An elegant study from Minervina et al. (28) used 18 DNA-barcoded MHC class I multimers for HLA-A*01:01, HLA-A2*01, HLA-A*24:02, HLA-B*15:01, and HLA-B*40:02, together with scRNAseq and scTCRseq to further characterize and compare tetramer-specific CD8+ T cell responses in patients with COVID-19 and vaccinees. The gene discussed is HLA-B; the disease is COVID-19.