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Purity and integrity of the reagents used to scale up stem cells for clinical use are of the utmost importance. Removal of all animal or human-serum derived proteins is key since these reagents are notorious for viral contamination as well as varying cell performance between preparation lots. Therefore, replacement of these proteins with highly pure recombinant versions ensures reproducible cell scale up and subsequent in vivo performance of the implanted cells. However, this must be done while keeping the reagents economically feasible. The novel rice-derived rhLIF described in this blog represents just one example of how we addressed a limitation in the current LIF market as other more expensive LIF proteins have high endotoxin contamination that can potentially be problematic if used in clinical preparations of stem cells. By using the ExpressTec expression platform, we have the potential to produce kg quantities of LIF with almost undetectable endotoxin contamination. Other recombinant proteins critical in stem cell culture must follow in order to facilitate the translation of stem cell technology to the clinic.