In one aspect, the present invention provides, for example, an improved method for identifying an epitope on a protein, comprising the following steps: (A) contacting a major histocompatibility complex (MHC molecule)-expressing cell differentiated from a stem cell or a progenitor cell derived therefrom with a target protein； (B) isolating a complex of a peptide contained in the target protein and the MHC molecule from the MHC molecule-expressing cell； and (C) eluting the peptide from the complex and identifying the peptide.
