Lymphatic vessels play a crucial role in the drainage of interstitial fluids. Vascular lymphatic insufficiency leads to the formation of lymphedema which result in the swelling of a part of the body due to the accumulation of fluids. In breast cancer, near 15% of patients who have undergone axillary lymph node dissection develop a lymphedema of the arm. The consequences are disabling and remain without efficient treatment. Transplantation of stem cells and/or precursor cells of the lymphatic endothelium to regenerate a functional lymphatic vessel network is one of the therapeutic strategies currently under development.

Therefore, there is a particular interest in identifying and characterizing the factors and the regulatory mechanisms involved in the differentiation of stem cells in this cell lineage, as well as in the expansion of lymphatic progenitors and their progeny. Researchers from our laboratory, previously established ^[1] that BMP9 (Bone Morphogenetic Protein 9) displayed a role in lymphatic endothelium maturation and valve formation. They had also shown that the co-culture of embryonic stem (ES) cells-derived vascular progenitors on a stromal cell layer allowed the production of lymphatic endothelial precursors ^[2]. 
These researchers now identify another role for BMP9 in the early steps of murine ES cell differentiation: they show that the addition of low amounts of BMP9 allows the expansion of this population of cell precursors ^[3].

These studies, which need to be further validated with human stem cell models, allow to consider the use of BMP9 to expand in vitro a population of lymphatic cell precursors, before transplantation aimed at reconstructing in humans a functional lymphatic vessel network.