Immunoselected STRO-3+ mesenchymal precursor cells and restoration of the extracellular matrix of degenerate intervertebral discs: Laboratory investigation

Object. Chronic low-back pain of discal origin is linked strongly to disc degeneration. Current nonsurgical treatments are palliative and fail to restore the disc extracellular matrix. In this study the authors examined the capacity of ovine mesenchymal precursor cells (MPCs) to restore the extracellular matrix of degenerate discs in an ovine model. Methods. Three adjacent lumbar discs of 24 adult male sheep were injected intradiscally with chondroitinase-ABC (cABC) to initiate disc degeneration. The remaining lumbar discs were used as normal controls. Three months after cABC injection, the L3-4 discs of all animals were injected with either a high dose (4 x 10 ⁶ cells, in 12 sheep) or low dose (0.5 x 10 ⁶ cells, in 12 sheep) of MPCs suspended in hyaluronic acid (HA). The adjacent L4-5 degenerate discs remained untreated; the L5-6 discs were injected with HA only. The animals were euthanized at 3 or 6 months after MPC injections (6 sheep from each group at each time point), and histological sections of the lumbar discs were prepared. Radiographs and MR images were obtained prior to cABC injection (baseline), 3 months after cABC injection (pretreatment), and just prior to necropsy (posttreatment). Results. Injection of cABC decreased the disc height index (DHI) of target discs by 45%-50%, confirming degeneration. Some recovery in DHI was observed 6 months after treatment in all cABC-injected discs, but the DHI increased to within baseline control values only in the MPC-injected discs. This improvement was accompanied by a reduction in MRI degeneration scores. The histopathology scores observed at 3 months posttreatment for the high-dose MPC-injected discs and at 6 months posttreatment for the low-dose MPC-injected discs were significantly different from those of the noninjected and HA-injected discs (p < 0.001) but not from the control disc scores. Conclusions. On the basis of the findings of this study, the authors conclude that the injection of MPCs into degenerate intervertebral discs can contribute to the regeneration of a new extracellular matrix.