IS-Therapeutics — Characterization of the targets of the immunosuppressive domain of retroviral envelope proteins: receptor and signaling pathways / new therapeutic approaches

The Research Unit UMR8122 led by the Project Coordinator has identified within the envelope protein of oncoretroviruses a domain endowed in vivo with immunosuppressive activity (IS domain). The IS domain has been mapped and mutations that inactivate its immunosuppressive functions while preserving the “mechanical” properties of the envelope protein have been discovered. Introduction of these mutations into a model mouse leukemia retrovirus (Friend virus) enabled us to demonstrate that the IS domain is absolutely required for induction of a persistent viremia in vivo: whereas immunodeficient mice are infected to the same level by both the mutant and wild-type virus, only the wild-type virus can induce viremia in immunocompetent mice. Moreover, we have shown that envelope proteins whose IS domain has been inactivated by mutation are powerful immunogens, with immunogenicity levels 10 to 100-fold higher than those of the wild-type protein, leading to the design of performing vaccine approaches, notably the implementation of an “optimized” veterinary vaccine against the feline leukemia virus FeLV (marketed in mid-2012, under a license granted to Mérial by Viroxis), and the elaboration of prototype prophylactic vaccines against the feline and human immunodeficiency retroviruses (FIV and HIV) that have previously been allocated funding by an ANR-RPIB grant (LENTIxIS, ending September 2014) and presently undergoing preclinical trials and on their way for further developments. The purpose of the present project –at variance with the previous one of a preventive nature (prophylactic vaccines)- is now to design an approach of a therapeutic nature (“medication” molecules) against retroviruses, based on the same theoretical substratum. The basic research studies conducted by UMR8122 having indeed demonstrated that a retrovirus whose IS domain has been inactivated can ultimately be cleared by the host immune system, we are planning to develop molecules capable of neutralizing the effects of this domain, through the screening of chemical libraries carried out in vitro to identify “hit” molecules able to block either the binding of the IS domain to its receptor or the downstream transduction pathways. The proposed work project draws on both the expertise of UMR8122 in the fields of the molecular and cellular biology of the IS domain and the skills of Viroxis to bring to completion high-throughput screenings of chemical libraries, as well as in vivo assays on animal models (mouse and monkey). A fruitful interaction has already taken place previously between these two organizations that led to the filing of patent applications in common and to successful developments ending in the marketing of a vaccine (see above). A first step will consist in identifying IS domain interactants, and this through different approaches, on the one hand, “proteomic” ones involving covalent labeling of molecules targeted by the IS domain, itself “labeled” with photoactivatable amino acids, and their identification by mass spectrometry after purification, and on the other end, “molecular genetic” approaches bringing into play expression libraries and their screening. Among the latter, a double hybrid screen conducted by the company Hybrigenics has already provided candidate genes, whose products are presently being assayed in vitro for direct binding to a labeled IS domain (e.g. co-immunoprecipitation, biacore) and which can already be regarded as basic components for the screening of chemical libraries. Screening of lentiviral expression libraries followed by iterative selection rounds using cell sorting and reseeding in culture will also be carried out. The screening of chemical libraries will be performed in collaboration with labs from the Labex LERMIT, of which UMR8122 is one of the founding teams.