Percent of patients with rank titers for antibodies to DAB₃₈₉IL-2, DT, and IL-2 by course. Relative rank titers are shown with the following designations: rank titer 1, dilution, 1:5; rank titer, 2 to 3, dilution, 1:25 to 1:125; rank titer, 4 to 5, dilution, 1:625 to 1:3125; rank titer, 6, dilution, 1:15625.