MHC class I-peptide complexes are usually stable for hours or even days. We have found that small molecules – for example certain dipeptides – that bind into the F pocket can dramatically accelerate peptide dissociation and replacement with exogenous peptides. This works on recombinant class I molecules, where the technology can be used to rapidly manufacture MHC multimers for T cell staining, and on cell surfaces, from which peptides can now be natively eluted.