Figure 1. Summary of experimental approach and salient conclusions.

As reported in this issue, Pearson et al. isolated B cells from 18 individuals, expressing a total of 27 MHC class I allomorphs, and identified surface-presented peptides using mild acid elution coupled with mass spectrometry. Simultaneously, personalized genetic databases were created using transcriptome and exome sequencing from each donor. Together, the peptide identification and sequencing information allowed for the mapping of MAPs at their source locations within the genome.