Growth hormone effective in increasing thymic activity

In many patients, treatment with highly active antiretroviral therapy (HAART) can lead to a significant recovery from the immunosuppression associated with advanced HIV disease. Still, some patients only experience a partial recovery, if any.

Several studies have indicated that thymic function, which may be impaired by age, HIV and other factors, is critical in determining immune recovery on HAART. In a study published in AIDS, investigators found that growth hormone, which plays a role in thymopoiesis, may increase thymic activity and CD4+ T cell counts in HIV-infected patients treated with HAART.

The prospective, open-label study, enrolled five HIV-infected men with a mean age of 52 years and CD4+ T cell count of 419 cells/mm3. All of the enrolled patients had been on stable ART for 18 months or more prior to enrollment in the study.

The patients were treated with growth hormone for six to 12 months and outcomes were compared to six closely matched patients drawn from a historical control.

The investigators found that growth hormone treatment was associated with a marked increase in thymic mass in all patients. This increase was evident by three months after growth hormone initiation and remained increased through the completion of therapy.

An analysis performed at six months of treatment showed a significant increase in thymic density and a mean increase in thymic volume of 88%. No similar changes were seen in the thymus of the control subjects. In addition to increases in thymic mass, naïve CD4+ T cells also increased significantly in all patients during growth hormone therapy. Relative to baseline levels, the mean absolute gain in naive CD4+ cell percentage was 6% at six months, 10% at nine months, and 12% at 12 months of treatment.

The authors conclude, “At present, we believe that HIV-1-infected patients on effective ART, with radiological evidence of thymic atrophy, and with a low CD4 cell count have the greatest chance of deriving immunological benefit from [growth hormone]-mediated enhancement of thymopoiesis. In particular, individuals on effective ART who have not experienced a gain in CD4 T cells despite prolonged virological suppression may especially benefit from [growth hormone] therapy.

“However, it is possible that such intervention may be ineffective if thymic or bone marrow reserves cannot be restored because of irreversible destruction caused by HIV-1 or advanced age.”