SARS-CoV-2 protein ORF8 limits expression levels of Spike antigen and facilitates immune evasion of infected host cells

Recovery from COVID-19 depends on the ability of the host to effectively neutralize virions and infected cells, a process largely driven by antibody-mediated immunity. However, with the newly emerging variants that evade Spike-targeting antibodies, re-infections and breakthrough infections are increasingly common. A full characterization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mechanisms counteracting antibody-mediated immunity is therefore needed. Here, we report that ORF8 is a virally encoded SARS-CoV-2 factor that controls cellular Spike antigen levels. We show that ORF8 limits the availability of mature Spike by inhibiting host protein synthesis and retaining Spike at the endoplasmic reticulum, reducing cell-surface Spike levels and recognition by anti-SARS-CoV-2 antibodies. In conditions of limited Spike availability, we found ORF8 restricts Spike incorporation during viral assembly, reducing Spike levels in virions. Cell entry of these virions then leaves fewer Spike molecules at the cell surface, limiting antibody recognition of infected cells. Based on these findings, we propose that SARS-CoV-2 variants may adopt an ORF8-dependent strategy that facilitates immune evasion of infected cells for extended viral production.

ZnO-Based Electrochemical Immunosensor to Assess Vaccine-Induced Antibody-Mediated Immunity against Wild-Type and Gamma SARS-CoV-2 Strains

The evaluation of serological responses to COVID-19 is crucial for population-level surveillance, developing new vaccines, and evaluating the efficacy of different immunization programs. Research and development of point-of-care test technologies remain essential to improving immunity assessment, especially for SARS-CoV-2 variants that partially evade vaccine-induced immune responses. In this work, an impedimetric biosensor based on the immobilization of the recombinant trimeric wild-type spike protein (S protein) on zinc oxide nanorods (ZnONRs) was employed for serological evaluation. We successfully assessed its applicability using serum samples from spike-based COVID-19 vaccines: ChAdOx1-S (Oxford-AstraZeneca) and BNT162b2 (Pfizer-BioNTech). Overall, the ZnONRs/ spike-modified electrode displayed accurate results for both vaccines, showing excellent potential as a tool for assessing and monitoring seroprevalence in the population. A refined outcome of this technology was achieved when the ZnO immunosensor was functionalized with the S protein from the P.1 linage (Gamma variant). Serological responses against samples from vaccinated individuals were acquired with excellent performance. Following studies based on traditional serological tests, the ZnONRs/spike immunosensor data reveal that ChAdOx1-S vaccinated individuals present significantly less antibody-mediated immunity against the Gamma variant than the BNT162b2 vaccine, highlighting the great potential of this point-of-care technology for evaluating vaccine-induced humoral immunity against different SARS-CoV-2 strains.

SARS-CoV-2 Evolution and Patient Immunological History Shape the Breadth and Potency of Antibody-Mediated Immunity

Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), humans have been exposed to distinct SARS-CoV-2 antigens, either by infection with different variants, and/or vaccination. Population immunity is thus highly heterogeneous, but the impact of such heterogeneity on the effectiveness and breadth of the antibody-mediated response is unclear. We measured antibody-mediated neutralization responses against SARS-CoV-2Wuhan, SARS-CoV-2α, SARS-CoV-2δ, and SARS-CoV-2ο pseudoviruses using sera from patients with distinct immunological histories, including naive, vaccinated, infected with SARS-CoV-2Wuhan, SARS-CoV-2α, or SARS-CoV-2δ, and vaccinated/infected individuals. We show that the breadth and potency of the antibody-mediated response is influenced by the number, the variant, and the nature (infection or vaccination) of exposures, and that individuals with mixed immunity acquired by vaccination and natural exposure exhibit the broadest and most potent responses. Our results suggest that the interplay between host immunity and SARS-CoV-2 evolution will shape the antigenicity and subsequent transmission dynamics of SARS-CoV-2, with important implications for future vaccine design.

Antibody Levels Poorly Reflect on the Frequency of Memory B Cells Generated following SARS-CoV-2, Seasonal Influenza, or EBV Infection

The scope of immune monitoring is to define the existence, magnitude, and quality of immune mechanisms operational in a host. In clinical trials and praxis, the assessment of humoral immunity is commonly confined to measurements of serum antibody reactivity without accounting for the memory B cell potential. Relying on fundamentally different mechanisms, however, passive immunity conveyed by pre-existing antibodies needs to be distinguished from active B cell memory. Here, we tested whether, in healthy human individuals, the antibody titers to SARS-CoV-2, seasonal influenza, or Epstein-Barr virus antigens correlated with the frequency of recirculating memory B cells reactive with the respective antigens. Weak correlations were found. The data suggest that the assessment of humoral immunity by measurement of antibody levels does not reflect on memory B cell frequencies and thus an individual's potential to engage in an anamnestic antibody response against the same or an antigenically related virus. Direct monitoring of the antigen-reactive memory B cell compartment is both required and feasible towards that goal.

Effects of elevated corticosterone on humoral innate and antibody-mediated immunity in southern leopard frog (Lithobates sphenocephalus) tadpoles

As a free-living larval stage of a vertebrate, tadpoles are good subjects for the study of the development of physiological systems and the study of evolutionarily conserved, context-dependent responses to variable environments. While the basic components of innate and adaptive immune defenses in tadpoles are known, the impact of glucocorticoids on immune defenses in tadpoles is not well-studied. We completed four experiments to assess effects of elevation of corticosterone on humoral innate defenses and antibody-mediated immunity in southern leopard frog tadpoles (Lithobates sphenocephalus). To test humoral innate defense within the tadpoles exposed to short-term and long-term elevation of glucocorticoids, we exposed tadpoles to exogenous corticosterone for different lengths of time in each experiment (0-84 days). We used bacterial killing assays to assess humoral innate immune defense. To test antibody-mediated immune responses, we again exposed tadpoles to exogenous corticosterone, while also exposing them to Aeromonas hydrophila. We used A. hydrophila ELISA comparing IgM and IgY responses among groups. Plasma from corticosterone-dosed tadpoles killed more A. hydrophila than control tadpoles each following a short-term (14 day) and long-term (56 day) exposure to exogenous corticosterone. Conversely, corticosterone-dosed tadpoles had significantly lower IgM and IgY against A. hydrophila after 12 weeks. Our fourth experiment revealed that the lower IgY response is a product of weaker, delayed isotype switching compared with controls. These results show that elevated corticosterone has differential effects on innate and acquired immunity in larval southern leopard frogs, consistent with patterns in more derived vertebrates and in adult frogs.

Pentablock Copolymer Micelle Nanoadjuvants Enhance Cytosolic Delivery of Antigen and Improve Vaccine Efficacy while Inducing Low Inflammation

As the focus has shifted from traditional killed or live, attenuated vaccines toward subunit vaccines, improvements in vaccine safety have been confronted with low immunogenicity of protein antigens. This issue has been addressed by synthesizing and designing a wide variety of antigen carriers and adjuvants, such as Toll-like receptor agonists (e.g., MPLA, CpG). Studies have focused on optimizing adjuvants for improved cellular trafficking, cytosolic availability, and improved antigen presentation. In this work, we describe the design of novel amphiphilic pentablock copolymer (PBC) adjuvants that exhibit high biocompatibility and reversible pH- and temperature-sensitive micelle formation. We demonstrate improved humoral immunity in mice in response to single-dose immunization with PBC micelle adjuvants compared with soluble antigen alone. With the motive of exploring the mechanism of action of these PBC micelles, we studied intracellular trafficking of these PBC micelles with a model antigen and demonstrated that the PBC micelles associate with the antigen and enhance its cytosolic delivery to antigen-presenting cells. We posit that these PBC micelles operate via immune-enhancing mechanisms that are different from that of traditional Toll-like receptor activating adjuvants. The metabolic profile of antigen-presenting cells stimulated with traditional adjuvants and the PBC micelles also suggests distinct mechanisms of action. A key finding from this study is the low production of nitric oxide and reactive oxygen species by antigen-presenting cells when stimulated by PBC micelle adjuvants in sharp contrast to TLR adjuvants. Together, these studies provide a basis for rationally developing novel vaccine adjuvants that are safe, that induce low inflammation, and that can efficiently deliver antigen to the cytosol.

Interpreting challenge data from early phase malaria blood stage vaccine trials

INTRODUCTION

As the quest for an effective blood stage malaria vaccine continues, there is increasing reliance on the use of controlled human malaria infections (CHMI) in non-endemic settings to test vaccine efficacy at the earliest possible time. This is seen as a way to accelerate vaccine research and quickly eliminate candidates with poor efficacy. Areas covered: The data from these studies need to be carefully examined and interpreted in light of the very different roles that antibody and cellular immunity play in protection and within the context of the distinct clinical sensitivities of volunteers living in malaria-non-endemic countries compared to those living in endemic countries. With current strategies, it is likely that vaccines with protective immunological 'signatures' will be missed and potentially good candidates discarded. Expert commentary: Efficacy data from early phase vaccine trials in non-endemic countries should not be used to decide whether or not to proceed to vaccine trials in endemic countries.

HIV-1 Consensus Envelope-Induced Broadly Binding Antibodies

Antibodies that cross-react with multiple HIV-1 envelopes (Envs) are useful reagents for characterizing Env proteins and for soluble Env capture and purification assays. We previously reported 10 murine monoclonal antibodies induced by group M consensus Env, CON-6 immunization. Each demonstrated broad cross-reactivity to recombinant Envs. Here we characterized the Env epitopes to which they bind. Seven mapped to linear epitopes in gp120, five at the Env N-terminus, and two at the Env C-terminus. One antibody, 13D7, bound at the gp120 N-terminus (aa 30-42), reacted with HIV-1-infected CD4+ T cells, and when expressed in a human IgG1 backbone, mediated antibody-dependent cellular cytotoxicity. Antibody 18F11 bound at the gp120 C-terminus (aa 445-459) and reactivity was glycan dependent. Antibodies 13D7, 3B3, and 16H3 bound to 100 percent of HIV-1 Envs tested in ELISA and sodium dodecyl sulfate/polyacrylamide gel electrophoresis/western blot analysis. These data define the epitopes of monoclonal antibody reagents for characterization of recombinant Envs, one epitope of which is also expressed on the surface of HIV-1-infected CD4+ T cells.

Association of Human Antibodies to Arabinomannan With Enhanced Mycobacterial Opsonophagocytosis and Intracellular Growth Reduction

Background. The relevance of antibodies (Abs) in the defense against Mycobacterium tuberculosis infection remains uncertain. We investigated the role of Abs to the mycobacterial capsular polysaccharide arabinomannan (AM) and its oligosaccharide (OS) fragments in humans.

Methods. Sera obtained from 29 healthy adults before and after primary or secondary bacillus Calmette-Guerin (BCG) vaccination were assessed for Ab responses to AM via enzyme-linked immunosorbent assays, and to AM OS epitopes via novel glycan microarrays. Effects of prevaccination and postvaccination sera on BCG phagocytosis and intracellular survival were assessed in human macrophages.

Results. Immunoglobulin G (IgG) responses to AM increased significantly 4–8 weeks after vaccination (P < .01), and sera were able to opsonize BCG and M. tuberculosis grown in both the absence and the presence of detergent. Phagocytosis and intracellular growth inhibition were significantly enhanced when BCG was opsonized with postvaccination sera (P < .01), and these enhancements correlated significantly with IgG titers to AM (P < .05), particularly with reactivity to 3 AM OS epitopes (P < .05). Furthermore, increased phagolysosomal fusion was observed with postvaccination sera.

Conclusions. Our results provide further evidence for a role of Ab-mediated immunity to tuberculosis and suggest that IgG to AM, especially to some of its OS epitopes, could contribute to the defense against mycobacterial infection in humans.

Colostral antibody-mediated and cell-mediated immunity contributes to innate and antigen-specific immunity in piglets

Immunoglobulins and immune cells are critical components of colostral immunity; however, their transfer to and function in the neonate, especially maternal lymphocytes, is unclear. Cell-mediated and antibody-mediated immunity in sow blood and colostrum and piglet blood before (PS) and after (AS) suckling were assessed to investigate transfer and function of maternal immunity in the piglet. CD4, CD8, and γδ lymphocytes were found in sow blood and colostrum and piglet blood PS and AS; each had a unique T lymphocyte profile. Immunoglobulins were detected in sow blood, colostrum, and in piglet blood AS; the immunoglobulin profile of piglet serum AS mimicked that of sow serum. These results suggest selectivity in lymphocyte concentration into colostrum and subsequent lymphocyte transfer into the neonate, but that immunoglobulin transfer is unimpeded. Assessment of colostral natural killer activity and antigen-specific proliferation revealed that colostral cells are capable of influencing the innate and specific immune response of neonatal pigs.

Antidotes, antibody-mediated immunity and the future of pharmaceutical product development

If new scientific knowledge is to be more efficiently generated and applied toward the advancement of health, human safety must be more effectively addressed in the conduct of research. Given the present difficulties of accurately predicting biological outcomes of novel interventions in vivo, the imperative of human safety suggests the development of novel pharmaceutical products in tandem with their prospective antidotes in anticipation of possible adverse events, to render the risks of initial clinical trials more acceptable from a regulatory standpoint. Antibody-mediated immunity provides a generally applicable mechanistic basis for developing antidotes to both biologicals and small-molecule drugs (such that antibodies may serve as antidotes to pharmaceutical agents as a class including other antibodies) and also for the control and prevention of both infectious and noninfectious diseases via passive or active immunization. Accordingly, the development of prophylactic or therapeutic passive-immunization strategies using antipeptide antibodies is a plausible prelude to the development of corresponding active-immunization strategies using peptide-based vaccines. In line with this scheme, global proliferation of antibody- and vaccine-production technologies, especially those that obviate dependence on the cold chain for storage and transport of finished products, could provide geographically distributed breakout capability against emerging and future health challenges.