PKM and cancer: By developing a scFv-based immunoprecipitation method, we were able to use liquid chromatography tandem mass spectrometry (LC–MS/MS) to identify the antigen bound by one of the Abs (H103) as the M2 splice isoform of pyruvate kinase (PKM2), an enzyme that is a key regulator of aerobic glycolysis (known as the Warburg effect) in cancer cells [22–24].