Immunophenotype and lymphocyte function at 16 days after neonatal BMT. All mice were age-matched (16 days) in the experimental arms: (1) Ada^−/− (n = 4), (2) Ada^−/− ERT (n = 4), (3) Ada^−/− BMT (n = 7), and (4) Ada^+/+ (n = 5). *Significantly higher than untreated ADA-deficient mice (P < .001). **Significantly higher than untreated ADA-deficient mice (P < .007). Data are means plus or minus SEM. (A) Absolute numbers of thymocytes and splenocytes. (B) Absolute numbers in each thymocyte subpopulation (CD4⁺, CD8⁺, double-positive (DP): CD4⁺, CD8⁺, double-negative (DN): CD4⁻, CD8⁻) were calculated by multiplying the total numbers of cells collected from the thymus by the percentage of cells in each subpopulation. (C) Absolute numbers in each splenocyte subpopulation (CD4⁺, CD8⁺, CD19⁺) were calculated by multiplying the total numbers of cells collected from the spleen by the percentage of cells in each subpopulation. (D) Lymphocyte proliferative function was assessed by stimulating splenocytes with concanavalin A (conA) for 48 hours, pulsing with ³H-thymidine for 20 hours, and determining the stimulation index compared with cells not treated with ConA.