Cell-Mediated Immune Predictors of Vaccine Effect on Viral Load and CD4 Count in a Phase 2 Therapeutic HIV-1 Vaccine Clinical Trial.

Background: In a placebo-controlled trial of the peptide-based therapeutic HIV-1 p24 vaccine candidate Vacc-4x, participants on combination antiretroviral therapy (cART) received six immunizations over 18weeks, followed by analytical treatment interruption (ATI) between weeks 28 and 52. Cell-mediated immune responses were investigated as predictors of Vacc-4x effect (VE) on viral load (VL) and CD4 count during ATI.

Methods: All analyses of week 28 responses and fold-changes relative to baseline considered per-protocol participants (Vacc-4x:placebo=72:32) resuming cART after week 40. Linear regression models with interaction tests were used. VE was estimated as the Vacc-4x-placebo difference in log-transformed VL (VE) or CD4 count (VE).

Findings: A lower fold-change of CD4+ T-cell proliferation was associated with VE at week 48 (p=0.036, multiplicity adjusted q=0.036) and week 52 (p=0.040, q=0.080). A higher fold-change of IFN-γ in proliferation supernatants was associated with VE at week 44 (p=0.047, q=0.07). A higher fold-change of TNF-α was associated with VE at week 44 (p=0.045, q=0.070), week 48 (p=0.028, q=0.070), and week 52 (p=0.037, q=0.074). A higher fold-change of IL-6 was associated with VE at week 48 (p=0.017, q=0.036). TNF-α levels (>median) were associated with VE at week 48 (p=0.009, q=0.009).

Interpretation: These exploratory analyses highlight the potential value of investigating biomarkers in T-cell proliferation supernatants for VE in clinical studies.