AIDS Pioneer Robert C. Gallo Advocates for Inclusion of Inactivated Tat Toxoid in HIV Vaccines

Strategic Insights -

AIDS vaccines could include inactivated Tat toxoid, an antigen capable of inducing antibodies against the HIV Tat protein, according to Robert C. Gallo, a pioneer in AIDS research. Preliminary results from studies at Gallo's Institute of Human Virology indicate that the chemically detoxified toxin is safe and immunogenic in healthy human volunteers. The immunogen could be used both to treat and to prevent HIV infection, Gallo suggested. A composite vaccine that includes a "detoxified" Tat will be an important component of a prophylactic or therapeutic vaccine, coupled with a vector delivery of HIV-1 structural proteins, which will trigger long-lasting Tat antibodies.

Key Takeaways:

  • The inactivated Tat toxoid is a promising antigen capable of inducing antibodies against the HIV Tat protein, which could be used in HIV vaccines.
  • Preliminary results from studies at Gallo's Institute of Human Virology show that the chemically detoxified toxin is safe and immunogenic in healthy human volunteers.
  • A composite vaccine that includes a "detoxified" Tat will trigger long-lasting Tat antibodies, which may facilitate control of Tat-induced immune suppression and allow development of cell-mediated immunity to HIV-1 structural antigens.
  • The Tat protein is a small nuclear protein (14 kDa) but is copiously released from infected cells, making it a potential culprit in immune suppression.
  • Extracellular Tat induces macrophage production of interferon alpha (INF-alpha), which occurs in high levels in people with AIDS and exerts immunosuppressive effects.
  • Tat also inhibits T-cell proliferation and promotes apoptosis, but antibodies to both Tat and INF-alpha can restore T-cell function.
  • Natural-killer-cell (NK) function is inhibited by Tat, and recent studies suggest that rapid progression to AIDS is associated with few Tat-specific cytotoxic lymphocytes (CTLs).

Statistics:

  • Tat toxoid induces anti-Tat antibodies at titers ranging from 1:16,000 to 1:64,000 and lasting for more than a year after a single inoculation.
  • Human studies show that Tat toxoid is safe and immunogenic in healthy human volunteers.
  • The Tat protein is 14 kDa in size.

Sources:

  • "Tat as One Key to HIV-Induced Immune Pathogenesis and Tat Toxoid as an Important Component of a Vaccine" published in the Proceedings of the National Academy of Sciences (PNAS, 1999;96:8324-6).