Recombinant chimpanzee adenovirus AdC7 expressing dimeric tandem-repeat spike protein RBD protects mice against COVID-19

One HA stalk topping multiple heads as a novel influenza vaccine

Classic chimeric hemagglutinin (cHA) was designed to induce immune responses against the conserved stalk domain of HA. However, it is unclear whether combining more than one HA head domain onto one stalk domain is immunogenic and further induce immune responses against influenza viruses. Here, we constructed numerous novel cHAs comprising two or three fuzed head domains from different subtypes grafted onto one stalk domain, designated as cH1-H3, cH1-H7, cH1-H3-H7, and cH1-H7-H3. The three-dimensional structures of these novel cHAs were modelled using bioinformatics simulations. Structural analysis showed that the intact neutralizing epitopes were exposed in cH1-H7 and were predicted to be immunogenic. The immunogenicity of the cHAs constructs was evaluated in mice using a chimpanzee adenoviral vector (AdC68) vaccine platform. The results demonstrated that cH1-H7 expressed by AdC68 (AdC68-cH1-H7) induced the production of high levels of binding antibodies, neutralizing antibodies, and hemagglutinin inhibition antibodies against homologous pandemic H1N1, drifted seasonal H1N1, and H7N9 virus. Moreover, vaccinated mice were fully protected from a lethal challenge with the aforementioned influenza viruses. Hence, cH1-H7 cHAs with potent immunogenicity might be a potential novel vaccine to provide protection against different subtypes of influenza virus.

Protective RBD-dimer vaccines against SARS-CoV-2 and its variants produced in glycoengineered Pichia pastoris

Protective vaccines are crucial for preventing and controlling coronavirus disease 2019 (COVID-19). Updated vaccines are needed to confront the continuously evolving and circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. These vaccines should be safe, effective, amenable to easily scalable production, and affordable. Previously, we developed receptor binding domain (RBD) dimer-based protein subunit vaccines (ZF2001 and updated vaccines) in mammalian cells. In this study, we explored a strategy for producing RBD-dimer immunogens in Pichia pastoris. We found that wild-type P. pastoris produced hyperglycosylated RBD-dimer protein containing four N-glycosylation sites in P. pastoris. Therefore, we engineered the wild type P. pastoris (GS strain) into GSΔOCH1pAO by deleting the OCH1 gene (encoding α-1,6-mannosyltransferase enzyme) to decrease glycosylation, as well as by overexpressing the HIS4 gene (encoding histidine dehydrogenase) to increase histidine synthesis for better growth. In addition, RBD-dimer protein was truncated to remove the R328/F329 cleavage sites in P. pastoris. Several homogeneous RBD-dimer proteins were produced in the GSΔOCH1pAO strain, demonstrating the feasibility of using the P. pastoris expression system. We further resolved the cryo-EM structure of prototype-Beta RBD-dimer complexed with the neutralizing antibody CB6 to reveal the completely exposed immune epitopes of the RBDs. In a murine model, we demonstrated that the yeast-produced RBD-dimer induces robust and protective antibody responses, which is suitable for boosting immunization. This study developed the yeast system for producing SARS-CoV-2 RBD-dimer immunogens, providing a promising platform and pipeline for the future continuous updating and production of SARS-CoV-2 vaccines.

Three in one: An effective and universal vaccine expressing heterologous tandem RBD trimer by rabies virus vector protects mice against SARS-CoV-2

The rapid emergence of Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) variants, coupled with severe immune evasion and imprinting, has jeopardized the vaccine efficacy, necessitating urgent development of broad protective vaccines. Here, we propose a strategy employing recombinant rabies viruses (RABV) to create a universal SARS-CoV-2 vaccine expressing heterologous tandem receptor-binding domain (RBD) trimer from the SARS-CoV-2 Prototype, Delta, and Omicron strains (SRV-PDO). The results of mouse immunization indicated that SRV-PDO effectively induced cellular and humoral immune responses, and demonstrated higher immunogenicity and broader SARS-CoV-2 neutralization compared to the recombinant RABVs that only expressed RBD monomers. Moreover, SRV-PDO exhibited full protection against SARS-CoV-2 in the challenge assay. This study demonstrates that recombinant RABV expressing tandem RBD-heterotrimer as a multivalent immunogen could elicit a broad-spectrum immune response and potent protection against SARS-CoV-2, making it a promising candidate for future human or veterinary vaccines and offering a novel perspective in other vaccine design.

Recombinant chimpanzee adenovirus expressing spike protein protects chickens against infectious bronchitis virus

Infectious bronchitis (IB) is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV), resulting in significant economic losses in the global poultry industry. In this study, we utilized a replication-incompetent adenovirus vector derived from chimpanzees for the first time to express the S gene of IBV. The adenovirus was successfully rescued and demonstrated convenient production, good growth performance, and stability on HEK293 A cells. Morphologically, the recombinant adenovirus (named PAD-S) appeared normal under transmission electron microscopy, and efficient expression of the exogenous gene was confirmed through immunofluorescence analysis and immunoblotting. Administration of PAD-S via ocular and nasal routes induced a strong immune response in the chicken population, as evidenced by specific antibody and cytokine measurements. PAD-S was unable to replicate within chickens and showed low pre-existing immunity, demonstrating high safety and environmental friendliness. The robust immune response triggered by PAD-S immunization effectively suppressed viral replication in various tissues, alleviating clinical symptoms and tissue damage, thus providing complete protection against viral challenges in the chicken population. In conclusion, this study successfully developed an IBV candidate vaccine strain that possesses biosafety, high protective efficacy, and ease of production.

Classification of five SARS-CoV-2 serotypes based on RBD antigenicities

The continuous evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a significant number of variants, particularly with the emergence of Omicron with many sub-variants. These variants have exhibited increased immune escape, leading to reduced efficacy of existing vaccines and therapeutic antibodies. Given the diminished cross-neutralization observed among these variants, it is plausible that SARS-CoV-2 has developed multiple serotypes. As the major antigenic site, the receptor-binding domain (RBD) of viral spike (S) protein was chosen for serotyping. We selected 23 representative variants, including pre-Omicron variants and Omicron sub-variants, and classified them into five serotypes based on systematic evaluation of the antigenicities of their RBDs. Each serotype includes several genetically distinct variants. Serotype-I encompasses all pre-Omicron variants (with two subtypes), while the remaining four serotypes are all comprised of Omicron sub-variants at different stages of evolution. We propose that these serotypes can serve as a foundation for rapid classification of newly emerging SARS-CoV-2 variants, and guide the development of future broad-spectrum vaccines and neutralizing antibodies against the coronavirus disease 2019 (COVID-19).

Trivalent mRNA Vaccine against SARS-CoV-2 and Variants with Effective Immunization

mRNA vaccines encoding a single spike protein effectively prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the emergence of SARS-CoV-2 variants leads to a wide range of immune evasion. Herein, a unique trivalent mRNA vaccine based on ancestral SARS-CoV-2, Delta, and Omicron variant spike receptor-binding domain (RBD) mRNAs was developed to tackle the immune evasion of the variants. First, three RBD mRNAs of SARS-CoV-2, Delta, and Omicron were coencapsulated into lipid nanoparticles (LNPs) by using microfluidic technology. After that, the physicochemical properties and time-dependent storage stability of the trivalent mRNA vaccine nanoformulation were tested by using dynamic light scattering (DLS). In vitro, the trivalent mRNA vaccine exhibited better lysosomal escape ability, transfection efficiency, and biocompatibility than did the commercial transfection reagent Lipo3000. In addition, Western blot analyses confirmed that the three RBD proteins can be detected in cells transfected with the trivalent mRNA vaccine. Furthermore, ex vivo imaging analysis indicated that the livers of BALB/c mice had the strongest protein expression levels after intramuscular (IM) injection. Using a prime-boost strategy, this trivalent vaccine elicited robust humoral and T-cell immune responses in both the high-dose and low-dose groups and showed no toxicity in BALB/c mice. Three specific IgG antibodies in the high-dose group against SARS-CoV-2, Delta, and Omicron variants approached ∼1/1,833,333, ∼1/1,866,667, and ∼1/925,000, respectively. Taken together, two doses of inoculation with the trivalent mRNA vaccine may provide broad and effective immunization responses against SARS-CoV-2 and variants.

Multi-valent mRNA vaccines against monkeypox enveloped or mature viron surface antigens demonstrate robust immune response and neutralizing activity

Monkeypox was declared a global health emergency by the World Health Organization, and as of March 2023, 86,000 confirmed cases and 111 deaths across 110 countries have been reported. Its causal agent, monkeypox virus (MPV) belongs to a large family of double-stranded DNA viruses, Orthopoxviridae, that also includes vaccinia virus (VACV) and others. MPV produces two distinct forms of viral particles during its replication cycles: the enveloped viron (EV) that is released via exocytosis, and the mature viron (MV) that is discharged through lysis of host cells. This study was designed to develop multi-valent mRNA vaccines against monkeypox EV and MV surface proteins, and examine their efficacy and mechanism of action. Four mRNA vaccines were produced with different combinations of surface proteins from EV (A35R and B6R), MV (A29L, E8L, H3L and M1R), or EV and MV, and were administered in Balb/c mice to assess their immunogenicity potentials. A dynamic immune response was observed as soon as seven days after initial immunization, while a strong IgG response to all immunogens was detected with ELISA after two vaccinations. The higher number of immunogens contributed to a more robust total IgG response and correlating neutralizing activity against VACV, indicating the additive potential of each immunogen in generating immune response and nullifying VACV infection. Further, the mRNA vaccines elicited an antigen-specific CD4+ T cell response that is biased towards Th1. The mRNA vaccines with different combinations of EV and MV surface antigens protected a mouse model from a lethal dose VACV challenge, with the EV and MV antigens-combined vaccine offering the strongest protection. These findings provide insight into the protective mechanism of multi-valent mRNA vaccines against MPV, and also the foundation for further development of effective and safe mRNA vaccines for enhanced protection against monkeypox virus outbreak.

Characterization of SARS-CoV-2 Convalescent Patients' Serological Repertoire Reveals High Prevalence of Iso-RBD Antibodies

While our understanding of SARS-CoV-2 pathogenesis and antibody responses following infection and vaccination has improved tremendously since the outbreak in 2019, the sequence identities and relative abundances of the individual constituent antibody molecules in circulation remain understudied. Using Ig-Seq, we proteomically profiled the serological repertoire specific to the whole ectodomain of SARS-CoV-2 prefusion-stabilized spike (S) as well as to the receptor binding domain (RBD) over a 6-month period in four subjects following SARS-CoV-2 infection before SARS-CoV-2 vaccines were available. In each individual, we identified between 59 and 167 unique IgG clonotypes in serum. To our surprise, we discovered that ∼50% of serum IgG specific for RBD did not recognize prefusion-stabilized S (referred to as iso-RBD antibodies), suggesting that a significant fraction of serum IgG targets epitopes on RBD inaccessible on the prefusion-stabilized conformation of S. On the other hand, the abundance of iso-RBD antibodies in nine individuals who received mRNA-based COVID-19 vaccines encoding prefusion-stabilized S was significantly lower (∼8%). We expressed a panel of 12 monoclonal antibodies (mAbs) that were abundantly present in serum from two SARS-CoV-2 infected individuals, and their binding specificities to prefusion-stabilized S and RBD were all in agreement with the binding specificities assigned based on the proteomics data, including 1 iso-RBD mAb which bound to RBD but not to prefusion-stabilized S. 2 of 12 mAbs demonstrated neutralizing activity, while other mAbs were non-neutralizing. 11 of 12 mAbs also bound to S (B.1.351), but only 1 maintained binding to S (B.1.1.529). This particular mAb binding to S (B.1.1.529) 1) represented an antibody lineage that comprised 43% of the individual's total S-reactive serum IgG binding titer 6 months post-infection, 2) bound to the S from a related human coronavirus, HKU1, and 3) had a high somatic hypermutation level (10.9%), suggesting that this antibody lineage likely had been elicited previously by pre-pandemic coronavirus and was re-activated following the SARS-CoV-2 infection. All 12 mAbs demonstrated their ability to engage in Fc-mediated effector function activities. Collectively, our study provides a quantitative overview of the serological repertoire following SARS-CoV-2 infection and the significant contribution of iso-RBD antibodies, demonstrating how vaccination strategies involving prefusion-stabilized S may have reduced the elicitation of iso-RBD serum antibodies which are unlikely to contribute to protection.

The triangle relationship between human genome, gut microbiome, and COVID-19: opening of a Pandora's box

Since the pandemic started, the coronavirus disease 2019 (COVID-19) has spread worldwide. In patients with COVID-19, the gut microbiome (GM) has been supposed to be closely related to the progress of the disease. The gut microbiota composition and human genetic variation are also connected in COVID-19 patients, assuming a triangular relationship between the genome, GM, and COVID-19. Here, we reviewed the recent developments in the study of the relationship between gut microbiota and COVID-19. The keywords "COVID-19," "microbiome," and "genome" were used to search the literature in the PubMed database. We first found that the composition of the GM in COVID-19 patients varies according to the severity of the illness. Most obviously, Candida albicans abnormally increased while the probiotic Bifidobacterium decreased in severe cases of COVID-19. Interestingly, clinical studies have consistently emphasized that the family Lachnospiraceae plays a critical role in patients with COVID-19. Additionally, we have demonstrated the impact of microbiome-related genes on COVID-19. Specially, we focused on angiotensin-converting enzyme 2's dual functions in SARS-CoV-2 infection and gut microbiota alternation. In summary, these studies showed that the diversity of GMs is closely connected to COVID-19. A triangular relationship exists between COVID-19, the human genome, and the gut flora, suggesting that human genetic variations may offer a chance for a precise diagnosis of COVID-19, and the important relationships between genetic makeup and microbiome regulation may affect the therapy of COVID-19.

Inside-out assembly of viral antigens for the enhanced vaccination

Current attempts in vaccine delivery systems concentrate on replicating the natural dissemination of live pathogens, but neglect that pathogens evolve to evade the immune system rather than to provoke it. In the case of enveloped RNA viruses, it is the natural dissemination of nucleocapsid protein (NP, core antigen) and surface antigen that delays NP exposure to immune surveillance. Here, we report a multi-layered aluminum hydroxide-stabilized emulsion (MASE) to dictate the delivery sequence of the antigens. In this manner, the receptor-binding domain (RBD, surface antigen) of the spike protein was trapped inside the nanocavity, while NP was absorbed on the outside of the droplets, enabling the burst release of NP before RBD. Compared with the natural packaging strategy, the inside-out strategy induced potent type I interferon-mediated innate immune responses and triggered an immune-potentiated environment in advance, which subsequently boosted CD40⁺ DC activations and the engagement of the lymph nodes. In both H1N1 influenza and SARS-CoV-2 vaccines, rMASE significantly increased antigen-specific antibody secretion, memory T cell engagement, and Th1-biased immune response, which diminished viral loads after lethal challenge. By simply reversing the delivery sequence of the surface antigen and core antigen, the inside-out strategy may offer major implications for enhanced vaccinations against the enveloped RNA virus.

Safety and immunogenicity of a protein subunit COVID-19 vaccine (ZF2001) in healthy children and adolescents aged 3-17 years in China: a randomised, double-blind, placebo-controlled, phase 1 trial and an open-label, non-randomised, non-inferiority, phase 2 trial

BACKGROUND

ZF2001 is a recombinant protein subunit vaccine against SARS-CoV-2 that has been approved for use in China, Colombia, Indonesia, and Uzbekistan in adults aged 18 years or older, but not yet in children and adolescents younger than 18 years. We aimed to evaluate the safety and immunogenicity of ZF2001 in children and adolescents aged 3-17 years in China.

METHODS

The randomised, double-blind, placebo-controlled, phase 1 trial and the open-label, non-randomised, non-inferiority, phase 2 trial were done at the Xiangtan Center for Disease Control and Prevention (Hunan Province, China). Healthy children and adolescents aged 3-17 years, without a history of SARS-CoV-2 vaccination, without a history of COVID-19, without COVID-19 at the time of the study, and without contact with patients with confirmed or suspected COVID-19 were included in the phase 1 and phase 2 trials. In the phase 1 trial, participants were divided into three groups according to age (3-5 years, 6-11 years, and 12-17 years). Each group was randomly assigned (4:1), using block randomisation with five blocks, each with a block size of five, to receive three 25 μg doses of the vaccine, ZF2001, or placebo intramuscularly in the arm 30 days apart. The participants and investigators were masked to treatment allocation. In the phase 2 trial, participants received three 25 μg doses of ZF2001 30 days apart and remained stratified by age group. For phase 1, the primary endpoint was safety and the secondary endpoint was immunogenicity (humoral immune response on day 30 after the third vaccine dose: geometric mean titre [GMT] of prototype SARS-CoV-2 neutralising antibodies and seroconversion rate, and geometric mean concentration [GMC] of prototype SARS-CoV-2 receptor-binding domain [RBD]-binding IgG antibodies and seroconversion rate). For phase 2, the primary endpoint was the GMT of SARS-CoV-2 neutralising antibodies with seroconversion rate on day 14 after the third vaccine dose, and the secondary endpoints included the GMT of RBD-binding antibodies and seroconversion rate on day 14 after the third vaccine dose, the GMT of neutralising antibodies against the omicron BA.2 subvariant and seroconversion rate on day 14 after the third vaccine dose, and safety. Safety was analysed in participants who received at least one dose of the vaccine or placebo. Immunogenicity was analysed in the full-analysis set (ie, participants who received at least one dose and had antibody results) by intention to treat and in the per-protocol set (ie, participants who completed the whole vaccination course and had antibody results). Non-inferiority in the phase 2 trial (neutralising antibody titre of participants from this trial aged 3-17 years vs that of participants aged 18-59 years from a separate phase 3 trial) for clinical outcome assessment was based on the geometric mean ratio (GMR) and was considered met if the lower bound of the 95% CI for the GMR was 0·67 or greater. These trials are registered with ClinicalTrials.gov, NCT04961359 (phase 1) and NCT05109598 (phase 2).

FINDINGS

Between July 10 and Sept 4, 2021, 75 children and adolescents were randomly assigned to receive ZF2001 (n=60) or placebo (n=15) in the phase 1 trial and were included in safety and immunogenicity analyses. Between Nov 5, 2021, and Feb 14, 2022, 400 participants (130 aged 3-7 years, 210 aged 6-11 years, and 60 aged 12-17 years) were included in the phase 2 trial and were included in the safety analysis; six participants were excluded from the immunogenicity analyses. 25 (42%) of 60 participants in the ZF2001 group and seven (47%) of 15 participants in the placebo group in phase 1, and 179 (45%) of 400 participants in phase 2, had adverse events within 30 days after the third vaccination, without a significant difference between groups in phase 1. Most adverse events were grade 1 or 2 (73 [97%] of 75 in the phase 1 trial, and 391 [98%] of 400 in the phase 2 trial). One participant in the phase 1 trial and three in the phase 2 trial who received ZF2001 had serious adverse events. One serious adverse event (acute allergic dermatitis) in the phase 2 trial was possibly related to the vaccine. In the phase 1 trial, on day 30 after the third dose, in the ZF2001 group, seroconversion of neutralising antibodies against SARS-CoV-2 was observed in 56 (93%; 95% CI 84-98) of 60 participants, with a GMT of 176·5 (95% CI 118·6-262·8), and seroconversion of RBD-binding antibodies was observed in all 60 (100%; 95% CI 94-100) participants, with a GMC of 47·7 IU/mL (95% CI 40·1-56·6). In the phase 2 trial, on day 14 after the third dose, seroconversion of neutralising antibodies against SARS-CoV-2 was seen in 392 (99%; 95% CI 98-100) participants, with a GMT of 245·4 (95% CI 220·0-273·7), and seroconversion of RBD-binding antibodies was observed in all 394 (100%; 99-100) participants, with a GMT of 8021 (7366-8734). On day 14 after the third dose, seroconversion of neutralising antibodies against the omicron subvariant BA.2 was observed in 375 (95%; 95% CI 93-97) of 394 participants, with a GMT of 42·9 (95% CI 37·9-48·5). For the non-inferiority comparison of participants aged 3-17 years with those aged 18-59 years for SARS-CoV-2 neutralising antibodies, the adjusted GMR was 8·6 (95% CI 7·0-10·4), with the lower bound of the GMR greater than 0·67.

INTERPRETATION

ZF2001 is safe, well tolerated, and immunogenic in children and adolescents aged 3-17 years. Vaccine-elicited sera can neutralise the omicron BA.2 subvariant, but with reduced activity. The results support further studies of ZF2001 in children and adolescents.

FUNDING

Anhui Zhifei Longcom Biopharmaceutical and the Excellent Young Scientist Program from National Natural Science Foundation of China.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

A China-developed adenovirus vector-based COVID-19 vaccine: review of the development and application of Ad5-nCov

INTRODUCTION

The global spread of COVID-19 has prompted the development of vaccines. A recombinant adenovirus type-5 vectored COVID-19 vaccine (Ad5-nCoV) developed by Chinese scientists has been authorized for use as a prime and booster dose in China and several other countries.

AREAS COVERED

We searched published articles as of 4 May 2023, on PubMed using keywords related to Adenovirus vector, vaccine, and SARS-CoV-2. We reported the progress and outcomes of Ad5-nCov, including vaccine efficacy, safety, immunogenicity based on pre-clinical trials, clinical trials, and real-world studies for primary and booster doses.

EXPERT OPINION

Ad5-nCoV is a significant advancement in Chinese vaccine development technology. Evidence from clinical trials and real-world studies has demonstrated well-tolerated, highly immunogenic, and efficacy of Ad5-nCoV in preventing severe/critical COVID-19. Aerosolized Ad5-nCoV, given via a novel route, could elicit mucosal immunity and improve the vaccine efficacy, enhance the production capacity and availability, and reduce the potential negative impact of preexisting antibodies. However, additional research is necessary to evaluate the long-term safety and immunogenicity of Ad5-nCoV, its efficacy against emerging variants, its effectiveness in a real-world context of hybrid immunity, and its cost-effectiveness, particularly with respect to aerosolized Ad5-nCoV.

A tandem-repeat dimeric RBD protein-based covid-19 vaccine zf2001 protects mice and nonhuman primates

Safe, efficacious, and deployable vaccines are urgently needed to control COVID-19 in the large-scale vaccination campaigns. We report here the preclinical studies of an approved protein subunit vaccine against COVID-19, ZF2001, which contains tandem-repeat dimeric receptor-binding domain (RBD) protein with alum-based adjuvant. We assessed vaccine immunogenicity and efficacy in both mice and non-human primates (NHPs). ZF2001 induced high levels of RBD-binding and SARS-CoV-2 neutralizing antibody in both mice and non-human primates, and elicited balanced T_H1/T_H2 cellular responses in NHPs. Two doses of ZF2001 protected Ad-hACE2-transduced mice against SARS-CoV-2 infection, as detected by reduced viral RNA and relieved lung injuries. In NHPs, vaccination of either 25 μg or 50 μg ZF2001 prevented infection with SARS-CoV-2 in lung, trachea, and bronchi, with milder lung lesions. No evidence of disease enhancement was observed in both animal models. ZF2001 has been approved for emergency use in China, Uzbekistan, Indonesia, and Columbia. The high safety, immunogenicity, and protection efficacy in both mice and NHPs found in this preclinical study was consistent with the results in human clinical trials.

Intranasal immunization with recombinant Vaccinia virus encoding trimeric SARS-CoV-2 spike receptor-binding domain induces neutralizing antibody

Respiratory transmission of SARS-CoV-2 is considered to be the major dissemination route for COVID-19, therefore, mucosal immune responses have great importance in preventing SARS-CoV-2 from infection. In this study, we constructed a recombinant Vaccinia virus (VV) harboring trimeric receptor-binding domain (RBD) of SARS-CoV-2 spike protein (VV_-tRBD), and evaluated the immune responses towards RBD following intranasal immunization against mice and rabbits. In BALB/c mice, intranasal immunization with VV_-tRBD elicited robust humoral and cellular immune responses, with high-level of both neutralizing IgG and IgA in sera against SARS-CoV-2 psudoviruses, and a number of RBD-specific IFN-γ-secreting lymphocytes. Sera from immunized rabbits also exhibited neutralization effects. Notably, RBD-specific secretory IgA (sIgA) in both nasal washes and bronchoalveolar lavage fluids (BALs) were detectable and showed substantial neutralization activities. Collectively, a recombinant VV expressing trimeric RBD confers robust systemic immune response and mucosal neutralizing antibodies, thus warranting further exploration as a mucosal vaccine.

Neutralizing Potency of Prototype and Omicron RBD mRNA Vaccines Against Omicron Variant

The newly emerged Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contains more than 30 mutations on the spike protein, 15 of which are located within the receptor binding domain (RBD). Consequently, Omicron is able to extensively escape existing neutralizing antibodies and may therefore compromise the efficacy of current vaccines based on the original strain, highlighting the importance and urgency of developing effective vaccines against Omicron. Here we report the rapid generation and evaluation of an mRNA vaccine candidate specific to Omicron, and explore the feasibility of heterologous immunization with WT and Omicron RBD vaccines. This mRNA vaccine encodes the RBD of Omicron (designated as RBD-O) and is formulated with lipid nanoparticle. Two doses of the RBD-O mRNA vaccine efficiently induce neutralizing antibodies in mice; however, the antisera are effective only on the Omicron variant but not on the wildtype and Delta strains, indicating a narrow neutralization spectrum. It is noted that the neutralization profile of the RBD-O mRNA vaccine is opposite to that observed for the mRNA vaccine expressing the wildtype RBD (RBD-WT). Importantly, booster with RBD-O mRNA vaccine after two doses of RBD-WT mRNA vaccine can significantly increase neutralization titers against Omicron. Additionally, an obvious increase in IFN-γ, IL-2, and TNF-α-expressing RBD-specific CD4⁺ T cell responses was observed after immunization with the RBD-WT and/or RBD-O mRNA vaccine. Together, our work demonstrates the feasibility and potency of an RBD-based mRNA vaccine specific to Omicron, providing important information for further development of heterologous immunization program or bivalent/multivalent SARS-CoV-2 vaccines with broad-spectrum efficacy.

Recombinant chimpanzee adenovirus vector vaccine expressing the spike protein provides effective and lasting protection against SARS-CoV-2 infection in mice

SARS-CoV-2 infection is a global public health threat. Vaccines are considered amongst the most important tools to control the SARS-CoV-2 pandemic. As expected, deaths from SARS-CoV-2 infection have dropped dramatically with widespread vaccination. However, there are concerns over the duration of vaccine-induced protection, as well as their effectiveness against emerging variants of concern. Here, we constructed a recombinant chimpanzee adenovirus vectored vaccine expressing the full-length spike of SARS-CoV-2 (AdC68-S). Rapid and high levels of humoral and cellular immune responses were observed after immunization of C57BL/6J mice with one or two doses of AdC68-S. Notably, neutralizing antibodies were observed up to at least six months after vaccination, without substantial decline. Single or double doses AdC68-S immunization resulted in lower viral loads in lungs of mice against SARS-CoV-2 challenge both in the short term (21 days) and long-term (6 months). Histopathological examination of AdC68-S immunized mice lungs showed mild histological abnormalities after SARS-CoV-2 infection. Taken together, this study demonstrates the efficacy and durability of the AdC68-S vaccine and constitutes a promising candidate for clinical evaluation.

The Emergence of SARS-CoV-2 Variants With a Lower Antibody Response: A Genomic and Clinical Perspective

The emergence of several novel SARS-CoV-2 variants regarded as variants of concern (VOCs) has exacerbated pathogenic and immunologic prominences, as well as reduced diagnostic sensitivity due to phenotype modification-capable mutations. Furthermore, latent and more virulent strains that have arisen as a result of unique mutations with increased evolutionary potential represent a threat to vaccine effectiveness in terms of incoming and existing variants. As a result, resisting natural immunity, which leads to higher reinfection rates, and avoiding vaccination-induced immunization, which leads to a lack of vaccine effectiveness, has become a crucial problem for public health around the world. This study attempts to review the genomic variation and pandemic impact of emerging variations of concern based on clinical characteristics management and immunization effectiveness. The goal of this study is to gain a better understanding of the link between genome level polymorphism, clinical symptom manifestation, and current vaccination in the instance of VOCs.

Intranasal COVID-19 vaccines: From bench to bed

Currently licensed COVID-19 vaccines are all designed for intramuscular (IM) immunization. However, vaccination today failed to prevent the virus infection through the upper respiratory tract, which is partially due to the absence of mucosal immunity activation. Despite the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, the next generation of COVID-19 vaccine is in demand and intranasal (IN) vaccination method has been demonstrated to be potent in inducing both mucosal and systemic immune responses. Presently, although not licensed, various IN vaccines against SARS-CoV-2 are under intensive investigation, with 12 candidates reaching clinical trials at different phases. In this review, we give a detailed description about current status of IN COVID-19 vaccines, including virus-vectored vaccines, recombinant subunit vaccines and live attenuated vaccines. The ongoing clinical trials for IN vaccines are highlighted. Additionally, the underlying mechanisms of mucosal immunity and potential mucosal adjuvants and nasal delivery devices are also summarized.

Heterologous prime-boost immunizations with chimpanzee adenoviral vectors elicit potent and protective immunity against SARS-CoV-2 infection

A safe and effective vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to tackle the COVID-19 global pandemic. Here, we describe the development of chimpanzee adenovirus serotypes 6 and 68 (AdC6 and AdC68) vector-based vaccine candidates expressing the full-length transmembrane spike glycoprotein. We assessed the vaccine immunogenicity, protective efficacy, and immune cell profiles using single-cell RNA sequencing in mice. Mice were vaccinated via the intramuscular route with the two vaccine candidates using prime-only regimens or heterologous prime-boost regimens. Both chimpanzee adenovirus-based vaccines elicited strong and long-term antibody and T cell responses, balanced Th1/Th2 cell responses, robust germinal center responses, and provided effective protection against SARS-CoV-2 infection in mouse lungs. Strikingly, we found that heterologous prime-boost immunization induced higher titers of protective antibodies, and more spike-specific memory CD8+ T cells in mice. Potent neutralizing antibodies produced against the highly transmissible SARS-CoV-2 variants B.1.1.7 lineage (also known as N501Y.V1) and B.1.351 lineage (also known as N501Y.V2) were detectable in mouse sera over 6 months after prime immunization. Our results demonstrate that the heterologous prime-boost strategy with chimpanzee adenovirus-based vaccines is promising for further development to prevent SARS-CoV-2 infection.