Reactivity of canine postvaccinate sera to endogenous human and canine tyrosinase. Cultured human melanoma cells SK-MEL-188, canine melanoma cells CML 83-2, and canine MDCK cells were permeabilized and incubated with sera (diluted 1:500) from patients A (panel a; 100 µg huTyr DNA dose), B (b; 100 µg huTyr DNA dose), and C (c; 1500 µg huTyr DNA dose). Flow cytometry analysis showed an increase in mean fluorescence intensity for melanoma cells (but not canine MDCK cells) stained by the postvaccinate and recheck sera, and not by preimmune sera or secondary antibodies. This indicates specific recognition of cells expressing human or canine tyrosinase by the antibodies induced in the postvaccinate canine sera. Data shown are representative of two independent flow analyses for each patient.