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Table 1 Source, definition, mechanism, advantage, and current limitation of stem cells in SCI

From: Crosstalk between stem cell and spinal cord injury: pathophysiology and treatment strategies

 

Description

Possible therapeutic effects in SCI

Advantages

Current limitation

Mesenchymal stem cell

Mesodermal lineage multipotent progenitors can be obtained from bone marrow, umbilical cord, amnion, placenta, and fat tissue [13].

Secreting anti-inflammatory factors, cytokines, growth factors, and cell adhesion factors to improve the microenvironment of the lesion and further promotes self-repair after SCI; immunomodulatory, neurotrophic and anti-apoptotic effects [13, 14].

High multilineage differentiation, easily isolated and grafted, suitable for different stages of SCI, raising no ethical concern, limited risk of developing tumors, minimal immunoreactivity [15, 16].

Mechanism requires further research which limits the efficiency of treatment; results of clinical trials are still far from obtaining functional recovery and restoring neural circuits; effective way to deliver cells still needs further research [16].

Embryonic stem cells

Highly undifferentiated cells that are pluripotent and can differentiate into different tissue cells [17].

Differentiated neurons and glial cells are used to supplement cell defects caused by SCI; secrete active factors to inhibit further damage, support nerve tissue regeneration [18,19,20,21,22,23].

Long history of research, proven to have a certain effect in a variety of diseases; pluripotent cells that can differentiate into all tissue cells [17, 18].

Immune rejection and the risk of tumor formation; ethical issues needed to be solved [24,25,26].

Neural stem cells

Stem cells located in the lateral ventricle of the brain, the dentate gyrus of the hippocampus, and the central canal of the spinal cord [27].

Modulation of the formation of glial scar, enhancing oligodendrocyte differentiation and neuronal differentiation; replace necrotic damaged cells and reconstruct local loops which in turn promotes the recovery of body function; secrete growth-promoting factors to promote the survival and growth of damaged neurons; immunomodulatory effects [28,29,30,31,32].

A reducing tumorigenicity due to the maturation is restricted to glial and neuronal subtypes; can be harvested from either adult or fetal spinal cord tissue [33, 34].

Further studies are necessary to confirm neurological and functional benefits, safety, adjusting doses and administrations periods as well as the most promising cellular sources to obtain NSCs [34].

Induced pluripotent

stem cells

Considered to be effective alternative cell sources for ESCs.

Induced to be neural progenitor cells, neurons, oligodendrocytes, and astrocytes; promote remyelination, axonal regeneration and the secretion of neurotrophic factors; reducing inflammation [35].

Self-renew and differentiate into various types of neural cells; Free of ethical issues associated with some transplant sources and importantly can be performed in an autologous manner removing the need for immune suppression [36].

High risk of immune rejection and tumorigenesis: teratoma and true tumors [13, 36].

Spermatogonial stem cells

A subtype of spermatogonia [37].

Have the potential to differentiate into various cells nervous system including functional GABAergic neurons, glutamatergic neurons, serotonergic neurons, and glial cells [38, 39].

Multidifferentiation potential; self-replication and self-renewal abilities; able to differentiate into functional dopaminergic neurons directly without an intermediate transition process of ESCs or NSCs; pass the genetic material to the offspring; can be produced throughout the lifetime and lacking of ethical problems, tumorigenicity and immune rejection [37, 40,41,42,43].

Multi-differentiation potential is susceptible to environmental influences; SSC treatment of nervous system diseases is exclusively designed to substitute for differentiation at present, and no reports of secretion of various factors by these cells have been found [42].

Adult endogenous stem cells

Stem cells located in the adult nervous system [27].

Activate and proliferate to produce glial cells when spinal cord is injured; differentiate into astrocytes and oligodendrocytes [27, 44, 45].

Noninvasive cell therapy that directly activated to function without the need for traumatic cell transplantation.

Ability to differentiate into neurons is limited [46].