Growth Hormone to Increase Immune Function in People With HIV

Overview

Growth hormone plays an important role in the development of the immune system. Studies suggest that growth hormone may promote growth of the thymus, a gland responsible for the production of important immune cells called T cells. Since these cells are lost during the course of HIV infection, it is possible that growth hormone treatment could help restore the immune system. This study will determine whether the administration of growth hormone can increase the size and function of the thymus and cause an increase in the number of new T cells in the blood of people infected with HIV. Study hypothesis: Growth hormone treatment will enhance T cell production in HIV infected adults.

The thymus is the major organ of T cell production and is generally believed to be nonfunctional in adults. Even if nonfunctional, it is destroyed by HIV infection while T cells are destroyed in the peripheral lymphoid system. Given the absence of new T cell production and a pathologic acceleration of T cell destruction, the immune system collapses and immunodeficiency ensues. However, some studies have demonstrated thymic function in adults with HIV disease. Such function may be induced by positive feedback regulation of T cell production and the presence or absence of such function may play a determinant role in disease progression and response to highly active antiretroviral therapy (HAART). These studies suggest that the thymus is functional in many adults with HIV disease and that thymic function might be induced as a consequence of HIV-mediated peripheral T cell depletion. Growth hormone is a potent regulator of thymic function. This study will determine whether true thymic function can be induced in HIV infected adults, whether such induction is indeed prompted by growth hormone, and whether thymic function plays a role in sustaining the T cell compartment in the face of peripheral T cell depletion. Twenty-four volunteers will be enrolled in this 2 year study. All participants will receive 12 months of treatment with human growth hormone. Participants will be randomly assigned to one of two study arms. Twelve participants (Arm 1) will receive growth hormone during the first year of the study (3 mg given daily by subcutaneous injection, with dose reduction to 1.5 mg after 6 months). Twelve participants (Arm 2) will be enrolled in an observational control arm (no placebo injections) that will cross over to growth hormone treatment after 1 year. Participants, whether in Arm 1 or Arm 2, will have as many as 24 scheduled study visits during the 2 years after enrollment. In general, study visits occur every every 1 to 3 months. Study visits will include physical exams, blood tests, CT scans, PET scans, and DEXA scans.