Ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase1, ENTPD1, or CD39) is an enzyme that catalyzes the phosphohydrolysis of extracellular adenosine triphosphate (eATP) and diphosphate (eADP), that are released following inflammatory stress and cell injury, to adenosine monophosphate (AMP). AMP is then used by the ecto-5’-nucleotidase CD73 to synthesize adenosine¹.

Hydrolysis of adenosine triphosphate and adenosine diphosphate, performed by CD39, suppresses the immune system and inhibits T-cell and Natural killer (NK) cell responses. This inhibition has a role in promoting Chronic lymphocytic leukemia (CLL) and hence it is proposed that blockade or inhibition of CD39 may be a target for new immune therapy for CLL². CD39 activity is also related to the occurrence of calcific aortic valve disease (CAVD)³, and to various other types of immune responses⁴. In addition, CD39 plays a dominant role in the purinergic regulation of inflammation¹.

The transcription of CD39 is constitutive in microvascular endothelium and certain immune cells. The modulated expression of NTPDase1 has been closely associated with inflammatory cytokines, oxidative stress and hypoxia in vitro and in vivo⁵.

Localization of CD39 within lipid rafts suggests that this ecto-enzyme may be involved in cell-cell contact and signaling⁶.

CD39 is a part of the ectonucleoside triphosphate dyphosphohydrolases (eNTDPase) protein family which shares a unique structural feature: instead of being anchored in the membrane by a single transmembrane domain or lipid link like other ectoenzymes, these proteins contain two transmembrane domains, one at each end of the protein. The active site lies in the large extracellular region. In addition, all family members share a set of short sequences termed apyrase conserved regions (ACRs)⁷.