Background & Aim Human mesenchymal stem/stromal cells (MSCs) have been applied in more than 900 NIH-registered clinical trials with different outcomes. In a proportion of studies pro-regenerative and/or immunomodulatory therapeutic effects were observed. Against the initial assumption, preclinical data demonstrated that – if functional - MSCs act in a paracrine rather than in a cellular manner. Efforts to search for the active paracrine components ended in the identification of extracellular vesicle (EVs). Indeed, in several preclinical models EVs harvested from MSC conditioned media exerted comparable therapeutic effects than the MSCs themselves. Methods, Results & Conclusion EVs released by virtually all cell types represent a heterogenous population of vesicles of different origin, including exosomes (70-150 nm), microvesicles (100-1000 nm), and apoptotic bodies (> 500 nm). Classically, they are prepared by differential centrifugation. Due to volume restricitions during ultracentrifugation only smaller amounts of EV containing liquids can be processed with this method. To efficiently translate MSC-EVs into the clinics, they need to be produced in a scaled manner. Previously, we established and successfully used a polyehtylen glycol (PEG) precipitation procedure allowing to process up to 10 l conditioned medium. Intending to further scale the MSC-EV production, optimally in a closed system, we have started to optimize tangential flow filtration (TFF) protocols, in principal being scalable up to several 1000 litres. At first, we compared different TFF devices and selected the holofiber-based TFF system. Although EVs can efficiently be prepared from serum-free conditioned media, the processing of serum or human platelet lysate (hPL) containing conditioned media remains challenging. The high protein content of serum and hPL supplemented media quickly results in protein aggregate formation and clogging of the pores of the TFF system, which negatively affect the EV purification process. Currently, by changing flow rates and and re-addition of buffers, we optimize the TFF protocols to enable us obtaining MSC-EV preparations with comparable purities than with the PEG method.