Abstract
VAC-3S is a therapeutic vaccine comprising a highly conserved HIV-gp41 motif coupled with the CRM197 carrier protein. High levels of anti-3S antibodies (Abs) have been associated with improved protection of CD4+ T-cell survival. A previous phase 1 study demonstrated the safety of VAC-3S. This multicentre, randomised, double-blind, placebo-controlled phase 2 clinical trial enroled between January 2014 and March 2015 HIV-1-infected patients under ART with plasma HIV RNA levels below 50 copies/mL and CD4 counts between 200 and 500 cells/μL. Participants were immunised with 16, 32, or 64 μg of VAC-3S, and compared to placebo. The primary outcome was immunogenicity assessed by changes from baseline of anti-3S Abs levels at week 12. Secondary outcomes included adverse events and the course of plasma HIV RNA level, CD4 count, CD4/CD8 ratio, inflammation and immune checkpoints from week 0 to week 48. Vaccination was well tolerated with no serious adverse events and induced a significant increase in anti-3S Ab response in vaccinated patients (p < 0.0001), compared to placebo. In high responders, the robust increased of CD4 count was associated with a significant and sustained reduction of PD-1 expression on CD4+ T cells through week 48 (variance p = 0.0017). PD-1 expression was correlated with level of anti-3S Abs (p = 0.0092, r = -0.68) and expression of NKp44L (p < 0.0001; r = 0.54) in CD4+ T cells. Our findings regarding the increase of non-exhausted CD4+ T cells have potentially important application in personalised HIV vaccination for HIV-infected patients with high level of PD-1 to improve their T-cell immune function.