This question is part of the following Ask The Expert session:
When expanding organoids under defined conditions, we recommend avoiding the use of serum. In all medium recipes developed by the lab of Hans Clevers, the presence of serum is found when the tissue-specific organoid model requires the presence of Wnt3a (i.e. human intestinal models). The Wnt3a conditioned medium contains 5% fetal bovine system (FBS) and it has been the most robust way to produce active Wnt3a. Luckily, alternative sources of serum-free Wnt3a are becoming available, such as Surrogate Wnt (Garcia lab, Stanford), making possible to expand organoids in the absence of serum.