Autologous cell therapy of fracture nonunion - cell phenotype as a predictor of outcome

This study is about using patients? own stem cells to help them heal defects in their bones - usually the consequence of fractures sustained in high energy accidents. The particular group we will study are those receiving treatment by the Ilizarov technique, where missing bone is regenerated by gradually stretching a cut in the bone using an external frame(bone transport). This technique is powerful, resolving otherwise intractable problems of bone loss, but patients consistently say they would value a reduction in the time they need to spend in the frame. One of the rate-limiting steps is healing of the site where the two bone ends meet. We currently try to speed this up by drilling across it and injecting bone marrow. We will test whether we achieve better stimulation by first culturing the stem cells from the bone marrow and injecting them in large numbers. We will measure the result using CT scans, which can quantify bone formation. However we will also study the variation between stem cells from different patients and try to identify features that lead to more vigorous bone formation. This will provide guidance as to how we should develop the protocols used in the culture process, to optimise the cells before use. The answers to these questions will be useful to patients undergoing bone transport, but they will also have implications for other patients with bone defects or fractures that will not heal.

Although most fractures heal well, the significant minority that progress to nonunion carry a heavy price, both in quality of life and NHS costs. Preclinical work suggests that culture-expanded autologous mesenchymal stem cells (MSC) could be helpful in stimulating the healing of human fracture nonunions. However, clinical experience has been that implanted cells are inconsistent in their ability to stimulate healing and this may be partly due to variation in their phenotype. We will conduct a randomised controlled trial comparing MSC (40 patients) with fresh bone marrow (20 patients). The clinical model will be the docking site in tibial bone transport and the primary outcome measure will be the increase in bone mineral content, measured by spiral CT, of a defined region of interest at this site in the first 12 weeks after implantation. We will characterise the phenotype of the implanted cells using proteomics, avoiding the potential pitfalls of assessing only the transcriptome. We will correlate the proteome of implanted cells with the extent to which they stimulate bone formation, aiming to lay the foundation for the development of more effective protocols for culture expansion.

The proposal comes from a partnership of UCL Proteomics and two established Limb Reconstruction Services, both with strong academic leadership, at the Royal National Orthopaedic Hospital (UCL) and Bristol Royal Infirmary (University of Bristol). Between them, these provide a service to a population of several million and apply the (Ilizarov) technique of bone transport to substantial numbers of patients. A regenerative approach based on adult stem cells holds promise for many clinical situations of bone loss or failed fracture healing,however the extreme variability of such cases makes it difficult to conduct robust trials. The tibial docking site is chosen for this study because it is a relatively constant test-bed in which to establish efficacy.
In UCL Proteomics, stable isotope labelling with amino acids in cell culture (SILAC) will be used to comprehensively characterise the proteomes of the implanted cell batches. Samples will be frozen and analysed once the clinical outcome has become clear. Samples from the six patients who produced the most bone regeneration in response to cells will be compared with those from the six who produced the least. We will focus on known bone-associated proteins but also screen for unexpected differences. The proteomic findings will be validated by quantitative Western blotting or ELISA, applied to all 40 MSC-treated cases.