Structured Coculture of Stem Cells and Disc Cells Prevent Disc Degeneration in a Rat Model

Background Context: Harnessing the potential of stem cells is an important strategy for regenerative medicine. This study explores the use of bilaminar coculture pellets (BCPs) of mesenchymal stem cells (MSCs) and nucleus pulposus cells (NPCs) as a cell-based therapy for intervertebral disc regeneration. Prior in vitro experiments have shown that BCP can help differentiate MSCs and substantially improve new matrix deposition.

Purpose: To evaluate the clinical relevance of BCPs by testing the system in vivo.

Study Design/setting: We have designed a novel spherical BCP where MSCs are enclosed in a shell of NPCs. The pellets were tested in vivo in a rat tail model of disc degeneration.

Methods: Rat caudal intervertebral discs were denucleated and treated with BCP in a fibrin sealant (FS) carrier (controls were MSCs suspended in FS; NPCs suspended in FS; MSCs and NPCs suspended in FS; FS only; and surgery only). At 14 and 35 days after implantation, the animals were euthanized and discs were evaluated for proteoglycan content, enzyme-linked immunosorbent assay for inflammatory cytokines, cell retention using polymerase chain reaction, disc height, histology, and disc grade based on a blinded scoring system.

Results: The proteoglycan and cytokine levels were not significantly different among groups. The BCP group had higher cell retention than controls. Disc height and disc grade increased over time only in the BCP group. Bilaminar coculture pellets were the only treatment to show proteoglycan staining in the nucleus space at 35 days.

Conclusions: This study shows that BCPs may prevent postnucleotomy disc degeneration in vivo. Larger animals and longer time points will be necessary to further judge potential clinical impact. As opposed to strategies that require growth factor supplements, predifferentiation, or genetic manipulations, BCPs are a self-sustaining and targeted method for tissue regeneration in situ.