You are here

| Neural Stem Cells

Analyses of Immunosuppressants Effect on NSCs Therapeutic Function

Comment

Discuss

Stem cell therapy in humans currently relies on the use of immunosuppressants to ensure long-term cell survival and function. Commonly used immunosuppressants include Cyclosporine A (CsA), tacrolimus (FK506) and sirolimus (rapamycin); all of which have been shown to have some effect on pathways present in neural cells (Aramburu et al and Hoeffer et al). Researchers from the groups of Aileen J. Anderson and Brian J. Cummings at the University of California, Irvine, California, USA have previously shown robust engraftment, survival, and differentiation of transplanted human central nervous system-derived neural stem cells propagated as neurospheres (hCNS-SCns) (Uchida et al) following SCI in mouse (Cummings et aland Salazar et al). Now, in a report in Stem Cells Translational Medicine, Sontag et al have investigated the potential effects of immunosuppressant treatment in this in vivo model system.

High and low levels of the immunosuppressants were initially tested in vitro for their effects on hCNS-SCns compared to untreated cells. Both low and high levels of CsA and FK506 mediated an increase in the number of βTub+ (neurons) and a decrease in GFAP+ (astroglia) cells, while rapamycin treatment led to an increase in βTub+ and GFAP+ cells. Furthermore, high-dose CsA, low-dose rapamycin and high-dose rapamycin treatment led to reduced cell number suggesting a toxic/anti-proliferative effect. However, no effect on cytotoxicity or apoptotic/necrotic cell death was observed at 24 hours or 7 days, although EdU-detection assays did find a decrease in proliferation for high doses of CsA, low and high doses of rapamycin, but no change with FK506. The final piece of in vitro analysis found that immunosuppressants did not exert a chemoattractant/chemorepellent effects and therefore did not affect hCNS-SCns migration.

In vivo analysis was carried out through the examination of transplanted hCNS-SCns 9 days in NOD-scid mice after a moderate contusion spinal cord injury. Interestingly, engraftment, proliferation and cell fate were not altered by the addition of immunosuppressants compared to an untreated control. Further stereological quantification analyses also found that the distribution and migration of hCNS-SCns was unaltered.Finally, the researchers investigated functional recovery mediated by hCNS-SCns in the presence of FK506 and anti-CD4 antibody to deplete T-cells and allow for meaningful graft survival (Yan et al). Moderate contusion spinal cord injury was followed by cell transplantation during the chronic phase of the injury (60 days post injury) and mice were then assessed at 10 weeks. In mice treated with FK506 alone, no cell engraftment was observed, whereas addition of FK506 + anti-CD4 antibody mediated engraftment in 50% of animals, where they differentiated mainly into the oligodendrocytic lineage (52.3%), but into the neuronal (<1%) and astrocytic (4.9%) lineages. Locomotor recovery assessment though an open-field test found that mice with engrafted hCNS-SCns had significantly improved recovery with no signs of mechanical allodynia (pain upon contact) of the forepaws or hindpaws, a potential side effect of neural stem cell (NSC) transplantation in animal models of SCI (Hofstetter et al).

Sontag et alprovide an interesting comparison with some even more interesting conclusions – in vitro and in vivo cellular responses of hCNS-SCns to immunosuppressants are different. Therefore, while many immunosuppressants are known to affect signalling pathways known to influence neural cells, the results in this report suggest that these potential interactions do not have a detrimental effect on their in vivo attributes, and underline the necessity for appropriate immunosuppression in cell transplantation. While this is an important finding to this specific case, it perhaps also underlies the over-simplification of many in vitro safety/efficacy analyses for potentially therapeutic cell and/or drug mediated therapies.

References

Aramburu J et al (2004)
Calcineurin: A central controller of signalling in eukaryotes.
EMBO Rep 5:343–348

Cummings BJ et al (2005)
Human neural stem cells differentiate and promote locomotor recovery in spinal cord-injured mice.
Proc Natl Acad Sci USA 102:14069–14074

Hoeffer CA, Klann E (2010)
mTOR signaling: At the crossroads of plasticity, memory and disease.
Trends Neurosci 33:67–75

Hofstetter CP et al. (2005)
Allodynia limits the usefulness of intraspinal neural stem cell grafts; directed differentiation improves outcome.
Nat Neurosci 8:346–353

Salazar DL et al (2010)
Human neural stem cells differentiate and promote locomotor recovery in an early chronic spinal cord injury NOD-scid mouse model.
PLoS One 5:e12272

Uchida N et al (2000)
Direct isolation of human central nervous system stem cells.
Proc Natl Acad Sci USA 97:14720–14725

Yan J et al. (2006)
Combined immunosuppressive agents or CD4 antibodies prolong survival of human neural stem cell grafts and improve disease outcomes in amyotrophic lateral sclerosis transgenic mice.
Stem Cells 24:1976–1985

Stem Cell Correspondent Stuart P Atkinson reports on those studies appearing in current journals that are destined to make an impact on stem cell research and clinical studies.