How to assess the binding strength of antibodies elicited by vaccination against HIV and other viruses

Easy assessment of the avidity of polyclonal allergen-specific serum antibodies

INTRODUCTION

Allergen-specific IgE-blocking IgG antibodies contribute to successful allergen immunotherapy (AIT), however, not much is known about their affinity. Since affinity measurements of polyclonal antibodies in serum are technically challenging we evaluated the applicability of acidic disruption of antibody-allergen complexes by a modified ELISA protocol with monoclonal antibodies (mAbs) specific for the relevant major allergens Betv1 and Mald1. Then, AIT-induced blocking and non-blocking Mald1-specific antibodies in sera from individuals with or without reduced apple allergy were compared.

METHODS

After testing their pH stability coated recombinant allergens were incubated with (i) mAbs diluted in PBS or human serum and (ii) sera from individuals after sublingual administration of Mald1 or Betv1 for 16 weeks. Immune complexes were exposed to buffers in the pH range of 6.4-3.4 and residual antibodies were measured. Avidity indexes (AI), defined as the pH removing 50% of antibodies, were compared to the dissociation constants (KD) of mAbs determined by surface plasmon resonance.

RESULTS

The selected pH range was applicable to disrupt allergen complexes with highly affine mAbs without compromising allergen integrity. AIs of mAbs accorded with KD values and were unaffected by epitope specificity or the presence of serum proteins. The inter-assay variability was <4% CV. Protective Mald1-specific IgG antibodies from individuals with reduced apple allergy showed a higher collective binding strength than that of the non-protective antibodies of individuals without reduced apple allergy.

CONCLUSION

Acidic disruption of allergen-antibody complexes may be used to estimate the net-binding force of polyclonal serum antibodies and eases the investigation of affinity-related research questions in AIT.

Binding and Avidity Signatures of Polyclonal Sera From Individuals With Different Exposure Histories to Severe Acute Respiratory Syndrome Coronavirus 2 Infection, Vaccination, and Omicron Breakthrough Infections

BACKGROUND

The number of exposures to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to vaccine antigens affect the magnitude and avidity of the polyclonal response.

METHODS

We studied binding and avidity of different antibody isotypes to the spike, the receptor-binding domain (RBD), and the nucleoprotein (NP) of wild-type (WT) and BA.1 SARS-CoV-2 in convalescent, mRNA vaccinated and/or boosted, hybrid immune individuals and in individuals with breakthrough cases during the peak of the BA.1 wave.

RESULTS

We found an increase in spike-binding antibodies and antibody avidity with increasing number of exposures to infection and/or vaccination. NP antibodies were detectible in convalescent individuals and a proportion of breakthrough cases, but they displayed low avidity. Omicron breakthrough infections elicited high levels of cross-reactive antibodies between WT and BA.1 antigens in vaccinated individuals without prior infection directed against the spike and RBD. The magnitude of the antibody response and avidity correlated with neutralizing activity against WT virus.

CONCLUSIONS

The magnitude and quality of the antibody response increased with the number of antigenic exposures, including breakthrough infections. However, cross-reactivity of the antibody response after BA.1 breakthroughs, was affected by the number of prior exposures.

A tool for evaluating heterogeneity in avidity of polyclonal antibodies

Diversity in specificity of polyclonal antibody (pAb) responses is extensively investigated in vaccine efficacy or immunological evaluations, but the heterogeneity in antibody avidity is rarely probed as convenient tools are lacking. Here we have developed a polyclonal antibodies avidity resolution tool (PAART) for use with label-free techniques, such as surface plasmon resonance and biolayer interferometry, that can monitor pAb-antigen interactions in real time to measure dissociation rate constant (kd ) for defining avidity. PAART utilizes a sum of exponentials model to fit the dissociation time-courses of pAb-antigens interactions and resolve multiple kd contributing to the overall dissociation. Each kd value of pAb dissociation resolved by PAART corresponds to a group of antibodies with similar avidity. PAART is designed to identify the minimum number of exponentials required to explain the dissociation course and guards against overfitting of data by parsimony selection of best model using Akaike information criterion. Validation of PAART was performed using binary mixtures of monoclonal antibodies of same specificity but differing in kd of the interaction with their epitope. We applied PAART to examine the heterogeneity in avidities of pAb from malaria and typhoid vaccinees, and individuals living with HIV-1 that naturally control the viral load. In many cases, two to three kd were dissected indicating the heterogeneity of pAb avidities. We showcase examples of affinity maturation of vaccine induced pAb responses at component level and enhanced resolution of heterogeneity in avidity when antigen-binding fragments (Fab) are used instead of polyclonal IgG antibodies. The utility of PAART can be manifold in examining circulating pAb characteristics and could inform vaccine strategies aimed to guide the host humoral immune response.

Frailty impacts immune responses to Moderna COVID-19 mRNA vaccine in older adults

BACKGROUND

Immune responses to COVID-19 mRNA vaccines have not been well characterized in frail older adults. We postulated that frailty is associated with impaired antibody and cellular mRNA vaccine responses.

METHODS

We followed older adults in a retirement facility with longitudinal clinical and serological samples from the first Moderna mRNA-1273 vaccine dose starting in February 2021 through their 3rd (booster) vaccine dose. Outcomes were antibody titers, antibody avidity, and AIM+ T cell function and phenotype. Statistical analysis used linear regression with clustered error for antibody titers over multiple timepoints with clinical predictors including, age, sex, prior infection status, and clinical frailty scale (CFS) score. T cell function analysis used linear regression models with clinical predictors and cellular memory phenotype variables.

RESULTS

Participants (n = 15) had median age of 90 years and mild, moderate, or severe frailty scores (n = 3, 7, or 5 respectively). Over the study time course, anti-spike antibody titers were 10-fold higher in individuals with lower frailty status (p = 0.001 and p = 0.005, unadjusted and adjusted for prior COVID-19 infection). Following the booster, titers to spike protein improved regardless of COVID-19 infection or degree of frailty (p = 0.82 and p = 0.29, respectively). Antibody avidity significantly declined over 6 months in all participants following 2 vaccine doses (p < 0.001), which was further impaired with higher frailty (p = 0.001). Notably, avidity increased to peak levels after the booster (p < 0.001). Overall antibody response was inversely correlated with a phenotype of immune-senescent T cells, CD8 + CD28- TEMRA cells (p = 0.036, adjusted for COVID-19 infection). Furthermore, there was increased detection of CD8 + CD28- TEMRA cells in individuals with greater frailty (p = 0.056, adjusted for COVID-19).

CONCLUSIONS

We evaluated the immune responses to the Moderna COVID-19 mRNA vaccine in frail older adults in a retirement community. A higher degree of frailty was associated with diminished antibody quantity and quality. However, a booster vaccine dose at 6 months overcame these effects. Frailty was associated with an increased immune-senescence phenotype that may contribute to the observed changes in the vaccine response. While the strength of our conclusions was limited by a small cohort, these results are important for guiding further investigation of vaccine responses in frail older adults.

The role of IgG1 and IgG4 as dominant IgE-blocking antibodies shifts during allergen immunotherapy

BACKGROUND

The induction of allergen-specific IgE-blocking antibodies is a hallmark of allergen immunotherapy (AIT). The inhibitory bioactivity has largely been attributed to IgG₄; however, our recent studies indicated the dominance of IgG₁ early in AIT.

OBJECTIVES

Here, the IgE-blocking activity and avidity of allergen-specific IgG₁ and IgG₄ antibodies were monitored throughout 3 years of treatment.

METHODS

Serum samples from 24 patients were collected before and regularly during AIT with birch pollen. Bet v 1-specific IgG₁ and IgG₄ levels were determined by ELISA and ImmunoCAP, respectively. Unmodified and IgG₁- or IgG₄-depleted samples were compared for their inhibition of Bet v 1-induced basophil activation. The stability of Bet v 1-antibody complexes was compared by ELISA and by surface plasmon resonance.

RESULTS

Bet v 1-specific IgG₁ and IgG₄ levels peaked at 12 and 24 months of AIT, respectively. Serological IgE-blocking peaked at 6 months and remained high thereafter. In the first year of therapy, depletion of IgG₁ clearly diminished the inhibition of basophil activation while the absence of IgG₄ hardly reduced IgE-blocking. Then, IgG₄ became the main inhibitory isotype in most individuals. Both isotypes displayed high avidity to Bet v 1 ab initio of AIT, which did not increase during treatment. Bet v 1-IgG₁ complexes were enduringly more stable than Bet v 1-IgG₄ complexes were.

CONCLUSIONS

In spite of the constant avidity of AIT-induced allergen-specific IgG₁ and IgG₄ antibodies, their dominance in IgE-blocking shifted in the course of treatment. The blocking activity of allergen-specific IgG₁ should not be underestimated, particularly early in AIT.

TLR agonists induce sustained IgG to hemagglutinin stem and modulate T cells following newborn vaccination

The newborn immune system is characterized by diminished immune responses that leave infants vulnerable to virus-mediated disease and make vaccination more challenging. Optimal vaccination strategies for influenza A virus (IAV) in newborns should result in robust levels of protective antibodies, including those with broad reactivity to combat the variability in IAV strains across seasons. The stem region of the hemagglutinin (HA) molecule is a target of such antibodies. Using a nonhuman primate model, we investigate the capacity of newborns to generate and maintain antibodies to the conserved stem region following vaccination. We find adjuvanting an inactivated vaccine with the TLR7/8 agonist R848 is effective in promoting sustained HA stem-specific IgG. Unexpectedly, HA stem-specific antibodies were generated with a distinct kinetic pattern compared to the overall response. Administration of R848 was associated with increased influenza-specific T follicular helper cells as well as Tregs with a less suppressive phenotype, suggesting adjuvant impacts multiple cell types that have the potential to contribute to the HA-stem response.

Frailty and Age Impact Immune Responses to Moderna COVID-19 mRNA Vaccine

BACKGROUND

Immune responses to COVID-19 mRNA vaccines have not been well characterized in frail older adults. We postulated that frailty is associated with impaired antibody and cellular mRNA vaccine responses.

METHODS

We followed older adults in a retirement facility with longitudinal clinical and serological samples from the first Moderna mRNA-1273 vaccine dose starting in February 2021 through their 3rd (booster) vaccine dose. Outcomes were antibody titers, antibody avidity, and AIM+ T cell function and phenotype. Statistical analysis used antibody titers in linear mixed-effects linear regression with clinical predictors including, age, sex, prior infection status, and clinical frailty scale (CFS) score. T cell function analysis used clinical predictors and cellular phenotype variables in linear regression models.

RESULTS

Participants (n=15) had median age of 90 years and mild, moderate, or severe frailty scores (n=3, 7, or 5 respectively). After 2 vaccine doses, anti-spike antibody titers were higher in 5-fold higher in individuals with mild frailty compared to severe frailty and 9-fold higher in individuals with prior COVID-19 infection compared to uninfected (p=0.02 and p<0.001). Following the booster, titers improved regardless of COVID-19 infection or frailty. Antibody avidity significantly declined following 2 vaccine doses regardless of frailty status, but reached maximal avidity after the booster. Spike-specific CD4+ T cell responses were modulated by frailty and terminally differentiated effector memory TEMRA cells, and spike-specific TFH cell responses were inversely correlated with age. Additionally, an immune-senescent memory T cell phenotype was correlated with frailty and functional decline.

CONCLUSIONS

We described the separate influences of frailty and age on adaptive immune responses to the Moderna COVID-19 mRNA vaccine. Though overall antibody responses were robust, higher frailty diminished initial antibody quantity, and all older adults had impaired antibody avidity. Following the booster, antibody responses improved, overcoming the effects of age and frailty. CD4+ T cell responses were independently impacted by age, frailty, and burden of immune-senescence. Frailty was correlated with increased burden of immune-senescence, suggesting an immune-mediated mechanism for physiological decline.

Reappraising the Value of HIV-1 Vaccine Correlates of Protection Analyses

With the much-debated exception of the modestly reduced acquisition reported for the RV144 efficacy trial, HIV-1 vaccines have not protected humans against infection, and a vaccine of similar design to that tested in RV144 was not protective in a later trial, HVTN 702. Similar vaccine regimens have also not consistently protected nonhuman primates (NHPs) against viral acquisition. Conversely, experimental vaccines of different designs have protected macaques from viral challenges but then failed to protect humans, while many other HIV-1 vaccine candidates have not protected NHPs. While efficacy varies more in NHPs than humans, vaccines have failed to protect in the most stringent NHP model. Intense investigations have aimed to identify correlates of protection (CoPs), even in the absence of net protection. Unvaccinated animals and humans vary vastly in their susceptibility to infection and in their innate and adaptive responses to the vaccines; hence, merely statistical associations with factors that do not protect are easily found. Systems biological analyses, including artificial intelligence, have identified numerous candidate CoPs but with no clear consistency within or between species. Proposed CoPs sometimes have only tenuous mechanistic connections to immune protection. In contrast, neutralizing antibodies (NAbs) are a central mechanistic CoP for vaccines that succeed against other viruses, including SARS-CoV-2. No HIV-1 vaccine candidate has yet elicited potent and broadly active NAbs in NHPs or humans, but narrow-specificity NAbs against the HIV-1 isolate corresponding to the immunogen do protect against infection by the autologous virus. Here, we analyze why so many HIV-1 vaccines have failed, summarize the outcomes of vaccination in NHPs and humans, and discuss the value and pitfalls of hunting for CoPs other than NAbs. We contrast the failure to find a consistent CoP for HIV-1 vaccines with the identification of NAbs as the principal CoP for SARS-CoV-2.

Measurements of SARS-CoV-2 antibody dissociation rate constant by chaotrope-free biolayer interferometry in serum of COVID-19 convalescent patients

Kinetics measurements of antigen-antibody binding interactions are critical to understanding the functional efficiency of SARS-CoV-2 antibodies. Previously reported chaotrope-based avidity assays that rely on artificial disruption of binding do not reflect the natural binding kinetics. This study developed a chaotrope- and label-free biolayer interferometry (BLI) assay for the real-time monitoring of receptor binding domain (RBD) binding kinetics with SARS-CoV-2 spike protein in convalescent COVID-19 patients. An improved conjugation biosensor probe coated with streptavidin-polysaccharide (SA-PS) led to a six-fold increase of signal intensities and two-fold reduction of non-specific binding (NSB) compared to streptavidin only probe. Furthermore, by utilizing a separate reference probe and biotin-human serum albumin (B-HSA) blocking process to subtracted NSB signal in serum, this BLI biosensor can measure a wide range of the dissociation rate constant (k_off), which can be measured without knowledge of the specific antibody concentrations. The clinical utility of this improved BLI kinetics assay was demonstrated by analyzing the k_off values in sera of 24 pediatric (≤18 years old) and 63 adult (>18 years old) COVID-19 convalescent patients. Lower k_off values for SARS-CoV-2 serum antibodies binding to RBD were measured in samples from children. This rapid, easy to operate and chaotrope-free BLI assay is suitable for clinical use and can be readily adapted to characterize SARS-CoV-2 antibodies developed by COVID-19 patients and vaccines.

HPV16 infection decreases vaccine-induced HPV16 antibody avidity: the CVT trial

The HPV vaccine has shown sustained efficacy and consistent stabilization of antibody levels, even after a single dose. We defined the HPV16-VLP antibody avidity patterns over 11 years among women who received one- or three doses of the bivalent HPV vaccine in the Costa Rica HPV Vaccine Trial. Absolute HPV16 avidity was lower in women who received one compared to three doses, although the patterns were similar (increased in years 2 and 3 and remained stable over the remaining 8 years). HPV16 avidity among women who were HPV16-seropositive women at HPV vaccination, a marker of natural immune response to HPV16 infection, was significantly lower than those of HPV16-seronegative women, a difference that was more pronounced among one-dose recipients. No differences in HPV16 avidity were observed by HPV18 serostatus at vaccination, confirming the specificity of the findings. Importantly, point estimates for vaccine efficacy against incident, six-month persistent HPV16 infections was similar between women who were HPV16 seronegative and seropositive at the time of initial HPV vaccination for both one-dose and three-dose participants. It is therefore likely that this lower avidity level is still sufficient to enable antibody-mediated protection. It is encouraging for long-term HPV-vaccine protection that HPV16 antibody avidity was maintained for over a decade, even after a single dose.

Avidity of Polyclonal Antibodies to Foot-and-Mouth Disease Virus in Bovine Serum Measured Using Bio-Layer Interferometry

Foot-and-mouth disease (FMD) is a disease of cloven-hoofed livestock caused by FMD virus (FMDV). FMD can be controlled through the use of inactivated vaccines, and it is well established that the protection afforded by FMD vaccines correlates strongly with neutralising antibody titres. However, the overall strength of binding, referred to as avidity, is also an important parameter with respect to the ability of antibodies to neutralise virus infection, and there is evidence that avidity can affect the level of protection afforded by FMDV vaccines. Here, as an alternative to modified enzyme-linked immunosorbent assays (avidity ELISAs) incorporating a chaotropic wash step, we used bio-layer interferometry (BLI) to measure the avidity of bovine polyclonal antibodies against FMDV capsids. We conducted preliminary experiments using recombinant FMDV capsids, as well as peptides representing antigenic loops, to demonstrate that the binding of monoclonal antibodies targeting specific antigenic sites could be detected using BLI. Subsequent experiments using polyclonal sera derived from FMD vaccinated cattle provided evidence of a positive correlation between the neutralising titre of the serum and the avidity as measured by BLI. Furthermore, we observed an increase in BLI avidity, as well as in the titre, in vaccinated animals upon challenge with the live virus.

CoVaccine HT™ adjuvant is superior to Freund's in eliciting ovine polyclonal antibodies against human tumor necrosis factor-alpha

INTRODUCTION

Passive immunotherapy using polyclonal antibodies plays an important role in preventing and treating antigenic and pathogenic diseases. Polyclonal antibodies are used for therapeutic, diagnostic and investigational purposes, with adjuvants employed to enhance the immune response against proteins that are poorly antigenic or self-antigens. This study aimed to optimize current immunization methods by evaluating the novel adjuvant CoVaccine HT™ against the established Freund's at producing ovine polyclonal antibodies against pro-inflammatory cytokine human recombinant tumor necrosis factor alpha (TNF-α).

METHODS

Castrated male Aberfield cross sheep were immunized with TNF-α in CoVaccine HT™ or Freund's adjuvant. The binding titer of antibodies for TNF-α and neutralization titer were determined in vitro, as well as the strength of antibody binding by a simple small scale affinity chromatography elution experiment. Animal welfare was monitored through inspection of immunization site reactions at regular time points and graded according to reaction size. The second part of the study looked at re-immunization using Freund's adjuvant alone every 4- or 8-weeks.

RESULTS

Freund's generated significantly higher antibody binding titers than CoVaccine HT™ but were less effective at neutralizing TNF-alpha which is a better indicator of functional potency. CoVaccine HT™ also caused fewer immunization site reactions, while no statistical difference was observed in the binding strength of antibodies. Re-immunization every 4- and 8-weeks showed no statistical difference.

CONCLUSION

This study provides evidence that CoVaccine HT™ is superior to Freund's adjuvant for the production of antibodies to TNF-α, and supports the use of this alternative adjuvant for clinical and experimental use. The outcomes gained through this study are applicable to passive and active immunotherapy for the generation of polyclonal antibodies in human and veterinary medicine.

A scalable and highly immunogenic virus-like particle-based vaccine against SARS-CoV-2

BACKGROUND

SARS-CoV-2 caused one of the most devastating pandemics in the recent history of mankind. Due to various countermeasures, including lock-downs, wearing masks, and increased hygiene, the virus has been controlled in some parts of the world. More recently, the availability of vaccines, based on RNA or adenoviruses, has greatly added to our ability to keep the virus at bay; again, however, in some parts of the world only. While available vaccines are effective, it would be desirable to also have more classical vaccines at hand for the future. Key feature of vaccines for long-term control of SARS-CoV-2 would be inexpensive production at large scale, ability to make multiple booster injections, and long-term stability at 4℃.

METHODS

Here, we describe such a vaccine candidate, consisting of the SARS-CoV-2 receptor-binding motif (RBM) grafted genetically onto the surface of the immunologically optimized cucumber mosaic virus, called CuMVTT -RBM.

RESULTS

Using bacterial fermentation and continuous flow centrifugation for purification, the yield of the production process is estimated to be >2.5 million doses per 1000-litre fermenter run. We demonstrate that the candidate vaccine is highly immunogenic in mice and rabbits and induces more high avidity antibodies compared to convalescent human sera. The induced antibodies are more cross-reactive to mutant RBDs of variants of concern (VoC). Furthermore, antibody responses are neutralizing and long-lived. In addition, the vaccine candidate was stable for at least 14 months at 4℃.

CONCLUSION

Thus, the here presented VLP-based vaccine may be a good candidate for use as conventional vaccine in the long term.

A single-step, high throughput, and highly reproducible method for measuring IgM quantity and avidity directly from fish serum via biolayer interferometry (BLI)

Quantification of specific antibody responses is critical in determining activation of MHCII-dependent immune memory and is generally performed by enzyme-linked immunosorbent assay (ELISA). Antibody avidity for a particular antigen is also informative of the quality of the adaptive immune response following vaccination. Avidity can be determined by chaotropic elution ELISA, pre-absorption ELISA, or surface plasmon resonance (SPR), although multimeric antibodies such as IgM are problematic for SPR. ELISA-based assays are very time consuming, require secondary antibody reagents, and are poorly repeatable. Here we demonstrate that biolayer interferometry (BLI) using an Octet HTX instrument can robustly and reproducibly quantify and determine avidity of specific IgM for an antigen directly from fish serum in a single step. We collected sera from giant grouper (Epinephelus lanceolatus) that had been vaccinated with the hapten 2,4-dinitrophenol conjugated to keyhole limpet hemocyanin (DNP-KLH) and from control fish injected with phosphate buffered saline. The specific IgM in the serum and its avidity for DNP were quantified via ELISA and BLI. BLI was precise and highly repeatable for determination of the quantity and avidity of antibody in the serum compared to ELISA. The wet-lab preparation and machine running time for BLI was 3-5 times faster than ELISA to generate the same amount of data. The ELISA inter-plate variation significantly affected reproducibility while BLI was consistent and repeatable between samples and plates. Indeed, the consistency of BLI data indicated that technical triplicates were redundant. Biological replication alone was sufficient to elucidate the effect of treatments. However, BLI required a lower serum dilution than ELISA for similar sensitivity, and thus more serum was required to produce high resolution data. BLI is an extremely high-throughput assay, providing teleost serum IgM quantification and avidity data as a single-step, agile alternative to ELISA.

Poor CD4+ T Cell Immunogenicity Limits Humoral Immunity to P. falciparum Transmission-Blocking Candidate Pfs25 in Humans

Plasmodium falciparum transmission-blocking vaccines (TBVs) targeting the Pfs25 antigen have shown promise in mice but the same efficacy has never been achieved in humans. We have previously published pre-clinical data related to a TBV candidate Pfs25-IMX313 encoded in viral vectors which was very promising and hence progressed to human clinical trials. The results from the clinical trial of this vaccine were very modest. Here we unravel why, contrary to mice, this vaccine has failed to induce robust antibody (Ab) titres in humans to elicit transmission-blocking activity. We examined Pfs25-specific B cell and T follicular helper (Tfh) cell responses in mice and humans after vaccination with Pfs25-IMX313 encoded by replication-deficient chimpanzee adenovirus serotype 63 (ChAd63) and the attenuated orthopoxvirus modified vaccinia virus Ankara (MVA) delivered in the heterologous prime-boost regimen via intramuscular route. We found that after vaccination, the Pfs25-IMX313 was immunologically suboptimal in humans compared to mice in terms of serum Ab production and antigen-specific B, CD4⁺ and Tfh cell responses. We identified that the key determinant for the poor anti-Pfs25 Ab formation in humans was the lack of CD4⁺ T cell recognition of Pfs25-IMX313 derived peptide epitopes. This is supported by correlations established between the ratio of proliferated antigen-specific CD4⁺/Tfh-like T cells, CXCL13 sera levels, and the corresponding numbers of circulating Pfs25-specific memory B cells, that consequently reflected on antigen-specific IgG sera levels. These correlations can inform the design of next-generation Pfs25-based vaccines for robust and durable blocking of malaria transmission.

Characterising the Phenotypic Diversity of Antigen-Specific Memory B Cells Before and After Vaccination

The diversity of B cell subsets and their contribution to vaccine-induced immunity in humans are not well elucidated but hold important implications for rational vaccine design. Prior studies demonstrate that B cell subsets distinguished by immunoglobulin (Ig) isotype expression exhibit divergent activation-induced fates. Here, the antigen-specific B cell response to tetanus toxoid (TTd) booster vaccination was examined in healthy adults, using a dual-TTd tetramer staining flow cytometry protocol. Unsupervised analyses of the data revealed that prior to vaccination, IgM-expressing CD27⁺ B cells accounted for the majority of TTd-binding B cells. 7 days following vaccination, there was an acute expansion of TTd-binding plasmablasts (PB) predominantly expressing IgG, and a minority expressing IgA or IgM. Frequencies of all PB subsets returned to baseline at days 14 and 21. TTd-binding IgG⁺ and IgA⁺ memory B cells (MBC) exhibited a steady and delayed maximal expansion compared to PB, peaking in frequencies at day 14. In contrast, the number of TTd-binding IgM⁺IgD⁺CD27⁺ B cells and IgM-only CD27⁺ B cells remain unchanged following vaccination. To examine TTd-binding capacity of IgG⁺ MBC and IgM⁺IgD⁺CD27⁺ B cells, surface TTd-tetramer was normalised to expression of the B cell receptor-associated CD79b subunit. CD79b-normalised TTd binding increased in IgG⁺ MBC, but remained unchanged in IgM⁺IgD⁺CD27⁺ B cells, and correlated with the functional affinity index of plasma TTd-specific IgG antibodies, following vaccination. Finally, frequencies of activated (PD-1⁺ICOS⁺) circulating follicular helper T cells (cT_FH), particularly of the CXCR3^-CCR6^- cT_FH2 cell phenotype, at their peak expansion, strongly predicted antigen-binding capacity of IgG⁺ MBC. These data highlight the phenotypic and functional diversity of the B cell memory compartment, in their temporal kinetics, antigen-binding capacities and association with cT_FH cells, and are important parameters for consideration in assessing vaccine-induced immune responses.

The interaction of anti-DNA antibodies with DNA antigen: Evidence for hysteresis for high avidity binding

Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus. Previous studies have indicated that the phosphodiester backbone is the main antigenic target, with electrostatic interactions important for high avidity. To define further these interactions, the effects of ionic strength on anti-DNA binding of SLE plasmas were assessed in association and dissociation assays by ELISA. As these studies demonstrated, increasing ionic strength to a concentration of 1000 mM NaCl reduced antibody binding although the extent of the reduction varied among samples. In dissociation assays, differences among plasmas were also observed. For one of the plasmas, binding to DNA displayed resistance to dissociation by increasing ionic strength even though these concentrations limited binding in association assays. Time course studies showed a gradual change in binding interactions. These studies indicate that anti-DNA binding can involve both electrostatic and non-electrostatic interactions, with binding in some plasmas showing evidence of hysteresis.

TOP-Plus Is a Versatile Biosensor Platform for Monitoring SARS-CoV-2 Antibody Durability

BACKGROUND

Low initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers dropping to undetectable levels within months after infection have raised concerns about long-term immunity. Both the antibody levels and the avidity of the antibody-antigen interaction should be examined to understand the quality of the antibody response.

METHODS

A testing-on-a-probe "plus" panel (TOP-Plus) was developed to include a newly developed avidity assay built into the previously described SARS-CoV-2 TOP assays that measured total antibody (TAb), surrogate neutralizing antibody (SNAb), IgM, and IgG on a versatile biosensor platform. TAb and SNAb levels were compared with avidity in previously infected individuals at 1.3 and 6.2 months after infection in paired samples from 80 patients with coronavirus disease 2019 (COVID-19). Sera from individuals vaccinated for SARS-CoV-2 were also evaluated for antibody avidity.

RESULTS

The newly designed avidity assay in this TOP panel correlated well with a reference Bio-Layer Interferometry avidity assay (r = 0.88). The imprecision of the TOP avidity assay was <10%. Although TAb and neutralization activity (by SNAb) decreased between 1.3 and 6.2 months after infection, the antibody avidity increased significantly (P < 0.0001). Antibody avidity in 10 SARS-CoV-2 vaccinated individuals (median: 28 days after vaccination) was comparable to the measured antibody avidity in infected individuals (median: 26 days after infection).

CONCLUSIONS

This highly precise and versatile TOP-Plus panel with the ability to measure SARS-CoV-2 TAb, SNAb, IgG, and IgM antibody levels and avidity of individual sera on one sensor can become a valuable asset in monitoring not only patients infected with SARS-CoV-2 but also the status of individuals' COVID-19 vaccination response.

An R848-Conjugated Influenza Virus Vaccine Elicits Robust Immunoglobulin G to Hemagglutinin Stem in a Newborn Nonhuman Primate Model

Eliciting broadly protective antibodies is a critical goal for the development of more effective vaccines against influenza. Optimizing protection is of particular importance in newborns, who are highly vulnerable to severe disease following infection. An effective vaccination strategy for this population must surmount the challenges associated with the neonatal immune system as well as mitigate the inherent immune subdominance of conserved influenza virus epitopes, responses to which can provide broader protection. Here, we show that prime-boost vaccination with a TLR7/8 agonist (R848)-conjugated influenza A virus vaccine elicits antibody responses to the highly conserved hemagglutinin stem and promotes rapid induction of virus neutralizing stem-specific antibodies following viral challenge. These findings support the efficacy of R848 as an effective adjuvant for newborns and demonstrate its ability to enhance antibody responses to subdominant antigenic sites in this at-risk population.

Administration of Multivalent Influenza Virus Recombinant Hemagglutinin Vaccine in Combination-Adjuvant Elicits Broad Reactivity Beyond the Vaccine Components

Combining variant antigens into a multivalent vaccine is a traditional approach used to provide broad coverage against antigenically variable pathogens, such as polio, human papilloma and influenza viruses. However, strategies for increasing the breadth of antibody coverage beyond the vaccine are not well understood, but may provide more anticipatory protection. Influenza virus hemagglutinin (HA) is a prototypic variant antigen. Vaccines that induce HA-specific neutralizing antibodies lose efficacy as amino acid substitutions accumulate in neutralizing epitopes during influenza virus evolution. Here we studied the effect of a potent combination adjuvant (CpG/MPLA/squalene-in-water emulsion) on the breadth and maturation of the antibody response to a representative variant of HA subtypes H1, H5 and H7. Using HA protein microarrays and antigen-specific B cell labelling, we show when administered individually, each HA elicits a cross-reactive antibody profile for multiple variants within the same subtype and other closely-related subtypes (homosubtypic and heterosubtypic cross-reactivity, respectively). Despite a capacity for each subtype to induce heterosubtypic cross-reactivity, broader coverage was elicited by simply combining the subtypes into a multivalent vaccine. Importantly, multiplexing did not compromise antibody avidity or affinity maturation to the individual HA constituents. The use of adjuvants to increase the breadth of antibody coverage beyond the vaccine antigens may help future-proof vaccines against newly-emerging variants.

Patient-blood management for COVID19 convalescent plasma therapy: relevance of affinity and donor-recipient differences in concentration of neutralizing antibodies

BACKGROUND

Coronavirus disease 2019 (COVID-19) convalescent plasma (CCP) is being extensively investigated as a treatment, with mixed results to date. Overall, there has been a generalized lack of appropriateness in prescriptions, which, in the field of transfusion medicine, is termed patient-blood management.

OBJECTIVES

We aimed to separate study design variables that could affect clinical outcome after CCP therapy. We focus here on variables such as pretransfusion antibody testing in recipients, dose adjustments and antibody affinity measurements.

SOURCES

We searched PubMed and preprint servers for relevant preclinical and clinical studies discussing each of these variables in the field of CCP therapy.

CONTENT

We show evidence that neglecting those variables has affected the outcomes of the vast majority of CCP clinical trials to date.

IMPLICATIONS

A better understanding of such variables will improve the design of the next generation of CCP clinical trials. This will likely lead to better clinical outcomes and will minimize risks of immune evasion from subneutralizing doses of neutralizing antibodies.

Computational modeling of microfluidic data provides high-throughput affinity estimates for monoclonal antibodies

Affinity measurement is a fundamental step in the discovery of monoclonal antibodies (mAbs) and of antigens suitable for vaccine development. Innovative affinity assays are needed due to the low throughput and/or limited dynamic range of available technologies. We combined microfluidic technology with quantum-mechanical scattering theory, in order to develop a high-throughput, broad-range methodology to measure affinity. Fluorescence intensity profiles were generated for out-of-equilibrium solutions of labelled mAbs and their antigen-binding fragments migrating along micro-columns with immobilized cognate antigen. Affinity quantification was performed by computational data analysis based on the Landau probability distribution. Experiments using a wide array of human or murine antibodies against bacterial or viral, protein or polysaccharide antigens, showed that all the antibody-antigen capture profiles (n = 841) generated at different concentrations were accurately described by the Landau distribution. A scale parameter W, proportional to the full-width-at-half-maximum of the capture profile, was shown to be independent of the antibody concentration. The W parameter correlated significantly (Pearson's r [p-value]: 0.89 [3 × 10-8]) with the equilibrium dissociation constant KD, a gold-standard affinity measure. Our method showed good intermediate precision (median coefficient of variation: 5%) and a dynamic range corresponding to KD values spanning from ~10-7 to ~10-11 Molar. Relative to assays relying on antibody-antigen equilibrium in solution, even when they are microfluidic-based, the method's turnaround times were decreased from 2 days to 2 h. The described computational modelling of antibody capture profiles represents a fast, reproducible, high-throughput methodology to accurately measure a broad range of antibody affinities in very low volumes of solution.

AP205 VLPs Based on Dimerized Capsid Proteins Accommodate RBM Domain of SARS-CoV-2 and Serve as an Attractive Vaccine Candidate

COVID-19 is a novel disease caused by SARS-CoV-2 which has conquered the world rapidly resulting in a pandemic that massively impacts our health, social activities, and economy. It is likely that vaccination is the only way to form “herd immunity” and restore the world to normal. Here we developed a vaccine candidate for COVID-19 based on the virus-like particle AP205 displaying the spike receptor binding motif (RBM), which is the major target of neutralizing antibodies in convalescent patients. To this end, we genetically fused the RBM domain of SARS-CoV-2 to the C terminus of AP205 of dimerized capsid proteins. The fused VLPs were expressed in E. coli, which resulted in insoluble aggregates. These aggregates were denatured in 8 M urea followed by refolding, which reconstituted VLP formation as confirmed by electron microscopy analysis. Importantly, immunized mice were able to generate high levels of IgG antibodies recognizing eukaryotically expressed receptor binding domain (RBD) as well as spike protein of SARS-CoV-2. Furthermore, induced antibodies were able to neutralize SARS-CoV-2/ABS/NL20. Additionally, this vaccine candidate has the potential to be produced at large scale for immunization programs.

TOP-Plus is a Versatile Biosensor Platform for Monitoring SARS-CoV-2 Antibody Durability

BACKGROUND

There is a concern that low initial SARS-CoV-2 antibody titers in individuals may drop to undetectable levels within months after infection. Although this may raise concerns over long term immunity, both the antibody levels and avidity of the antibody-antigen interaction should be examined to understand the quality of the antibody response.

METHODS

A testing-on-a-probe-plus panel (TOP-Plus) was developed, which included a newly developed avidity assay built into the previously described SARS-CoV-2 TOP assays that measured total antibody (TAb), surrogate neutralizing antibody (SNAb), IgM and IgG on a versatile biosensor platform. TAb and SNAb levels were compared with avidity in previously infected individuals at 1.3 and 6.2 months post-infection in paired samples from 80 COVID-19 patients.

RESULTS

The newly designed avidity assay in this TOP panel correlated well with a reference Bio-Layer Interferometry avidity assay (R=0.88). The imprecision of the TOP avidity assay was less than 9%. Although TAb and neutralization activity (by SNAb) decreased between 1.3 and 6.2 months post infection, the antibody avidity increased significantly (P < 0.0001).

Development of a novel assay to assess the avidity of dengue virus-specific antibodies elicited in response to a tetravalent dengue vaccine

Antibody affinity maturation is a critical step in development of functional antiviral immunity; however, accurate measurement of affinity maturation of polyclonal serum antibody responses to particulate antigens such as virions is challenging. We describe a novel avidity assay employing biolayer interferometry and dengue virus-like particles. After validation using anti-dengue monoclonal antibodies, the assay was used to assess avidity of antibody responses to a tetravalent dengue vaccine candidate (TAK-003) in children, adolescents, and adults during two phase 2 clinical trials conducted in dengue-endemic regions. Vaccination increased avidity index and avidity remained high through 1 year postvaccination. Neutralizing antibody titers and avidity index did not correlate overall; however, a correlation was observed between neutralizing antibody titer and avidity index in those subjects with the highest degree of antibody affinity maturation. Therefore, vaccination with TAK-003 stimulates polyclonal affinity maturation and functional antibody responses, including neutralizing antibodies.

A facile method of mapping HIV-1 neutralizing epitopes using chemically masked cysteines and deep sequencing

Identification of specific epitopes targeted by neutralizing antibodies is essential to advance epitope-based vaccine design strategies. We report a facile methodology for rapid epitope mapping of neutralizing antibodies (NAbs) against HIV-1 Envelope (Env) at single-residue resolution, using Cys labeling, viral neutralization assays, and deep sequencing. This was achieved by the generation of a library of Cys mutations in Env glycoprotein on the viral surface, covalent labeling of the Cys residues using a Cys-reactive label that masks epitope residues, followed by infection of the labeled mutant virions in mammalian cells in the presence of NAbs. Env gene sequencing from NAb-resistant viruses was used to accurately delineate epitopes for the NAbs VRC01, PGT128, and PGT151. These agreed well with corresponding experimentally determined structural epitopes previously inferred from NAb:Env structures. HIV-1 infection is associated with complex and polyclonal antibody responses, typically composed of multiple antibody specificities. Deconvoluting the epitope specificities in a polyclonal response is a challenging task. We therefore extended our methodology to map multiple specificities of epitopes targeted in polyclonal sera, elicited in immunized animals as well as in an HIV-1-infected elite neutralizer capable of neutralizing tier 3 pseudoviruses with high titers. The method can be readily extended to other viruses for which convenient reverse genetics or lentiviral surface display systems are available.

A general strategy to control antibody specificity against targets showing molecular and biological similarity: Salmonella case study

The control of antibody specificity plays pivotal roles in key technological fields such as diagnostics and therapeutics. During the development of immunoassays (IAs) for the biosensing of pathogens in food matrices, we have found a way to rationalize and control the specificity of polyclonal antibodies (sera) for a complex analytical target (the Salmonella genus), in terms of number of analytes (Salmonella species) and potential cross-reactivity with similar analytes (other bacteria strains). Indeed, the biosensing of Salmonella required the development of sera and serum mixtures displaying homogeneous specificity for a large set of strains showing broad biochemical variety (54 Salmonella serovars tested in this study), which partially overlaps with the molecular features of other class of bacteria (like specific serogroups of E. coli). To achieve a trade-off between specificity harmonisation and maximization, we have developed a strategy based on the conversion of the specificity profiles of individual sera in to numerical descriptors, which allow predicting the capacity of serum mixtures to detect multiple bacteria strains. This approach does not imply laborious purification steps and results advantageous for process scaling-up, and may help in the customization of the specificity profiles of antibodies needed for diagnostic and therapeutic applications such as multi-analyte detection and recombinant antibody engineering, respectively.

Modelling the roles of antibody titre and avidity in protection from Plasmodium falciparum malaria infection following RTS,S/AS01 vaccination

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Models capturing key malaria life-cycle stages can help us evaluate vaccine candidates.

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Model fitting revealed antibody avidity to be an important determinant of RTS,S vaccine efficacy.

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High avidity and titre were associated with increased levels of vaccine efficacy.

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Did not identify any thresholds of protection for either immune marker.

Anti-circumsporozoite antibody titres have been established as an essential indicator for evaluating the immunogenicity and protective capacity of the RTS,S/AS01 malaria vaccine. However, a new delayed-fractional dose regime of the vaccine was recently shown to increase vaccine efficacy, from 62.5% (95% CI 29.4–80.1%) under the original dosing schedule to 86.7% (95% CI, 66.8–94.6%) without a corresponding increase in antibody titres. Here we reanalyse the antibody data from this challenge trial to determine whether IgG avidity may help to explain efficacy better than IgG titre alone by adapting a within-host mathematical model of sporozoite inoculation. We demonstrate that a model incorporating titre and avidity provides a substantially better fit to the data than titre alone. These results also suggest that in individuals with a high antibody titre response that also show high avidity (both metrics in the top tercile of observed values) delayed-fractional vaccination provided near perfect protection upon first challenge (98.2% [95% Credible Interval 91.6–99.7%]). This finding suggests that the quality of the vaccine induced antibody response is likely to be an important determinant in the development of highly efficacious pre-erythrocytic vaccines against malaria.

Development and Validation of the Elecsys Anti-SARS-CoV-2 Immunoassay as a Highly Specific Tool for Determining Past Exposure to SARS-CoV-2

The Elecsys Anti-SARS-CoV-2 immunoassay (Roche Diagnostics) was developed to provide accurate, reliable detection of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated sensitivity, specificity, cross-reactivity, and agreement with a vesicular stomatitis virus-based pseudoneutralization assay for the Elecsys Anti-SARS-CoV-2 immunoassay. Sensitivity and agreement between Elecsys Anti-SARS-CoV-2 immunoassay and pseudoneutralization assay measurements were evaluated using samples from patients with PCR-confirmed SARS-CoV-2 infection, a majority of whom were hospitalized. Specificity was evaluated using samples from routine diagnostic testing/blood donors collected before December 2019 and thus deemed negative for SARS-CoV-2-specific antibodies. Cross-reactivity was evaluated using samples containing a wide range of potentially cross-reacting analytes, purchased from commercial vendors. For sensitivity and specificity, point estimates and 95% confidence intervals (CIs) were calculated. Agreement between the Elecsys Anti-SARS-CoV-2 immunoassay and the pseudoneutralization assay was calculated. The sensitivity of the Elecsys Anti-SARS-CoV-2 immunoassay in patients with prior PCR-confirmed SARS-CoV-2 infection was 99.5% (95% CI, 97.0 to 100.0%) at ≥14 days post-PCR confirmation. Overall specificity (n = 10,453) was 99.80% (95% CI, 99.69 to 99.88%). Only 4/792 samples containing potential cross-reacting analytes were reactive with the Elecsys Anti-SARS-CoV-2 immunoassay, resulting in an overall specificity in this cohort of 99.5% (95% CI, 98.6 to 99.9%). Positive, negative, and overall agreement (n = 46) between the Elecsys Anti-SARS-CoV-2 immunoassay and the pseudoneutralization assay were 86.4% (95% CI, 73.3 to 93.6%), 100% (95% CI, 34.2 to 100%), and 87.0% (95% CI, 74.3 to 93.9%), respectively. The Elecsys Anti-SARS-CoV-2 immunoassay demonstrated high sensitivity (99.5% at ≥14 days post-PCR confirmation) and specificity (99.80%), supporting its use as a tool for identification of past SARS-CoV-2 infection, including use in populations with low disease prevalence.

CTLA-4 Blockade, during HIV Virus-Like Particles Immunization, Alters HIV-Specific B-Cell Responses

Studies have shown that blockade of CTLA-4 promoted the expansion of germinal center B-cells in viral infection or immunization with model antigens. Few studies have evaluated the immunological consequences of CTLA-4 blockade during immunization against relevant vaccine candidates. Here, we investigated the effects of CTLA-4 blockade on HIV virus-like particles (VLPs) vaccination in a C57BL/6J mouse model. We found that CTLA-4 blockade during HIV VLP immunization resulted in increased CD4+ T-cell activation, promoted the expansion of HIV envelope (Env)-specific follicular helper T cell (Tfh) cells, and significantly increased HIV Gag- and Env-specific IgG with higher avidity and antibody-dependent cellular cytotoxicity (ADCC) capabilities. Furthermore, after only a single immunization, CTLA-4 blockade accelerated T-cell dependent IgG class switching and the induction of significantly high serum levels of the B-cell survival factor, A proliferation-inducing ligand (APRIL). Although no significant increase in neutralizing antibodies was observed, increased levels of class-switched Env- and Gag-specific IgG are indicative of increased polyclonal B-cell activation, which demonstrated the ability to mediate and enhance ADCC in this study. Altogether, our findings show that CTLA-4 blockade can increase the levels of HIV antigen-specific B-cell and antigen-specific Tfh cell activity and impact humoral immune responses when combined with a clinically relevant HIV VLP-based vaccine.

Anti-EGF antibodies as surrogate biomarkers of clinical efficacy in stage IIIB/IV non-small-cell lung cancer patients treated with an optimized CIMAvax-EGF vaccination schedule

We previously reported that CIMAvax-EGF vaccine is safe, immunogenic and efficacious to treat advanced non-small-cell lung cancer (NSCLC) patients. A phase III trial was designed using an optimized immunization schedule. It included higher antigen dose and injections at multiple sites. Immune response and circulating biomarkers were studied in a subset of patients. EGF-specific antibody titers, IgG subclasses, peptide immunodominance and circulating biomarkers were assessed by ELISA. In vitro EGF-neutralization capacity of immune sera and EGF-IgG binding kinetics was evaluated by Western Blot and Surface Plasmon Resonance (SPR) technology, respectively. We show that CIMAvax-EGF elicited mainly IgG3/IgG4 antibodies at titers exceeding 1:4000 in 80% of vaccinated patients after 3 months of treatment. The EGF-specific humoral response was directed against the central region of the EGF molecule. For the first time, the kinetic constants of EGF-specific antibodies were measured evidencing affinity maturation of antibody repertoire up to month 12 of vaccination. Notably, the capacity of post-immune sera to inhibit EGFR phosphorylation significantly increased during the course of the immunization scheme and was related to clinical outcome (P = .013, log-rank test). Basal concentrations of EGF and TGFα in the serum were affected by EGF-based immunization. In conclusion, the CIMAvax-EGF vaccine induces an EGF-specific protective humoral response in a high percent of NSCLC vaccinated patients, the quantity and quality of which were associated with clinical benefit (clinical trial registration number: RPCEC00000161, http://registroclinico.sld.cu/).

Abbreviations

EGF: epidermal growth factor; EGFR: epidermal growth factor receptor; Ab: antibody; AR: amphiregulin; NSCLC: non-small-cell lung cancer; rhEGF: recombinant human epidermal growth factor; BSC: best supportive care; TGFα: tumor growth factor alpha; IL-8: interleukin 8; MAb: monoclonal antibody; SPR: surface plasmon resonance

Influenza-infected newborn and adult monkeys exhibit a strong primary antibody response to hemagglutinin stem

The specificity of antibodies (Abs) generated against influenza A virus (IAV) infection can significantly alter protection and viral clearance. At present, the impact of age upon this process is relatively unexplored. Here, we evaluated the Ab response in newborn and adult African green monkeys following infection with IAV using a strain that enables us to determine the immunodominance (ID) hierarchy of the Ab response to hemagglutinin (HA), the principal target of protective Abs. This revealed altered ID patterns in the early IgM anti-HA response in newborns versus adults that converged over time. While the IgG ID profiles for HA in newborn and adult monkeys were similar, this was not the case for IgA. Importantly, HA stem-specific Abs were generated robustly and similarly in newborns and adults in terms of quality and quantity. Together, these results demonstrate that newborns and adults can differ in the Ab ID pattern established following infection and that the ID pattern can vary across isotypes. In addition, newborns have the ability to generate potent HA stem-specific Ab responses. Our findings further the understanding of the newborn response to IAV antigens and inform the development of improved vaccines for this at-risk population.

Serum dilutions as a predictive biomarker for peri-operative desensitization: An exploratory approach to transplanting sensitized heart candidates

Antibody-mediated rejection (AMR) of cardiac allografts mediated by anti-HLA Donor Specific Antibodies (DSA) is one of the major barriers to successful transplantation for the treatment of end-stage heart failure. Therapeutic plasma exchange (TPE) is a first-line treatment for pre-transplant desensitization. However, indications for treatment regimens and treatment end-points have not been well established. In this study, we investigated how sera dilutions could guide TPE regimens for effective peri-operative desensitization and early AMR treatment. Our data show that 1:16 dilutions of EDTA-treated sera and 1.5 volume TPE reduce anti-HLA class I and class II antibody levels in the same manner and, therefore, allows to predict which antibodies would respond to peri-operative TPE. We successfully applied this approach to transplanting three highly sensitized cardiac recipients (CPRA 85-93%) with peri-operative desensitization based on a virtual crossmatch performed on 1:16 diluted serum. Furthermore, we have used sera dilutions to guide DSA treatment post-transplant. Although these findings have to be confirmed in a larger prospective study, our data suggest that serum dilutions can serve as a predictive biomarker to guide peri-operative desensitization and post-transplant immunologic management.

Neutralizing Antibody Induction by HIV-1 Envelope Glycoprotein SOSIP Trimers on Iron Oxide Nanoparticles May Be Impaired by Mannose Binding Lectin

We covalently attached human immunodeficiency virus type 1 (HIV-1) Env SOSIP trimers to iron oxide nanoparticles (IO-NPs) to create a particulate immunogen for neutralizing antibody (NAb) induction. The attached trimers, ∼20 per particle, retained native-like antigenicity, judged by reactivity with NAbs and non-NAbs. Bivalent (BG505 and B41) trimer IO-NPs were made, as were IO-NPs displaying B41 trimers carrying a PADRE T-cell helper epitope (TCHE). We immunized mice with B41 soluble or IO-NP trimers after PADRE peptide priming. After two immunizations, IO-NP presentation and the TCHE tag independently and substantially increased anti-trimer antibody responses, but titer differences waned after two further doses. Notable and unexpected findings were that autologous NAbs to the N289 glycan hole epitope were consistently induced in mice given soluble but not IO-NP trimers. Various recombinant mannose binding lectins (MBLs) and MBLs in sera of both murine and human origin bound to soluble and IO-NP trimers. MBL binding occluded the autologous NAb epitope on the B41 IO-NP trimers, which may contribute to its poor immunogenicity. The exposure of a subset of broadly active NAb epitopes was also impaired by MBL binding, which could have substantial implications for the utility of trimer-bearing nanoparticles in general and perhaps also for soluble Env proteins.IMPORTANCE Recombinant trimeric SOSIP proteins are vaccine components intended to induce neutralizing antibodies (NAbs) that prevent cells from infection by human immunodeficiency virus type 1 (HIV-1). A way to increase the strength of antibody responses to these proteins is to present them on the surface of nanoparticles (NPs). We chemically attached about 20 SOSIP trimers to NPs made of iron oxide (IO). The resulting IO-NP trimers had appropriate properties when we studied them in the laboratory but, unexpectedly, were less able to induce NAbs than nonattached trimers when used to immunize mice. We found that mannose binding lectins, proteins naturally present in the serum of mice and other animals, bound strongly to the soluble and IO-NP trimers, blocking access to antibody epitopes in a way that may impede the development of NAb responses. These findings should influence how trimer-bearing NPs of various designs are made and used.

Constituting a glutathione S-transferase-cocktail vaccine against tick infestation

Cocktail vaccines are proposed as an attractive way to increase protection efficacy against specific tick species. Furthermore, such vaccines made with different tick antigens have the potential of cross-protecting against a broad range of tick species. However, there are still limitations to the selection of immunogen candidates. Acknowledging that glutathione S-transferases (GSTs) have been exploited as vaccines against ticks and other parasites, this study aimed to analyze a GST-cocktail vaccine as a potential broad-spectrum tick vaccine. To constitute the GST-cocktail vaccine, five tick species of economic importance for livestock industry were studied (Rhipicephalus appendiculatus, Rhipicephalus decoloratus, Rhipicephalus microplus, Amblyomma variegatum, and Haemaphysalis longicornis). Tick GST ORF sequences were cloned, and the recombinant GSTs were produced in Escherichia coli. rGSTs were purified and inoculated into rabbits, and the immunological response was characterized. The humoral response against rGST-Rd and rGST-Av showed a stronger cross-reactivity against heterologous rGSTs compared to rGST-Hl, rGST-Ra, and rGST-Rm. Therefore, rGST-Rd and rGST-Av were selected for constituting an experimental rGST-cocktail vaccine. Vaccination experiment in rabbits showed that rGST-cocktail caused 35% reduction in female numbers in a Rhipicephalus sanguineus infestation. This study brings forward an approach to selecting immunogens for cocktail vaccines, and the results highlight rGST-Rd and rGST-Av as potentially useful tools for the development of a broad-spectrum tick vaccine.

Characterising antibody avidity in individuals of varied Mycobacterium tuberculosis infection status using surface plasmon resonance

There is increasing evidence supporting a role for antibodies in protection against tuberculosis (TB), with functional antibodies being described in the latent state of TB infection. Antibody avidity is an important determinant of antibody-mediated protection. This study characterised the avidity of antibodies against Ag85A, an immunodominant Mycobacterium tuberculosis (M.tb) antigen and constituent of several anti-TB vaccine candidates, in individuals of varied M.tb infection status. Avidity of Ag85A specific antibodies was measured in 30 uninfected controls, 34 individuals with latent TB infection (LTBI) and 75 active pulmonary TB (APTB) cases, employing the more commonly used chaotrope-based dissociation assays, and surface plasmon resonance (SPR). Chaotrope-based assays indicated that APTB was associated with a higher antibody avidity index compared to uninfected controls [adjusted geometric mean ratio (GMR): 1.641, 95% confidence interval (CI): 1.153, 2.337, p = 0.006, q = 0.018] and to individuals with LTBI [adjusted GMR: 1.604, 95% CI: 1.282, 2.006, p < 0.001, q <0.001]. SPR assays showed that APTB was associated with slower dissociation rates, an indication of higher avidity, compared to uninfected controls (adjusted GMR: 0.796, 95% CI: 0.681, 0.932, p = 0.004, q = 0.012) and there was also weak evidence of more avid antibodies in the LTBI compared to the uninfected controls (adjusted GMR: 0.871, 95% CI: 0.763, 0.994, p = 0.041, q = 0.123). We found no statistically significant differences in anti-Ag85A antibody avidity between the APTB and LTBI groups. This study shows that antibodies of increased avidity are generated against a principle vaccine antigen in M.tb infected individuals. It would be important to determine whether TB vaccines are able to elicit a similar response. Additionally, more research is needed to determine whether antibody avidity is important in protection against infection and disease.

Qualified Biolayer Interferometry Avidity Measurements Distinguish the Heterogeneity of Antibody Interactions with Plasmodium falciparum Circumsporozoite Protein Antigens

Ab avidity is a measure of the overall strength of Ab–Ag interactions and hence is important for understanding the functional efficiency of Abs. In vaccine evaluations, Ab avidity measurements can provide insights into immune correlates of protection and generate hypotheses regarding mechanisms of protection to improve vaccine design to achieve higher levels of efficacy. The commonly used Ab avidity assays require the use of chaotropic reagents to measure avidity index. In this study, using real-time detection of Ab–Ag binding by biolayer interferometry (BLI) technique, we have developed a qualified assay for measuring avidity of vaccine-induced Abs specific for Plasmodium falciparum circumsporozoite protein (CSP) Ags. Human mAb derived from plasmablasts of recipients of RTS,S/AS01 (RTS,S), the most advanced malaria vaccine candidate, were used in the assay development to measure Ag-specific binding responses and rate constants of association and dissociation. The optimized BLI binding assay demonstrated 1) good precision (percentage of coefficient of variation <20), 2) high specificity, 3) a lower limit of detection and quantitation in the 0.3–3.3 nM range, and 4) a range of linearity up to 50–100 nM for the CSP Ags tested. Analysis of polyclonal sera of malaria vaccinees demonstrated the suitability of this method to distinguish among vaccinees and rank Ab responses by avidity. These results demonstrate that precise, specific, and sensitive BLI measurements of Ab avidity in polyclonal sera from malaria vaccinees can map Ab response heterogeneity and potentially help to determine the role of Ab avidity as an immune correlate of protection for vaccines.

Activation of the endoplasmic reticulum stress sensor IRE1α by the vaccine adjuvant AS03 contributes to its immunostimulatory properties

The oil-in-water emulsion Adjuvant System 03 (AS03) is one of the few adjuvants used in licensed vaccines. Previous work indicates that AS03 induces a local and transient inflammatory response that contributes to its adjuvant effect. However, the molecular mechanisms involved in its immunostimulatory properties are ill-defined. Upon intramuscular injection in mice, AS03 elicited a rapid and transient downregulation of lipid metabolism-related genes in the draining lymph node. In vitro, these modifications were associated with profound changes in lipid composition, alteration of endoplasmic reticulum (ER) morphology and activation of the unfolded protein response pathway. In vivo, treatment with a chemical chaperone or deletion of the ER stress sensor kinase IRE1α in myeloid cells decreased AS03-induced cytokine production and its capacity to elicit high affinity antigen-specific antibodies. In summary, our results indicate that IRE1α is a sensor for the metabolic changes induced by AS03 in monocytic cells and may constitute a canonical pathway that could be exploited for the design of novel vaccine adjuvants.

Systems serology: profiling vaccine induced humoral immunity against HIV

The results of the RV144 HIV vaccine, in combination with several recent non-human primate vaccine studies continue to highlight the potentially protective role of non-neutralizing Fc functional antibodies in HIV vaccine design. For many currently licensed vaccines, assays that detect antigen-specific antibody titers or neutralization levels have been used as a correlate of protection. However, antibodies can confer protection through multiple other mechanisms beyond neutralization, or mechanisms which are not dependent on total antibody titers. Alternative strategies that allow us to further understand the precise mechanisms by which antibodies confer protection against HIV and other infectious pathogens is vitally important for the development of future vaccines. Systems serology aims to comprehensively survey a diverse array of antibody features and functions, in order to simultaneously examine the mechanisms behind and distinguish the most important antibody features required for protection, thus identifying key targets for future experimental vaccine testing. This review will focus on the technical aspects required for the application of Systems serology and summarizes the recent advances provided by application of this systemic analytical approach.

Prospects from systems serology research

Antibodies are highly functional glycoproteins capable of providing immune protection through multiple mechanisms, including direct pathogen neutralization and the engagement of their Fc portions with surrounding effector immune cells that induce anti-pathogenic responses. Small modifications to multiple antibody biophysical features induced by vaccines can significantly alter functional immune outcomes, though it is difficult to predict which combinations confer protective immunity. In order to give insight into the highly complex and dynamic processes that drive an effective humoral immune response, here we discuss recent applications of 'Systems Serology', a new approach that uses data-driven (also called 'machine learning') computational analysis and high-throughput experimental data to infer networks of important antibody features associated with protective humoral immunity and/or Fc functional activity. This approach offers the ability to understand humoral immunity beyond single correlates of protection, assessing the relative importance of multiple biophysical modifications to antibody features with multivariate computational approaches. Systems Serology has the exciting potential to help identify novel correlates of protection from infection and may generate a more comprehensive understanding of the mechanisms behind protection, including key relationships between specific Fc functions and antibody biophysical features (e.g. antigen recognition, isotype, subclass and/or glycosylation events). Reviewed here are some of the experimental and computational technologies available for Systems Serology research and evidence that the application has broad relevance to multiple different infectious diseases including viruses, bacteria, fungi and parasites.

HIV-1 Env- and Vpu-Specific Antibody-Dependent Cellular Cytotoxicity Responses Associated with Elite Control of HIV

Studying HIV-infected individuals who control HIV replication (elite controllers [ECs]) enables exploration of effective anti-HIV immunity. HIV Env-specific and non-Env-specific antibody-dependent cellular cytotoxicity (ADCC) may contribute to protection from progressive HIV infection, but the evidence is limited. We recruited 22 ECs and matched them with 44 viremic subjects. HIV Env- and Vpu-specific ADCC responses in sera were studied using a novel enzyme-linked immunosorbent assay (ELISA)-based dimeric recombinant soluble FcγRIIIa (rsFcγRIIIa)-binding assay, surface plasmon resonance, antibody-dependent natural killer (NK) cell activation assays, and ADCC-mediated killing assays. ECs had higher levels of HIV Env-specific antibodies capable of binding FcγRIIIa, activating NK cells, and mediating granzyme B activity (all P < 0.01) than viremic subjects. ECs also had higher levels of antibodies against a C-terminal 13-mer Vpu peptide capable of mediating FcγRIIIa binding and NK cell activation than viremic subjects (both P < 0.05). Our data associate Env-specific and Vpu epitope-specific ADCC in effective immune responses against HIV among ECs. Our findings have implications for understanding the role of ADCC in HIV control.IMPORTANCE Understanding immune responses associated with elite control of HIV may aid the development of immunotherapeutic and vaccine strategies for controlling HIV infection. Env is a major HIV protein target of functional antibody responses that are heightened in ECs. Interestingly, EC antibodies also target Vpu, an accessory protein crucial to HIV, which degrades CD4 and antagonizes tetherin. Antibodies specific to Vpu are a common feature of the immune response of ECs that may prove to be of functional importance to the design of improved ADCC-based immunotherapy and preventative HIV vaccines.

Antibody-antigen kinetics constrain intracellular humoral immunity

During infection with non-enveloped viruses, antibodies stimulate immunity from inside cells by activating the cytosolic Fc receptor TRIM21. This intracellular humoral response relies on opsonized viral particles reaching the cytosol intact but the antigenic and kinetic constraints involved are unknown. We have solved the structure of a potent TRIM21-dependent neutralizing antibody in complex with human adenovirus 5 hexon and show how these properties influence immune activity. Structure-guided mutagenesis was used to generate antibodies with 20,000-fold variation in affinity, on-rates that differ by ~50-fold and off-rates by >175-fold. Characterization of these variants during infection revealed that TRIM21-dependent neutralization and NFκB activation was largely unaffected by on-rate kinetics. In contrast, TRIM21 antiviral activity was exquisitely dependent upon off-rate, with sub-μM affinity antibodies nevertheless unable to stimulate signaling because of fast dissociation kinetics. These results define the antibody properties required to elicit an efficient intracellular immune response during viral infection.

Structure-Based Reverse Vaccinology Failed in the Case of HIV Because it Disregarded Accepted Immunological Theory

Two types of reverse vaccinology (RV) should be distinguished: genome-based RV for bacterial vaccines and structure-based RV for viral vaccines. Structure-based RV consists in trying to generate a vaccine by first determining the crystallographic structure of a complex between a viral epitope and a neutralizing monoclonal antibody (nMab) and then reconstructing the epitope by reverse molecular engineering outside the context of the native viral protein. It is based on the unwarranted assumption that the epitope designed to fit the nMab will have acquired the immunogenic capacity to elicit a polyclonal antibody response with the same protective capacity as the nMab. After more than a decade of intensive research using this type of RV, this approach has failed to deliver an effective, preventive HIV-1 vaccine. The structure and dynamics of different types of HIV-1 epitopes and of paratopes are described. The rational design of an anti-HIV-1 vaccine is shown to be a misnomer since investigators who claim that they design a vaccine are actually only improving the antigenic binding capacity of one epitope with respect to only one paratope and not the immunogenic capacity of an epitope to elicit neutralizing antibodies. Because of the degeneracy of the immune system and the polyspecificity of antibodies, each epitope studied by the structure-based RV procedure is only one of the many epitopes that the particular nMab is able to recognize and there is no reason to assume that this nMab must have been elicited by this one epitope of known structure. Recent evidence is presented that the trimeric Env spikes of the virus possess such an enormous plasticity and intrinsic structural flexibility that it is it extremely difficult to determine which Env regions are the best candidate vaccine immunogens most likely to elicit protective antibodies.