T cells play a protective role in maintaining spinal health after intervertebral disc injury

Introduction/Rationale: The intervertebral disc (IVD) is an essential joint of the spine that is prone to injury and exhibits limited regenerative capacity, leading to degeneration and chronic back pain. While T cells are known mediators of tissue repair, the specific T cell subtypes that infiltrate the IVD following injury remain poorly defined. We previously demonstrated a temporally oscillatory T cell response after IVD injury in C57BL/6J mice, with reduced degeneration associated with γδ T cell infiltration in females only (Clayton et al., 2024). In other tissues, γδ T cells promote repair following injury; however, their presence and role in the IVD have not been explored. We hypothesize that T cells, particularly γδ T cells, are essential for IVD repair.

Methods: Using a mouse model of accelerated IVD degeneration, control (non-injured) and injured (needle puncture) IVDs were harvested from the same female, 4-month-old female C57BL/6J wildtype (WT) mice, WT mice treated with TCRγδ-depleting or IgG control antibodies, and T cell knockout (TCRβδKO) mice (n=3/group). IVDs were analyzed by Safranin O/Fast Green histology (n=3–4) and flow cytometry (n=3). Deidentified human IVD tissue was collected from female patients undergoing spinal fusion surgery (n=3).

Results: Histological analyses revealed significantly increased injury-induced degeneration in TCRβδKO mice compared to WT controls. Depletion of TCRγδ more severely exacerbated degeneration relative to IgG-treated and TCRβδKO injured mice. Comparative analyses of WT mouse and human samples showed similar proportions of infiltrating CD3⁺ T cells following injury, with CD4⁻CD8⁻ double-negative T cells comprising the largest population; γδ T cells represented the majority of this subset.

Conclusion: Collectively, these data demonstrate that γδ T cells infiltrate the injured IVD and play a protective role against degeneration. Loss of γδ T cells worsens injury-induced degeneration, indicating a key immunomodulatory function in maintaining IVD integrity following injury.