S100B and HIV infectious disease: In contrast, the phase IIB study of the replication-defective Merck rAd5-vectored vaccine (Merck 023/HVTN 502; the STEP Study) composed of clade B Gag, Nef and Pol (without Env) and given at 0, 1 and 6 months to high-risk men who have sex with men and women was stopped prematurely when a pre-defined futility criteria was met and there was no evidence that the vaccine provided protection against HIV infection or reduced viral load among infected participants, despite frequent and strong CD8+ T-cell responses to vaccine specific antigens [13].