Brain and Lung Cross-Protection against Ancestral or Emerging SARS-CoV-2 by Intranasal Lentiviral Vaccination in a New hACE2 Transgenic Murine Model (preprint)

COVID-19 vaccines already in use or in clinical development may have safety concerns, limited immunogenicity in high-risk groups or reduced efficacy against emerging SARS-CoV-2 variants. In addition, although the neurotropism of SARS-CoV-2 is well established, the vaccine strategies currently developed have not taken into account the protection of the central nervous system. Here, we generated a transgenic mouse strain expressing the human Angiotensin Converting Enzyme 2, with unprecedented brain as well as lung permissibility to SARS-CoV-2 replication. Using this stringent transgenic model, we demonstrated that a non-integrative lentiviral vector, encoding for the spike glycoprotein of the ancestral Wuhan SARS-CoV-2, used in intramuscular prime and intranasal boost elicits sterilizing protection of lung and brain against both the Wuhan and the most genetically distant Manaus P.1 SARS-CoV-2 variants. Beyond the induction of strong neutralizing antibodies, the mechanism underlying this broad protection spectrum involves a robust protective spike-specific CD8+ T-cell immunity, unaffected by the recent mutations accumulated in the emerging SARS-CoV-2 variants.

Full Brain and Lung Prophylaxis against SARS-CoV-2 by Intranasal Lentiviral Vaccination in a New hACE2 Transgenic Mouse Model or Golden Hamsters (preprint)

Non-integrative, non-cytopathic and non-inflammatory lentivectors are particularly suitable for mucosal vaccination and recently emerge as a promising strategy to elicit sterilizing prophylaxis against SARS-CoV-2 in preclinical animal models. Here, we demonstrate that a single intranasal administration of a lentivector encoding a prefusion form of SARS-CoV-2 spike glycoprotein induces full protection of respiratory tracts and totally avoids pulmonary inflammation in the susceptible hamster model. More importantly, we generated a new transgenic mouse strain, expressing the human Angiotensin Converting Enzyme 2, with unprecedent brain permissibility to SARS-CoV-2 replication and developing a lethal disease in <4 days post infection. Even though the neurotropism of SARS-CoV-2 is now well established, so far other vaccine strategies under development have not taken into account the protection of central nervous system. Using our highly stringent transgenic model, we demonstrated that an intranasal booster immunization with the developed lentivector vaccine candidate achieves full protection of both respiratory tracts and central nervous system against SARS-CoV-2.

High seroprevalence but short-lived immune response to SARS-CoV-2 infection in Paris (preprint)

Background Although the COVID-19 pandemic peaked in March/April 2020 in France, the prevalence of infection is barely known. Herein, we assessed the serological response against the SARS-CoV-2 virus in a large population working in one institution of the Paris conurbation. We set up two high-throughput and sensitive methods to assess SARS CoV-2 Nucleoprotein and Spike protein-specific IgG response along with a pseudo-neutralization assay in sera. We studied 1847 participants who also answered a web-based survey on clinical symptoms. Methods and Results In May-July 2020, 11% (95% CI: 9.7-12.6) of serums were positive for IgG against the SARS-CoV-2 N and S protein and 9.5% (CI:8.2-11.0) were pseudo-neutralizer. The prevalence of immunization was 11.6% (CI:10.2-13.2) considering positivity in at least one assays. In 5% (CI:3.9-7.1) of RT-qPCR positive individuals, no systemic IgGs were detected. Among immune individuals, 21% had been asymptomatic. Anosmia and ageusia occurred in 52% of the IgG-positive individuals and in 3% of the negative ones. In contrast, 30% of the anosmia-ageusia cases were seronegative suggesting that the true prevalence of infection may reach 16.6%. In sera obtained 4-8 weeks after the first sampling anti-N and anti-S IgG titers and pseudo-neutralization activity declined by 31%, 17% and 53%, respectively with half-life of 35, 87 and 28 days, respectively. Conclusions The population studied being not particularly exposed to SARS-CoV-2 infection is representative of active workers in the Paris conurbation, suggesting that the current epidemiological models may underestimate the true prevalence of infection. The short lifespan of the serological systemic responses hinders retrospective assessment of the epidemic extent.

Intranasal Immunization with a Lentiviral Vector Coding for SARS-CoV-2 Spike Protein Confers Vigorous Protection in Pre-Clinical Animal Models (preprint)

We developed a potent vaccination strategy, based on lentiviral vector (LV), capable of inducing neutralizing antibodies specific to the Spike glycoprotein (S) of SARS-CoV-2, the etiologic agent of CoronaVirus Disease 2019 (COVID-19). Among several LV encoding distinct variants of S, a single one encoding the full-length, membrane anchored S (LV::SFL) triggered high antibody titers in mice, with neutralization activities comparable to patients recovered from COVID-19. LV::SFL systemic vaccination in mice, in which the expression of the CoV2 receptor hACE2 was induced by transduction of the respiratory tract cells by an adenoviral type 5 (Ad5) vector, despite an intense serum neutralizing activity, only {approx}1 log10 reduction of lung viral loads was observed after SARS-CoV2 challenge. We thus explored the strategy of targeting the immune response to the upper respiratory tract through an intranasal boost administration. Even though, after a prime and target regimen, the systemic neutralizing activity did not increase substantially, {approx}5 log10 decrease in lung viral loads was achieved, with the loads in some animals under the limit of detection of a highly sensitive RT-PCR assay. The conferred protection also avoided largely pulmonary inflammation. We confirmed the vaccine efficacy and inhibition of lung inflammation using both integrative and non-integrative LV platforms in golden hamsters, naturally permissive to SARS-CoV2 replication and restituting human COVID-19 physiopathology. Our results provide the proof-of-principle evidence of marked prophylactic effects of an LV-based vaccination strategy against SARS-CoV-2 in two pre-clinical animal models and designate the intranasal LV::SFL-based immunization as a vigorous and promising vaccine approach against COVID-19.