Secretome and Extracellular Vesicles as New Biological Therapies for Knee Osteoarthritis: A Systematic Review.

Secretome and extracellular vesicles (EVs) are considered a promising option to exploit mesenchymal stem cells' (MSCs) properties to address knee osteoarthritis (OA). The aim of this systematic review was to analyze both the in vitro and in vivo literature, in order to understand the potential of secretome and EVs as a minimally invasive injective biological approach. A systematic review of the literature was performed on PubMed, Embase, and Web of Science databases up to 31 August 2019. Twenty studies were analyzed; nine in vitro, nine in vitro and in vivo, and two in vivo. The analysis showed an increasing interest in this emerging field, with overall positive findings. Promising in vitro results were documented in terms of enhanced cell proliferation, reduction of inflammation, and down-regulation of catabolic pathways while promoting anabolic processes. The positive in vitro findings were confirmed in vivo, with studies showing positive effects on cartilage, subchondral bone, and synovial tissues in both OA and osteochondral models. However, several aspects remain to be clarified, such as the different effects induced by EVs and secretome, which is the most suitable cell source and production protocol, and the identification of patients who may benefit more from this new biological approach for knee OA treatment.