Investigational Tat Vaccine Improves Response to HIV Drugs

Treatment reduces “viral reservoir”

A phase 2 clinical trial conducted in South Africa has confirmed that the therapeutic Tat vaccine against human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) can improve the response to antiretroviral drugs in HIV patients. The vaccine was developed in Italy by the National AIDS Center.

The study, conducted at the Clinical Research Unit of Sefako Makgatho University, enrolled 200 subjects receiving antiretroviral treatment who had undetectable levels of HIV in their blood. The subjects were randomly assigned to receive three intradermal injections of 30 mcg of the vaccine or placebo one month apart.

After 48 weeks, the vaccinated subjects showed significant increases in CD4+ T cells compared with the placebo group. This gain was particularly significant in participants with low CD4+ T cells at study entry. CD4+ T cells are pivotal players in the immune response against pathogens but are progressively lost during HIV infection, a condition that leads to AIDS. Although antiretroviral treatment is effective at suppressing virus replication, levels of CD4+ T cells can remain low, particularly in patients starting treatment late, the researchers noted.

The Tat vaccine acts by inducing protective antibodies capable of neutralizing the HIV Tat protein from various viral subtypes, including the A, B, and C clades circulating in America, Asia, and Africa.

The vaccine’s inventor, Dr. B. Ensoli, explained: “The vaccine was developed to target the HIV protein Tat, which is produced very early in the infection. Tat has a key role in viral replication and progression of the disease by weakening the immune system. By designing a vaccine that included a small amount of the Tat protein, we were able to induce an immune response capable of improving the effects of HIV drugs.”

The study, published in Retrovirology, confirmed the results of a previous phase 2 trial of the Tat vaccine in 155 Italian patients treated with antiretroviral agents. That study also demonstrated the induction of antibodies against Tat and the restoration of CD4+ T cells. Three years after vaccination, the Italian trial also showed a significant reduction in the “virus reservoir” in the subjects’ blood. This reservoir is resistant to antiretroviral drugs and is responsible for virus rebound after the interruption of therapy.

A follow-up study is ongoing in South Africa to confirm the reduced HIV reservoir observed in the Italian trial.

The Italian and South African co-investigators expect to advance to phase 3 studies with financial support from international organizations.

Source: PR Newswire; June 8, 2016.