Absolute lymphocyte counts and proliferative responses after gene transfer. (A) Results from subjects not receiving busulfan conditioning and remaining on ERT (201-204) and (B) results from subjects having PEG-ADA ERT withdrawn and receiving busulfan before transplantation (301-306). n.v. indicates normal values for age range. The time when ERT was resumed for subjects 304 and 306 is indicated. (C) Proliferative responses to PHA of PBMC from subjects over time. Open symbols represent subjects remaining on ERT and not receiving busulfan; filled symbols represent subjects receiving busulfan with ERT stopped.