Development of scFv(FRP5)-ETA-specific antibodies after treatment. Relative levels of scFv(FRP5)-ETA-specific antibodies induced in patients by the treatment were determined by ELISA with plates coated with the antibody toxin. Sera taken on day 0 before treatment, and sera taken at the indicated days after onset of therapy were diluted 1:50 for analysis. The baseline was determined using several human control sera negative for scFv(FRP5)-ETA-specific antibodies (not shown). Dose levels and patients are indicated.