Real-time, high-throughput measurements of peptide–MHC-I dissociation using a scintillation proximity assay

Efficient presentation of peptide–MHC class I complexes to immune T cells depends upon stable peptide–MHC class I interactions. Theoretically, determining the rate of dissociation of a peptide–MHC class I complexes is straightforward; in practical terms, however, generating the accurate and closely timed data needed to determine the rate of dissociation is not simple. Ideally, one should use a homogenous assay involving an inexhaustible and label-free assay principle. Here, we present a homogenous, high-throughput peptide–MHC class I dissociation assay, which by and large fulfill these ideal requirements. To avoid labeling of the highly variable peptide, we labeled the invariant β2m and monitored its dissociation by a scintillation proximity assay, which has no separation steps and allows for real-time quantitative measurement of dissociation. Validating this work-around to create a virtually label-free assay, we showed that rates of peptide–MHC class I dissociation measured in this assay correlated well with rates of dissociation rates measured conventionally with labeled peptides. This assay can be used to measure the stability of any peptide–MHC class I combination, it is reproducible and it is well suited for high-throughput screening. To exemplify this, we screened a panel of 384 high-affinity peptides binding to the MHC class I molecule, HLA-A*02:01, and observed the rates of dissociation that ranged from 0.1 h to 46 h depending on the peptide used.

Research Highlights
► The stability of peptide-MHC-I complexes is measured using radio labeled β2m.
► Dissociation of β2m correlates with dissociation peptide.
► Scintillation proximity assay is highly reproducible and high-throughput friendly.