DPP4 and rheumatoid arthritis: DPP-4 is expressed in different tissues as either an anchored transmembrane protease or a soluble circulating one, and its anomalous activity has also been linked to cancer (solid tumors), hematological malignancies, immune diseases, and infectious diseases.4,5 Studies have identified DPP-4 as a promising biomarker for early diagnosis and treatment of diseases such as lung diseases, diabetic kidney disease,11 rheumatoid arthritis,12 post-kidney transplant tubulitis,12 and liver disease.13 There is thus a need to develop probes to monitor DPP-4 activity real-time.