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Keywords:

  • enteric nervous system;
  • motility disorders;
  • neural stem cells;
  • transplantation

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

Abstract  The enteric nervous system (ENS) is vulnerable to a variety of genetic, metabolic or environmental threats, resulting in clinical disorders characterized by loss or malfunction of neuronal elements. These disorders have been difficult to treat and there is much enthusiasm for novel therapies such as neural stem cell (NSC) transplantation to restore ENS function in diseased segments of the gut. Recent research has indicated the potential for a variety of innovative approaches to this effect using NSC obtained from the central nervous system (CNS) as well as gut derived enteric neuronal progenitors. The main goal of this review is to summarize the current status of NSC research as it applies to the ENS, delineate a roadmap for effective therapeutic strategies using NSC transplantation and point out the numerous challenges that lie ahead.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

Like other nervous systems in the body, the enteric nervous system (ENS) is markedly restricted in its ability to replace dead or damaged neurons. This has left the ENS vulnerable to a variety of genetic, metabolic or environmental threats, resulting in clinical disorders such as achalasia, gastroparesis, neuropathic forms of pseudo-obstruction, enteric neuronal dysplasia, colonic inertia and Hirschsprung’s disease. There is a paucity of effective therapies for these and other disorders of motility. Further, there are intrinsic limits to a pharmacological approach to modulate a system that is as delicately and intricately inter-dependent as the ENS.1 This is best illustrated by the lack of clinical efficacy of exogenous cholinomimetics such as bethanechol, which though capable of augmenting muscle tone, do not result in effective propulsion. Moreover, even drugs that are capable of producing coordinated activity require an intact neuronal circuitry, and in its absence, will fail. The promise of replacing dysfunctional or dead neurons by neural stem cell (NSC) transplantation is therefore tremendously appealing.

Neural stem cell transplantation: state-of-the-art

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

The replacement of the ENS by adequate neuronal and glial cells was, until recently, considered more of a futuristic vision than a near term reality. Early attempts to reconstitute the ENS in vivo were undertaken by several groups, using isolated mature enteric ganglia with some limited success in forming neuronal networks (Fig. 1).2,3 More recently, the explosion of research on stem cells in this decade has stimulated scientists to explore their therapeutic potential also for the ENS. Stem cells are uncommitted cells that are capable of self-renewal (the ability to give rise to more uncommitted stem cells) and are also able to generate a progeny of specialized cells, in response to the appropriate developmental cues. During development, NSC give rise to more committed progenitor cells that in turn generate the fully differentiated neuronal and glial elements of the nervous system.4–6 A common neuroectodermal stem cell is believed to be parent to NSC that give rise to the central nervous system (CNS-NSC), and to neural crest stem cells (NCSC) that migrate into the gut and form the ENS. Both CNS-NSC, NCSC and the more committed enteric neuronal progenitor (ENP) cells isolated from the fetal or postnatal gut have been studied for their ability to re-populate the ENS.7–14 A list of the experimental approaches for re-populating the mammalian ENS and the models used are summarized in Table 1. This list clearly shows that, with few exceptions, the majority of the work conducted so far relies on the generation of neurospheres (a surrogate for stem cells, as will be discussed more in details later) and is limited to extremely short-term, and generally ex vivo testing of their ability to integrate into the ENS. However, many fundamental questions remain unanswered, as summarized in Table 2.

image

Figure 1.  Transplantation of isolated myenteric plexus into the submucosal layer of adult rats cecum (A). The dissociated myenteric plexus cells were labelled with Hoechst stain prior to transplantation. (B) PGP9.5 immunoreactivity in grafted cells 7 days after transplantation. Secondary neuronal network is visible in the submucous layer. (From Schaefer3). LM, circular muscle; CM, longitudinal muscle; Muc, mucosa; MP, myenteric plexus; T: transplanted cells.

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Table 1.   Summary of experimental studies on NSC transplantation
SourceSelectionHost tissueDelivery routeEngraftment and neural differentiationFunctional effectsReference
CNS-derived NSC from embryonic mouse brainNeurospheresMouse pylorusIn vivo injection into seromuscular layerYesImproved gastric functionMicci et al.7
Neural crest-derived cells from E11.5 mouse gutSorted Ret+ cellsWild-type and aganglionic embryonic mouse gut explantsEx vivo grafting in organotypic cultureYesNot reportedNatarajan et al.9
Neuroepithelial stem cells from the neural tube of embryonic ratNeurospheresChemically denervated rat colon in vivoIn vivo injection into seromuscular layerYesImproved intestinal motilityLiu et al.10
Neural crest-derived neuroblasts from the vagal portion of the neural tube of embryonic miceNeural crest cellsAganglionic mouse megacolonIn vivo injection into muscle or peritoneumYesNot reportedMartucciello et al.11
ENS progenitor cells from fetal and postnatal mouse gutNeurospheresWild-type and aganglionic embryonic mouse gut explantsEx vivo grafting in organotypic cultureYesNot reportedBondurand et al.22
ENS progenitor cells from embryonic mouse and neonatal human gutNeurospheresAganglionic embryonic mouse hindgut explantEx vivo grafting in organotypic cultureYesRestored contractile properties of aganglionic bowelLindley et al.13
ENS progenitor cells from E11.5 mouse coecum or postnatal human myenteric plexusNeurospheresAganglionic embryonic mouse hindgut explantEx vivo grafting in organotypic cultureYesNot reportedAlmond et al.12
ENS progenitor cells from developing and postnatal human gutNeurospheresAganglionic embryonic mouse hindgut explantEx vivo grafting in organotypic cultureYesNot reportedRauch et al.14
Postnatal human gut mucosal tissueNeurospheresAganglionic chick and human hindgut explantEx vivo grafting in organotypic cultureYesNot reportedMetzger et al.46
Postnatal rat gutP75+ sortingChick embryo hind limb somitesIn vivo injectionPeripheral nerve – yes Gut – noNot reportedKruger et al.26
Table 2.   Important questions on the functional potential of harvested neural progenitors
How does the developmental age of cells effect migration and differentiation properties and engraftment potential?
How does in vitro culturing prior to transplantation effect the above?
Can stem cells be nudged towards a better transplantation outcome by in vitro manipulation of culture conditions?
If the gut contains an abundance of neural progenitors, why does the ENS not appear to be capable of repairing itself?

Moreover, expanding on the theme of CNS researchers,15 many important issues need to be addressed in order for the promise of cell replacement therapy to become a reality. These can be summarized as follows: (i) what is the ideal stem cell source for transplantation? (ii) what is the most appropriate route and method of stem cell administration? (iii) does functional restoration require faithful recreation of myenteric ganglia and related structures? (iv) what is the best approach (including in vitro preparation and post-transplantation manipulation) to achieve an appropriate, functional, and long-lasting integration of transplanted stem cells into the host tissue? and (v) what should the first clinical targets be? This review will suggest possible pathways to clinical trials as well as the many gaps in our knowledge.

Potential sources of stem cells for ENS therapy

When it comes to the issue of transplanting cells for the restoration of the neuronal network in the gut, the central question is: what is the source of the cells to be used? There are legions of approaches for all kinds of diseases using various types of stem cells, and the right choice is not clear. Some of these sources, such as embryonic or haematopoietic stem cells not only have great potential but also may have severe drawbacks. Thus, there are several theoretical advantages of embryonic stem cell lines for ENS restoration. Firstly, they can be maintained and expanded in culture without losing their ‘stemness’. Secondly, they can potentially give rise to many more cell types (e.g. interstitial cells of Cajal) than just neurons or glia, an attribute that could be particularly useful in certain diseases states where multiple lineages are affected. In an appropriate environment, embryonic stem-derived neural precursors have been shown to generate successfully both central and peripheral neurons, glia, enteric neurons and other neural crest derivatives.16–19 However, the use of embryonic stem cells is ethically restricted, can produce teratoma-like growths,20,21 and further, as with cells from other lineages (bone marrow, skin, adipose tissue, etc.), may require additional and perhaps intense reprogramming by as yet poorly defined protocols to produce an enteric neuronal phenotype. A more feasible and perhaps suitable type of cell therefore may be one that is already programmed for a neuronal fate, i.e. a NSC. These can be derived from the CNS, neural crest or postmigratory enteric neural progenitor population. However, before discussing the merits of each of these sources, it is important to first clarify that most of the literature consists of studies on neurospheres and not a pure stem cell population.

Neurospheres vs stem cells  When putative NSC are isolated in culture from their source organs, they characteristically grow and proliferate in floating spheroid colonies called neurospheres. Several investigators have successfully isolated neurospheres from both the rodent and human gut which appear to be similar to their CNS-derived counterparts.14,22,23 As in the CNS, neurospheres continue to form the starting material for most studies published to date in the ENS field. However, although this feature has been used as a surrogate marker for ‘stemness’,24 the neurosphere is actually a very heterogeneous entity, consisting of progenitor cells at various levels of commitment as well as neurons, glia and other terminally differentiated cell types. Only 3–4% of the cells within neurospheres are actually true stem cells in that they are self-renewing and can give rise to all three neural lineages.25 Although it is clearly desirable to start with a relatively homogenous population of NSC, this goal has been difficult to attain because of the lack of a suitable marker. Amongst the studies shown in Table 1, only two have started with a relatively homogenous population based on cell sorting by expression of either the Ret receptor9 or the neurotrophin receptor p75,26 and only one of these performed clonal analysis to prove the true stem cell nature of these cells.26 It is not clear whether these receptors represent universal markers for ENS-NSC that can be applied to different species or at different stages of development, as most investigators appear to have limited themselves to using neurospheres. It may therefore be necessary to identify additional and perhaps more specific markers in the self-renewing stem cell population that will allow us to rigorously prove their stemness and consistently and reproducibly isolate them from the gut.

In the CNS, the NSC phenotype has been distinguished by the expression of nestin,27,28 and the low to absent expression of both peanut agglutinin and heat stable antigen (nestin+, PNAlo,HASlo).29 Nestin is an intermediate filament protein whose expression is widely used to identify mammalian neuronal precursor cells or stem cells. The stem cell is initially positive for nestin, but secondary progenitor cells lose this property. However, it is not completely specific: in the adult brain, nestin is expressed not only in NSC in the subependymal zone but also in reactive astrocytes, and in other organs, nestin also stains endothelial or glandular cells.30 A further problem with nestin is that it is not expressed on the surface, making it difficult to isolate these cells based on cell sorting techniques. Despite these limitations, nestin positivity, along with neurosphere generation, has become almost synonymous with stemness in the hands of most investigators. In rodents, neuronal precursors have also been isolated from the embryonic and postnatal guts using antibodies to specific markers known to be expressed by enteric neural crest-derived cells: Ret28 and p75 (the low-affinity receptor for nerve growth factor).26,31 However, it is not known that an approach using these techniques to isolate a more uniform population of precursor cells actually leads to better engraftment and functional restoration as compared with neurospheres alone.

There is therefore obviously a need for investigators to go ‘beyond the neurosphere’ and put greater efforts towards the identification of markers with both high specificity and selectivity, that will allow to harvest stem cells in larger quantities, using minimally invasive techniques, and without other ‘contaminating’ cell types. Such strategies will allow the delivery of a pure source of neuronal tissue, eliminating several confounding variables affecting the post-transplantation outcome.

Heterologous vs autologous sources  Although neurospheres can be obtained relatively easily from a variety of sources, there are both ethical and immunological problems associated with their origin. Heterologous transplantation of stem cells into the ENS works relatively well in animal models without immunosuppression,32 but it is not clear whether this will also be true for long-term survival and functional benefit in clinical situations. Further, ethical issues, while surmountable, will continue to present challenges for the use of stem cells from tissues obtained from dead or aborted donors. Clearly, therefore, the best source to be used will be cells isolated from the patient itself, preferably from the same organ as the intended target. This may be feasible even in disorders such as Hirschsprung’s disease, in which the failure to develop ganglia may be caused by defects either in the NCSC or in the environment they need to inhabit [e.g. with endothelin receptor or glial cell line-derived neurotrophic factor (GDNF) mutations]. It is presumed that in the latter group of patients, the autologous source of stem cells will be the ganglionic segment but it remains to be seen whether these cells are actually effective in repairing the ENS. In this regard, one of the authors (Karl-Herbert Schäfer) has been successful in isolating neurospheres from the ganglionic or the transitional zone of Hirschsprung’s disease patients (Fig. 2, Karl-Herbert Schäfer, unpublished data).

image

Figure 2.  Neurospheres derived from either the ganglionic (A) or transitional (B) areas of children undergoing surgery for Hirschsprung’s disease showing that the transitional zone gives rise to smaller spheres, which is consistent with the finding of Bondurand et al.22 in an animal model. The neurospheres were generated by isolating myenteric plexus or single ganglia from both areas using a technique based on enzymatical (collagenase) digestion and mechanical agitation.60 Briefly, the resected areas were stored on ice and processed within hours from surgery. Muscle and submucous layer were separated and the muscle tissue from the most proximal, ganglionic, as well as from the transitional zone was incubated in a collagenase solution (1 mg mL−1) for up to 5 h. After vortexing, muscle cells and myenteric plexus could be identified in both samples. The plexus tissue was dissociated and plated in a stem cell medium as previously reported14 (Karl-Herbert Schäfer, unpublished data).

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Source tissues  Central nervous system-derived NSC remain the most well characterized and studied of all NSC and appear to be closest to clinical reality, at least for CNS diseases. Interest in the use of fetal NSC as a therapeutic tool has also been fuelled in part by a report of the isolation of a human fetal NSC that can be expanded in vitro for years and that can be readily differentiated into neurons and glia, thus holding the promise of a renewable, plentiful and standardized source of human neural cells;33,34 recent studies show that such an approach is useful for adult subventricular zone cells as well.35 Indeed, CNS-NSC provided the earliest in vivo proof-of-principle for successful functional engraftment in the gut.7 However, long-term survival is still an issue as more than 90% of the grafted neurons usually die upon grafting, both in animal and in human studies.36,37 A large portion of this cell death occurs as programmed cell death, or apoptosis, and occurs within the first week after transplantation.38,39 Therefore, CNS-NSC treatment for gastrointestinal neuromuscular disorders will require strategies to circumvent or attenuate this phenomenon.

Although NCSC and differentiated CNS cells share a common progenitor,40,41 NCSC are potentially more attractive because in nature, they give rise to both the peripheral nervous system and the ENS, in addition to smooth muscle cells, pigment cells, bone and cartilage in other regions of the body.42,43 However, it can logically be argued that the most appropriate cell type for ENS therapy is the postmigratory ENP. These cells are downstream of the NCSC and appear to be more committed than other neural crest derivatives (such as sciatic nerve stem cells) in terms of their commitment to a neuronal fate.44 Recent developments have added to the enthusiasm for this approach. These include the discovery of endogenous NSC within the immature as well as adult ENS.5,26,44–46 NSC isolated from the small intestine of lactating and adult mice express nestin, vimentin, and the pro-neural transcription factors neurogenin-2 (ngn-2), Sox-10 and Mash-1.45 These cells can differentiate into various cell types, particularly neurons, smooth muscle, and glia with the neurons expressing several characteristic neurotransmitters and receptors including calcitonin gene-related peptide, neuropeptide Y, peptide YY, substance P, vasoactive intestinal polypeptide, galanin and c-KIT. However, in keeping with the previous discussion, it should be pointed out that these experiments used unfractionated primary cell cultures of whole gut and therefore it is difficult to ascribe any of these attributes to those emanating from pure NSC.

It is not known whether CNS-NSC can also express such a profile but these results do suggest that ENP are more likely to respond to gut-specific environmental cues. Indeed, isolation and expansion of precursor cells from the developing and postnatal human ENS have recently been reported using bowel samples from human fetuses and children (from the ninth week of gestation to 5 years postnatal). Such cells can be differentiated and also be transplanted after dissociation into aganglionic bowel in vitro.11–13 Another advantage of ENP, particularly for autologous approaches, lies in the accessibility of the gut by minimally invasive means (unlike the CNS). This has been highlighted by the recent dramatic discovery of potential neuronal progenitors in the mucosa and submucosal region which can be accessed by performing a simple mucosal biopsy. These cells can give rise to neurospheres in vitro which can be differentiated into neurons.47 Although it has still to be proven whether this method can generate all the neurons required to restore fully gastrointestinal function, this is a very promising and exciting development for the field.

Another attractive source for ENP is the appendix which harbours a fully developed ENS48 and can easily be removed by minimal invasive surgery. Thus, enteric nervous tissue can be isolated from surgically removed appendices and neurospheres generated and neuronal and glial cells cultivated (Karl-Herbert Schäfer, unpublished data).

Finally, endoscopic techniques are being developed that can provide access to the muscular layer and associated ganglia in a relatively non-invasive manner.49,50 It is quite possible that these layers may provide an alternative source for stem cells in the future.

Although these locations are very promising autologous sources for enteric NSC, further studies and more effort have to be directed at characterizing the amount and quality of neurospheres that can be obtained from individual biopsies or appendices.

Potential routes of delivery

The accessibility of the gut by minimally invasive means allows one to envision a number of potential routes of delivery of NSC or ENP to target areas in the gut. The cells can be injected directly under visual or ultrasound control into the affected tissue. This procedure will allow for a precise injection of cells within a layer of the gut where they would have an optimal chance for engraftment and regeneration of the neuronal circuitry. This approach would work best when the defect is limited to a relatively small and well-defined region of the gut. For example, this procedure can be used in achalasia or Hirschsprung’s disease patients that have undergone pull-through surgery, where cell suspensions or single neurospheres can be directly injected into the affected sphincteric region. For more widespread aganglionosis, therapy will be more challenging both in terms of the cell numbers required and the method of delivery. One approach is to administer multiple injections along the length of the affected gut and hope that post-transplantation migration will eventually cover the ‘gaps’. Another approach is to attempt delivery via selected arterial canulation or perhaps even intravenously. Surprisingly, NSC injected intravenously have been shown to cross the blood–brain-barrier and induce recovery in various disease models including multiple sclerosis; the mechanism appears to involve ‘hijacking’ of the endothelial transport mechanism utilizing CD44.51,52 Finally, serosally directed transplantation via intraperitoneal injections with the hope that the cells will home into the aganglionic areas of the gut, presumably following guidance cues, as has been shown recently.11

Effects of NSC on the ENS: reconstruction or bystander?

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

Even if the progenitor cells reach the desired segment of the gut, there is still the question of finding the appropriate intramural zone – myenteric plexus or muscularis propria. This can be achieved by sophisticated imaging techniques including endoscopic ultrasound or by direct visualization at surgery. However, it is not clear that this is necessary. We have shown that a significant therapeutic effect can be accomplished without necessarily achieving an anatomically and physiologically correct recreation of myenteric ganglia.7 While the latter goal is ideal, it may not be essential. Indeed, it is becoming increasingly clear from the CNS literature that replacing affected cell populations (or structural components like myelin) and their connections is not the only mechanism by which stem cells can promote functional recovery. As in our studies, they can deliver missing neurotransmitters, provide a tissue scaffold for host axonal regeneration, and provide neurotrophic and other active molecules that promote endogenous growth and repair (so-called ‘bystander’ effects).53,54 Thus, anatomic precision may not be a critical factor for a successful functional outcome after NSC transplantation.

Optimizing post-transplantation fate

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

This is perhaps the most formidable challenge to overcome. As mentioned previously, in most experimental studies, the majority, or all of the transplanted cells die after a relatively short period after transplantation. Cell sources can be optimized, progenitors can be ‘primed’ and appropriate and adequate delivery ensured; however, after transplantation the fate of the NSC becomes largely under the influence of factors that can affect both survival and differentiation. However, these factors are poorly understood and difficult to manipulate adequately.

One can conceptualize the various phases that progenitor neurons have to undergo after transplantation; although somewhat overlapping, each has its own set of perils (Table 3). Thus, the transfer from the controlled media of the culture dish to an active organic environment can be expected to be very stressful physiologically. This may be further compounded if the method of administration involves direct injection into the wall of the gut. The target layers of the muscularis propria are tightly packed and trauma to both host and transplanted tissue is inevitable, made worse by the ensuing tissue injury response. It may therefore be helpful to provide some protection to the stem cells while they establish a ‘beach-head’ during this phase. This could be in the form of encapsulation in an extracellular matrix or gel suspension which facilitates a more gradual contact of the stem cells with their immediate environment while maintaining trophic support (such as by the incorporation of nutrients, growth factors or anti-apoptotic agents into the protective material) (Fig. 3, Karl-Herbert Schäfer, unpublished data).

Table 3.   Post-transplantation phases and challenges
Phase I: Expeditionary
 Space constraints
 Early inflammation and injury response
Phase II: Engagement
 Target homing and contact
 Trophic deprivation and adaptation
 Host immune response
Phase III: Integration
 Functional interaction with neighbours
 Phenotypic stability
 Long-term survival and/or capacity for self-renewal
image

Figure 3.  (A) Mouse ENS-derived neurospheres cultured in a 3-dimensional gel (extracellular matrix, ECM from Sigma Aldrich, St Louis, MO, USA), demonstrating the innervation potential of freshly explanted neural stem cells. Briefly, enteric neurospheres were harvested, centrifuged and the supernatant completely removed. The pellet was topped with 50 μL of ice-cold extracellular matrix gel (ECM; Sigma), resuspended and plated on coverslips in drops of 10 μL. The ECM solution was allowed to gel in an incubator for 15 min before adding media. The sphere started to develop neurite outgrowth within hours. (B) This picture represents a magnified view of (A) showing increased density of fibres between the single embedded spheres (Karl-Herbert Schäfer, unpublished data).

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During the second phase, as transplanted cells start engaging with their neighbours, they face other threats to their survival that include host immunity (in case of heterologous transplants) as well as the lack of target-derived trophic factors. The former is relatively easy to overcome, if necessary, with pharmacological methods but the latter is still problematic, in part because the exact nature and mix of environmental factors are complicated and not fully understood. Thus, a non-permissive environment may involve an over-expression of factors such as laminin that push the cells towards (premature) differentiation or a lack of neurotrophic factors such as GDNF. For instance, both laminin55 and GDNF56–58 vary in their expression in the colon in Hirschsprung’s disease, depending on the colonic region as well as with the nature of the genetic defect. In the future, one could envision customizing and administering a ‘cocktail’ of factors that are designed for the target genetic background and that could be administered locally either with the transplanted cells or in adjacent areas to facilitate this phase.

In the ‘final’ phase, transplanted NSC have ideally assumed a long-lasting mutually beneficial equilibrium with their environment and achieved phenotypic stability that is maintained by the appropriate signals from their targets as well as adaptive gene plasticity. Perhaps the biggest threat at this stage is persistence of the original insult that led to neuronal loss in the first place (e.g. an auto-immune disorder); this will need to be addressed by either treatment directed at the underlying disease or careful selection of the stem cells from sources that may not express the vulnerable antigen or its presenting molecule. It is also not clear whether some capacity for self-renewal will be required to maintain a stable population in the long-term.

Theoretically, many of the therapeutic manipulations discussed above can be addressed by genetic modification of the stem cells prior to transplantation. However, it is likely that safety concerns will prevent these from being implemented at least for the first generation or two of this therapy.

First clinical targets

There are some intuitively obvious features that characterize a relatively easy disease target for NSC therapy in the gut. These features include ease of access, a relatively limited target area for innervation, a requirement for a single physiological effect (and hence single neurotransmitter production) and the lack of satisfactory alternatives. Further, there should be no clinical urgency so that harvesting and in vitro preparation of autologous NSC can be performed carefully. Finally, the success of the transplantation should be easily demonstrable by objective physiological assays (e.g. manometric, radiological or electromyographical studies). Good candidate diseases therefore include achalasia or residual anal sphincter dysfunction after surgical pull through for Hirschsprung’s disease, both of which require only a neural relaxatory component.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References

The use of NSC for the restoration of function in the aganglionic gut is feasible. This review has suggested possible pathways to clinical trials as well as the many gaps in our knowledge. A cautious approach would suggest that it is too early to take this therapy to patients as the biological basis for a successful outcome remains largely unknown. Clearly, much more fundamental research is needed before we can make significant progress. However, it is perhaps also important to consider, in parallel, pilot human studies that can provide early signals on the direction for which this research should take. In this regard, one can draw from the experience (and early success) of myoblast and fibroblast injections for relief of urinary incontinence, coupled with the relative safety of using autologous stem cells.59 These early trials will supplement and provide direction for the more fundamental research that is also clearly required as we go down this new and very exciting therapeutic road.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Neural stem cell transplantation: state-of-the-art
  5. Effects of NSC on the ENS: reconstruction or bystander?
  6. Optimizing post-transplantation fate
  7. Conclusions
  8. References