Tendon grafts deliver gene therapy

A potential gene therapy implant to help repair damaged tendons has been tested, reported BBC News on January 12 2008. Some injuries to tendons, particularly over the front of the fingers, in the human hand are very difficult to treat as they tend to become inflamed and stick to the sheaths around the tendon as they heal. Studies have shown that “implants could accelerate healing, and help restore a wide range of movement”, the report added.

The story is based on a complex tissue engineering study carried out in mice, which highlights an approach to delivering gene therapy that may one day be applicable to humans. However, for now, such developments are a long way off. Further refinements to the processes and research in human cells are needed.

Where did the story come from?

Dr Patrick Basile and colleagues from the University of Rochester Medical Center carried out this research. The study was funded by grants from the National Institutes of Health, the Whitaker Foundation, the Danish Medical Research Council, the Musculoskeletal Transplant Foundation, the Orthopaedic Research Education Foundation and DePuy J&J. It was published in the peer-reviewed medical journal: Molecular Therapy .

What kind of scientific study was this?

The study was a complex laboratory study in the field of tissue engineering, with a number of different parts. The research was mainly conducted in mice, using both mouse cells in culture and living mice. The researchers were investigating whether the action of a particular protein (Gdf5) around the site of an injury would encourage the healing of the damaged tendon that had previously been repaired using a tendon graft.

There were three main parts to their experiment. First, the researchers needed to find a way to encourage the cells around the site of an injury to produce Gdf5, the protein they were interested in. To get the cells to produce the proteins, they needed to get them to express the Gdf5 gene. A virus was used as a “virus vehicle” to carry these particular genes into cells and insert them into the DNA. The researchers tried loading the “virus vehicle” onto freeze-dried tendon grafts that acted as a scaffold, both for carrying the virus, and for new cells to attach to.

In the second part, the researchers looked at whether the protein Gdf5 improved healing in the cells. They caused injury in a culture of mouse embryonic cells that they then treated with the Gdf5-carrying virus and compared this with a culture that was treated with a virus carrying a “control” gene. This is a common “wound model” used to assess healing, in which “microwounds” are created by growing a layer of cells in the laboratory, and then scratching them.

In the final part of their experiment, the researchers inserted the tendon grafts that were carrying the therapeutic genes into live mice and compared the effects with grafts carrying a “control” gene. At both two weeks and four weeks after the graft, they killed the mice and assessed the range of their joint function and how their tendons were healing. Through this, the researchers could find out whether using tendon grafts to deliver gene therapy improved function.

What were the results of the study?

The researchers found that tendon grafts carrying the “virus vehicle” were able to carry genes to the tendon site, and that the genes of interest were expressed (i.e. their proteins were produced) around the graft site. They also found that layers of mouse cells grown in the laboratory that could produce the Gdf5 protein healed better than those that could not.

Finally, the researchers found that mice receiving the tendon graft carrying the Gdf5 gene had improved joint flexibility and better tendon function than those carrying the “control” gene.  They also found that compared with the control group of mice, those receiving the Gdf5 tendon grafts had more organised tissue that integrated with the tendon graft. The control mice showed disorganised tissue around the graft. The researchers acknowledge that they would need to conduct further tests on the tissue to confirm this difference.

What interpretations did the researchers draw from these results?

The researchers conclude that their research has shown that the protein Gdf5 has an important role in remodelling the tendons following injury. They demonstrated that freeze-dried tendon grafts could successfully carry the Gdf5 gene (using a “virus vehicle”) to the injury site, and that the gene is then expressed in surrounding tissue. They also showed that this method is associated with improvements in joint function at the site of the transplant in mice.

What does the NHS Knowledge Service make of this study?

Healing of injuries to the flexor tendons is a particular challenge for healthcare professionals, even if tendon grafts are used. The technology highlighted by this study may one day be used to carry gene therapy through grafts to the site of tendon injuries in humans. Tissue engineering is an important and complex field and the findings of this study will be most relevant to the scientific community who are always on the look out for new approaches to healing and delivery of gene therapy. Importantly, this is a preliminary study, and it may be some time before we can see its application to human health.

Sir Muir Gray adds...

This is a relatively simple task for stem cells, compared with making complex tissues, but any human use is still some years off.