Nature here notes progress towards tissue engineering of replacement thyroid glands and a demonstration of the ability to repair the thyroid in situ:
The thyroid is the latest in a growing list of body parts that can now be 'fixed' in mice, with the potential to treat diseases from diabetes to Parkinson's ... Progress has been very rapid over the past decade. In recent years we've seen a number of very important studies in which mouse stem cells have been converted to a desired cell type that has then been shown to be functional in vivo, and to confer benefits in mouse models of human diseases.
[Researchers] first genetically engineered embryonic stem cells to express two proteins - NKX2-1 and PAX8 - that are expressed together only in the thyroid. When these cells were grown in Petri dishes in the presence of thyroid-stimulating hormone, they turned into thyroid cells. Thyroid cells, however, have to be organized into a particular three-dimensional shape before they can work. They need to form small, spherical follicles containing a cavity in which iodide - a component of some hormones produced in the thyroid gland - can be concentrated before being absorbed and used for hormone synthesis. Remarkably, the stem-cell-derived thyroid cells spontaneously grouped into follicles similar to those in an intact thyroid gland [and] the follicles were able to trap iodide and synthesize thyroid hormones.
The next step was to see how these follicles would function in live mice, and to assess their potential to correct hypothyroidism. This condition was induced in mice with an injection of radioactive iodine that accumulated in their thyroid glands, causing the tissue to wither away. Four weeks later, once hypothyroidism had been established, the mice received a graft of stem-cell-derived thyroid follicles. Out of nine mice treated in this way, eight showed complete rescue - their thyroid hormones returned to normal levels.