Abstract
Unraveling the long-term kinetics of antibodies to SARS-CoV-2 and the individual characteristics influencing it, including the impact of pre-existing antibodies to human coronaviruses ...causing common cold (HCoVs), is essential to understand protective immunity to COVID-19 and devise effective surveillance strategies. IgM, IgA and IgG levels against six SARS-CoV-2 antigens and the nucleocapsid antigen of the four HCoV (229E, NL63, OC43 and HKU1) were quantified by Luminex, and antibody neutralization capacity was assessed by flow cytometry, in a cohort of health care workers followed up to 7 months (
N
= 578). Seroprevalence increases over time from 13.5% (month 0) and 15.6% (month 1) to 16.4% (month 6). Levels of antibodies, including those with neutralizing capacity, are stable over time, except IgG to nucleocapsid antigen and IgM levels that wane. After the peak response, anti-spike antibody levels increase from ~150 days post-symptom onset in all individuals (73% for IgG), in the absence of any evidence of re-exposure. IgG and IgA to HCoV are significantly higher in asymptomatic than symptomatic seropositive individuals. Thus, pre-existing cross-reactive HCoVs antibodies could have a protective effect against SARS-CoV-2 infection and COVID-19 disease.
Neoantigens are patient- and tumor-specific peptides that arise from somatic mutations. They stand as promising targets for personalized therapeutic cancer vaccines. The identification process for ...neoantigens has evolved with the use of next-generation sequencing technologies and bioinformatic tools in tumor genomics. However, in-silico strategies for selecting immunogenic neoantigens still have very low accuracy rates, since they mainly focus on predicting peptide binding to Major Histocompatibility Complex (MHC) molecules, which is key but not the sole determinant for immunogenicity. Moreover, the therapeutic potential of neoantigen-based vaccines may be enhanced using an optimal delivery platform that elicits robust de novo immune responses.
We developed a novel neoantigen selection pipeline based on existing software combined with a novel prediction method, the Neoantigen Optimization Algorithm (NOAH), which takes into account structural features of the peptide/MHC-I interaction, as well as the interaction between the peptide/MHC-I complex and the TCR, in its prediction strategy. Moreover, to maximize neoantigens' therapeutic potential, neoantigen-based vaccines should be manufactured in an optimal delivery platform that elicits robust de novo immune responses and bypasses central and peripheral tolerance.
We generated a highly immunogenic vaccine platform based on engineered HIV-1 Gag-based Virus-Like Particles (VLPs) expressing a high copy number of each in silico selected neoantigen. We tested different neoantigen-loaded VLPs (neoVLPs) in a B16-F10 melanoma mouse model to evaluate their capability to generate new immunogenic specificities. NeoVLPs were used in in vivo immunogenicity and tumor challenge experiments.
Our results indicate the relevance of incorporating other immunogenic determinants beyond the binding of neoantigens to MHC-I. Thus, neoVLPs loaded with neoantigens enhancing the interaction with the TCR can promote the generation of de novo antitumor-specific immune responses, resulting in a delay in tumor growth. Vaccination with the neoVLP platform is a robust alternative to current therapeutic vaccine approaches and a promising candidate for future personalized immunotherapy.
The emerging SARS-CoV-2 variants of concern (VOCs) may display enhanced transmissibility, more severity and/or immune evasion; however, the pathogenesis of these new VOCs in experimental SARS-CoV-2 ...models or the potential infection of other animal species is not completely understood. Here we infected K18-hACE2 transgenic mice with B.1, B.1.351/Beta, B.1.617.2/Delta and BA.1.1/Omicron isolates and demonstrated heterogeneous infectivity and pathogenesis. B.1.351/Beta variant was the most pathogenic, while BA.1.1/Omicron led to lower viral RNA in the absence of major visible clinical signs. In parallel, we infected wildtype (WT) mice and confirmed that, contrary to B.1 and B.1.617.2/Delta, B.1.351/Beta and BA.1.1/Omicron can infect them. Infection in WT mice coursed without major clinical signs and viral RNA was transient and undetectable in the lungs by day 7 post-infection.
modeling supported these findings by predicting B.1.351/Beta receptor binding domain (RBD) mutations result in an increased affinity for both human and murine ACE2 receptors, while BA.1/Omicron RBD mutations only show increased affinity for murine ACE2.
Here we report the characterization of 17T2, a SARS-CoV-2 pan-neutralizing human monoclonal antibody isolated from a COVID-19 convalescent individual infected during the first pandemic wave. 17T2 is ...a class 1 VH1-58/κ3-20 antibody, derived from a receptor binding domain (RBD)-specific IgA
memory B cell, with a broad neutralizing activity against former and new SARS-CoV-2 variants, including XBB.1.16 and BA.2.86 Omicron subvariants. Consistently, 17T2 demonstrates in vivo prophylactic and therapeutic activity against Omicron BA.1.1 infection in K18-hACE2 mice. Cryo-electron microscopy reconstruction shows that 17T2 binds the BA.1 spike with the RBD in "up" position and blocks the receptor binding motif, as other structurally similar antibodies do, including S2E12. Yet, unlike S2E12, 17T2 retains its neutralizing activity against all variants tested, probably due to a larger RBD contact area. These results highlight the impact of small structural antibody changes on neutralizing performance and identify 17T2 as a potential candidate for future clinical interventions.
Antigen display on the surface of Virus-Like Particles (VLPs) improves immunogenicity compared to soluble proteins. We hypothesised that immune responses can be further improved by increasing the ...antigen density on the surface of VLPs. In this work, we report an HIV-1 Gag-based VLP platform engineered to maximise the presence of antigen on the VLP surface. An HIV-1 gp41-derived protein (Min), including the C-terminal part of gp41 and the transmembrane domain, was fused to HIV-1 Gag. This resulted in high-density MinGag-VLPs. These VLPs demonstrated to be highly immunogenic in animal models using either a homologous (VLP) or heterologous (DNA/VLP) vaccination regimen, with the latter yielding 10-fold higher anti-Gag and anti-Min antibody titres. Despite these strong humoral responses, immunisation with MinGag-VLPs did not induce neutralising antibodies. Nevertheless, antibodies were predominantly of an IgG2b/IgG2c profile and could efficiently bind CD16-2. Furthermore, we demonstrated that MinGag-VLP vaccination could mediate a functional effect and halt the progression of a Min-expressing tumour cell line in an in vivo mouse model.
The elicitation of cross-variant neutralizing antibodies against SARS-CoV-2 represents a major goal for current COVID-19 vaccine strategies. Additionally, natural infection may also contribute to ...broaden neutralizing responses. To assess the contribution of vaccines and natural infection, we cross-sectionally analyzed plasma neutralization titers of six groups of individuals, organized according to the number of vaccines they received and their SARS-CoV-2 infection history. Two doses of vaccine had a limited capacity to generate cross-neutralizing antibodies against Omicron variants of concern (VOCs) in uninfected individuals, but efficiently synergized with previous natural immunization in convalescent individuals. In contrast, booster dose had a critical impact on broadening the cross-neutralizing response in uninfected individuals, to level similar to hybrid immunity, while still improving cross-neutralizing responses in convalescent individuals. Omicron breakthrough infection improved cross-neutralization of Omicron subvariants in non-previously infected vaccinated individuals. Therefore, ancestral Spike-based immunization, via infection or vaccination, contributes to broaden SARS-CoV-2 humoral immunity.
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•Initial mRNA vaccine schedule achieved limited cross-neutralization of Omicron VOCs•Previous infection increased Omicron neutralization in vaccinated individuals•Booster vaccine had a critical impact on broadening cross-neutralizing responses•Omicron breakthrough infection further improved Omicron cross-neutralization
Biochemistry; Immune response; Microbiology
With the spread of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there is a need to assess the protection conferred by both previous infections and current ...vaccination. Here we tested the neutralizing activity of infected and/or vaccinated individuals against pseudoviruses expressing the spike of the original SARS-CoV-2 isolate Wuhan-Hu-1 (WH1), the D614G mutant and the B.1.1.7 variant. Our data show that parameters of natural infection (time from infection and nature of the infecting variant) determined cross-neutralization. Uninfected vaccinees showed a small reduction in neutralization against the B.1.1.7 variant compared to both the WH1 strain and the D614G mutant. Interestingly, upon vaccination, previously infected individuals developed more robust neutralizing responses against B.1.1.7, suggesting that vaccines can boost the neutralization breadth conferred by natural infection.
Age is associated with reduced efficacy of vaccines and linked to higher risk of severe COVID-19. Here we determined the impact of ageing on the efficacy of a SARS-CoV-2 vaccine based on a stabilised ...Spike glycoprotein (S-29) that had previously shown high efficacy in young animals. Thirteen to 18-month-old golden Syrian hamsters (GSH) and 22-23-month-old K18-hCAE2 mice were immunised twice with S-29 protein in AddaVax
adjuvant. GSH were intranasally inoculated with SARS-CoV-2 either two weeks or four months after the booster dose, while all K18-hACE2 mice were intranasally inoculated two weeks after the second immunisation. Body weight and clinical signs were recorded daily post-inoculation. Lesions and viral load were investigated in different target tissues. Immunisation induced seroconversion and production of neutralising antibodies; however, animals were only partially protected from weight loss. We observed a significant reduction in the amount of viral RNA and a faster viral protein clearance in the tissues of immunized animals. Infectious particles showed a faster decay in vaccinated animals while tissue lesion development was not altered. In GSH, the shortest interval between immunisation and inoculation reduced RNA levels in the lungs, while the longest interval was equally effective in reducing RNA in nasal turbinates; viral nucleoprotein amount decreased in both tissues. In mice, immunisation was able to improve the survival of infected animals. Despite the high protection shown in young animals, S-29 efficacy was reduced in the geriatric population. Our research highlights the importance of testing vaccine efficacy in older animals as part of preclinical vaccine evaluation.
Recent studies suggest that particular dendritic cells (DC) subpopulations may be tolerogenic. To test the capacity of different DC subpopulations to modulate allograft rejection, we generated two ...distinct populations of rat bone marrow‐derived DCs (BMDC) with low doses of GM‐CSF and IL‐4. The non‐adherent population (nBMDC), which are the ‘classical’ DCs was able to stimulate naïve allogeneic T cells and could be induced to completely mature using various stimuli. In contrast, the adherent population (aBMDC), which displayed an immature phenotype, was unable to stimulate T cells and was more resistant to maturation. We found that syngeneic aBMDCs, injected one day before transplantation, induced significant prolongation of heart allograft survival and decreased anti‐donor humoral and cellular responses. Similarly, syngeneic aBMDCs inhibited T‐cell responses to KLH in the spleen but not in lymph node in a KLH immunization model without graft. This effect was not antigen specific and could be reversed using an inhibitor of inducible nitric oxide synthase. This compartmentalized inhibition could be in part explained by the fact that the majority of syngeneic adherent cells administered intravenously were found in the spleen with some of them reaching the T‐cell areas. These data suggest that syngeneic aBMDCs can modulate immune responses.
We have previously reported that a distinct subset of splenic CD4(-) rat dendritic cells (DC) induces a rapid and caspase-independent apoptosis-like cell death in a large number of tumor cells in ...vitro. The killing activity of these killer DC (KDC) was restricted to their immature state and was immediately followed by their engulfment of the apoptotic target cells, suggesting that these KDC could directly link innate and adaptive immunity to tumors. Here, we addressed this question using a transplantable model of rat osteosarcoma. First, we showed that rat KDC have an MHC II(+)CD103(+)CD11b(+)NKp46(-) phenotype and are therefore distinct from natural killer cells, which are MHC II(-)CD103(-)CD11b(-)NKp46(+). KDC numbers could be specifically and strongly (up to 10-fold) enhanced by Flt3L in vivo. The OSRGa cell line derived from the osteosarcoma tumor was killed and phagocytosed in vitro by both normal and Flt3L-induced splenic KDC. Such tumor antigen-loaded KDC were used to s.c. vaccinate progressive tumor-bearing rats. Vaccination with OSRGa-loaded KDC but not KDC loaded with irrelevant tumor cells (Jurkat) delayed tumor progression or even induced tumor regression. This vaccine effect was not observed in CD8 T cell-depleted animals and protective against tumor rechallenge. These results suggest that KDC possess the intrinsic capability not only to kill and then engulf tumor cells but also to efficiently cross-present tumor cell-derived antigen in vivo and subsequently induce an adaptive antitumor immune response.
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