This project investigates in situ deprotection reactions catalyzed by the Ni–BCS system in MC38 cells and the subsequent impact on the immunopeptidome. Two independent MC38 cell preparations (2 × 10⁷ cells each) were pulsed with either the P2 peptide or P2 peptide followed by Ni–BCS catalyzed in situ deprotection (P2+Ni). MHC-associated peptides were analysed by Immunoprecipitation-Mass Spectrometry.