SVILUPPO DI NUOVI VACCINI. RISPOSTA MUCOSALE. T CELLULARE

Hadeel T. Zedan et al.

Assessment of Broadly Reactive Responses in Patients With MERS-CoV Infection and SARS-CoV-2 Vaccination

JAMA, June 2023; doi:10.1001/jamanetworkopen.2023.19222

Abstract

Importance In the ongoing COVID-19 pandemic, there remain unanswered questions regarding the nature and importance of the humoral immune response against other coronaviruses. Although coinfection of the Middle East respiratory syndrome coronavirus (MERS-CoV) with the SARS-CoV-2 has not been documented yet, several patients previously infected with MERS-CoV received the COVID-19 vaccine; data describing how preexisting MERS-CoV immunity may shape the response to SARS-CoV-2 following infection or vaccination are lacking.

Objective To characterize the cross-reactive and protective humoral responses in patients exposed to both MERS-CoV infection and SARS-CoV-2 vaccination.

Design, Setting, and Participants This cohort study involved a total of 18 sera samples collected from 14 patients with MERS-CoV infection before (n = 12) and after (n = 6) vaccination with 2 doses of COVID-19 mRNA vaccine (BNT162b2 or mRNA-1273). Of those patients, 4 had prevaccination and postvaccination samples. Antibody responses to SARS-CoV-2 and MERS-CoV were assessed as well as cross-reactive responses to other human coronaviruses.

Main Outcomes and Measures The main outcomes measured were binding antibody responses, neutralizing antibodies, and antibody-dependent cellular cytotoxicity (ADCC) activity. Binding antibodies targeting SARS-CoV-2 main antigens (spike [S], nucleocapsid, and receptor-binding domain) were detected using automated immunoassays. Cross-reactive antibodies with the S1 protein of SARS-CoV, MERS-CoV, and common human coronaviruses were analyzed using a bead-based assay. Neutralizing antibodies (NAbs) against MERS-CoV and SARS-CoV-2 as well as ADCC activity against SARS-CoV-2 were assessed.

Results A total of 18 samples were collected from 14 male patients with MERS-CoV infection (mean [SD] age, 43.8 [14.6] years). Median (IQR) duration between primary COVID-19 vaccination and sample collection was 146 (47-189) days. Prevaccination samples had high levels of anti-MERS S1 immunoglobin M (IgM) and IgG (reactivity index ranging from 0.80 to 54.7 for IgM and from 0.85 to 176.3 for IgG). Cross-reactive antibodies with SARS-CoV and SARS-CoV-2 were also detected in these samples. However, cross-reactivity against other coronaviruses was not detected by the microarray assay. Postvaccination samples showed significantly higher levels of total antibodies, IgG, and IgA targeting SARS-CoV-2 S protein compared with prevaccination samples (eg, mean total antibodies: 8955.0 AU/mL; 95% CI, −5025.0 to 22936.0 arbitrary units/mL; P = .002). In addition, significantly higher anti-SARS S1 IgG levels were detected following vaccination (mean reactivity index, 55.4; 95% CI, −9.1 to 120.0; P = .001), suggesting potential cross-reactivity with these coronaviruses. Also, anti-S NAbs were significantly boosted against SARS-CoV-2 (50.5% neutralization; 95% CI, 17.6% to 83.2% neutralization; P < .001) after vaccination. Furthermore, there was no significant increase in antibody-dependent cellular cytotoxicity against SARS-CoV-2 S protein postvaccination.

Conclusions and Relevance This cohort study found a significant boost in cross-reactive NAbs in some patients exposed to MERS-CoV and SARS-CoV-2 antigens. These findings suggest that isolation of broadly reactive antibodies from these patients may help guide the development of a pancoronavirus vaccine by targeting cross-reactive epitopes between distinct strains of human coronaviruses.

George F. Gao

Two-birds-one-stone approach to combine protein and mRNA vaccines for COVID-19

Nature, June 2023; doi.org/10.1038/s41590-023-01539-5

Abstract

COVID-19 vaccines have been successful, but their duration and level of protection could be improved to cover all SARS-CoV-2 variants. A self-assembling enveloped virus-like particle vaccine combining features of mRNA and protein vaccines might provide a way forward.

Stefania Capone et al.

GRAd-COV2 vaccine provides potent and durable humoral and cellular immunity to SARS-CoV-2 in randomized placebo-controlled phase 2 trial

Cell, May 2023; doi.org/10.1016/j.xcrm.2023.101084

Abstract

The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic and heterologous immunization approaches implemented worldwide for booster doses call for diversified vaccine portfolios. GRAd-COV2 is a gorilla adenovirus-based COVID-19 vaccine candidate encoding prefusion-stabilized spike. The safety and immunogenicity of GRAd-COV2 is evaluated in a dose- and regimen-finding phase 2 trial (COVITAR study, ClinicalTrials.gov: NCT04791423) whereby 917 eligible participants are randomized to receive a single intramuscular GRAd-COV2 administration followed by placebo, or two vaccine injections, or two doses of placebo, spaced over 3 weeks. Here, we report that GRAd-COV2 is well tolerated and induces robust immune responses after a single immunization; a second administration increases binding and neutralizing antibody titers. Potent, variant of concern (VOC) cross-reactive spike-specific T cell response peaks after the first dose and is characterized by high frequencies of CD8s. T cells maintain immediate effector functions and high proliferative potential over time. Thus, GRAd vector is a valuable platform for genetic vaccine development, especially when robust CD8 response is needed.Xiaolei Wang et al.

Vaccine-induced protection against SARS-CoV-2 requires IFN-γ-driven cellular immune response

Nature, June 2023; doi.org/10.1038/s41467-023-39096-y

Abstract

The overall success of worldwide mass vaccination in limiting the negative effect of the COVID-19 pandemics is inevitable, however, recent SARS-CoV-2 variants of concern, especially Omicron and its sub-lineages, efficiently evade humoral immunity mounted upon vaccination or previous infection. Thus, it is an important question whether these variants, or vaccines against them, induce anti-viral cellular immunity. Here we show that the mRNA vaccine BNT162b2 induces robust protective immunity in K18-hACE2 transgenic B-cell deficient (μMT) mice. We further demonstrate that the protection is attributed to cellular immunity depending on robust IFN-γ production. Viral challenge with SARS-CoV-2 Omicron BA.1 and BA.5.2 sub-variants induce boosted cellular responses in vaccinated μMT mice, which highlights the significance of cellular immunity against the ever-emerging SARS-CoV-2 variants evading antibody-mediated immunity. Our work, by providing evidence that BNT162b2 can induce significant protective immunity in mice that are unable to produce antibodies, thus highlights the importance of cellular immunity in the protection against SARS-CoV-2.

Charles B. Stauft et al.

Intranasal or airborne transmission-mediated delivery of an attenuated SARS-CoV-2 protects Syrian hamsters against new variants

Nature, June 2023; doi.org/10.1038/s41467-023-39090-4

Abstract

Detection of secretory antibodies in the airway is highly desirable when evaluating mucosal protection by vaccines against a respiratory virus, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We show that intranasal delivery of an attenuated SARS-CoV-2 (Nsp1-K164A/H165A) induces both mucosal and systemic IgA and IgG in male Syrian hamsters. Interestingly, either direct intranasal immunization or airborne transmission-mediated delivery of Nsp1-K164A/H165A in Syrian hamsters offers protection against heterologous challenge with variants of concern (VOCs) including Delta, Omicron BA.1, BA.2.12.1 and BA.5. Vaccinated animals show significant reduction in both tissue viral loads and lung inflammation. Similarly attenuated viruses bearing BA.1 and BA.5 spike boost variant-specific neutralizing antibodies in male mice that were first vaccinated with modified vaccinia virus Ankara vectors (MVA) expressing full-length WA1/2020 Spike protein. Together, these results demonstrate that our attenuated virus may be a promising nasal vaccine candidate for boosting mucosal immunity against future SARS-CoV-2 VOCs.

Stefania Capone et al

GRAd-COV2 vaccine provides potent and durable humoral and cellular immunity to SARS-CoV-2 in randomized placebo-controlled phase 2 trial

Cell, May 2023; doi.org/10.1016/j.xcrm.2023.101084

Abstract

Julia M. Adler et al

A non-transmissible live attenuated SARS-CoV-2 vaccine

Cell, May 2023; doi.org/10.1016/j.ymthe.2023.05.004

Abstract

Live attenuated vaccines (LAVs) administered via the mucosal route may offer better control of the COVID-19 pandemic than non-replicating vaccines injected intramuscularly. Conceptionally, LAVs have several advantages, including presentation of the entire antigenic repertoire of the virus, and the induction of strong mucosal immunity. Thus, immunity induced by LAV could offer superior protection against future surges of COVID-19 cases caused by emerging SARS-CoV-2 variants. However, LAVs carry the risk of unintentional transmission. To address this issue, we investigated whether transmission of a SARS-CoV-2 LAV candidate can be blocked by removing the furin cleavage site (FCS) from the spike protein. The level of protection and immunity induced by the attenuated virus with the intact FCS was virtually identical to the one induced by the attenuated virus lacking the FCS. Most importantly, removal of the FCS completely abolished horizontal transmission of vaccine virus between cohoused hamsters. Furthermore, the vaccine was safe in immunosuppressed animals and showed no tendency to recombine in vitro or in vivo with a SARS-CoV-2 field strain. These results indicate that removal of the FCS from SARS-CoV-2 LAV is a promising strategy to increase vaccine safety and prevent vaccine transmission without compromising vaccine efficacy.

Tabea M. Eser et al

Nucleocapsid-specific T cell responses associate with control of SARS-CoV-2 in the upper airways before seroconversion

Nature, May 2023; doi.org/10.1038/s41467-023-38020-8

Abstract

Despite intensive research since the emergence of SARS-CoV-2, it has remained unclear precisely which components of the early immune response protect against the development of severe COVID-19. Here, we perform a comprehensive immunogenetic and virologic analysis of nasopharyngeal and peripheral blood samples obtained during the acute phase of infection with SARS-CoV-2. We find that soluble and transcriptional markers of systemic inflammation peak during the first week after symptom onset and correlate directly with upper airways viral loads (UA-VLs), whereas the contemporaneous frequencies of circulating viral nucleocapsid (NC)-specific CD4+ and CD8+ T cells correlate inversely with various inflammatory markers and UA-VLs. In addition, we show that high frequencies of activated CD4+ and CD8+ T cells are present in acutely infected nasopharyngeal tissue, many of which express genes encoding various effector molecules, such as cytotoxic proteins and IFN-γ. The presence of IFNG mRNA-expressing CD4+ and CD8+ T cells in the infected epithelium is further linked with common patterns of gene expression among virus-susceptible target cells and better local control of SARS-CoV-2. Collectively, these results identify an immune correlate of protection against SARS-CoV-2, which could inform the development of more effective vaccines to combat the acute and chronic illnesses attributable to COVID-19.

Nanda Kishore Routhu et al

Efficacy of mRNA-1273 and Novavax ancestral or BA.1 spike booster vaccines against SARS-CoV-2 BA.5 infection in non-human primates

Science, May 2023; doi/10.1126/sciimmunol.adg7015

Abstract

Omicron SARS-CoV-2 variants escape vaccine-induced neutralizing antibodies and cause nearly all current COVID-19 cases. Here, we compared the efficacy of three booster vaccines against Omicron BA.5 challenge in rhesus macaques: mRNA-1273, the Novavax ancestral spike protein vaccine (NVX-CoV2373), or Omicron BA.1 spike protein version (NVX-CoV2515). All three booster vaccines induced a strong BA.1 cross-reactive binding antibody and changed immunoglobulin G dominance from IgG1 to IgG4 in the serum. All three booster vaccines also induced strong and comparable neutralizing antibody responses against multiple variants of concern, including BA.5 and BQ.1.1, along with long-lived plasma cells in the bone marrow. The ratio of BA.1 to WA-1 spike-specific antibody-secreting cells in the blood was higher in NVX-CoV2515 animals compared to NVX-CoV2373 animals, suggesting a better recall of BA.1 specific memory B cells by the BA.1 spike-specific vaccine compared to the ancestral spike-specific vaccine. Further, all three booster vaccines induced low levels of spike-specific CD4 but not CD8 T cell responses in the blood. Following challenge with SARS-CoV-2 BA.5 variant, all three vaccines showed strong protection in the lungs and controlled virus replication in the nasopharynx. In addition, both Novavax vaccines blunted viral replication in nasopharynx at day 2. The protection against SARS-CoV-2 BA.5 infection in the upper respiratory airways correlated with binding, neutralizing, and ADNP activities of the serum antibody. These data have important implications for COVID-19 vaccine development, as vaccines that lower nasopharyngeal virus may help to reduce transmission.

Natalia Martin-Orozco et al

Phase I randomized, observer-blinded, placebo-controlled study of a SARS-CoV-2 mRNA vaccine PTX-COVID19-B

Nature, May 2023; doi.org/10.1038/s41598-023-35662-y

Abstract

Access to vaccines against SARS-CoV-2 virus was limited in poor countries during the COVID-19 pandemic. Therefore, a low-cost mRNA vaccine, PTX-COVID19-B, was produced and evaluated in a Phase 1 trial. PTX-COVID19-B encodes Spike protein D614G variant without the proline-proline (986–987) mutation present in other COVID-19 vaccines. The aim of the study was to evaluate safety, tolerability, and immunogenicity of PTX-COVID19-B vaccine in healthy seronegative adults 18–64 years old. The trial design was observer-blinded, randomized, placebo-controlled, and tested ascending doses of 16-µg, 40-µg, or 100-µg in a total of 60 subjects who received two intramuscular doses, 4 weeks apart. Participants were monitored for solicited and unsolicited adverse events after vaccination and were provided with a Diary Card and thermometer to report any reactogenicity during the trial. Blood samples were collected on baseline, days 8, 28, 42, 90, and 180 for serum analysis of total IgG anti-receptor binding domain (RBD)/Spike titers by ELISA, and neutralizing antibody titers by pseudovirus assay. Titers in BAU/mL were reported as geometric mean and 95% CI per cohort. After vaccination, few solicited adverse events were observed and were mild to moderate and self-resolved within 48 h. The most common solicited local and systemic adverse event was pain at the injection site, and headache, respectively. Seroconversion was observed in all vaccinated participants, who showed high antibody titers against RBD, Spike, and neutralizing activity against the Wuhan strain. Neutralizing antibody titers were also detected against Alpha, Beta, and Delta variants of concerns in a dose dependent manner. All tested doses of PTX-COVID19-B were safe, well-tolerated, and provided a strong immunogenicity response. The 40-µg dose showed fewer adverse reactions than the 100-µg dose, and therefore was selected for a Phase 2 trial, which is currently ongoing.

Nanda Kishore Routhu et al.

Efficacy of mRNA-1273 and Novavax ancestral or BA.1 spike booster vaccines against SARS-CoV-2 BA.5 infection in non-human primates

Science, May 2023; doi/10.1126/sciimmunol.adg7015

Abstract

Hong Lei et al.

Cationic crosslinked carbon dots-adjuvanted intranasal vaccine induces protective immunity against Omicron-included SARS-CoV-2 variants

Nature, May 2023; doi.org/10.1038/s41467-023-38066-8

Abstract

Mucosal immunity plays a significant role in the first-line defense against viruses transmitted and infected through the respiratory system, such as SARS-CoV-2. However, the lack of effective and safe adjuvants currently limits the development of COVID-19 mucosal vaccines. In the current study, we prepare an intranasal vaccine containing cationic crosslinked carbon dots (CCD) and a SARS-CoV-2 antigen, RBD-HR with spontaneous antigen particlization. Intranasal immunization with CCD/RBD-HR induces high levels of antibodies with broad-spectrum neutralization against authentic viruses/pseudoviruses of Omicron-included variants and protects immunized female BALB/c mice from Omicron infection. Despite strong systemic cellular immune response stimulation, the intranasal CCD/RBD-HR vaccine also induces potent mucosal immunity as determined by the generation of tissue-resident T cells in the lungs and airway. Moreover, CCD/RBD-HR not only activates professional antigen-presenting cells (APCs), dendritic cells, but also effectively targets nasal epithelial cells, promotes antigen binding via sialic acid, and surprisingly provokes the antigen-presenting of nasal epithelial cells. We demonstrate that CCD is a promising intranasal vaccine adjuvant for provoking strong mucosal immunity and might be a candidate adjuvant for intranasal vaccine development for many types of infectious diseases, including COVID-19.

Kathryn M Edwards, Kathleen M Neuzi

Developing Mucosal Vaccines for Severe Acute Respiratory Syndrome Coronavirus 2: What Will It Take?

CID, December2022; doi.org/10.1093/cid/ciac935

Abstract

Initial efficacy results from the randomized clinical trials of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) messenger RNA vaccines were impressive. Vaccine efficacy against laboratory-confirmed coronavirus disease 2019 (COVID-19) approached 95% after 2 doses of vaccine [1, 2]. We were pleased by these findings and encouraged that the vaccines would also reduce infection and subsequent transmission. However, the outbreak of COVID-19 in a largely vaccinated group of adults in July 2021 in Barnstable County, Massachusetts, highlighted that prevention of infection and subsequent transmission with parenteral vaccines was a daunting task [3]. Subsequent population-based studies have confirmed the limitations of vaccines and prior infection in conferring sterilizing immunity. While binding and neutralizing antibody responses and systemic cellular responses have been standard measures of infection and vaccine-induced immunity, mucosal antibody or cellular responses in tissue-resident lymphocytes have been less well studied. Since SARS-CoV-2 infection is initiated at the mucosal surfaces in the respiratory tract, generation of robust adaptive immunity at respiratory mucosal sites has the potential to prevent infection and subsequent transmission, in addition to protecting against disease.

The work presented by Cohen and his colleagues at the National Institutes of Health (NIH) in this issue of Clinical Infectious Diseases provides some understanding of the challenges of using parenteral vaccines to stimulate mucosal immunity [4]. They measured antibody levels to the SAR-CoV-2 spike and nucleocapsid proteins in the plasma, nose, and saliva of vaccine recipients and infected persons who were employees at the NIH in Bethesda, Maryland. After vaccination, anti-spike antibody levels in the plasma were higher and declined more slowly than antibody levels in the nose and saliva. In addition, vaccination of previously infected persons boosted anti-spike antibody levels more in the plasma than in the nose or saliva. Both nasal and saliva anti-spike antibody levels correlated significantly with plasma antibody, suggesting that mucosal antibodies were derived from transudation from the blood rather than local production. The authors concluded, “these observations indicate the need for development of mucosal vaccines to induce potent immune responses at sites where SARS-CoV-2 infection occurs.”

Mucosal vaccines with the potential to generate effective local immunity to SARS-CoV-2 in the respiratory tract would be attractive options, although historically mucosal vaccines have posed unique challenges. Currently, there are 5 prototype mucosal vaccines licensed for human use, with 4 administered orally and only 1 vaccine licensed for intranasal administration, live attenuated influenza vaccine (LAIV). As another example of the challenges with intranasal vaccines, the first licensed mucosal vaccine in Europe, an intranasal inactivated influenza vaccine with a unique adjuvant, was associated with Bell's palsy in a significant number of vaccine recipients and led to the removal of that mucosal vaccine from the European market [8]. Thus, live mucosal vaccines represent a delicate balance between “overattenuation,” generating poorly immunogenic responses, and “underattenuation,” leading to increased rates of local and systemic adverse events after vaccine receipt. In addition, as shown with the intranasal inactivated vaccine with the adjuvant, such vaccines may pose unique risks associated with their route of administration.

Despite the previous challenges with mucosal vaccines for respiratory infections, there are many mucosal vaccines in preclinical studies for SAR-CoV-2.

Few human studies have been conducted with mucosal vaccines.

How will these mucosal vaccines be evaluated to determine their efficacy? One approach used in the human studies thus far is to simply compare the immune responses both locally and systemically between the mucosal and the parenteral vaccines. However, this poses challenges because the level of antibody needed to prevent infection or disease has not been precisely determined. Another approach would be to conduct large efficacy studies, such as the study being conducted by Codagenix and the Serum Institute of India where the efficacy will be determined by comparing the number of laboratory-confirmed cases in the vaccine and the placebo groups, like the pivotal trials of the parenteral vaccines. However, this approach poses challenges as well since many people are already vaccinated, and thus the population is not generalizable. The selection of an appropriate and generalizable vaccinated population may likewise be difficult. The ethics of a placebo-controlled trial in susceptible individuals when effective vaccines exist raises additional concerns. One potential option to study the impact of the vaccines on infectivity would be to use human challenge models; some of these studies are ongoing. Like the animal studies, the challenge model could more precisely determine the impact of the vaccine on infectivity. However, human challenge studies have only been performed with the original Wuhan strain; how earlier findings would extrapolate to the evolving variants has not been determined.

Overall, we agree with Cohen et al that mucosal vaccines for SARS-CoV-2 need to be pursued. However, there are significant hurdles to mucosal vaccine development, including incomplete knowledge of the nature of protective mucosal immune response, ensuring the safety and efficacy of new mucosal adjuvants that might be needed to provide a robust immune response, and the most effective ways to test the effectiveness of the vaccines for prevention of infection in a largely vaccinated and/or previously infected population.This is further complicated by the continued circulation of evolved SARS-CoV-2 viruses that cause human infections. We propose that the best path to success is the coordinated, multidisciplinary effort that was used to accelerate the development of the initial parenteral SARS-CoV-2 vaccines. Such an approach will require a public investment of funds to ensure the best scientific and strategic path forward for development of mucosal vaccines.

GuibinLin et al.

Self-replicating RNA nanoparticle vaccine elicits protective immune responses against SARS-CoV-2

Cell, April 2023; doi.org/10.1016/j.omtn.2023.04.021

Abstract

The creation of safe and effective vaccines that induce potent cellular and humoral immune responses against SARS-CoV-2 is urgently needed to end the global COVID-19 epidemic. Here we developed an alphavirus-derived self-replicating RNA (repRNA)-based vaccine platform encoding the receptor binding domain (RBD) of SARS-CoV-2 spike glycoprotein. The repRNA triggers prolonged antigen expression compared to conventional mRNA due to the replication machinery of repRNA. To improve the delivery and vaccine efficacy of repRNA, we developed a self-assembling liposome-protamine-RNA (LPR) nanoparticle with highly efficient encapsulation and transfection of repRNA. LPR-repRNA vaccines substantially activated type I interferon response and innate immune signaling pathways. Subcutaneous immunization of LPR-repRNA-RBD led to prolonged antigen expression, stimulation of innate immune cells and induction of germinal center response in draining lymph nodes. LPR-repRNA-RBD induced antigen-specific T-cell responses and skewed cellular immunity towards an effector memory CD8+ T cell response. Immunizations with LPR-repRNA-RBD triggered the production of anti-RBD IgG antibodies and induced neutralizing antibody response against SARS-CoV-2 pseudovirus. LPR-repRNA-RBD vaccines reduced SARS-CoV-2 infection and lung inflammation in mice. Altogether, these data suggest that LPR-repRNA platform can be a promising avenue for COVID-19 vaccine development.

Zixi Yin et al.

Evaluation of T cell responses to naturally processed variant SARS-CoV-2 spike antigens in individuals following infection or vaccination

Cell, April 2023; doi.org/10.1016/j.celrep.2023.112470

Abstract

Most existing studies characterising SARS-CoV-2-specific T cell responses are peptide based. This does not allow evaluation of whether tested peptides are processed and presented canonically. In this study, we use recombinant vaccinia virus (rVACV)-mediated expression of SARS-CoV-2 spike protein and SARS-CoV-2 infection of ACE-2-transduced B cell lines to evaluate overall T cell responses in a small cohort of recovered COVID-19 patients and uninfected donors vaccinated with ChAdOx1 nCoV-19. We show that rVACV expression of SARS-CoV-2 antigen can be used as an alternative to SARS-CoV-2 infection to evaluate T cell responses to naturally processed spike antigens. In addition, rVACV system can be used to evaluate the cross-reactivity of memory T cells to variants of concern (VOCs) and to identify epitope escape mutants. Finally, our data show that both natural infection and vaccination could induce multi-functional T cell responses with overall T cell responses remaining despite the identification of escape mutations.