Lmo2 expression defines tumor cell identity during T-cell leukemogenesis

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