Biomedical Engineering Reference
In-Depth Information
degenerated IVDs. Second, any remaining viable cells may exhibit altered pheno-
types or varying degrees of senescence. The NP cell population found in the
degenerative IVD is no exception to this fact [
43
]. Finally, as shown below, use
of scaffolds without cells has provided only limited successes. A variety of cell
sources have been described in the literature, including NP cells, chondrocytes,
notochordal cells, and stem cells. A short survey of the pros and cons of these cell
sources follows.
8.1.1 Autologous and Allogenic NP Cells
Theoretically, autogenic NPs would prove immunologically ideal. However,
Richardson et al. suggest that use of these cells may not be not clinically feasible
for several reasons: (1) NP cells are sparse and do not provide adequate quantity
for self repair, (2) harvest of NP cells from a healthy adjacent IVD will lead
to degeneration of that IVD, (3) harvest of NP cells from a degenerating IVD
will accelerate the degenerative process, (4) NP cells from degenerated discs
exhibit altered phenotype, increased senescence, increased expression of catabolic
cytokines and degradative enzymes as well as a diminished capacity for matrix
production [
74
]. Cadaveric NP cells from non-degenerated allogenic discs may also
prove to be a feasible option; however, optimal cryopreservation techniques are still
being developed, [
75
] and thus warrant further investigation. Although animal and
human studies utilizing autogenic and allogenic NP cell transplantation provide
some evidence of success in mitigating the progression of degeneration, these
results do not appear to indicate that implantation of these cells alone (without
scaffolds) have the capability to fully restore a degenerated disc to a normal healthy
status [
76
].
8.1.2 Chondrocytes
NP cells are often described as “chondrocyte-like” owing to their round morphol-
ogy and their ability to synthesize an ECM rich in collagen type II and the
proteoglycan aggrecan. In a study performed in New Zealand white rabbits, autol-
ogous auricular chondrocytes were expanded and re-inserted into nucleotomized
IVDs, which resulted in neo-formation of hyaline cartilage within the IVDs [
77
].
Although these results appear intriguing, it must be kept in mind that a striking
difference between ECMs produced by chondrocytes and NP cells does exist [
23
].
More recently, use of human fetal chondrocytes (hFCs) to mitigate IDD in a lapine
model was presented at the 23rd annual meeting of the North American Spine
Society [
78
]. Discs receiving hFC injection retained 87.1% of their pre-operative
disc height, and 60% of these discs had brighter MRI signal intensities compared
with untreated degenerative controls. Moreover, the authors state that the injected
human cells did not elicit immunological reactions, possibly due to the hFCs
lacking major histocompatibility complex (MHC) class II molecules and to the
