Thymus rejuvenation

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Growth hormone enhances thymic function in HIV-1–infected adults

AI summary :

Study Design
​Participants: 22 HIV-1-infected adults who were already on stable antiretroviral therapy (cART).
​The Problem: HIV accelerates “thymic involution” (the shrinking of the thymus), leaving patients with low levels of new, “naïve” T-cells, even if the virus is controlled.
​The Intervention: Participants were randomized to receive either recombinant human growth hormone (rhGH) or no hormone (observational control) for one year.

Key Findings: Physical Regrowth
​The researchers used CT scans to measure the density and mass of the thymus.
​Reversing Fat Replacement: At the start, most participants’ thymuses were almost entirely replaced by fat (adipose tissue).
​Significant Mass Gain: After 6 months of GH treatment, there was a robust increase in thymic density (up to +50 Hounsfield units compared to +1 in the control group).
​Visible Architecture: The scans showed the reappearance of dense “cellular” thymic tissue, indicating the organ was structurally rebuilding itself.

Key Findings: Functional Immune Output
​Regrowing the organ is only useful if it produces “working” immune cells. The study confirmed this using two biomarkers:
​TRECs (T-cell Receptor Rearrangement Excision Circles): These are tiny loops of DNA found only in “newborn” T-cells. The GH group saw a significant increase in TREC frequency, proving the thymus was producing de novo T-cells from scratch.
​Naïve CD4+ T-cell Counts: The number of circulating naïve CD4+ T-cells (the “infantry” of the immune system) increased by 96.4% in the GH group, compared to only 17.6% in the control group.