ENTPD1 and myeloid sarcoma: The increase in CD39 expression in Tregs and in CD39 activity in PMBCs during a RR-MS exacerbation showed here might be an attempt to counterbalance the partial dysfunction of Treg cells in MS patients7,8, by mobilizing activated CD39+ Tregs from the lymphoid organs, showing an increased CD39 expression and activity due to the pro-inflammatory status found during a relapse in a MS patient.