Since the regeneration of thyroid glands has remained challenging, patients with thyroid disorders who have their glands surgically removed must take hormone replacement medication for the rest of their lives. 

But what if they were grown inside of another organ?

Study authors from Nanjing University detail a method involving transplanting blocks of thyroid tissue to the spleen to regenerate thyroid glands and restore full thyroid function in mice. An ectopically produced thyroid that is still whole can merge with the splenic tissue around it without affecting its ability to stay separate from the lymphatic system. The data suggests that the functional restoration by the ectopic thyroid is better than the gold standard of oral levothyroxine treatment for controlling hormone levels in response to body signals.

This study provides new information for developing treatment options for thyroid-related diseases by showing that intrasplenic thyroid gland regeneration can fully restore thyroid functions after thyroidectomy.

The research article, “Regeneration of Thyroid Glands in the Spleen Restores Homeostasis in Thyroidectomy Mice,” was published in Advanced Science.

Thyroid gland regeneration inside a spleen

Because of its loose tissue structure and abundant blood supply, the spleen is chosen for thyroid gland regeneration because it can accommodate relatively intact thyroid tissue fragments. When thyroid tissue is transplanted into the spleen, unlike muscle, the transplanted tissue is not at risk of future damage. Transplanted thyroid tissue in the spleen successfully rebuilt the blood vessels in only 48 hours, an essential step in the regeneration process.

After being transplanted into the spleen, the thyroid tissue showed signs of regrowth and eventually reached a size similar to that of a natural thyroid gland. As a result, in actual practice, only a tiny fraction of the thyroid tissue harvested from a patient undergoing a thyroidectomy is likely to be transplantable.

The data show that the spleen-regenerated thyroid can respond to stimuli by releasing thyroid hormones and keeping physiological concentrations steady over time. It also has structural features that are unique to the thyroid. Further, it can eliminate the many side effects of oral thyroid hormone treatment while completely restoring physiological functions regulated by thyroid hormone.

To mimic allogeneic transplantation, the researchers used genetically diverse mice to simulate transferring thyroid tissue. However, even with immunosuppressive medications, the natural immune system rejected the attempt. Allogeneic transplantation becomes more problematic in light of this, particularly in cases where autologous transplantation is considered risky because of tumor recurrence. Alternatives to autologous transplantation, such as gene correction or autologous induced pluripotent stem cell (iPSC) methods, may be more effective in preventing immune rejection.

The risks of bleeding and the complexity of the procedure raise questions about the safety of injecting into the spleen. According to the authors, type-B ultrasound-guided percutaneous intra-splenic injections are a simple procedure in the field of minimally invasive surgery. Still, clinical trials and experiments with larger animals should carefully assess these factors.

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