Decoding the HLA-I ligandome of extracellular vesicles (EVs)
EVs are nanosized membrane-bound vesicles secreted by cells. EVs can mediate antigen presentation via HLA-I/-II and they have been explored as cell-free anti-tumor vaccine vectors. However, a deep characterization of the EV ligandome is still missing to help guide these studies. The low protein yields in EV preparations highly complicate immunoprecipitation of HLA-complexes and mass-spectrometry analysis of eluted ligands. Here, we immunoprecipitated HLA-complexes from 100µg lysates, unprecedently yielding thousands of ligands from EVs and parent cells. We show that EV are densely packed with HLA complexes, preferentially HLA-B. EVs present a broader variety of ligands than parent cells, including cysteinylated ligands, which can have implications for vaccine development.