"Background: Altered high-density lipoprotein (HDL)-cholesterol homeostasis has been observed in hematologic malignancies but genetic evidences proving causality have been lacking. The ability of HDL to promote cholesterol efflux depends on two ATP-binding cassette transporters ABCA1 and ABCG1, which exhibit anti-myeloproliferative activity in preclinical mouse models.Hypothesis: Somatic mutations in ABCA1 and ABCG1 may be observed in myeloproliferative disorders and could be functionally inactive disabling both cholesterol efflux and anti-tumor activity.Preliminary data: Five new somatic mutations in ABCA1 were identified out of 26 tumor samples from patients with chronic myelomonocytic leukaemia (CMML) with an unexpected frequency of 19% and conferred a proliferative advantage when transfected into HEK293 cells.Aims: The aim of this study is to 1) test the functional relevance of newly identified ABCA1 mutants on myeloproliferative diseases and 2) apprehend the molecular mechanisms that could provide a proliferative advantage to these mutants.Methods: We will take advantage of the generation of these mutants to test their relevance (Aim. 1) and mechanisms of action (Aim. 2) both in vitro in relevant myeloblast cell lines and in vivo by performing a transplantation of bone marrow cells transduced with these mutants.Keywords: Leukaemia, HDL cholesterol, ATP-binding cassette transporters, human somatic mutations"