Increase In Neutralizing Activity Research Articles

Evaluation of Long-Term Adaptive Immune Responses Specific to SARS-CoV-2: Effect of Various Vaccination and Omicron Exposure.

The immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) becomes increasingly complex as individuals receive different combinations of vaccine doses and encounter breakthrough infections. Our study focused on the immunogenicity observed over a two-year period in healthy individuals who completed a two-dose series and then experienced booster and/or Omicron infection. In June 2023, we recruited 78 healthcare workers who had previously participated in clinical research initiated in March 2021 at a single medical center in South Korea. At 1, 5, 11, and 25 months after a second dose, we assessed SARS-CoV-2-specific humoral and cellular immune responses. Longitudinal monitoring revealed a significant decline in humoral immunity levels after the second vaccine dose, followed by a substantial increase post-third vaccination or breakthrough infection. In contrast, stable cellular immune responses were consistently observed, with peak humoral and cellular immune measures reached at 25 months after the second dose. Among infection-naïve participants, three-dose vaccinated individuals had decreased neutralizing activity against wild-type (WT) and negative activities against Omicron subvariants BA.2 and BA.4/5, whereas those who received a fourth dose of bivalent BNT had significantly increased neutralizing activity (p < 0.05). All immune metrics tended to increase as the number of vaccine doses increased. Among participants with 4-exposure, homologous vaccination (mRNA × 4) led to higher humoral immunity, whereas heterologous vaccination (ChAd × 2/mRNA × 2) induced stronger cellular responses against multiple SARS-CoV-2 variants by enzyme-linked immunospot assays (p < 0.05). Immune responses from bivalent vaccines or Omicron infection did not show statistically significant differences among exposure number-matched participants (p > 0.05). Omicron exposure significantly increased cross-neutralizing activity, but magnitude of cellular immunity was not significantly altered by Omicron exposure. Our longitudinal study highlights the evolving complexity of SARS-CoV-2 immune responses, showing enhanced immunity with multiple vaccine doses and robust cellular responses from heterologous vaccination. These findings emphasize the need for ongoing surveillance to optimize vaccination strategies against emerging variants.

A Novel Polymer Nanoparticle Polydimethyl Diallyl Ammonium Chloride as An Adjuvant Enhances the Immune Response of SARS-CoV-2 Subunit Vaccine.

The Coronavirus Disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 has a significant impact on global health and the economy. It has underscored the urgent need for a stable, easily produced and effective vaccine. This study presents a novel approach using SARS-CoV-2 spike (S) protein-conjugated nanoparticles (NPs) in combination with cyclic GMP-AMP (cGAMP) (S-NPs-cGAMP) as a subunit vaccine. When mice are immunized, the antiserum of S-NPs-cGAMP group exhibits a 16-fold increase in neutralizing activity against a pseudovirus, compared to S protein group. Additionally, S-NPs-cGAMP induces even higher levels of neutralizing antibodies. Remarkably, the vaccine also triggers a robust humoral immune response, as evidenced by a notable elevation in virus-specific IgG and IgM antibodies. Furthermore, after 42 days of immunization, there is an observed increase in specific immune cell populations in the spleen. CD3+CD4+ and CD3+CD8+T lymphocytes, as well as B220+CD19+ and CD3-CD49b+ NK lymphocytes, show an upward trend, indicating a positive cellular immune response. Moreover, the S-NPs-cGAMP demonstrates promising results against the Delta strain and exhibits good cross-neutralization potential against other variants. These findings suggest that pDMDAAC NPs is potential adjuvant and could serve as a versatile platform for future vaccine development.

Vpr attenuates antiviral immune responses and is critical for full pathogenicity of SIVmac239 in rhesus macaques

The accessory viral protein R (Vpr) is encoded by all primate lentiviruses. Vpr counteracts DNA repair pathways, modulates viral immune sensing, and induces cell-cycle arrest in cell culture. However, its impact invivo is controversial. Here, we show that deletion of vpr is associated with delayed viral replication kinetics, rapid innate immune activation, development and maintenance of strong B and Tcell responses, and increased neutralizing activity against SIVmac239 in rhesus macaques. All wild-type SIVmac239-infected animals maintained high viral loads, and five of six developed fatal immunodeficiency during ∼80weeks of follow-up. Lack of Vpr was associated with better preservation of CD4+ Tcells, lower viral loads, and an attenuated clinical course of infection in most animals. Our results show that Vpr contributes to efficient viral immune evasion and the full pathogenic potential of SIVmacinvivo. Inhibition of Vpr may improve humoral immune control of viral replication.

Hepatitis E virus neutralization by porcine serum antibodies.

The consumption of raw or undercooked meat products poses a serious risk for human hepatitis E virus (HEV) infections. In many high-income countries, domestic pigs and wild boars represent the main animal reservoirs for HEV and are usually identified by reverse transcription-PCR and antibody enzyme-linked immunosorbent assay (ELISA). In order to characterize the humoral immune response in more detail, a cell culture-based serum neutralization assay using a culture-adapted HEV strain was established here. Measurement of neutralizing antibodies was only possible after removing the viral quasi-envelope by detergent treatment. Serum samples of 343 wild boars from Northern Germany were first analyzed for anti-HEV IgG using an in-house ELISA, resulting in 19% positive samples. Subsequently, a subset of 41 representative samples was tested with the neutralization assay, and the results correlated well with those obtained by ELISA. Not only the human HEV strain 47832c but also two porcine HEV strains were shown to be neutralized by porcine serum antibodies. Neutralizing activity was also found in samples containing both HEV-specific antibodies and HEV RNA. Testing of serum samples derived from two experimentally infected domestic pigs showed a steep increase in neutralizing activity at 24 or 51 days post infection, dependent on the used infectious dose. The developed assay can be useful for characterization of the humoral immune response after HEV infection and for assessing the efficiency of HEV vaccine candidates.

Prior Vaccination Exceeds Prior Infection in Eliciting Innate and Humoral Immune Responses in Omicron Infected Outpatients.

Antibody response following Omicron infection is reported to be less robust than that to other variants. Here we investigated how prior vaccination and/or prior infection modulates that response. Disease severity, antibody responses and immune transcriptomes were characterized in four groups of Omicron-infected outpatients (n=83): unvaccinated/no prior infection, vaccinated/no prior infection, unvaccinated/prior infection and vaccinated/prior infection. The percentage of patients with asymptomatic or mild disease was highest in the vaccinated/no prior infection group (87%) and lowest in the unvaccinated/no prior infection group (47%). Significant anti-Omicron spike antibody levels and neutralizing activity were detected in the vaccinated group immediately after infection but were not present in the unvaccinated/no prior infection group. Within two weeks, antibody levels against Omicron, increased. Omicron neutralizing activity in the vaccinated group exceeded that of the prior infection group. No increase in neutralizing activity in the unvaccinated/no prior infection group was seen. The unvaccinated/prior infection group showed an intermediate response. We then investigated the early transcriptomic response following Omicron infection in these outpatient populations and compared it to that found in unvaccinated hospitalized patients with Alpha infection. Omicron infected patients showed a gradient of transcriptional response dependent upon whether or not they were previously vaccinated or infected. Vaccinated patients showed a significantly blunted interferon response as compared to both unvaccinated Omicron infected outpatients and unvaccinated Alpha infected hospitalized patients typified by the response of specific gene classes such as OAS and IFIT that control anti-viral responses and IFI27, a predictor of disease outcome.

Longitudinal Analysis of Coronavirus-Neutralizing Activity in COVID-19 Patients.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has now been continuing for more than two years. The infection causes COVID-19, a disease of the respiratory and cardiovascular system of variable severity. Here, the humoral immune response of 80 COVID-19 patients from the University Hospital Frankfurt/Main, Germany, was characterized longitudinally. The SARS-CoV-2 neutralization activity of serum waned over time. The neutralizing potential of serum directed towards the human alpha-coronavirus NL-63 (NL63) also waned, indicating that no cross-priming against alpha-coronaviruses occurred. A subset of the recovered patients (n = 13) was additionally vaccinated with the mRNA vaccine Comirnaty. Vaccination increased neutralization activity against SARS-CoV-2 wild-type (WT), Delta, and Omicron, although Omicron-specific neutralization was not detectable prior to vaccination. In addition, the vaccination induced neutralizing antibodies against the more distantly related SARS-CoV-1 but not against NL63. The results indicate that although SARS-CoV-2 humoral immune responses induced by infection wane, vaccination induces a broad neutralizing activity against multiple SARS-CoVs, but not to the common cold alpha-coronavirus NL63.

Single-Domain Antibodies Efficiently Neutralize SARS-CoV-2 Variants of Concern.

Virus-neutralizing antibodies are one of the few treatment options for COVID-19. The evolution of SARS-CoV-2 virus has led to the emergence of virus variants with reduced sensitivity to some antibody-based therapies. The development of potent antibodies with a broad spectrum of neutralizing activity is urgently needed. Here we isolated a panel of single-domain antibodies that specifically bind to the receptor-binding domain of SARS-CoV-2 S glycoprotein. Three of the selected antibodies exhibiting most robust neutralization potency were used to generate dimeric molecules. We observed that these modifications resulted in up to a 200-fold increase in neutralizing activity. The most potent heterodimeric molecule efficiently neutralized each of SARS-CoV-2 variant of concern, including Alpha, Beta, Gamma, Delta and Omicron variants. This heterodimeric molecule could be a promising drug candidate for a treatment for COVID-19 caused by virus variants of concern.

A Step-By-Step Method to Detect Neutralizing Antibodies Against AAV using a Colorimetric Cell-Based Assay.

Recombinant adeno-associated viruses (rAAV) have proven to be a safe and successful vector for transferring genetic material to treat various health conditions in both the laboratory and the clinic. However, pre-existing neutralizing antibodies (NAbs) against AAV capsids pose an ongoing challenge for the successful administration of gene therapies in both large animal experimental models and human populations. Preliminary screening for host immunity against AAV is necessary to ensure the efficacy of AAV-based gene therapies as both a research tool and as a clinically viable therapeutic agent. This protocol describes a colorimetric in vitro assay to detect neutralizing factors against AAV serotype 6 (AAV6). The assay utilizes the reaction between an AAV encoding an alkaline phosphatase (AP) reporter gene and its substrate NBT/BCIP, which generates an insoluble quantifiable purple stain upon combination. In this protocol, serum samples are combined with an AAV expressing AP and incubated to permit potential neutralizing activity to occur. Virus serum mixture is subsequently added to cells to allow for viral transduction of any AAVs that have not been neutralized. The NBT/BCIP substrate is added and undergoes a chromogenic reaction, corresponding to viral transduction and neutralizing activity. The proportion of area colored is quantitated using a free software tool to generate neutralizing titers. This assay displays a strong positive correlation between coloration and viral concentration. Assessment of serum samples from sheep before and after administration of a recombinant AAV6 led to a dramatic increase in neutralizing activity (125 to >10,000-fold increase). The assay displayed adequate sensitivity to detect neutralizing activity in >1:32,000 serum dilutions. This assay provides a simple, rapid, and cost-effective method to detect NAbs against AAVs.

Deep dissection of the antiviral immune profile of patients with COVID-19

In light of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants potentially undermining humoral immunity, it is important to understand the fine specificity of the antiviral antibodies. We screened 20 COVID-19 patients for antibodies against 9 different SARS-CoV-2 proteins observing responses against the spike (S) proteins, the receptor-binding domain (RBD), and the nucleocapsid (N) protein which were of the IgG1 and IgG3 subtypes. Importantly, mutations which typically occur in the B.1.351 “South African” variant, significantly reduced the binding of anti-RBD antibodies. Nine of 20 patients were critically ill and were considered high-risk (HR). These patients showed significantly higher levels of transforming growth factor beta (TGF-β) and myeloid-derived suppressor cells (MDSC), and lower levels of CD4+ T cells expressing LAG-3 compared to standard-risk (SR) patients. HR patients evidenced significantly higher anti-S1/RBD IgG antibody levels and an increased neutralizing activity. Importantly, a large proportion of S protein-specific antibodies were glycosylation-dependent and we identified a number of immunodominant linear epitopes within the S1 and N proteins. Findings derived from this study will not only help us to identify the most relevant component of the anti-SARS-CoV-2 humoral immune response but will also enable us to design more meaningful immunomonitoring methods for anti-COVID-19 vaccines.

Long-term analysis of antibodies elicited by SPUTNIK V: A prospective cohort study in Tucumán, Argentina

BackgroundGam-COVID-Vac (SPUTNIK V) has been granted emergency use authorization in 70 nations and has been administered to millions worldwide. However, there are very few peer-reviewed studies describing its effects. Independent reports regarding safety and effectiveness could accelerate the final approval by the WHO. We aimed to study the long-term humoral immune response in naïve and previously infected volunteers who received SPUTNIK V.MethodsHumoral immune responses, assayed by anti-SARS-CoV-2-spike-RBD IgG ELISA and neutralization assays, were measured in 602 healthcare workers at 0, 14, 28, 60 and 180 days after receiving SPUTNIK V between December 2020 and July 2021 in Tucumán, Argentina.FindingsSeroconversion was detected in 97% of individuals after 28 days post-vaccination (dpv) (N = 405). Anti-RBD titers began to decrease after 60 dpv (N = 328), but remained detectable in 94% at 90 dpv (N = 224). At 180 dpv, anti-RDB titers persisted in 31% (N = 146). Previous infection triggered an increased immune response to the first dose and increased neutralization activity against variants of concern (VOC). Second doses in previously infected individuals further increased titers, even 90 dpv (N = 75). Basal antibody titers had more influence on post-vaccination anti-RBD responses than the time elapsed between diagnosis and vaccination (N = 274).InterpretationData presented herein provides essential knowledge regarding the kinetics of antibodies induced by SPUTNIK V up to six months after immunization, and suggests that when considering one-dose vaccination policies for individuals with previous SARS-CoV-2 infection, serological studies to determine basal titers may be important, independent of when diagnosis occurred.FundingTucumán Public Health System (SIPROSA), Argentinean National Research Council (CONICET), National University of Tucumán (UNT).

Anti-SARS-CoV-2 receptor-binding domain antibody evolution after mRNA vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection produces B cell responses that continue to evolve for at least a year. During that time, memory B cells express increasingly broad and potent antibodies that are resistant to mutations found in variants of concern1. As a result, vaccination of coronavirus disease 2019 (COVID-19) convalescent individuals with currently available mRNA vaccines produces high levels of plasma neutralizing activity against all variants tested1,2. Here we examine memory B cell evolution five months after vaccination with either Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) mRNA vaccine in a cohort of SARS-CoV-2-naive individuals. Between prime and boost, memory B cells produce antibodies that evolve increased neutralizing activity, but there is no further increase in potency or breadth thereafter. Instead, memory B cells that emerge five months after vaccination of naive individuals express antibodies that are similar to those that dominate the initial response. While individual memory antibodies selected over time by natural infection have greater potency and breadth than antibodies elicited by vaccination, the overall neutralizing potency of plasma is greater following vaccination. These results suggest that boosting vaccinated individuals with currently available mRNA vaccines will increase plasma neutralizing activity but may not produce antibodies with equivalent breadth to those obtained by vaccinating convalescent individuals.

Long-Term Analysis of Antibodies Elicited by Sputnik V in Tucuman, Argentina

Background: Gam-COVID-Vac, also known as SPUTNIK V, is the first COVID-19 vaccine registered, has emergency use authorization in 70 nations, and has been administered to millions worldwide. However, there are very few peer-reviewed studies describing its effects. As independent reports begin to be published, a more accurate picture regarding safety and effectiveness could accelerate approval by the WHO.Methods: An ELISA that detects anti-SARS-CoV-2-spike-RBD IgG was used, in both transversal and longitudinal studies, to analyze humoral immune responses in 602 healthcare workers who received SPUTNIK V between December 2020 and July 2021.Findings: Seroconversion was detected in 97% of individuals after 28 days post-vaccination (dpv). Anti-RBD titers began to decrease after 60 dpv, but remained detectable in 94% of volunteers at 90 dpv. At 180 dpv, anti-RDB titers persisted in 31% of volunteers. Previous SARS-CoV-2 infection triggered increased immune response to the first dose, and increased neutralization activity against different variants of concern. The second dose in previously infected individuals further increased anti-RBD titers, even after 90 dpv. However, not all individuals with previous infection responded equally, as only those with basal titers above a certain threshold showed robust responses. Time elapsed between COVID-19 diagnosis and vaccination did not influence titers elicited.Interpretation: Data presented herein provides essential knowledge regarding the kinetics of antibodies induced by SPUTNIK V up to six months after immunization, and suggests that when considering one-dose vaccination policies for individuals with previous SARS-CoV-2 infection, serological studies to determine basal titers may be important, independent of when diagnosis occurred.Funding Statement: This research was supported by the Ministry of Public Health of Tucumán (Argentina), Argentinean Research Council-CONICET (PIP 722 and 806), Argentinean Research Agency-MINCYT grants (PICT-2018-3379 and PICT2018-02989), National University of Tucuman (PIUNT-UNT D644/1 and D624), and Florencio Fiorini Foundation.Declaration of Interests: B. L. is a named inventor on a patent filed by the Icahn School of Medicine which includes the 293T-ACE2-TMPRSS2 (F8-2) cells used for the virus neutralization assay. All other have nothing to declare. Ethics Approval Statement: Protocols were approved by the regional ethics research boards (Ex. N° 3929-410-P-2020), following the Declaration of Helsinki. Personal data from all volunteers were encrypted. Eligibility criteria were age between 18 to 60 years without any COVID-19 symptoms at the time of vaccination. Individuals provided a signed informed consent to be included in the database of the present study.

IgA tetramerization improves target breadth but not peak potency of functionality of anti-influenza virus broadly neutralizing antibody.

Mucosal immunoglobulins comprise mainly secretory IgA antibodies (SIgAs), which are the major contributor to pathogen-specific immune responses in mucosal tissues. These SIgAs are highly heterogeneous in terms of their quaternary structure. A recent report shows that the polymerization status of SIgA defines their functionality in the human upper respiratory mucosa. Higher order polymerization of SIgA (i.e., tetramers) leads to a marked increase in neutralizing activity against influenza viruses. However, the precise molecular mechanisms underlying the effects of SIgA polymerization remain elusive. Here, we developed a method for generating recombinant tetrameric monoclonal SIgAs. We then compared the anti-viral activities of these tetrameric SIgAs, which possessed variable regions identical to that of a broadly neutralizing anti-influenza antibody F045-092 against influenza A viruses, with that of monomeric IgG or IgA. The tetrameric SIgA showed anti-viral inhibitory activity superior to that of other forms only when the antibody exhibits low-affinity binding to the target. By contrast, SIgA tetramerization did not substantially modify anti-viral activity against targets with high-affinity binding. Taken together, the data suggest that tetramerization of SIgA improved target breadth, but not peak potency of antiviral functions of the broadly neutralizing anti-influenza antibody. This phenomenon presumably represents one of the mechanisms by which SIgAs present in human respiratory mucosa prevent infection by antigen-drifted influenza viruses. Understanding the mechanisms involved in cross neutralization of viruses by SIgAs might facilitate the development of vaccine strategies against viral infection of mucosal tissues.

Enhanced Bioactivity of the Anti-LOX-1 scFv Engineered by Multimerization Strategy.

Single-chain variable fragment (scFv) antibodies as therapeutic agents have the potential to reduce the production cost and immunogenicity relative to monoclonal antibodies, but their monovalency and lack of a fragment crystallizable region can lead to reduced function. Multimerization is one strategy for recovering the function; however, their application is limited by the production of multimeric proteins. In our previous study, an anti-lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) scFv showed potential use in diagnosis and therapy of atherosclerotic diseases, but is limited by its inherent low antigen-binding activity. In this study, to improve the efficacy of the anti-LOX-1 scFv, we constructed the anti-LOX-1 scFv multimers by modifying the linker length between the variable domains of the scFv or by fusing the scFv with self-merization domains and expressed these scFv multimers in Brevibacillus choshinensis hosts. After optimization, all of the scFv multimers obtained efficient secretion expression. Compared with the scFv monomer, the multimers that are successfully fractionated displayed increased neutralization activity and showed elevated antigen-binding avidity, especially the tetramer, which improved the antigen avidity by two orders of magnitude. Moreover, the scFv dimer and the tetramer both displayed better stability and longer half-life in serum, which can be attractive candidates for the next-generation anti-LOX-1 therapeutic antibody.

Effects of modification of the HIV-1 Env cytoplasmic tail on immunogenicity of VLP vaccines

We investigated the effects on assembly and antigenic properties of specific modifications of the transmembrane spanning (TMS) and cytoplasmic tail (CT) domains of HIV-1 Env from a transmitted/founder (T/F) ZM53 Env glycoprotein. A construct containing a short version of the TMS domain derived from the mouse mammary tumor virus (MMTV) Env with or without a GCN4 trimerization sequence in the CT exhibited the highest levels of incorporation into VLPs and induced the highest titers of anti-Env IgG immune responses in a VLP context. Sera from guinea pigs immunized by VLPs with high Env content, and containing the CT trimerization sequence, had increased neutralization activity and antibody avidity. A cross-clade prime-boost regimen with clade B SF162 or clade C ZM53 Env DNA priming and boosting with VLPs containing modified ZM53 Env further enhanced these immune responses. The modified VLPs demonstrate improved potential as HIV-1 vaccine antigens.

In vitro neutralization of prions with PrPSc-specific antibodies

Prion diseases reflect the misfolding of a self-protein (PrPC) into an infectious, pathological isomer (PrPSc). By targeting epitopes uniquely exposed by misfolding, our group developed PrPSc-specific vaccines to 3 disease specific epitopes (DSEs). Here, antibodies induced by individual DSE vaccines are evaluated for their capacity to neutralize prions in vitro. For both purified antibodies and immunoreactive sera, the PrPSc-specific antibodies were equally effective in neutralizing prions. Further, there was no significant increase in neutralizing activity when multiple DSEs were targeted within an assay. At a low antibody concentration, the PrPSc-specific antibodies matched the neutralization achieved by an antibody that may act via both PrPC and PrPSc. At higher doses, however, this pan-specific antibody was more effective, potentially due to a combined deactivation of PrPSc and depletion of PrPC.

Immunization with HSV-2 gB-CCL19 Fusion Constructs Protects Mice against Lethal Vaginal Challenge.

There is a lack of an HSV-2 vaccine, in part as the result of various factors that limit robust and long-term memory immune responses at the mucosal portals of viral entry. We previously demonstrated that chemokine CCL19 augmented mucosal and systemic immune responses to HIV-1 envelope glycoprotein. Whether such enhanced immunity can protect animals against virus infection remains to be addressed. We hypothesized that using CCL19 in a fusion form to direct an immunogen to responsive immunocytes might have an advantage over CCL19 being used in combination with an immunogen. We designed two fusion constructs, plasmid (p)gBIZCCL19 and pCCL19IZgB, by fusing CCL19 to the C- or N-terminal end of the extracellular HSV-2 glycoprotein B (gB) with a linker containing two (Gly4Ser)2 repeats and a GCN4-based isoleucine zipper motif for self-oligomerization. Following immunization in mice, pgBIZCCL19 and pCCL19IZgB induced strong gB-specific IgG and IgA in sera and vaginal fluids. The enhanced systemic and mucosal Abs showed increased neutralizing activity against HSV-2 in vitro. Measurement of gB-specific cytokines demonstrated that gB-CCL19 fusion constructs induced balanced Th1 and Th2 cellular immune responses. Moreover, mice vaccinated with fusion constructs were well protected from intravaginal lethal challenge with HSV-2. Compared with pgB and pCCL19 coimmunization, fusion constructs increased mucosal surface IgA(+) cells, as well as CCL19-responsive immunocytes in spleen and mesenteric lymph nodes. Our findings indicate that enhanced humoral and cellular immune responses can be achieved by immunization with an immunogen fused to a chemokine, providing information for the design of vaccines against mucosal infection by HSV-2 and other sexually transmitted viruses.

Germlining of the HIV-1 broadly neutralizing antibody domain m36

Engineered antibody domains (eAds) have emerged as a novel class of HIV-1 inhibitors and are currently under preclinical testing as promising drug candidates for prevention and therapy of HIV-1 infection. Reverse mutation of antibodies to germline sequences (germlining) could not only identify less mutated variants with lower probability of immunogenicity and other improved properties but also help elucidate their mechanisms of action. In this study, we sequentially reverted the framework (FRs) and complementary determining regions (CDRs) of m36, a human antibody heavy chain variable domain-based eAd targeting the coreceptor binding site of the viral envelope glycoprotein gp120, back to germline sequences. Two types of amino acid mutations and one region in the antibody V segment were identified that are critical for HIV-1 neutralization. These include four mutations to acidic acid residues distributed in the CDR1 and CDR2, two mutations to hydrophobic residues in the FR3 and CDR3, and partial FR2 and FR3 sequences flanking the CDR2 that are derived from a different gene family. An m36 variant with all five mutations in the FRs reverted back to germline showed slightly increased neutralizing activity against two HIV-1 isolates tested. Another variant with seven of twelve mutations in the V segment reverted retained potency within threefold of that of the mature antibody. These results, together with an analysis of m36–gp120-CD4 docking structures, could have implications for the further development of m36 and elucidation of its mechanism of potent and broad HIV-1 neutralization.

Mutations flanking the carbohydrate binding site of surfactant protein D confer antiviral activity for pandemic influenza A viruses

We recently reported that a trimeric neck and carbohydrate recognition domain (NCRD) fragment of human surfactant protein D (SP-D), a host defense lectin, with combinatorial substitutions at the 325 and 343 positions (D325A+R343V) exhibits markedly increased antiviral activity for seasonal strains of influenza A virus (IAV). The NCRD binds to glycan-rich viral envelope proteins including hemagglutinin (HA). We now show that replacement of D325 with serine to create D325S+R343V provided equal or increased neutralizing activity compared with D325A+R343V. The activity of the double mutants was significantly greater than that of either single mutant (D325A/S or R343V). D325A+R343V and D325S+R343V also strongly inhibited HA activity, and markedly aggregated, the 1968 pandemic H3N2 strain, Aichi68. D325S+R343V significantly reduced viral loads and mortality of mice infected with Aichi68, whereas wild-type SP-D NCRD did not. The pandemic H1N1 strains of 1918 and 2009 have only one N-linked glycan side on the head region of the HA and are fully resistant to inhibition by native SP-D. Importantly, we now show that D325A+R343V and D325S+R343V inhibited Cal09 H1N1 and related strains, and reduced uptake of Cal09 by epithelial cells. Inhibition of Cal09 was mediated by the lectin activity of the NCRDs. All known human pandemic strains have at least one glycan attachment on the top or side of the HA head, and our results indicate that they may be susceptible to inhibition by modified host defense lectins.

CCL19 and CCL28 Augment Mucosal and Systemic Immune Responses to HIV-1 gp140 by Mobilizing Responsive Immunocytes into Secondary Lymph Nodes and Mucosal Tissue

Induction of broad and potent neutralizing Abs at the mucosal portals of entry remains a primary goal for most vaccines against mucosally acquired viral infections. Selection of appropriate adjuvants capable of promoting both systemic and mucosal responses will be crucial for the development of effective immunization strategies. In this study, we investigated whether plasmid codelivery of cytokines APRIL, CCL19, or CCL28 can enhance Ag-induced immune responses to HIV-1 gp140. Our results demonstrated that pCCL19 and pCCL28, but not pAPRIL, significantly enhanced Ag-specific systemic and mucosal Ab responses. gp140-specific Abs in serum enhanced by pCCL19 or pCCL28 were broadly distributed across all four IgG subclasses, of which IgG1 was predominant. The enhanced systemic and mucosal Abs showed increased neutralizing activity against both homologous and heterologous HIV-1, and potency correlated with gp140-specific serum IgG and vaginal IgA levels. Measurement of gp140-specific cytokines produced by splenocytes demonstrated that pCCL19 and pCCL28 augmented balanced Th1/Th2 responses. pCCL19 and pCCL28 also increased IgA(+) cells in colorectal mucosal tissue. pCCL19 codelivery resulted in an increase of CCR7(+) CD11c(+) cells in mesenteric lymph nodes and both CCR7(+) CD11c(+) cells and CCR7(+) CD3e(+) cells in spleen, whereas pCCL28 codelivery resulted in an augment of CCR10(+) CD19(+) cells in both spleen and mesenteric lymph nodes. Together, our data indicate that pCCL19 and pCCL28 can enhance HIV-1 envelope-specific systemic and mucosal Ab responses, as well as T cell responses. Such enhancements appear to be associated with mobilization of responsive immunocytes into secondary lymphoid organs and mucosal tissues through interactions with corresponding receptors.