The invention provides polynucleotides isolated from cDNA libraries of human fetal liver-spleen and macrophage as well as polypeptides encoded by these polynucleotides and mutants or variants thereof. The polypeptides correspond to a human CD39-like protein. Other aspects of the invention include vectors containing polynucleotides of the invention and related host cells as well a processes for producing CD39-like polypeptides, and antibodies specific for such polypeptides.