Hongguang Huo

Reprogramming of human somatic cells to pluripotency with defined factors.

Pluripotency pertains to the cells of early embryos that can generate all of the tissues in the organism. Embryonic stem cells are embryo-derived cell lines that retain pluripotency and represent invaluable tools for research into the mechanisms of tissue formation. Recently, murine fibroblasts have been reprogrammed directly to pluripotency by ectopic expression of four transcription factors (Oct4, Sox2, Klf4 and Myc) to yield induced pluripotent stem (iPS) cells. Using these same factors, we have derived iPS cells from fetal, neonatal and adult human primary cells, including dermal fibroblasts isolated from a skin biopsy of a healthy research subject. Human iPS cells resemble embryonic stem cells in morphology and gene expression and in the capacity to form teratomas in immune-deficient mice. These data demonstrate that defined factors can reprogramme human cells to pluripotency, and establish a method whereby patient-specific cells might be established in culture.

Disease-Specific Induced Pluripotent Stem Cells

Tissue culture of immortal cell strains from diseased patients is an invaluable resource for medical research but is largely limited to tumor cell lines or transformed derivatives of native tissues. Here we describe the generation of induced pluripotent stem (iPS) cells from patients with a variety of genetic diseases with either Mendelian or complex inheritance; these diseases include adenosine deaminase deficiency-related severe combined immunodeficiency (ADA-SCID), Shwachman-Bodian-Diamond syndrome (SBDS), Gaucher disease (GD) type III, Duchenne (DMD) and Becker muscular dystrophy (BMD), Parkinson disease (PD), Huntington disease (HD), juvenile-onset, type 1 diabetes mellitus (JDM), Down syndrome (DS)/trisomy 21, and the carrier state of Lesch-Nyhan syndrome. Such disease-specific stem cells offer an unprecedented opportunity to recapitulate both normal and pathologic human tissue formation in vitro, thereby enabling disease investigation and drug development.

Generation of induced pluripotent stem cells from human blood.

Human dermal fibroblasts obtained by skin biopsy can be reprogrammed directly to pluripotency by the ectopic expression of defined transcription factors. Here, we describe the derivation of induced pluripotent stem cells from CD34+ mobilized human peripheral blood cells using retroviral transduction of OCT4/SOX2/KLF4/MYC. Blood-derived human induced pluripotent stem cells are indistinguishable from human embryonic stem cells with respect to morphology, expression of surface antigens, and pluripotency-associated transcription factors, DNA methylation status at pluripotent cell-specific genes, and the capacity to differentiate in vitro and in teratomas. The ability to reprogram cells from human blood will allow the generation of patient-specific stem cells for diseases in which the disease-causing somatic mutations are restricted to cells of the hematopoietic lineage.

Live cell imaging distinguishes bona fide human iPS cells from partially reprogrammed cells

Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells by enforced expression of transcription factors. Using serial live imaging of human fibroblasts undergoing reprogramming, we identified distinct colony types that morphologically resemble embryonic stem (ES) cells yet differ in molecular phenotype and differentiation potential. By analyzing expression of pluripotency markers, methylation at the OCT4 and NANOG promoters and differentiation into teratomas, we determined that only one colony type represents true iPS cells, whereas the others represent reprogramming intermediates. Proviral silencing and expression of TRA-1-60, DNMT3B and REX1 can be used to distinguish the fully reprogrammed state, whereas alkaline phosphatase, SSEA-4, GDF3, hTERT and NANOG are insufficient as markers. We also show that reprogramming using chemically defined medium favors formation of fully reprogrammed over partially reprogrammed colonies. Our data define molecular markers of the fully reprogrammed state and highlight the need for rigorous characterization and standardization of putative iPS cells.

Generation of human-induced pluripotent stem cells.

Pluripotent cells, such as embryonic stem cells, are invaluable tools for research and can potentially serve as a source of cell- and tissue-replacement therapy. Rejection after transplantation of cells and tissue derived from embryonic stem cells is a significant obstacle to their clinical use. Recently, human somatic cells have been reprogrammed directly to pluripotency by ectopic expression of four transcription factors (Oct4, Sox2, Klf4 and Myc) to yield induced pluripotent stem (iPS) cells. Human iPS cells are a potential source of patient-specific pluripotent stem cells that would bypass immune rejection. iPS cells can also be used to study diseases for which there are no adequate human in vitro or animal models. In this protocol, we describe how to establish primary human fibroblasts lines and how to derive iPS cells by retroviral transduction of reprogramming factors. Overall, it takes 2 months to complete reprogramming human primary fibroblasts starting from biopsy.

Telomere elongation in induced pluripotent stem cells from dyskeratosis congenita patients

Patients with dyskeratosis congenita (DC), a disorder of telomere maintenance, suffer degeneration of multiple tissues. Patient-specific induced pluripotent stem (iPS) cells represent invaluable in vitro models for human degenerative disorders like DC. A cardinal feature of iPS cells is acquisition of indefinite self-renewal capacity, which is accompanied by induction of the telomerase reverse transcriptase gene (TERT). We investigated whether defects in telomerase function would limit derivation and maintenance of iPS cells from patients with DC. Here we show that reprogrammed DC cells overcome a critical limitation in telomerase RNA component (TERC) levels to restore telomere maintenance and self-renewal. We discovered that TERC upregulation is a feature of the pluripotent state, that several telomerase components are targeted by pluripotency-associated transcription factors, and that in autosomal dominant DC, transcriptional silencing accompanies a 3′ deletion at the TERC locus. Our results demonstrate that reprogramming restores telomere elongation in DC cells despite genetic lesions affecting telomerase, and show that strategies to increase TERC expression may be therapeutically beneficial in DC patients.

Human embryonic stem cell derivation from poor-quality embryos

During in vitro fertilization, embryos deemed clinically useless based on poor morphology are typically discarded. Here we demonstrate a statistical correlation between the developmental stage of such poor-quality embryos and the yield of human embryonic stem (hES) cell lines. Early-arrested or highly fragmented embryos only rarely yield cell lines, whereas those that have achieved blastocyst stage are a robust source of normal hES cells.

Derivation and maintenance of human embryonic stem cells from poor-quality in vitro fertilization embryos

Human embryonic stem (hES) cells are self-renewing, pluripotent cells that are valuable research tools and hold promise for use in regenerative medicine. Most hES cell lines are derived from cryopreserved human embryos that were created during in vitro fertilization (IVF) and are in excess of clinical need. Embryos that are discarded during the IVF procedure because of poor morphology and a low likelihood for generating viable pregnancies or surviving the cryopreservation process are also a viable source of hES cells. In this protocol, we describe how to derive novel hES cells from discarded poor-quality embryos and how to maintain the hES cell lines.

Clump Passaging and Expansion of Human Embryonic and Induced Pluripotent Stem Cells on Mouse Embryonic Fibroblast Feeder Cells

The ability of human embryonic stem cells (hESCs) to differentiate into essentially all somatic cell types has made them a valuable tool for studying human development and has positioned them for broad applications in toxicology, regenerative medicine, and drug discovery. This unit describes a protocol for the large-scale expansion and maintenance of hESCs in vitro. hESC cultures must maintain a balance between the cellular states of pluripotency and differentiation; thus, researchers must use care when growing these technically demanding cells. The culture system is based largely on the use of a proprietary serum-replacement product and basic fibroblast growth factor (bFGF), with mouse embryonic fibroblasts as a feeder layer. These conditions provide the basis for relatively inexpensive maintenance and expansion of hESCs, as well as their engineered counterparts, human induced pluripotent stem cells (hiPSCs).

Derivation of human embryonic stem cells with NEMO deficiency.

Deficiency of the nuclear factor-kappa-B essential modulator (NEMO) is a rare X-linked disorder that presents in boys as hypohydrotic ectodermal dysplasia with immunodeficiency due to defective nuclear factor-κB activation. Here we report on the generation of 2 human embryonic stem cell lines from discarded in vitro fertilization (IVF) embryos ascertained via preimplantation genetic diagnosis. We have derived two human embryonic stem cell lines that carry a T458G hypomorphic mutation in exon 4 of the NEMO (or IKBKG) gene. One of the lines is diploid male; the other is diploid female but has clonally inactivated the X-chromosome that harbors the wild-type IKBKG gene. We show that both lines are pluripotent, have the capacity to differentiate into hematopoietic progenitors, and have defective inhibitor of nuclear factor kappa-B kinase activity. These NEMO deficiency hES cell lines provide an unlimited source for differentiated cell types and may serve as a unique tool to study NEMO deficiency and potentially lead to the development of new therapies for this disease.