Expression of human adenosine deaminase in murine haematopoietic progenitor cells following retroviral transfer

Adenosine deaminase (ADA) deficiency, an autosomal recessive inborn error of metabolism, leads to severe combined immune deficiency in man 1 . This enzyme, although constitutively expressed in most tissues, is expressed at high level in immature T cells, and study of the pathophysiology of the disorder indicates that increased deoxyadenosine or altered methylation capacity have toxic effects on T-cell maturation 1 . Although bone marrow transplantation can correct the immune deficiency 2,3 , this therapy is associated with graft-versus-host disease and incomplete immune restoration,and so our laboratory and others have sought to develop a method of gene replacement as a possible treatment for the disease 4 . Moreover, characterization of the complementary DNA of the human ADA gene and some of its mutants 5,6 makes it possible to design gene transfer strategies. We have now sub-cloned a human adenosine deaminase cDNA into the retrovirus shuttle vector pZIP-SV(B),and in this way have isolated a cell line, 4.2T, which produces high titres of replication-defective retro-virus which have been used to transfer the gene for human ADA to mouse bone marrow cells. Transfer and expression of the neomycin-resistance gene ( neo ) and the ADA gene in murine bone marrow colony-forming units (CFU) was demonstrated by in vitro colony formation in the presence of the antibiotic G418 or 9-xylofuranosyladenine plus deoxycoformycin, respectively.Isoenzyme analysis also showed human ADA expression in the cultured mouse bone marrow.