Myeloid leukaemia inhibitory factor maintains the developmental potential of embryonic stem cells

Embryonic stem (ES) cells, the totipotent outgrowths of bias-tocysts1,2, can be cultured and manipulated in vitro and then returned to the embryonic environment where they develop normally and can contribute to all cell lineages3–9. Maintenance of the stem-cell phenotype in vitro requires the presence of a feeder layer of fibroblasts1,2,10or of a soluble factor, differentiation inhibitory activity (DIA) produced by a number of sources5,11,12; in the absence of DIA the ES cells differentiate into a wide variety of cell types. We recently noted several similarities between partially purified DIA and a haemopoietic regulator, myeloid leukaemia inhibitory factor (LIF), a molecule which induces differentiation in Ml myeloid leukaemic cells and which we have recently purified, cloned and characterized13–18. We demonstrate here that purified, recombinant LIF can substitute for DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.