Deficiency of CD73/Ecto-5'-Nucleotidase Enhances Acute Graft-Versus-Host Disease

Abstract 312

Acute graft-versus-host disease (GvHD) limits the success of allogeneic hematopoietic cell transplantation (allo-HCT). We have recently shown that extracellular adenosine triphosphate (ATP) enhances GvHD by activation of the purinergic receptor P2X₇R. The abundance of extracellular ATP is regulated by ecto-nucleotidases such as CD39, which dephosphorylate ATP to ADP and AMP. Ecto-5'-nucleotidase (CD73) degrades AMP to adenosine, which can itself exert tolerogenic functions via activation of A_2A and/or A_2B adenosine receptors (AR). Extracellular ATP and adenosine have immunoregulatory roles under different inflammatory conditions. Deficiency of CD73, the enzyme that metabolizes AMP to adenosine, could therefore have pro- or antiinflammatory activity by reducing adenosine levels in the microenvironment. Currently, the roles of CD73 and adenosine in GvHD are unclear.

By using cd73^−/− donor or recipient mice and a specific CD73/ecto-5'-nucleotidase inhibitor we observed enhanced GvHD severity when CD73 was genetically deleted or pharmacologically blocked. CD73 was upregulated on CD4⁺ and CD11c⁺ cells after irradiation, suggesting an inducible rescue mechanism along with CD39 to counteract ATP accumulation resulting from tissue damage due to the preconditioning treatment. CD73 deficiency led to enhanced T cell expansion and IFN-γ and IL-6 production in GvHD mice. Migratory capacity of cd73^−/− T cells was increased, compatible with the ability of adenosine to inhibit transendothelial migration. A_2A receptor deficiency led to increased numbers of proliferating allogeneic T cells in allo-HCT recipient mice, suggesting that signaling through the A_2A receptor via CD73-generated adenosine is a significant part of the mechanism by which CD73 limits the severity of GvHD. Furthermore, pharmacological blockade of CD73 improved graft-versus-tumor activity in an in vivo B cell leukemia model.

In conclusion, we demonstrate that CD73 plays a protective role in GvHD with enhanced disease severity in its absence, while blocking CD73 led to increased graft-versus-tumor effect. These data have potential clinical implications as the alloimmune response could be enhanced by CD73 blocking in patients with residual tumor burden after transplantation. Conversely, immune modulation by addition of CD73 enzyme or an adenosine receptor agonist could improve the outcome of GvHD patients.