Using therapeutic cloning to fight human disease: a conundrum or reality?

PRIMARY FIBROBLAST CELL CYCLE SYNCHRONIZATION AND EFFECTS ON HANDMADE CLONED (HMC) BOVINE EMBRYOS

Abstract Spatial and temporal synchrony and compatibility between the receptor oocyte and the donor cell nucleus are necessary for the process of embryo cloning to allow nuclear reprogramming and early embryonic development. The objective of the present study was to evaluate three cell cycle synchronization methods on a primary bovine fibroblast culture for 24, 48, or 72 h. These fibroblasts were used as nuclear donors to evaluate their in vitro developmental potential and the quality of the embryos produced through handmade cloning (HMC). No differences were found between the methods used for fibroblast synchronization in G0/G1 (p > 0.05). Production of clones from fibroblasts in four groups- no treatment at 0 h and using serum restriction SR, high culture confluence HCC, and SR+HCC at 24 h- resulted in high cleavage rates that were not different. Embryo production rates were 37.9%, 29.5%, and 30.9% in the 0h, SR24h, and SR+HHC24h groups, respectively, and 19.3% in the HCC group, which was significantly different from the other three (p < 0.05). There were no differences in the quality parameter among the clones produced with fibroblasts subjected to the different synchronization. Finally, when overall clone production was compared versus parthenotes and IVF embryos, the only difference was between clones and parthenogenetic embryos with zona pellucida (30.2% vs 38.6%). The number of blastomeres from the blastocytes produced through IVF was significantly greater than those from embryos activated parthenogenetically and from clones (117, 80, 75.9, and 67.1, respectively). The evaluation of three synchronization methods at different time points did not demonstrate an increase in the percentage of fibroblasts in the G0/G1 phases of the cell cycle; however, good quality and high cloning rates were obtained, suggesting that it is not always necessary to subject the cells to any synchronization treatments, as they would yield equally good cloning results.

Towards a richer debate on tissue engineering: a consideration on the basis of NEST-ethics

In their 2007 paper, Swierstra and Rip identify characteristic tropes and patterns of moral argumentation in the debate about the ethics of new and emerging science and technologies (or "NEST-ethics"). Taking their NEST-ethics structure as a starting point, we considered the debate about tissue engineering (TE), and argue what aspects we think ought to be a part of a rich and high-quality debate of TE. The debate surrounding TE seems to be predominantly a debate among experts. When considering the NEST-ethics arguments that deal directly with technology, we can generally conclude that consequentialist arguments are by far the most prominently featured in discussions of TE. In addition, many papers discuss principles, rights and duties relevant to aspects of TE, both in a positive and in a critical sense. Justice arguments are only sporadically made, some "good life" arguments are used, others less so (such as the explicit articulation of perceived limits, or the technology as a technological fix for a social problem). Missing topics in the discussion, at least from the perspective of NEST-ethics, are second "level" arguments-those referring to techno-moral change connected to tissue engineering. Currently, the discussion about tissue engineering mostly focuses on its so-called "hard impacts"-quantifiable risks and benefits of the technology. Its "soft impacts"-effects that cannot easily be quantified, such as changes to experience, habits and perceptions, should receive more attention.

Successful reprogramming of differentiated cells by somatic cell nuclear transfer, using in vitro-matured oocytes with a modified activation method

Therapeutic cloning has tremendous potential for cell therapy and tissue repair in some diseases. However, the efficiency of development of cloned human embryos by somatic cell nuclear transfer is still low. In the present study, the activation of cloned human embryos was investigated while using in vitro-matured oocytes. Pseudo-pronuclear formation and the subsequent development was compared with different activation parameters, including different durations of ionomycin and 6-dimethylaminopurine treatment. The results showed that somatic cells were successfully reprogrammed by modification of activation treatments while using in vitro-matured oocytes. The activation efficiency of cloned human embryos was significantly increased at durations of ionomycin at both 5 and 7 min, despite different durations of 6-DMAP treatment. The results of blastocyst development showed that 20% of activated embryos developed to the blastocyst stage when the embryos were activated with 5 µm ionomycin for 5 min and 2 mm 6-DMAP for 5 h, which was significantly higher than those activated with other parameters. Moreover, we found that an increasing duration of 6-DMAP induced the formation of a single, large, pseudo-pronucleus in cloned human embryos and impaired subsequent development competence. In conclusion, successful reprogramming of human somatic cells was achieved using in vitro-matured oocytes by somatic cell nuclear transfer and improved with a modified activation method.

Enucleated ovine oocyte supports human somatic cells reprogramming back to the embryonic stage

Increased possibility of universality of ooplasmic reprogramming factors resulted in a parallel increased interest to use interspecies somatic cell nuclear transfer (iSCNT) to address basic questions of developmental biology and to improve the feasibility of cell therapy. In this study, the interactions between human somatic cells and ovine oocytes were investigated. Nuclear remodeling events were first observed 3 h post-iSCNT as nuclear swelling, chromosome condensation, and spindle formation. A time-dependent decrease in maturation promoting activity of inactivated reconstructs coincided with increased aberrations in chromosome and spindle organization of the newly developed embryos. The sequence and duration of nuclear remodeling events were irrespective of donor cell type used. Although the majority of the reconstituted embryos arrested before embryonic genome activation (8-16-cell) stage, less than 5% of them could progress beyond transcription-requiring developmental stage and formed blastocyst-like structures with distinct inner cell mass and trophectoderm at days 7 and 8 post-SCNT. Importantly, real-time assessment of three developmentally important genes (Oct4, Sox2, and Nanog) indicated their upregulation in iSCNT blastocysts. Blastocyst-derived outgrowths had alkaline phosphatase activity that was lost upon passage. Collectively, this study introduced ovine oocyte as a credible cytoplast for remodeling and reprogramming of human somatic cells back to the embryonic stage and provided a platform for further studies to unravel possible differences exist between reprogramming ability of oocytes of different mammalian species.

Generation of leukemia inhibitory factor and basic fibroblast growth factor-dependent induced pluripotent stem cells from canine adult somatic cells

For more than thirty years, the dog has been used as a model for human diseases. Despite efforts made to develop canine embryonic stem cells, success has been elusive. Here, we report the generation of canine induced pluripotent stem cells (ciPSCs) from canine adult fibroblasts, which we accomplished by introducing human OCT4, SOX2, c-MYC, and KLF4. The ciPSCs expressed critical pluripotency markers and showed evidence of silencing the viral vectors and normal karyotypes. Microsatellite analysis indicated that the ciPSCs showed the same profile as the donor fibroblasts but differed from cells taken from other dogs. Under culture conditions favoring differentiation, the ciPSCs could form cell derivatives from the ectoderm, mesoderm, and endoderm. Further, the ciPSCs required leukemia inhibitory factor and basic fibroblast growth factor to survive, proliferate, and maintain pluripotency. Our results demonstrate an efficient method for deriving canine pluripotent stem cells, providing a powerful platform for the development of new models for regenerative medicine, as well as for the study of the onset, progression, and treatment of human and canine genetic diseases.

Evaluation of x-inactivation status and cytogenetic stability of human dermal fibroblasts after long-term culture

Human primary fibroblasts are a popular type of somatic cells for the production of induced pluripotent stem (iPS) cells. Here we characterized biological properties of primary fibroblasts in terms of cell-growth rate, cytogenetic stability, and the number of inactive X chromosomes during long-term passaging. We produced eight lines of female human dermal fibroblasts (HDFs) and found normal karyotype and expected pattern of X chromosome inactivation (XCI) at low passages (Passage P1-5). However, four out of the eight HDF lines at high passage numbers (≥ P10) exhibited duplicated hallmarks of inactive X chromosome including two punctuate signals of histone H3 lysine 27 trimethylation (H3K27me3) and X inactive-specific transcript (XIST) RNA signals in approximately 8.5–18.5% of the cells. Our data suggest that the copy number of inactive X chromosomes in a subset of female HDF is increased by a two-fold. Consistently, DNA fluorescent in situ hybridization (FISH) identified 3-4 copies of X chromosomes in one nucleus in this subset of cells with two inactive Xs. We conclude that female HDF cultures exhibit a higher risk of genetic anomalies such as carrying an increased number of X chromosomes including both active and inactive X chromosomes at a high passage (≥ P10).

Efficient derivation of embryonic stem cells from nuclear transfer and parthenogenetic embryos derived from cryopreserved oocytes

Deriving histocompatible embryonic stem (ES) cells by somatic cell nuclear transfer (SCNT) and parthenogenetic activation (PA) requires fresh oocytes, which prevents their applications in humans. Here, we evaluated the efficiency of deriving ES cells from mature metaphase II (MII) and immature metaphase I (MI) vitrified oocytes, by PA or SCNT, in a mouse model. We successfully generated ES cell lines from PA (MII and MI) and SCNT (MII and MI) blastocysts. These cell lines expressed genes and antigens characteristic of pluripotent ES cells and produced full-term pups upon tetraploid embryo complementation. This study established an animal model for efficient generation of patient-specific ES cell lines using cryopreserved oocytes. This is a major step forward in the application of therapeutic cloning and parthenogenetic technology in human regenerative medicine and will serve as an important alternative to the iPS cell technology in countries/regions where these technologies are permitted.

The innate immune system in host mice targets cells with allogenic mitochondrial DNA

Tumors or embryonic stem cells bearing foreign mitochondrial DNA are rejected by the innate immune system via a mechanism that depends on MyD88.

Mitochondrial DNA (mtDNA) has been proposed to be involved in respiratory function, and mtDNA mutations have been associated with aging, tumors, and various disorders, but the effects of mtDNA imported into transplants from different individuals or aged subjects have been unclear. We examined this issue by generating trans-mitochondrial tumor cells and embryonic stem cells that shared the syngenic C57BL/6 (B6) strain–derived nuclear DNA background but possessed mtDNA derived from allogenic mouse strains. We demonstrate that transplants with mtDNA from the NZB/B1NJ strain were rejected from the host B6 mice, not by the acquired immune system but by the innate immune system. This rejection was caused partly by NK cells and involved a MyD88-dependent pathway. These results introduce novel roles of mtDNA and innate immunity in tumor immunology and transplantation medicine.

Tissue engineering and regenerative medicine research perspectives for pediatric surgery

Tissue engineering and regenerative medicine research is being aggressively pursued in attempts to develop biological substitutes to replace lost tissue or organs. Remarkable degrees of success have been achieved in the generation of a variety of tissues and organs as a result of concerted contributions by multidisciplinary groups in the field of biotechnology. Engineering of an organ is a complex process which is initiated by appropriate sourcing of cells and their controlled proliferation to achieve critical numbers for seeding on biodegradable scaffolds in order to create cell-scaffold constructs, which are thereafter maintained in bioreactors to generate tissues identical to those required for replacement. Extensive efforts in understanding the characteristics of cells and their interaction with specifically tailored scaffolds holds the key to their attachment, controlled proliferation and differentiation, intercommunication, and organization to form tissues. The demand for tissue-engineered organs is enormous and this technology holds the promise to supply customized organs to overcome the severe shortages that are currently faced by the pediatric patient, especially due to organ-size mismatch. The contemporary state of tissue-engineering technology presented in this review summarizes the advances in the various areas of regenerative medicine and addresses issues that are associated with its future implementation in the pediatric surgical patient.

Saviour embryos? Preimplantation genetic diagnosis as a therapeutic technology

The creation of 'saviour siblings' is one of the most controversial uses of preimplantation genetic diagnosis (PGD). This paper outlines and invites ethical discussion of an extension of this technology, namely, the creation of 'saviour embryos' to serve as a source of stem cells to be used in potentially life-saving therapy for an existing child. A number of analogies between this hypothetical use of PGD and existing uses of IVF are offered and, in addition, between saviour embryos and proposed therapeutic applications of stem cell technology. The ethical significance of a number of disanalogies between these cases are explored and investigated. While the creation of saviour embryos would involve a significant shift in the rationale for IVF and PGD, it is suggested here that the urgent need of an existing individual should be prioritised over any obligations that might exist in relation to the creation or destruction of human embryos.

Towards organ printing: engineering an intra-organ branched vascular tree

IMPORTANCE OF THE FIELD

Effective vascularization of thick three-dimensional engineered tissue constructs is a problem in tissue engineering. As in native organs, a tissue-engineered intra-organ vascular tree must be comprised of a network of hierarchically branched vascular segments. Despite this requirement, current tissue-engineering efforts are still focused predominantly on engineering either large-diameter macrovessels or microvascular networks.

AREAS COVERED IN THIS REVIEW

We present the emerging concept of organ printing or robotic additive biofabrication of an intra-organ branched vascular tree, based on the ability of vascular tissue spheroids to undergo self-assembly.

WHAT THE READER WILL GAIN

The feasibility and challenges of this robotic biofabrication approach to intra-organ vascularization for tissue engineering based on organ-printing technology using self-assembling vascular tissue spheroids including clinically relevantly vascular cell sources are analyzed.

TAKE HOME MESSAGE

It is not possible to engineer 3D thick tissue or organ constructs without effective vascularization. An effective intra-organ vascular system cannot be built by the simple connection of large-diameter vessels and microvessels. Successful engineering of functional human organs suitable for surgical implantation will require concomitant engineering of a 'built in' intra-organ branched vascular system. Organ printing enables biofabrication of human organ constructs with a 'built in' intra-organ branched vascular tree.

Complete genetic correction of ips cells from Duchenne muscular dystrophy

Human artificial chromosome (HAC) has several advantages as a gene therapy vector, including stable episomal maintenance that avoids insertional mutations and the ability to carry large gene inserts including the regulatory elements. Induced pluripotent stem (iPS) cells have great potential for gene therapy, as such cells can be generated from the individual's own tissues, and when reintroduced can contribute to the specialized function of any tissue. As a proof of concept, we show herein the complete correction of a genetic deficiency in iPS cells derived from Duchenne muscular dystrophy (DMD) model (mdx) mice and a human DMD patient using a HAC with a complete genomic dystrophin sequence (DYS-HAC). Deletion or mutation of dystrophin in iPS cells was corrected by transferring the DYS-HAC via microcell-mediated chromosome transfer (MMCT). DMD patient- and mdx-specific iPS cells with the DYS-HAC gave rise to differentiation of three germ layers in the teratoma, and human dystrophin expression was detected in muscle-like tissues. Furthermore, chimeric mice from mdx-iPS (DYS-HAC) cells were produced and DYS-HAC was detected in all tissues examined, with tissue-specific expression of dystrophin. Therefore, the combination of patient-specific iPS cells and HAC-containing defective genes represents a powerful tool for gene and cell therapies.

Ethical aspects of tissue engineering: a review

Tissue engineering (TE) is a promising new field of medical technology. However, like other new technologies, it is not free of ethical challenges. Identifying these ethical questions at an early stage is not only part of science's responsibility toward society, but also in the interest of the field itself. In this review, we map which ethical issues related to TE have already been documented in the scientific literature. The issues that turn out to dominate the debate are the use of human embryonic stem cells and therapeutic cloning. Nevertheless, a variety of other ethical aspects are mentioned, which relate to different phases in the development of the field. In addition, we discuss a number of ethical issues that have not yet been raised in the literature.

Neural differentiation and potential use of stem cells from the human umbilical cord for central nervous system transplantation therapy

The human umbilical cord is a rich source of autologous stem and progenitor cells. Interestingly, subpopulations of these, particularly mesenchymal-like cells from both cord blood and the cord stroma, exhibited a potential to be differentiated into neuron-like cells in culture. Umbilical cord blood stem cells have demonstrated efficacy in reducing lesion sizes and enhancing behavioral recovery in animal models of ischemic and traumatic central nervous system (CNS) injury. Recent findings also suggest that neurons derived from cord stroma mesenchymal cells could alleviate movement disorders in hemiparkinsonian animal models. We review here the neurogenic potential of umbilical cord stem cells and discuss possibilities of their exploitation as an alternative to human embryonic stem cells or neural stem cells for transplantation therapy of traumatic CNS injury and neurodegenerative diseases.

Interspecies nuclear transfer: implications for embryonic stem cell biology

Accessibility of human oocytes for research poses a serious ethical challenge to society. This fact categorically holds true when pursuing some of the most promising areas of research, such as somatic cell nuclear transfer and embryonic stem cell studies. One approach to overcoming this limitation is to use an oocyte from one species and a somatic cell from another. Recently, several attempts to capture the promises of this approach have met with varying success, ranging from establishing human embryonic stem cells to obtaining live offspring in animals. This review focuses on the challenges and opportunities presented by the formidable task of overcoming biological differences among species.

The mitochondrial genome, a growing interest inside an organelle

Mitochondria are semi-autonomously reproductive organelles within eukaryotic cells carrying their own genetic material, called the mitochondrial genome (mtDNA). Until some years ago, mtDNA had primarily been used as a tool in population genetics. As scientists began associating mtDNA mutations with dozens of mysterious disorders, as well as the aging process and a variety of chronic degenerative diseases, it became increasingly evident that the information contained in this genome had substantial potential applications to improve human health. Today, mitochondria research covers a wide range of disciplines, including clinical medicine, biochemistry, genetics, molecular cell biology, bioinformatics, plant sciences and physiology. The present review intends to present a summary of the most exiting fields of the mitochondrial research bringing together several contributes in terms of original prospective and future applications.

Correction of a genetic defect in multipotent germline stem cells using a human artificial chromosome

Human artificial chromosomes (HACs) have several advantages as gene therapy vectors, including stable episomal maintenance that avoids insertional mutations and the ability to carry large gene inserts including regulatory elements. Multipotent germline stem (mGS) cells have a great potential for gene therapy because they can be generated from an individual's testes, and when reintroduced can contribute to the specialized function of any tissue. As a proof of concept, we herein report the functional restoration of a genetic deficiency in mouse p53-/- mGS cells, using a HAC with a genomic human p53 gene introduced via microcell-mediated chromosome transfer. The p53 phenotypes of gene regulation and radiation sensitivity were complemented by introducing the p53-HAC and the cells differentiated into several different tissue types in vivo and in vitro. Therefore, the combination of using mGS cells with HACs provides a new tool for gene and cell therapies. The next step is to demonstrate functional restoration using animal models for future gene therapy.

Human embryonic stem cells: preclinical perspectives

Human embryonic stem cells (hESCs) have been extensively discussed in public and scientific communities for their potential in treating diseases and injuries. However, not much has been achieved in turning them into safe therapeutic agents. The hurdles in transforming hESCs to therapies start right with the way these cells are derived and maintained in the laboratory, and goes up-to clinical complications related to need for patient specific cell lines, gender specific aspects, age of the cells, and several post transplantation uncertainties. The different types of cells derived through directed differentiation of hESC and used successfully in animal disease and injury models are described briefly. This review gives a brief outlook on the present and the future of hESC based therapies, and talks about the technological advances required for a safe transition from laboratory to clinic.

Pluripotential reprogramming of the somatic genome in hybrid cells occurs with the first cell cycle

The fusion of pluripotent embryonic cells with somatic cells results in reprogramming of the somatic cell genome. Oct4-green fluorescent protein (GFP) transgenes that do not contain the proximal enhancer (PE) region are widely used to visualize reprogramming of the somatic to the pluripotent cell state. The temporal onset of Oct4-GFP activation has been found to occur 40-48 hours postfusion. We asked whether activation of the transgene actually reflects activation of the endogenous Oct4 gene. In the current study, we show that activation of an Oct4-GFP transgene that contains the PE region occurs within 22 hours of fusion. In addition, demethylation of the Oct4-GFP transgene and that of the endogenous Oct4 and Nanog genes was found to occur within 24 hours of fusion. As this timing corresponds with the timing of cell cycle completion in embryonic stem cells and fusion hybrids (approximately 22 hours), we postulate that pluripotential reprogramming of the somatic cell genome begins during the first cell cycle after the fusion of a somatic cell with a pluripotent cell and has been completed by day 2 postfusion.

Commentary: is totipotency of a human cell a sufficient reason to exclude its patentability under the European law?

This article argues that totipotent character of human totipotent cells--defined as the capacity of a cell "to differentiate into all somatic lineages (ectoderm, mesoderm, endoderm), the germ line and extra-embryonic tissues such as the placenta"--is not a sufficient reason to exclude their patentability on the basis of Article 5(1) of the Directive 98/44/EC on the Legal Protection of Biotechnological Inventions (Biopatent Directive), which maintains that "the human body, at the various stages of its formation and development, [...] cannot constitute patentable inventions." Since human totipotent cells have both the potential to generate an entire new organism or to generate only different tissues or organs of an organism, they simultaneously fit the definition of the unpatentable human body at the earliest stage of its formation as well as of an element of the human body, which "may constitute a patentable invention" pursuant to Article 5(2) of the Biopatent Directive, whether that element is isolated from the human body or otherwise produced by means of a technical process. Therefore, this article suggests that, when evaluating patentability of human totipotent cells, they should be further evaluated according to their location and their method of derivation (i.e., whether human totipotent cells are located in the human body, whether they are isolated from the human body, or whether they are produced otherwise by means of a technical process). Disclosure of potential conflicts of interest is found at the end of this article.

Human embryonic stem cell derivation and nuclear transfer: impact on regenerative therapeutics and drug discovery

This review aims to introduce current and future uses of human embryonic stem cells derived from in vitro-fertilized embryos. These and stem cells derived from parthenogenetic and nuclear transfer embryos could be used for cell therapy, as in vitro cell models for drug discovery/screening, and for studying early human development and pathogenesis of human diseases. However, development of therapeutic and screening applications and products from embryonic stem cells is hampered by several barriers. Therefore, gaps in our current understanding of the basic science of stem cells need to be filled before either application can move forward with confidence.

Duplication of the sperm genome by human androgenetic embryo production: towards testing the paternal genome prior to fertilization

There is currently no technique for evaluating the sperm genome before fertilization. However, sperm genome duplication could offer a way forward, whereby one of the sister blastomeres of a 2-cell haploid androgenetic embryo could be analysed. A method was developed for production of human androgenotes by enucleation of oocytes at telophase II (TII) after intracellular sperm injection (ICSI). The results were compared with those obtained via the more usual procedure of oocyte enucleation at metaphase II (MII) prior to ICSI. TII enucleation led to an improvement in the rate of embryo survival, increased the production rate of 1PN-embryos, and also the production of 2- to 8-cell-stage embryos (85.0, 74.9 and 65.8% in TII enucleation, versus 73.8, 48.9 and 33.3% in MII enucleation). Fluorescence in-situ hybridization (FISH) analysis of 30 2- to 5-cell androgenic embryos for two to seven chromosomes revealed the correct chromosome distribution in 76.7% of haploid human androgenotes.

Biomaterials approach to expand and direct differentiation of stem cells

Stem cells play increasingly prominent roles in tissue engineering and regenerative medicine. Pluripotent embryonic stem (ES) cells theoretically allow every cell type in the body to be regenerated. Adult stem cells have also been identified and isolated from every major tissue and organ, some possessing apparent pluripotency comparable to that of ES cells. However, a major limitation in the translation of stem cell technologies to clinical applications is the supply of cells. Advances in biomaterials engineering and scaffold fabrication enable the development of ex vivo cell expansion systems to address this limitation. Progress in biomaterial design has also allowed directed differentiation of stem cells into specific lineages. In addition to delivering biochemical cues, various technologies have been developed to introduce micro- and nano-scale features onto culture surfaces to enable the study of stem cell responses to topographical cues. Knowledge gained from these studies portends the alteration of stem cell fate in the absence of biological factors, which would be valuable in the engineering of complex organs comprising multiple cell types. Biomaterials may also play an immunoprotective role by minimizing host immunoreactivity toward transplanted cells or engineered grafts.

Genetic modification of somatic cells for producing animal models and for cellular transplantation

Great progress has been made in two technologies related to biomedical research: (1) manipulating the genomes of cells; and (2) inducing stem cells in culture to differentiate into potentially useful cell types. These technologies can be used to create animal models of human disease and to provide cells for transplantation to ameliorate human disease. Both embryonic stem cells and adult stem cells have been studied for these purposes. Genetically modified somatic cells provide another source of cells for creating animal models and for cellular transplantation.

The status of human nuclear transfer

Human therapeutic cloning is a recently emerged application of somatic cell nuclear transfer (SCNT), which is currently being performed to produce patient-specific stem cell lines for future stem cell therapies. The advantages in producing human nuclear transfer (NT) embryos to derive NT stem cell lines are that these can be tailor-made (i.e., are autologous in nature) for the patient and may overcome the need to administer life-long immunosuppression following stem cell transplantation. Although the rationale for using NT embryos is not for reproductive purposes, human NT remains clouded in ethical, moral, and religious controversies. The recent retraction of high-impact factor publications in the field of human NT from a research group in South Korea has placed stem cell research in a delicate situation. These heavily publicized issues may hinder the progress of this research and may threaten to bring current research to a complete halt. This review outlines the recent status of human NT, its continuing progress and the difficulties the field faces. Of most concern are the ethical issues, which surround obtaining human oocytes for research. Recent evidence suggests that failed-to-fertilize oocytes are poor sources for human SCNT, but obtaining fresh, viable oocytes may be even more problematic. The current status of human SCNT is outlined in this review with particular reference made to, lessons learnt from animal research, the oocyte dilemma and optimization of human NT.

Screening for hereditary hemochromatosis: a clinical practice guideline from the American College of Physicians

Hereditary hemochromatosis is a genetic disorder of iron metabolism. Diagnosis of hereditary hemochromatosis is usually based on a combination of various genetic or phenotypic criteria. Decisions regarding screening are difficult because of the variable penetrance of mutations of the HFE gene and the absence of any definitive trials addressing the benefits and risks of therapeutic phlebotomy in asymptomatic patients or those with only laboratory abnormalities. The purpose of this guideline is to increase physician awareness of hereditary hemochromatosis, particularly the variable penetrance of genetic mutations; aid in case finding; and explain the role of genetic testing. This guideline provides recommendations based on a review of evidence in the accompanying background paper by Schmitt and colleagues. The target audience for this guideline is internists and other primary care physicians. The target patient population is all persons who have a probability or susceptibility of developing hereditary hemochromatosis, including the relatives of individuals who already have the disease.