Type
1 diabetes (T1D) results from CD8 T cell–mediated β-cell destruction. Major
risk-determining factors include possession of HLA class I alleles and variants
in the gene encoding insulin (INS),
one of the major autoantigens in the disease. We set out to test the hypothesis
that genetic susceptibility to T1D is determined in part by preferential presentation
of preproinsulin (PPI) peptide epitopes by class I HLA susceptibility molecules,
a feature that could facilitate recruitment of cytotoxic CD8 T cells and
targeting of β-cells. We generated a modified HLA-negative cell line K562,
transfected to express HLA class I molecules of interest and secreting
proinsulin, as a surrogate β-cell line and examined the peptide ligandome by
immunoaffinity purification and mass spectrometry to identify naturally
processed and presented peptides. We studied HLA-A*02:01 (susceptible),
-A*11:01 (protective), and -B*18:01 (susceptible) molecules. Using a novel, unbiased
search-approach we identified the previously described epitope PPI15-24 (ALWGPDPAAA)
from HLA-A*02:01, thereby validating our approach. No other HLA-A*02:01
restricted PPI peptide was identified, highlighting the dominance of PPI15-24 presentation
in this model. We were unable to identify a PPI peptide for the risk-associated
HLA-B*18:01 allele, but identified a PPI peptide originating from the proinsulin
C-peptide region for A*11:01. The current study indicates that T1D
susceptibility defined by HLA class I variants may not solely be explained by
the presentation of PPI epitopes and CD8 T cell-mediated destruction.
Potentially, other β-cell autoantigens could be important, or non-CD8 T cell
mediated MHC class I-dependent mechanisms are factors that determine risk.