Functional haematopoietic progenitor cells in the adult human lung.

The bone marrow is classically viewed as the main site of blood cell production in adults, however, rare pools of haematopoietic stem and progenitor cells with self-renewal and differentiation potential have been described in extramedullary organs. The lung is primarily known for its role in gas exchange but has recently been identified as a site of blood (platelet) production in mice. Here, we show that functional haematopoietic precursors reside in the extravascular spaces of the human lung, at a frequency similar to the bone marrow, and are capable of proliferation and engraftment. Comparative transcriptomic profiling of pulmonary and medullary CD34 + haematopoietic progenitor cells revealed organ-specific gene signatures and indicated greater baseline activation of immune, megakaryocyte/platelet and erythroid-related pathways in progenitors from the lung. In the lung, these cells predominately reside in the vascular-rich alveolar interstitium and near macrophages. These results identify the lung as an important niche for uniquely programmed blood stem and progenitor cells with considerable potential to support haematopoiesis in humans.