Direct detection and quantification of neoantigens

Many immunotherapeutic approaches under development rely on T-cell recognition of cancer-derived peptides bound to human leukocyte antigen molecules on the cell surface. Direct experimental demonstration that such peptides are processed and bound is currently challenging. Here, we describe a method that meets this challenge. The method entailed an optimized immunoprecipitation protocol coupled with twodimensional chromatography and mass spectrometry. The ability to detect and quantify minute amounts of predefined antigens should be useful both for basic research in tumor immunology and for the development of rationally designed cancer vaccines.