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Expanded neural precursor cells provide an attractive alternative to primary fetal tissue for cell replacement therapies in neurodegenerative diseases. In this study we transplanted epigenetically propagated human neural precursor cells into a rat model of Huntington's disease. Neural precursors survived transplantation and large numbers differentiated to express neuronal antigens, including some that expressed DARPP-32, indicating a mature striatal phenotype had been adopted. Neuronal fibers from the grafts projected diffusely throughout the host brain, although there was no evidence that outgrowth was specifically target directed. This study supports the contention that propagated human neural precursors may ultimately be of use in therapeutic neural transplantation paradigms for diseases such as Huntington's disease.

“Proof-of-principle” that cell replacement therapy works for neurodegeneration has been reported, but only using donor cells collected from fetal brain tissue obtained from surgical terminations of pregnancy. Surgical terminations of pregnancy represent an increasingly limited supply of donor cells due to the tendency towards performing medical termination in much of Europe. This imposes a severe constraint on further experimental and clinical cell transplantation research. Therefore, we explore here the feasibility of using medical termination tissue as a donor source. Products of conception were retrieved from surgical terminations over the last 7 years and from medical terminations over the last 2.5 years. The number of collections that yielded fetal tissue, viable brain tissue, and identifiable brain regions (ganglionic eminence, ventral mesencephalon, and neocortex) were recorded. We studied cell viability, cell physiological properties, and differentiation potential both in vitro and following transplantation into the central nervous system of rodent models of neurodegenerative disease. Within equivalent periods, we were able to collect substantially greater numbers of fetal remains from medical than from surgical terminations of pregnancy, and the medical terminations yielded a much higher proportion of identifiable and dissectible brain tissue. Furthermore, we demonstrate that harvested cells retain the capacity to differentiate into neurons with characteristics appropriate to the region from which they are dissected. We show that, contrary to widespread assumption, medical termination of pregnancy-derived fetal brain cells represent a feasible and more readily available source of human fetal tissue for experimental cell transplantation with the potential for use in future clinical trials in human neurodegenerative disease.

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.

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.

Transplantation of human fetal CNS tissue is a promising therapy for neurodegenerative conditions such as Huntington's disease (HD), but its widespread adoption is limited by restricted tissue availability. One method of overcoming this problem would be to store the tissue in hibernation medium, an approach that we reported previously for human fetal striatal tissue stored for up to 24 h. We now demonstrate the feasibility of storing such tissue for up to 8 days in hibernation medium. When either fresh or 8-day hibernated striatal cells were cultured under standard conditions for 4 days, the proportion of DARPP-32-positive neurons did not differ significantly, although the total number of cells was significantly less from tissue that had been hibernated. Six weeks after transplantation into cyclosporin A-immunosuppressed unilateral quinolinic acid-lesioned rats, there was no significant difference between fresh and hibernated grafts, both in terms of graft volume and extent of striatal phenotypic markers. This study therefore clearly demonstrates that hibernation of human fetal striatal tissue for up to 8 days is not deleterious to its differentiation in culture or survival following transplantation, and is therefore an appropriate method of storage for this tissue.

Embryonic neural precursors (ENPs), also termed neural stem cells or “neurospheres,” are an attractive potential source of tissue for neural transplantation, because of their capacity to expand in number in vitro while retaining the ability to develop into the major phenotypes of the CNS. ENPs are isolated from the developing brain and proliferate in the presence of mitogens such as FGF-2 and EGF. Subsequent withdrawal of these mitogens and exposure to a suitable substrate results in differentiation into the major cell types of the CNS. As well as its role in precursor cell expansion, FGF-2 also plays a key role in the division of astrocytes, and in neuronal differentiation. Thus, it is important to establish the optimal concentrations of this factor for expansion and differentiation of neuronal phenotypes. Here we explore the effect of FGF-2 concentrations ranging from 1 to 20 ng/ml on the expansion and differentiation capacity of ENPs isolated from the cortex and striatum of E14 mice. ENP expansion was seen under all conditions, but was greatest at 10 and 20 ng/ml and least at 1 ng/ml. The numbers of neurons (as a proportion of total cell number) differentiating from these ENP populations appeared to be greatest at 1 ng/ml. However, once adjustments were made for the amount of expansion at each dose, final neuronal yield was maximum at the highest concentration of FGF-2 used (20 ng/ml).