# An Ex Vivo Model of Intervertebral Disc Degeneration for Assessing Retention of Injectable Cell‐Based Grafts

## TL;DR

Researchers created a realistic lab model of spinal disc degeneration to test how well injectable cell treatments stay in place and function.

## Contribution

A novel ex vivo model of intervertebral disc degeneration was developed to evaluate injectable cell-based therapies.

## Key findings

- The model mimics human disc degeneration with reduced water and proteoglycan content.
- Injectable nasal chondrocyte spheroids localized and remained viable in the degenerated disc model.
- The model shows potential as a preclinical tool to reduce reliance on animal studies.

## Abstract

Cell therapies for painful intervertebral disc (IVD) degeneration (IDD) have not yet achieved widespread clinical adoption. Understanding therapeutic cell effects in native IVD remains challenging due to the complex IVD environment and limitations of current models. We present a physiologically relevant ex vivo model of IVD degeneration, which we employ to evaluate the retention of therapeutic cells in the IVD.

Bovine IVDs were cultured ex vivo for 14 days. IVD degeneration was induced under physiological loading by chondroitinase ABC (ChABC), or ChABC with pro‐inflammatory cytokines (Infl) aiming to mimic IDD. The nucleus pulposus (NP) tissue integrity was characterized by T2 MRI and modified Thompson grading and compared with human IVDs of different ages. The onset of IDD in the bovine model was assessed by IL‐8, MMP13, and COX‐2 expression. Spheroids derived from mCherry‐transduced human nasal chondrocytes (NCS) were injected into the NP. NCS retention within the IDD model was assessed by NCS ability to survive (c‐caspase 3), localize (mCherry), and produce chondrogenic proteins (SOX‐9, aggrecan).

ChABC injection reduced water and proteoglycan content in the NP, resembling human age‐related IVD degeneration. ChABC + Infl treatment led to a more pronounced loss of tissue integrity and upregulation of IL‐8, MMP13, and COX‐2, typically characterizing the transition to IDD. Upon injection into the IDD model, NCS localized in the NP, some remained viable, and maintained their chondrogenic features, demonstrating successful retention within the 7‐day time frame.

We developed an ex vivo IVD model with a controlled and physiologically relevant environment and used it for assessing the retention of cell‐based therapies for NP repair. The model recapitulated the progression of IVD degeneration, establishing its value as a preclinical research tool and reducing the reliance on animal studies during the early translational phase.

An ex vivo model of intervertebral disc (IVD) degeneration was generated using chondroitinase ABC (ChABC) and pro‐inflammatory cytokines (Infl) and used for assessing retention of injectable cell‐based grafts, namely nasal chondrocyte spheroids (NCS).