We are arguably a long way off from transplanting miniature brain blobs into people (although some have tried putting them in rodents). But we are getting closer to implanting other organoids—potentially those 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 thyroids from stem cells.
The thyroid is a butterfly-shaped structure in the neck that makes hormones. A lack of these hormones can make people very sick. Around 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 a replacement hormone treatment every single day.
After growing thyroid organoids in a lab for 45 days, Romitti and her colleagues could transplant them into mice that were lacking 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 puts it.
The focus is now on finding a way to safely transplant similar organoids in people. There is plenty of demand—Romitti says her colleague is constantly getting calls and emails from people who are desperate to get a transplanted mini thyroid. But we’re not quite there yet.
Romitti and her teammates made their mini thyroids from stem cells—cells in a “naïve,” flexible state that can be encouraged to form any one of many cell types. It has taken the scientists a decade of research and multiple attempts to find a way to get the cells to 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 several drugs to aid the growth of the organoids in a dish.
The stem cells the team used were embryonic stem cells—from a line of cells that were originally taken from a human embryo. These cells couldn’t be used clinically for several reasons—the recipient’s immune system would reject the cells as foreign, for example, and the destruction of embryos for disease treatments 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 individuals. Romitti says her team has made “promising” progress.
Of course, we’ll also have to make sure these organoids are safe. No one knows what they are likely to do in a human body. Will they grow? Shrink away and disappear? Form some kind of cancer? We’ll need more long-term studies to get a better idea of what might happen.