A new study offers hope that an HIV-ravaged immune system can rebuild itself after successful treatment with anti-HIV drugs. Researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID) have found that the thymus gland, which produces the immune system's T cells, appears to remain functional well into adulthood rather than just during infancy and early childhood, as current theory holds. They also found evidence that although HIV infection may adversely affect the thymus, the gland continues to produce new T cells after the infection is suppressed by intensive anti-HIV therapy. A report of their findings is published in the Dec. 17, 1998, issue of Nature.
"This is a very promising finding because it confirms that the thymus is active in adults and potentially can partially reconstitute an HIV-infected individual's T cells after his or her viral load has been driven down by highly active antiretroviral therapy (HAART)," says NIAID Director Anthony S. Fauci, M.D. "Moreover, the technique developed to track newly produced T cells could prove to be a valuable research tool for monitoring immune reconstitution in HIV-infected people."
A research team led by Richard A. Koup, M.D., and Daniel C. Douek, M.D., Ph.D., of the University of Texas Southwestern Medical Center in Dallas, measured a genetic byproduct of T-cell development in blood samples from 10 HIV-infected and 30 uninfected individuals. Before they are released from the thymus, T cells generate circular fragments of DNA, dubbed T-cell receptor rearrangement excision circles, or TRECs. Previous studies showed that TRECS are stable and are not reproduced during subsequent cycles of cell division. Drs. Koup, Douek and their colleagues hypothesized that the presence of TRECS would identify T cells that had recently left the thymus and thus serve as a marker of thymic output.
Using sensitive DNA tests, the scientists showed that TRECs are present in naïve
Contact: John Bowersox
NIH/National Institute of Allergy and Infectious Diseases