Ready-to-load MHC-I Nanoparticles for High-throughput T cell Screening Studies.

MHC-I proteins present epitopic peptides to CD8+ T cells to elicit multifaceted adaptive immune responses. The affinity and avidity of interactions between peptide-MHC molecules and T-cell receptors (TCR) are fundamental parameters that contribute to the induction of activated or anergic T cell states. Here, we present a loadable system, VLP-Open HLA, featuring a virus-like particle (VLP) that can accommodate up to 60 loadable HLA (HLA - human leukocyte antigen) molecules. HLA nanoparticles, pre-loaded with a placeholder ligand, allow efficient peptide exchange upon incubation with target peptides. We show that fluorescently tagged VLP-Open HLA particles can be used to stain antigen-specific CD8+ T cells, providing a screening tool for novel TCRs. Finally, we demonstrate that our system can induce activation of T cells in an antigen-specific manner. Our platform can be adapted to encompass multiple HLA allotypes and co-stimulatory molecules as mosaic nanoparticles, to enable a range of applications in experimental immunology.