Learn how to use this product The MEXi-TM transfection medium is an affordable, serum-free, chemically defined medium especially developed for the growth of high-density MEXi-293E cells. It is part of the MEXi mammalian expression system. The MEXi mammalian expression system includes the MEXi-293E cell line, various pDSG expression vectors, the MEXi-CM culture medium, and the MEXi-TM transfection medium.