Transplantation Of Human Fetal Tissue Research Articles

Combined cell-based therapy strategies for the treatment of Parkinson's disease: focus on mesenchymal stromal cells.

Parkinson's disease is a neurodegenerative condition characterized by motor impairments caused by the selective loss of dopaminergic neurons in the substantia nigra. Levodopa is an effective and well-tolerated dopamine replacement agent. However, levodopa provides only symptomatic improvements, without affecting the underlying pathology, and is associated with side effects after long-term use. Cell-based replacement is a promising strategy that offers the possibility to replace lost neurons in Parkinson's disease treatment. Clinical studies of transplantation of human fetal ventral mesencephalic tissue have provided evidence that the grafted dopaminergic neurons can reinnervate the striatum, release dopamine, integrate into the host neural circuits, and improve motor functions. One of the limiting factors for cell therapy in Parkinson's disease is the low survival rate of grafted dopaminergic cells. Different factors could cause cell death of dopaminergic neurons after grafting such as mechanical trauma, growth factor deprivation, hypoxia, and neuroinflammation. Neurotrophic factors play an essential role in the survival of grafted cells. However, direct, timely, and controllable delivery of neurotrophic factors into the brain faces important limitations. Different types of cells secrete neurotrophic factors constitutively and co-transplantation of these cells with dopaminergic neurons represents a feasible strategy to increase neuronal survival. In this review, we provide a general overview of the pioneering studies on cell transplantation developed in patients and animal models of Parkinson's disease, with a focus on neurotrophic factor-secreting cells, with a particular interest in mesenchymal stromal cells; that co-implanted with dopaminergic neurons would serve as a strategy to increase cell survival and improve graft outcomes.

Designing stem-cell-based dopamine cell replacement trials for Parkinson's disease.

Clinical studies of Parkinson's disease (PD) using a dopamine cell replacment strategy have been tried for more than 30 years. The outcomes following transplantation of human fetal ventral mesencephalic tissue (hfVM) have been variable, with some patients coming off their anti-PD treatment for many years and others not responding and/or developing significant side effects, including graft-induced dyskinesia. This led to a re-appraisal of the best way to do such trials, which resulted in a new European-Union-funded allograft trial with fetal dopamine cells across several centers in Europe. This new trial, TRANSEURO ( NCT01898390 ), is an open-label study in which some individuals in a large observational cohort of patients with mild PD who were undergoing identical assessments were randomly selected to receive transplants of hfVM. The TRANSEURO trial is currently ongoing as researchers have completed both recruitment into a large multicenter observational study of younger onset early-stage PD and transplantation of hfVM in 11 patients. While completion of TRANSEURO is not expected until 2021, we feel that sharing the rationale for the design of TRANSEURO, along with the lessons we have learned along the way, can help inform researchers and facilitate planning of transplants of dopamine-producing cells derived from human pluripotent stem cells for future clinical trials.

In Honor of LeRoy Walters: Introduction from the Editors.

In Honor of LeRoy Walters: Introduction from the Editors Eric M. Meslin (bio), Eric T. Juengst (bio), and Carol Mason Spicer (bio) Since the birth of bioethics, a persistent refrain has been that advances in science, technology, and health are occurring so quickly that they threaten to outpace society’s ability to understand and react to them. Genomics, big data, and synthetic biology preoccupy current scholarly and policy debates, just as organ transplantation, in vitro fertilization, human subjects research, and gene therapy did over the past forty years. But the history of bioethics is more than the topics it has addressed. It is also the story of the people whose voices shaped its debates and built society’s capacity to manage the escalating pace of technological change. LeRoy Walters is one of those contributors who made a difference. He is part of an original community of scholars and intellectuals who were involved in these issues from the earliest days of bioethics. Now an Emeritus Faculty at the Kennedy Institute of Ethics at Georgetown University, Walters joined the Kennedy Institute in 1971 as its first faculty member appointed to a multi-year term by the new Director, Andre Hellegers, and has remained affiliated with the Institute ever since. His academic training at Messiah College, Associated Mennonite Seminaries, University of Heidelberg, Free University of Berlin, and Yale University focused on religious studies culminating in a Ph.D. on just war theory that provided the moral foundation for his ongoing work. Rising through the academic ranks until becoming the Joseph P. Kennedy, Sr., Professor of Christian Ethics in 1993, Walters was also Director of the Kennedy Institute for a three-year period. In addition to teaching and mentoring during his tenure at the Institute, he was also a bioethics “builder.” He envisioned and implemented Bioethicsline, one of the first online, annotated databases for bioethics research in the world. Linked to the National Library of Medicine, Bioethicsline served as a portal to what would become the National Reference Center for Bioethics Literature, the largest resource of its kind in the world. During his tenure, the Kennedy Institute began housing the collections of past [End Page xi] bioethics commissions and advisory bodies and an innovative DNA Patent Database, an unusual project for a bioethicist. Walters was a recently appointed Associate Professor when the editors and contributors to this special issue of KIEJ first encountered him as graduate students and colleagues in the early 1980s. Generations of students and colleagues have subsequently benefitted from his wisdom and gracious mentoring, but so too have countless federal agencies, departments, advisory committees, and working groups that he assisted as a consultant, member, or chair. Walters was involved in many of the most significant bioethics policy discussions occurring in the U.S. from the 1970s through the 2000s. He was a consultant to the National Institute of Child Health and Human Development, the DHEW Ethics Advisory Board, and the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research, for whom he prepared a key background paper on fetal research and participated in the development of its Belmont Report. He served for three terms on the NIH Recombinant DNA Advisory Committee, chairing the committee’s Working Group on Human Gene Therapy, which established review criteria for clinical gene transfer research and is still functioning four decades later. He chaired the NIH Human Fetal Tissue Transplantation Research Panel; sat on the Ethical, Legal and Social Implications Research Planning and Evaluation Group Program of the National Human Genome Research Institute; was a member of the Bioethics Committee of the National March of Dimes, the DHEW Secretary’s Task Force on Compensation of Injured Research Subjects, and as a committee member of Institute of Medicine studies on AIDS and vaccine development. He was an influential advisor and consultant to the Congressional Office of Technology Assessment, Office for Protection from Research Risks, and two presidential bioethics commissions. In addition to his policy influence, he is a prolific writer and aggregator of resources for use by others. Walters is responsible for creating and co-editing with Tamar Joy Kahn and Doris Mueller Goldstein thirty-five volumes of the Bibliography of Bioethics...

Strategies for bringing stem cell-derived dopamine neurons to the clinic: A European approach (STEM-PD).

The treatment of Parkinson's disease (PD) has for over 50 years relied on dopaminergic therapies that are highly effective especially in the early years of the condition, but ultimately are limited by the development of side effects that relate to the nonphysiological stimulation of dopamine receptors including in nonstriatal areas. Targeted regenerative therapies designed to restore specifically the lost dopaminergic innervation of the striatum would therefore represent a major advance in treating PD. Transplantation of human fetal ventral midbrain tissue to the striatum of PD patients has provided proof-of-principle that such an approach can provide long-term clinical benefits with a reduced dependency on any oral dopaminergic agents. However, fetal tissue is associated with several ethical and logistical problems and therefore does not represent a realistic route to the clinical treatment of PD in the future. As a result, alternative cell sources have been explored and the methods for producing authentic midbrain dopaminergic neurons from pluripotent cells have now advanced to a stage which makes it possible to efficiently and reproducibly produce DA progenitors at a much higher purity than can be obtained from human fetal tissue. A stem cell-based therapy for PD therefore has the potential to circumvent many of the problems currently associated with fetal tissue grafting. Here, we describe the challenges faced and the strategies that have been pursued in our European effort to bring a human embryonic stem cell (hESC)-derived dopamine cell product to clinical trial for PD.

Modeling Human Leukemia Immunotherapy in Humanized Mice

The currently available human tumor xenograft models permit modeling of human cancers in vivo, but in immunocompromised hosts. Here we report a humanized mouse (hu-mouse) model made by transplantation of human fetal thymic tissue plus hematopoietic stem cells transduced with a leukemia-associated fusion gene MLL-AF9. In addition to normal human lymphohematopoietic reconstitution as seen in non-leukemic hu-mice, these hu-mice showed spontaneous development of B-cell acute lymphoblastic leukemia (B-ALL), which was transplantable to secondary recipients with an autologous human immune system. Using this model, we show that lymphopenia markedly improves the antitumor efficacy of recipient leukocyte infusion (RLI), a GVHD-free immunotherapy that induces antitumor responses in association with rejection of donor chimerism in mixed allogeneic chimeras. Our data demonstrate the potential of this leukemic hu-mouse model in modeling leukemia immunotherapy, and suggest that RLI may offer a safe treatment option for leukemia patients with severe lymphopenia.

Human melanoma immunotherapy using tumor antigen-specific T cells generated in humanized mice

A major factor hindering the exploration of adoptive immunotherapy in preclinical settings is the limited availability of tumor-reactive human T cells. Here we developed a humanized mouse model that permits large-scale production of human T cells expressing the engineered melanoma antigen MART-1-specific TCR. Humanized mice, made by transplantation of human fetal thymic tissue and CD34+ cells virally-transduced with HLA class I-restricted melanoma antigen (MART-1)-specific TCR gene, showed efficient development of MART-1-TCR+ human T cells with predominantly CD8+ cells. Importantly, MART-1-TCR+CD8+ T cells developing in these mice were capable of mounting antigen-specific responses in vivo, as evidenced by their proliferation, phenotypic conversion and IFN-γ production following MART-1 peptide immunization. Moreover, these MART-1-TCR+CD8+ T cells mediated efficient killing of melanoma cells in an HLA/antigen-dependent manner. Adoptive transfer of in vitro expanded MART-1-TCR+CD8+ T cells induced potent antitumor responses that were further enhanced by IL-15 treatment in melanoma-bearing recipients. Finally, a short incubation of MART-1-specific T cells with rapamycin acted synergistically with IL-15, leading to significantly improved tumor-free survival in recipients with metastatic melanoma. These data demonstrate the practicality of using humanized mice to produce potentially unlimited source of tumor-specific human T cells for experimental and preclinical exploration of cancer immunotherapy. This study also suggests that pretreatment of tumor-reactive T cells with rapamycin in combination with IL-15 administration may be a novel strategy to improve the efficacy of adoptive T cell therapy.

Treatment of Parkinson's disease using cell transplantation.

The clinical trials with intrastriatal transplantation of human fetal mesencephalic tissue, rich in dopaminergic neurons, in Parkinson's disease (PD) patients show that cell replacement can work and in some cases induce major, long-lasting improvement. However, owing to poor tissue availability, this approach can only be applied in very few patients, and standardization is difficult, leading to wide variation in functional outcome. Stem cells and reprogrammed cells could potentially be used to produce dopaminergic neurons for transplantation. Importantly, dopaminergic neurons of the correct substantia nigra phenotype can now be generated from human embryonic stem cells in large numbers and standardized preparations, and will soon be ready for application in patients. Also, human induced pluripotent stem cell-derived dopaminergic neurons are being considered for clinical translation. Available data justify moving forward in a responsible way with these dopaminergic neurons, which should be tested, using optimal patient selection, cell preparation and transplantation procedures, in controlled clinical studies.

Developing dopaminergic cell therapy for Parkinson's disease—give up or move forward?

Despite 3 decades of basic and clinical studies, there is still no dopaminergic cell therapy for Parkinson's disease. Several arguments have been put forward why this approach, so far tested with transplantation of human fetal mesencephalic dopamine-rich tissue, will never be of clinical use and should be abandoned: (1) Lack of efficacy in 2 sham surgery-controlled trials; (2) occurrence of troublesome off-medication dyskinesias in a subgroup of grafted patients; (3) disease process destroys grafted neurons; and (4) non-motor symptoms will not be influenced by intrastriatal dopaminergic grafts. Here, the author argues that, based on recent scientific advancements, the development of a dopaminergic cell therapy for Parkinson's disease should continue. Factors influencing the outcome after transplantation have now been identified, and dopaminergic neurons can be generated in large numbers from stem cells. Mechanisms of graft-induced dyskinesias are much better understood, and patients with well functioning grafts can exhibit long-term motor recovery of therapeutic value even in the presence of non-motor symptoms.

The long-term safety and efficacy of bilateral transplantation of human fetal striatal tissue in patients with mild to moderate Huntington's disease

Huntington's disease (HD) is a fatal autosomal dominant neurodegenerative disease involving progressive motor, cognitive and behavioural decline, leading to death approximately 20 years after motor onset. The disease is characterised...

Neuronal Transplants Reconstitute Complex Neuronal Circuitry and Rescue Phenotype

Neuronal Transplants Reconstitute Complex Neuronal Circuitry and Rescue Phenotype

Rebuilding the human brain

Creating new organs from the correspondent primordia is the goal of organogenesis in transplantation medicine (Hammerman, 2005). Unlike embryonic stem cells, primordia differentiate along defined organ-committed lines and steered differentiation is unnecessary. Rebuilding human brain structures through in situ organogenesis is a real clinical working hypothesis of our time. The challenge of such an approach is that a grafted primordium recapitulates the ontogenesis without neoplasia/teratoma or overgrowth, generates proper circuits, and establishes connections with the host. We previously showed the generation of new tissue with neostriatal-like morphological features after transplantation of human striatal fetal tissue in five Huntington’s disease (HD) patients, whose clinical course was positively affected by grafting (Gallina et al., 2008; 2010). These findings were interpreted as the capacity of neuroblasts to continue their development in the host. Here, we show some of the steps of the primordium growth in the brain of a further grafted HD patient and analyzed those intrinsic regulatory factors that may have played a role in promoting its development. The primordium graft expressed various neurotrophic factors, enriched with seladin-1, and also showed high levels of huntingtin. Moreover, the graft expressed a high level of neural recognition molecules and integrins, proteins that are involved in cell recognition function. Neuroblasts expressed connexin43-rich gap junctions. The presence of such proteins, which are involved in the intercellular communication process, indicates the potential of neuroblasts to establish graft-host connections. Currently, a real graft-host integration cannot be demonstrated. However, the establishment of some cellular connections is suggested by the results of cerebral metabolic imaging, which demonstrate not only the survival and longitudinal growth of the striatal grafts, but also a beneficial effect on distant cortical metabolism. Similarly, it is not clear whether the new structure works as a striatum or just has a striatal- like morphology. Nevertheless, the increase of D2 receptor binding at the striatal level suggests that the new structure sustains the striatal function and influences the patient’s clinical course.

Optimizing functional imaging protocols for assessing the outcome of fetal cell transplantation in Parkinson's disease

Clinical trials aiming to assess the safety and efficacy of fetal cell transplantation in Parkinson's disease rely on the hypothesis that the grafted tissue will survive and grow, restore striatal dopaminergic neurotransmission, improve the connectivity between striatum, thalamus and cortex and, thereby, produce long-lasting clinical improvement while avoiding the development of adverse effects. Although transplantation of human fetal ventral mesencephalic tissue has been reported as one of the most effective reparative therapies in Parkinson's disease patients to date, different studies have shown inconsistent results causing a paucity of new trials over the last decade. However, during this period, functional imaging alongside other scientific developments from clinical observations and animal work has significantly aided in understanding the mechanisms responsible for the success or failure of grafting human fetal tissue. Recent advances in functional imaging including both positron emission tomography and functional magnetic resonance imaging could be proven useful in vivo tools for the development and assessment of new clinically competitive trials. In this commentary we discuss how an optimized functional imaging protocol could assist new clinical trials using fetal cell transplantation in Parkinson's disease.

Plasticity and therapeutic potential of human fetal tissue

Rebuilding of brain structures and nervous circuitries with grafting of fetal tissue is currently being explored as a strategy to repair the damaged nervous system (Handb Clin Neurol 2009). Experimental studies demonstrated that transplanted neuroblasts can survive and proliferate in the host. Migration of primary or expanded neural precursors following transplantation has also been well documented. Cell migration plays a pivotal role in the organogenesis and contributes to multiple processes in adulthood, such as tissue repair and immune response. Migrating neuroblasts are capable of anatomically re-establishing damaged neural circuitries in the adult animal brain. These results suggest that there might also be a real potential for neurotransplantation in humans in order to promote reconstruction after brain injury. The challenge of such an approach is that the primordium recapitulates its ontogenesis in the host, being deprived of the fetal brain environmental cues, while it is subject to extrinsic cues coming from the diseased adult brain. In animals, recapitulation of normal development was achieved “simply“ by implanting fetal neurons. Striatal fetal grafting as a strategy of cell replacement has been extensively investigated in Huntington’s disease (HD) animal models. There is evidence that primary grafts of human fetal striatal tissue contain proliferative cells capable of migrating, differentiating and establishing robust graft-host interconnectivity, significantly recovering lesion-induced damage, without graft overgrowth or neoplastic proliferation (Lancet Neurol 2006). Based on these studies and the fact that current therapies do not prevent the unrelenting clinical course of HD, a clinical trial of human fetal striatal tissue transplantation for the treatment of HD has been initiated at the University of Florence. Fifteen HD patients underwent bilateral transplantation. The current report provides the first “in vivo“ evidence that unmanipulated grafted neural precursors from human striatal anlagen developed within the diseased striatum of HD patients and moved into the adult brain, reaching shortand long-distance appropriate anatomical targets. The anlagen development resulted in the building of metabolically active new nervous structures displaying striatal-like imaging features (Exp Neurol 2008, 2010). These events were accompanied by beneficial effects on the disease clinical course without negative outcomes, such as grafted tissue overgrowth or cyst formation.

Tissue culture before transplantation of frozen-thawed human fetal ovarian tissue into immunodeficient mice

To evaluate the effects of tissue culture on the viability and development of follicles in frozen-thawed human fetal ovarian tissue before transplantation into severe combined immunodeficient (SCID) mice and to determine the optimal duration of pretransplant tissue culture. Experimental prospective study. Animal center and reproductive laboratories in university hospitals. Frozen-thawed human fetal ovarian tissue samples from 20-week-old abortuses were randomly divided into four groups and cultured in vitro for 0, 3, 6, or 9 days before being xenografted into kidney capsules of bilaterally oophorectomized severe combined immunodeficient (SCID) mice. Grafts were removed 16 weeks after transplantation. Histological analysis and assessment of proliferative cell nuclear antigen (PCNA) expression levels were used to evaluate the survival and development of follicles. The proportion of growing follicles was significantly increased in groups cultured before transplantation as compared with the noncultured group. Sixteen weeks after transplantation, the number of follicles in the cultured grafts was higher than that in the noncultured grafts. Grafts cultured for 6 or 9 days showed higher proportions of preantral and antral follicles than grafts cultured for 0 or 3 days. PCNA immunohistochemical analysis indicated that follicle cells were in a proliferative state after culture and transplantation. The viability and development of human fetal follicles may be improved by pretransplant tissue culture. The optimal culture duration before transplantation of fetal ovarian tissue is 6 days.

A patient with Huntington’s disease and long-surviving fetal neural transplants that developed mass lesions

Transplantation of human fetal neural tissue into adult neostriatum is an experimental therapy for Huntington's disease (HD). Here we describe a patient with HD who received ten intrastriatal human fetal neural transplants and, at one site, an autologous sural nerve co-graft. Although initially clinically stable, she developed worsening asymmetric upper motor neuron symptoms in addition to progression of HD, and ultimately died 121 months post transplantation. Eight neural transplants, up to 2.9 cm, and three ependymal cysts, up to 2.0 cm, were identified. The autologous sural nerve co-graft was found adjacent to the largest mass lesion, which, along with the ependymal cyst, exhibited pronounced mass effect on the internal capsules bilaterally. Grafts were composed of neurons and glia embedded in disorganized neuropil; robust Y chromosome labeling was present in a subset of grafts and cysts. The graft-host border was discrete, and there was no evidence of graft rejection or HD pathologic changes within donor neurons. This report, for the first time, highlights the potential for graft overgrowth in a patient receiving fetal neural transplantation.

Neural Transplantation in Huntington's Disease: The NEST-UK Donor Tissue Microbiological Screening Program and Review of the Literature

Neural transplantation of human fetal tissue for Huntington's disease (HD) is now entering the clinical arena. The safety of the procedure has now been demonstrated in a number of studies, although the efficacy of such an approach is still being investigated. Stringent but practicable screening of the donor tissue for potential pathogens is an essential prerequisite for successful implementation of any novel transplant program that uses human fetal tissue. In this article we summarize the UK-NEST protocol for the screening of human fetal tissue being grafted to patients with mild to moderate HD. We describe the results of microbiological screening of 87 potential tissue donors in a pilot study, and of the first four donor-recipient patients included in the UK-NEST series. The rationale for the adoption and interpretation of the various tests is described and our methodology is compared with those previously used by other centers. This article therefore presents a comprehensive, logical yet pragmatic screening program that could be employed in any clinical studies that use human fetal tissue for neurotransplantation.

Das Transplantationsgesetz vom 8. Oktober 2004

The Transplantation Law was approved by Parliament on 8 October 2004. Its key features are a ban on trade in human organs, tissue and cells; the non-entitlement of donors of their next of kin to payment for organs; the definition of when death is considered to have occurred; the need for consent before removal takes place; the criteria for donations by living persons; the criteria and procedure for assigning donated organs to recipients; xenotransplantation; and the transplantation of human embryonic and fetal tissue and cells. As things stand at present, the law is expected to take effect at the beginning of 2007. The current fragmented legislation on transplant medicine will therefore be replaced in two years' time by a modern, consistent and comprehensive legal framework.

Huntingtons Disease: New Frontiers for Molecular and Cell Therapy

Huntington's disease (HD) is an incurable, adult-onset, dominantly inherited neurodegenerative disease, caused by a CAG expansion in the 5' coding region of the gene HD [encoding huntingtin (htt), which is ubiquitously expressed in all tissues]. The disease progresses inexorably with devastating clinical effects on motor, cognitive and psychological functions; death occurring approximately 18 years from the time of onset. These clinical symptoms primarily relate to the progressive death of medium-spiny GABA-ergic neurons of the striatum and in the deep layers of the cortex; during the later stages of the disease, the degeneration extends to a variety of brain regions, including the hypothalamus and hippocampus. The mechanism by which mutant htt leads to neuronal cell death and the question of why striatal neurons are targeted both remain to be further investigated. Certainly htt is required for cell survival and impairment of wild-type htt function can be involved in neurodegeneration, but considerable evidence also shows that trinucleotide repeat expansion into glutamine (polyQ domain) endows the protein with a newly acquired toxic activity. The increasing availability of HD animal models have allowed not only to investigate the function of htt, but also to screen and test potential therapeutic drugs in the promising area of neurotherapeutics. So, thorough analysis of these molecular and biochemical events, assessing the validity of candidate mechanisms, provides a means to identify effective therapeutic strategies for cellular repair. Here, the rationale and efficacy of different therapies are compared and alternative therapies are reviewed including intrastriatal transplantation of human fetal striatal tissue to support the cell replacement strategy in HD. Since functional restoration through neuronal replacement probably could be combined with neuroprotective strategies for optimum clinical benefit, in vivo and ex vivo gene therapy for delivery of neuroprotective growth factor molecules are also considered.

Progress in cerebral transplantation of expanded neuronal stem cells.

Given the success and limitations of human fetal primary neural tissue transplantation, neuronal stem cells (NSCs) that can be adequately expanded in culture have been the focus of numerous attempts to develop a superior source of replacement cells for restorative neurosurgery. To clarify recent progress toward this goal, the transplantation into the adult brain of NSCs, expanded in vitro before grafting, was reviewed. Neuronal stem cells can be expanded from a variety of sources, including embryos, fetuses, adult bone marrow, and adult brain tissue. Recent investigations of each of these expanded stem cell types have generated a large body of information along with a great number of unanswered questions regarding the ability of these cells to replace damaged neurons. Expanded NSCs offer many advantages over their primary tissue predecessors, but also may exhibit different functional abilities as grafted cells. Because expanded NSCs will most likely ultimately replace primary tissue grafting in clinical trials, this review was undertaken to focus solely on this distinct body of work and to summarize clearly the existing preclinical data regarding the in vivo successes, limits, and unknowns of using each expanded NSC type when transplanted into the adult brain. Embryonic stem cell-derived cells have demonstrated appropriate neuronal phenotypes after transplantation into nonneurogenic areas of the adult brain. Understanding the mechanisms responsible for this may lead to similar success with less studied adult neuronal progenitor cells, which offer the potential for autologous NSC transplantation with less risk of tumorigenesis.

Staging and preparation of human fetal striatal tissue for neural transplantation in Huntington's disease.

Transplantation of human fetal central nervous system tissue has been shown to be of benefit in Parkinson's disease, and is currently being explored as a therapeutic option in Huntington's disease. The success of a neural transplant is dependent on a number of factors, including the requirement that donor cells are harvested within a given developmental window and that the cell preparation protocols take account of the biological parameters identified in animal models. Although many of the criteria necessary for a successful neural transplant have been defined in animal models, ultimately they must be validated in human studies, and some issues can only ever be addressed in human studies. Furthermore, because neural transplantation of human fetal tissue is limited to small numbers of patients in any one surgical center, largely due to practical constraints, it is crucial that tissue preparation protocols are clearly defined and reproducible, so that (i) multicenter trials are possible and are based on consistent tissue preparation parameters, and (ii) results between centers can be meaningfully analyzed. Here we describe the preparation of human fetal striatum for neural transplantation in Huntington's disease, and report on the validation of a method for estimating the developmental stage of the fetus based on direct morphometric measurements of the embryonic tissue.