Induction of Pluripotent Stem Cells From Adult Human Fibroblasts by Defined Factors

If it were possible to reprogram differentiated human somatic cells into a pluripotent state, patient-specific and disease-specific stem cells could be developed. Previous work generated induced pluripotent stem (iPS) cells capable of germline transmission from murine somatic cells by transducing 4 transcription factors: Oct3/4, Sox2, Klf4, and c-Myc. The investigators now report generating iPS cells from adult human dermal fibroblasts using the same 4 factors. The first step was to optimize retroviral transduction in human fibroblasts as well as conditions of culture. Amphotrophic retrovirus was utilized. Colonies resembling human embryonic stem (hES) cell colonies were observed about 25 days after sampling cells from the facial dermis of a 36-year-old Caucasian female. In general, the human iPS cells expressed hES cell-specific surface antigens rather than stage-specific embryonic antigen. The cells expressed many undifferentiated ES cell-marker genes and they exhibited high telomerase activity. The cells proliferated exponentially for at least 4 months. It proved possible for iPS cells to differentiate into 3 germ layers in vitro. The cells resembled hES cells with regard to morphology, proliferation, gene expression, and epigenetic status of pluripotent cell-specific genes. Among the cell types formed from directed differentiation of human iPS cells were dopaminergic neurons and cardiac myocytes. Injection of human iPS cells subcutaneously into immunodeficient mice was followed after 9 weeks by teratomas containing gut-like epithelial tissues, striated muscle, cartilage, neural tissues, and keratin-containing epidermal tissues. The human iPS clones were not a result of cross-contamination. Although human iPS cells are not identical to hES cells, they should find applications in regenerative medicine once safety issues are overcome.