Pattern of serological immune responses. Sera from four patients known to have anti-NY-ESO-1 antibody responses were either analyzed on yeast induced to express NY-ESO-1 protein (filled symbols) or an irrelevant antigen as negative controls (open symbols). The reciprocal dilution factor is shown on the x-axis. According to prior experiments (data not shown), a sample at a particular dilution was determined to be positive if the ratio between the fluorescence intensity on NY-ESO-1 protein expressing yeast and that on non-induced yeast exceeded two. All assays were repeated three times. Sera from patients without NY-ESO-1 antibody responses were used as controls (data not shown).