Subclasses of anti-hFVIII IgG immunoglobulin in hemophilia A mice after naked plasmid transfer of pBS-HCRHPI-hFVIIIA with or without immunomodulation (costimulation blockade). Titers of subclasses of IgG including IgG1, IgG2a, IgG2b, and IgG3 produced at 2 months following gene transfer were determined by IgG subclass-specific ELISA. All animals treated as described in Figure 3 were tested, and their levels were averaged except that in the MMF-treated group, the IgG levels from only 3 mice that developed inhibitors were averaged.