A comparative characterization of SARS-CoV-2-specific T cells induced by mRNA or inactive virus COVID-19 vaccines

mRNA vaccine design using the proteome of Theileria annulata through immunoinformatics approaches

Theileriosis exerts a substantial impact on ruminants, resulting in significant economic losses within the animal husbandry sector. The current vaccine, a live attenuated parasite, has several limitations that hinder effective disease control. This study utilized immunoinformatics to prioritize potential vaccine candidates and pointed to the design of a novel mRNA vaccine against Theileria annulata using in silico methods. Nine antigenic proteins were selected using various software, and their epitopes were identified through immunoinformatics tools. These epitopes were assessed for their biological traits and homology. Their presentation by major histocompatibility complex (MHC) cells and other immune cells was analyzed using molecular docking techniques. A multi-epitope protein was then modeled and optimized, followed by structural and stability analyses of the mRNA vaccine construct. Finally, the immune response to the new vaccine was simulated. The identified epitopes were localized within the antigen-binding sites of their respective MHC alleles. The newly formulated vaccine demonstrated stability, exhibited no toxicity, and showed non-allergenic characteristics. It effectively elicited responses from both the humoral and cellular immune systems. The findings suggest that the desired engineered mRNA vaccine paves the way for the development of the deterrence of theileriosis. This potential merits additional exploration through rigorous laboratory experiments and subsequent clinical trials.IMPORTANCEThis study presents a cutting-edge approach in vaccine design against bovine theileriosis, a devastating disease affecting cattle globally. By leveraging immunoinformatics methodologies, a novel mRNA vaccine candidate was tailored using computational analyzes of Theileria annulata proteins. Antigenic protein identification, epitope evaluation, and structural optimization of the multi-epitope mRNA vaccine are pivotal advancements in vaccine development. Using computational modeling tools to predict immune responses enhances the efficiency and accuracy of vaccine design, potentially revolutionizing preventive strategies against bovine theileriosis. This research not only demonstrates the potential of immunoinformatics in vaccine innovation but also sheds light on a promising avenue for combating a significant livestock health concern, offering hope for more effective and targeted veterinary interventions.

Role of antiviral CD8+ T cell immunity to SARS-CoV-2 infection and vaccination

The COVID-19 pandemic has greatly enhanced our understanding of CD8+ T cell immunity and their role in natural infection and vaccine-induced protection. Rapid and early SARS-CoV-2-specific CD8+ T cell responses have been associated with efficient viral clearance and mild disease. Virus-specific CD8+ T cell responses can compensate for waning, morbidity-related, and iatrogenic reduction of humoral immunity. After infection or vaccination, SARS-CoV-2-specific memory CD8+ T cells are formed, which mount an efficient recall response in the event of breakthrough infection and help to protect from severe disease. Due to their breadth and ability to target mainly highly conserved epitopes, SARS-CoV-2-specific CD8+ T cells are also able to cross-recognize epitopes of viral variants, thus maintaining immunity even after the emergence of viral evolution. In some cases, however, CD8+ T cells may contribute to the pathogenesis of severe COVID-19. In particular, delayed and uncontrolled, e.g., nonspecific and hyperactivated, cytotoxic CD8+ T cell responses have been linked to poor COVID-19 outcomes. In this minireview, we summarize the tremendous knowledge about CD8+ T cell responses to SARS-CoV-2 infection and COVID-19 vaccination that has been gained over the past 5 years, while also highlighting the critical knowledge gaps that remain.

Pan-Variant SARS-CoV-2 Vaccines Induce Protective Immunity by Targeting Conserved Epitopes

The development of a globally effective COVID-19 vaccine faces significant challenges, particularly in redirecting the B-cell response from immunodominant yet variable regions of viral proteins toward their conserved domains. To address this, an integrated strategy is implemented that combines classical B-cell epitope prediction with protein-antibody cluster docking and antibody titer analysis from 30 vaccinated and convalescent individuals. This approach yields stable immunodominant and immunoprevalent B-cell epitopes capable of eliciting robust antibody responses in BALB/c mice and effectively neutralizing pseudoviruses expressing the Spike protein of SARS-CoV-2 variants of concern, including Alpha, Beta, Gamma, Delta, and Omicron. To achieve a broader T-cell-based immune response, promiscuous T-cell epitopes are identified by integrating classical T-cell epitope predictions, differential scanning fluorimetry, and peptide-MHC structural analysis. Unique peptides with conserved MHC-anchoring residues are identified, enabling binding to a spectrum of MHC-I and MHC-II haplotypes. These peptides elicit strong interferon gamma responses in human peripheral blood mononuclear cells and demonstrate cross-species efficacy by activating both CD4+ and CD8+ T-cells in BALB/c mice. Collectively, these findings highlight the significance of innovative vaccine strategies targeting immunodominant/immunoprevalent B-cell and promiscuous T-cell epitopes to drive broad and robust humoral and cellular immune responses against a wide range of SARS-CoV-2 variants.

A Universal Therapeutic Vaccine Leveraging Autologous Pre-Existing Immunity to Eliminate in Situ Uniformly Engineered Heterogeneous Tumor Cells

Tumor vaccines that activate the autologous immune system to eliminate tumor cells represent a promising approach in cancer immunotherapy. However, challenges such as tumor heterogeneity, limited antigen selection, insufficient antigen presentation, and the slow onset of de novo immune responses have resulted in poor universality and suboptimal response rates. In contrast, pathogen-specific pre-existing immunity acquired through infection or vaccination, can rapidly generate a more potent and enduring immune response upon re-encounter with the same antigen. Here, an adeno-associated virus (AAV)-based therapeutic vaccine capable of genetically modifying diverse tumor cells to uniformly overexpress and efficiently present the highly immunogenic transmembrane SARS-CoV-2 receptor binding domain (RBD), and to release RBD-enveloped virus-like particles, which awaken and enhance the RBD-specific pre-existing immunity, leading to significant tumor remission, is engineered. Mechanistically, this therapeutic vaccine leverages the robust RBD-specific pre-existing immunity and heightened antibody-mediated phagocytosis to eliminate engineered tumor cells while inducing antigen spreading, thereby provoking a more diverse tumor-specific cellular immune responses. Notably, widespread administration of vaccines against various pathogens has provided a versatile pool of pre-existing immunity that can be redirected to eradicate tumors. These findings offer a novel perspective on overcoming the limitations posed by tumor heterogeneity and personalized medicine.

The Role of Memory T-Cell Mediated Immunity in Long-term COVID-19: Effects of Vaccination Status

T-cell-mediated immunity is essential for controlling severe acute respiratory syndrome coronavirus 2 (SARSCoV2) infection, preventing severe disease, and potentially reducing the risk of long-term coronavirus disease (COVID). This study investigated the impact of natural infection, vaccination, and hybrid immunity on T-cell responses, with a particular emphasis on the role of memory T-cells in long-term COVID-19. The present study reviewed current literature on T-cell responses, including memory T-cell development, in individuals with natural SARS-CoV-2 infection, those vaccinated with messenger RNA (mRNA) vaccines, and those with hybrid immunity. It examined studies that compared T-cell activity, immune regulation, and the prevalence of long-term COVID-19 across these groups. Natural infection induces variable T-cell responses, with severe cases showing stronger but sometimes dysregulated immunological activity, which may contribute to prolonged COVID-19. Vaccination, particularly with mRNA vaccines, elicits targeted and consistent T-cell responses, including memory T-cells, reducing disease severity, and the incidence of long-term COVID-19. Hybrid immunity combines natural infection and vaccination, provides the most robust protection, enhanceds memory T-cell responses, and reduces the risk of long-term COVID-19 through balanced immune regulation. Memory T-cells play a critical role in mitigating long-term COVID-19. Vaccination significantly enhances T-cell-mediated immunity, minimizing the risk of chronic symptoms compared to natural infection alone. Hybrid immunity provides the most effective defense, emphasizing the importance of vaccination, even after natural infection, to prevent long-term COVID-19.

The guided fire from within: intratumoral administration of mRNA-based vaccines to mobilize memory immunity and direct immune responses against pathogen to target solid tumors

We investigated a novel cancer immunotherapy strategy that effectively suppresses tumor growth in multiple solid tumor models and significantly extends the lifespan of tumor-bearing mice by introducing pathogen antigens into tumors via mRNA-lipid nanoparticles. The pre-existing immunity against the pathogen antigen can significantly enhance the efficacy of this approach. In mice previously immunized with BNT162b2, an mRNA-based COVID-19 vaccine encoding the spike protein of the SARS-CoV-2 virus, intratumoral injections of the same vaccine efficiently tagged the tumor cells with mRNA-expressed spike protein. This action rapidly mobilized the pre-existing memory immunity against SARS-CoV-2 to kill the cancer cells displaying the spike protein, while concurrently reprogramming the tumor microenvironment (TME) by attracting immune cells. The partial elimination of tumor cells in a normalized TME further triggered extensive tumor antigen-specific T cell responses through antigen spreading, eventually resulting in potent and systemic tumor-targeting immune responses. Moreover, combining BNT162b2 treatment with anti-PD-L1 therapy yielded a more substantial therapeutic impact, even in "cold tumor" types that are typically less responsive to treatment. Given that the majority of the global population has acquired memory immunity against various pathogens through infection or vaccination, we believe that, in addition to utilizing the widely held immune memory against SARS-CoV-2 via COVID-19 vaccine, mRNA vaccines against other pathogens, such as Hepatitis B Virus (HBV), Common Human Coronaviruses (HCoVs), and the influenza virus, could be rapidly transitioned into clinical use and holds great promise in treating different types of cancer. The extensive selection of pathogen antigens expands therapeutic opportunities and may also overcome potential drug resistance.

Effectiveness of COVID-19 vaccines against SARS-CoV-2 infection and severe outcomes in adults: a systematic review and meta-analysis of European studies published up to 22 January 2024

BACKGROUND

Up-to-date evidence from European studies on long-term vaccine effectiveness (VE) of COVID-19 vaccines is lacking. This review aimed to evaluate effectiveness and durability of primary vaccine series and boosters in preventing infection and severe outcomes in the European population.

METHODS

We conducted systematic searches of PubMed and Embase up to 22 January 2024. We included observational studies that evaluated VE against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or severe disease (hospitalisation, intensive care unit admission or death) for primary series and boosters in Europe. We applied a random-effects meta-analysis model.

RESULTS

We included 33 studies and over 56 million participants. The overall VE of the complete primary series against infection with any SARS-CoV-2 variant was 70.7%. VE was lower for Omicron, at 26.1%, than for pre-Omicron strains, at 77.0%. Over time, VE against infection by any variant decreased from 68.9% to 38.9% after 6 months. Boosters restored VE to 76.4% and maintained at 58.4% after 3 months. The overall VE of a complete primary series for severe outcomes due to any variant was 87.4%, with 93.3% for pre-Omicron and 62.8% for Omicron strains. Protection against severe outcomes declined less than for infection. 6 months after the primary series, the vaccine still provided over 50% protection against severe outcomes caused by Omicron. Boosters restored VE to 87.9% and maintained at 78.5% after 3 months.

CONCLUSION

VE against SARS-CoV-2 infection declines markedly with time and Omicron variants. Protection against severe outcomes was more durable and resistant to viral mutation. Boosters restored protection, emphasising the need for timely booster vaccination for vulnerable populations.

COVID-19 vaccinated children, adolescents, and young adults with acute lymphoblastic leukemia show spike reactive antibodies and multifunctional T-cells

Little is known about the efficacy of COVID-19 vaccines during acute lymphoblastic leukemia therapy (ALL); data for COVID-19 vaccine immune responses in pediatric leukemia remain sparse. We conducted a single center study of patients aged 5-25 years undergoing ALL chemotherapy who received COVID-19 vaccination. Twenty-one patients were enrolled; efficacy was evaluable in 20. Twenty were vaccinated while receiving chemotherapy. Twenty received the BNT162b2 mRNA vaccine. Spike reactive antibodies (S-IgG) and/or T-cells (SRT) were detected in 16 of 20 (80%) vaccinated patients; 13 (65%) and 9 (45%) were positive for S-IgG and SRT, respectively. Six (30%) showed both spike reactive B and T-cell responses. Eleven of the 13 with S-IgG positivity were negative for anti-Nucleocapsid IgG, an antibody profile consistent with a vaccine induced immune response. All 13S-IgG+ patients showed neutralizing antibodies. SRT included CD4+ (7) and CD8+ (6) T-cells; both CD4+ and CD8+ SRT were seen in 4. SRT were multifunctional (producing multiple cytokines) in most patients (8 of 9); 4 showed SRT with triple cytokine and B-cell co-stimulatory responses, indicating a multimodal adaptive immune response. Immune responses were seen among patients vaccinated in the settings of lymphopenia (6 of 12) intensive chemotherapy (3 of 4), and Peg allergy (6 of 8). Sequencing revealed public CD4+ and CD8+ TCR sequences reactive to epitopes across the spike protein. In conclusion, COVID-19 vaccination induced B and/or T-cell responses in a majority of children and young adults undergoing ALL chemotherapy.

Improved influenza vaccine responses after expression of multiple viral glycoproteins from a single mRNA

Influenza viruses cause substantial morbidity and mortality every year despite seasonal vaccination. mRNA-based vaccines have the potential to elicit more protective immune responses, but for maximal breadth and durability, it is desirable to deliver both the viral hemagglutinin and neuraminidase glycoproteins. Delivering multiple antigens individually, however, complicates manufacturing and increases cost, thus it would be beneficial to express both proteins from a single mRNA. Here, we develop an mRNA genetic configuration that allows the simultaneous expression of unmodified, full-length NA and HA proteins from a single open reading frame. We apply this approach to glycoproteins from contemporary influenza A and B viruses and, after vaccination, observe high levels of functional antibodies and protection from disease in female mouse and male ferret challenge models. This approach may further efforts to utilize mRNA technology to improve seasonal vaccine efficacy by efficiently delivering multiple viral antigens simultaneously and in their native state.

Evaluation of the Effect of mRNA and Inactivated SARS-CoV-2 Vaccines on the Levels of Cytokines IL-2, IFN-γ, and Anti-RBD Spike SARS-CoV-2 Antibodies in People Living with HIV (PLHIV)

The safety of the mRNA and inactivated SARS-CoV-2 vaccine has been demonstrated for people living with HIV (PLHIV). However, vaccine studies in PLHIV are limited, and there is a gap in which vaccine type provides the best response in PLHIV. Thus, PLHIV may benefit from mRNA vaccine types compared to inactivated vaccines. This study aims to assess the immune responses to vaccination by measuring specific antibodies (IgG) targeting the receptor binding sites (RBDs) of the SARS-CoV-2 virus and the levels of IL-2 and IFN-γ in plasma. A total of 41 PLHIV who regularly take antiretroviral therapy (ART) over a period of six months, along with 31 individuals in a healthy control group (HC), were administered either two mRNA or inactivated vaccines. Data regarding demographics and clinical information were gathered from the medical records. An analysis was conducted on the neutralisation antibody IgG specific to RBD using the chemiluminescence microparticle assay (CMIA). The levels of IL-2 and IFN-γ were quantified using the Luminex assay method from plasma samples. Data were collected in the laboratory 28 days after each vaccination. After the first vaccination, the level of anti-SARS-CoV-2 RBD IgG was higher in PLHIV who received the mRNA vaccines than those who received inactivated vaccines (p = 0.006). The levels of mRNA in the PLHIV group showed a significant correlation with IL-2 and IFN-γ after the second vaccination (r = 0.51, p = 0.0035; r = 0.68, p = 0.002). The group of PLHIV who received the inactivated vaccine showed increased IL-2 and IFN-γ after the initial vaccination, compared to PLHIV who received the mRNA vaccine (p = 0.04; p = 0.08). Administering a two-dose vaccination is essential to increase the levels of neutralising antibodies significantly (p = 0.013) in PLHIV who have received inactivated vaccines; further study is needed to make this a recommendation. The responses observed after vaccination in PLHIV were not affected by their CD4 cell counts. PLHIV showed higher levels of SARS-CoV-2 IgG and increased IL-2 and IFN-γ levels. Our study encourages SARS-CoV-2 vaccination in PLHIV regardless of its CD4 cell counts. Furthermore, the mRNA vaccine may give robust high antibody responses in PLHIV.

Nanoplatform Based Intranasal Vaccines: Current Progress and Clinical Challenges

Multiple vaccine platforms have been employed to develop the nasal SARS-CoV-2 vaccines in preclinical studies, and the dominating pipelines are viral vectored as protein-based vaccines. Among them, several viral vectored-based vaccines have entered clinical development. Nevertheless, some unsatisfactory results were reported in these clinical studies. In the face of such urgent situations, it is imperative to rapidly develop the next-generation intranasal COVID-19 vaccine utilizing other technologies. Nanobased intranasal vaccines have emerged as an approach against respiratory infectious diseases. Harnessing the power of nanotechnology, these vaccines offer a noninvasive yet potent defense against pathogens, including the threat of COVID-19. The improvements made in vaccine mucosal delivery technologies based on nanoparticles, such as lipid nanoparticles, polymeric nanoparticles, inorganic nanoparticles etc., not only provide stability and controlled release but also enhance mucosal adhesion, effectively overcoming the limitations of conventional vaccines. Hence, in this review, we overview the evaluation of intranasal vaccine and highlight the current barriers. Next, the modern delivery systems based on nanoplatforms are summarized. The challenges in clinical application of nanoplatform based intranasal vaccine are finally discussed.

The Improvement of Adaptive Immune Responses towards COVID-19 Following Diphtheria-Tetanus-Pertussis and SARS-CoV-2 Vaccinations in Indonesian Children: Exploring the Roles of Heterologous Immunity

BACKGROUND

Routine childhood vaccination, e.g., for diphtheria, tetanus, and pertussis (DTP), might provide additional protection against SARS-CoV-2 infection. This concept of heterologous immunity was explored in healthy children receiving both DTP and inactivated SARS-CoV-2 vaccines.

METHODS

A cross-sectional study was performed on 154 healthy children aged 6-8 years old in Jakarta, Indonesia. Their vaccination status for the DTP (including a diphtheria-tetanus booster vaccine at 5 years old) and CoronaVac (from 6 years old) vaccines were recorded. Peripheral blood samples were collected from all participants, in which anti-diphtheria toxoid IgG and anti-SARS-CoV-2 S-RBD antibodies and T cell-derived IFN-γ were measured.

RESULTS

The study participants with complete DTP vaccination had significantly higher titers of anti-diphtheria toxoid IgG than the ones without (median = 0.9349 versus 0.2113 IU/mL; p < 0.0001). Upon stratification based on DTP and CoronaVac vaccination statuses, the participants with complete DTP and CoronaVac vaccinations had the highest titer of anti-SARS-CoV-2 S-RBD antibodies (median = 1196 U/mL) and the highest concentration of SARS-CoV-2-specific T cell-derived IFN-γ (median = 560.9 mIU/mL) among all the groups.

CONCLUSIONS

Healthy children aged 6-8 years old with complete DTP and CoronaVac vaccinations exhibited stronger SARS-CoV-2-specific T cell immune responses. This might suggest an additional benefit of routine childhood vaccination in generating protection against novel pathogens, presumably via heterologous immunity.

Antibody Fc receptor binding and T cell responses to homologous and heterologous immunization with inactivated or mRNA vaccines against SARS-CoV-2

Whole virion inactivated vaccine CoronaVac (C) and Spike (S) mRNA BNT162b2 (B) vaccines differ greatly in their ability to elicit neutralizing antibodies but have somewhat comparable effectiveness in protecting from severe COVID-19. We conducted further analyses for a randomized trial (Cobovax study, NCT05057169) of third dose homologous and heterologous booster vaccination, i.e. four interventions CC-C, CC-B, BB-C and BB-B. Here, we assess vaccine immunogenicity beyond neutralizing function, including S and non-S antibodies with Fc receptor (FcR) binding, antibody avidity and T cell specificity to 6 months post-vaccination. Ancestral and Omicron S-specific IgG and FcR binding are significantly higher by BNT162b2 booster than CoronaVac, regardless of first doses. Nucleocapsid (N) antibodies are only increased in homologous boosted CoronaVac participants (CC-C). CoronaVac primed participants have lower baseline S-specific CD4+ IFNγ+ cells, but are significantly increased by either CoronaVac or BNT162b2 boosters. Priming vaccine content defined T cell peptide specificity preference, with S-specific T cells dominating B primed groups and non-S structural peptides contributing more in C primed groups, regardless of booster type. S-specific CD4+ T cell responses, N-specific antibodies, and antibody effector functions via Fc receptor binding may contribute to protection and compensate for less potent neutralizing responses in CoronaVac recipients.

Safety, Immunogenicity, and Effectiveness of Chinese-Made COVID-19 Vaccines in the Real World: An Interim Report of a Living Systematic Review

Background: Several COVID-19 vaccines were developed and approved in China. Of these, the BIBB-CorV and CoronaVac inactivated whole-virion vaccines were widely distributed in China and developing countries. However, the performance of the two vaccines in the real world has not been summarized. Methods: A living systematic review based on findings from ongoing post-licensure studies was conducted, applying standardized algorithms. Articles published between 1 May 2020 and 31 May 2022 in English and Chinese were searched for in Medline, Embase, WanFang Data, medRxiv, bioRxiv, arXiv, SSRN, and Research Square, using SARS-CoV-2, COVID-19, and vaccine as the MeSH terms. Studies with estimates of safety, immunogenicity, and effectiveness from receiving the BIBB-CorV or CoronaVac vaccine that met the predefined screening criteria underwent a full-text review. The Joanna Briggs Institute's Critical Appraisal Checklist and the Cochrane risk of bias were used for assessment of the quality. A random-effects meta-regression model was applied to identify the potential impact factors on the vaccines' effectiveness. Results: In total, 32578 articles were identified, of these, 770 studies underwent a full-text review. Eventually, 213 studies were included. The pooled occurrence of solicited and unsolicited adverse events after any dose of either vaccine varied between 10% and 40%. The top five commonly reported rare adverse events were immunization stress-related responses (211 cases, 50.0%), cutaneous responses (43 cases, 10.2%), acute neurological syndrome (39 cases, 9.2%), anaphylaxis (17 cases, 4.0%), and acute stroke (16 cases, 3.8%). The majority (83.3%) recovered or were relieved within several days. The peak neutralization titers against the ancestral strain was found within 1 month after the completion of the primary series of either vaccine, with a GMT (geometric mean titer) of 43.7 (95% CI: 23.2-82.4), followed by a dramatic decrease within 3 months. At Month 12, the GMT was 4.1 (95% CI: 3.8-4.4). Homologous boosting could restore humoral immunity, while heterologous boosting elicited around sixfold higher neutralization titers in comparison with homologous boosting. The effectiveness of receiving either vaccine against death and severe disease was around 85% for both shortly after the primary series. At Month 12, the protection against death did not decline, while the protection against severe disease decreased to ~75%. Conclusions: Both the BIBP-CorV and CoronaVac inactivated vaccines are safe. Sustained vaccine effectiveness against death was determined 12 months after the primary series, although protection against severe disease decreased slightly over time. A booster dose could strengthen the waning effectiveness; however, the duration of the incremental effectiveness and the additional benefit provided by a heterologous booster need to be studied.

Harnessing T-Cells for Enhanced Vaccine Development against Viral Infections

Despite significant strides in vaccine research and the availability of vaccines for many infectious diseases, the threat posed by both known and emerging infectious diseases persists. Moreover, breakthrough infections following vaccination remain a concern. Therefore, the development of novel vaccines is imperative. These vaccines must exhibit robust protective efficacy, broad-spectrum coverage, and long-lasting immunity. One promising avenue in vaccine development lies in leveraging T-cells, which play a crucial role in adaptive immunity and regulate immune responses during viral infections. T-cell recognition can target highly variable or conserved viral proteins, and memory T-cells offer the potential for durable immunity. Consequently, T-cell-based vaccines hold promise for advancing vaccine development efforts. This review delves into the latest research advancements in T-cell-based vaccines across various platforms and discusses the associated challenges.

Blended BA.5 infection within 8 days after a boosted bivalent mRNA vaccination strengthens and lengthens the host immunity

The impact of SARS-CoV-2 infection shortly after vaccination on vaccine-induced immunity is unknown, which is also one of the concerns for some vaccinees during the pandemic. Here, based on a cohort of individuals who encountered BA.5 infection within 8 days after receiving the fourth dose of a bivalent mRNA vaccine, preceded by three doses of inactivated vaccines, we show that booster mRNA vaccination provided 48% protection efficacy against symptomatic infections. At Day 7 postvaccination, the level of neutralizing antibodies (Nabs) against WT and BA.5 strains in the uninfected group trended higher than those in the symptomatic infection group. Moreover, there were greater variations in Nabs levels and a significant decrease in virus-specific CD4+ T cell response observed in the symptomatic infection group. However, symptomatic BA.5 infection significantly increased Nab levels against XBB.1.9.1 and BA.5 (symptomatic > asymptomatic > uninfected group) at Day 10 and resulted in a more gradual decrease in Nabs against BA.5 compared to the uninfected group at Day 90. Our data suggest that BA.5 infection might hinder the early generation of Nabs and the recall of the CD4+ T cell response but strengthens the Nab and virus-specific T cell response in the later phase. Our data confirmed that infection can enhance host immunity regardless of the short interval between vaccination and infection and alleviate concerns about infections shortly after vaccination, which provides valuable guidance for developing future vaccine administration strategies.

B-cell and antibody responses to SARS-CoV-2: infection, vaccination, and hybrid immunity

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019 prompted scientific, medical, and biotech communities to investigate infection- and vaccine-induced immune responses in the context of this pathogen. B-cell and antibody responses are at the center of these investigations, as neutralizing antibodies (nAbs) are an important correlate of protection (COP) from infection and the primary target of SARS-CoV-2 vaccine modalities. In addition to absolute levels, nAb longevity, neutralization breadth, immunoglobulin isotype and subtype composition, and presence at mucosal sites have become important topics for scientists and health policy makers. The recent pandemic was and still is a unique setting in which to study de novo and memory B-cell (MBC) and antibody responses in the dynamic interplay of infection- and vaccine-induced immunity. It also provided an opportunity to explore new vaccine platforms, such as mRNA or adenoviral vector vaccines, in unprecedented cohort sizes. Combined with the technological advances of recent years, this situation has provided detailed mechanistic insights into the development of B-cell and antibody responses but also revealed some unexpected findings. In this review, we summarize the key findings of the last 2.5 years regarding infection- and vaccine-induced B-cell immunity, which we believe are of significant value not only in the context of SARS-CoV-2 but also for future vaccination approaches in endemic and pandemic settings.

Can the Revolution in mRNA-Based Vaccine Technologies Solve the Intractable Health Issues of Current Ruminant Production Systems?

To achieve the World Health Organization's global Sustainable Development Goals, increased production of high-quality protein for human consumption is required while minimizing, ideally reducing, environmental impacts. One way to achieve these goals is to address losses within current livestock production systems. Infectious diseases are key limiters of edible protein production, affecting both quantity and quality. In addition, some of these diseases are zoonotic threats and potential contributors to the emergence of antimicrobial resistance. Vaccination has proven to be highly successful in controlling and even eliminating several livestock diseases of economic importance. However, many livestock diseases, both existing and emerging, have proven to be recalcitrant targets for conventional vaccination technologies. The threat posed by the COVID-19 pandemic resulted in unprecedented global investment in vaccine technologies to accelerate the development of safe and efficacious vaccines. While several vaccination platforms emerged as front runners to meet this challenge, the clear winner is mRNA-based vaccination. The challenge now is for livestock industries and relevant stakeholders to harness these rapid advances in vaccination to address key diseases affecting livestock production. This review examines the key features of mRNA vaccines, as this technology has the potential to control infectious diseases of importance to livestock production that have proven otherwise difficult to control using conventional approaches. This review focuses on the challenging diseases of ruminants due to their importance in global protein production. Overall, the current literature suggests that, while mRNA vaccines have the potential to address challenges in veterinary medicine, further developments are likely to be required for this promise to be realized for ruminant and other livestock species.

Dynamic immune landscape in vaccinated-BA.5-XBB.1.9.1 reinfections revealed a 5-month protection-duration against XBB infection and a shift in immune imprinting

BACKGROUND

The impact of previous vaccination on protective immunity, duration, and immune imprinting in the context of BA.5-XBB.1.9.1 reinfection remains unknown.

METHODS

Based on a 2-year longitudinal cohort from vaccination, BA.5 infection and XBB reinfection, several immune effectors, including neutralizing antibodies (Nabs), antibody-dependent cellular cytotoxicity (ADCC), virus-specific T cell immunity were measured to investigate the impact of previous vaccination on host immunity induced by BA.5 breakthrough infection and BA.5-XBB.1.9.1 reinfection.

FINDINGS

In absence of BA.5 Nabs, plasma collected 3 months after receiving three doses of inactivated vaccine (I-I-I) showed high ADCC that protected hACE2-K18 mice from fatality and significantly reduced viral load in the lungs and brain upon BA.5 challenge, compared to plasma collected 12 months after I-I-I. Nabs against XBB.1.9.1 induced by BA.5 breakthrough infection were low at day 14 and decreased to a GMT of 10 at 4 months and 28% (9/32) had GMT ≤4, among whom 67% (6/9) were reinfected with XBB.1.9.1 within 1 month. However, 63% (20/32) were not reinfected with XBB.1.9.1 at 5 months post BA.5 infection. Interestingly, XBB.1.9.1 reinfection increased Nabs against XBB.1.9.1 by 24.5-fold at 14 days post-reinfection, which was much higher than that against BA.5 (7.3-fold) and WT (4.5-fold), indicating an immune imprinting shifting from WT to XBB antigenic side.

INTERPRETATION

Overall, I-I-I can provide protection against BA.5 infection and elicit rapid immune response upon BA.5 infection. Furthermore, BA.5 breakthrough infection effectively protects against XBB.1.9.1 lasting more than 5 months, and XBB.1.9.1 reinfection results in immune imprinting shifting from WT antigen induced by previous vaccination to the new XBB.1.9.1 antigen. These findings strongly suggest that future vaccines should target variant strain antigens, replacing prototype strain antigens.

FUNDING

This study was supported by R&D Program of Guangzhou National Laboratory (SRPG23-005), National Key Research and Development Program of China (2022YFC2604104, 2019YFC0810900), S&T Program of Guangzhou Laboratory (SRPG22-006), and National Natural Science Foundation of China (81971485, 82271801, 81970038), Emergency Key Program of Guangzhou Laboratory (EKPG21-30-3), Zhongnanshan Medical Foundation of Guangdong Province (ZNSA-2020013), and State Key Laboratory of Respiratory Disease (J19112006202304).

Assessment of Human SARS CoV-2-Specific T-Cell Responses Elicited In Vitro by New Computationally Designed mRNA Immunogens (COVARNA)

The COVID-19 pandemic has brought significant changes and advances in the field of vaccination, including the implementation and widespread use of encapsidated mRNA vaccines in general healthcare practice. Here, we present two new mRNAs expressing antigenic parts of the SARS-CoV-2 spike protein and provide data supporting their functionality. The first mRNA, called RBD-mRNA, encodes a trimeric form of the virus spike protein receptor binding domain (RBD). The other mRNA, termed T-mRNA, codes for the relevant HLA I and II spike epitopes. The two mRNAs (COVARNA mRNAs) were designed to be used for delivery to cells in combination, with the RBD-mRNA being the primary source of antigen and the T-mRNA working as an enhancer of immunogenicity by supporting CD4 and CD8 T-cell activation. This innovative approach substantially differs from other available mRNA vaccines, which are largely directed to antibody production by the entire spike protein. In this study, we first show that both mRNAs are functionally transfected into human antigen-presenting cells (APCs). We obtained peripheral blood mononuclear cell (PBMC) samples from three groups of voluntary donors differing in their immunity against SARS-CoV-2: non-infected (naïve), infected-recovered (convalescent), and vaccinated. Using an established method of co-culturing autologous human dendritic cells (hDCs) with T-cells, we detected proliferation and cytokine secretion, thus demonstrating the ability of the COVARNA mRNAs to activate T-cells in an antigen-specific way. Interestingly, important differences in the intensity of the response between the infected-recovered (convalescent) and vaccinated donors were observed, with the levels of T-cell proliferation and cytokine secretion (IFNγ, IL-2R, and IL-13) being higher in the vaccinated group. In summary, our data support the further study of these mRNAs as a combined approach for future use as a vaccine.

Evaluation of immunogenicity-induced DNA vaccines against different SARS-CoV-2 variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 and caused the coronavirus disease 2019 (COVID-19) pandemic worldwide. As of September 2023, the number of confirmed coronavirus cases has reached over 770 million and caused nearly 7 million deaths. The World Health Organization assigned and informed the characterization of variants of concern (VOCs) to help control the COVID-19 pandemic through global monitoring of circulating viruses. Although many vaccines have been proposed, developing an effective vaccine against variants is still essential to reach the endemic stage of COVID-19. We designed five DNA vaccine candidates composed of the first isolated genotype and major SARS-CoV-2 strains from isolated Korean patients classified as VOCs, such as Alpha, Beta, Gamma, and Delta. To evaluate the immunogenicity of each genotype via homologous and heterologous vaccination, mice were immunized twice within a 3-week interval, and the blood and spleen were collected 1 week after the final vaccination to analyze the immune responses. The group vaccinated with DNA vaccine candidates based on the S genotype and the Alpha and Beta variants elicited both humoral and cellular immune responses, with higher total IgG levels and neutralizing antibody responses than the other groups. In particular, the vaccine candidate based on the Alpha variant induced a highly diverse cytokine response. Additionally, we found that the group subjected to homologous vaccination with the S genotype and heterologous vaccination with S/Alpha induced high total IgG levels and a neutralization antibody response. Homologous vaccination with the S genotype and heterologous vaccination with S/Alpha and S/Beta significantly induced IFN-γ immune responses. The immunogenicity after homologous vaccination with S and Alpha and heterologous vaccination with the S/Alpha candidate was better than that of the other groups, indicating the potential for developing novel DNA vaccines against different SARS-CoV-2 variants.

Antibody Response to SARS-CoV-2 Vaccination in Patients with End-Stage Kidney Disease on Hemodialysis

Patients with end-stage kidney disease on hemodialysis (ESKD-HD) have a high risk of contracting severe COVID-19. Vaccination can help reduce disease severity, but the immune dysregulation observed in these patients may result in an inadequate antibody response. Therefore, we aimed to evaluate the immune response postvaccination in ESKD-HD patients. This prospective cohort study was conducted in two hemodialysis centers in Indonesia. We enrolled ESKD-HD patients (n = 143) pre- and postvaccination and compared them to healthy subjects (n = 67). SARS-CoV-2 antibody response was assessed using anti-S-RBD antibodies and SVNT % inhibition tests. We performed bivariate and multivariate analysis to determine factors associated with SARS-CoV-2 antibody levels. Seropositive conversion was observed in 97% ESKD-HD subjects postvaccination. Compared with healthy subjects, ESKD-HD patients showed a comparable anti-S-RBD antibody titer postvaccination. mRNA vaccines remained a significant factor for the high immune response, while hypoalbuminemia correlated with lower immune response. In conclusion, ESKD-HD patients showed a robust immune response postvaccination. mRNA vaccines induced a stronger antibody response than other vaccines. Lower levels of serum albumin correlate with lower immune responses in ESKD-HD patients after vaccination.

T cell immune memory after covid-19 and vaccination

The T cell memory response is a crucial component of adaptive immunity responsible for limiting or preventing viral reinfection. T cell memory after infection with the SARS-CoV-2 virus or vaccination is broad, and spans multiple viral proteins and epitopes, about 20 in each individual. So far the T cell memory response is long lasting and provides a high level of cross reactivity and hence resistance to viral escape by variants of the SARS-CoV-2 virus, such as the omicron variant. All current vaccine regimens tested produce robust T cell memory responses, and heterologous regimens will probably enhance protective responses through increased breadth. T cell memory could have a major role in protecting against severe covid-19 disease through rapid viral clearance and early presentation of epitopes, and the presence of cross reactive T cells might enhance this protection. T cell memory is likely to provide ongoing protection against admission to hospital and death, and the development of a pan-coronovirus vaccine might future proof against new pandemic strains.

Engineering immunosuppressive drug-resistant armored (IDRA) SARS-CoV-2 T cells for cell therapy

Solid organ transplant (SOT) recipients receive immunosuppressive drugs (ISDs) and are susceptible to developing severe COVID-19. Here, we analyze the Spike-specific T-cell response after 3 doses of mRNA vaccine in a group of SOT patients (n = 136) treated with different ISDs. We demonstrate that a combination of a calcineurin inhibitor (CNI), mycophenolate mofetil (MMF), and prednisone (Pred) treatment regimen strongly suppressed the mRNA vaccine-induced Spike-specific cellular response. Such defects have clinical consequences because the magnitude of vaccine-induced Spike-specific T cells was directly proportional to the ability of SOT patients to rapidly clear SARS-CoV-2 after breakthrough infection. To then compensate for the T-cell defects induced by immunosuppressive treatment and to develop an alternative therapeutic strategy for SOT patients, we describe production of 6 distinct SARS-CoV-2 epitope-specific ISD-resistant T-cell receptor (TCR)-T cells engineered using the mRNA electroporation method with reactivity minimally affected by mutations occurring in Beta, Delta, Gamma, and Omicron variants. This strategy with transient expression characteristics marks an improvement in the immunotherapeutic field and provides an attractive and novel therapeutic possibility for immunosuppressed COVID-19 patients.

Immunity Induced by Inactivated SARS-CoV-2 Vaccine: Breadth, Durability, Potency, and Specificity in a Healthcare Worker Cohort

Vaccination has proven to be highly effective against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the long-term immunogenicity and the functional preserved immune responses of vaccines are needed to inform evolving evidence-based guidelines for boosting schedules. We enrolled 205 healthcare workers into a cohort study; all had received three doses of BBIBP-CorV (China Sinopharm Bio-Beijing Company, Beijing, China) inactivated vaccine. We assessed SARS-CoV-2 specific binding antibodies, neutralizing antibodies, and peripheral T and B cell responses. We demonstrated that more robust antibody responses to SARS-CoV-2 were elicited by booster immunization compared with primary vaccination. Neutralizing antibody titers to SARS-CoV-2 Omicron BA.1 were also efficiently elevated post-homologous vaccine booster despite being in a lower titer compared with the prototype stain. In addition to S-specific humoral and cellular immunity, BBIBP-CorV also induced N-specific antibody and effector T cell responses. The third-dose vaccination led to further expansion of critical polyfunctional T cell responses, likely an essential element for vaccine protection. In particular, a functional role for Tfh cell subsets in immunity was suggested by the correlation between both CD4+ Tfh and CD8+ Tfh with total antibody, IgG, B cell responses, and neutralizing antibodies. Our study details the humoral and cellular responses generated by the BBIBP-CorV booster vaccination in a seven-month follow-up study. There is a clear immunologic boosting value of homologous inactivated SARS-CoV-2 vaccine boosters, a consideration for future vaccine strategies.

Polyfunctional CD4 T-cells correlating with neutralising antibody is a hallmark of COVISHIELDTM and COVAXIN® induced immunity in COVID-19 exposed Indians

Detailed characterisation of immune responses induced by COVID-19 vaccines rolled out in India: COVISHIELDTM (CS) and COVAXIN® (CO) in a pre-exposed population is only recently being discovered. We addressed this issue in subjects who received their primary series of vaccination between November 2021 and January 2022. Both vaccines are capable of strongly boosting Wuhan Spike-specific neutralising antibody, polyfunctional Th1 cytokine producing CD4+ T-cells and single IFN-γ + CD8+ T-cells. Consistent with inherent differences in vaccine platform, the vector-based CS vaccine-induced immunity was of greater magnitude, breadth, targeting Delta and Omicron variants compared to the whole-virion inactivated vaccine CO, with CS vaccinees showing persistent CD8+ T-cells responses until 3 months post primary vaccination. This study provides detailed evidence on the magnitude and quality of CS and CO vaccine induced responses in subjects with pre-existing SARS-CoV-2 immunity in India, thereby mitigating vaccine hesitancy arguments in such a population, which remains a global health challenge.

Longitudinal analysis of memory Tfh cells and antibody response following CoronaVac vaccination

The inactivated vaccine CoronaVac is one of the most widely used COVID-19 vaccines globally. However, the longitudinal evolution of the immune response induced by CoronaVac remains elusive compared with other vaccine platforms. Here, we recruited 88 healthy individuals who received 3 doses of CoronaVac vaccine. We longitudinally evaluated their polyclonal and antigen-specific CD4+ T cells and neutralizing antibody response after receiving each dose of vaccine for over 300 days. Both the second and third doses of vaccine induced robust spike-specific neutralizing antibodies, with a third vaccine further increasing the overall magnitude of antibody response and neutralization against Omicron sublineages B.1.1.529, BA.2, BA.4/BA.5, and BA.2.75.2. Spike-specific CD4+ T cells and circulating T follicular helper (cTfh) cells were markedly increased by the second and third dose of CoronaVac vaccine, accompanied by altered composition of functional cTfh cell subsets with distinct effector and memory potential. Additionally, cTfh cells were positively correlated with neutralizing antibody titers. Our results suggest that CoronaVac vaccine-induced spike-specific T cells are capable of supporting humoral immunity for long-term immune protection.

Seeing the T cell Immunity of SARS-CoV-2 and SARS-CoV: Believing the Epitope-Oriented Vaccines

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the end of 2019 stimulated vigorous research efforts in immunology and vaccinology. In addition to innate immune responses, both virus-specific humoral and cellular immune responses are of importance for viral clearance. T cell epitopes play a central role in T cell-based immune responses. Herein, we summarized the peptide/major histocompatibility complex (pMHC) structures of the SARS-CoV-2-derived T cell epitopes available in the Protein Data Bank (PDB) and proposed the challenge and opportunities for using of T cell epitopes in future vaccine development efforts. A total of 27 SARS-CoV-2 related pMHC structures and five complexes with T cell receptors were retrieved. The peptides are mainly distributed on spike (S), nucleocapsid (N), and ORF1ab proteins. Most peptides are conserved among variants of concerns (VOCs) for SARS-CoV-2, except for several mutated peptides located in the S protein. The structures of human leukocyte antigen (HLA) complexed with seven epitopes derived from SARS-CoV were also retrieved, which showed a potential cross T cell immunity with SARS-CoV-2. Structural studies of antigenic peptides from SARS-CoV-2 and SARS-CoV help to visualize the processes and the mechanisms of cross T cell immunity. T cell epitope-oriented vaccines are potential next-generation vaccines for SARS-CoV-2, which are worthy of further investigation.

Immunogenicity of Mix-and-Match CoronaVac/BNT162b2 Regimen versus Homologous CoronaVac/CoronaVac Vaccination: A Single-Blinded, Randomized, Parallel Group Superiority Trial

(1) Background: This study aimed to compare the immunogenicity of the mix-and-match CoronaVac/BNT162b2 vaccination to the homologous CoronaVac/CoronaVac regimen. (2) Methods: We conducted a simple-blinded randomized superiority trial to measure SARS-CoV-2 neutralization antibodies and anti-spike receptor binding domain (RBD) IgG concentrations in blood samples of participants who had received the first dose of CoronaVac vaccine followed by a dose of BNT162b2 or CoronaVac vaccine. The primary endpoint for immunogenicity was the serum-neutralizing antibody level with a percentage of inhibition at 90% at 21-35 days after the boost. A difference of 25% between groups was considered clinically relevant. (3) Results: Among the 240 eligible participants, the primary endpoint data were available for 100 participants randomly allocated to the mix-and-match group versus 99 participants randomly allocated to the homologous dose group. The mix-and-match regimen elicited significantly higher levels of neutralizing antibodies (median level of 96%, interquartile range (IQR) (95-97) versus median level of 94%, IQR (81-96) and anti-spike IgG antibodies (median level of 13,460, IQR (2557-29,930) versus median level of 1190, IQR (347-4964) compared to the homologous group. Accordingly, the percentage of subjects with a percentage of neutralizing antibodies > 90% was significantly higher in the mix-and-match group (90.0%) versus the homologous (60.6%). Interestingly, no severe events were reported within 30 days after the second dose of vaccination in both groups. (4) Conclusions: Our data showed the superiority of the mix-and-match CoronaVac/BNT162b2 vaccination compared to the CoronaVac/CoronaVac regimen in terms of immunogenicity, thus constituting a proof-of-concept study supporting the use of inactivated vaccines in a mix-and-match strategy while ensuring good immunogenicity and safety.

T-cell immunity to SARS-CoV-2: what if the known best is not the optimal course for the long run? Adapting to evolving targets

Humanity did surprisingly well so far, considering how unprepared it was to respond to the coronavirus disease 2019 (COVID-19) threat. By blending old and ingenious new technology in the context of the accumulated knowledge on other human coronaviruses, several vaccine candidates were produced and tested in clinical trials in record time. Today, five vaccines account for the bulk of the more than 13 billion doses administered worldwide. The ability to elicit biding and neutralizing antibodies most often against the spike protein is a major component of the protection conferred by immunization but alone it is not enough to limit virus transmission. Thus, the surge in numbers of infected individuals by newer variants of concern (VOCs) was not accompanied by a proportional increase in severe disease and death rate. This is likely due to antiviral T-cell responses, whose evasion is more difficult to achieve. The present review helps navigating the very large literature on T cell immunity induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and vaccination. We examine the successes and shortcomings of the vaccinal protection in the light of the emergence of VOCs with breakthrough potential. SARS-CoV-2 and human beings will likely coexist for a long while: it will be necessary to update existing vaccines to improve T-cell responses and attain better protection against COVID-19.

Comparing T- and B-cell responses to COVID-19 vaccines across varied immune backgrounds

The emergence of adapted variants of the SARS-CoV-2 virus has led to a surge in breakthrough infections worldwide. A recent analysis of immune responses in people who received inactivated vaccines has revealed that individuals with no prior infection have limited resistance to Omicron and its sub-lineages, while those with previous infections exhibit a significant amount of neutralizing antibodies and memory B cells. However, specific T-cell responses remain largely unaffected by the mutations, indicating that T-cell-mediated cellular immunity can still provide protection. Moreover, the administration of a third dose of vaccine has resulted in a marked increase in the spectrum and duration of neutralizing antibodies and memory B cells in vivo, which has enhanced resistance to emerging variants such as BA.2.75 and BA.2.12.1. These results highlight the need to consider booster immunization for previously infected individuals and the development of novel vaccination strategies. The rapid spread of adapted variants of the SARS-CoV-2 virus presents a significant challenge to global health. The findings from this study underscore the importance of tailoring vaccination strategies based on individual immune backgrounds and the potential need for booster shots to combat emerging variants. Continued research and development are crucial to discovering new immunization strategies that will effectively protect public health against the evolving virus.

Blood unconjugated bilirubin and tacrolimus are negative predictors of specific cellular immunity in kidney transplant recipients after SAR-CoV-2 inactivated vaccination

The immunogenicity of SARS-CoV-2 vaccines is poor in kidney transplant recipients (KTRs). The factors related to poor immunogenicity to vaccination in KTRs are not well defined. Here, observational study demonstrated no severe adverse effects were observed in KTRs and healthy participants (HPs) after first or second dose of SARS-CoV-2 inactivated vaccine. Different from HPs with excellent immunity against SARS-CoV-2, IgG antibodies against S1 subunit of spike protein, receptor-binding domain, and nucleocapsid protein were not effectively induced in a majority of KTRs after the second dose of inactivated vaccine. Specific T cell immunity response was detectable in 40% KTRs after the second dose of inactivated vaccine. KTRs who developed specific T cell immunity were more likely to be female, and have lower levels of total bilirubin, unconjugated bilirubin, and blood tacrolimus concentrations. Multivariate logistic regression analysis found that blood unconjugated bilirubin and tacrolimus concentration were significantly negatively associated with SARS-CoV-2 specific T cell immunity response in KTRs. Altogether, these data suggest compared to humoral immunity, SARS-CoV-2 specific T cell immunity response are more likely to be induced in KTRs after administration of inactivated vaccine. Reduction of unconjugated bilirubin and tacrolimus concentration might benefit specific cellular immunity response in KTRs following vaccination.

Immunodominant SARS-CoV-2-specific CD4+ and CD8+ T-cell responses elicited by inactivated vaccines in healthy adults

Safety profiles and humoral responses to inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines have been previously assessed, but cellular immune responses to inactivated SARS-CoV-2 vaccines remain understudied. Here, we report the comprehensive characteristics of SARS-CoV-2-specific CD4⁺ and CD8⁺ T-cell responses elicited by the BBIBP-CorV vaccine. A total of 295 healthy adults were recruited, and SARS-CoV-2-specific T-cell responses were detected after stimulation with overlapping peptide pools spanning the entire length of the envelope (E), membrane (M), nucleocapsid (N), and spike (S) proteins. Robust and durable CD4⁺ (p < 0.0001) and CD8⁺ (p < 0.0001) T-cell responses specific to SARS-CoV-2 were detected following the third vaccination, with an increase in specific CD8⁺ T-cells, compared to CD4⁺ T-cells. Cytokine profiles showed that interferon gamma and tumor necrosis factor-α were predominantly expressed with the negligible expression of interleukin (IL)-4 and IL-10, indicating a Th1- or Tc1-biased response. Compared to E and M proteins, N and S activated a higher proportion of specific T-cells with broader functions. The predominant frequency of the N antigen (49/89) was highest for CD4⁺ T-cell immunity. Furthermore, N_19-36 and N_391-408 were identified to contain dominant CD8⁺ and CD4⁺ T-cell epitopes, respectively. In addition, N_19-36 -specific CD8⁺ T-cells were mainly effector memory CD45RA cells, whereas N_391-408 -specific CD4⁺ T-cells were mainly effector memory cells. Therefore, this study reports comprehensive features of T-cell immunity induced by the inactivated SARS-CoV-2 vaccine BBIBP-CorV and proposes highly conserved candidate peptides which may be beneficial in vaccine optimization.

Study of the Effects of Several SARS-CoV-2 Structural Proteins on Antiviral Immunity

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike (S) protein is a critical viral antigenic protein that enables the production of neutralizing antibodies, while other structural proteins, including the membrane (M), nucleocapsid (N) and envelope (E) proteins, have unclear roles in antiviral immunity. In this study, S1, S2, M, N and E proteins were expressed in 16HBE cells to explore the characteristics of the resultant innate immune response. Furthermore, peripheral blood mononuclear cells (PBMCs) from mice immunized with two doses of inactivated SARS-CoV-2 vaccine or two doses of mRNA vaccine were isolated and stimulated by these five proteins to evaluate the corresponding specific T-cell immune response. In addition, the levels of humoral immunity induced by two-dose inactivated vaccine priming followed by mRNA vaccine boosting, two homologous inactivated vaccine doses and two homologous mRNA vaccine doses in immunized mice were compared. Our results suggested that viral structural proteins can activate the innate immune response and elicit a specific T-cell response in mice immunized with the inactivated vaccine. However, the existence of the specific T-cell response against M, N and E is seemingly insufficient to improve the level of humoral immunity.

Design and preclinical evaluation of a universal SARS-CoV-2 mRNA vaccine

Because of the rapid mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an effective vaccine against SARS-CoV-2 variants is needed to prevent coronavirus disease 2019 (COVID-19). T cells, in addition to neutralizing antibodies, are an important component of naturally acquired protective immunity, and a number of studies have shown that T cells induced by natural infection or vaccination contribute significantly to protection against several viral infections including SARS-CoV-2. However, it has never been tested whether a T cell-inducing vaccine can provide significant protection against SARS-CoV-2 infection in the absence of preexisting antibodies. In this study, we designed and evaluated lipid nanoparticle (LNP) formulated mRNA vaccines that induce only T cell responses or both T cell and neutralizing antibody responses by using two mRNAs. One mRNA encodes SARS-CoV-2 Omicron Spike protein in prefusion conformation for induction of neutralizing antibodies. The other mRNA encodes over one hundred T cell epitopes (multi-T cell epitope or MTE) derived from non-Spike but conserved regions of the SARS-CoV-2. We show immunization with MTE mRNA alone protected mice from lethal challenge with the SARS-CoV-2 Delta variant or a mouse-adapted virus MA30. Immunization with both mRNAs induced the best protection with the lowest viral titer in the lung. These results demonstrate that induction of T cell responses, in the absence of preexisting antibodies, is sufficient to confer protection against severe disease, and that a vaccine containing mRNAs encoding both the Spike and MTE could be further developed as a universal SARS-CoV-2 vaccine.

Adaptive immune responses and cytokine immune profiles in humans following prime and boost vaccination with the SARS-CoV-2 CoronaVac vaccine

BACKGROUND

Adaptive immune response has been thought to play a key role in SARS-CoV-2 infection. The role of B cells, CD4+T, and CD8+T cells are different in vaccine-induced immune response, thus it is imperative to explore the functions and kinetics of adaptive immune response. We collected blood samples from unvaccinated and vaccinated individuals. To assess the mechanisms contributing to protective immunity of CoronaVac vaccines, we mapped the kinetics and durability of humoral and cellular immune responses after primary and boost vaccination with CoronaVac vaccine in different timepoints.

MATERIALS AND METHODS

We separate PBMC and plasma from blood samples. The differentiation and function of RBD-spcific CD4+T and CD8+T cells were analyzed by flow cytometry and ELISA. Antibodies response was analyzed by ELISA. ELISPOT analysis was perfomed to detected the RBD-spcific memory B cells. CBA analysis was performed to detected the cytokine immune profiles. Graphpad prism 8 and Origin 2021 were used for statistical analysis.

RESULTS

Vaccine-induced CD4+T cell responses to RBD were more prominent than CD8+T cell responses, and characterized by a predominant Th1 and weak Th17 helper response. CoronaVac vaccine triggered predominant IgG1 antibody response and effectively recalled specific antibodies to RBD protein after booster vaccination. Robust antigen-specific memory B cells were detected (p < 0.0001) following booster vaccination and maintained at 6 months (p < 0.0001) following primary vaccination. Vaccine-induced CD4+T cells correlated with CD8+T cells (r = 0.7147, 0.3258, p < 0.0001, p = 0.04), memory B cell responses (r = 0.7083, p < 0.0001), and IgG and IgA (r = 0.6168, 0.5519, p = 0.0006, 0.003) after vaccination. In addition, vaccine induced a broader and complex cytokine pattern in plasma at early stage.

CONCLUSION

Taken together, these results highlight the potential role of B cell and T cell responses in vaccine-induced long-term immunity.