Immunization with HIV-1 gp41 subunit virosomes induces mucosal antibodies protecting nonhuman primates against vaginal SHIV challenges. Immunity. 2011;34:269-280. [PMID: 21315623 DOI: 10.1016/j.immuni.2011.01.015]

Saccharomyces cerevisiae cells that display norovirus P induce both systemic and mucosal neutralizing antibodies

The human norovirus (HuNov) is the leading cause of acute gastroenteritis (AGE) worldwide. Mucosal secretory IgA (sIgA) in the gastrointestinal tract interrupts the interaction between host cells and HuNov, thus inhibiting viral infection. In this study, we constructed a recombinant Saccharomyces cerevisiae (S. cerevisiae) expressing the HuNov P protein (GII. 4) and evaluated its immunogenicity in mice after oral delivery. First, the recombinant S. cerevisiae (EBY100/pYD1-P) efficiently expressed P, as evidenced by western blotting and indirect fluorescent assay. Second, after oral administration, EBY100/pYD1-P, especially the high-dose group (5 × 109 clone formation units), elicited systemic and mucosal immune responses characterized by significant sera IgG, IgA, and mucosal sIgA. More importantly, these antibodies showed a substantial neutralization effect against P. Lastly, EBY100/pYD1-P induced significant P-specific IFN-γ-secreting T cells and IL4-secreting T cells. Collectively, the recombinant S. cerevisiae expressing HuNov P is a promising mucosal vaccine candidate against HuNov.

Particulate antigens administrated by intranasal and intravaginal routes in a prime-boost strategy improve HIV-specific TFH generation, high-quality antibodies and long-lasting mucosal immunity

Mucosal surfaces serve as the primary entry points for pathogens such as SARS- CoV-2 coronavirus or HIV in the human body. Mucosal vaccination plays a crucial role to successfully induce long-lasting systemic and local immune responses to confer sterilizing immunity. However, antigen formulations and delivery methods must be properly selected since they are decisive for the quality and the magnitude of the elicited immune responses in mucosa. We investigated the significance of using particulate antigen forms for mucosal vaccination by comparing VLP- or protein- based vaccines in a mouse model. Based on a mucosal prime-boost immunization protocol combining (i) HIV- pseudotyped recombinant VLPs (HIV-VLPs) and (ii) plasmid DNA encoding HIV- VLPs (pVLPs), we demonstrated that combination of intranasal primes and intravaginal boosts is optimal to elicit both humoral and cellular memory responses in mucosa. Interestingly, our results show that in contrast to proteins, particulate antigens induce high-quality humoral responses characterized by a high breadth, long-term neutralizing activity and cross-clade reactivity, accompanying with high T follicular helper cell (TFH) response. These results underscore the potential of a VLP-based vaccine in effectively instigating long-lasting, HIV-specific immunity and point out the specific role of particulate antigen form in driving high-quality mucosal immune responses.

Enhanced HPV16 E6/E7+ tumor eradication via induction of tumor-specific T cells by therapeutic vaccination with virosomes presenting synthetic long peptides

Therapeutic cancer vaccines trigger CD4 + and CD8 + T cell responses capable of established tumor eradication. Current platforms include DNA, mRNA and synthetic long peptide (SLP) vaccines, all aiming at robust T cell responses. SLPs linked to the Amplivant® adjuvant (Amplivant-SLP) have shown effective delivery to dendritic cells, resulting in improved immunogenicity in mice. We have now tested virosomes as a delivery vehicle for SLPs. Virosomes are nanoparticles made from influenza virus membranes and have been used as vaccines for a variety of antigens. Amplivant-SLP virosomes induced the expansion of more antigen-specific CD8 + T memory cells in ex vivo experiments with human PBMCs than Amplivant-SLP conjugates alone. The immune response could be further improved by including the adjuvants QS-21 and 3D-PHAD in the virosomal membrane. In these experiments, the SLPs were anchored in the membrane through the hydrophobic Amplivant adjuvant. In a therapeutic mouse model of HPV16 E6/E7+ cancer, mice were vaccinated with virosomes loaded with either Amplivant-conjugated SLPs or lipid-coupled SLPs. Vaccination with both types of virosomes significantly improved the control of tumor outgrowth, leading to elimination of the tumors in about half the animals for the best combinations of adjuvants and to their survival beyond 100 days.

Reconstruction of a polyclonal ADCC antibody repertoire from an HIV-1 non-transmitting mother

Human natural history and vaccine studies support a protective role of antibody dependent cellular cytotoxicity (ADCC) activity against many infectious diseases. One setting where this has consistently been observed is in HIV-1 vertical transmission, where passively acquired ADCC activity in HIV-exposed infants has correlated with reduced acquisition risk and reduced pathogenesis in HIV+ infants. However, the characteristics of HIV-specific antibodies comprising a maternal plasma ADCC response are not well understood. Here, we reconstructed monoclonal antibodies (mAbs) from memory B cells from late pregnancy in mother MG540, who did not transmit HIV to her infant despite several high-risk factors. Twenty mAbs representing 14 clonal families were reconstructed, which mediated ADCC and recognized multiple HIV Envelope epitopes. In experiments using Fc-defective variants, only combinations of several mAbs accounted for the majority of plasma ADCC of MG540 and her infant. We present these mAbs as evidence of a polyclonal repertoire with potent HIV-directed ADCC activity.

Intracellular immunoglobulin A (icIgA) in protective immunity and vaccines

Virus neutralization at respiratory mucosal surfaces is important in the prevention of infection. Mucosal immunity is mediated mainly by extracellular secretory immunoglobulin A (sIgA) and its role has been well studied. However, the protective role of intracellular specific IgA (icIgA) is less well defined. Initially, in vitro studies using epithelial cell lines with surface expressed polymeric immunoglobulin receptor (pIgR) in transwell culture chambers have shown that icIgA can neutralize influenza, parainfluenza, HIV, rotavirus and measles viruses. This effect appears to involve an interaction between polymeric immunoglobulin A (pIgA) and viral particles within an intracellular compartment, since IgA is transported across the polarized cell. Co-localization of specific icIgA with influenza virus in patients' (virus culture positive) respiratory epithelial cells using well-characterized antisera was initially reported in 2018. This review provides a summary of in vitro studies with icIgA on colocalization and neutralization of the above five viruses. Two other highly significant respiratory infectious agents with severe global impacts viz. SARS-2 virus (CoViD pandemic) and the intracellular bacterium-Mycobacterium tuberculosis-are discussed. Further studies will provide more detailed understanding of the mechanisms and kinetics of icIgA neutralization in relation to viral entry and early replication steps with a specific focus on mucosal infections. This will inform the design of more effective vaccines against infectious agents transmitted via the mucosal route.

Antibody Fc-chimerism and effector functions: When IgG takes advantage of IgA

Recent advances in the development of therapeutic antibodies (Abs) have greatly improved the treatment of otherwise drug-resistant cancers and autoimmune diseases. Antibody activities are mediated by both their Fab and the Fc. However, therapeutic Abs base their protective mechanisms on Fc-mediated effector functions resulting in the activation of innate immune cells by FcRs. Therefore, Fc-bioengineering has been widely used to maximise the efficacy and convenience of therapeutic antibodies. Today, IgG remains the only commercially available therapeutic Abs, at the expense of other isotypes. Indeed, production, sampling, analysis and related in vivo studies are easier to perform with IgG than with IgA due to well-developed tools. However, interest in IgA is growing, despite a shorter serum half-life and a more difficult sampling and purification methods than IgG. Indeed, the paradigm that the effector functions of IgG surpass those of IgA has been experimentally challenged. Firstly, IgA has been shown to bind to its Fc receptor (FcR) on effector cells of innate immunity with greater efficiency than IgG, resulting in more robust IgA-mediated effector functions in vitro and better survival of treated animals. In addition, the two isotypes have been shown to act synergistically. From these results, new therapeutic formats of Abs are currently emerging, in particular chimeric Abs containing two tandemly expressed Fc, one from IgG (Fcγ) and one from IgA (Fcα). By binding both FcγR and FcαR on effector cells, these new chimeras showed improved effector functions in vitro that were translated in vivo. Furthermore, these chimeras retain an IgG-like half-life in the blood, which could improve Ab-based therapies, including in AIDS. This review provides the rationale, based on the biology of IgA and IgG, for the development of Fcγ and Fcα chimeras as therapeutic Abs, offering promising opportunities for HIV-1 infected patients. We will first describe the main features of the IgA- and IgG-specific Fc-mediated signalling pathways and their respective functional differences. We will then summarise the very promising results on Fcγ and Fcα containing chimeras in cancer treatment. Finally, we will discuss the impact of Fcα-Fcγ chimerism in prevention/treatment strategies against infectious diseases such as HIV-1.

Highly mutated monoclonal antibody 3F2 targets a conformational and strain-restricted epitope in human immunodeficiency virus gp41 with significant antibody-dependent cell cytotoxicity

Identifying epitope targets by studying the native antibody (Ab) response can identify potential novel vaccine constructs. Studies suggest that long-term non-progressor (LTNP) subjects have inherent immune mechanisms that help to control viremia and disease progression. To explore a role for antibodies (Abs) in LTNP progression, our lab has previously characterized a number of highly mutated Abs that target conformational epitopes of the human immunodeficiency virus (HIV) envelope protein from a single LTNP subject (10076). One Ab clone, 10076-Q3-2C6, had significant cross-clade Ab-dependent cell cytotoxicity. To assess if other LTNP subjects produced similar Abs, we expressed another highly mutated Ab from another subject; subject 10002, clone 10002-Q1-3F2 (variable heavy chain, 63.2% amino acid sequence identity to predicted germline). After expression with its native light chain, the recombinant Ab 3F2 bound to the trimeric envelope protein of HIV (trimer), as well as to the ectodomain of gp41. 3F2 binding to gp41 peptide libraries was consistent with non-linear epitope binding and showed possible overlap with the epitope of 2C6. Ab competition assays suggested that 3F2 may bind near the immunodominant epitope 1 loop region (ID1) of gp41. 2C6 blocked the binding of ID1-loop-binding Abs and 3F2 to the trimer, but 3F2 failed to block 2C6 binding. Together, these results suggest that 3F2 binds to a non-linear conformational epitope primarily localized between the epitope of 2C6 and the ID1. Since they are targeted by functional Abs, a more complete understanding of these ID1 and near-ID1 epitopes may be exploited in future immunization strategies.

Persistent but dysfunctional mucosal SARS-CoV-2-specific IgA and low lung IL-1β associate with COVID-19 fatal outcome: A cross-sectional analysis

The role of the mucosal pulmonary antibody response in coronavirus disease 2019 (COVID-19) outcome remains unclear. Here, we found that in bronchoalveolar lavage (BAL) samples from 48 patients with severe COVID-19-infected with the ancestral Wuhan virus, mucosal IgG and IgA specific for S1, receptor-binding domain (RBD), S2, and nucleocapsid protein (NP) emerged in BAL containing viruses early in infection and persist after virus elimination, with more IgA than IgG for all antigens tested. Furthermore, spike-IgA and spike-IgG immune complexes were detected in BAL, especially when the lung virus has been cleared. BAL IgG and IgA recognized the four main RBD variants. BAL neutralizing titers were higher early in COVID-19 when virus replicates in the lung than later in infection after viral clearance. Patients with fatal COVID-19, in contrast to survivors, developed higher levels of mucosal spike-specific IgA than IgG but lost neutralizing activities over time and had reduced IL-1β in the lung. Altogether, mucosal spike and NP-specific IgG and S1-specific IgA persisting after lung severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) clearance and low pulmonary IL-1β correlate with COVID-19 fatal outcome. Thus, mucosal SARS-CoV-2-specific antibodies may have adverse functions in addition to protective neutralization.

Intranasal vaccination with lipid-conjugated immunogens promotes antigen transmucosal uptake to drive mucosal and systemic immunity

To combat the HIV epidemic and emerging threats such as SARS-CoV-2, immunization strategies are needed that elicit protection at mucosal portals of pathogen entry. Immunization directly through airway surfaces is effective in driving mucosal immunity, but poor vaccine uptake across the mucus and epithelial lining is a limitation. The major blood protein albumin is constitutively transcytosed bidirectionally across the airway epithelium through interactions with neonatal Fc receptors (FcRn). Exploiting this biology, here, we demonstrate a strategy of "albumin hitchhiking" to promote mucosal immunity using an intranasal vaccine consisting of protein immunogens modified with an amphiphilic albumin-binding polymer-lipid tail, forming amph-proteins. Amph-proteins persisted in the nasal mucosa of mice and nonhuman primates and exhibited increased uptake into the tissue in an FcRn-dependent manner, leading to enhanced germinal center responses in nasal-associated lymphoid tissue. Intranasal immunization with amph-conjugated HIV Env gp120 or SARS-CoV-2 receptor binding domain (RBD) proteins elicited 100- to 1000-fold higher antigen-specific IgG and IgA titers in the serum, upper and lower respiratory mucosa, and distal genitourinary mucosae of mice compared to unmodified protein. Amph-RBD immunization induced high titers of SARS-CoV-2-neutralizing antibodies in serum, nasal washes, and bronchoalveolar lavage. Furthermore, intranasal amph-protein immunization in rhesus macaques elicited 10-fold higher antigen-specific IgG and IgA responses in the serum and nasal mucosa compared to unmodified protein, supporting the translational potential of this approach. These results suggest that using amph-protein vaccines to deliver antigen across mucosal epithelia is a promising strategy to promote mucosal immunity against HIV, SARS-CoV-2, and other infectious diseases.

Immunoglobulin A antibody composition is sculpted to bind the self gut microbiome

Despite being the most abundantly secreted immunoglobulin isotype, the pattern of reactivity of immunoglobulin A (IgA) antibodies toward each individual's own gut commensal bacteria still remains elusive. By colonizing germ-free mice with defined commensal bacteria, we found that the binding specificity of bulk fecal and serum IgA toward resident gut bacteria resolves well at the species level and has modest strain-level specificity. IgA hybridomas generated from lamina propria B cells of gnotobiotic mice showed that most IgA clones recognized a single bacterial species, whereas a small portion displayed cross-reactivity. Orally administered hybridoma-produced IgAs still retained bacterial antigen binding capability, implying the potential for a new class of therapeutic antibodies. Species-specific IgAs had a range of strain specificities. Given the distinctive bacterial species and strain composition found in each individual's gut, our findings suggest the IgA antibody repertoire is shaped uniquely to bind "self" gut bacteria.

Towards the future exploration of mucosal mRNA vaccines against emerging viral diseases; lessons from existing next-generation mucosal vaccine strategies

The mRNA vaccine platform has offered the greatest potential in fighting the COVID-19 pandemic owing to rapid development, effectiveness, and scalability to meet the global demand. There are many other mRNA vaccines currently being developed against different emerging viral diseases. As with the current COVID-19 vaccines, these mRNA-based vaccine candidates are being developed for parenteral administration via injections. However, most of the emerging viruses colonize the mucosal surfaces prior to systemic infection making it very crucial to target mucosal immunity. Although parenterally administered vaccines would induce a robust systemic immunity, they often provoke a weak mucosal immunity which may not be effective in preventing mucosal infection. In contrast, mucosal administration potentially offers the dual benefit of inducing potent mucosal and systemic immunity which would be more effective in offering protection against mucosal viral infection. There are however many challenges posed by the mucosal environment which impede successful mucosal vaccination. The development of an effective delivery system remains a major challenge to the successful exploitation of mucosal mRNA vaccination. Nonetheless, a number of delivery vehicles have been experimentally harnessed with different degrees of success in the mucosal delivery of mRNA vaccines. In this review, we provide a comprehensive overview of mRNA vaccines and summarise their application in the fight against emerging viral diseases with particular emphasis on COVID-19 mRNA platforms. Furthermore, we discuss the prospects and challenges of mucosal administration of mRNA-based vaccines, and we explore the existing experimental studies on mucosal mRNA vaccine delivery.

Antiviral Activities of HIV-1-Specific Human Broadly Neutralizing Antibodies Are Isotype-Dependent

Broadly neutralizing antibodies (bNAbs) offer promising opportunities for preventing HIV-1 infection. The protection mechanisms of bNAbs involve the Fc domain, as well as their Fab counterpart. Here, different bNAb isotypes including IgG1, IgA1, IgA2, and IgA122 (IgA2 with the hinge of IgA1) were generated and then produced in CHO cells. Their ability to neutralize pseudovirus and primary HIV-1 isolates were measured, as well as their potential ADCC-like activity using a newly developed assay. In our work, gp41-specific IgA seems to be more efficient than IgG1 in inducing ADCC-like activity, but not in its virus neutralization effect. We show that either gp120-specific IgA or IgG1 isotypes are both efficient in neutralizing different viral strains. In contrast, gp120-specific IgG1 was a better ADCC-like inducer than IgA isotypes. These results provide new insights into the neutralization and ADCC-like activity of different bNAbs that might be taken into consideration when searching for new treatments or antibody-based vaccines.

Bioinspired and Biomimetic Nanomedicines for Targeted Cancer Therapy

Undesirable side effects and multidrug resistance are the major obstacles in conventional chemotherapy towards cancers. Nanomedicines provide alternative strategies for tumor-targeted therapy due to their inherent properties, such as nanoscale size and tunable surface features. However, the applications of nanomedicines are hampered in vivo due to intrinsic disadvantages, such as poor abilities to cross biological barriers and unexpected off-target effects. Fortunately, biomimetic nanomedicines are emerging as promising therapeutics to maximize anti-tumor efficacy with minimal adverse effects due to their good biocompatibility and high accumulation abilities. These bioengineered agents incorporate both the physicochemical properties of diverse functional materials and the advantages of biological materials to achieve desired purposes, such as prolonged circulation time, specific targeting of tumor cells, and immune modulation. Among biological materials, mammalian cells (such as red blood cells, macrophages, monocytes, and neutrophils) and pathogens (such as viruses, bacteria, and fungi) are the functional components most often used to confer synthetic nanoparticles with the complex functionalities necessary for effective nano-biointeractions. In this review, we focus on recent advances in the development of bioinspired and biomimetic nanomedicines (such as mammalian cell-based drug delivery systems and pathogen-based nanoparticles) for targeted cancer therapy. We also discuss the biological influences and limitations of synthetic materials on the therapeutic effects and targeted efficacies of various nanomedicines.

Emerging vaccine nanotechnology: From defense against infection to sniping cancer

Looking retrospectively at the development of humanity, vaccination is an unprecedented medical landmark that saves lives by harnessing the human immune system. During the ongoing coronavirus disease 2019 (COVID-19) pandemic, vaccination is still the most effective defense modality. The successful clinical application of the lipid nanoparticle-based Pfizer/BioNTech and Moderna mRNA COVID-19 vaccines highlights promising future of nanotechnology in vaccine development. Compared with conventional vaccines, nanovaccines are supposed to have advantages in lymph node accumulation, antigen assembly, and antigen presentation; they also have, unique pathogen biomimicry properties because of well-organized combination of multiple immune factors. Beyond infectious diseases, vaccine nanotechnology also exhibits considerable potential for cancer treatment. The ultimate goal of cancer vaccines is to fully mobilize the potency of the immune system as a living therapeutic to recognize tumor antigens and eliminate tumor cells, and nanotechnologies have the requisite properties to realize this goal. In this review, we summarize the recent advances in vaccine nanotechnology from infectious disease prevention to cancer immunotherapy and highlight the different types of materials, mechanisms, administration methods, as well as future perspectives.

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

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

Combined Subcutaneous-Intranasal Immunization With Epitope-Based Antigens Elicits Binding and Neutralizing Antibody Responses in Serum and Mucosae Against PRRSV-2 and SARS-CoV-2

New vaccine design approaches, platforms, and immunization strategies might foster antiviral mucosal effector and memory responses to reduce asymptomatic infection and transmission in vaccinated individuals. Here, we investigated a combined parenteral and mucosal immunization scheme to induce local and serum antibody responses, employing the epitope-based antigens 3BT and NG19m. These antigens target the important emerging and re-emerging viruses PRRSV-2 and SARS-CoV-2, respectively. We assessed two versions of the 3BT protein, which contains conserved epitopes from the GP5 envelope protein of PRRSV-2: soluble and expressed by the recombinant baculovirus BacDual-3BT. On the other hand, NG19m, comprising the receptor-binding motif of the S protein of SARS-CoV-2, was evaluated as a soluble recombinant protein only. Vietnamese mini-pigs were immunized employing different inoculation routes: subcutaneous, intranasal, or a combination of both (s.c.-i.n.). Animals produced antigen-binding and neut1ralizing antibodies in serum and mucosal fluids, with varying patterns of concentration and activity, depending on the antigen and the immunization schedule. Soluble 3BT was a potent immunogen to elicit binding and neutralizing antibodies in serum, nasal mucus, and vaginal swabs. The vectored immunogen BacDual-3BT induced binding antibodies in serum and mucosae, but PRRSV-2 neutralizing activity was found in nasal mucus exclusively when administered intranasally. NG19m promoted serum and mucosal binding antibodies, which showed differing neutralizing activity. Only serum samples from subcutaneously immunized animals inhibited RBD-ACE2 interaction, while mini-pigs inoculated intranasally or via the combined s.c.-i.n. scheme produced subtle neutralizing humoral responses in the upper and lower respiratory mucosae. Our results show that intranasal immunization, alone or combined with subcutaneous delivery of epitope-based antigens, generates local and systemic binding and neutralizing antibodies. Further investigation is needed to evaluate the capability of the induced responses to prevent infection and reduce transmission.

Cooperation Between Systemic and Mucosal Antibodies Induced by Virosomal Vaccines Targeting HIV-1 Env: Protection of Indian Rhesus Macaques Against Low-Dose Intravaginal SHIV Challenges

A virosomal vaccine inducing systemic/mucosal anti-HIV-1 gp41 IgG/IgA had previously protected Chinese-origin rhesus macaques (RMs) against vaginal SHIV_SF162P3 challenges. Here, we assessed its efficacy in Indian-origin RMs by intramuscular priming/intranasal boosting (n=12/group). Group K received virosome-P1-peptide alone (harboring the Membrane Proximal External Region), Group L combined virosome-rgp41 plus virosome-P1, and Group M placebo virosomes. Vaccination induced plasma binding but no neutralizing antibodies. Five weeks after boosting, all RMs were challenged intravaginally with low-dose SHIV_SF162P3 until persistent systemic infection developed. After SHIV challenge #7, six controls were persistently infected versus only one Group L animal (vaccine efficacy 87%; P=0.0319); Group K was not protected. After a 50% SHIV dose increase starting with challenge #8, protection in Group L was lost. Plasmas/sera were analyzed for IgG phenotypes and effector functions; the former revealed that protection in Group L was significantly associated with increased binding to FcγR2/3(A/B) across several time-points, as were some IgG measurements. Vaginal washes contained low-level anti-gp41 IgGs and IgAs, representing a 1-to-5-fold excess over the SHIV inoculum's gp41 content, possibly explaining loss of protection after the increase in challenge-virus dose. Virosomal gp41-vaccine efficacy was confirmed during the initial seven SHIV challenges in Indian-origin RMs when the SHIV inoculum had at least 100-fold more HIV RNA than acutely infected men's semen. Vaccine protection by virosome-induced IgG and IgA parallels the cooperation between systemically administered IgG1 and mucosally applied dimeric IgA2 monoclonal antibodies that as single-agents provided no/low protection - but when combined, prevented mucosal SHIV transmission in all passively immunized RMs.

Nanovaccine Delivery Approaches and Advanced Delivery Systems for the Prevention of Viral Infections: From Development to Clinical Application

Viral infections causing pandemics and chronic diseases are the main culprits implicated in devastating global clinical and socioeconomic impacts, as clearly manifested during the current COVID-19 pandemic. Immunoprophylaxis via mass immunisation with vaccines has been shown to be an efficient strategy to control such viral infections, with the successful and recently accelerated development of different types of vaccines, thanks to the advanced biotechnological techniques involved in the upstream and downstream processing of these products. However, there is still much work to be done for the improvement of efficacy and safety when it comes to the choice of delivery systems, formulations, dosage form and route of administration, which are not only crucial for immunisation effectiveness, but also for vaccine stability, dose frequency, patient convenience and logistics for mass immunisation. In this review, we discuss the main vaccine delivery systems and associated challenges, as well as the recent success in developing nanomaterials-based and advanced delivery systems to tackle these challenges. Manufacturing and regulatory requirements for the development of these systems for successful clinical and marketing authorisation were also considered. Here, we comprehensively review nanovaccines from development to clinical application, which will be relevant to vaccine developers, regulators, and clinicians.

A recombinant measles virus vaccine strongly reduces SHIV viremia and virus reservoir establishment in macaques

Replicative vectors derived from live-attenuated measles virus (MV) carrying additional non-measles vaccine antigens have long demonstrated safety and immunogenicity in humans despite pre-existing immunity to measles. Here, we report the vaccination of cynomolgus macaques with MV replicative vectors expressing simian-human immunodeficiency virus Gag, Env, and Nef antigens (MV-SHIV Wt) either wild type or mutated in the immunosuppressive (IS) domains of Nef and Env antigens (MV-SHIV Mt). We found that the inactivation of Nef and Env IS domains by targeted mutations led to the induction of significantly enhanced post-prime cellular immune responses. After repeated challenges with low doses of SHIV-SF162p3, vaccinees were protected against high viremia, resulting in a 2-Log reduction in peak viremia, accelerated viral clearance, and a decrease -even complete protection for nearly half of the monkeys- in reservoir cell infection. This study demonstrates the potential of a replicative viral vector derived from the safe and widely used measles vaccine in the development of a future human vaccine against HIV-1.

Evaluation of Cell-Penetrating Peptides as Mucosal Immune Enhancers for Nasal Vaccination

Cell-penetrating peptides (CPPs) have been evaluated as enhancers in drug delivery, their addition in medical formulations favors drug absorption allowing obtaining the pharmacological effect with lower doses. In vaccine formulations their inclusion has been also explored with interesting results. Currently mucosal vaccination constitutes a promising alternative with the main advantage of inducing both systemic and mucosal immune responses, which are crucial for control tumors and infections at mucosal tissues. In the present work the nasal immune-enhancing effect of four CPPs was evaluated in Balb/c mice. Animals were intranasally immunized with CPP and the recombinant hepatitis B surface protein (HBsAg) as model antigen. The antibody response in sera and mucosal tissue was measured by ELISA. The IFN-γ secretion response at spleen was also evaluated by ELISPOT and ELISA. Among the CPPs studied one novel peptide stand out by its ability to potentiate the humoral and cellular immune response against the co-administered antigen. Considering that the use of mucosal routes is a promising strategy in vaccination, which are gaining special relevance nowadays in the development of novel candidates against SARS-CoV-2 and other potential emerging respiratory virus, the searching and development of safe mucosal adjuvants constitute a current need.

Importance of Cry Proteins in Biotechnology: Initially a Bioinsecticide, Now a Vaccine Adjuvant

A hallmark of Bacillus thuringiensis bacteria is the formation of one or more parasporal crystal (Cry) proteins during sporulation. The toxicity of these proteins is highly specific to insect larvae, exerting lethal effects in different insect species but not in humans or other mammals. The aim of this review is to summarize previous findings on Bacillus thuringiensis, including the characteristics of the bacterium, its subsequent contribution to biotechnology as a bioinsecticide due to the presence of Cry proteins, and its potential application as an adjuvant. In several studies, Cry proteins have been administered together with specific antigens to immunize experimental animal models. The results have shown that these proteins can enhance immunogenicity by generating an adequate immune response capable of protecting the model against an experimental infectious challenge, whereas protection is decreased when the specific antigen is administered without the Cry protein. Therefore, based on previous results and the structural homology between Cry proteins, these molecules have arisen as potential adjuvants in the development of vaccines for both animals and humans. Finally, a model of the interaction of Cry proteins with different components of the immune response is proposed.

Roles of fragment crystallizable-mediated effector functions in broadly neutralizing antibody activity against HIV

PURPOSE OF REVIEW

'Broadly neutralizing antibodies' (bNAbs), are rare HIV-specific antibodies which exhibit the atypical ability to potently neutralize diverse viral isolates. While efforts to elicit bNAbs through vaccination have yet to succeed, recent years have seen remarkable preclinical and clinical advancements of passive immunization approaches targeting both HIV prevention and cure. We focus here on the potential to build upon this success by moving beyond neutralization to additionally harness the diverse effector functionalities available to antibodies via fragment crystallizable-effector (Fc) functions.

RECENT FINDINGS

Recent studies have leveraged the ability to engineer bNAb Fc domains to either enhance or abrogate particular effector functions to demonstrate that activities such as antibody-dependent cell-mediated cytotoxicity contribute substantially to in-vivo antiviral activity. Intriguingly, recent studies in both nonhuman primates and in humans have suggested that passive bNAb infusion can lead to durable immunity by enhancing virus-specific T-cell responses through a 'vaccinal effect'.

SUMMARY

The combination of antibody engineering strategies designed to enhance effector functions, with the broad and potent antigen recognition profile of bNAbs, has the potential to give rise to powerful new therapeutics for HIV. We aim to provide a timely review of recent advances to catalyze this development.

Cooperation Between Systemic IgG1 and Mucosal Dimeric IgA2 Monoclonal Anti-HIV Env Antibodies: Passive Immunization Protects Indian Rhesus Macaques Against Mucosal SHIV Challenges

Understanding the interplay between systemic and mucosal anti-HIV antibodies can provide important insights to develop new prevention strategies. We used passive immunization via systemic and/or mucosal routes to establish cause-and-effect between well-characterized monoclonal antibodies and protection against intrarectal (i.r.) SHIV challenge. In a pilot study, for which we re-used animals previously exposed to SHIV but completely protected from viremia by different classes of anti-HIV neutralizing monoclonal antibodies (mAbs), we made a surprise finding: low-dose intravenous (i.v.) HGN194-IgG1, a human neutralizing mAb against the conserved V3-loop crown, was ineffective when given alone but protected 100% of animals when combined with i.r. applied HGN194-dIgA2 that by itself had only protected 17% of the animals. Here we sought to confirm the unexpected synergy between systemically administered IgG1 and mucosally applied dIgA HGN194 forms using six groups of naïve macaques (n=6/group). Animals received i.v. HGN194-IgG1 alone or combined with i.r.-administered dIgA forms; controls remained untreated. HGN194-IgG1 i.v. doses were given 24 hours before - and all i.r. dIgA doses 30 min before - i.r. exposure to a single high-dose of SHIV-1157ipEL-p. All controls became viremic. Among passively immunized animals, the combination of IgG1+dIgA2 again protected 100% of the animals. In contrast, single-agent i.v. IgG1 protected only one of six animals (17%) - consistent with our pilot data. IgG1 combined with dIgA1 or dIgA1+dIgA2 protected 83% (5/6) of the animals. The dIgA1+dIgA2 combination without the systemically administered dose of IgG1 protected 67% (4/6) of the macaques. We conclude that combining suboptimal antibody defenses at systemic and mucosal levels can yield synergy and completely prevent virus acquisition.

The current and future role of nanovaccines in HIV-1 vaccine development

Introduction: An efficacious vaccine for HIV-1 has been sought for over 30 years to eliminate the virus from the human population. Many challenges have occurred in the attempt to produce a successful immunogen, mainly caused by the basic biology of the virus. Immunogens have been developed focusing on inducing one or more of the following types of immune responses; neutralizing antibodies, non-neutralizing antibodies, and T-cell mediated responses. One way to better present and develop an immunogen for HIV-1 is through the use of nanotechnology and nanoparticles.Areas covered: This article gives a basic overview of the HIV-1 vaccine field, as well as nanotechnology, specifically nanovaccines. It then covers the application of nanovaccines made from biological macromolecules to HIV-1 vaccine development for neutralizing antibodies, non-neutralizing antibodies, and T-cell-mediated responses.Expert opinion: Nanovaccines are an area that is ripe for further exploration in HIV-1 vaccine field. Not only are nanovaccines capable of carrying and presenting antigens in native-like conformations, but they have also repeatedly been shown to increase immunogenicity over recombinant antigens alone. Only through further research can the true role of nanovaccines in the development of an efficacious HIV-1 vaccine be established.

Invaplex functions as an intranasal adjuvant for subunit and DNA vaccines co-delivered in the nasal cavity of nonhuman primates

Development of intranasal vaccines for HIV-1 and other mucosal pathogens has been hampered by the lack of adjuvants that can be given safely to humans. We have found that an intranasal Shigella vaccine (Invaplex) which is well tolerated in humans can also function as an adjuvant for intranasal protein and DNA vaccines in mice. To determine whether Invaplex could potentially adjuvant similar vaccines in humans, we simultaneously administered a simian immunodeficiency virus (SIV) envelope (Env) protein and DNA encoding simian-human immunodeficiency virus (SHIV) with or without Invaplex in the nasal cavity of female rhesus macaques. Animals were intranasally boosted with adenoviral vectors expressing SIV env or gag,pol to evaluate memory responses. Anti-SIV antibodies in sera and nasal, genital tract and rectal secretions were quantitated by ELISA. Intracellular cytokine staining was used to measure Th1-type T cells in blood. Macaques given DNA/protein immunizations with 0.5 mg Invaplex developed greater serum IgG, nasal IgA and cervicovaginal IgA responses to SIV Env and SHIV Gag,Pol proteins when compared to non-adjuvanted controls. Rectal IgA responses to Env were only briefly elevated and not observed to Gag,Pol. Invaplex increased frequencies of IFNγ-producing CD4 and CD8 T cells to the Env protein, but not T cell responses induced by the DNA. Ad-SIV boosting increased Env-specific polyfunctional T cells and Env- and Gag,Pol-specific antibodies in serum and all secretions. The data suggest that Invaplex could be highly effective as an adjuvant for intranasal protein vaccines in humans, especially those intended to prevent infections in the genital or respiratory tract.

Virosome-based nanovaccines; a promising bioinspiration and biomimetic approach for preventing viral diseases: A review

Vaccination is the most effective means of controlling infectious disease-related morbidity and mortality. However, due to low immunogenicity of viral antigens, nanomedicine as a new opportunity in new generation of vaccine advancement attracted researcher encouragement. Virosome is a lipidic nanomaterial emerging as FDA approved nanocarriers with promising bioinspiration and biomimetic potency against viral infections. Virosome surface modification with critical viral fusion proteins is the cornerstone of vaccine development. Surface antigens at virosomes innovatively interact with targeted receptors on host cells that evoke humoral or cellular immune responses through antibody-producing B cell and internalization by endocytosis-mediated pathways. To date, several nanovaccine based on virosome formulations have been commercialized against widespread and life-threatening infections. Recently, Great efforts were made to fabricate a virosome-based vaccine platform against a new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Thus, this review provides a novel overview of the virosome based nanovaccine production, properties, and application on the viral disease, especially its importance in SARS-CoV-2 vaccine discovery.

The Importance of Regulation in Natural Immunity to HIV

Worldwide, most Human Immunodeficiency Virus (HIV) infections are acquired through heterosexual intercourse, and in sub-Saharan Africa, 59% of new HIV infections affect women. Vaccines and microbicides hold promise for preventing the acquisition of HIV. To this end, the study of HIV highly exposed seronegative (HESN) female commercial sex workers (CSWs), who constitute a model of natural immunity to HIV, provides an exceptional opportunity to determine important clues for the development of preventive strategies. Studies using both female genital tract (FGT) and peripheral blood samples of HESN CSWs, have allowed identifying distinct features, notably low-inflammatory patterns associated with resistance to infection. How this seemingly regulated response is achieved at the initial site of HIV infection remains unknown. One hypothesis is that populations presenting regulatory profiles contribute to the orchestration of potent anti-viral and low-inflammatory responses at the initial site of HIV transmission. Here, we view to update our knowledge regarding this issue.

IL-7-Adjuvanted Vaginal Vaccine Elicits Strong Mucosal Immune Responses in Non-Human Primates

Mucosal immune responses are crucial in protecting against pathogens entering through mucosal surfaces. However, due to poor T-cell responsiveness upon mucosal antigenic stimulation, mucosal immunity remains difficult to obtain through vaccines and requires appropriate adjuvants. We previously demonstrated that administered systemically to healthy macaques or locally expressed in the intestinal mucosa of acutely SIV-infected macaques, interleukin-7 (IL-7) triggers chemokine expression and immune cell homing into mucosae, suggesting its important role in the development of mucosal immune responses. We therefore examined whether local delivery of recombinant glycosylated simian IL-7 (rs-IL-7gly) to the vaginal mucosa of rhesus macaques could prepare the lower female genital tract (FGT) for subsequent immunization and act as an efficient mucosal adjuvant. First, we showed that local administration of rs-IL-7gly triggers vaginal overexpression of chemokines and infiltration of mDCs, macrophages, NKs, B- and T-cells in the lamina propria while MamuLa-DR⁺ APCs accumulated in the epithelium. Subsequent mucosal anti-DT immunization in macaques resulted in a faster, stronger, and more persistent mucosal antibody response compared to DT-immunization alone. Indeed, we detected robust productions of DT-specific IgAs and IgGs in their vaginal secretions and identified cells secreting DT-specific IgAs in their vaginal mucosa and IgGs in draining lymph nodes. Finally, the expression of chemokines involved in the organization of tertiary lymphoid structures (TLS) was only increased in the vaginal mucosa of IL-7-adjuvanted immunized macaques. Interestingly, TLSs developed around PNAd⁺ high endothelial venules in their lower FGT sampled 2 weeks after the last immunization. Non-traumatic vaginal administration of rs-IL-7gly prepares the mucosa to respond to subsequent local immunization and allows the development of a strong mucosal immune response in macaques, through the chemokine-dependent recruitment of immune cells, the activation of mDCs and the formation of TLSs. The localization of DT-specific IgA⁺ plasma cells in the upper vaginal mucosa argues for their contribution to the production of specific immunoglobulins in the vaginal secretions. Our results highlight the potential of IL-7 as a potent mucosal adjuvant to stimulate the FGT immune system and elicit vaginal antibody responses to local immunization, which is the most promising way to confer protection against many sexually transmitted diseases.

Parainfluenza Virus 5 Priming Followed by SIV/HIV Virus-Like-Particle Boosting Induces Potent and Durable Immune Responses in Nonhuman Primates

The search for a preventive vaccine against HIV infection remains an ongoing challenge, indicating the need for novel approaches. Parainfluenza virus 5 (PIV5) is a paramyxovirus replicating in the upper airways that is not associated with any animal or human pathology. In animal models, PIV5-vectored vaccines have shown protection against influenza, RSV, and other human pathogens. Here, we generated PIV5 vaccines expressing HIV envelope (Env) and SIV Gag and administered them intranasally to macaques, followed by boosting with virus-like particles (VLPs) containing trimeric HIV Env. Moreover, we compared the immune responses generated by PIV5-SHIV prime/VLPs boost regimen in naïve vs a control group in which pre-existing immunity to the PIV5 vector was established. We demonstrate for the first time that intranasal administration of PIV5-based HIV vaccines is safe, well-tolerated and immunogenic, and that boosting with adjuvanted trimeric Env VLPs enhances humoral and cellular immune responses. The PIV5 prime/VLPs boost regimen induced robust and durable systemic and mucosal Env-specific antibody titers with functional activities including ADCC and neutralization. This regimen also induced highly polyfunctional antigen-specific T cell responses. Importantly, we show that diminished responses due to PIV5 pre-existing immunity can be overcome in part with VLP protein boosts. Overall, these results establish that PIV5-based HIV vaccine candidates are promising and warrant further investigation including moving on to primate challenge studies.

The Protective HIV-1 Envelope gp41 Antigen P1 Acts as a Mucosal Adjuvant Stimulating the Innate Immunity

Mucosal nasal vaccine development, although ideal to protect from pathogens invading mucosally, is limited by the lack of specific adjuvant. We recently used P1, a conserved region of HIV-1 gp41-envelope glycoprotein, as efficient antigen in a prophylactic HIV-1 mucosal vaccine applied nasally. Herein, P1 immunomodulation properties were assessed on human nasal mucosal models by measuring induction of cytokine and chemokine production, intracellular signaling pathways, mucosal dendritic cell (DC) activation, and T cell proliferation. P1 adjuvant properties were evaluated by quantification of antigen-specific B cell responses against a model antigen in an in vitro immunization model. We now demonstrated that P1 has additional immunological properties. P1 initiates immune responses by inducing nasal epithelial cells to secrete the Th2-cytokine thymic stromal lymphopoietin (TSLP), a described mucosal adjuvant. Secreted TSLP activates, in turn, intracellular calcium flux and PAR-2-associated NFAT signaling pathway regulated by microRNA-4485. Thereafter, P1 induces mucosal dendritic cell maturation, secretion of TSLP in a TSLP-receptor (R)-dependent autocrine loop, but also IL-6, IL-10, IL-8, CCL20, CCL22, and MMP-9, and proliferation of CD4+ T cells. Finally, P1 acts as an adjuvant to stimulate antigen-specific B cell responses in vitro. Overall, P1 is a multi-functional domain with various immuno-modulatory properties. In addition to being a protective vaccine antigen for HIV prevention, P1 acts as adjuvant for other mucosal vaccines able to stimulate humoral and cellular antigen-specific responses.

HIV-1 Entry and Prospects for Protecting against Infection

Human Immunodeficiency Virus type-1 (HIV-1) establishes a latent viral reservoir soon after infection, which poses a major challenge for drug treatment and curative strategies. Many efforts are therefore focused on blocking infection. To this end, both viral and host factors relevant to the onset of infection need to be considered. Given that HIV-1 is most often transmitted mucosally, strategies designed to protect against infection need to be effective at mucosal portals of entry. These strategies need to contend also with cell-free and cell-associated transmitted/founder (T/F) virus forms; both can initiate and establish infection. This review will discuss how insight from the current model of HIV-1 mucosal transmission and cell entry has highlighted challenges in developing effective strategies to prevent infection. First, we examine key viral and host factors that play a role in transmission and infection. We then discuss preventive strategies based on antibody-mediated protection, with emphasis on targeting T/F viruses and mucosal immunity. Lastly, we review treatment strategies targeting viral entry, with focus on the most clinically advanced entry inhibitors.

The CH1α domain of mucosal gp41 IgA contributes to antibody specificity and antiviral functions in HIV-1 highly exposed Sero-Negative individuals

The antibody molecule comprises a variable domain conferring antigen specificity and affinity distinct from the heavy chain constant (CH) domains dictating effector functions. We here interrogate this paradigm by evaluating the unique influence of the CH1α domain on epitope specificity and functions using two mucosal gp41-specific Fab-IgAs (FabA) derived from HIV-1 highly-exposed but persistently seronegative individuals (HESN). These HESN develop selectively affinity-matured HIV-1-specific mucosal IgA that target the gp41 viral envelope and might provide protection although by unclear mechanisms. Isotype-switching FabAs into Fab-IgGs (FabGs) results in a >10-fold loss in affinity for HIV-1 clade A, B, and C gp41, together with reduced neutralization of HIV-1 cross-clade. The FabA conformational epitopes map selectively on gp41 in 6-Helix bundle and pre-fusion conformations cross-clade, unlike FabGs. Finally, we designed in silico, a 12 amino-acid peptide recapitulating one FabA conformational epitope that inhibits the FabA binding to gp41 cross-clade and its neutralizing activity. Altogether, our results reveal that the CH1α domain shapes the antibody paratope through an allosteric effect, thereby strengthening the antibody specificity and functional activities. Further, they clarify the mechanisms by which these HESN IgAs might confer protection against HIV-1-sexual acquisition. The IgA-specific epitope we characterized by reverse vaccinology could help designing a mucosal HIV-1 vaccine.

Neutralizing Antibodies Targeting HIV-1 gp41

HIV-1 vaccine research has obtained an enormous boost since the discovery of many broadly neutralizing antibodies (bnAbs) targeting all accessible sites on the HIV-1 envelope glycoprotein (Env). This in turn facilitated high-resolution structures of the Env glycoprotein in complex with bnAbs. Here we focus on gp41, its highly conserved heptad repeat region 1 (HR1), the fusion peptide (FP) and the membrane-proximal external region (MPER). Notably, the broadest neutralizing antibodies target MPER. Both gp41 HR1 and MPER are only fully accessible once receptor-induced conformational changes have taken place, although some studies suggest access to MPER in the close to native Env conformation. We summarize the data on the structure and function of neutralizing antibodies targeting gp41 HR1, FP and MPER and we review their access to Env and their complex formation with gp41 HR1, MPER peptides and FP within native Env. We further discuss MPER bnAb binding to lipids and the role of somatic mutations in recognizing a bipartite epitope composed of the conserved MPER sequence and membrane components. The problematic of gp41 HR1 access and MPER bnAb auto- and polyreactivity is developed in the light of inducing such antibodies by vaccination.

A Zigzag but Upward Way to Develop an HIV-1 Vaccine

After decades of its epidemic, the human immunodeficiency virus type 1 (HIV-1) is still rampant worldwide. An effective vaccine is considered to be the ultimate strategy to control and prevent the spread of HIV-1. To date, hundreds of clinical trials for HIV-1 vaccines have been tested. However, there is no HIV-1 vaccine available yet, mostly because the immune correlates of protection against HIV-1 infection are not fully understood. Currently, a variety of recombinant viruses-vectored HIV-1 vaccine candidates are extensively studied as promising strategies to elicit the appropriate immune response to control HIV-1 infection. In this review, we summarize the current findings on the immunological parameters to predict the protective efficacy of HIV-1 vaccines, and highlight the latest advances on HIV-1 vaccines based on viral vectors.

Antibody-Dependent Cellular Phagocytosis of HIV-1-Infected Cells Is Efficiently Triggered by IgA Targeting HIV-1 Envelope Subunit gp41

Antibodies mediate a broad array of non-neutralizing Fc-mediated functions against HIV-1 including antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Accordingly, ADCC and ADCP induced by anti-HIV envelope gp120 IgG have been correlated to the limited success of the HIV-1 phase III vaccine trial RV144. It remains elusive whether ADCP can also be triggered by IgA, the isotype predominant at mucosal surfaces through which HIV-1 is mainly transmitted. Yet, we have previously shown that the HIV envelope subunit gp41-specific broadly neutralizing antibody 2F5 under the IgA isotype (2F5-IgA) triggers ADCC and cooperates with 2F5-IgG to increase HIV-1-infected cell lysis. Here, we now demonstrate that 2F5-IgA, more efficiently than 2F5-IgG, induces ADCP not only of gp41-coated beads but also of primary HIV-1-infected cells in a FcαRI-dependent manner. Both primary monocytes and neutrophils can act as effector cells of 2F5-IgA-mediated ADCP, although with different kinetics with faster neutrophil phagocytosis. However, unlike for ADCC, 2F5-IgA and 2F5-IgG do not cooperate to increase ADCP. Altogether, our results reveal that gp41-specific IgA mediate the efficient phagocytosis of HIV-1-infected cells. Inducing such ADCC and ADCP-prone IgA response by vaccination in addition to anti-HIV envelope IgG, might increase the protection against HIV acquisition at mucosal level.

New GMP manufacturing processes to obtain thermostable HIV-1 gp41 virosomes under solid forms for various mucosal vaccination routes

The main objective of the MACIVIVA European consortium was to develop new Good Manufacturing Practice pilot lines for manufacturing thermostable vaccines with stabilized antigens on influenza virosomes as enveloped virus-like particles. The HIV-1 gp41-derived antigens anchored in the virosome membrane, along with the adjuvant 3M-052 (TLR7/8 agonist) on the same particle, served as a candidate vaccine for the proof of concept for establishing manufacturing processes, which can be directly applied or adapted to other virosomal vaccines or lipid-based particles. Heat spray-dried powders suitable for nasal or oral delivery, and freeze-dried sublingual tablets were successfully developed as solid dosage forms for mucosal vaccination. The antigenic properties of vaccinal antigens with key gp41 epitopes were maintained, preserving the original immunogenicity of the starting liquid form, and also when solid forms were exposed to high temperature (40 °C) for up to 3 months, with minimal antigen and adjuvant content variation. Virosomes reconstituted from the powder forms remained as free particles with similar size, virosome uptake by antigen-presenting cells in vitro was comparable to virosomes from the liquid form, and the presence of excipients specific to each solid form did not prevent virosome transport to the draining lymph nodes of immunized mice. Virosome integrity was also preserved during exposure to <−15 °C, mimicking accidental freezing conditions. These “ready to use and all-in-one” thermostable needle-free virosomal HIV-1 mucosal vaccines offer the advantage of simplified logistics with a lower dependence on the cold chain during shipments and distribution.

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

Over 90% of pathogens of medical importance invade the organism through mucosal surfaces, which makes it urgent to develop safe and effective mucosal vaccines and mucosal immunization protocols. Besides, parenteral immunization does not provide adequate protective immunity in mucosal surfaces. Effective mucosal vaccination could protect local and systemic compartments and favor herd immunity. Although various mucosal adjuvants and Ag-delivery systems have been developed, none has filled the gap to control diseases caused by complex mucosal pathogens. Among the strategies to counteract them, recombinant virions from the baculovirus Autographa californica multiple nucleopolyhedrovirus (rAcMNPV) are useful vectors, given their safety and efficacy to produce mucosal and systemic immunity in animal infection models. Here, we review the immunogenic properties of rAcMNPV virions from the perspectives of mucosal immunology and vaccinology. Some features, which are analyzed and extrapolated from studies with different particulate antigens, include size, shape, surface molecule organization, and danger signals, all needed to break the tolerogenic responses of the mucosal immune tissues. Also, we present a condensed discussion on the immunity provided by rAcMNPV virions against influenza virus and human papillomavirus in animal models. Through the text, we highlight the advantages and limitations of this experimental immunization platform.

An HIV-1 vaccine based on bacterium-like particles elicits Env-specific mucosal immune responses

Although many vaccines have been designed to induce effective mucosal immune responses against HIV-1, designing an effective HIV-1 vaccine remains a challenge. Bacterium-like particles (BLPs) are a new type of vector used to induce mucosal immune responses, and have already been used for some vaccines against respiratory tract viruses. In this study, we designed a mucosal vaccine against HIV-1 based on BLPs. The vaccine was used to immunize both mice and guinea pigs via intramuscular (i.m.) injection or intranasal (i.n.) drip. We found that gp120 trimers bound to BLPs delivered via i.n. drip successfully induced Env-specific secretory IgA (sIgA) at mucosal sites in mice. Furthermore, nasal washes from guinea pigs immunized via i.n. drip showed neutralizing activity against HIV-1 tier 1 pseudoviruses. Thus, gp120 trimers bound to BLPs may be an effective vaccine strategy against HIV-1.

Trimeric HIV-1 gp140 fused with APRIL, BAFF, and CD40L on the mucosal gp140-specific antibody responses in mice

HIV-1 envelope (Env)-specific antibody present at mucosal surfaces can block entry of HIV-1 into these portals and thus should be elicited by an HIV-1 preventive vaccine. Since three molecules of tumor necrosis factor superfamily (TNFSF), APRIL, BAFF, and CD40L, could promote mucosal antibody responses, we made fusion constructs of them with an HIV-1 gp140 trimer and tested the mucosal gp140-specific antibody elicited by the fusion constructs in mice using a DNA prime-protein boost vaccination regimen. The fusion constructs formed trimers and displayed both broadly neutralizing antibody epitopes and non-broadly neutralizing antibody epitopes. Compared with the control construct, trimeric gp140, trimeric gp140-APRIL and gp140-BAFF fusion proteins mildly promoted B cell proliferation in vitro, enhanced HIV-1 gp140-binding IgG responses in vaginal lavage or fecal pellets, respectively, and decreased HIV-1 gp140-binding IgA in sera. Gp140-APRIL also augmented HIV-1 gp140-binding IgG in sera. Surprisingly, gp140-CD40L did not promote B cell proliferation in vitro and inhibited mucosal and systemic HIV-1 gp140-binding IgG or IgA. These results suggest that APRIL and BAFF should be further explored as molecular adjuvants for HIV-1 vaccines to enhance mucosal antibody responses, but covalent fusion of TNFSFs to gp140 may hinder their adjuvancy due to steric interactions.

Nanoparticles for mucosal vaccine delivery

Mucosal surfaces represent important routes of entry into the human body for the majority of pathogens, and they constitute unique sites for targeted vaccine delivery. Nanoparticle-based drug delivery systems are emerging technologies for delivering and improving the efficacy of mucosal vaccines. Recent studies have provided new insights into formulation and delivery aspects of importance for the design of safe and efficacious mucosal subunit vaccines based on nanoparticles. These include novel nanomaterials, their physicochemical properties and formulation approaches, nanoparticle interaction with immune cells in the mucosa, and mucosal immunization and delivery strategies. Here, we present recent progress in the application of nanoparticle-based approaches for mucosal vaccine delivery and discuss future research challenges and opportunities in the field.

Evaluation of immunogenicity and protection of the Mic1-3 knockout Toxoplasma gondii live attenuated strain in the feline host

Toxoplasmosis is a zoonotic disease caused by the parasite Toxoplasma gondii. Up to a third of the global human population is estimated to carry a T. gondii infection, which can result in severe complications in immunocompromised individuals and pregnant women. Humans and animals can become infected by ingesting either tissue cysts containing T. gondii bradyzoites, from raw or undercooked meat, or sporulated oocysts from environmental sources. T. gondii oocysts are released in the faeces of cats and other felids, which are the parasite's definitive hosts, leading to environmental contamination. Therefore, vaccination of the feline host against T. gondii is an interesting strategy to interrupt the parasitic life cycle and subsequently limit contamination of intermediate hosts. With this goal in mind, we tested in cats, an attenuated live strain of T. gondii deleted for the Mic1 and Mic3 genes (Mic1-3KO) that was previously shown to be an efficient vaccine candidate in mouse and sheep models. Subcutaneous or oral vaccination routes induced a high specific antibody titer in the cat sera, indicating that the Mic1-3KO strain is immunogenic for cats. To assess protection induced by the vaccine candidate strain, we followed oocysts shedding by vaccinated cats, after oral challenge with a T. gondii wild-type strain. Surprisingly, a high antibody titer did not prevent cats from shedding oocysts from the challenge strain, regardless of the vaccination route. Our results show that the Mic1-3KO vaccine candidate is immunogenic in the feline host, is well tolerated and safe, but does not confer protection against oocysts shedding after natural infection with wild type T. gondii. This result highlights the particular relationship between T. gondii and its unique definitive host, which indicates the need for further investigations to improve vaccination strategies to limit environmental and livestock contaminations.

An Engineered Biomimetic MPER Peptide Vaccine Induces Weakly HIV Neutralizing Antibodies in Mice

A vaccine that induces broadly neutralizing antibodies (bnAbs) against the human immunodeficiency virus (HIV) would be instrumental in controlling the disease. The membrane proximal external region (MPER) peptide is an appealing antigen candidate since it is conserved and is the target of several human bnAbs, such as 2F5. We previously found that liposomes containing cobalt porphyrin-phospholipid (CoPoP) can bind to a his-tagged MPER peptide, resulting in biomimetic antigen presentation on a lipid bilayer. The present study generated various his-tagged, synthetic MPER fragments, which were bound to liposomes containing CoPoP and a synthetic monophosphoryl lipid A (MPLA) and assessed for immunogenicity in mice. MPER peptides with amino acids stretches originating from the membrane insertion point that were at least 25 amino acids in length, had greater 2F5 reactivity and induced stronger antibody responses, compared to shorter ones. Immunization with the lipid-presented MPER elicited stronger antibody responses compared to Alum and Montanide adjuvants, which could recognize recombinant gp41 and gp140 proteins that contained MPER sequences. The induced antibodies neutralized a tier 1A virus that is sensitive to neutralizing antibodies (W61D(TCLA)0.71), but not another tier 1A nor a tier 2 strain. Co-formulation of the MPER peptide with an unrelated malaria protein antigen (Pfs25) that is effectively adjuvanted with liposomes containing CoPoP and MPLA resulted in elicitation of higher MPER antibody levels, but did not improve neutralization, possibly due to interference with proper peptide presentation in the membrane. Murine hybridomas were generated that produced MPER antibodies, but they were non-neutralizing. These results do not show that bnAbs could be generated with MPER peptides and CoPoP liposomes, but do not rule out this possibility with additional improvements to the approach.

Mucosal Antibodies: Defending Epithelial Barriers against HIV-1 Invasion

The power of mucosal anti-HIV-1 envelope immunoglobulins (Igs) to block virus transmission is underappreciated. We used passive immunization, a classical tool to unequivocally prove whether antibodies are protective. We mucosally instilled recombinant neutralizing monoclonal antibodies (nmAbs) of different Ig classes in rhesus macaques (RMs) followed by mucosal simian–human immunodeficiency virus (SHIV) challenge. We gave anti-HIV-1 IgM, IgG, and dimeric IgA (dIgA) versions of the same human nmAb, HGN194 that targets the conserved V3 loop crown. Surprisingly, dIgA1 with its wide-open, flat hinge protected 83% of the RMs against intrarectal R5-tropic SHIV-1157ipEL-p challenge, whereas dIgA2, with its narrow hinge, only protected 17% of the animals—despite identical epitope specificities and in vitro neutralization curves of the two dIgA isotypes (Watkins et al., AIDS 2013 27(9):F13-20). These data imply that factors in addition to neutralization determine in vivo protection. We propose that this underlying protective mechanism is immune exclusion, which involves large nmAb/virion aggregates that prevent virus penetration of mucosal barriers. Future studies need to find biomarkers that predict effective immune exclusion in vivo. Vaccine development strategies against HIV-1 and/or other mucosally transmissible pathogens should include induction of strong mucosal Abs of different Ig classes to defend epithelial barriers against pathogen invasion.

Nasal route for vaccine and drug delivery: Features and current opportunities

Mucosal administration, and specifically nasal route, constitutes an alternative and promising strategy for drug and vaccine delivery. Mucosal routes have several advantages supporting their selective use for different pathologies. Currently, many efforts are being made to develop effective drug formulations and novel devices for nasal delivery. This review described the structure and main characteristics of the nasal cavity. The advantages, achievements and challenges of the nasal route use for medical purposes are discussed, with particular focus on vaccine delivery. Compelling evidences support the potentialities and safety of the nasal delivery of vaccines and drugs. This alternative route could become a solution for many unmet medical issues and also may facilitate and cheapen massive immunization campaigns or long-lasting chronic treatments. Nowadays, in spite of certain remaining skepticism, the field of nasal delivery of drugs and vaccines is growing fast, bolstered by current developments in nanotechnology, imaging and administration devices. A notable increase in the number of approved drugs for nasal administration is envisaged.

Recent Approaches for Solid Dose Vaccine Delivery

Recent studies on vaccine delivery systems are exploring the possibility of replacing liquid vaccines with solid dose vaccines due to the many advantages that solid dose vaccines can offer. These include the prospect of a needle-free vaccine delivery system leading to better patient compliance, cold chain storage, less-trained vaccinators and fewer chances for needle stick injury hazards. Some studies also indicate that vaccines in a solid dosage form can result in a higher level of immunogenicity compared to the liquid form, thus providing a dose-sparing effect. This review outlines the different approaches in solid vaccine delivery using various routes of administration including, oral, pulmonary, intranasal, buccal, sublingual, and transdermal routes. The various techniques and their current advancements will provide a knowledge base for future work to be carried out in this arena.

Monoclonal Antibody 2C6 Targets a Cross-Clade Conformational Epitope in gp41 with Highly Active Antibody-Dependent Cell Cytotoxicity

Previous studies in our laboratory characterized a panel of highly mutated HIV-specific conformational epitope-targeting antibodies (Abs) from a panel of HIV-infected long-term nonprogressors (LTNPs). Despite binding HIV envelope protein and having a high number of somatic amino acid mutations, these Abs had poor neutralizing activity. Because of the evidence of antigen-driven selection and the long CDR3 region (21 amino acids [aa]), we further characterized the epitope targeting of monoclonal Ab (MAb) 76-Q3-2C6 (2C6). We confirmed that 2C6 binds preferentially to trimeric envelope and recognizes the clades A, B, and C SOSIP trimers. 2C6 binds gp140 constructs of clades A, B, C, and D, suggesting a conserved binding site that we localized to the ectodomain of gp41. Ab competition with MAb 50-69 suggested this epitope localizes near aa 579 to 613 (referenced to HXB2 gp160). Peptide library scanning showed consistent binding in this region but to only a single peptide. Lack of overlapping peptide binding supported a nonlinear epitope structure. The significance of this site is supported by 2C6 having Ab-dependent cell cytotoxicity (ADCC) against envelope proteins from two clades. Using 2C6 and variants, alanine scanning mutagenesis identified three amino acids (aa 592, 595, and 596) in the overlapping region of the previously identified peptide. Additional amino acids at sites 524 and 579 were also identified, helping explain its conformational requirement. The fact that different amino acids were included in the epitope depending on the targeted protein supports the conclusion that 2C6 targets a native conformational epitope. When we mapped these amino acids on the trimerized structure, they spanned across oligomers, supporting the notion that the epitope targeted by 2C6 lies in a recessed pocket between two gp41 oligomers. A complete understanding of the epitope specificity of ADCC-mediating Abs is essential for developing effective immunization strategies that optimize protection by these Abs.IMPORTANCE This paper further defines the function and area of the HIV trimeric envelope protein targeted by the monoclonal antibody 2C6. 2C6 binding is influenced by amino acid mutations across two separate gp41 sections of the envelope trimer. This epitope is recognized on multiple clades (variant groups of circulating viruses) of gp41, gp140 trimers, and SOSIP trimers. For the clades tested, 2C6 has robust ADCC. As the target of 2C6 is available in the major clades of HIV and has robust ADCC activity, further definition and appreciation of targeting of antibodies similar to 2C6 during vaccine development should be considered.

Current advances in HIV vaccine preclinical studies using Macaque models

The macaque simian or simian/human immunodeficiency virus (SIV/SHIV) challenge model has been widely used to inform and guide human vaccine trials. Substantial advances have been made recently in the application of repeated-low-dose challenge (RLD) approach to assess SIV/SHIV vaccine efficacies (VE). Some candidate HIV vaccines have shown protective effects in preclinical studies using the macaque SIV/SHIV model but the model's true predictive value for screening potential HIV vaccine candidates needs to be evaluated further. Here, we review key parameters used in the RLD approach and discuss their relevance for evaluating VE to improve preclinical studies of candidate HIV vaccines.

Knowns and Unknowns of Assaying Antibody-Dependent Cell-Mediated Cytotoxicity Against HIV-1

It is now well-accepted that Fc-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC), can contribute to vaccine-elicited protection as well as post-infection control of HIV viremia. This picture was derived using a wide array of ADCC assays, no two of which are strictly comparable, and none of which is qualified at the clinical laboratory level. An earlier comparative study of assay protocols showed that while data from different ADCC assay formats were often correlated, they remained distinct in terms of target cells and the epitopes and antigen(s) available for recognition by antibodies, the effector cells, and the readout of cytotoxicity. This initial study warrants expanded analyses of the relationships among all current assay formats to determine where they detect overlapping activities and where they do not. Here we summarize knowns and unknowns of assaying ADCC against HIV-1.