Transplantation of activated nucleus pulposus cells after cryopreservation: efficacy study in a canine disc degeneration model

Transplantation of activated nucleus pulposus (NP) cells obtained by coculturing NP cells and bone marrow mesenchymal stromal cells having cell-to-cell contact has been shown to be effective in animal models and, more recently, in human clinical trials. If the NP cells can be cryopreserved, then autologous cell transplantation could be offered to patients as and when required. In a previous study, we confirmed that activated NP cells can be obtained by coculturing with mesenchymal cells after cryopreservation. However, the in vivo effects of cell transplantation therapy using activated NP cells prepared from cryopreserved cells are not known. In this in vivo canine model, we compared indicators of disc degeneration in animals that received transplanted activated normal NP cells, transplanted cryopreserved NP cells, and no cell transplantation after induction of disc degeneration. The intervertebral disc height on radiographs and T2-weighted magnetic resonance imaging were significantly higher in both cell transplantation groups compared with the degenerated disc group. Macroscopic and histological findings demonstrated attenuated disc degeneration in the two transplanted groups. Intense staining of proteoglycan and collagen type II was seen in green fluorescent protein-labelled transplanted cells, which suggested that the cells had survived and were functioning after transplantation. No significant differences were observed between the two transplanted groups. Transplanted activated cryopreserved NP cells induced a similar attenuation of intervertebral disc degeneration as that of conventionally activated NP cells. These findings suggest that the use of cryopreserved cells specific to a patient's condition has potential in transplantation therapy.