Immunomodulation with intrathymic grafts or anti-lymphocyte serum promotes long-term intraspinal allograft survival

Intermittent hypoxia and neurorehabilitation

In recent years, it has become clear that brief, repeated presentations of hypoxia [i.e., acute intermittent hypoxia (AIH)] can boost the efficacy of more traditional therapeutic strategies in certain cases of neurologic dysfunction. This hypothesis derives from a series of studies in animal models and human subjects performed over the past 35 yr. In 1980, Millhorn et al. (Millhorn DE, Eldridge FL, Waldrop TG. Respir Physiol 41: 87-103, 1980) showed that electrical stimulation of carotid chemoafferent neurons produced a persistent, serotonin-dependent increase in phrenic motor output that outlasts the stimulus for more than 90 min (i.e., a "respiratory memory"). AIH elicits similar phrenic "long-term facilitation" (LTF) by a mechanism that requires cervical spinal serotonin receptor activation and de novo protein synthesis. From 2003 to present, a series of studies demonstrated that AIH can induce neuroplasticity in the injured spinal cord, causing functional recovery of breathing capacity after cervical spinal injury. Subsequently, it was demonstrated that repeated AIH (rAIH) can induce recovery of limb function, and the functional benefits of rAIH are greatest when paired with task-specific training. Since uncontrolled and/or prolonged intermittent hypoxia can elicit pathophysiology, a challenge of intermittent hypoxia research is to ensure that therapeutic protocols are well below the threshold for pathogenesis. This is possible since many low dose rAIH protocols have induced functional benefits without evidence of pathology. We propose that carefully controlled rAIH is a safe and noninvasive modality that can be paired with other neurorehabilitative strategies including traditional activity-based physical therapy or cell-based therapies such as intraspinal transplantation of neural progenitors.

Feasibility and safety of neural tissue transplantation in patients with syringomyelia

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.

Transplant therapy: recovery of function after spinal cord injury

Spinal cord injuries (SCI) result in devastating loss of function and altered sensation. Presently, victims of SCI have few remedies for the loss of motor function and the altered sensation often experienced subsequent to the injury. A goal in SCI research is to improve function in both acute and chronic injuries. Among the most successful interventions is the utilization of transplanted tissues toward improved recovery. The theory is that the transplanted tissue could (1) bridge the spinal lesion and provide chemical and/or mechanical guidance for host neurons to grow across the lesion, (2) bridge the spinal lesion and provide additional cellular elements to repair the damaged circuitry, (3) provide factors that would rescue neurons that would otherwise die and/or modulate neural circuits to improve function. A variety of tissues and cells have been added to the adult mammalian spinal cord to encourage restoration of function. These include Schwann cells, motor neurons, dorsal root ganglia, adrenal tissue, hybridomas, peripheral nerves, and fetal spinal cord (FSC) tissue en bloc or as disassociated cells. It is postulated that these tissues would rescue or replace injured adult neurons, which would then integrate or promote the regeneration of the spinal cord circuitry and restore function. In some instances, host-appropriate circuitry is supplied by the transplant and functional improvement is demonstrated. In this presentation, specific examples of recent work with transplanted tissue and cells that demonstrate improved behavioral outcome are presented. New recent work describing the in vitro propagation and characterization of human fetal spinal cord multipotential progenitor cells are also described in the context of a potential resource for transplantable cells. Additionally, data from transplantation experiments of human FSC cells into nonimmunosuppressed rat spinal cord are described, and the resultant improvements in behavioral outcome reported. Lastly, directions for future SCI research are proposed.