Dubious analysis of a therapeutic tat vaccine trial

Richard Jefferys, TAG

Toward the end of last year, a group of Italian researchers led by Barbara Ensoli published some limited data from an ongoing trial of a therapeutic HIV vaccine [1], and issued a press release to draw attention to the paper. [2]

The resulting press coverage was generally favorable. Somewhat lost in the discussion of the results was the fact that they were obtained in an “ad hoc exploratory interim analysis,” which is generally considered to be a dubious and unreliable way to analyse trial data. The vaccine candidate contains the Tat protein from HIV-1, and Ensoli’s group has been developing it for many years now. The question of whether the approach has any potential has been controversial [3]; a macaque study suggesting protection against SHIV was not confirmed [4] and there have also been reports of disputes about the vaccine’s development among the Italian research community. [5]

In light of this background, trumpeting the results of an ad hoc exploratory interim analysis via press release seems an imprudent strategy for the researchers to pursue.

The trial described in the paper is not placebo controlled, which adds to the challenge of trying to interpret the results. Because there is no control arm, comparisons in the paper are made between vaccine recipients and HIV positive individuals enrolled in “a parallel prospective observational study at the same sites.” Most of the immunological analyses reported in the paper involve small subsets of the 87 participants, but it is not clear how these subsets were selected. The primary aim of the trial is to compare the immunogenicity (ability to induce anti-Tat immune responses) of two different doses and two different dosing schedules of the vaccine. The secondary aim is monitor safety. The trial protocol, which is included in the supporting information for the paper, does not make reference to the conduct of ad hoc exploratory interim analyses or their publication.

Amidst this sea of caveats, the researchers report that the higher vaccine dose was more immunogenic but no significant differences were apparent between the 3-dose and 5-dose immunisation schedules. The vaccine was also found to be generally safe and well tolerated. From these top-line results, the paper descends into murky sub-analyses suggesting that the vaccine may have decreased CD8 T cell activation, both increased and decreased in CD4 T cell activation (depending on the marker), increased regulatory CD4 T cells, increased CD4 T cells and B cells, decreased CD8 T cells and natural killer cells, and altered representation of different memory T cell subsets. None of the reported analyses are statistically corrected for the multiple comparisons being performed.

Although the suggestion that therapeutic vaccination might reduce immune activation in HIV is not unprecedented, there is a discomforting gap between the murkiness of the methodology and the breezily conclusive title of the paper: “Therapeutic Immunisation with HIV-1 Tat Reduces Immune Activation and Loss of Regulatory T-Cells and Improves Immune Function in Subjects on HAART.” The only way to show whether the vaccine can achieve these outcomes is with a randomised placebo-controlled study. [6]

Source: TAG Basic Science Blog (24 Jan 2011).


  1. Barbara Ensoli et al. Therapeutic immunization with HIV-1 Tat reduces immune activation and loss of regulatory T-cells and improves immune function in subjects on HAART. PLoS ONE 5(11): e13540. doi:10.1371/journal.pone.00135.
  2. National AIDS Centre press release. HIV/AIDS: Interim analysis of phase II trial of TAT vaccine in HIV-infected patients. (11 Nov 2010).
  3. Aurelio Cafaro et. Al, Control of SHIV-89.6P-infection of cynomolgus monkeys by HIV-1 Tat protein vaccine Nature Medicine 5, 643 – 650 (1999) doi:10.1038/9488:
  4. Xiaoping Liang et al. Vectored Gag and Env but not Tat show efficacy against Simian-Human Immunodeficiency Virus 89.6P challenge in mamu-A*01-negative rhesus monkeys. J Virol. 2005 October; 79(19): 12321–12331. doi: 10.1128/JVI.79.19.12321-12331.2005.
  5. Jon Cohen. Feud over AIDS vaccine trials leads prominent Italian researchers to court. Science 10 August 2007: Vol. 317 no. 5839 pp. 738-739 DOI: 10.1126/science.317.5839.738
  6. Fernandez-Cruz E et al. 3-year evaluation of a therapeutic vaccine (HIV-1 Immunogen) administered with antiretrovirals versus antiretroviral therapy alone in patients with HIV chronic infection. Int Conf AIDS. 2002 Jul 7-12; 14: abstract no. ThOrA1482.

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