The repeated failures of previous clinical HIV-1 vaccine candidates and the moderate efficacy of the RV144 vaccine (31% at 42 months) have emphasized the need of new vectors inducing new immune functions and the setup of vaccine regimens combining several pre-existing immunogens/vaccine strategies. Measles virus (MV) vector priming combined with protein boosts could fulfill these conditions. In fact, in an initial study we demonstrated that vaccination with MV vectors expressing Gag, Env and Nef simian-human immunodeficiency virus immunogens (MV-SHIV) controlled the SHIVSF162p3 challenge virus in cynomolgus macaques. Indeed, the peak viral load median of the vaccinated monkeys was nearly 2 logs lower compared to the placebo group, and plasma virus load was strongly reduced within a week (p=0.0001, Wilcoxon test). Moreover in contrast to the control monkeys, the vaccinated monkeys maintained plasma CD4+ T-cell counts >1000 cells/µl following challenges. Consequently, the MV-SHIV vaccine markedly reduced the reservoir size in PBMCs, spleen, axillary and inguinal lymph nodes and rectum, as evidenced by 50% of the animals exhibiting = 10 proviral DNA copies per million of cells. Interestingly, the control of SHIV162p3 found in the vaccinated monkeys was correlated with the Gag-specific cellular immune responses. However MV-SHIV vaccine alone was not able to delay SHIV acquisition after repeated intrarectal challenges, which is crucial for a HIV-vaccine to prevent virus integration. This could be attributed to the lack of induction of plasma neutralizing IgG (against tier-2 SHIV162p3) and mucosal IgA (in rectal secretions), which are known to be associated in vivo with a sterilizing protection against SHIV and SIV challenges, or at least with a delay of acquisition. Thus, we propose in this study to combine the MV-SHIV vaccine with protein boosts of the external region of the HIV gp41 envelope subunit. That gp41 polypeptide will include 3 highly conserved functional domains: the immunosuppressive domain ISD (the target of IgA antibodies in “Exposed Uninfected” patients), the “3S-motif” (anti-3S antibodies inhibit NK activity and cytotoxicity) and the membrane-proximal external region MPER (recognized by neutralizing and anti-HIV transcytosis antibodies in macaques challenged by the SHIVSF162p3). Chemically synthesized gp41 polypeptide in the presence of PLGA-based nanoparticles and TLR4 and TLR7/8 agonists adjuvants, or recombinant gp41 expressed by measles virus vector will be first assessed in mice to define the protein-boost regimen yielding the highest levels of circulating and mucosal antibodies. Then, cynomolgus macaques will be primed with the previously assessed MV-SHIV vaccine and boosted with the best protein-boost regimen before intravaginal challenges with the SHIVSF162p3 strain. We aim to provide the proof of concept of the protective efficacy for this new vaccine regimen/combination in the perspective of a first-in-man Phase I clinical trial. The final objectives of this project are the evaluation in patients of this vaccine candidate as a prophylactic and therapeutic vaccine.

Flaviviruses, which are principally transmitted by mosquitoes and ticks, cause devastating human diseases such as Dengue fever in the tropics and subtropics and are a constant source of emerging pathogens of pandemic potential (such as ZIKA and Usutu viruses). Relative to the gravity of flaviviral infections and the recognized threat of future outbreaks, current understanding of flaviviral pathogenesis – and more particularly as regards tick-borne flaviviruses – is disproportionately underdeveloped. Like all viruses, flaviviruses are obligate intracellular life forms whose survival requires subversion of metabolic circuits and evasion of anti-viral pathways. Within the cell, these pathways are embedded in extensive protein-protein interaction (PPI) networks, and their misappropriation by viruses is largely mediated by binary interactions between dedicated viral proteins and critical network proteins. Indeed, the targeted host proteins tend to be highly connected, such that the functional impact of a single interaction may be transmitted well beyond its immediate neighbourhood. Virus-host PPI thus represent molecular determinants of critical pathobiologic traits of flaviviruses, including host-range, zoonotic potential and virulence. Such interactions represent realistic targets for anti-viral therapies, thus providing a compelling reason to resolve the complete set of virus-cell interactions at the molecular level. Comparative analysis of PPI established by different viruses is emerging as a means of discerning those responsible for particular pathobiological traits. We have recently performed a high throughput screen for protein-protein interactions involving the entire set of open reading frames for two tick-borne flaviviruses of concern to human and veterinary health —the tick-borne encephalitis and louping ill viruses (TBEV and LIV), respectively — and cDNA libraries of human and ruminant hosts. We have established a large data set of shared and virus-specific PPI, most of which have never been documented in the literature. In the course of the hIPsTER project, state-of-the-art wet lab and in silico approaches will be applied to elucidate the biological meaning of these virus-host PPIs in flaviviral pathogenesis. In particular, we intend to define the functional significance of these PPI in viral infection as enhancing or restricting factors using an RNA interference (RNAi) approach. We will then determine their role in susceptibility or resistance of neural cells to infection and in neuropathogenesis in a recently developed pathological model of TBEV infection (co-cultures of human neuronal/glial cells derived from fetal neural progenitors) that reproduces major hallmarks of natural infection, such as high neuronal tropism and neuronal death. For selected PPI, we will investigate the mechanisms by which they disarm critical anti-viral defense pathways, and more particularly the type 1 interferon system, whose suppression is a virtual sine qua non for successful viral infection. We will explore the impact of the PPIs on the most salient biological processes of the human PIN through in silico analyses using Graph theory, and finally, perturbation of the vicinal protein-protein interaction network by viral proteins will be directly addressed in wet lab experiments using affinity purification coupled with mass spectrometry. For the latter, targeted cellular proteins will be selected on the basis of both viral and topological criteria; that is, viral-specificity and/or high degree of network connectivity. We expect this work to illuminate the strategies by which tick-borne flaviviruses control cellular processes and cause disease, and ultimately disclose viral vulnerabilities that can be exploited therapeutically. Beyond its ramifications for tick-borne flaviviruses, we expect hIPsTER to serve as a new paradigm for network-oriented analyses of viral pathobiology.