In T1D, we observed no clear correlations between NK cells and their subsets with C-peptide levels, which reflect endogenous insulin production, except for the inverse correlations with EOMES–NKG2A– and CD161+NKG2A– NK cells, and a positive correlation with EOMES+NKG2A+ NK cells. This evidence concerns the gene KLRB1 and type 1 diabetes mellitus.