Antibody-mediated immunomodulation: a strategy to improve host responses against microbial antigens

Engineering of Cytolethal Distending Toxin B by Its Reducing Immunogenicity and Maintaining Stability as a New Drug Candidate for Tumor Therapy; an In Silico Study

The cytolethal distending toxin (CDT), Haemophilus ducreyi, is one of the bacterial toxins that have recently been considered for targeted therapies, especially in cancer therapies. CDT is an A-B2 exotoxin. Its catalytic subunit (CdtB) is capable of inducing DNA double strand breaks, cell cycle arrest and apoptosis in host eukaryotic cells. The sequence alignment indicates that the CdtB is structurally homologyr to phosphatases and deoxyribonucleases I (DNase I). Recently, it has been found that CdtB toxicity is mainly related to its nuclease activity. The immunogenicity of CDT can reduce its effectiveness in targeted therapies. However, the toxin can be very useful if its immunogenicity is significantly reduced. Detecting hotspot ectopic residues by computational servers and then mutating them to eliminate B-cell epitopes is a promising approach to reduce the immunogenicity of foreign protein-based therapeutics. By the mentioned method, in this study, we try to reduce the immunogenicity of the CdtB- protein sequence. This study initially screened residue of the CdtB is B-cell epitopes both linearly and conformationally. By overlapping the B-cell epitopes with the excluded conserve residues, and active and enzymatic sites, four residues were allowed to be mutated. There were two mutein options that show reduced antigenicity probability. Option one was N19F, G74I, and S161F with a VaxiJen score of 0.45 and the immune epitope database (IEDB) score of 1.80, and option two was N19F, G74I, and S161W with a VaxiJen score of 0.45 and IEDB score of 1.88. The 3D structure of the proposed sequences was evaluated and refined. The structural stability of native and mutant proteins was accessed through molecular dynamic simulation. The results showed that the mutations in the mutants caused no considerable changes in their structural stability. However, mutant 1 reveals more thermodynamic stability during the simulation. The applied approaches in this study can be used as rough guidelines for finding hot spot immunogen regions in the therapeutic proteins. Our results provide a new version of CdtB that, due to reduced immunogenicity and increased stability, can be used in toxin-based drugs such as immunotoxins.

Stimulatory Effect of CMV Immunoglobulin on Innate Immunity and on the Immunogenicity of CMV Antigens

Background.

Cytomegalovirus (CMV) immunoglobulin (CMVIG) is used for the prophylaxis of CMV infection after transplantation. Beyond providing passive CMV-specific immunity, CMVIG exerts enhancing and suppressive immunomodulatory functions. Although the anti-inflammatory activities of CMVIG have been extensively documented, its immunostimulatory activities remain poorly characterized.

Methods.

This exploratory study analyzed the capacity of CMVIG to modulate cell-mediated innate and adaptive immunities in vitro on freshly isolated peripheral blood mononuclear cells (PBMCs) of CMV-seropositive and -seronegative healthy individuals, using interferon-γ (IFN-γ) enzyme-linked immunospot and intracellular cytokine staining assays.

Results.

We showed that CMVIG treatment increases the number of IFN-γ–secreting PBMCs of both CMV-seronegative and -seropositive individuals, indicating a global stimulatory effect on innate immune cells. Indeed, CMVIG significantly increased the frequency of natural killer cells producing the T helper cell 1–type cytokines tumor necrosis factor and IFN-γ. This was associated with the induction of interleukin-12–expressing monocytes and the activation of cluster of differentiation (CD) 4⁺ and CD8⁺ T cells, as measured by the expression of tumor necrosis factor and IFN-γ. Interestingly, stimulation of PBMCs from CMV-seropositive subjects with CMVIG-opsonized CMV antigens (phosphoprotein 65, CMV lysate) enhanced CD4⁺ and CD8⁺ T-cell activation, suggesting that CMVIG promotes the immunogenicity of CMV antigens.

Conclusions.

Our data demonstrate that CMVIG can stimulate effector cells of both innate and adaptive immunities and promote the immunogenicity of CMV antigens. These immunostimulatory properties might contribute to the protective effect against CMV infection mediated by CMVIG.

Successful treatment of COVID-19 infection with convalescent plasma in B-cell-depleted patients may promote cellular immunity

Treatment with convalescent plasma has been shown to be safe in coronavirus disease in 2019 (COVID‐19) infection, although efficacy reported in immunocompetent patients varies. Nevertheless, neutralizing antibodies are a key requisite in the fight against viral infections. Patients depleted of antibody‐producing B cells, such as those treated with rituximab (anti‐CD20) for hematological malignancies, lack a fundamental part of their adaptive immunity. Treatment with convalescent plasma appears to be of general benefit in this particularly vulnerable cohort. We analyzed clinical course and inflammation markers of three B‐cell‐depleted patients suffering from COVID‐19 who were treated with convalescent plasma. In addition, we measured serum antibody levels as well as peripheral blood CD38/HLA‐DR‐positive T‐cells ex vivo and CD137‐positive T‐cells after in vitro stimulation with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2)‐derived peptides in these patients. We observed that therapy with convalescent plasma was effective in all three patients and analysis of CD137‐positive T‐cells after stimulation with SARS‐CoV‐2 peptides showed an increase in peptide‐specific T‐cells after application of convalescent plasma.

In conclusion, we here demonstrate efficacy of convalescent plasma therapy in three B‐cell‐depleted patients and present data that suggest that while application of convalescent plasma elevates systemic antibody levels only transiently, it may also boost specific T‐cell responses.

Protein-Based Vaccine Protect Against Piscirickettsia salmonis in Atlantic Salmon (Salmo salar)

An effective and economical vaccine against the Piscirickettsia salmonis pathogen is needed for sustainable salmon farming and to reduce disease-related economic losses. Consequently, the aquaculture industry urgently needs to investigate efficient prophylactic measures. Three protein-based vaccine prototypes against Piscirickettsia salmonis were prepared from a highly pathogenic Chilean isolate. Only one vaccine effectively protected Atlantic salmon (Salmo salar), in correlation with the induction of Piscirickettsia-specific IgM antibodies and a high induction of transcripts encoding pro-inflammatory cytokines (i.e., Il-1β and TNF-α). In addition, we studied the proteome fraction protein of P. salmonis strain Austral-005 using multidimensional protein identification technology. The analyzes identified 87 proteins of different subcellular origins, such as the cytoplasmic and membrane compartment, where many of them have virulence functions. The other two prototypes activated only the innate immune responses, but did not protect Salmo salar against P. salmonis. These results suggest that the knowledge of the formulation of vaccines based on P. salmonis proteins is useful as an effective therapy, this demonstrates the importance of the different research tools to improve the study of the different immune responses, resistance to diseases in the Atlantic salmon. We suggest that this vaccine can help prevent widespread infection by P. salmonis, in addition to being able to be used as a booster after a primary vaccine to maintain high levels of circulating protective antibodies, greatly helping to reduce the economic losses caused by the pathogen.

SARS-CoV-2 viral load and antibody responses: the case for convalescent plasma therapy

Most patients with COVID-19 lack antibody to SARS-CoV-2 in the first 10 days of illness while the virus drives disease pathogenesis. SARS-CoV-2 antibody deficiency in the setting of a tissue viral burden suggests that using an antibody as a therapeutic agent would augment the antiviral immune response. In this issue of the JCI, Wang and collaborators describe the kinetics of viral load and the antibody responses of 23 individuals with COVID-19 experiencing mild and severe disease. The researchers found that (a) individuals with mild and severe disease produced neutralizing IgG to SARS-CoV-2 10 days after disease onset, (b) SARS-CoV-2 persisted longer in those with severe disease, and (c) there was cross-reactivity between antibodies to SARS-CoV-1 and SARS-CoV-2, but only antibodies from patients with COVID-19 neutralized SARS-CoV-2. These observations provide important information on the serological response to SARS-CoV-2 of hospitalized patients with COVID-19 that can inform the use of convalescent plasma therapy.

Early exposure to broadly neutralizing antibodies may trigger a dynamical switch from progressive disease to lasting control of SHIV infection

Antiretroviral therapy (ART) for HIV-1 infection is life-long. Stopping therapy typically leads to the reignition of infection and progressive disease. In a major breakthrough, recent studies have shown that early initiation of ART can lead to sustained post-treatment control of viremia, raising hopes of long-term HIV-1 remission. ART, however, elicits post-treatment control in a small fraction of individuals treated. Strikingly, passive immunization with broadly neutralizing antibodies (bNAbs) of HIV-1 early in infection was found recently to elicit long-term control in a majority of SHIV-infected macaques, suggesting that HIV-1 remission may be more widely achievable. The mechanisms underlying the control elicited by bNAb therapy, however, remain unclear. Untreated infection typically leads to progressive disease. We hypothesized that viremic control represents an alternative but rarely realized outcome of the infection and that early bNAb therapy triggers a dynamical switch to this outcome. To test this hypothesis, we constructed a model of viral dynamics with bNAb therapy and applied it to analyse clinical data. The model fit quantitatively the complex longitudinal viral load data from macaques that achieved lasting control. The model predicted, consistently with our hypothesis, that the underlying system exhibited bistability, indicating two potential outcomes of infection. The first had high viremia, weak cytotoxic effector responses, and high effector exhaustion, marking progressive disease. The second had low viremia, strong effector responses, and low effector exhaustion, indicating lasting viremic control. Further, model predictions suggest that early bNAb therapy elicited lasting control via pleiotropic effects. bNAb therapy lowers viremia, which would also limit immune exhaustion. Simultaneously, it can improve effector stimulation via cross-presentation. Consequently, viremia may resurge post-therapy, but would encounter a primed effector population and eventually get controlled. ART suppresses viremia but does not enhance effector stimulation, explaining its limited ability to elicit post-treatment control relative to bNAb therapy.

In a remarkable advance in HIV cure research, a recent study showed that 3 weekly doses of HIV-1 broadly neutralizing antibodies (bNAbs) soon after infection kept viral levels controlled for years in most macaques treated. If translated to humans, this bNAb therapy may elicit a functional cure, or long-term remission, of HIV-1 infection, eliminating the need for life-long antiretroviral therapy (ART). How early bNAb therapy works remains unknown. Here, we elucidate the mechanism using mathematical modeling and analysis of in vivo data. We predict that early bNAb therapy suppresses viremia, which reduces exhaustion of cytotoxic effector cells, and enhances antigen uptake and effector stimulation. Collectively, these effects drive infection to lasting control. Model predictions based on these effects fit in vivo data quantitatively. ART controls viremia but does not improve effector stimulation, explaining its weaker ability to induce lasting control post-treatment. Our findings may help improve strategies for achieving functional cure of HIV-1 infection.

A Plant-Derived Antigen-Antibody Complex Induces Anti-Cancer Immune Responses by Forming a Large Quaternary Structure

The antigen–antibody complex (AAC) has novel functions for immunomodulation, encouraging the application of diverse quaternary protein structures for vaccination. In this study, GA733 antigen and anti-GA733 antibody proteins were both co-expressed to obtain the AAC protein structures in a F1 plant obtained by crossing the plants expressing each protein. In F1 plant, the antigen and antibody assembled to form a large quaternary circular ACC structure (~30 nm). The large quaternary protein structures induced immune response to produce anticancer immunoglobulins G (IgGs) that are specific to the corresponding antigens in mouse. The serum containing the anticancer IgGs inhibited the human colorectal cancer cell growth in the xenograft nude mouse. Taken together, antigens and antibodies can be assembled to form AAC protein structures in plants. Plant crossing represents an alternative strategy for the formation of AAC vaccines that efficiently increases anticancer antibody production.

Fusion of pseudorabies virus glycoproteins to IgG Fc enhances protective immunity against pseudorabies virus

Molecular adjuvants are vaccine delivery vehicle to increase specific antigens effectiveness. Herein, we concentrated on IgG Fc, an effective molecular adjuvant, to develop novel pseudorabies virus (PRV) subunit vaccines. Two major protective antigen genes of PRV were constructed and linked into the mouse IgG Fc fragment. The gD, gD-IgG2aFc, gB and gB-IgG2aFc proteins were expressed using a baculovirus system. Mice intranasally immunized with gD-IgG2aFc or gB-IgG2aFc subunit vaccine exhibited significantly higher PRV-specific antibodies, neutralizing antibodies and intracellular cytokines than the mice intranasally immunized with gD or gB subunit vaccine. Moreover, no histopathological lesions were observed in mice immunized with gB-IgG2aFc subunit vaccine via histopathology examination. Further, the gB-IgG2aFc subunit vaccine was efficient for PRV infection compared with live attenuated vaccine. Overall, these results suggest that IgG2a Fc fragment, as a potential molecular adjuvant, fused with PRV antigen might be a promising and efficient PRV vaccine candidate.

Emerging Themes for the Role of Antibodies in Tuberculosis

The best way to debunk a scientific dogma is to throw irrefutable evidence at it. This is especially true if the dogma in question has been nurtured over many decades, as is the case with the apparent redundancy of antibodies (Abs) against intracellular pathogens. Although not fully compelling yet, that ‘hard core’ evidence is nevertheless now slowly beginning to emerge. This is true for several clinically relevant infections but none more so than Mycobacterium tuberculosis, the archetype intracellular pathogen that poses a great health challenge to the mankind. Here, prompted by a spate of recent high-profile reports on the effects of Abs in various experimental models of tuberculosis, we step back and take a critical look at the progress that has been made in the last 5 years and highlight some of the strengths and shortcomings of the presented evidence. We conclude that the tide of the opinion has begun to turn in favour of Abs but we also caution against overinterpreting the currently available limited evidence. For, until definitive evidence that can withstand even the most rigorous of experimental tests is produced, the dogma may yet survive. Or indeed, we may find that the truth is hidden somewhere in between the dogma and the unfulfilled scientific prophecy.

HIV Superinfection Drives De Novo Antibody Responses and Not Neutralization Breadth

Eliciting antibodies that neutralize a broad range of circulating HIV strains (broadly neutralizing antibodies [bnAbs]) represents a key priority for vaccine development. HIV superinfection (re-infection with a second strain following an established infection) has been associated with neutralization breadth, and can provide insights into how the immune system responds to sequential exposure to distinct HIV envelope glycoproteins (Env). Characterizing the neutralizing antibody (nAb) responses in four superinfected women revealed that superinfection does not boost memory nAb responses primed by the first infection or promote nAb responses to epitopes conserved in both infecting viruses. While one superinfected individual developed potent bnAbs, superinfection was likely not the driver as the nAb response did not target an epitope conserved in both viruses. Rather, sequential exposure led to nAbs specific to each Env but did not promote bnAb development. Thus, sequential immunization with heterologous Envs may not be sufficient to focus the immune response onto conserved epitopes.

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HIV superinfection does not efficiently recruit cross-reactive memory B cells

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Superinfection results in antibody responses specific to each infecting strain

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No evidence that superinfection drives the development of bnAbs

Anti-bacterial Monoclonal Antibodies

The failing efficacy of antibiotics and the high mortality rate among high-risk patients calls for new treatment modalities for bacterial infections. Due to the vastly divergent pathogenesis of human pathogens, each microbe requires a tailored approach. The main modes of action of anti-bacterial antibodies are virulence factor neutralization, complement-mediated bacterial lysis and enhancement of opsonophagocytic uptake and killing (OPK). Gram-positive bacteria cannot be lysed by complement and their pathogenesis often involves secreted toxins, therefore typically toxin-neutralization and OPK activity are required to prevent and ameliorate disease. In fact, the success stories in terms of approved products, in the anti-bacterial mAb field are based on toxin neutralization (Bacillus anthracis, Clostridium difficile). In contrast, Gram-negative bacteria are vulnerable to antibody-dependent complement-mediated lysis, while their pathogenesis rarely relies on secreted exotoxins, and involves the pro-inflammatory endotoxin (lipopolysaccharide). Given the complexity of bacterial pathogenesis, antibody therapeutics are expected to be most efficient upon targeting more than one virulence factor and/or combining different modes of action. The improved understanding of bacterial pathogenesis combined with the versatility and maturity of antibody discovery technologies available today are pivotal for the design of novel anti-bacterial therapeutics. The intensified research generating promising proof-of-concept data, and the increasing number of clinical programs with anti-bacterial mAbs, indicate that the field is ready to fulfill its promise in the coming years.

What Are the Primary Limitations in B-Cell Affinity Maturation, and How Much Affinity Maturation Can We Drive with Vaccination? A Role for Antibody Feedback

We discuss the impact of antibody feedback on affinity maturation of B cells. Competition from epitope-specific antibodies produced earlier during the immune response leads to immune complex formation, which is essential for transport and deposition of antigen onto follicular dendritic cells (FDCs). It also reduces the concentration of free epitopes into the μm to nm range, which is essential for B-cell receptors (BCRs) to sense affinity-dependent changes in binding capacity. Antibody feedback may also induce epitope spreading, leading to a broader selection of epitopes recognized by newly emerging B-cell clones. This may be exploitable, providing ways to manipulate epitope usage induced by vaccination.

Fused IgY Fc and Polysaccharide Adjuvant Enhanced the Immune Effect of the Recombinant VP2 and VP5 Subunits-A Prospect for Improvement of Infectious Bursal Disease Virus Subunit Vaccine

Infectious bursal disease virus (IBDV) is a highly contagious pathogen that causes damage in lymphoid organs and remains a threat to the poultry industry worldwide. Currently, subunit vaccines based on VP2 antigen expressed in prokaryotic systems are widely used in clinical settings. However, the immunogenicity of VP2 vaccines is limited because of their inherent defect that the structure of the antigen expressed in Escherichia coli (E. coli) may be different from its natural conformation. In this study, we fused VP2 and VP5 protective antigen genes and linked the chicken IgY Fc gene onto it. The eukaryotic expression plasmid carrying the fusion gene was transformed into Pichia pastoris (P. pastoris) to express the recombinant VP2–VP5–Fc protein. The recombinant protein was used as immunogen for evaluating immune response, and the recombinant VP2–Fc and VP2 proteins expressed in P. pastoris and the commercial VP2 subunit vaccines were used as controls. Moreover, Taishan Pinus massoniana pollen polysaccharide (TPPPS), an immunomodulator found by our laboratory, was used as adjuvant to investigate its immune modulatory effects on immunogens. Chickens were divided into six groups and inoculated with VP2–VP5–Fc+TPPPS, VP2–VP5–Fc, VP2–Fc, VP2 vaccine, commercial VP2 subunit vaccine, and phosphate buffered saline (PBS). The recombinant VP2 subunit vaccine expressed in P. pastoris exhibited higher immunogenicity than the commercial VP2 subunit vaccine. The VP2–Fc protein showed a better effect than the VP2 protein, and the VP2–VP5–Fc subunit further improved the immune effects. In addition, TPPPS was proved to be a good immunopotentiator for the VP2–VP5–Fc subunit vaccine. Hence, the recombinant VP2–VP5–Fc subunit combined with TPPPS adjuvant exhibits potential as efficient IBDV vaccine to prevent infectious bursal disease.

An HIV Envelope gp120-Fc Fusion Protein Elicits Effector Antibody Responses in Rhesus Macaques

A goal for HIV prevention programs is to develop safe, effective vaccines that elicit durable and broadly protective antibodies. Many vaccine programs focus on the immune responses to critical epitopes in the gp120 portion of HIV envelope glycoprotein (Env) and seek to improve the quality and quantity of antibodies by altering the sequence, conformation, oligomerization, or glycosylation of gp120 to activate appropriate germ line B cells and mimic the subsequent maturation pathways seen in infected individuals. As a complement to these strategies, we developed dimeric fusion protein immunogens consisting of HIV_BaL gp120 monomer attached to a Gly/Ser linker that is, in turn, fused to one half of the dimeric Fc domain from rhesus macaque IgG1 (Env-rFc). We envisioned that Env-rFc may mimic some aspects of immune complexes by binding Fc gamma receptors (FcγRs) on immune cells to increase the strength, breadth, and durability of Env-specific antibody responses. The Env-rFc retained a capacity to bind both cell surface CD4 and FcγRs. In a rhesus macaque immunization study, Env-rFc elicited higher gp120 binding antibody titers than Env and elicited antibodies that recognize CD4-induced epitopes. Env-rFc also induced antibodies capable of neutralizing tier 1A HIV pseudotyped viruses and mediating antibody-dependent cellular cytotoxicity, outcomes not observed with monomeric gp120 in our study. Serum antibodies produced in Env-rFc-immunized macaques had increased durability compared to that of Env monomer immunization. Our work suggests that adding IgG1 Fc to Env-based immunogens may stimulate increased effector capacity in the immune sera and improve the protective serum antibody response.

Status of vaccine research and development of vaccines for Chlamydia trachomatis infection

Genital infection with Chlamydia trachomatis, a gram-negative obligate intracellular bacterium, is the most common bacterial sexually transmitted infection globally. Ascension of chlamydial infection to the female upper genital tract can cause acute pelvic inflammatory disease, tubal factor infertility, ectopic pregnancy, and chronic pelvic pain. Shortcomings of current chlamydia control strategies, especially for low- and middle-income countries, highlight the need for an effective vaccine. Evidence from animal models, human epidemiological studies, and early trachoma vaccine trials suggest that a C. trachomatis vaccine is feasible. Vaccine development for genital chlamydial infection has been in the preclinical phase of testing for many years, but the first Phase I trials of chlamydial vaccine candidates are underway, and scientific advances hold promise for additional candidates to enter clinical evaluation in the coming years. We describe the clinical and public health need for a C. trachomatis vaccine, provide an overview of Chlamydia vaccine development efforts, and summarize current vaccine candidates in the development pipeline.

Chlamydia trachomatis Genital Infections

Etiology, transmission and protection: Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infection (STI) globally. However, C. trachomatis also causes trachoma in endemic areas, mostly Africa and the Middle East, and is a leading cause of preventable blindness worldwide. Epidemiology, incidence and prevalence: The World Health Organization estimates 131 million new cases of C. trachomatis genital infection occur annually. Globally, infection is most prevalent in young women and men (14-25 years), likely driven by asymptomatic infection, inadequate partner treatment and delayed development of protective immunity. Pathology/Symptomatology: C. trachomatis infects susceptible squamocolumnar or transitional epithelial cells, leading to cervicitis in women and urethritis in men. Symptoms are often mild or absent but ascending infection in some women may lead to Pelvic Inflammatory Disease (PID), resulting in reproductive sequelae such as ectopic pregnancy, infertility and chronic pelvic pain. Complications of infection in men include epididymitis and reactive arthritis. Molecular mechanisms of infection: Chlamydiae manipulate an array of host processes to support their obligate intracellular developmental cycle. This leads to activation of signaling pathways resulting in disproportionate influx of innate cells and the release of tissue damaging proteins and pro-inflammatory cytokines. Treatment and curability: Uncomplicated urogenital infection is treated with azithromycin (1 g, single dose) or doxycycline (100 mg twice daily x 7 days). However, antimicrobial treatment does not ameliorate established disease. Drug resistance is rare but treatment failures have been described. Development of an effective vaccine that protects against upper tract disease or that limits transmission remains an important goal.

Converting monoclonal antibody-based immunotherapies from passive to active: bringing immune complexes into play

Monoclonal antibodies (mAbs), which currently constitute the main class of biotherapeutics, are now recognized as major medical tools that are increasingly being considered to fight severe viral infections. Indeed, the number of antiviral mAbs developed in recent years has grown exponentially. Although their direct effects on viral blunting have been studied in detail, their potential immunomodulatory actions have been overlooked until recently. The ability of antiviral mAbs to modulate antiviral immune responses in infected organisms has recently been revealed. More specifically, upon recognition of their cognate antigens, mAbs form immune complexes (ICs) that can be recognized by the Fc receptors expressed on different immune cells of infected individuals. This binding may be followed by the modulation of the host immune responses. Harnessing this immunomodulatory property may facilitate improvements in the therapeutic potential of antiviral mAbs. This review focuses on the role of ICs formed with different viral determinants and mAbs in the induction of antiviral immune responses in the context of both passive immunotherapies and vaccination strategies. Potential deleterious effects of ICs on the host immune response are also discussed.

Preserved antiviral adaptive immunity following polyclonal antibody immunotherapy for severe murine influenza infection

Passive immunotherapy may have particular benefits for the treatment of severe influenza infection in at-risk populations, however little is known of the impact of passive immunotherapy on the formation of memory responses to the virus. Ideally, passive immunotherapy should attenuate the severity of infection while still allowing the formation of adaptive responses to confer protection from future exposure. In this study, we sought to determine if administration of influenza-specific ovine polyclonal antibodies could inhibit adaptive immune responses in a murine model of lethal influenza infection. Ovine polyclonal antibodies generated against recombinant PR8 (H1N1) hemagglutinin exhibited potent prophylactic capacity and reduced lethality in an established influenza infection, particularly when administered intranasally. Surviving mice were also protected against reinfection and generated normal antibody and cytotoxic T lymphocyte responses to the virus. The longevity of ovine polyclonal antibodies was explored with a half-life of over two weeks following a single antibody administration. These findings support the development of an ovine passive polyclonal antibody therapy for treatment of severe influenza infection which does not affect the formation of subsequent acquired immunity to the virus.

Cryptococcal therapies and drug targets: the old, the new and the promising

Half a century after the introduction of Amphotericin B the management of cryptococcosis remains unsatisfactory. The disease, caused primarily by the two fungal species Cryptococcus neoformans and Cryptococcus gattii, remains responsible for considerable morbidity and mortality despite standard medical care. Current therapeutic options are limited to Amphotericin B, azoles and 5-flucytosine. However, this organism has numerous well-characterized virulence mechanisms that are amenable to pharmacological interference and are thus potential therapeutic targets. Here, we discuss existing approved antifungal drugs, resistance mechanisms to these drugs and non-standard antifungal drugs that have potential in treatment of cryptococcosis, including immunomodulatory strategies that synergize with antifungal drugs, such as cytokine administration or monoclonal antibodies. Finally, we summarize attempts to target well-described virulence factors of Cryptococcus, the capsule or fungal melanin. This review emphasizes the pressing need for new therapeutic alternatives for cryptococcosis.

Potent In Vitro and In Vivo Activity of Plantibody Specific for Porphyromonas gingivalis FimA

Fimbrial protein fimbrillin (FimA), a major structural subunit of Porphyromonas gingivalis, has been suggested as a vaccine candidate to control P. gingivalis-induced periodontal disease. Previously, cDNAs encoding IgG monoclonal antibodies (MAbs) against purified FimA from P. gingivalis 2561 have been cloned, and the MAbs have been produced in rice cell suspension. Here we examined the biological activities of the plant-produced MAb specific for FimA (anti-FimA plantibody) of P. gingivalis in vitro and in vivo. The anti-FimA plantibody recognized oligomeric/polymeric forms of native FimA in immunoblot analysis and showed high affinity for native FimA (KD = 0.11 nM). Binding of P. gingivalis (10(8) cells) to 2 mg of saliva-coated hydroxyapatite beads was reduced by 53.8% in the presence of 1 μg/ml plantibody. Anti-FimA plantibody (10 μg/ml) reduced invasion of periodontal ligament cells by P. gingivalis (multiplicity of infection, 100) by 68.3%. Intracellular killing of P. gingivalis opsonized with the anti-FimA plantibody by mouse macrophages was significantly increased (77.1%) compared to killing of bacterial cells with irrelevant IgG (36.7%). In a mouse subcutaneous chamber model, the number of recoverable P. gingivalis cells from the chamber fluid was significantly reduced when the numbers of bacterial cells opsonized with anti-FimA plantibody were compared with the numbers of bacterial cells with irrelevant IgG, 66.7% and 37.1%, respectively. These in vitro and in vivo effects of anti-FimA plantibody were comparable to those of the parental MAb. Further studies with P. gingivalis strains with different types of fimbriae are needed to investigate the usefulness of anti-FimA plantibody for passive immunization to control P. gingivalis-induced periodontal disease.

Design of nanomaterial based systems for novel vaccine development

With lower cell toxicity and higher specificity, novel vaccines have been greatly developed and applied to emerging infectious and chronic diseases. However, due to problems associated with low immunogenicity and complicated processing steps, the development of novel vaccines has been limited. With the rapid development of bio-technologies and material sciences, nanomaterials are playing essential roles in novel vaccine design. Incorporation of nanomaterials is expected to improve delivery efficiency, to increase immunogenicity, and to reduce the administration dosage. The purpose of this review is to discuss the employment of nanomaterials, including polymeric nanoparticles, liposomes, virus-like particles, peptide amphiphiles micelles, peptide nanofibers and microneedle arrays, in vaccine design. Compared to traditional methods, vaccines made from nanomaterials display many appealing benefits, including precise stimulation of immune responses, effective targeting to certain tissue or cells, and desirable biocompatibility. Current research suggests that nanomaterials may improve our approach to the design and delivery of novel vaccines.

Chlamydia trachomatis: Protective Adaptive Responses and Prospects for a Vaccine

Chlamydia trachomatis is the most common cause of sexually transmitted bacterial infection globally. These infections translate to a significant public health burden, particularly women's healthcare costs due to serious disease sequelae such as pelvic inflammatory disease (PID), tubal factor infertility, chronic pelvic pain, and ectopic pregnancy. There is no evidence that natural immunity can provide complete, long-term protection necessary to prevent chronic pathology, making human vaccine development critical. Vaccine design will require careful consideration of protective versus pathological host-response mechanisms in concert with elucidation of optimal antigens and adjuvants. Evidence suggests that a Th1 response, facilitated by IFN-γ-producing CD4 T cells, will be instrumental in generating long-term, sterilizing immunity. Although the role of antibodies is not completely understood, they have exhibited a protective effect by enhancing chlamydial clearance. Future work will require investigation of broadly neutralizing antibodies and antibody-augmented cellular immunity to successfully design a vaccine that potently elicits both arms of the immune response. Sterilizing immunity is the ultimate goal. However, vaccine-induced partial immunity that prevents upper genital tract infection and inflammation would be cost-effective compared to current screening and treatment strategies. In this chapter, we examine evidence from animal and human studies demonstrating protective adaptive immune responses to Chlamydia and discuss future challenges and prospects for vaccine development.

Do IgA antibodies to Chlamydia trachomatis have protective role in humoral immunity: a study in reactive arthritis patients

Chlamydia trachomatis-induced genitourinary Reactive Arthritis (ReA) can serve as good model for host-pathogen interaction. However, due to poor antigen presentation, cell-mediated immunity does not contribute as anticipated. Present study aims to evaluate protective role of anti-C. trachomatis antibodies vis-a-vis inflammatory chlamydial Major Outer Membrane Protein (MOMP). Prospective study was undertaken in 30 patients with genitourinary ReA. 30 Rheumatoid Arthritis (RA) and 30 osteoarthritis patients constituted controls. Subjects found to be PCR-positive for C. trachomatis were investigated for presence of MOMP in Synovial Fluid (SF) by fluorescence assay while anti-C. trachomatis IgA/IgM antibodies were estimated in SF/venous blood by ELISA. C. trachomatis MOMP was evident by the presence of elementary bodies in SF of 9 ReA PCR-positive patients (30%; p < 0.05 versus controls). Local secretory IgA antibodies were detected in 12 (40%) patients with ReA (p < 0.0001 versus controls); among 12 patients with anti-chlamydial IgA antibodies, 9 showed the presence of both MOMP and IgA antibodies in SF. 58.3% ReA patients (7/12) with secretory IgA antibodies were also positive for circulatory IgA antibodies (p < 0.01 versus controls). Serum IgM antibodies were present in 4 ReA (13.3%) and in 1 RA (3.3%) patient, respectively. In conclusion, the present study suggests that in ReA patients with chronic, persistent C. trachomatis infection in synovium, the chlamydial MOMP is triggering factor for generating a protective immune response by inducing anti-C. trachomatis IgA antibodies in the SF of large number of patients.

Immunization with Immune Complexes Modulates the Fine Specificity of Antibody Responses to a Flavivirus Antigen

The antibody response to proteins may be modulated by the presence of preexisting antigen-specific antibodies and the formation of immune complexes (ICs). Effects such as a general increase or decrease of the response as well as epitope-specific phenomena have been described. In this study, we investigated influences of IC immunization on the fine specificity of antibody responses in a structurally well-defined system, using the envelope (E) protein of tick-borne encephalitis (TBE) virus as an immunogen. TBE virus occurs in Europe and Asia and-together with the yellow fever, dengue, West Nile, and Japanese encephalitis viruses-represents one of the major human-pathogenic flaviviruses. Mice were immunized with a dimeric soluble form of E (sE) alone or in complex with monoclonal antibodies specific for each of the three domains of E, and the antibody response induced by these ICs was compared to that seen after immunization with sE alone. Immunoassays using recombinant domains and domain combinations of TBE virus sE as well as the distantly related West Nile virus sE allowed the dissection and quantification of antibody subsets present in postimmunization sera, thus generating fine-specificity patterns of the polyclonal responses. There were substantially different responses with two of the ICs, and the differences could be mechanistically related to (i) epitope shielding and (ii) antibody-mediated structural changes leading to dissociation of the sE dimer. The phenomena described may also be relevant for polyclonal responses upon secondary infections and/or booster immunizations and may affect antibody responses in an individual-specific way.

IMPORTANCE

Infections with flaviviruses such as yellow fever, dengue, Japanese encephalitis, West Nile, and tick-borne encephalitis (TBE) viruses pose substantial public health problems in different parts of the world. Antibodies to viral envelope protein E induced by natural infection or vaccination were shown to confer protection from disease. Such antibodies can target different epitopes in E protein, and the fine specificities of polyclonal responses can differ between individuals. We conducted a mouse immunization study with TBE E protein alone or complexed to monoclonal antibodies specific for each of the three protein domains. We demonstrated that phenomena such as epitope shielding and antibody-induced structural changes can profoundly influence the fine specificity of antibody responses to the same immunogen. The study thus provided important new information on the potential immunomodulatory role of preexisting antibodies in a flavivirus system that can be relevant for understanding individual-specific factors influencing antibody responses in sequential flavivirus infections and/or immunizations.

The Split Virus Influenza Vaccine rapidly activates immune cells through Fcγ receptors

Seasonal influenza vaccination is one of the most common medical procedures and yet the extent to which it activates the immune system beyond inducing antibody production is not well understood. In the United States, the most prevalent formulations of the vaccine consist of degraded or "split" viral particles distributed without any adjuvants. Based on previous reports we sought to determine whether the split influenza vaccine activates innate immune receptors-specifically Toll-like receptors. High-dimensional proteomic profiling of human whole-blood using Cytometry by Time-of-Flight (CyTOF) was used to compare signaling pathway activation and cytokine production between the split influenza vaccine and a prototypical TLR response ex vivo. This analysis revealed that the split vaccine rapidly and potently activates multiple immune cell types but yields a proteomic signature quite distinct from TLR activation. Importantly, vaccine induced activity was dependent upon the presence of human sera indicating that a serum factor was necessary for vaccine-dependent immune activation. We found this serum factor to be human antibodies specific for influenza proteins and therefore immediate immune activation by the split vaccine is immune-complex dependent. These studies demonstrate that influenza virus "splitting" inactivates any potential adjuvants endogenous to influenza, such as RNA, but in previously exposed individuals can elicit a potent immune response by facilitating the rapid formation of immune complexes.

A systems approach to designing next generation vaccines: combining α-galactose modified antigens with nanoparticle platforms

Innovative vaccine platforms are needed to develop effective countermeasures against emerging and re-emerging diseases. These platforms should direct antigen internalization by antigen presenting cells and promote immunogenic responses. This work describes an innovative systems approach combining two novel platforms, αGalactose (αGal)-modification of antigens and amphiphilic polyanhydride nanoparticles as vaccine delivery vehicles, to rationally design vaccine formulations. Regimens comprising soluble αGal-modified antigen and nanoparticle-encapsulated unmodified antigen induced a high titer, high avidity antibody response with broader epitope recognition of antigenic peptides than other regimen. Proliferation of antigen-specific CD4⁺ T cells was also enhanced compared to a traditional adjuvant. Combining the technology platforms and augmenting immune response studies with peptide arrays and informatics analysis provides a new paradigm for rational, systems-based design of next generation vaccine platforms against emerging and re-emerging pathogens.

Alterations in immunodominance of Streptococcus mutans AgI/II: lessons learned from immunomodulatory antibodies

Streptococcus mutans antigen I/II (AgI/II) has been widely studied as a candidate vaccine antigen against human dental caries. In this report we follow up on prior studies that indicated that anti-AgI/II immunomodulatory monoclonal antibodies (MAbs) exerted their effects by destabilizing the native protein structure and exposing cryptic epitopes. We show here that similar results can be obtained by immunizing mice with truncated polypeptides out of the context of an intra-molecular interaction that occurs within the full-length molecule and that appears to dampen the functional response against at least two important target epitopes. Putative T cell epitopes that influenced antibody specificity were identified immediately upstream of the alanine-rich repeat domain. Adherence inhibiting antibodies could be induced against two discrete domains of the protein, one corresponding to the central portion of the molecule and the other corresponding to the C-terminus.

Multi-therapeutic potential of autoantibodies induced by immune complexes trapped on follicular dendritic cells

Induction of autoantibodies (autoAbs) targeting disease drivers / mediators is emerging as a potential immunotherapeutic strategy. Auto-immune complex (IC)-retaining follicular dendritic cells (FDCs) critically regulate pathogenic autoAb production in autoreactive germinal centers (GCs); however, their ability to induce potentially therapeutic autoAbs has not been explored. We hypothesized that deliberate display of clinically targeted antigens (Ags) in the form of ICs on FDC membranes induces target-specific autoreactive GCs and autoAbs that may be exploited therapeutically. To test our hypothesis, three therapeutically relevant Ags: TNF-α, HER2/neu and IgE, were investigated. Our results indicated that TNF-α-, HER2/neu- and IgE-specific autoAbs associated with strong GC reactions were induced by TNF-α-, HER2/neu- and IgE-IC retention on FDCs. Moreover, the induced anti-TNF-α autoAbs neutralized mouse and human TNF-α with half maximal Inhibitory Concentration (IC₅₀) of 7.1 and 1.6 nM respectively. In addition, we demonstrated that FDC-induced Ab production could be non-specifically inhibited by the IgG-specific Endo-S that accessed the light zones of GCs and interfered with FDC-IC retention. In conclusion, the ability of FDCs to productively present autoAgs raises the potential for a novel immunotherapeutic platform targeting mediators of autoimmune disorders, allergic diseases, and Ab responsive cancers.

B cells regulate neutrophilia during Mycobacterium tuberculosis infection and BCG vaccination by modulating the interleukin-17 response

We have previously demonstrated that B cells can shape the immune response to Mycobacterium tuberculosis, including the level of neutrophil infiltration and granulomatous inflammation at the site of infection. The present study examined the mechanisms by which B cells regulate the host neutrophilic response upon exposure to mycobacteria and how neutrophilia may influence vaccine efficacy. To address these questions, a murine aerosol infection tuberculosis (TB) model and an intradermal (ID) ear BCG immunization mouse model, involving both the μMT strain and B cell-depleted C57BL/6 mice, were used. IL (interleukin)-17 neutralization and neutrophil depletion experiments using these systems provide evidence that B cells can regulate neutrophilia by modulating the IL-17 response during M. tuberculosis infection and BCG immunization. Exuberant neutrophilia at the site of immunization in B cell-deficient mice adversely affects dendritic cell (DC) migration to the draining lymph nodes and attenuates the development of the vaccine-induced Th1 response. The results suggest that B cells are required for the development of optimal protective anti-TB immunity upon BCG vaccination by regulating the IL-17/neutrophilic response. Administration of sera derived from M. tuberculosis-infected C57BL/6 wild-type mice reverses the lung neutrophilia phenotype in tuberculous μMT mice. Together, these observations provide insight into the mechanisms by which B cells and humoral immunity modulate vaccine-induced Th1 response and regulate neutrophila during M. tuberculosis infection and BCG immunization.

Mycobacterium tuberculosis poses a serious threat to public health globally. It has been well established that T cells are critical in protection against M. tuberculosis. The role of B cells and humoral immunity in the process is less well understood. We previously showed that B cells and humoral immunity regulate the immune response against M. tuberculosis. The present study examined the mechanisms by which B cells regulate the host neutrophilic response upon exposure to mycobacteria and how neutrophilia may modulate the development of vaccine-induced protective immunity. The data reveal that B cells can regulate neutrophilia during M. tuberculosis infection and BCG vaccination by modulating the IL-17 response. Vaccination studies show that excess neutrophilia adversely affects the development of BCG-elicited Th1 response. These observations suggest that B cells can optimize the development of protective immunity upon BCG vaccination by regulating the IL-17/neutrophilic response. Understanding the mechanisms by which B cells and humoral immunity modulate the immune response during M. tuberculosis infection and BCG immunization, particularly those that regulate IL-17 levels and neutrophilia, may lead to the development of novel strategies for the control of the tubercle bacillus, including efficacious vaccines.

HIV-1 and influenza antigens synthetically linked to IgG2a Fc elicit superior humoral responses compared to unmodified antigens in mice

Using murine IgG subclass molecules (IgG1 or IgG2a) synthetically fused to HIV-1 or influenza test antigens, we explored the potential for IgG Fc scaffolds to augment immunogenicity. Each antigen (Ag) was grafted onto a hinge-Fc scaffold containing all critical residues necessary for interaction with effector cells, thus retaining effector functions of the native IgG subclass. We hypothesized that the differential affinity of FcγRs for specific IgG subclasses would influence the magnitude of immune responses elicited by immunization with an Ag-IgG Fc fusion vaccine. We demonstrate here that the antigen-specific humoral response elicited by Ag-IgG2a fusion vaccines is at least tenfold greater than that elicited by native antigen, that this response is superior to that elicited by Ag-IgG1, and that the augmented antigen-specific humoral response elicited is Fcγ receptor-dependent.

A therapeutic anti-Streptococcus mutans monoclonal antibody used in human passive protection trials influences the adaptive immune response

The adhesin known as Antigen I/II, P1 or PAc of the cariogenic dental pathogen Streptococcus mutans is a target of protective immunity and candidate vaccine antigen. Previously we demonstrated that immunization of mice with S. mutans complexed with anti-AgI/II monoclonal antibodies (MAbs) resulted in changes in the specificity, isotype and functionality of elicited anti-AgI/II antibodies in the serum of immunized mice compared to administration of bacteria alone. In the current study, an anti-AgI/II MAb reported in the literature to confer unexplained long term protection against S. mutans re-colonization following passive immunization in human clinical trials (MAb Guy's 13), and expressed in tobacco plants (MAb Guy's 13 plantibody), was evaluated for its potential immunomodulatory properties. Immunization of BALB/c mice with immune complexes of Guy's 13 plantibody bound to S. mutans whole cells resulted in a similar change in specificity, isotype, and functionality of elicited anti-AgI/II antibodies as had been observed for other immunomodulatory MAbs. This new information, coupled with the recently solved crystal structure of the adhesin, now provides a rational explanation and plausible mechanism of action of passively administered Guy's 13/Guy's 13 plantibody in human clinical trials, and how long-term prevention of S. mutans carriage well past the application period of the therapeutic antibody could have been achieved.

An anti-HIV-1 V3 loop antibody fully protects cross-clade and elicits T-cell immunity in macaques mucosally challenged with an R5 clade C SHIV

Neutralizing antibodies have been shown to protect macaques against SHIV challenge. However, genetically diverse HIV-1 clades have evolved, and a key question left unanswered is whether neutralizing antibodies can confer cross-clade protection in vivo. The novel human monoclonal antibody HGN194 was isolated from an individual infected with an HIV-1 clade AG recombinant circulating recombinant form (CRF). HGN194 targets an epitope in the third hypervariable loop (V3) of HIV-1 gp120 and neutralizes a range of relatively neutralization-sensitive and resistant viruses. We evaluated the potential of HGN194 to protect infant rhesus monkeys against a SHIV encoding a primary CCR5-tropic HIV-1 clade C envelope. After high-dose mucosal challenge, all untreated controls became highly viremic while all HGN194-treated animals (50 mg/kg) were completely protected. When HGN194 was given at 1 mg/kg, one out of two monkeys remained aviremic, whereas the other had delayed, lower peak viremia. Interestingly, all protected monkeys given high-dose HGN194 developed Gag-specific proliferative responses of both CD4+ and CD8+ T cells. To test whether generation of the latter involved cryptic infection, we ablated CD8+ cells after HGN194 clearance. No viremia was detected in any protected monkeys, thus ruling out virus reservoirs. Thus, induction of CD8 T-cell immunity may have resulted from transient "Hit and Run" infection or cross priming via Ag-Ab-mediated cross-presentation. Together, our data identified the HGN194 epitope as protective and provide proof-of-concept that this anti-V3 loop mAb can prevent infection with sterilizing immunity after challenge with virus of a different clade, implying that V3 is a potential vaccine target.

CD4+ T cells and antibody are required for optimal major outer membrane protein vaccine-induced immunity to Chlamydia muridarum genital infection

Despite effective antimicrobial chemotherapy, control of Chlamydia trachomatis urogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarum major outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log(10) to 3 log(10) fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4(+) or CD8(+) T cells, and then challenged vaginally with C. muridarum. Depletion of CD4(+) T cells, but not depletion of CD8(+) T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log(10) to 4 log(10) more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log(10) to 3 log(10) decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4(+) T cells and antibody.

A crucial role for infected-cell/antibody immune complexes in the enhancement of endogenous antiviral immunity by short passive immunotherapy

Antiviral monoclonal antibodies (mAbs) represent promising therapeutics. However, most mAbs-based immunotherapies conducted so far have only considered the blunting of viral propagation and not other possible therapeutic effects independent of virus neutralization, namely the modulation of the endogenous immune response. As induction of long-term antiviral immunity still remains a paramount challenge for treating chronic infections, we have asked here whether neutralizing mAbs can, in addition to blunting viral propagation, exert immunomodulatory effects with protective outcomes. Supporting this idea, we report here that mice infected with the FrCas^E murine retrovirus on day 8 after birth die of leukemia within 4–5 months and mount a non-protective immune response, whereas those rapidly subjected to short immunotherapy with a neutralizing mAb survive healthy and mount a long-lasting protective antiviral immunity with strong humoral and cellular immune responses. Interestingly, the administered mAb mediates lysis of infected cells through an antibody-dependent cell cytotoxicity (ADCC) mechanism. In addition, it forms immune complexes (ICs) with infected cells that enhance antiviral CTL responses through FcγR-mediated binding to dendritic cells (DCs). Importantly, the endogenous antiviral antibodies generated in mAb-treated mice also display the same properties, allowing containment of viral propagation and enhancement of memory cellular responses after disappearance of the administered mAb. Thus, our data demonstrate that neutralizing antiviral mAbs can act as immunomodulatory agents capable of stimulating a protective immunity lasting long after the end of the treatment. They also show an important role of infected-cells/antibody complexes in the induction and the maintenance of protective immunity through enhancement of both primary and memory antiviral T-cell responses. They also indicate that targeting infected cells, and not just viruses, by antibodies can be crucial for elicitation of efficient, long-lasting antiviral T-cell responses. This must be considered when designing antiviral mAb-based immunotherapies.

Monoclonal antibodies (mAbs) constitute the largest class of bio-therapeutic proteins and are increasingly being considered as drugs to fight both acute and chronic severe human viral diseases. Most antiviral mAb-based treatments conducted so far, whether in humans or in animal models, have only considered the blunting of viral propagation through direct virus neutralization. However, mAbs might also operate via complementary mechanisms owing to their ability to interact with various components of the immune system. Using a lethal mouse model of retrovirally-induced leukemia, we report here that a neutralizing mAb administered to infected mice for a short period of time can, in addition to its direct effect on viral spread, induce a strong, long-lasting antiviral immune response protecting mice from disease development long after the end of the treatment. Although the initiation and maintenance of this long-term immunity is multi-factorial, we demonstrate a crucial role for the immune complexes formed between antiviral antibodies and infected cells in this process. Our work reveals a thus far underappreciated vaccine-like effect of antiviral neutralizing mAbs, which will have to be considered for future treatment of life-threatening viral infections.

Toll-like receptors and B-cell receptors synergize to induce immunoglobulin class-switch DNA recombination: relevance to microbial antibody responses

Differentiation of naïve B cells, including immunoglobulin class-switch DNA recombination, is critical for the immune response and depends on the extensive integration of signals from the B-cell receptor (BCR), tumor necrosis factor (TNF) family members, Toll-like receptors (TLRs), and cytokine receptors. TLRs and BCR synergize to induce class-switch DNA recombination in T cell-dependent and T cell-independent antibody responses to microbial pathogens. BCR triggering together with simultaneous endosomal TLR engagement leads to enhanced B-cell differentiation and antibody responses. Te requirement of both BCR and TLR engagement would ensure appropriate antigen-specific activation in an infection. Co-stimulation of TLRs and BCR likely plays a significant role in anti-microbial antibody responses to contain pathogen loads until the T cell-dependent antibody responses peak. Furthermore, the temporal sequence of different signals is also critical for optimal B cell responses, as exemplified by the activation of B cells by initial TLR engagement, leading to the up-regulation of co-stimulatory CD80 and MCH-II receptors, which result in more efficient interactions with T cells, thereby enhancing the germinal center reaction and antibody affinity maturation. Overall, BCR and TLR stimulation and the integration with signals from the pathogen or immune cells and their products determine the ensuing B-cell antibody response.

Immunobiological outcomes of repeated chlamydial infection from two models of within-host population dynamics

Background

Chlamydia trachomatis is a common human pathogen that mediates disease processes capable of inflicting serious complications on reproduction. Aggressive inflammatory immune responses are thought to not only direct a person's level of immunity but also the potential for immunopathology. With human immunobiology being debated as a cause of prevailing epidemiological trends, we examined some fundamental issues regarding susceptibility to multiple chlamydial infections that could have implications for infection spread. We argue that, compared to less-frequent exposure, frequent exposure to chlamydia may well produce unique immunobiological characteristics that likely to have important clinical and epidemiological implications.

Methods and Results

As a novel tool for studying chlamydia, we applied principles of modeling within-host pathogen dynamics to enable an understanding of some fundamental characteristics of an individual's immunobiology during multiple chlamydial infections. While the models were able to reproduce shorter-term infection kinetics of primary and secondary infections previously observed in animal models, it was also observed that longer periods between initial and second infection may increase an individual's chlamydial load and lengthen their duration of infectiousness. The cessation of short-term repeated exposure did not allow for the formation of long-lasting immunity. However, frequent re-exposure non-intuitively linked the formation of protective immunity, persistent infection, and the potential for immunopathology.

Conclusions

Overall, these results provide interesting insights that should be verified with continued study. Nevertheless, these results appear to raise challenges for current evidence of the development of long-lasting immunity against chlamydia, and suggest the existence of a previously unidentified mechanism for the formation of persistent infection. The obvious next goal is to investigate the qualitative impact of these results on the spread of chlamydia.

Immune complex relay by subcapsular sinus macrophages and noncognate B cells drives antibody affinity maturation

Subcapsular sinus (SCS) macrophages capture antigens from lymph and present them intact for B cell encounter and follicular delivery. However, the properties of SCS macrophages are poorly defined. Here we show SCS macrophage development depended on lymphotoxin-alpha1beta2, and the cells had low lysosomal enzyme expression and retained opsonized antigens on their surface. Intravital imaging revealed immune complexes moving along macrophage processes into the follicle. Moreover, noncognate B cells relayed antigen opsonized by newly produced antibodies from the subcapsular region to the germinal center, and affinity maturation was impaired when this transport process was disrupted. Thus, we characterize SCS macrophages as specialized antigen-presenting cells functioning at the apex of an antigen transport chain that promotes humoral immunity.

Plant-derived EpCAM antigen induces protective anti-cancer response

Immunotherapy holds great promise for treatment of infectious and malignant diseases and might help to prevent the occurrence and recurrence of cancer. We produced a plant-derived tumor-associated colorectal cancer antigen EpCAM (pGA733) at high yields using two modern plant expression systems. The full antigenic domain of EpCAM was efficiently purified to confirm its antigenic and immunogenic properties as compared to those of the antigen expressed in the baculovirus system (bGA733). Recombinant plant-derived antigen induced a humoral immune response in BALB/c mice. Sera from those mice efficiently inhibited the growth of SW948 colorectal carcinoma cells xenografted in nude mice, as compared to the EpCAM-specific mAb CO17-1A. Our results support the feasibility of producing anti-cancer recombinant vaccines using plant expression systems.

Basis of beneficial immunomodulation by monoclonal antibodies against Streptococcus mutans adhesin P1

We previously identified five monoclonal antibodies (MAbs) against Streptococcus mutans adhesin P1 that modulate the humoral response when bound to whole bacteria and immune complexes (ICs) are administered to BALB/c mice. The two MAbs that redirected the response towards increased efficacy recognize discontinuous epitopes involving pre-alanine-rich domain sequence; therefore, to evaluate whether epitope specificity contributes to a desirable outcome a further MAb with this characteristic was tested. A beneficial immune response was promoted. None of the three MAbs that promoted a beneficial response was opsonic, suggesting that increased uptake of ICs by phagocytes does not mediate the improvement of the IC-elicited antibodies to inhibit bacterial adherence. Finally, two of the six anti-P1 MAbs activated complement but did not partition according to desirable vs. nondesirable effects.

Characterization of epitopes recognized by anti-Streptococcus mutans P1 monoclonal antibodies

Sequences contributing to epitopes recognized by a panel of monoclonal antibodies (mAbs) against the Streptococcus mutans surface protein P1 were delineated by Western blot and enzyme-linked immunosorbent assay using a battery of deletion constructs and recombinant polypeptides. mAbs that recognize complex discontinuous epitopes reconstituted by combining the alanine-rich and proline-rich repeat domains and varying degrees of flanking sequence were identified as well as mAbs that bound epitopes contained within contiguous segments of P1. Cross-reactivity with SspA and SspB from Streptococcus gordonii is also reported. This information enables insight into the structure and function of a streptococcal adhesin and its correlates of protection and furthers our understanding of the immunomodulatory and bacterial-adherence inhibition activities of anti-P1 mAbs.

A case for passive immunoprophylaxis against tuberculosis

HIV-associated tuberculosis is escalating ominously in Africa and southeast Asia despite existing control measures. Therefore, new approaches to tuberculosis control need to be explored. We discuss the potential use of passive immunoprophylaxis with antibodies in tuberculosis control. Although the predominant type of active host resistance is T-cell mediated, recent results in mouse experimental models suggest that monoclonal antibodies to certain antigens (eg, Acr or lipoarabinomannan) can impart substantial passive protection against tuberculous infection. These results are corroborated by data from other laboratories on passive vaccination against a number of intracellular microbial pathogens. Further work is needed to develop human (or humanised) antibody reagents, to increase their protective efficacy, and to expand our understanding of the mechanisms of antibody action.

Cloning and characterization of porcine Fc gamma receptor II (FcγRII)

Receptors for the Fc region (FcgammaRs) of IgG play a crucial role in the immune system and host protection against infection. In the present study, we describe the cloning, sequencing and characterization of porcine FcgammaRII. By screening a translated EST database with the protein sequence of the human FcgammaRII (CD32) we identified a putative porcine homologue. Using rapid amplification of cDNA ends (RACE), we isolated the full-length cDNA encoding porcine FcgammaRII from peripheral blood leucocyte RNA. The porcine FcgammaRII cDNA was 1488bp long, encoding a 297 amino acid trans-membrane glycoprotein composed of two immunoglobulin-like extracelluar domains, a trans-membrane region and a cytoplasmic tail with an immunoreceptor tyrosine-based inhibitory motif (ITIM). The predicted amino acid sequence was found to be 67% and 52% identitical with human and mouse FcgammaRIIB. RT-PCR indicated porcine FcgammaRII transcripts expressed in liver, alveolar, mesenteric lymph node and PBLs. COS-7 cells transfected with the pig FcgammaRII cDNA were able to bind chicken erythrocytes sensitized with porcine IgG. Identification of porcine FcgammaRII will aid in the understanding IgG-FcgammaR interactions, and may help in developing new immunization protocols.

Molecular cloning and expression of the porcine high-affinity immunoglobulin G Fc receptor (FcgammaRI)

Receptors for the Fc region (FcgammaRs) of immunoglobulin G (IgG) play a crucial role in the immune system and host protection against infection. In this study, we describe the cloning, sequencing, and expression of the high-affinity IgG receptor from pig. By screening a translated Expressed Sequence Tags database with the human FcgammaRI (CD64) protein sequence, we identified a putative porcine homologue. Subsequent polymerase chain reaction amplification confirmed that the identified full-length cDNA was expressed in porcine cells. Rosetting analysis shows that COS-7 cells transfected with a plasmid containing the cloned cDNA were able to bind chicken erythrocytes sensitized with porcine IgG. Scatchard analysis indicated that monomeric IgG bound to transiently transfected cells with an affinity of approximately 4x10(7) M(-1). The porcine FcgammaRI cDNA is 1,038 nucleotides long and is predicted to encode a 346-amino-acid transmembrane glycoprotein composed of three Ig-like domains, a transmembrane region, and a short cytoplasmic tail. The overall identity of the porcine FcgammaRI to its human and mouse counterparts at the level of the amino acid sequence was 75% and 57%, respectively. Identification of porcine FcgammaRI will aid in the understanding of the molecular basis of the porcine immune system and further studies of the receptor function.

A predominant role for antibody in acquired immunity to chlamydial genital tract reinfection

Acquired immunity to murine Chlamydia trachomatis genital tract reinfection has long been assumed to be solely dependent on cell-mediated immunity. However, in this study, we identify a previously unrecognized protective role for Ab. Immunity develops in Ab-deficient mice following the resolution of primary chlamydial genital infection. Subsequent depletion of CD4+ T cells, but not CD8+ T cells, in those immune Ab-deficient mice before secondary infectious challenge, resulted in an infection that did not resolve. Passive immunization with immune (convalescent) serum conferred a marked level of protective immunity to reinfection, which was characterized by a striking decrease in bacterial shedding, from >100,000 inclusion forming units to fewer than 10 inclusion forming units, and a shortened duration of infection. Furthermore, mAbs to the chlamydial major outer membrane protein and LPS conferred significant levels of immunity to reinfection and reduced chlamydial shedding by >100-fold. Anti-heat shock protein 60 mAb had no protective effect. In contrast to the marked protective efficacy of immune serum on reinfection, the course of primary infection was essentially unaltered by the passive transfer of immune serum. Our results convincingly demonstrate that Abs contribute importantly to immunity to chlamydial genital tract reinfection, and that Ab-mediated protection is highly dependent on CD4+ T cell-mediated adaptive changes that occur in the local genital tract tissues during primary infection. These results impact our understanding of immunity to chlamydial genital infection and may provide important insight into vaccine development.

A Reappraisal of Humoral Immunity Based on Mechanisms of Antibody‐Mediated Protection Against Intracellular Pathogens

Sometime in the mid to late twentieth century the study of antibody-mediated immunity (AMI) entered the doldrums, as many immunologists believed that the function of AMI was well understood, and was no longer deserving of intensive investigation. However, beginning in the 1990s studies using monoclonal antibodies (mAbs) revealed new functions for antibodies, including direct antimicrobial effects and their ability to modify host inflammatory and cellular responses. Furthermore, the demonstration that mAbs to several intracellular bacterial and fungal pathogens were protective issued a serious challenge to the paradigm that host defense against such microbes was strictly governed by cell-mediated immunity (CMI). Hence, a new view of AMI is emerging. This view is based on the concept that a major function of antibody (Ab) is to amplify or subdue the inflammatory response to a microbe. In this regard, the "damage-response framework" of microbial pathogenesis provides a new conceptual viewpoint for understanding mechanisms of AMI. According to this view, the ability of an Ab to affect the outcome of a host-microbe interaction is a function of its capacity to modify the damage ensuing from such an interaction. In fact, it is increasingly apparent that the efficacy of an Ab cannot be defined either by immunoglobulin or epitope characteristics alone, but rather by a complex function of Ab variables, such as specificity, isotype, and amount, host variables, such as genetic background and immune status, and microbial variables, such as inoculum, mechanisms of avoiding host immune surveillance and pathogenic strategy. Consequently, far from being understood, recent findings in AMI imply a system with unfathomable complexity and the field is poised for a long overdue renaissance.

The potential of antibody-mediated immunity in the defence against biological weapons

Antibody-mediated immunity (AMI) has been used for the treatment and prevention of infectious diseases for > 100 years, and has a remarkable record of safety, efficacy and versatility. AMI can be used for defence against a wide variety of biological weapons, and passive antibody (Ab) therapy has the potential to provide immediate immunity to susceptible individuals. Recent advances in the Ab field make it possible to generate Abs with enhanced antimicrobial functions. There are significant gaps in our understanding of Ab function, such that the development of Ab-based strategies remains a largely empirical exercise. Nevertheless, the advantages inherent in the therapeutic and prophylactic use of AMI provide a powerful rationale for continued development that will undoubtedly yield many new vaccines and therapeutic Abs.