Immortalized keratinocyte lines derived from human embryonic stem cells.

Cells of the human embryonic stem (hES) cell line H9, when cultured in the form of embryoid bodies, give rise to cells with markers of the keratinocyte of stratified squamous epithelia. Keratinocytes also form in nodules produced in scid mice by injected H9 cells; the hES-derived keratinocytes could be recovered in culture, where their colonies underwent a peculiar form of fragmentation. Whether formed from embryoid bodies or in nodules, hES-derived keratinocytes differed from postnatal keratinocytes in their much lower proliferative potential in culture; isolated single keratinocytes could not be expanded into mass cultures. Although their growth was not improved by transduction with the hTERT gene, these keratinocytes were immortalized by transduction with the E6E7 genes of HPV16. Clonally derived lines isolated from E6E7-transduced keratinocytes continued to express markers of the keratinocyte lineage, but the frequency with which they terminally differentiated was reduced compared with keratinocytes cultured from postnatal human epidermis. If other hES-derived somatic cell types also prove to be restricted in growth potential, not identical to the corresponding postnatal cell types, and to require immortalization for clonal isolation and expansion, these properties will have to be considered in planning their therapeutic use.