Adjuvanted SARS-CoV-2 spike protein vaccination elicits long-lived plasma cells in nonhuman primates

Individuals Infected with SARS-CoV-2 Prior to COVID-19 Vaccination Maintain Vaccine-Induced RBD-Specific Antibody Levels and Viral Neutralization Activity for One Year

The effectiveness of multiple COVID-19 vaccinations in individuals with a history of SARS-CoV-2 infection remains unclear; specifically, elucidation of the durability of anti-viral antibody responses could provide important insights for epidemiological applications. We utilized the BU ELISA protocol to measure the circulating SARS-CoV-2 receptor-binding domain (RBD) and nucleocapsid (N) specific IgG and IgA antibody levels in a cohort of individuals infected with SARS-CoV-2 in the spring of 2020, with the sample collection spanning six months to two years post-symptom onset. Further, we interrogated the neutralization activity of these samples against the ancestral SARS-CoV-2 (WA-1) and Delta and Omicron (BA.1) variants. Consistent with previous studies, we found a more rapid waning of anti-N compared to anti-RBD antibodies in months prior to the first vaccinations. Vaccine-induced antibody responses in individuals previously infected with SARS-CoV-2 were elevated and sustained for more than one year post-vaccination. Similarly, neutralization activity against WA-1, Delta, and Omicron increased and remained higher than pre-vaccination levels for one year after the first COVID-19 vaccine dose. Collectively, these results indicate that infection followed by vaccination yields robust antibody responses against SARS-CoV-2 that endure for one year. These results suggest that an annual booster would stably boost anti-SARS-CoV-2 antibody responses, preventing infection and disease.

A Versatile High-Throughput Single-Cell Screening Platform for Profiling Antigen-Specific Long-Lived B Cells in Blood and Bone Marrow

Antigen-specific B cells play a crucial role in the long-term immune response following infection or vaccination, differentiating into antibody-secreting cells (ASCs) and memory B cells (MBCs). However, profiling ASCs is challenging primarily due to their lack of membrane-bound surface B cell receptors. In this study, the Modular Superhydrophobic Microwell Array Chip (MoSMAR-chip) is introduced as a versatile, cost-effective, and high-throughput platform for identifying and characterizing individual antigen-specific ASCs and MBCs at the single-cell level within seven days. Using this platform, comprehensive analyses of single ASCs could be performed from bone marrows of coronavirus disease 2019 (COVID-19) vaccine-immunized mice and a diverse set of antibodies capable of neutralizing the highly divergent JN1 variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were identified. These results demonstrate that the MoSMAR-chip facilitates efficient single-cell multi-omics and functional analyses of antigen-specific ASCs, offering a powerful tool for investigating complex long-term B cell immunity in diverse clinical conditions, such as infectious diseases, autoimmunity, and beyond.

Elucidating the molecular docking and binding dynamics of aptamers with spike proteins across SARS-CoV-2 variants of concern

DNA aptamers with high binding affinity against SARS-CoV-2 spike proteins have been selected and analyzed. To better understand the binding affinities between DNA aptamers and spike proteins (S-proteins) of relevant variants of concerns (VOCs), in silico and in vitro characterization are excellent approaches to implement. Here, we identified and generated DNA aptamer sequences targeting the S-protein of SARS-CoV-2 VOCs through systematic evolution of ligands by exponential enrichment (SELEX). In silico, prediction of aptamer binding was conducted, followed by a step-by-step workflow for secondary and tertiary aptamer structures determination, modeling, and molecular docking to target S-protein. The in silico strategy was limited to only providing predictions of possible outcomes based on scores, and ranking was complemented by characterization and analysis of identified DNA aptamers using a direct enzyme-linked oligonucleotides assay (ELONA), which showed dissociation constants (K d) within the 32 nM-193 nM range across the three significant VOCs. These three highly specific VOCs aptamers (Alpha Apt, Delta Apt, and Omicron Apt) can be further studied as potential candidates for both diagnostic and therapeutic applications.

SARS-CoV-2-specific plasma cells are not durably established in the bone marrow long-lived compartment after mRNA vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccines are effective at protecting from severe disease, but the protective antibodies wane rapidly even though SARS-CoV-2-specific plasma cells can be found in the bone marrow (BM). Here, to explore this paradox, we enrolled 19 healthy adults at 2.5-33 months after receipt of a SARS-CoV-2 mRNA vaccine and measured influenza-, tetanus- or SARS-CoV-2-specific antibody-secreting cells (ASCs) in long-lived plasma cell (LLPC) and non-LLPC subsets within the BM. Only influenza- and tetanus-specific ASCs were readily detected in the LLPCs, whereas SARS-CoV-2 specificities were mostly absent. The ratios of non-LLPC:LLPC for influenza, tetanus and SARS-CoV-2 were 0.61, 0.44 and 29.07, respectively. In five patients with known PCR-proven history of recent infection and vaccination, SARS-CoV-2-specific ASCs were mostly absent from the LLPCs. We show similar results with measurement for secreted antibodies from BM ASC culture supernatant. While serum IgG titers specific for influenza and tetanus correlated with IgG LLPCs, serum IgG levels for SARS-CoV-2, which waned within 3-6 months after vaccination, were associated with IgG non-LLPCs. In all, our studies suggest that rapid waning of SARS-CoV-2-specific serum antibodies could be accounted for by the absence of BM LLPCs after these mRNA vaccines.

Nanoparticle containing recombinant excretory/secretory-24 protein of Haemonchus contortus enhanced the cellular immune responses in mice

Haemonchus contortus poses a global challenge as a parasite affecting small ruminants, yet the problem of absence of an effective vaccine against H. contortus infection still exists. This investigation sought to appraise the immunological reaction induced by recombinant H. contortus excretory/secretory-24 (rHcES-24) in combination with complete Freund's adjuvant (CFA) and bio-polymeric nanoparticles (NPs) within a murine model. In this study, rHcES-24 was encapsulated in poly(d, l-lactide-co-glycolide) (PLGA) and chitosan (CS) NPs, administered subcutaneously to mice. Researchers analyzed the NPs using scanning electron microscope (SEM) and assessed lymphocyte proliferation, specific antibodies, cytokines, T cell proliferation (CD3e+CD4+, CD3e+CD8a+), and phenotypic alteration in splenocytes (CD11c+CD83+, CD11c+CD86+) through flow cytometry to understand the immune response. The results demonstrated that the administration of nanovaccines (NVs) prompted immune responses towards Th1 pathway. This was indicated by notable enhancements in the production of specific antibodies, heightened cytokine levels, and a robust proliferation of lymphocytes observed in mice that received the NVs compared to control groups. Remarkably, mice vaccinated with the antigen-loaded NPs formulations exhibited considerably higher proportions of splenic dendritic cells (DCs) and T cells in comparison to those receiving the traditional adjuvant or the control groups. Incorporating HcES-24 protein into NPs effectively conferred immunity against H. contortus, paving the way for developing a targeted and commercial vaccine.

Aggravating mechanisms from COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces immune-mediated diseases. The pathophysiology of COVID-19 uses the following three mechanisms: (1) inflammasome activation mechanism; (2) cGAS-STING signaling mechanism; and (3) SAMHD1 tetramerization mechanism, which leads to IFN-I production. Interactions between the host and virus govern induction, resulting in multiorgan impacts. The NLRP3 with cGAS-STING constitutes the primary immune response. The expression of SARS-CoV-2 ORF3a, NSP6, NSP7, and NSP8 blocks innate immune activation and facilitates virus replication by targeting the RIG-I/MDA5, TRIF, and cGAS-STING signaling. SAMHD1 has a target motif for CDK1 to protect virion assembly, threonine 592 to modulate a catalytically active tetramer, and antiviral IFN responses to block retroviral infection. Plastic and allosteric nucleic acid binding of SAMHD1 modulates the antiretroviral activity of SAMHD1. Therefore, inflammasome activation, cGAS-STING signaling, and SAMHD1 tetramerization explain acute kidney injury, hepatic, cardiac, neurological, and gastrointestinal injury of COVID-19. It might be necessary to effectively block the pathological courses of diverse diseases.

Multi-compartmental diversification of neutralizing antibody lineages dissected in SARS-CoV-2 spike-immunized macaques

The continued evolution of SARS-CoV-2 underscores the need to understand qualitative aspects of the humoral immune response elicited by spike immunization. Here, we combine monoclonal antibody (mAb) isolation with deep B cell receptor (BCR) repertoire sequencing of rhesus macaques immunized with prefusion-stabilized spike glycoprotein. Longitudinal tracing of spike-sorted B cell lineages in multiple immune compartments demonstrates increasing somatic hypermutation and broad dissemination of vaccine-elicited B cells in draining and non-draining lymphoid compartments, including the bone marrow, spleen and, most notably, periaortic lymph nodes. Phylogenetic analysis of spike-specific monoclonal antibody lineages identified through deep repertoire sequencing delineates extensive intra-clonal diversification that shaped neutralizing activity. Structural analysis of the spike in complex with a broadly neutralizing mAb provides a molecular basis for the observed differences in neutralization breadth between clonally related antibodies. Our findings highlight that immunization leads to extensive intra-clonal B cell evolution where members of the same lineage can both retain the original epitope specificity and evolve to recognize additional spike variants not previously encountered.

Basic implications on three pathways associated with SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) interacts between the host and virus and govern induction, resulting in multiorgan impacts. Its pathophysiology involves the followings: 1) the angiotensin-converting enzyme (ACE2) and Toll-like receptor (TLR) pathways: 2) the neuropilin (NRP) pathway: 3) the spike protein pathway. Therefore, it is necessary to block the pathological course with modulating innate lymphoid cells against diverse corona variants in the future.

Vaccine adjuvants: Tailoring innate recognition to send the right message

Adjuvants play pivotal roles in vaccine development, enhancing immunization efficacy through prolonged retention and sustained release of antigen, lymph node targeting, and regulation of dendritic cell activation. Adjuvant-induced activation of innate immunity is achieved via diverse mechanisms: for example, adjuvants can serve as direct ligands for pathogen recognition receptors or as inducers of cell stress and death, leading to the release of immunostimulatory-damage-associated molecular patterns. Adjuvant systems increasingly stimulate multiple innate pathways to induce greater potency. Increased understanding of the principles dictating adjuvant-induced innate immunity will subsequently lead to programming specific types of adaptive immune responses. This tailored optimization is fundamental to next-generation vaccines capable of inducing robust and sustained adaptive immune memory across different cohorts.

The Majority of SARS-CoV-2 Plasma Cells are Excluded from the Bone Marrow Long-Lived Compartment 33 Months after mRNA Vaccination

The goal of any vaccine is to induce long-lived plasma cells (LLPC) to provide life-long protection. Natural infection by influenza, measles, or mumps viruses generates bone marrow (BM) LLPC similar to tetanus vaccination which affords safeguards for decades. Although the SARS-CoV-2 mRNA vaccines protect from severe disease, the serologic half-life is short-lived even though SARS-CoV-2-specific plasma cells can be found in the BM. To better understand this paradox, we enrolled 19 healthy adults at 1.5-33 months after SARS-CoV-2 mRNA vaccine and measured influenza-, tetanus-, or SARS-CoV-2-specific antibody secreting cells (ASC) in LLPC (CD19-) and non-LLPC (CD19+) subsets within the BM. All individuals had IgG ASC specific for influenza, tetanus, and SARS-CoV-2 in at least one BM ASC compartment. However, only influenza- and tetanus-specific ASC were readily detected in the LLPC whereas SARS-CoV-2 specificities were mostly excluded. The ratios of non-LLPC:LLPC for influenza, tetanus, and SARS-CoV-2 were 0.61, 0.44, and 29.07, respectively. Even in five patients with known PCR-proven history of infection and vaccination, SARS-CoV-2-specific ASC were mostly excluded from the LLPC. These specificities were further validated by using multiplex bead binding assays of secreted antibodies in the supernatants of cultured ASC. Similarly, the IgG ratios of non-LLPC:LLPC for influenza, tetanus, and SARS-CoV-2 were 0.66, 0.44, and 23.26, respectively. In all, our studies demonstrate that rapid waning of serum antibodies is accounted for by the inability of mRNA vaccines to induce BM LLPC.

The Majority of SARS-CoV-2 Plasma Cells are Excluded from the Bone Marrow Long-Lived Compartment 33 Months after mRNA Vaccination

The goal of any vaccine is to induce long-lived plasma cells (LLPC) to provide life-long protection. Natural infection by influenza, measles, or mumps viruses generates bone marrow (BM) LLPC similar to tetanus vaccination which affords safeguards for decades. Although the SARS-CoV-2 mRNA vaccines protect from severe disease, the serologic half-life is short-lived even though SARS-CoV-2-specific plasma cells can be found in the BM. To better understand this paradox, we enrolled 19 healthy adults at 1.5-33 months after SARS-CoV-2 mRNA vaccine and measured influenza-, tetanus-, or SARS-CoV-2-specific antibody secreting cells (ASC) in LLPC (CD19 - ) and non-LLPC (CD19 + ) subsets within the BM. All individuals had IgG ASC specific for influenza, tetanus, and SARS-CoV-2 in at least one BM ASC compartment. However, only influenza- and tetanus-specific ASC were readily detected in the LLPC whereas SARS-CoV-2 specificities were mostly excluded. The ratios of non-LLPC:LLPC for influenza, tetanus, and SARS-CoV-2 were 0.61, 0.44, and 29.07, respectively. Even in five patients with known PCR-proven history of infection and vaccination, SARS-CoV-2-specific ASC were mostly excluded from the LLPC. These specificities were further validated by using multiplex bead binding assays of secreted antibodies in the supernatants of cultured ASC. Similarly, the IgG ratios of non-LLPC:LLPC for influenza, tetanus, and SARS-CoV-2 were 0.66, 0.44, and 23.26, respectively. In all, our studies demonstrate that rapid waning of serum antibodies is accounted for by the inability of mRNA vaccines to induce BM LLPC.

The durability of vaccine-induced protection: an overview

INTRODUCTION

Current vaccines vary widely in both their efficacy against infection and disease, and the durability of the efficacy. Some vaccines provide practically lifelong protection with a single dose, while others provide only limited protection following annual boosters. What variables make vaccine-induced immune responses last? Can breakthroughs in these factors and technologies help us produce vaccines with better protection and fewer doses? The durability of vaccine-induced protection is now a hot area in vaccinology research, especially after COVID-19 vaccines lost their luster. It has fueled discussion on the eventual utility of existing vaccines to society and bolstered the anti-vaxxer camp. To sustain public trust in vaccines, lasting vaccines must be developed.

AREAS COVERED

This review summarizes licensed vaccines' protection. It analyses immunological principles and vaccine and vaccinee parameters that determine longevity of antibodies. The review concludes with challenges and the way forward to improve vaccine durability.

EXPERT OPINION

Despite enormous advances, we still lack essential markers and reliable correlates of lasting protection. Most research has focused on humoral immune responses, but we must also focus on innate, mucosal, and cellular responses - their assessment, correlates, determinants, and novel adjuvants. Suitable vaccine designs and platforms for durable immunity must be found.