Kim Smuga-Otto

Somatic cell nuclear transfer allows trans-acting factors present in the mammalian oocyte to reprogram somatic cell nuclei to an undifferentiated state. We show that four factors (OCT4, SOX2, NANOG, and LIN28) are sufficient to reprogram human somatic cells to pluripotent stem cells that exhibit the essential characteristics of embryonic stem (ES) cells. These induced pluripotent human stem cells have normal karyotypes, express telomerase activity, express cell surface markers and genes that characterize human ES cells, and maintain the developmental potential to differentiate into advanced derivatives of all three primary germ layers. Such induced pluripotent human cell lines should be useful in the production of new disease models and in drug development, as well as for applications in transplantation medicine, once technical limitations (for example, mutation through viral integration) are eliminated.

Reprogramming differentiated human cells to induced pluripotent stem (iPS) cells has applications in basic biology, drug development, and transplantation. Human iPS cell derivation previously required vectors that integrate into the genome, which can create mutations and limit the utility of the cells in both research and clinical applications. We describe the derivation of human iPS cells with the use of nonintegrating episomal vectors. After removal of the episome, iPS cells completely free of vector and transgene sequences are derived that are similar to human embryonic stem (ES) cells in proliferative and developmental potential. These results demonstrate that reprogramming human somatic cells does not require genomic integration or the continued presence of exogenous reprogramming factors and removes one obstacle to the clinical application of human iPS cells.

Because the mammalian embryo is regulated by epigenetic rather than genetic events, differentiation is—in principle—reversible. Somatic cell nuclear transfer permits trans-acting factors resident in the mammalian oocyte to reprogram somatic cell nuclei to an undifferentiated state. The investigators have found that 4 genes (OCT4, SOX2, NANOG, and LIN28) are sufficient to reprogram human somatic cells to pluripotent stem cells that possess the defining features of embryonic stem (ES) cells. Each of 4 induced pluripotent stem (iPS) cells had the typical human ES cell morphology and a normal karyotype after up to 17 months of culture. Each iPS clone expressed telomerase activity and human ES cell-specific cell surface antigens. All of the reprogrammed iPS clones were able to give rise to differentiated derivatives of all 3 primary germ layers. When human newborn foreskin fibroblasts were transduced, each clone consisted of cells having a human ES cell morphology and genes characteristic of human ES cells. When last examined after 14 weeks, all of the iPS clones were proliferating vigorously. Each clone exhibited multilineage differentiation in both embryoid bodies and teratomas. Except for the fact that human iPS cells are not derived from embryos, they meet defining criteria for human ES cells. They should prove helpful when studying the development and function of human tissues. Once technical limitations such as mutation through viral integration are effectively addressed, the cells should find use in transplantation treatments. With the exception of autoimmune diseases, patient-specific iPS cell lines should mostly eliminate concern over immune rejection.

Induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity for modeling of human diseases in vitro, as well as for developing novel approaches for regenerative therapy based on immunologically compatible cells. In this study, we employed an OP9 differentiation system to characterize the hematopoietic and endothelial differentiation potential of seven human iPSC lines obtained from human fetal, neonatal, and adult fibroblasts through reprogramming with POU5F1, SOX2, NANOG, and LIN28 and compared it with the differentiation potential of five human embryonic stem cell lines (hESC, H1, H7, H9, H13, and H14). Similar to hESCs, all iPSCs generated CD34(+)CD43(+) hematopoietic progenitors and CD31(+)CD43(-) endothelial cells in coculture with OP9. When cultured in semisolid media in the presence of hematopoietic growth factors, iPSC-derived primitive blood cells formed all types of hematopoietic colonies, including GEMM colony-forming cells. Human induced pluripotent cells (hiPSCs)-derived CD43(+) cells could be separated into the following phenotypically defined subsets of primitive hematopoietic cells: CD43(+)CD235a(+)CD41a(+/-) (erythro-megakaryopoietic), lin(-)CD34(+)CD43(+)CD45(-) (multipotent), and lin(-)CD34(+)CD43(+)CD45(+) (myeloid-skewed) cells. Although we observed some variations in the efficiency of hematopoietic differentiation between different hiPSCs, the pattern of differentiation was very similar in all seven tested lines obtained through reprogramming of human fetal, neonatal, or adult fibroblasts with three or four genes. Although several issues remain to be resolved before iPSC-derived blood cells can be administered to humans for therapeutic purposes, patient-specific iPSCs can already be used for characterization of mechanisms of blood diseases and for identification of molecules that can correct affected genetic networks.

Induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity for modeling of human diseases in vitro, as well as for developing novel approaches for regenerative therapy based on immunologically compatible cells. In this study, we employed an OP9 differentiation system to characterize the hematopoietic and endothelial differentiation potential of seven human iPSC lines obtained from human fetal, neonatal, and adult fibroblasts through reprogramming with POU5F1, SOX2, NANOG, and LIN28 and compared it with the differentiation potential of five human embryonic stem cell lines (hESC, H1, H7, H9, H13, and H14). Similar to hESCs, all iPSCs generated CD34+CD43+ hematopoietic progenitors and CD31+CD43− endothelial cells in coculture with OP9. When cultured in semisolid media in the presence of hematopoietic growth factors, iPSC-derived primitive blood cells formed all types of hematopoietic colonies, including GEMM colony-forming cells. Human induced pluripotent cells (hiPSCs)-derived CD43+ cells could be separated into the following phenotypically defined subsets of primitive hematopoietic cells: CD43+CD235a+CD41a± (erythro-megakaryopoietic), lin−CD34+CD43+CD45− (multipotent), and lin−CD34+CD43+CD45+ (myeloid-skewed) cells. Although we observed some variations in the efficiency of hematopoietic differentiation between different hiPSCs, the pattern of differentiation was very similar in all seven tested lines obtained through reprogramming of human fetal, neonatal, or adult fibroblasts with three or four genes. Although several issues remain to be resolved before iPSC-derived blood cells can be administered to humans for therapeutic purposes, patient-specific iPSCs can already be used for characterization of mechanisms of blood diseases and for identification of molecules that can correct affected genetic networks.