ADA and severe combined immunodeficiency: The immunomodulatory role of Ado has been first described back to the early 70s, with the discovery of its role in the development and function of different immune cell populations [4], in parallel with the first report linking a defective Ado metabolism (Ado deaminase, ADA, deficiency) with the onset of severe combined immunodeficiency (ADA-SCID) [5].