Improvement of therapeutic vaccine strategies in the perspective of HIV cure is warranted. The DALIA-1 phase I trial evaluated a new DC-based therapeutic vaccine that consisted in ex-vivo generated IFN-α DC loaded with LIPO-5 (HIV-1 Nef 66-97, Nef 116-145, Gag 17-35, Gag 253-284 and Pol 325-355 lipopeptides). Nineteen patients on c-ART (antiretroviral treatment) received four injections followed by a 24-week c-ART interruption (ATI). Four weeks after the last injection, an increase in breadth of immune responses was detected by IFN-γ ELISpot and Luminex assays (Y. Levy et al, EJI 2014). An inverse correlation was found between the frequency of polyfunctional CD4+ T cells detected by intracellular staining (ICS) assays after vaccination and the maximum viral load (VL) post-ATI. Here, we performed epitope mapping to dissect anti-HIV-1 responses and correlations between vaccine-induced responses and maximum VL post-ATI.
PBMC from 16 participants were incubated with 36 (15-mer) and 56 (9-mer) overlapping peptides encompassing the LIPO-5 sequences. Cytokine responses were detected using 48h Luminex and 7 day ICS assays. Comparison of responses with predicted peptide/MHC class I and class II binding affinities (NetMHCpan 3.0 and NetMHCpanII 3.1 servers) was performed.
IL-13 and IL-2 (15-mer Luminex) T-cell responses detected after four vaccinations and before ATI were inversely correlated with maximum VL post-ATI (Spearman r=-0.66; P=0.007 and r=-0.58; P=0.02, respectively for breadth; r=-0.71; P=0.003 and r=-0.66; P=0.007, respectively for magnitude). Sum of IL-13 and IL-2 responses directed to six 15-mer peptides (from Gag, Pol and Nef regions of LIPO-5) was strongly associated with lower maximum VL post-ATI (Spearman r=-0.71; P=0.003). Using ICS, IL-13 and IL-2 were detected in both CD4+ and CD8+ T cells after 9-mer and 15-mer peptide stimulations. Luminex and ICS functional assays allowed us to identify vaccine-elicited CD4+ T cell responses that were not predicted a priori by peptide binding prediction bio-informatic tools.
We showed that ex vivo DC vaccination, as a vehicle of HIV lipopeptide delivery, was broadly immunogenic and elicited responses against a set of epitopes from Gag, Pol and Nef. IL-2 and IL-13 functional responses were associated with a better control of VL post-ATI. Moreover, new HIV-1 CD4+ T-cell immunogenic epitopes, not predicted by peptide/MHC binding algorithms, were identified.