Certain major histocompatibility complex class I (MHC-I) alleles (e.g., HLA-B*27) are enriched among human immunodeficiency virus type 1 (HIV-1)-infected individuals who suppress viremia without treatment (termed "elite controllers" [ECs]).Likewise, Mamu-B*08 expression also predisposes rhesus macaques to control simian immunodeficiency virus (SIV) replication. Given the similarities between Mamu-B*08 and HLA-B*27, SIV-infected Mamu-B*08؉ animals provide a model to investigate HLA-B*27-mediated elite control. We have recently shown that vaccination with three immunodominant Mamu-B*08-restricted epitopes (Vif RL8, Vif RL9, and Nef RL10) increased the incidence of elite control in Mamu-B*08 ؉ macaques after challenge with the pathogenic SIVmac239 clone. Furthermore, a correlate analysis revealed that CD8 ؉ T cells targeting Nef RL10 was correlated with improved outcome. Interestingly, this epitope is conserved between SIV and HIV-1 and exhibits a delayed and atypical escape pattern. These features led us to postulate that a monotypic vaccine-induced Nef RL10-specific CD8 ؉ T-cell response would facilitate the development of elite control in Mamu-B*08 ؉ animals following repeated intrarectal challenges with SIVmac239. To test this, we vaccinated Mamu-B*08؉ animals with nef inserts in which Nef RL10 was either left intact (group 1) or disrupted by mutations (group 2). Although monkeys in both groups mounted Nef-specific cellular responses, only those in group 1 developed Nef RL10-specific CD8 ؉ T cells. These vaccine-induced effector memory CD8 ؉ T cells did not prevent infection. Escape variants emerged rapidly in the group 1 vaccinees, and ultimately, the numbers of ECs were similar in groups 1 and 2. High-frequency vaccine-induced CD8 ؉ T cells focused on a single conserved epitope and therefore did not prevent infection or increase the incidence of elite control in Mamu-B*08 ؉ macaques. IMPORTANCESince elite control of chronic-phase viremia is a classic example of an effective immune response against HIV/SIV, elucidating the basis of this phenomenon may provide useful insights into how to elicit such responses by vaccination. We have previously established that vaccine-induced CD8 ؉ T-cell responses against three immunodominant epitopes can increase the incidence of elite control in SIV-infected Mamu-B*08؉ rhesus macaques-a model of HLA-B*27-mediated elite control. Here, we investigated whether a monotypic vaccine-induced CD8 ؉ T-cell response targeting the conserved "late-escaping" Nef RL10 epitope can increase the incidence of elite control in Mamu-B*08 ؉ monkeys. Surprisingly, vaccine-induced Nef RL10-specific CD8 ؉ T cells selected for variants within days after infection and, ultimately, did not facilitate the development of elite control. Elite control is, therefore, likely to involve CD8 ؉ T-cell responses against more than one epitope. Together, these results underscore the complexity and multidimensional nature of virologic control of lentivirus infection.

Effector memory T cell (T) responses display potent antiviral properties and have been linked to stringent control of simian immunodeficiency virus (SIV) replication. Since recurrent antigen stimulation drives the differentiation of CD8 T cells toward the T phenotype, in this study we incorporated a persistent herpesviral vector into a heterologous prime/boost/boost vaccine approach to maximize the induction of T responses. This new regimen resulted in CD8 T-biased responses in four rhesus macaques, three of which controlled viral replication to <1,000 viral RNA copies/ml of plasma for more than 6 months after infection with SIVmac239. Over the course of this study, we made a series of interesting observations in one of these successful controller animals. Indeed, in vivo elimination of CD8αβ T cells using a new CD8β-depleting antibody did not abrogate virologic control in this monkey. Only after its CD8α lymphocytes were depleted did SIV rebound, suggesting that CD8αα but not CD8αβ cells were controlling viral replication. By 2 weeks postinfection (PI), the only SIV sequences that could be detected in this animal harbored a small in-frame deletion in nef affecting six amino acids. Deep sequencing of the SIVmac239 challenge stock revealed no evidence of this polymorphism. However, sequencing of the rebound virus following CD8α depletion at week 38.4 PI again revealed only the six-amino acid deletion in nef. While any role for immunological pressure on the selection of this deleted variant remains uncertain, our data provide anecdotal evidence that control of SIV replication can be maintained without an intact CD8αβ T cell compartment.

The need for improved dengue vaccines remains since the only licensed vaccine, Dengvaxia, shows variable efficacy depending on the infecting dengue virus (DENV) type, and increases the risk of hospitalization for severe dengue in children not exposed to DENV before vaccination. Here, we developed a tetravalent dengue purified and inactivated vaccine (DPIV) candidate and characterized, in rhesus macaques, its immunogenicity and efficacy to control DENV infection by analyzing, after challenge, both viral replication and changes in biological markers associated with dengue in humans. Although DPIV elicited cross-type and long-lasting DENV-neutralizing antibody responses, it failed to control DENV infection. Increased levels of viremia/RNAemia (correlating with serum capacity at enhancing DENV infection in vitro ), AST, IL-10, IL-18 and IFN-γ, and decreased levels of IL-12 were detected in some vaccinated compared to non-vaccinated monkeys, indicating the vaccination may have triggered antibody-dependent enhancement of DENV infection. The dengue macaque model has been considered imperfect due to the lack of DENV-associated clinical signs. However, here we show that post-vaccination enhanced DENV infection can be detected in this model when integrating several parameters, including characterization of DENV-enhancing antibodies, viremia/RNAemia, and biomarkers relevant to dengue in humans. This improved dengue macaque model may be crucial for early assessment of efficacy and safety of future dengue vaccines.

The macaque is widely accepted as a suitable model for preclinical characterization of dengue vaccine candidates. However, the only vaccine for which both preclinical and clinical efficacy results were reported so far showed efficacy levels that were substantially different between macaques and humans. We hypothesized that this model’s predictive capacity may be improved using recent and minimally passaged dengue virus isolates, and by assessing vaccine efficacy by characterizing not only the post-dengue virus challenge viremia/RNAemia but also the associated-cytokine profile. Ten recent and minimally passaged Brazilian clinical isolates from the four dengue virus serotypes were tested for their infectivity in rhesus macaques. For the strains showing robust replication capacity, the associated-changes in soluble mediator levels, and the elicited dengue virus-neutralizing antibody responses, were also characterized. Three isolates from dengue virus serotypes 1, 2 and 4 induced viremia of high magnitude and longer duration relative to previously reported viremia kinetics in this model, and robust dengue virus-neutralizing antibody responses. Consistent with observations in humans, increased MCP-1, IFN-γ and VEGF-A levels, and transiently decreased IL-8 levels were detected after infection with the selected isolates. These results may contribute to establishing a dengue macaque model showing a higher predictability for vaccine efficacy in humans.