Background Hematopoietic stem cell (HSC) transplantation is a standard procedure in the treatment of hematological disorders and also applicable to support aggressive chemotherapy in cancer. In practice, the clinical outcome is often limited by inefficient bone marrow (BM) engraftment or by low numbers of available stem cells. It would therefore be desirable to enhance engraftment by pharmacological stimulation. HSC require several signals for successful migration into the bone marrow. One of these signals is provided by stimulation of Gas[1]. Pretreatment with prostaglandin (PG) E2 enhances engraftment via activation of Gas-coupled EP2 and EP4 receptors [2]. Treprostinil is a stable analogue of prostacyclin/PGI2, which acts via IP, EP2 and EP4 receptors and is approved for treatment of pulmonary hypertension. Here we tested the hypothesis that treprostinil stimulates stem cell engraftment.