Enzyme replacement and other biochemical approaches to the therapy of adenosine deaminase deficiency.

Addition of adenosine deaminase (ADA) restored in vitro responses of lymphocytes from a patient with ADA deficiency and severe combined immunodeficiency (SCID). Enzyme replacement therapy, using red blood cells as a source of encapsulated human ADA, restored both T and B cell function in this patient. Ten other ADA--SCID patients have been treated with this form of enzyme replacement and five have responded to therapy. Lymphocytes from ADA--SCID patients treated with enzyme replacement become immunocompetent but remain enzyme deficient. Studies of these cells provide evidence supporting both cyclic AMP- and dATP-mediated immunosuppressive mechanisms in ADA--SCID. These observations suggest that inhibition of cyclic AMP synthesis and/or deoxycytidine (and possibly thymidine) supplementation may be useful new biochemical approaches to the therapy of ADA--SCID.