Recombinant human growth hormone (rhGH), manufactured as Serostim by Serono Laboratories and approved for the treatment of AIDS-related wasting syndrome, may also prove to be useful as an immune-based therapy in people living with HIV. The drug, researchers reported in the March issue of the Journal of Clinical Investigation, restores the ability of the thymus gland to produce new CD4 cells.

CD4 cells are a type of immune system cell called a T-lymphocyte. They are made in the bone marrow and then travel to the thymus to mature, hence the T in their name. The thymus trains the T-lymphocytes to fight infections in the body, sometimes in the form of “helper” CD4 cells. 

The thymus produces the majority of CD4 cells the body needs within the first few years of life and becomes filled with fat—a process called involution—and almost completely inactive by adulthood. Scientists have long assumed that involution of the thymus is permanent and that it is not possible to coax the gland to produce new CD4 cells, even in people whose immune systems have been badly damaged by HIV.  

Laura Napolitano, MD of the Gladstone Institute of Virology and Immunology (GIVI) and the University of California, San Francisco, and her colleagues recruited 22 HIV-positive people who’d been taking antiretroviral therapy for at least a year but who had not seen significant CD4 cell increases.

Dr. Napolitano’s team wanted to study the effects of rhGH, a drug that not only helps the body build muscle but also break down fat. They theorized that the injectable hormone’s ability to shrink fat in the body may also help reverse involution of the thymus, thereby jump-starting the gland’s ability to produce new CD4 cells. 

The team followed its study volunteers for two years, conducting detailed analysis of the participants’ immune function. During the first year, one half of the group received rhGH, while the other half did not. In the second year, the group who’d been receiving rhGH stopped taking it and the group who’d not been taking rhGH started taking it.

Not only did rhGH decrease thymic fat mass, it increased patients’ CD4 cells by 30 percent. What’s more, CD4 cells continued to increase for three months after people stopped taking rhGH, and these gains were sustained for at least a year after stopping treatment.

Dr. Napolitano cautions that their findings are preliminary and that, “[rhGH] should not be used as a treatment for immune purposes in HIV disease or in any other individuals at this time, unless this treatment occurs within a research study. More research is needed to learn whether stimulating the production of new T-cells actually provides a health benefit.”