A Human Progenitor Cell-Based Tissue Engineered Intervertebral Disc

Abstract

Cell and tissue engineering therapies provide promise for regenerating damaged intervertebral disc (IVD) tissue and resolving the low back pain that often accompanies it. However, these treatments remain experimental and unavailable for patients. Furthermore, the large body of work characterizing and utilizing mesenchymal stromal cells (MSCs) for these applications has, unfortunately, not resulted in any FDA-approved spinal therapies. Herein, we characterized DiscGenics's human cadaver-derived discogenic nucleus pulposus (NP) progenitor cells and, for the first time, their discogenic annulus fibrosus (AF) progenitor cells. We then used these discogenic NP and AF cells to create biomimetic human-sized total tissue-engineered IVD replacements, also known as endplate-modified angle ply structures (eDAPS), and compared these with eDAPS formulated with goat or human MSCs. Prior to eDAPS fabrication, discogenic cells were expanded using either two-dimensional attachment culture or three-dimensional suspension culture. Currently, no data exist as to how these discogenic progenitor cells deposit extracellular matrix in a 3D culture environment, nor do data exist characterizing whether the unique expansion environment influences subsequent discogenic cell behavior. Our data support that NP and AF discogenic cells occupy unique niches and serve distinct functions, both in the IVD and in an in vitro 3D culture environment. As a result, discogenic cells deposited more matrix overall than did MSCs. That matrix was distinct between the NP and AF analogs of the tissue-engineered IVDs while also being more homogeneous within each region. Most importantly, unlike both MSC groups, discogenic cells deposited little to no collagen X, suggesting that discogenic eDAPS possess a more stable regional phenotype that will be less susceptible to hypertrophy and downstream calcification. Overall, DiscGenics's discogenic NP and AF cells made compositionally and mechanically superior eDAPS when compared with both human and goat MSCs, with only minor differences between attachment- and suspension-derived discogenic cell eDAPS, supporting their use as a cell source for the creation of human-scale living whole disc replacements.

Keywords: annulus fibrosus; electrospun scaffold; hydrogel; mesenchymal stromal cells; nucleus pulposus.