A method of selecting a patient of high WT1 vaccine response on the basis ofthe frequency of WT1-specific CTL precursor cells as an indicator； adiagnostic agent for the selection； etc. In particular, there is provided, forexample, a method of selecting a patient of high WT1 vaccine response,comprising the step (a) of isolating a biosample containing CTL precursorcells from a subject patient； the step (b) of measuring the existencefrequency or amount of WT1-specific CTL precursor cells present in thebiosample (a)； and the step (c) of adjudicating on whether or not the resultsof the measurement (b) are high as compared with those of healthy people andjudging the responsiveness to WT1 vaccine.
