Lab-grown vocal cord tissue

For the first time, scientists have successfully grown vocal cord tissue in the lab that can produce sound when transplanted into animals. But most importantly, the bioengineered structure was not rejected for as long as three months when transplanted into mice with human immune system.

The bioengineered vocal cord tissue was transplanted onto one side of larynges that had been removed from cadaver dogs. The dogs thus had one native tissue and one bioengineered tissue. When air was blown through the dogs’ voice box, the bioengineered tissue vibrated much like the native one on the opposite side. The produced sound by the natural and bioengineered tissue was “indistinguishable.”

“This tissue engineering approach has the potential to restore voice function in patients with otherwise untreatable VF [vocal fold] mucosal disease,” the authors of a paper published recently in the journal Science Translational Medicine write.

The Editor’s summary also underlines the importance of the study. “These data suggests feasibility for transplant and survival in the larynx as well as for function, ultimately giving patients back their voices,” it notes. The ability to effectively communicate is impaired in people with vocal fold tissue damage or loss.

The advantage of using a bioengineered tissue is that it can be customised to size so that it fits the size of the vocal fold of the recipient — adult (male or female) or child. Transplantation of vocal cord from a cadaver has either failed or has been ineffective.

“Certain congenital problems or scaring or tissue loss following surgery to remove invasive cancer can cause major damage to the vocal fold mucosa and can cause substantial voice loss that’s very challenging to treat with our current methods,” Dr. Nathan Welham from the University of Wisconsin School of Medicine and Public Health in Madison and one of the authors of the paper said during a press briefing.

Our vocal cords are two strong but flexible bands of muscle that are covered in a delicate tissue called mucosae. The flexible bands of muscle vibrate against each other up to a thousand times per second when we force air over them when we speak.

“Our vocal cords are made up of special tissue that has to be flexible enough to vibrate, yet strong enough to bang together hundreds of times per second. It’s an exquisite system and a hard thing to replicate,” Dr. Welham said in a release. The cells needed to create the vocal cord were taken from human vocal cord tissue and bioengineered in the lab. The vocal cord tissue in turn was taken from a cadaver and four patients who had their larynxes removed but did not have cancer.

Two types of cells that make up the mucosae — connective fibroblasts and epithelial cells — were isolated from the tissue and then applied to a 3-D collaged scaffold used for growing the cells.

In about two weeks, the cells grew together to form a tissue that “felt like vocal-cord tissue.” The tissue had the same physical characteristics as a normal tissue except for one thing — the fiber structure. According to Dr. Welham, the reason for that is not difficult to know — the human vocal cord continues to develop till the age of 13 years.

“It seems like the engineered vocal cord tissue may be like cornea tissue in that it is immunoprivileged, meaning that it doesn’t set off a host immune reaction,” he said in the release.

Published in The Hindu on December 14, 2015