Stem cells: moving the biology towards the clinic

Abstract

Regenerative MedicineVol. 2, No. 3 Conference SceneFree AccessStem cells: moving the biology towards the clinicJulie T DanielsJulie T DanielsCells for Sight Transplantation & Research Programme, Division of Pathology, UCL Institute of Ophthalmology, 11–43 Bath Street, London EC1V 9EL, UK. Search for more papers by this authorEmail the corresponding author at j.daniels@ucl.ac.ukPublished Online:21 May 2007https://doi.org/10.2217/17460751.2.3.313AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInRedditEmail The first Stem Cells World Congress, held in La Jolla, CA, USA, February 12–13, 2007, brought together a broad cross-section of academic and industry-based researchers to discuss the basic biology and therapeutic application of stem cells. The first part of the conference was dedicated to clinical perspectives and provided an update on therapeutic stem cell strategies in development and already in the clinic.The first talk of the meeting was given by Robert Harman of VetStem, Inc. who described the successful clinical use of autologous adipose-derived cells in over 2000 horses and dogs for the treatment of injuries and degenerative conditions. This presentation was followed by a lively debate about using material in the clinic without characterization of its properties and highlighted the importance of not overplaying the clinical potential of stem cells without ensuring that stem cells have actually been transplanted. It was generally felt that this would be vital for building and maintaining public and investor confidence in stem cells.Robin Ali, from the UCL Institute of Ophthalmology in London, UK, presented his recent work aimed at developing a therapeutic strategy for blinding retinal degeneration involving photoreceptor loss. Repair of damage by cell transplantation is one of the most feasible types of CNS repair; however, previous attempts to transplant brain- and retina-derived stem cells into the retina have been disappointing owing to poor integration and a lack of connectivity and functionality of the cells. Ali explained that this was likely to be due to the inability of the adult retina to incorporate stem cells or to promote photoreceptor differentiation. Therefore, his group took donor cells from the developing retina, at a time coincident with the peak of rod genesis, and transplanted those into a mouse model of adult retinal degeneration. Now, they could achieve integration, differentiation, connectivity and improve visual function, indicating the importance of understanding the normal stem cell developmental process in developing strategies to treat adult tissues.Stephen Minger of Kings College London, UK, delivered the first keynote address of the meeting, which outlined the biopolitical and therapeutic landscape of stem cell research. Minger described the legislative timeline from the birth of the first baby using the technique of in vitro fertilization, through to the establishment of the UK Human Fertilisation and Embryos Authority. Since 1990, it has been permitted in the UK to use spare embryos or to create embryos for research under license. Minger and colleagues were awarded one of the first two licenses to work with human embryonic stem cells in the UK in 2002. It is necessary to obtain informed consent from the donors, no financial inducement can be given and consent cannot be withdrawn once an embryo is in culture. The UK government have licensed 11 research establishments and have also set up a national stem cell bank into which all embryonic stem cell lines must be deposited. These lines are made freely available to other researchers, even if they are your competitors. Minger went on to discuss current research programs aimed at screening embryos in order to make a variety of disease-specific cell lines with a purpose of developing therapeutic strategies for conditions such as Parkinson’s disease, vascular disease or cardiac repair. Owing to the technical challenges involved in the differentiation of embryonic stem cells and the limited supply of donor material, Minger and colleagues wish to use somatic cell nuclear replacement to produce blastocysts from cow eggs containing human DNA. It is not yet known if regulatory approval will be given for this technology.Jay Sharma from Celprogen discussed the potential for using human embryonic stem cells harvested from amniotic membrane and amniotic fluid as autologous or allogeneic stem cell therapy. The company provides cells and culture reagents for research. Injected human amniotic membrane epithelial cells expressed markers of glial cells, astrocytes and neurofilaments 6 weeks post-transplantation into a rat model of spinal injury. These cells may have facilitated the recovery from the spinal cord injury.I discussed the blinding effects of the failure of limbal epithelial stem cells to maintain the epithelium of the cornea. I went on to present clinical data of the outcome of cultured limbal epithelial stem cell transplantation in patients at Moorfields Eye Hospital, London, UK. The current clinical success rate, defined as improved vision, is currently 70%. Both autologous and allogeneic donor cells can be used. Despite the clinical improvement, I pointed out that the mechanism of efficacy is still unknown. I also described the significant challenge faced by researchers to comply with the increasing burden of regulatory compliance required to get into the clinic.Maya Sieber-Blum from the Medical College of Wisconsin, WI, USA, gave the first talk of the stem cell biology series. She described a novel population of multipotent adult stem cells that reside in the bulge of hair follicles. These epidermal neural crest stem cells were found to exhibit a degree of plasticity as they produced neurons, myofibroblasts and bone cartilage from clonal populations. While these cells share the same niche as epidermal stem cells, Sieber-Blum used serial analysis of gene expression (SAGE) libraries to demonstrate that they have different patterns of gene expression. When the epidermal neural crest cells were transplanted from a green fluorescent protein (GFP) mouse into a contused spinal cord injury, they were found to remain at the implantation site, did not form tumors, did not proliferate and the scar tissue became vascularized. A subset of the transplanted cells expressed markers for neurons and oligodendrocytes and γ-aminobutyric acid (GABA)energic expressors.Fred Gage of the Salk Institute, CA, USA, delivered the second keynote address, which gave a whistlestop tour of his eminent career in the field of stem cells and the CNS. Gage was originally of the opinion that the adult CNS does not regenerate. However, his work has shown that neurogenesis does occur in areas of the adult brain where information is processed, specifically the hippocampus. The dentate gyrus of the hippocampus is one area where cell division occurs. Neurogenesis is thought to occur at three stages in life (E16, P5 and throughout life) and is enhanced by an enriched environment, exercise, stroke, epilepsy, genetic factors (most significant), stress and aging. For example, Gage showed that running increased neurogenesis in mice, with detectable changes apparent in the dentate gyrus. Methodology for the culture of adult neural stem cells have been developed in Gage’s laboratory. Fibroblast growth factor (FGF)-2 and insulin-like growth factor (IGF)-1 are two important requisites for this. Upon transplantation, the local environment dictates the fate of these cells after grafting. The presence of a vascular interface has an important influence on engraftment. Hippocampal astrocytes appear to create a neurogenic niche. Gage has found that the fate of neural stem cell commitment is regulated by Wnts, in particular Wnt3. Hippocampal neurogenesis is inhibited by blocking Wnt signaling. Gage and his team are now researching the downstream signals of Wnt involved in the early determination of neural stem cell fate.The next speaker, Thomas Zwaka from the Baylor College of Medicine, TX, USA, discussed the self-renewal properties of embryonic stem cells. Zwaka described embryonic stem cells as cancer cells owing to their capacity for infinite growth, sustained telomerase activity and ability to form tumors in vivo, which highlighted the concerns about transplanting an undifferentiated embryonic stem cell in a therapeutic setting. Encouragingly though, Zwaka provided evidence that embryonic stem cells do not divide asymmetrically, an unusual property for stem cells, and therefore it may be possible to eliminate undifferentiated cells from a population.Gregor Adams from Massachusetts General Hospital, MA, USA, explained the importance of understanding the role of the microenvironment and intracellular signaling pathways in stem cell function. Using hematopoesis as a model system, Adams and others have previously identified the osteoblast as a component of the adult hematopoetis stem cell niche and that activation of parathyroid hormone (PTH) receptor on these osteoblasts increases stem cell number. In this presentation, he demonstrated that the pharmacological use of PTH can increase the number of hematopoetic stem cells mobilized into the blood for stem cell harvests, that PTH protects these stem cells from repeated exposure to chemotherapy and can even increase hematopoetic stem cell numbers in recipients. These data suggest that the niche may be a suitable target for pharmacological manipulation of stem cells.The last speaker of the day was Stephen Sheridan from Millipore, who discussed a number of products available that may be of use to the stem cell researcher, including porous membrane chambers for co-culture experiments.The second day of the meeting in the stem cell biology section commenced with a talk by Thomas Skutella of the University of Tuebingen, Germany. His group demonstrated that spermatogonial stem cells isolated from the testis can be cultured in the presence of glial cell line-derived neurotrophic factor (GDNF) to form berry-like structures. With leukemia-inhibitory factor (LIF) and hematopeotic stem cell medium, they produced nest-like structures and expressed nanog, octamer (OCT)-4, stage-specific embryonic antigen (SSEA)-4 and E-cadherin – none of which are expressed in the testis. The spermatogonial cells are capable of undergoing osteogenic, pancreatic or neural differentiation. Once differentiated into a pancreatic lineage, 70% of the cells express insulin and continue to do so 2 weeks post-transplantation in vivo. Sketulla also explained the value of high-throughput in situ hybridization in the analysis of stem cell gene expression profiles in the intestine and enteric nervous system. He also demonstrated the importance of the repulsive guidance molecule in the differentiation of neural precursors.Anders Haegerstrand of Neuronova devoted his keynote presentation to the approach of discovering drugs that can activate endogenous stem cells. He explained some of the difficulties and challenges facing the therapeutic stem cell community, including market size and commercial viability. Before venture capitalists will invest in stem cell therapies, they will need to see evidence of large commercial returns. This has not yet occured. There are also intellectual property difficulties surrounding donor cells and the big pharmaceutical companies are not set up for large-scale therapeutic cell culture. As a result, many ‘therapy’ companies have become cell screening facilities. To make a good cell therapy product, it must be in good supply, expandable and be capable of stable differentiation, be safe and have public acceptance. These questions have not been fully answered for embryonic, fetal or adult stem cells. However, screening of drugs that may be capable of activating endogenous stem cells can follow the usual drug-discovery pathway and will be safer to commercialize. Neuronova are concentrating on Parkinson’s disease. Their approach is to identify the genes involved, to use neural stem cells in bioassays and also in vivo models to develop new pharmaceutical products.Cosimo de Bari from King’s College London discussed his approach to skeletal repair using mesenchymal stem cells. de Bari also recognized the challenge of producing a consistent stem cell therapy product and the difficulty in comparing the outcome data from different clinical trials. His hypothesis is that the synovial membrane acts as a reservoir of ‘joint stem cells’. He discussed some of his unpublished data, suggesting that periosteum-derived mesenchymal stem cells are more differentiated along the osteogenic pathway than synovial-derived mesenchymal stem cells. He suggested that it may be possible to expand and select highly purified and minimally manipulated mesenchymal stem cells for in situ tissue engineering.The next keynote address was given by Mahendra Rao of InVitrogen. The emphasis of his talk was the characterization of human embryonic stem cells. He pointed out that it is currently very difficult to standardize the culture of these cells owing to issues such as the use of different donors, developmental derivation stage and culture methodologies. However, despite this, the overall gene expression profiles of the embryonic stem cells currently available are very similar. Rao suggests quantitative polymerase chain reaction (qPCR) as a method to rapidly detect changes in positive and negative marker expression. He also pointed out that it will be necessary to establish markers of identity and stability. Still, the issue of comparing data with other laboratories must be addressed. Rao proposed the introduction of a freely available reference standard to facilitate this.The final section of the meeting discussed the commercial applications of stem cell research. Mario Salguero from Cell Line Genetics highlighted the problem of stem cell line contamination. Apparently, over a third of all cell lines are contaminated by inter- or intra-species contamination or are incorrectly labelled. Salguero suggested that short tandem repeat (STR) DNA markers would be useful in confirming the identity and purity of individual cells lines. It was interesting to hear that 13% of the human embryonic stem cell lines they had tested in the previous 9 months were positive for mouse or had the wrong human DNA.Dan Collins from BioE described a multilineage progenitor cell derived from human cord blood that expresses CD45, CD34 and CD9. He reported these cells to be capable of single cell colony formation and differentiation along osteoblastic, endothelial, myogenic, cardiac, neurogenic and hepatopancreatic pathways. The cells are commercially available.A new pluripotent human stem cell was described by James Kelly from Stem Cell Innovations. These primordial germ cells are isolated from fetal gonads recovered from late first trimester abortions. The company are able to culture the cells without feeders directly onto tissue culture plastic in the presence of knockout serum Dulbecco modified eagle’s minimal essential medium (DMEM). These cells share some markers of embryonic stem cells but do not contribute to tissues when injected into a mouse blastocyst. In culture, the cells can differentiate along neural or endothelial pathways, depending upon culture conditions.Ralph Snodgrass from VistaGen Therapeutics discussed the use of embryonic stem cells as tools for drug discovery and development. Since embryonic stem cells can be differentiated along specific pathways in vitro, the resulting cell types, for example, cardiac, liver and pancreatic cells, can be used for drug-screening applications. This speaker reiterated the challenges of attracting commercial and venture capital investment in the stem cell field.Finally, Alan Smith from Cognate Bioservices closed the meeting by outlining the onerous regulatory requirements for the manufacture of stem cells for clinical trials. He discussed issues of compliance with Good Manufacturing Practice, including quality control, quality assurance, third-party agreements, raw material sourcing and cell banking. This presentation reminded all of us that, before stem cell therapies can enter routine clinical practice, we must all keep in mind from the outset, the regulatory and commercialization hurdles that must be overcome in addition to those challenges currently presented by our unanswered scientific questions.Highlights• Stem cells are central to tissue development and repair, hence, their fascinating biology and tantalising clinical potential have put them on the scientific and political map.• Research emphasis is now focused not just on a stem cell of interest but also its niche environment, with the aim of understanding stem cell regulation.• While potentially more controversial than adult stem cells, the plasticity of embryonic stem cells makes them an essential research tool in understanding tissue development, homeostasis and disease and may in the future contribute to new treatments.• Few stem cell therapies have yet reached the clinic; however, the plethora of research activity being undertaken is driving a cautiously optimistic view for future of stem cells in the clinic.• The stem cell therapy field remains largely unproven, therefore significant commercial investment may only come with a significant breakthrough.FiguresReferencesRelatedDetailsCited ByOutlook for stem cells in medicine13 December 2009 | Herald of the Russian Academy of Sciences, Vol. 79, No. 6 Vol. 2, No. 3 Follow us on social media for the latest updates Metrics History Published online 21 May 2007 Published in print May 2007 Information© Future Medicine LtdPDF download