Idiopathic Chronic Thrombocytopenia of Undetermined Significance (ICTUS): pathogenesis and biomarker – ICTUS

Acquired chronic isolated thrombocytopenias are frequent disorders. Most of them are related to an auto-antibody mediated destruction leading to the diagnosis of Immune Thrombocytopenic Purpura (ITP). We previously demonstrated that some of these ITP are not due to an immune disorder, but rather are acquired hematological diseases characterized by a pure defect in platelet production. Indeed, we describe a defect of proplatelet formation by megakaryocytes (MKs). These thrombocytopenia are thus a form of a recent entity called idiopathic cytopenia of undetermined significance (ICUS), that we will call idiopathic chronic thrombocytopenia of undetermined significance (ICTUS). In a few women with ICTUS, we could demonstrate a clonal hematopoiesis by X inactivation skewing. Therefore we hypothesize that ICTUS is a form of clonal hematopoiesis of indeterminate potential (CHIP) in the majority of cases. As we have previously demonstrated that Bcl-xL, an anti-apoptotic molecule of the Bcl2 family is indispensable for proplatelet formation in mouse, we investigated if ICTUS was related to a Bcl-xL downregulation in MKs and platelets. Our preliminary results confirm this hypothesis both at the level of the protein and mRNA in around 50% of the cases. In this project we aim to amplify these preliminary results by precisely identifying this new entity and the mechanism of the thrombocytopenia. In addition we expect to facilitate its diagnosis by developing biomarkers; 1) the level of Bcl-xL in platelets and 2) a specific targeted NGS (New Generation Sequencing). Such an approach will permit to greatly improve the diagnosis of ICTUS and to facilitate therapeutic strategies.
To reach this goal, our project is divided into 4 scientific work packages (WP). In the first WP we will recruit the patient cohorts and their controls. Using this cohort, we want to demonstrate the existence of a clonal disorder and find the somatic mutation profile associated with ICTUS. This will be performed through a pangenomic approach including Whole Exome Sequencing, targeted NGS as well as CGH arrays and RNA-seq. The second WP will be entirely devoted to Bcl-xL: determine the frequency of Bcl-xL downregulation in ICTUS platelets and decipher the mechanisms of Bcl-xL down-regulation, and especially understand the link between clonality and Bcl-xL expression. In the third WP, we will study the mechanisms of the thrombocytopenia. This WP will be mostly focused on the role of Bcl-xL in human megakaryopoiesis. We will also determine whether Bcl-xL rescue will correct the proplatelet formation defect in ICTUS. In patients without Bcl-xL down-regulation we will investigate the mechanisms of thrombocytopenia guided by the transcriptomic analysis. In the last WP we will test the specificity and efficiency of Bcl-xL quantification as a biomarker for ICTUS. We will develop new specific antibodies against Bcl-xL that can be used in flow cytometry in routine to precisely decipher the level of Bcl-xL in platelets. Furthermore by the genomic approach we may define a specific panel for targeted NGS, which will facilitate the diagnosis of ICTUS .
This project will be rendered possible by the tight collaboration of three partners, two partners on the scientific part and one clinical team centralized in the university hospital of Bordeaux. The two scientific partners have a major expertise in megakaryopoiesis (cell and molecular biology) and have previously worked together. The coordinator Chloe James has performed all the preliminary works and defined this new entity. The clinical partners have an internationally recognized expertise in thrombocytopenia and are teams of references in ITP in France. They will greatly facilitate a precise clinical identification of this new entity.
At the end of this project we expect to have greatly improved the diagnosis of acquired chronic isolated thrombocytopenia and to have precisely defined the pathogenesis of ICTUS.