FOLR1 and cancer: For instance, murine MOv19 as a single-chain Fv (scFv) format has been fused with IL-2 to improve tissue penetration of IL-2,61 and with the retention signal KDEL designed to block the expression of FRα on the surface of cancer cells.58 The human Fab fragment AFRA5 was optimized into a chemical dimer AFRA 5.3 DFM.62 In preclinical intraperitoneal murine models, when radio-labeled with 131I, this Fab dimer specifically bound to FRα-expressing ovarian cancer cells, efficiently localizing to tumor masses due to its small size, where it promoted tumor regression and improved survival.63