A preliminary study using a cocktail of growth hormone and the antidiabetic drugs dehydroepiandrosterone and metformin findings suggests this could be possible.

The Thymus Regeneration, Immunorestoration and Insulin Mitigation (TRIIM) trial  tested nine white men between 51 and 65 years of age and was conducted at Stanford Medical Center in Palo Alto, California. The goal was to achieve restoration of tissue in the thymus gland, which plays a key role in immune system function: maturation of white blood cells to specialized T cells for fighting infections and cancer but starts to shrink and become clogged with fat shortly after puberty.

The participants were treated for one year with a cocktail of growth hormone and the antidiabetic drugs dehydroepiandrosterone and metformin because growth hormone promotes diabetes. Analysis of blood samples collected during the treatment period indicated that the blood-cell count was rejuvenated in each patient. In seven of the men, accumulated fat was also found to be replaced with regenerated thymus tissue using magnetic resonance imaging.

Furthermore, according to analyses using four previously developed epigenetic clocks, the men on average lost 2.5 years of their biological ages. The tests involve identification and mapping of DNA-methylation sites across the genome, which change with age. Notably, for the six participants who provided a blood sample six months after they were no longer taking the cocktail, the biological effects persisted.

Larger studies are being planned to see if these positive results can be confirmed.