γ-retroviral−mediated gene transfer into murine ADA-deficient marrow cells. BM cells from Ada−/− donor mice were transduced with the MMA γ-retroviral vector and administered to age-matched ADA-deficient recipients conditioned either with 200 or 900 cGy of TBI. After transplantation, the recipients were either maintained on PEG-ADA ERT (+ERT) or not (−ERT). (A) Map of the MMA γ-retroviral vector construct carrying a normal human Ada cDNA (HuAda). EcoRV restriction sites in the long-terminal repeats are indicated. SA (splice acceptor site), SD (splice donor site), and residual sequences from the Moloney Murine Leukemia Virus gag and env 5′-untranslated region (env utr) are indicated. (B) VCN by qPCR of BM harvested from Ada−/− donors after transduction with the MMA vector for 5 separate transplantation experiments.