You might not think that vocal cords would be high on the priority list for lab-grown tissues, but with some 20 million people in the U.S. alone suffering voice impairment, racking up bills in excess of $11 billion, solutions are clearly needed. Thankfully though, we’re getting somewhere, as scientists have just managed to bioengineer functional vocal cord tissue in a dish.
Not only could it produce sound when grafted into the voice boxes of animals, but it also avoided rejection after it was transplanted into mice modified to have human immune systems. This raises the tantalizing possibility that in the future, scientists might be able to achieve a similar feat in humans who have lost this tissue due to reasons such as injury or disease. The study has been published in Science Translational Medicine.
Husky, high-pitched or soft, our voices come from the vocal cords, two bits of specialized tissue in the larynx covered in a delicate layer of mucosa. They produce sound by rapidly vibrating, hundreds of times per second, as we expel air. Like many other parts of the body, the vocal cords do not repair well after injury and instead form tough scar tissue that is impaired in its ability to generate sound.
While some individuals afflicted by such damage can be given injections of materials like collagen, the tough protein that helps hold our tissues together, this is ineffective for those who are missing substantial chunks of their vocal cords, for example after cancer surgery. With more and more tissue being grown in the lab for transplantation, scientists saw this as a potential opportunity to help such patients, but getting the architecture right – flexible yet tough – was never going to be easy.
Scientists are proving it is possible, though. The team from the University of Wisconsin-Madison began by taking cells from the vocal cord mucosa of a cadaver and four patients who had their larynxes surgically removed. After culturing them in the lab, the scientists seeded them on to a 3D scaffold made of collagen in order to guide their growth.
About two weeks later, the cells had organized themselves into layers of connective tissue overlain with delicate epithelial cells that mimicked the architecture of the human body. The researchers then grafted these onto excised larynges of cadaver dogs and demonstrated that they could produce sound when air flowed through them. Furthermore, high-speed imaging demonstrated that the tissue did indeed vibrate like native vocal cords.
Finally, to examine their potential longevity following transplantation, they were grafted into mice that were engineered to have immune systems very similar to our own. Encouragingly, they weren’t rejected and persisted for up to three months, suggesting that vocal cord tissue may be “immunoprivileged,” or doesn’t rouse the immune system.
It’ll be a long time before we see the study translated into the clinic, of course, but it’s still certainly an encouraging step towards this goal.