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Despite viral vectors being potent inducers of antigen-specific T cells, strategies to further improve their immunogenicity are actively pursued. Of the numerous approaches investigated, fusion of the encoded antigen to major histocompatibility complex class II-associated invariant chain (Ii) has been reported to enhance CD8+ T-cell responses. We have previously shown that adenovirus vaccine encoding nonstructural (NS) hepatitis C virus (HCV) proteins induces potent T-cell responses in humans. However, even higher T-cell responses might be required to achieve efficacy against different HCV genotypes or therapeutic effect in chronically infected HCV patients. In this study, we assessed fusion of the HCV NS antigen to murine and human Ii expressed by the chimpanzee adenovirus vector ChAd3 or recombinant modified vaccinia Ankara in mice and nonhuman primates (NHPs). A dramatic increase was observed in outbred mice in which vaccination with ChAd3 expressing the fusion antigen resulted in a 10-fold increase in interferon-γ+ CD8+ T cells. In NHPs, CD8+ T-cell responses were enhanced and accelerated with vectors encoding the Ii-fused antigen. These data show for the first time that the enhancement induced by vector vaccines encoding li-fused antigen was not species specific and can be translated from mice to NHPs, opening the way for testing in humans. [ABSTRACT FROM AUTHOR]

Efficacy trials of antibody-inducing protein-in-adjuvant vaccines targeting the blood-stage Plasmodium falciparum malaria parasite have so far shown disappointing results. The induction of cell-mediated responses in conjunction with antibody responses is thought to be one alternative strategy that could achieve protective efficacy in humans. Here, we prepared chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) replication-deficient vectors encoding the well-studied P. falciparum blood-stage malaria antigen merozoite surface protein 1 (MSP1). A phase Ia clinical trial was conducted in healthy adults of a ChAd63-MVA MSP1 heterologous prime-boost immunization regime. The vaccine was safe and generally well tolerated. Fewer systemic adverse events (AEs) were observed following ChAd63 MSP1 than MVA MSP1 administration. Exceptionally strong T-cell responses were induced, and these displayed a mixed of CD4+ and CD8+ phenotype. Substantial MSP1-specific serum immunoglobulin G (IgG) antibody responses were also induced, which were capable of recognizing native parasite antigen, but these did not reach titers sufficient to neutralize P. falciparum parasites in vitro. This viral vectored vaccine regime is thus a leading approach for the induction of strong cellular and humoral immunogenicity against difficult disease targets in humans. Further studies are required to assess whether this strategy can achieve protective efficacy against blood-stage malaria infection. [ABSTRACT FROM AUTHOR]

The tetracycline (Tc)-dependent system in its “on” version (rtTA system) displays a baseline activity in the uninduced state, severely limiting its potential applicability in human gene therapy. So far, two different strategies to circumvent this limitation have been described. On one side, co-expression of the tetracycline regulated repressor tTSkid has proved capable of substantially reducing the baseline activity of rtTA. On the other, novel versions of the activator, namely rtTA2s-S2 and rtTA2s-M2, with a lower basal activity have been engineered. We have combined these two approaches by co-expressing TSkid with the novel transactivators. Bicistronic vectors were constructed that co-express TSkid with rtTA, rtTA2s-S2, or rtTA2s M2, through an internal ribosome entry site (plasmids IRES-A, IRES-S2, and IRES-M2, respectively). IRES-M2 proved to be the most effective construct ex vivo: it displayed a negligible basal activity, > 1000 fold inducibility, and high responsiveness to doxycycline (Dox). Upon delivery as plasmid DNA in mouse muscles, IRES-M2 facilitated 1000-fold induction of serum alkaline phosphatase (SEAP) gene expression and long-term, stringent, and strictly Dox-dose-dependent regulation of erythropoietin (Epo) gene expression. Tight regulation of the gene encoding SEAP was demonstrated also in non-human primates. Notably, the system was induced in animals by Dox-dosing regimens comparable to those used in humans. [Copyright &y& Elsevier]