Folding and assembly of proteins in secretory pathways are mediated by a sophisticated chaperone and quality control network whose structural and mechanistic organization is largely unknown. The peptide loading complex (PLC) plays a fundamental role in the biogenesis of MHC I molecules, orchestrating the adaptive immune response against pathogens, vaccines, and cancer1,2. Any misinterpretation can lead to inflammation and autoimmune disease. By using an integrative approach, we explore the cellular pathways, dynamic assemblies, and macromolecular membrane machineries in antigen processing and in view of viral and tumor immune evasion3-5. The conformational landscape and the mechanism of intracellular antigen translocation as well as MHC I quality control and immune evasion complexes will be illuminated.