[An anti-Covid-19 lentiviral vaccine candidate that can be administered by the nasal route]

Mice humanized for MHC and hACE2 with high permissiveness to SARS-CoV-2 omicron replication

Human Angiotensin-Converting Enzyme 2 (hACE2) is the major receptor enabling host cell invasion by SARS-CoV-2 via interaction with Spike. The murine ACE2 does not interact efficiently with SARS-CoV-2 Spike and therefore the laboratory mouse strains are not permissive to SARS-CoV-2 replication. Here, we generated new hACE2 transgenic mice, which harbor the hACE2 gene under the human keratin 18 promoter, in "HHD-DR1" background. HHD-DR1 mice are fully devoid of murine Major Histocompatibility Complex (MHC) molecules of class-I and -II and express only MHC molecules from Human Leukocyte Antigen (HLA) HLA 02.01, DRA01.01, DRB1.01.01 alleles, widely expressed in human populations. We selected three transgenic strains, with various hACE2 mRNA expression levels and distinctive profiles of lung and/or brain permissiveness to SARS-CoV-2 replication. These new hACE2 transgenic strains display high permissiveness to the replication of SARS-CoV-2 Omicron sub-variants, while the previously available B6.K18-ACE22Prlmn/JAX mice have been reported to be poorly susceptible to infection with Omicron. As a first application, one of these MHC- and ACE2-humanized strains was successfully used to show the efficacy of a lentiviral-based COVID-19 vaccine.

A lentiviral vector expressing a dendritic cell-targeting multimer induces mucosal anti-mycobacterial CD4+ T-cell immunity

Most viral vectors, including the potently immunogenic lentiviral vectors (LVs), only poorly direct antigens to the MHC-II endosomal pathway and elicit CD4⁺ T cells. We developed a new generation of LVs encoding antigen-bearing monomers of collectins substituted at their C-terminal domain with the CD40 ligand ectodomain to target and activate antigen-presenting cells. Host cells transduced with such optimized LVs secreted soluble collectin-antigen polymers with the potential to be endocytosed in vivo and reach the MHC-II pathway. In the murine tuberculosis model, such LVs induced efficient MHC-II antigenic presentation and triggered both CD8⁺ and CD4⁺ T cells at the systemic and mucosal levels. They also conferred a significant booster effect, consistent with the importance of CD4⁺ T cells for protection against Mycobacterium tuberculosis. Given the pivotal role of CD4⁺ T cells in orchestrating innate and adaptive immunity, this strategy could have a broad range of applications in the vaccinology field.