Risk of tumorigenicity in mesenchymal stromal cell-based therapies--bridging scientific observations and regulatory viewpoints.

In the past decade, the therapeutic value of mesenchymal stromal cells (MSCs) has been studied in various indications, thereby taking advantage of their immunosuppressive properties. Easy procurement from bone marrow, adipose tissue or other sources and conventional in vitro expansion culture have made their clinical use attractive. Bridging the gap between current scientific knowledge and regulatory prospects on the transformation potential and possible tumorigenicity of MSCs, the Cell Products Working Party and the Committee for Advanced Therapies organized a meeting with leading European experts in the field of MSCs. This meeting elucidated the risk of potential tumorigenicity related to MSC-based therapies from two angles: the scientific perspective and the regulatory point of view. The conclusions of this meeting, including the current regulatory thinking on quality, nonclinical and clinical aspects for MSCs, are presented in this review, leading to a clearer way forward for the development of such products.