• Thymic Volume Is Independently Associated With the Magnitude of CD4+ T-Cell Recovery After Short and Long Term on HAART (Oral 16)
  Authored by E. Ruiz-Mateos, A. Vallejo, A. Rubio, N. Soriano, R. de la Rosa, S. Molina, A. Sánchez-Quijano, E. Lissen, M. Leal, Viral Hepatitis and AIDS Study Group
  

Dr. Ruiz-Mateos presented data from his study on the effects of HIV medications on thymus size. The thymus is an important organ (located in the chest) which is necessary for proper functioning of the immune system. New T cells are made in the bone marrow, but are immature or naive -- they can't recognize antigen or work effectively unless they have been processed by the thymus, which gives them the ability to work effectively. The thymus is quite active when we are young. However, as we get older, it gradually shrinks and is not as active anymore. Previous data has indicated that baseline thymic volume (size) is a good predictor of how good CD4 cell recovery would be after starting HIV therapy. In other words, the larger one's thymus, the better the CD4 increase after starting therapy.

The study involved 54 subjects who had two pretreatment visits, and who then were seen at four, 12, 48 and 96 weeks after starting HIV treatment. The researchers performed chest CT scans to measure thymus size. Baseline thymus volume was 3.4 cm³. Most of the subjects were male, and about 50 percent were co-infected with hepatitis C virus. The mean baseline CD4 count was 255 cells/mm³. They also measured total, naive and memory CD4 cells at each time point and conducted a variety of other sophisticated immunologic tests. After starting HIV therapy, the results of the study showed that only thymic volume was correlated with increases in CD4 count, and that the number of naive and memory CD4 cells were not independently associated with treatment response. This relationship continued out to two years of observation.

For many years we thought that the thymus was not active in adulthood and that with HIV infection there was no hope of having proper thymic activity to process T cells, particularly after starting HIV treatment. This now appears not to be the case. We have learned that the thymus continues to be active even into late adulthood and that HIV-infected patients with a relatively normal size thymus can have significant immune reconstitution. This means that not only can CD4 cells be regained with treatment but also that with good thymic function they can be activated to function relatively normally and to provide important immunologic protection. Thymic function and how to improve this function continues to be a hot topic for researchers.