Effects of growth hormone in enhancing thymic regrowth and T-cell reconstitution.

Evaluation of: Napolitano LA, Schmidt D, Gotway MB et al. Growth hormone enhances thymic function in HIV-1-infected adults. J. Clin. Invest. 118, 1085-1098 (2008). Age-induced atrophy of the thymus results in a compromised immune system characterized by a restricted T-cell receptor repertoire, skewed towards memory T cells and a global reduction in immune responsiveness. This has important clinical implications in immune recovery from lymphopenic states, for example, after cytoablative treatment for cancer therapy, in conditioning regimes for bone marrow transplants and severe viral infections, such as HIV. The paper from Napolitano et al. evaluates the use of growth hormone (GH) to regenerate the thymus and replenish the naive T-cell population for immune recovery in adult HIV patients, albeit those carrying a low viral load. This study - an extension of an earlier paper from the same group - provides important evidence that GH, at least when administered over a long period of time, enhances thymopoiesis and therefore facilitates CD4(+) T-cell recovery in HIV-1-infected adults. Provided the side effects of GH treatment can be better controlled, these results could contribute towards developing strategies for a broader clinical use of GH in immune recovery.