Immunologic reconstitution in ADA^−/− mice treated with PEG-ADA, GT, and BMT. (A) After 18 weeks (wks), white blood cell counts (WBC) significantly increase in PEG-ADA–treated mice (n = 12) compared with GT (n = 8) or BMT (n = 15) treated ADA^−/− mice and ADA^+/+ mice (n = 17). Data are mean ± SD. *P < .05. (B) Compared with control groups, platelet (PLT) counts in PEG-ADA–treated mice significantly decrease after 18 weeks of treatment. Data are mean ± SD. **P < .005. Absolute numbers of PB lymphocyte populations measured by FACS analyses as percentage of WBC counts, at weeks 10, 14, and 18. Data are mean ± SEM. (C) CD4⁺ T cells. (D) CD8⁺ T cells. (E) B220⁺ B cells. *P = .05-.005. **P = .005-.0005. (B-E) PEG-ADA–treated ADA^−/− (n = 12), GT-treated ADA^−/− (n = 8), BMT-treated ADA^−/− (n = 15), and ADA^+/+ mice (n = 17). (F) IgG1 (ng/mL × 10⁷) serum immunoglobulin levels in PEG-ADA (n = 7), GT (n = 6), or BMT treated ADA^−/− mice (n = 10) compared with ADA^+/+ (n = 7) and 3-week-old ADA^−/− (n = 6) and ADA^+/+ (n = 6) mice. Data are mean ± SD.