Failure of STEP leads TAG to criticise the proposed PAVE100A vaccine trial

Simon Collins, HIV i-Base

The failure of STEP trial, using Merck’s adenovirus serotype 5 (Ad5)-based HIV vaccine, has implications for using another Ad5 candidate in the proposed PAVE100A Phase IIb efficacy trial.

The STEP trial neither reduced infection or post-infection viral load, and potentially increased infection rates among a subset of trial participants.

Treatment Action Group (TAG), a influential community-based policy think-tank published a Position Statement that raises serious concerns about continuing with the PAVE100A trial.

This includes an analysis of the scientific likely hood that this new candidate will produce a different response, and questioning both the relevance and safety of such a restricted study population:the PAVE trial is limiting recruitment to circumcised gay men with no detectable antibody responses to Ad5.

TAG proposes abandoning plans for this particular clinical trial and Ad5 vaccine candidate in favour of supporting research to rapidly address two key issues:

  1. The use of an alternate vector or DNA approach for the boosting immunisation that could be studied in a broader population.
  2. Inducing broader responses to proteins contained in the vaccine, particularly HIV-1 Gag.

They argue against spending human and fiscal resources on PAVE100A, and instead suggest focusing on improving T cell based immunogens so they can be studied in a broader population with a greater chance of success.

Source: TAG Basic Science Blog (30 May 2008)

The full statement “TAG position statement on the proposed PAVE100A vaccine trial” is available online:

Links to other websites are current at date of posting but not maintained.