Immunization with HIV-1 Gag Protein Conjugated to a TLR7/8 Agonist Results in the Generation of HIV-1 Gag-Specific Th1 and CD8+ T Cell Responses

Abstract

One strategy to induce optimal cellular and humoral immune responses following immunization is to use vaccines or adjuvants that target dendritic cells and B cells. Activation of both cell types can be achieved using specific TLR ligands or agonists directed against their cognate receptor. In this study, we compared the ability of the TLR7/8 agonist R-848, which signals only via TLR7 in mice, with CpG oligodeoxynucleotides for their capacity to induce HIV-1 Gag-specific T cell and Ab responses when used as vaccine adjuvants with HIV-1 Gag protein in mice. Injection of R-848 and CpG oligodeoxynucleotides alone enhanced the innate immune responses in vivo as demonstrated by high serum levels of inflammatory cytokines, including IL-12p70 and IFN-α, and increased expression of CD80, CD86, and CD40 on CD11c+ dendritic cells. By contrast, R-848 was a relatively poor adjuvant for inducing primary Th1 or CD8+ T cell responses when administered with HIV-1 Gag protein. However, when a TLR7/8 agonist structurally and functionally similar to R-848 was conjugated to HIV-1 Gag protein both Th1 and CD8+ T cells responses were elicited as determined by intracellular cytokine and tetramer staining. Moreover, within the population of HIV-1 Gag-specific CD8+ CD62low cells, ∼50% of cells expressed CD127, a marker shown to correlate with the capacity to develop into long-term memory cells. Overall, these data provide evidence that TLR7/8 agonists can be effective vaccine adjuvants for eliciting strong primary immune responses with a viral protein in vivo, provided vaccine delivery is optimized.

The dominant role of CD8+dendritic cells in cross-presentation is not dictated by antigen capture

“…It has been shown that targeting exogenous antigens to immature DC can induce tolerance, whereas if the antigen is inoculated together with an activatory stimulus the targeted DC induce immunity (15,16). These observations encourage a thorough investigation of efficient methods for delivery of antigens for cross-presentation in vivo (17)(18)(19). However, until now it has been unclear whether all DC are equipped with the capacity to cross-present and whether the form of antigen can influence this ability (6).…”

“…These conclusions contribute to a better understanding of the unique roles played by different DC populations and for the design of antigen-targeting strategies for the induction of tolerogenic or immunogenic reactions in vivo. Our results predict that antigens taken by CD8 Ϫ DC will not be efficiently cross-presented, so vaccination strategies based on antibody-mediated antigen targeting to induce cross-priming (15)(16)(17)(18)(19) should be designed to target specifically the CD8 ϩ DC subset. Naturally, our results do not discard that other DC populations not analyzed in this study, such as the ''tissuederived DC'' (5) found in lymph nodes, may also be endowed with cross-presentation machinery.…”

“…This finding suggested that CD8 ϩ DC possess specialized machinery for cross-presentation that is expressed poorly, if at all, by other DC subsets. We therefore hypothesized that the role of different DC subsets in crosspresentation is determined by their antigen-handling properties.Understanding whether the capacity to cross-present is dictated by antigen capture or handling is important for the design of vaccination strategies based on antigen targeting in vivo (15)(16)(17)(18)(19). For instance, if all of the DC subsets can cross-present, a vaccine antigen targeted to a receptor shared by all subsets might be cross-presented by all DC.…”

The Use of TLR7 and TLR8 Ligands for the Enhancement of Cancer Immunotherapy

“…Others also showed that CpG induced higher levels of T-cell responses than imiquimod or resiquimod [135,145]. Two methods are known to further enhance the adjuvant power of TLR7/8 agonists: (a) conjugation of the TLR7/8 agonist to the antigen [135] and (b) combination of TLR7/8 agonists with other factors.…”

Development of Vaccine Adjuvants: A Historical Perspective

“…One such product, Imiquimod, has been licensed for topical treatment of herpes simplex [162], but use of imidazoquinoline derivatives as adjuvants remains at preclinical stages. As for the ISS system, antigen conjugates of R848 (another imidazoquinoline derivative) are reported to offer greater activity than that of the soluble mixtures [163]. A number of other TLR7 and TLR8 agonists are under development.…”