported by the German Carreras Foundation (DJCLS R13/26) and by the German Federal Office for Radiation Protection (BfS)-Germany (FKZ: 3618S32274). G.R.H., A.C.-G and S.G.T.D. were supported by FSE-Conserjería de Educación de la Junta de Castilla y León (CSI001-15, CSI067-18 and CSI003-17, respectively). F.A. was supported by a Deutsche Forschungsgemeinschaft (DFG) fellowship (AU 525/1-1). ; Sí

The impact of LMO2 expression on cell lineage decisions during T-cell leukemogenesis remains largely elusive. Using genetic lineage tracing, we have explored the potential of LMO2 in dictating a T-cell malignant phenotype. We first initiated LMO2 expression in hematopoietic stem/progenitor cells and maintained its expression in all hematopoietic cells. These mice develop exclusively aggressive human-like T-ALL. In order to uncover a potential exclusive reprogramming effect of LMO2 in murine hematopoietic stem/progenitor cells, we next showed that transient LMO2 expression is sufficient for oncogenic function and induction of T-ALL. The resulting T-ALLs lacked LMO2 and its target-gene expression, and histologically, transcriptionally, and genetically similar to human LMO2-driven T-ALL. We next found that during T-ALL development, secondary genomic alterations take place within the thymus. However, the permissiveness for development of T-ALL seems to be associated with wider windows of differentiation than previously appreciated. Restricted Cre-mediated activation of Lmo2 at different stages of B-cell development induces systematically and unexpectedly T-ALL that closely resembled those of their natural counterparts. Together, these results provide a novel paradigm for the generation of tumor T cells through reprogramming in vivo and could be relevant to improve the response of T-ALL to current therapies. ; J.H. has been supported by the German Cancer Aid (Project 110997 and Translational Oncology Program 70112951), the German Jose Carreras Leukemia Foundation (DJCLS 02R/2016), Deutsches Konsortium für Translationale Krebsforschung (DKTK), Joint funding (Targeting MYC L*10), the Kinderkrebsstiftung (2016/17), and the "Elterninitiative Kinderkrebsklinik e.V. Düsseldorf". SG has been supported by a scholarship of the Hochschule Bonn-Rhein-Sieg. AB has been supported by the German Children's Cancer Foundation and the Federal Ministry of Education and Research, Bonn, Germany. Research in ISG group is partially supported by FEDER and by MINECO (SAF2012-32810, SAF2015-64420-R, and Red de Excelencia Consolider OncoBIO SAF2014-57791-REDC), Instituto de Salud Carlos III (PIE14/00066), ISCIII- Plan de Ayudas IBSAL 2015 Proyectos Integrados (IBY15/00003), by Junta de Castilla y León (BIO/SA51/15, CSI001U14, UIC-017, and CSI001U16), Fundacion Inocente Inocente, and by the ARIMMORA project (European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 282891). ISG Lab is a member of the EuroSyStem and the DECIDE Network funded by the European Union under the FP7 program. AB and ISG have been supported by the German Carreras Foundation (DJCLS R13/26). IGR was supported by BES-Ministerio de Economía y Competitividad (BES-2013-063789). AML and GRH were supported by FSE-Conserjería de Educación de la Junta de Castilla y León (CSI001-13, CSI001-15). Research in CVD group is partially supported by FEDER, "Miguel Servet" Grant (CP14/00082—AES 2013-2016) from the Instituto de Salud Carlos III (Ministerio de Economía y Competitividad), "Fondo de Investigaciones Sanitarias/Instituto de Salud Carlos III" (PI17/00167), and by the Lady Tata International Award for Research in Leukaemia 2016–2017.