Frequency of specific immune responses against different NPM1-derived epitopes from the mutational region in HVs and in AML patients with an NPM1 mutation. CD8⁺ T cells separated from 33 HVs and 27 AML patients with NPM1^mut were stimulated with NPM1#1 to NPM1#9 and wild-type in a MLPC. Epitope recognition by these T cells was measured as IFN-γ and granzyme B secretion by ELISPOT. Significant frequencies of CD8⁺ T cells specific for epitopes #1 and #3 derived from the mutational region NPM1 could be detected in HVs and in AML patients with NPM1^mut. Whereas the frequency of peptide #1–specific CD8⁺ T cells was equal in HVs and NPM1^mut AML patients (nonsignificant), responses to peptide #3 were more frequent in AML patients than in HVs (P = .046).