Reconstitution of T-cell function following intravenous gene therapy. (A) Proliferation of PBMCs from in vivo–treated dog 1547 following stimulation with IL-2 as determined by BrdU incorporation by flow cytometry. (B) Flow cytometry analysis for STAT5 phosphorylation in PBMCs from dog 1547 following IL-2 stimulation. A proliferative response and phosphorylation of STAT5 are evident primarily in GFP⁺ cells. Controls from age-matched normal dogs are shown in the top panels. (C) Comparison of STAT5 phosphorylation in PBMCs from an untreated XSCID dog and a normal dog (gray line indicates prestimulation; black line, after IL-2 stimulation).