Transient nonneutralizing anti-cFIX antibodies develop at high doses of of AAV2-cFIX vector delivered via ATVRX. (A) Canine FIX transgene antigen levels measured by ELISA. (B) Anti-cFIX IgG1 and IgG2 subclass antibody titer measured by ELISA. (C-D) Blood coagulation activity measured by WBCT (m indicates minutes) and aPTT (s indicates seconds). (E) Creatinine phosphokinase (CPK) levels. Shaded gray areas indicate the range of values for hemostatically normal animals. Vertical arrows represent normal pooled plasma administrations. x axis represents time in days.