Arguably, we’re a long way from transplanting miniature brain drops into people (although some have tried putting them into rodents). But we are getting closer to implanting other organoids, potentially ones that resemble lungs, livers or intestines, for example.
The latest progress has been made by Mírian Romitti at the Université libre de Bruxelles in Belgium and her colleagues who have successfully created miniature transplantable thyroid from stem cells.
The thyroid is a butterfly-shaped structure in the neck that produces hormones. A lack of these hormones can make people very sick. About 5% of people have an underactive thyroid, or hypothyroidism, which can lead to fatigue, aches and pains, weight gain, and depression. It can affect brain development in children. And those who are affected often have to take hormone replacement therapy every day.
After growing thyroid organoids in a lab for 45 days, Romitti and his colleagues were able to transplant them into mice that lacked their own thyroids. The operation appeared to restore the production of thyroid hormones, essentially curing the animals’ hypothyroidism. “The animals were very happy,” as Romitti says.
Attention is now turning to finding a way to safely transplant similar organoids into people. Demand is high: Romitti says his colleague is constantly getting calls and emails from people who are desperate to get a mini-thyroid transplant. But we haven’t gotten to that point yet.
Romitti and his teammates created their mini-thyroids from stem cells, cells in a flexible, “naive” state that can be stimulated to form any of many cell types. It has taken scientists a decade of research and multiple attempts to find a way to make the cells form a structure that looks like a thyroid. The end result required genetic modification using a virus to infect the cells, and the team used various drugs to help the organoids grow in a dish.
The stem cells the team used were embryonic stem cells, from a cell line that was originally taken from a human embryo. These cells could not be used clinically for several reasons: the recipient’s immune system would reject the cells as foreign, for example, and destroying embryos for disease treatment would be considered unethical. The next step is to use stem cells generated from a person’s own skin cells. In theory, mini-organs created from these cells could be custom-made for people. Romitti says his team has made “promising” progress.
Of course, we will also have to make sure that these organoids are safe. No one knows what they are likely to do to a human body. Will they grow? Shrink and disappear? Form some kind of cancer? We’ll need more long-term studies to get a better idea of what might happen.