STEP trial and HIV-1 vaccines inducing T-cell responses.

Recombinant, nonreplicating, human adenovirus serotype 5-vectored vaccine, known as MRKAd5, expressing three HIV-1 clade B-derived internal proteins when used in a homologous immunization regimen, did not decrease HIV-1 infection rate nor postinfection virus load in the first Phase IIb proof-of-concept trial. However, the vaccine did not reach the limits of vaccine T-cell induction and its design can be improved both from the point of the HIV-1-derived immunogens and their delivery. Therefore, failure of the first experimental HIV-1 vaccine focusing on induction of T-cell responses cannot be a reason for dismissal of the whole T-cell vaccine concept, nor for losing a positive attitude toward systematic HIV-1 vaccine development.