BACKGROUND

Macroencapsulated pancreatic endoderm cells (PECs) can reverse diabetes in rodents and preclinical studies revealed that thyroid hormones in vitro and in vivo bias PECs to differentiate into insulin-producing cells. In an ongoing clinical trial, PECs implanted in macroencapsulation devices into patients with type 1 diabetes were safe but yielded heterogeneous outcomes. Though most patients developed meal responsive C-peptide, levels were heterogeneous and explanted grafts had variable numbers of surviving cells with variable distribution of endocrine cells.

METHODS

We measured circulating triiodothyronine and thyroxine levels in all patients treated at 1 of the 7 sites of the ongoing clinical trial and determined if thyroid hormone levels were associated with the C-peptide or glucagon levels and cell fate of implanted PECs.

RESULTS

Both triiodothyronine and thyroxine levels were significantly associated with the proportion of cells that adopted an insulin-producing fate with a mature phenotype. Thyroid hormone levels were inversely correlated to circulating glucagon levels after implantation, suggesting that thyroid hormones lead PECs to favor an insulin-producing fate over a glucagon-producing fate. In mice, hyperthyroidism led to more rapid maturation of PECs into insulin-producing cells similar in phenotype to PECs in euthyroid mice.

CONCLUSION

These data highlight the relevance of thyroid hormones in the context of PEC therapy in patients with type 1 diabetes and suggest that a thyroid hormone adjuvant therapy may optimize cell outcomes in some PEC recipients.