Studies by our own group: We have developed N2-derived vectors which 
contain an ADA cDNA under the transcriptional control of a variety of different 
promoters, including the SV40 early gene promoter (the SAX vector), the human 
cytomegalovirus immediate early gene promoter (CAX), the murine major 
histocompatibility locus H2-D promoter (HAX), the human beta-actin gene 
promoter (BAX), and the herpes viral thymidine kinase gene promoter (TAX). 
Whereas all of these constructs allowed the generation of high titer virus, and 
efficiently expressed both neomycin phosphotransferase (NPT) and ADA activity 
In murine fibroblasts as well as in ADA-deficient lymphocytes in culture (see 
below), none expressed either ADA or NPT activity in mouse CFU-S (Table T3 and 
Zwiebel et al.. 1986). More recently we have detected ADA expression In mouse 
CFU-S following infection with a vector containing only the ADA cDNA driven off 
the mouse LTR (unpublished results). 
In summary, studies In mice, both In vitro and In vivo, have demonstrated 
that retroviral vectors are capable of transferring the human ADA gene into 
mouse stem cells In an efficient and stable manner. Expression of these 
vectors, described in detail in Section I . B . 2 . b below, is negative for some 
constructs and positive for others. 
II. Studies in Monkeys: 
In order to develop a protocol which might be a useful model for gene 
therapy in humans, a collaboration was established between NIH and the Bone 
Marrow Transplantation Program at the Memorial Sloan Kettering Cancer Center. 
Cynomolgus monkey bone marrow was infected with the ADA vector SAX and the 
infected bone marrow cells were used to autologously reconstitute the lethal ly 
Irradiated donor animal (see Kantoff et al.. J. Exp. Med., in press; copy 
provided in Appendix B). Of the six animals studied, two died due to failure 
to engraft because of excessive loss of bone marrow cells that resulted from 
the use of the Initial infection protocol (cocultivation). By performing 
Recombinant DNA Research, Volume 12 (27) 
