**2.2. Stem cell therapy for SCI repair**

induced to differentiate into a milieu of specialized cell types, thus holding promise for regenerative medicine. When these cells are isolated from adult fully differentiated tissues, they receive the attribute of adult stem cells, even though they are also present in infants and fetus. Therefore, it would be more appropriate to refer to them as tissue stem cells or mesenchymal stem cells to differentiate them from resident progenitors with limited differentiation capacity. MSCs can be isolated from a large number of tissues, such as bone marrow, adipose tissue, dental pulp, hair follicles, amniotic fluid, Wharton's jelly in the umbilical cord, and even from nervous or cardiac tissue. MSCs are multipotent and can be differentiated into chondrocytes, adipocytes, and osteoblasts under proper conditions [1, 2]. MSCs can be cloned and expanded *in vitro* more than a million fold without losing their differentiation potential [3] constituting, theoretically, a rich resource for tissue repair. However, their sensitivity to environmental cues and genetic factors together with a lack of standardized good manufacturing procedures (GMPs) using defined components has hampered their true therapeutic potential. Since the finding by Bartholomew et al. that MSCs inhibit mixed lymphocyte reactions and prevent the rejection of allogeneic skin grafts [4], a large number of reports have evidenced that MSCs are immunosuppressive and immunoregulatory, properties that can be harnessed therapeutically. However, challenges to fully understand and control MSC regenerative potential remain.

In addition to MSC, the reprograming of terminally differentiated cells or induction of de-differentiation by the introduction of particular sets of transcription factors [5–7] opened an additional avenue of opportunities in the field of regenerative medicine. iPScs or induced pluripotent stem cells facilitate the production of patient-specific cells overcoming immune rejection and also ethical concerns. Although they have shown their value in the generation of *in vitro* models of human disease [8, 9], the low efficiency of reprogramming events and the safety concerns associated with the process of reprogramming has prevented their use in the clinic [6, 10].

Based on the research interests of our labs, this chapter, while reviewing the advances to generate clinical-grade stem cells or their by-products, highlights the potential benefits of stem cell-based therapeutics for the treatment of spinal cord injuries (SCI) and the neuroimmune

Spinal cord injury (SCI) is often mentioned among the first conditions for which stem cells may provide a new therapy. While recent decades have brought significant improvements in rescuing neuronal activity after SCI at preclinical phases testing several individual approaches, translation to the clinic still remains inefficiently explored. Management for SCI efficient treatment is a difficult task by the intrinsic nature of the pathological cascade of events that makes the SCI a dynamic and progressive disorder. The sentence "Time is spine" defines the crucial importance of timing to rapidly diagnose patients and implement neuroprotective interventions during the acute injury phase (≤2 h) in order to diminish the devastating effects of the secondary phase of the injury (≥2–48 h) which are known to be key determinants of the final extent of neurological deficits. The secondary injury leads to necrosis and/or apoptosis of neurons and glial cells, such as oligodendrocytes, which can lead to demyelination and

disease myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

**2.1. Spinal cord injury pathological events and timing sequence**

**2. Stem cell therapy for spinal cord repair**

112 Cell Culture

Cell transplantation methods constitute a very promising strategy for SCI repair. Numerous studies with a diversity of cell types have clearly showed benefits to different extents, for

**Figure 1.** Summary of physiopathological events after SCI (a) and stem cell transplantation (b).

instance, therapeutic effects in sensorimotor function recovery in preclinical models [22, 23] and in several ongoing clinical trials [24–26].

**3. Stem cell therapy for other neuroimmune-related health problems: potential benefits for the treatment of myalgic encephalomyelitis/**

Mesenchymal stromal cells (MSCs) have been used in clinical trials (CTs) for a broad range of immune-related health problems such as acute and chronic inflammatory disorders, autoimmune diseases, and transplant rejection by their potent immunosuppressive and antiinflammatory properties [42–45]. As reviewed by Wang et al., as of April 2016, over 500 MSCrelated clinical trials were registered on the NIH clinical trial database (https://clinicaltrials. gov/). Although the immunomodulatory properties of MSCs have more recently been identified, almost half of the registered CTs (230 or 42% of them) have or are being conducted for

Culturing Adult Stem Cells for Cell-Based Therapeutics: Neuroimmune Applications

http://dx.doi.org/10.5772/intechopen.80714

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Multiple sclerosis (MS) and its animal model (experimental autoimmune encephalomyelitis or EAE) associate with CNS inflammation, gliosis, demyelination, and axonal loss. MSCs' pleiotropic properties, including immunomodulation, immunosuppression, neurotrophy, and repair-promotion, make them attractive candidates for the treatment of neurodegenerative diseases, including MS [42–46]. The remyelination benefits reported in MS are largely attributed to paracrine signals and secreted soluble molecules such as tumor growth factor (TGF-β1), interferon (INF)-γ, indoleamine 2,3-dioxygenase (IDO), and prostaglandin E2 (PGE2) [46–48]. On another side, neural precursors obtained from induced pluripotent stem cells (iPSCs) promote the viability of endogenous OPCs facilitating remyelination through the secretion of leukemia inhibitory factor (LIF) in EAE [46, 49–51]. LIF, a member of the IL-6 cytokine family implicated in the pathophysiology of MS, has shown to offer neuroprotection

**Figure 2.** Summary of the number of clinical trials using MSC therapy in immune- or inflammation-mediated diseases, as registered on the website https://clinicaltrials.gov (accessed April 2016). MS, multiple sclerosis; T1DM, type 1 diabetes mellitus; GVHD, graft-versus-host disease; OA, osteoarthritis; IBD, inflammatory bowel disease (a). MSC-derived paracrine factors mediating immunomodulatory functions, particularly toward T lymphocytes, in preclinical animal

**chronic fatigue syndrome (ME/CFS)**

immune- or inflammation-mediated diseases (see **Figure 2**) [45].

and axonal regeneration as well as prevention of demyelination [49–51].

studies of various immune- and inflammation-mediated diseases (b). Source: Wang et al. [45].

Among these cell types used, mesenchymal stem cells (MSCs) from the adipose tissue, bone marrow [27], umbilical cord, [28] or dental pulp [29], in addition to olfactory ensheathing glial (OEG) cells [30], Schwann cells [31], or neural precursor cells [32], have been used.

Preclinical studies have shown that MSCs have potent anti-inflammatory, anti-apoptotic, immunomodulatory, and angiogenic effects post-SCI [33]. MSC transplantation, overall, results in substantially improved locomotor recovery among animal models of SCI [34]. There have also been several clinical trials using autologous bone marrow-derived MSCs. These early studies confirm the safety of different administration protocols using MSCs post-SCI. It seems that sufficient quantities of transplanted allogeneic MSCs combined with immunosuppression prolong the survival of engrafted cells and improve functional and morphological outcomes after SCI [35].

Transplantation of neural stem/progenitor cells (NSPCs) has shown promising results in the repair and regeneration of lost neural tissues and the associated restoration of neurological deficits [36] with particular benefits among other cell types. The engrafted transplanted NSPCs generate a favorable non-inhibitory environment for functional recovery creating additional paracrine activity modulating the post-SCI inflammatory response, feeding the injured area with growth factors, and rendering additional neurotrophic support by releasing, among others, GDNF. NSPCs include multipotent stem cells present in the ependymal region lining the central canal of the spinal cord (epSPC) [37]. epSPC represents an ideal candidate for stem cell therapy based on noted functional improvements after transplantation and the absence of malignant transformation, offering a safe and relevant cell type for clinical applications. The rationale for the therapeutic application of epSPC for SCI includes the replacement of damaged neurons and glial cells, secretion of trophic factors, regulation of gliosis and scar formation, prevention of cyst formation, and enhancement of axon elongation. After SCI, epSPCs proliferate and migrate to the injured area and produce new oligodendrocyte precursor cells (OPCs) [37]. Acute [38] and chronic [39] transplantation of undifferentiated epSPCs from SCI donors or *in vitro* differentiated OPCs into a rat model of severe spinal cord contusion produced significant locomotion recovery 1 week after injury. Transplantation of epSPCs provides trophic support and positively modulates the local immune response. It reduces purinergic receptor expression associated with neurodegenerative and neuropathic pain, thereby inducing signals promoting neuronal protection and survival with axonal outgrowth [40]. Interestingly, an immortalized human fetal epSPC line (HuCNS-SC) has been the main focus of cell therapies developed by the company Neuralstem, Inc. (USA), and therapies based on this product have been applied to human subjects in a phase II clinical trial. Phase I/II trial has declared no adverse effects of treatment, with modest functional improvements [41].

Stem cell therapy can contribute to SCI repair not only by restoring the damaged tissue through differentiation and engraftment but also by potentiating endogenous tissue regenerative potential. Both processes are influenced by the action of the immune system controlling local inflammation, and thus stem cell paracrine factor role in this context should be carefully evaluated.
