Adolescents infected with the virus that causes AIDS have a surprisingly robust immune response and may benefit particularly well from aggressive early treatment with anti-HIV medications, according to a research team led by an immunologist at The Children's Hospital of Philadelphia. The study is reported in the April issue of the Archives of Pediatric and Adolescent Medicine.
Studying 270 HIV-infected and uninfected teenagers, the researchers measured the levels of T lymphocytes, cells that originate in the thymus gland and play important roles in the immune system. Among those cells, they found an unexpectedly higher number of CD8 naïve T lymphocytes in adolescents who had been infected with HIV, compared to uninfected adolescents. Naïve T lymphocytes are cells that have not been previously exposed to invading microorganisms, including HIV. "The high levels of naïve CD8 cells that we found suggests that these cells may be capable of mounting an immune response," said the study's lead author, Steven D. Douglas, M.D., Chief of Immunology at Children's Hospital, who added, "CD8 cells are major players in killing the virus."
The naïve T lymphocytes are produced by the thymus gland, which gradually shrinks after puberty, becoming less active in immune function during adulthood. "If the thymus continues to produce immune system cells in HIV-infected adolescents, the adolescent immune system may be stronger than previously thought," said Dr. Douglas. "With aggressive use of current medications, we may be able to rebuild immune systems in HIV-infected adolescents."
Adolescents represent the fastest growing segment of the U.S. population newly infected with HIV; a 1996 White House report estimated that a new infection occurs every hour of every day. However, because of the long incubation period before symptoms appear, relatively small numbers of HIV-infected teenagers are aware of their infection and receiving medical care for it. Another complicating factor is the social situation of many infected adolescents, which may leave them with inadequate access to the health care system.
"Although HIV infection has been moving into adolescents, relatively little is known about the specifics of how adolescents' immune system respond to the virus," says Bret Rudy, M.D., medical director of the Adolescent AIDS Initiative at Children's Hospital, and a co-author of the study. The current study builds on earlier work by Drs. Douglas and Rudy, who recently published the first reference measurements for cells that act as immune system markers for both HIV-infected and healthy adolescents.
The current standard of treatment for controlling HIV infection is called highly active antiretroviral therapy (HAART), a combination of drugs that interfere with the virus' ability to replicate. "Because of their robust immune systems, HIV-infected adolescents may be the best candidates to benefit from aggressive drugs such as HAART," says Dr. Rudy. "However, it's imperative for individuals to become aware of their infections before they actually become sick, because early treatment may give their immune systems the best opportunity for a strong response." Dr. Rudy is co-chair of Project ACCESS, a social marketing campaign aimed at educating at-risk youth about the importance of HIV counseling and testing.
The current study was co-sponsored by the National Institute of Child Health and Human Development, the National Institute of Allergy and Infectious Diseases, the National Institute of Drug Abuse, the National Institute of Mental Health, and the Health Resources and Services Administration. Blood samples were drawn from adolescents at 16 clinical sites throughout the United States participating in the Adolescent Medicine HIV/AIDS Research Network, established by the National Institutes of Health and the Health Resources and Services Administration. Further studies will be conducted on how the immune system of adolescents responds to HIV infection over a period of time.
The Children's Hospital of Philadelphia, the nation's first children's hospital, is a leader in patient care, education and research. This 373-bed multispecialty hospital provides comprehensive pediatric services, including home care, to children from before birth through age 19. The hospital is second in the United States among all children's hospitals in total research funding from the National Institutes of Health.