This question is part of the following Ask The Expert session:
Traditionally LIF has been supplied to ESCs by secretion directly into the culture media by mitotically-inactivated mouse embryonic fibroblasts (MEFs). However, feeder layers have limitations. Not only are they very labor intensive to prepare, but problems also arise with isolating stem cells due to inefficient separation of the two cell types. Further, variations between MEF preparations can lead to marked differences in stem cell performance. Therefore, the integrity of obtained results from in vitro assays that utilize MEFs and reproducibility between assays presents a challenge for traditional co-culture systems. Given the potential problems and challenges of using MEF-derived LIF, I would recommend using recombinant LIF in stem cell systems. Now the question becomes which LIF to use? Early publications (PMID 8006010) have shown that human LIF is able to bind the LIF receptor on mouse cells. We have also observed that human LIF is active on mESCs in that it can be used to maintain markers of pluripotency. Therefore, the answer of which LIF to use comes down to selecting the most cost-efficient LIF that won’t break the bank.