Roadblocks of Urinary EV Biomarkers: Moving Toward the Clinic.

Despite remarkable interest in the biomarker potential of urinary extracellular vesicles (uEVs) and the identification of numerous promising candidates, their clinical translation still presents multiple challenges. The opportunities for successful translation are obvious, yet the main roadblocks on the way have hardly been systematically considered and more coordinated approaches are needed to overcome them. In the present review article, we have identified the most relevant roadblocks of clinical translation of urinary EV-based biomarkers and discuss possible solutions to overcome them. These roadblocks are categorized as fundamental and technical but also related to development of novel biomarker assays and clinical acceptance. In addition, hurdles within the regulatory approval process are discussed. It is clear that various roadblocks to clinical translation of urinary EV biomarkers exist; however, they are addressable by promoting rigor and reproducibility as well as collaboration between basic and clinical scientists, clinicians, industry and regulatory bodies. Moreover, knowledge of obstacles for assay development and regulatory requirements should already be considered when developing a new biomarker to maximize the chance of successful translation. This review presents not only a status quo, but also a roadmap for the further development of the field.