A neo cassette replaces exon 3 of the ecto-5' nucleotidase (Nt5e) gene, abolishing CD73 enzyme activity. A shorter transcript is produced at about 10% of WT levels, but no functional protein is detectable. Nt5e encodes Cd73, a membrane-bound glycoprotein expressed on many cell types including subsets of T and B lymphocytes including regulator T cell (Tregs), endothelial cells, and mesenchymal cells. CD73 can hydrolyze nucleoside monophosphates, such as AMP, into bioactive intermediates like adenosine. CD73-generated adenosine activates transmembrane adenosine receptors and can act as either a pro- or anti-inflammatory mediator. Adenosine also regulates endothelial permeability, platelet activation, leukocyte adhesion, and lymphocyte migration into draining lymph nodes after an inflammatory stimulus. CD73-dependent adenosine receptor signaling protects mice during renal ischemia and inhibits vascular leakage during hypoxia. CD73 inhibits antitumor immune responses and is tolerogenic for cardiac and airway allografts. Homozygous CD73-/- mice are viable and fertile. Under hypoxic conditions, these CD73-deficient mice exhibit increased vascular leakage and display increased edema in all organs except the brain. CD73 deficient mice are protected from experimental autoimmune encephalomyelitis (EAE). The severity of graft-vs-host disease (GVHD) is increased in these mice, as are anti-tumor immune responses.
