Serum immunoglobulin levels 2 or more years after gene therapy. Serum IgM (A) and IgA (B) levels were measured in all subjects and IgG (C) in the 4 subjects who discontinued IgRT. Horizontal dashed red line indicates lower limits of normal. Horizontal bars in each patient’s data points represent medians. The numbers in parentheses in panel C represent the time (months) after GT that IgRT was stopped.