Discussion
dengue, erythema, swelling
DENGUE, DISEASE, ERYTHEMA
The distinctive feature of PepGNP-Dengue lies in its design–a synthetic peptide nanoparticle-based vaccine–which aims to specifically elicit, or boost, a CD8+ T cell response, in order to provide protection without the need of vaccine-induced antibodies.In general, the two formulations (LD and HD) of PepGNP-Dengue appeared to be safe and well tolerated. No vaccine-related SAEs were reported, and the majority of AEs were mild. Interestingly, AEs were more frequently observed after the first injection than after the second. Frequent local reactogenicity (erythema and/or swelling) was noted, in line with previous reports of intradermal dengue vaccine administration.As expected, PepGNP-Dengue did not induce significant humoral responses against the four DENV serotypes, a result that supports the further development of the present platform for vaccines to avoid/prevent antibody-dependent disease enhancement. Nevertheless, PepGNP-Dengue induced modulation of IgG levels with a vaccine dose-dependent profile. Two types of humoral response were observed: a polyclonal non-specific (bystander) antibody response, particularly in the LD group with an increase in anti-TT IgG, and an antibody response which may result from previous flavivirus exposure or TBE vaccination (and therefore potentially cross-reactive in the anti-dengue IgG ELISA). Indeed, the three participants positive at baseline for DENV IgG by ELISA (all in the vehicle-GNP group) received TBE vaccination one or two years prior. In the absence of previous TBE vaccination, one LD PepGNP-Dengue participant developed anti-DENV IgG, but the baseline level was in the upper level of the normal range, which may suggest prior exposure to flavivirus antigens. The observed seroconversion at day 21 may also be explained by a general increase in IgG (of anti-DENV 1-4, NS1 1-4, TBE, and to a lesser extent of TT IgG), but we cannot exclude a positive humoral response to PepGNP-Dengue as a booster.As expected, the vaccine candidate elicited dengue-specific cellular immunity, with vaccine peptide-specific CD8+ T cell responses detected in AIM and dextramer analyses. Overall, 67% and 10% of participants in the LD and HD groups respectively, presented positive AIM+CD8+ T-cell at any timepoint. This indicates that the vaccine is able to induce CD8+ T cells with cytolytic activity. Altogether, 38% of participants in the LD group and 13% in the HD group showed at least one positive dextramer response at any timepoint. An absence of statistically significant intra- and inter-group differences in AIM and dextramer analyses except for CD137+CD69+CD8+ at day 90 in the LD group indicates that PepGNP-Dengue induced low-intensity CD8+ T cell responses or involved low percentages of responders at each timepoint. Responder analyses indicated a different time course for markers of activation as compared to peak CD8+ T cell dextramer recognition, and for peak response in the LD and HD PepGNP-Dengue groups, although participant numbers involved were small.Analysis of D-dext+CD8+ memory T cell subsets showed a significant vaccine-induced increase in the total memory population measurable in peripheral blood, specifically Tcm and TemRA subsets, at day 35. Demonstrating the presence of vaccine-specific memory T cells in trial participants is important, for this is crucial for protection against full-blown disease following (re)encounter with DENV. The specific memory cell subsets induced are of relevance, for Tcm cells can provide long-term, self-renewing, immunological memory, and virus-specific CD8+ TemRA cells were associated with protective immunity against viral challenge in the context of vaccination with a live attenuated tetravalent DENV vaccine.