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Transplantation of fetal spinal cord (FSC) tissue has demonstrated significant potential in animal models for achieving partial anatomical and functional restoration following spinal cord injury (SCI). To determine whether this strategy can eventually be translated to humans with SCI, a pilot safety and feasibility study was initiated in patients with progressive posttraumatic syringomyelia (PPTS). A total of eight patients with PPTS have been enrolled to date, and this report presents findings for the first two patients through 18 months postoperative. The study design included detailed assessments of each subject at multiple pre- and postoperative time points. Outcome data were then compared with each subject's own baseline. The surgical protocol included detethering, cyst drainage, and implantation of 6-9-week postconception human FSC tissue. Immunosuppression with cyclosporine was initiated a few days prior to surgery and continued for 6 months postoperatively. Key outcome measures included: serial magnetic resonance imaging (MRI) exams, standardized measures of neurological impairment and functional disability, detailed pain assessment, and extensive neurophysiological testing. Through 18 months, the first two patients have been stable neurologically and the MRIs have shown evidence of solid tissue at the graft sites, without evidence of donor tissue overgrowth. Although it is still too soon to draw any firm conclusions, the findings from the initial two patients in this study suggest that intraspinal grafting of human FSC tissue is both feasible and safe.

The feasibility and safety of a procedure involving fetal spinal cord tissue transplantation in patients with syringomyelia was assessed using a neurophysiological protocol designed to quantitate peripheral nerve function, spinal cord reflex excitability, and spinal cord conduction pathways essential for somatosensory evoked potentials. We report here data obtained before and for 18 months following the transplantation procedure performed on the first two patients in this study. The neurophysiological assessment protocols included measures of cortical and spinal cord evoked potentials, H-reflex excitability, and peripheral nerve conduction. Prior to the procedure, both patients had significant deficits on some of the neurophysiological measures, for example, lower extremity cortical evoked potentials. However, robust measures of intact pathways, such as upper extremity cortical evoked potentials, were also observed preoperatively in both patients. Thus, it was anticipated that conduction in these intact pathways could be at risk either from complications from the transplantation procedure and/or from continued expansion of the syrinx. Following the transplantation procedure, no negative changes were observed in any of the neurophysiological measures in either patient. In addition, patient 1 showed a decrease in the rate potentiation of tibial H-reflexes on the right side and an increase in the response probability of left tibial H-reflexes. The results of this postoperative longitudinal assessment provide a first-level demonstration of the safety of the intraspinal neural tissue transplantation procedure. However, the consideration of safety is currently limited to the grafting procedure itself, since the long-term fates of the donor tissue in these two patients remain to be shown more definitively.

Extrinsic factors appear to contribute to the lack of regeneration in the injured adult spinal cord. It is likely that these extrinsic factors include a group of putative growth inhibitory molecules known as chondroitin sulfate proteoglycans (CSPGs). The aims of this study were to determine: (1) the consequences of spinal cord contusion injury on CSPG expression, (2) if CSPGs can be degraded in vivo by exogenous enzyme application, and (3) the effects of intraspinal transplantation on the expression of CSPGs. Chondroitin 6-sulfate proteoglycan immunoreactivity (CSPG-IR) dramatically increased following spinal cord contusion injury both at and adjacent to the injury site compared to normal controls (no surgical procedure) and laminectomy-only controls by 4 days postinjury. The dramatic increase in CSPG-IR persisted around the lesion and in the dorsal one-half to two-thirds of the spinal cord for at least 40 days postinjury. Glial fibrillary acidic protein (GFAP)-IR patterns were similarly intensified and spatially restricted as CSPG-IR patterns. These results suggest that: (1) CSPGs may contribute to the lack of regeneration following spinal cord injury and (2) astrocytes may contribute to the production of CSPGs. In addition, our results show that CSPGs could be cleaved in vivo with exogenous chondroitinase ABC application. This demonstration of cleavage may the basis for a model to directly assess CSPGs' role in growth inhibition in vivo (studies in progress) and hold potential as a therapeutic approach to enhance growth. Interestingly, the robust, injury-induced CSPG-IR patterns were not altered by intraspinal grafts of fetal spinal cord. The CSPG expression profile in the host spinal cord was similar to time-matched contusion-only animals. This was also true of GFAP-IR patterns. Furthermore, the fetal spinal cord tissue, which was generally CSPG negative at the time of transplantation, developed robust CSPG expression by 30 days posttransplantation. This increase in CSPG expression in the graft was paired with a moderate increase in GFAP-IR. CSPG-IR patterns suggest that these molecules may contribute to the limited regeneration seen following intraspinal transplantation. In addition, it suggests that the growth permissiveness of the graft may change overtime as CSPG expression develops within the graft. These correlations in the injured and transplanted spinal cord support CSPGs' putative growth inhibitory effect in the adult spinal cord.

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved., (Copyright 1997 Academic Press.)

Human fetal spinal cord (FSC) tissue was obtained from elective abortions at 6-14 wk gestational age (GA). The specimens were then either immediately processed for immunohistochemical analysis or xenotransplantation. In the latter case, donor tissue was prepared as a dissociated cell suspension and then introduced either subpially or intraspinally into contusion lesions of the adult rat midthoracic spinal cord. The xenografts were subsequently examined by conventional histological and immunohistochemical methods at 2-3 mo postgrafting. Immunostaining showed that MAP2 was expressed heavily in cells residing in the mantle layer of the human fetal spinal cord in situ as early as 6 wk GA. Subpial and intraparenchymal xenografts also were intensely immunoreactive for MAP2, but no staining of surrounding host neural tissue was detected. We conclude that the differential expression of MAP2 can be used to distinguish human graft tissue from the surrounding rat spinal cord in this xenograft paradigm. Under appropriate staining conditions, MAP2 can thus serve to facilitate analyses of host-graft integration, donor cell migration, and neuritic outgrowth.

Solid or suspension grafts of fetal spinal cord (FSC), caudal brainstem (FBSt), neocortex (FNCx) or a combination of either FSC/FNCx or FSC/FBSt were placed into cavities produced by static loading (i.e., compression) of the spinal cord of adult cats two to 30 weeks after injury. Extensively vascularized, viable graft tissue was found in all animals with the exception of two cats which showed active rejection of their transplants. Surviving grafts showed many immature characteristics 6-9 weeks after transplantation. However, by 20-30 weeks, FSC and FBSt grafts were more mature. Grafts integrated with the host gray and white matter and neuritic processes from both host and graft were seen crossing the host-graft interface. Host calcitonin gene related peptide (CGRP)-like immunoreactive axons could be traced into FSC and FBSt grafts. A more restricted ingrowth of host serotonin (5-HT)-like immunoreactive fibers was seen in FSC grafts. Our results suggest that the capacity of homotypic transplants to promote recovery of function is greater than heterotypic transplants. Additionally, it appears that the functional capacity of the graft depends upon graft survival, the time interval between injury and transplantation, and whether or not the lesion cavity was debrided prior to grafting.

Neural tissue transplantation has become recognized widely as a powerful experimental tool for studying structure-function relationships, development, plasticity, and capacities for regeneration in the adult CNS. In addition, this area of investigation has generated considerable interest in approaches that might be applicable to a variety of catastrophic neurological disorders. In this regard, attention has been given to neural tissue grafting as a potential therapeutic strategy in various forms of neurodegenerative disease. More recently, however, other investigations have begun to focus on the possible application of peripheral and central neural tissue transplants for promoting repair in forms of CNS trauma. This review highlights various neural transplantation approaches that have been explored primarily in the context of injury to the adult CNS, with emphasis on spinal cord injury. An overview is presented of the evolution of this area of research in terms of emerging biological perspectives, technological advances, and experimental modelling. Discussion centers on progress that has been made and a variety of theoretical and practical issues that remain to be resolved.

Magnetic resonance (MR) imaging was evaluated for its possible diagnostic application in determining the survival of fetal central nervous system tissue grafts in the injured spinal cord. Hemisection cavities were made at the T11-L1 level of eight adult female cats. Immediately thereafter, several pieces of tissue, either obtained from the fetal cat brain stem on embryonic Day 37 (E-37), from the fetal neocortex on E-37, or from the fetal spinal cord on E-23, were implanted into the cavities made in seven cats. The eighth cat served as a control for the effect of the lesion only. In another group of four animals, a static-load compression injury was made at the L-2 level. Seven weeks later, the lesion was resected in three cases and fragments of either fetal brain-stem or spinal cord tissue were introduced. A small cyst was observed in a fourth cat in the compression injury group and a suspension of dissociated E-23 brain-stem cells was injected into this region of cavitation without disturbing the surrounding leptomeninges. Five months to 2 years posttransplantation, MR imaging was performed with a 2.0-tesla VIS imaging spectrometer by acquiring multislice spin-echo images (TR 1000 msec, TE 30 msec) in both the transverse and sagittal planes. Collectively, these intermediate-weighted images revealed homogeneous, slightly hyperintense signals at the graft site relative to the neighboring host tissue in seven of the 11 graft recipients. Two of the remaining four cats exhibited signals from the graft site that were approximately isointense with the adjacent host spinal cord, and the final two cats and the lesion-only control presented with very hypointense transplant/resection regions. The hyperintense and isointense images were tentatively interpreted as representing viable graft tissue, whereas the hypointense transplant/resection sites were considered to be indicative of a lack of transplant survival or the absence of tissue in the lesion-only control animal. Postmortem gross inspection of fixed specimens and light microscopy verified the MR findings in the control animal in 10 of the 11 graft recipients by showing either transplants and/or cysts corresponding to the MR images obtained. In one cat in the hemisection group, histological analysis revealed a very small piece of graft tissue that was not detected on the MR images. Therefore, it is suggested that within certain spatial- and contrast-resolution limits, MR imaging can reliably detect the presence of transplanted neural tissue in both the hemisected and compression-injured spinal cord of living animals.(ABSTRACT TRUNCATED AT 400 WORDS)

This article reviews recent findings concerning the feasibility, basic neurobiology, and potential functional benefits of fetal CNS tissue grafts into acute and chronic lesions of the adult spinal cord. In the rat, neuro-anatomical observations suggest that transplants into resection cavities establish neuritic projections that could functionally reunite separated rostral and caudal segments of the host spinal cord. Furthermore, some complementary electrophysiological evidence has been obtained for synaptic connectivity between host and graft neurons. In these studies, extracellular single-unit activity was evoked in fetal spinal cord (FSC) transplants by stimulating host dorsal roots that had been juxtaposed to donor tissue at the time of transplantation. In other investigations, we examined whether grafts could also establish axonal projections to appropriate areas of gray matter in the chronically injured spinal cord. For this purpose, fetal serotoninergic (5-HT) neurons were injected caudal to complete spinal cord transections that had been made 1-3 months earlier. Immunocytochemistry revealed that these cells projected their axons into gray matter regions normally innervated by bulbospinal 5-HT neurons. To investigate transplantation in a more clinically relevant lesion model, a third group of experiments involved injection of dissociated cell suspensions into acute [less than 24 h postinjury (p.i.)]), subchronic (7-10 days p.i), and chronic (greater than or equal to one month, p.i.) contusion lesions. Such grafts routinely filled areas that otherwise would have been regions of cavitation extending rostral-caudal distances of approximately 7 mm. FSC transplants in such injuries also appeared to influence some aspects of motoneuron excitability and hindlimb locomotion. More recent studies of the cat spinal cord have extended these findings in the rat by showing long-term survival (greater than 2 years) of fetal CNS allografts in recipients with either subtotal transection or compression lesions. Preliminary studies of connectivity have also shown host-graft projection patterns similar to those seen in the rat. Behavioral analyses are currently underway to examine the effects of fetal grafts in cats with chronic postcompression lesions. These observations in the rat and cat are discussed in the general context of basic biological and clinical issues relevant to the long-term objective of promoting functional improvement in the damaged spinal cord.