Abstract Purpose of study: The study was designed to assess whether autologous disc chondrocyte transplantation will prevent disc degeneration after discectomy. Cultured autologous cells were transplanted into the nucleus pulposus of 18 dogs by a closed procedure. Although it has been shown that disc cells sustain a phenotype in culture, the fate of re-implanted cells is not fully understood. Methods used: Mature dogs were radiographed before surgery. Blunt dissection was used to reach the margin of the outer annulus, and 100 mg of nucleus and inner annulus material was sampled from two levels (L1–L2 and L3–L4). The L1–L2 disc of each dog served as a control, and the L3–L4 level was used as the site for transplantation. Although the L2–L3 site was approached, the annulus was not violated. Disc chondrocytes were propagated in culture and reimplanted 10 weeks later under fluoroscopic guidance. Cells from four dogs were treated with BrdU during cultivation to assess viability and location posttransplantation. Postoperative radiographs were taken monthly, and the animals were euthanized at 3 months, 6 months, 9 months and at 1 year. Intervertebral discs were assessed by histology, radiography and magnetic resonance imaging (MRI). Vertebral segments T-13 through S-1 were removed en bloc, radiographed and prepared for MRI. Images were collected at 1.5 T in both T1 and T2 weightings. Disc heights were calculated using a spine index that averaged the height of the disc relative to the two adjacent vertebrae. of findings: MRI exhibited changes in the surgical defect and central retention of characteristic disc morphology. Although experimental levels demonstrated less proton density than the unoperated control, the level receiving cell transplantation (L3–L4) demonstrated a difference in quantity and intensity of signal. The chief pathology evident from the MRI examination was a loss of intensity in the central portion of the L1–L2 intervertebral discs. Although differences in disc height were apparent between levels receiving the cell transplantation and those that had not, no statistical correlation could be demonstrated. Over the 1-year study, positive changes associated with the level receiving cells were a reduction in marrow fibrosis and restoration of end plate morphology. Cells that were reintroduced into the disc appeared to populate, make matrix and suppress inflammatory reaction. Introduction of cells seemed to have a positive effect on cell height, MRI signal and matrix appearance. MRI changes were positive over time, showing enhanced central disc signal and reduction in end plate effusion. Although disc height could not be correlated with cell transplantation statistically, a difference in tissue structure was evident at both the micro and macro level. Relationship between findings and existing knowledge: Autologous cells transplanted into a damaged intervertebral disc appear to slow degeneration. Evidence of matrix production, suppressed inflammation and cell viability was evident grossly (dissection), by MRI, radiography, by histology and by nuclear marker. From these early results, autologous disc chondrocyte cell transplantation appears to offer the promise of retarding degeneration, maintaining intervertebral height and stimulating matrix regeneration after discectomy. Overall significance of findings: While cell viability, matrix production and matrix integration suggest autologous cell transplantation may be a valuable clinical tool, refining technology will strengthen the value in application. Disclosures: No disclosures. Conflict of interest: Timothy Ganey, stockholder; Timothy Ganey, other support.