Abstract
Accumulating clinical evidence of functional neurorestoration for nervous system damages or diseases has been reported using a variety of therapies, especially cell-based therapies, supporting the theory that nerve damage in the CNS can be restored. Neurorestoratology is becoming an important core and interesting field in neuroscience, representing a promising direction of translational medicine. This International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation mainly focuses on the progress of the clinical studies and exciting preclinical evidences for neurorestoration, which are summarized below.
Cell therapy has now been used in people in more than 30 countries with proven safety and some effects; its application for the neurological diseases, however, is under a lack of consensus standards. Based on the abundant experiences of the application of cell transplantation in many neurological insults, Chinese researchers and clinicians of the Chinese Branch of the IANR and the Preparatory Committee of Chinese Association of Neurorestoratology have created the Standard Recommendations (2012) for the Application of Chinese Clinical Cell Therapy for Neurorestoration. These standards include the guiding principles for neurorestorative cell therapy, cell name, cell quality control, cell dose, the patient informed consent, operation name, cell transplantation indications, cell transplantation contraindications, safety evaluation, efficacy evaluation, and additional points in the hope of promoting the healthy development in this area.
Cellular transplantation is becoming a promising and novel alternative for the alleviation of chronic pain. Chen et al. reviewed and proposed the strategy of cell therapy for the treatment of pain, which focused on cell-based analgesia and neural repair. These strategies, no doubt, are still in their infancy phase for Pain Neurorestoratology; however, cell-based therapies could open a new door for the relief of pain. Traditionally, as biological or living minipumps, adrenal medullary chromaffin cells and PC12 cell line produce and secrete pain-reducing neuroactive substances. Furthermore, cell implantation for pain neurorestorative therapy is a new concept for pain control along with neural repair. Relevant neurorestorative mechanisms include neuroprotective, neurotrophic, neuroreparative, neuroregenerative, neuromodulation, or neuroconstructive interventions, as well as immunomodulation and enhancing microcirculation, and the candidate cells nowadays include neural progenitor cells, spinal cord progenitors, mesenchymal stromal cells, and CD34+ cells.
Olfactory ensheathing cells (OECs) are still one of the crucial candidates for neurorestoration by cell transplantation in spinal cord injury (SCI). A long-term positive outcome of OEC transplantation for chronic complete SCI is reported by Rao et al. in this issue. Autologous OEC transplantation was performed, and the patients were followed for 24 months. Scores of the American Spinal Cord Injury Association (ASIA) and International Association of Neurorestoratology-Spinal Cord Injury Functional Rating Scale (IANR-SCIFRS) were significantly increased after OEC transplantation. Sensory function, motor function, and autonomic nerve function had increased.
Sun et al. investigated the ability of cotransplantation of OECs and Schwann cells (SCs) together with treadmill training in facilitating neuronal plasticity and promoting hindlimb function recovery in animal models of subacute (2 weeks) moderate thoracic (T10) spinal cord contusion. SCs were injected directly into the damaged area, and OECs were injected into the adjacent tissues. The treadmill training started day 7 postinjury. At the 11th week, OECs were found migrating longitudinally and laterally from the injection site to the injury site through the gray and white matter, while some traveled along the central canal or pia. In contrast, the SCs remained densely packed and concentrated at the implant site. The transplanted SCs supported the ingrowth of numerous, densely populated axons, and the OECs promoted elongation of axons. The glial fibrillary acidic protein (GFAP) immunoreactivity in the spared tissue surrounding the graft of both SCs and OECs at the lesion site was less intense than that in the controls. Treadmill training increased the number of tyrosine hydroxylase (TH) immunoreactive neurons in the gray matter of L2 spinal cord. Cotransplantation of OECs and SCs combined with treadmill training resulted in the highest Basso, Beattie, and Bresnahan (BBB) score with possible synergistic mechanisms: axon growth and remyelination induced by cotransplantation of OECs and SCs and neuron plasticity below the lesion enhanced by treadmill training.
In an attempt to increase the efficacy of these cells, Fan et al. developed OEC-based scaffolds and investigated optimal manipulation and regulation of OEC behavior by comparing the different electrospun silk fibroin fibers. Tussah silk fibroin (TSF) fibers exhibited a much higher rate of cell attachment, proliferation, and protein expression of cultured OECs than Bombyx mori silk fibroin (BSF) fibers. The diameters and the alignment of TSF fibers further markedly affected the OECs' shape: OECs elongated with the fiber direction in the aligned scaffolds, and the cell nuclei were also observed to be parallel to the aligned fiber. TSF nanofiber alignment represents an attractive guidance cue for the migration of OECs. A combination of OECs and advanced TSF fibers may provide a support for SCI repair.
Li and her coworkers' report on the animal experiment evidence to support the hypothesis of the key point for neural network restoration (KPNNR) that exists in the brain. In early clinical practice, interestingly, OEC transplantation into the KPNNR could slow the rate of clinical progression in amyotrophic lateral sclerosis (ALS) patients. In rat experiments, on the basis of the hypothesis of KPNNR, the cells should initiate and modulate the wide neural network including the cerebrum, cerebellum, and spinal cord. This study demonstrated that more motor neurons at both motor cortices and ventral horns of the spinal cord survived in grafted ALS rats than in control rats after transplantation. Prolonged survival and behavioral tests including a screen test, hindlimb extension, rotarod, and gait control showed that the treated animals were significantly better off than the control group.
In addition, transplanting cells preseeded onto scaffolds into mammalian brain tissue may allow the cells to escape the host's immune system and protect neural tissue from neuroinflammatory injury. The study by Sarnowska et al. performed in situ analysis of laminin-linked dextran and gelatin macroporous scaffolds. They revealed the protective action of gelatin–laminin (GL) scaffolds seeded with mesenchymal stem cells derived from donated human Wharton's jelly (hUCMSCs) against neuroinflammatory reactions of injured mammalian brain tissue. These bioscaffolds have been implanted into (1) intact or (2) ischemic rat hippocampal organotypic slices and into the striatum of (3) normal and (4) focally injured brains of adult rats. They found that transplantation of hUCMSCs encapsulated in GL scaffolds had a significant impact on the prevention of glial scar formation (low GFAP) and in the reduction of neuroinflammation [low interleukin-6 (IL-6) and the microglial markers ED1 (cluster of differentiation 68) and ionized calcium-binding adapter molecule 1 (Iba1)] in the recipient tissue. Moreover, hUCMSCs encapsulated within GL scaffolds induced matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9) proteolytic activities in the surrounding brain tissue.
Stroke is the third leading neurodegenerative disease, and Chen et al. demonstrated the beneficial role of transplanting multiple cells in chronic stroke. Ten patients with chronic stroke were treated using combined cell transplantation based on an intraparenchymal approach. Their courses ranged from 6 months to 20 years. Six patients suffered cerebral infarction, while four patients had brain hemorrhage. The cells including OECs, umbilical cord mesenchymal cells, as well as Schwann cells were delivered through selected routes such as intracranial parenchymal implantation, intrathecal implantation, and intravenous administration. The clinical neurological function was assessed before treatment and during a long-term follow-up using the Clinic Neurologic Impairment Scale and the Barthel Index. The patients were successfully observed for 6 months to 2 years after cell therapy. Every subject achieved neurological function amelioration including the improved speech, muscle strength, muscular tension, balance, pain, and breathing; most patients had an increased Barthel Index score and Clinic Neurologic Impairment Scale score.
Multiple system atrophy (MSA) is an unknown etiology and progressive neurodegenerative disorder with limited symptomatic treatments. Xi et al. attempted to study the initial safety and possible effect of multiple cell transplantations in MSA. They treated 10 patients by the strategy of multiple cells (umbilical cord mesenchymal cells, Schwann cells, OECs, neural progenitor cells) through combination approaches (intravenous, intrathecal, and intracranial). Of them, five patients were followed up for over 6 months after cell therapy. The data evaluated by using International Cooperative Ataxia Rating Scale (ICARS) demonstrated that the patients achieved part neurological function recovery, which involves walking, standing, speech, and muscular tension.
Luan et al. reported that 52 patients with cerebral injury and cortical visual impairment (CVI) were randomly divided into two groups, in which one group received intracerebroventricular transplantation of human neural stem/progenitor cells (NS/PCs) and rehabilitation training and the other only received rehabilitation training. After 2 years of follow-up, patients within the cell transplantation group showed not only an earlier visual improvement but also higher improvement rates and degrees than that of the control group.
Adipose-derived mesenchymal stem cells (ADSCs) are a promising new cell source for regenerative therapy. Ma et al. reported that intracerebral transplantation of ADSCs likely activate microglia and ameliorate neuropathological deficits in Alzheimer's disease (AD) mice. Results showed that ADSC transplantation reduced Aβ peptide deposition and restored the learning/memory function in amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice as a model of AD. It was observed that in both regions of the hippocampus and cortex there were more activated microglia, which preferentially surrounded and infiltrated into plaques following ADSC transplantation. The activated microglia exhibited an alternatively activated phenotype, as indicated by their decreased expression levels of proinflammatory factors and elevated expression levels of alternative activation markers, as well as Aβ degrading enzymes.
Sharma et al. performed a clinical study of safety and efficacy of autologous bone marrow mononuclear cell therapy in muscular dystrophy patients. One hundred and fifty patients diagnosed with muscular dystrophy were recruited. They were administered with autologous bone marrow-derived mononuclear cells intrathecally and intramuscularly at the motor points of the antigravity weak muscles. Assessment after transplantation showed neurological improvements in trunk muscle strength and limb strength on Manual Muscle Testing (MMT), with gait improvements, and a shift on assessment scales such as Functional Independence Measure (FIM) and Brooke and Vignos Scale. Imaging and electrophysiological studies also showed changes in selective cases. Within a mean follow-up of 12 months, overall 86.67% cases showed symptomatic and functional improvements, with six patients showing changes with respect to muscle regeneration and decrease in fatty infiltration on musculoskeletal magnetic resonance imaging (MRI) and nine showing improved muscle electrical activity on electromyography (EMG). Fifty-three percent of cases showed increase in trunk muscle strength, 48% showed an increase in upper limb strength, 59% in lower limb strength, and about 10% showed improved gait.
Using granulocyte colony-stimulating factor (G-CSF), a major growth factor in the activation and differentiation of granulocytes, Derakhshanrad et al. treated 19 patients with chronic motor complete SCI, subcutaneously with G-CSF for 5 days. The median duration of SCI after trauma was 34 months. The follow-up period was at least 6 months, and the ASIA scale was used for motor and sensory assessment and the IANR-SCIFRS as well as the Spinal Cord Independence Measure (SCIM) III were used to assess improvements in the ability of performing basic daily tasks. The ASIA neurological examination scale showed that upper extremity motor scores improved 10 scores, while there was no significant change in lower extremity motor scores. The median of light touch sensory scores improved 5 scores; pin prick sensory scores significantly improved. The median increment in SCIM III total score was 7 scores. The improvements in bladder and bowel management as well as moderate distance mobility subscales were also significant. Total IANR-SCIFRS changed from 17 to 32 scores, and again the bladder and bowel management subscale improvements. There were no long-term side effects.
Cure or total restoration for damages and diseases in the CNS is still a long way away, but happily we are on the road. Currently, any single method may not be sufficient to satisfy the patients' higher and higher expectations for neurorestoration. Therefore, combined neurorestorative therapies or the so-called generation 2 (2G) of neurorestorative therapies should be a direction of treatment being explored in Neurorestoratology, which may help humankind know further their own brain and spinal cord and restore their functions. Therapeutic restoration is important for patients having suffered from diseases; preventive restoration for aging is also important. Attention should therefore be paid to antiaging through preventive neurorestoration in this field in the future.