The evolution and ongoing challenge of unproven cell-based interventions.

Unproven cell-based interventions (CBIs) emerged early in the 2000s as a particularly problematic form of unproven therapy and remain a vexing policy problem to this day. These unproven interventions can harm patients both physically and financially and can complicate the process of developing a rigorous evidence base to support the translation of novel stem cell or other cell therapies. In this concise review, we examine the emergence of unproven CBIs and the various policy approaches that have been pursued or proposed to address this problem. We review the evolution of this field over the last 2 decades and explore why these policy efforts have proven challenging. We conclude by highlighting potential directions that the field could evolve and urging continued attention to both current and future forms of unproven CBIs to minimize future risks to patients and the field and to promote the development of evidence-based cell therapies.