Fap is structurally and functionally similar to Dpp4,69 which is a dipeptidyl peptidase that shares many substrates with Fap.70 DPP4 inhibitors, such as sitagliptin, are orally available drugs that have been approved by the FDA to treat type 2 diabetes.71 Although the FAPi we used in this study is only 9-fold selective over Dpp4,55 it showed no therapeutic effects in Fap KO mice (Fig. 2). Here, DPP4 is linked to type 2 diabetes mellitus.