Proteoliposomal formulations of an HIV-1 gp41-based miniprotein elicit a lipid-dependent immunodominant response overlapping the 2F5 binding motif

Production and Immunogenicity of FeLV Gag-Based VLPs Exposing a Stabilized FeLV Envelope Glycoprotein

The envelope glycoprotein (Env) of retroviruses, such as the Feline leukemia virus (FeLV), is the main target of neutralizing humoral response, and therefore, a promising vaccine candidate, despite its reported poor immunogenicity. The incorporation of mutations that stabilize analogous proteins from other viruses in their prefusion conformation (e.g., HIV Env, SARS-CoV-2 S, or RSV F glycoproteins) has improved their capability to induce neutralizing protective immune responses. Therefore, we have stabilized the FeLV Env protein following a strategy based on the incorporation of a disulfide bond and an Ile/Pro mutation (SOSIP) previously used to generate soluble HIV Env trimers. We have characterized this SOSIP-FeLV Env in its soluble form and as a transmembrane protein present at high density on the surface of FeLV Gag-based VLPs. Furthermore, we have tested its immunogenicity in DNA-immunization assays in C57BL/6 mice. Low anti-FeLV Env responses were detected in SOSIP-FeLV soluble protein-immunized animals; however, unexpectedly no responses were detected in the animals immunized with SOSIP-FeLV Gag-based VLPs. In contrast, high humoral response against FeLV Gag was observed in the animals immunized with control Gag VLPs lacking SOSIP-FeLV Env, while this response was significantly impaired when the VLPs incorporated SOSIP-FeLV Env. Our data suggest that FeLV Env can be stabilized as a soluble protein and can be expressed in high-density VLPs. However, when formulated as a DNA vaccine, SOSIP-FeLV Env remains poorly immunogenic, a limitation that must be overcome to develop an effective FeLV vaccine.

Exploring FeLV-Gag-Based VLPs as a New Vaccine Platform-Analysis of Production and Immunogenicity

Feline leukemia virus (FeLV) is one of the most prevalent infectious diseases in domestic cats. Although different commercial vaccines are available, none of them provides full protection. Thus, efforts to design a more efficient vaccine are needed. Our group has successfully engineered HIV-1 Gag-based VLPs that induce a potent and functional immune response against the HIV-1 transmembrane protein gp41. Here, we propose to use this concept to generate FeLV-Gag-based VLPs as a novel vaccine strategy against this retrovirus. By analogy to our HIV-1 platform, a fragment of the FeLV transmembrane p15E protein was exposed on FeLV-Gag-based VLPs. After optimization of Gag sequences, the immunogenicity of the selected candidates was evaluated in C57BL/6 and BALB/c mice, showing strong cellular and humoral responses to Gag but failing to generate anti-p15E antibodies. Altogether, this study not only tests the versatility of the enveloped VLP-based vaccine platform but also sheds light on FeLV vaccine research.

An engineered HIV-1 Gag-based VLP displaying high antigen density induces strong antibody-dependent functional immune responses

Antigen display on the surface of Virus-Like Particles (VLPs) improves immunogenicity compared to soluble proteins. We hypothesised that immune responses can be further improved by increasing the antigen density on the surface of VLPs. In this work, we report an HIV-1 Gag-based VLP platform engineered to maximise the presence of antigen on the VLP surface. An HIV-1 gp41-derived protein (Min), including the C-terminal part of gp41 and the transmembrane domain, was fused to HIV-1 Gag. This resulted in high-density MinGag-VLPs. These VLPs demonstrated to be highly immunogenic in animal models using either a homologous (VLP) or heterologous (DNA/VLP) vaccination regimen, with the latter yielding 10-fold higher anti-Gag and anti-Min antibody titres. Despite these strong humoral responses, immunisation with MinGag-VLPs did not induce neutralising antibodies. Nevertheless, antibodies were predominantly of an IgG2b/IgG2c profile and could efficiently bind CD16-2. Furthermore, we demonstrated that MinGag-VLP vaccination could mediate a functional effect and halt the progression of a Min-expressing tumour cell line in an in vivo mouse model.

Enhancing HIV-1 Neutralization by Increasing the Local Concentration of Membrane-Proximal External Region-Directed Broadly Neutralizing Antibodies

Broadly neutralizing antibodies (bNAbs) against the membrane-proximal external region (MPER) of the gp41 component of the human immunodeficiency virus type 1 (HIV-1) envelope (Env) are characterized by long, hydrophobic, heavy chain complementarity-determining region 3s (HCDR3s) that interact with the MPER and some viral membrane lipids to achieve increased local concentrations. Here, we show that increasing the local concentration of MPER-directed bNAbs at the cell surface via binding to the high-affinity Fc receptor FcγRI potentiates their ability to prevent viral entry in a manner analogous to the previously reported observation wherein the lipid-binding activity of MPER bNAbs increases their concentration at the viral surface membrane. However, binding of MPER-directed bNAb 10E8 to FcγRI abolishes the neutralization synergy that is seen with the N-heptad repeat (NHR)-targeting antibody D5_AR and NHR-targeting small molecule enfuvirtide (T20), possibly due to decreased accessibility of the NHR in the FcγRI-10E8-MPER complex. Taken together, our results suggest that lipid-binding activity and FcγRI-mediated potentiation function in concert to improve the potency of MPER-directed bNAbs by increasing their local concentration near the site of viral fusion. Therefore, lipid binding may not be a strict requirement for potent neutralization by MPER-targeting bNAbs, as alternative methods can achieve similar increases in local concentrations while avoiding potential liabilities associated with immunologic host tolerance. IMPORTANCE The trimeric glycoprotein Env, the only viral protein expressed on the surface of HIV-1, is the target of broadly neutralizing antibodies and the focus of most vaccine development efforts. Broadly neutralizing antibodies targeting the membrane proximal external region (MPER) of Env show lipid-binding characteristics, and modulating this interaction affects neutralization. In this study, we tested the neutralization potencies of variants of the MPER-targeting antibody 10E8 with different viral-membrane-binding and host FcγRI-binding capabilities. Our results suggest that binding to both lipid and FcγRI improves the neutralization potency of MPER-directed antibodies by concentrating the antibodies at sites of viral fusion. As such, lipid binding may not be uniquely required for MPER-targeting broadly neutralizing antibodies, as alternative methods to increase local concentration can achieve similar improvements in potency.

T-Follicular-Like CD8+ T Cell Responses in Chronic HIV Infection Are Associated With Virus Control and Antibody Isotype Switching to IgG

T cell responses are considered critical for the in vivo control of HIV, but the contribution of different T cell subsets to this control remains unclear. Using a boosted flow cytometric approach that is able to differentiate CD4+ and CD8+ T cell Th1/Tc1, Th2/Tc2, Th17/Tc17, Treg and Tfh/Tfc-like HIV-specific T cell populations, we identified CD8+ Tfc responses that were related to HIV plasma viral loads and associated with rate of antibody isotype class switching to IgG. This favorable balance towards IgG responses positively correlated with increased virus neutralization, higher avidity of neutralizing antibodies and more potent antibody-dependent cell cytotoxicity (ADCC) in PBMCs from HIV controllers compared to non-controllers. Our results identified the CD8+ Tfc-like T-cell response as a component of effective virus control which could possibly be exploited therapeutically.

The Curious Case of Earthworms and COVID-19

Simple Summary

Earthworms have been used for centuries in traditional medicine, and more than a century ago were praised by Charles Darwin as one of the most important organisms in the history of the world. These worms are well-studied with a wealth of information available, for example on the genome, the gene expression, the immune system, the general biology, and ecology. These worms live in many habitats, and they had to find solutions for severe environmental challenges. The common compost worm, Eisenia fetida, has developed a unique mechanism to deal with intruding (nano)materials, bacteria, and viruses. It deals with the intruders by covering these with a defence toxin (lysenin) targeted to kill the intruder. We outline how this mechanism probably can be used as a therapeutic model for human COVID-19 (Severe Acute Respiratory Syndrome Coronavirus 2, SARS-CoV-2) and other corona viruses.

Abstract

Earthworms have been used for centuries in traditional medicine and are used globally as an ecotoxicological standard test species. Studies of the earthworm Eisenia fetida have shown that exposure to nanomaterials activates a primary corona-response, which is covering the nanomaterial with native proteins, the same response as to biological invaders such as a virus. We outline that the earthworm Eisenia fetida is possibly immune to COVID-19 (Severe Acute Respiratory Syndrome Coronavirus 2, SARS-CoV-2), and we describe the likely mechanisms of highly receptor-specific pore-forming proteins (PFPs). A non-toxic version of this protein is available, and we hypothesize that it is possible to use the earthworm’s PFPs based anti-viral mechanism as a therapeutic model for human SARS-CoV-2 and other corona viruses. The proteins can be used as a drug, for example, delivered with a nanoparticle in a similar way to the current COVID-19 vaccines. Obviously, careful consideration should be given to the potential risk of toxicity elicited by lysenin for in vivo usage. We aim to share this view to activate its exploration by the wider scientific community while promoting a potential therapeutic development.

Production and Evaluation of the Properties of HIV-1-Nef-MPER-V3 Fusion Protein Harboring IMT-P8 Cell Penetrating Peptide

BACKGROUND

Finding a safe and effective vaccine for HIV-1 infection is still a major concern.

OBJECTIVE

This study aimed to design and produce a recombinant Nef-MPER V3 protein fused with IMT-P8 using E. coli expression system to provide a potential HIV vaccine with high cellular penetrance.

METHODS

After synthesizing the DNA sequence of the fusion protein, the construct was inserted into the pET-28 expression vector. The recombinant protein expression was induced using 1 mM IPTG and the product was purified through affinity chromatography. Characterization of cellular delivery, toxicity and immunogenicity of the protein was carried out.

RESULTS

The recombinant protein was expressed and confirmed by the anti-Nef antibody through western blotting. Data analyses showed that the protein possessed no considerable toxicity effect and has improved the IMT-P8 penetration rate in comparison to a control sample. Moreover, the antigen immunogenicity of the protein induced specific humoral response in mice.

CONCLUSION

It was concluded that IMT-P8-Nef-MPER-V3 fusion protein has a high penetrance rate in mammalian cell line and low toxicity, thus it can be potentially considered as a vaccine against HIV-1.

Liposomes used as a vaccine adjuvant-delivery system: From basics to clinical immunization

Liposomes are widely utilized as a carrier to improve therapeutic efficacy of agents thanks to their merits of high loading capacity, targeting delivery, reliable protection of agents, good biocompatibility, versatile structure modification and adjustable characteristics, such as size, surface charge, membrane flexibility and the agent loading mode. In particular, in recent years, through modification with immunopotentiators and targeting molecules, and in combination with innovative immunization devices, liposomes are rapidly developed as a multifunctional vaccine adjuvant-delivery system (VADS) that has a high capability in inducing desired immunoresponses, as they can target immune cells and even cellular organelles, engender lysosome escape, and promote Ag cross-presentation, thus enormously enhancing vaccination efficacy. Moreover, after decades of development, several products developed on liposome VADS have already been authorized for clinical immunization and are showing great advantages over conventional vaccines. This article describes in depth some critical issues relevant to the development of liposomes as a VADS, including principles underlying immunization, physicochemical properties of liposomes as the immunity-influencing factors, functional material modification to enhance immunostimulatory functions, the state-of-the-art liposome VADSs, as well as the marketed vaccines based on a liposome VADS. Therefore, this article provides a comprehensive reference to the development of novel liposome vaccines.

HIV-1 envelope glycoproteins isolated from Viremic Non-Progressor individuals are fully functional and cytopathic

In untreated HIV-1-infected individuals, viremia is positively associated with disease progression. However, some viremic non progressors (VNPs) individuals show paradoxical high CD4⁺ T cell counts. HIV-1 envelope glycoprotein complex (Env) is a major cytopathic determinant in viral replication; therefore, we have deeply characterized Env function in this rare clinical phenotype. Full-length Env clones isolated from individuals with Viral Load (VL) > 10,000 copies/mL classified as VNPs (n = 15) or rapid progressors (RPs, n = 17) were geno- and phenotypically analyzed by determining diversity, expression, CD4 binding/signaling, fusogenicity, infectivity and autophagy induction. Selected Env clones from VNPs and RPs (n = 32) showed similar expression, fusion and infection abilities. Env clones from both groups showed similar affinity for CD4 during cell-to-cell transmission and consistently induced similar levels of CD4 signaling, measured by α-tubulin acetylation. Moreover, we demonstrate for the first time that primary Env clones from VNP and RP induce autophagy in uninfected cells and that this feature correlated with fusogenic capacity but was unrelated to disease progression. In conclusion, our data suggest that Env clones from VNP individuals are fully functional. Therefore, the paradoxical CD4⁺ T cell count stability coexisting with high levels of viral replication is unrelated to Env function.

The development of HIV vaccines targeting gp41 membrane-proximal external region (MPER): challenges and prospects

A human immunodeficiency virus type-1 (HIV-1) vaccine which is able to effectively prevent infection would be the most powerful method of extinguishing pandemic of the acquired immunodeficiency syndrome (AIDS). Yet, achieving such vaccine remains great challenges. The membrane-proximal external region (MPER) is a highly conserved region of the envelope glycoprotein (Env) gp41 subunit near the viral envelope surface, and it plays a key role in membrane fusion. It is also the target of some reported broadly neutralizing antibodies (bNAbs). Thus, MPER is deemed to be one of the most attractive vaccine targets. However, no one can induce these bNAbs by immunization with immunogens containing the MPER sequence(s). The few attempts at developing a vaccine have only resulted in the induction of neutralizing antibodies with quite low potency and limited breadth. Thus far, vaccine failure can be attributed to various characteristics of MPER, such as those involving structure and immunology; therefore, we will focus on these and review the recent progress in the field from the following perspectives: (1) MPER structure and its role in membrane fusion, (2) the epitopes and neutralization mechanisms of MPER-specific bNAbs, as well as the limitations in eliciting neutralizing antibodies, and (3) different strategies for MPER vaccine design and current harvests.

DNA Vaccine-Encoded Flagellin Can Be Used as an Adjuvant Scaffold to Augment HIV-1 gp41 Membrane Proximal External Region Immunogenicity

Flagellin's potential as a vaccine adjuvant has been increasingly explored over the last three decades. Monomeric flagellin proteins are the only known agonists of Toll-like receptor 5 (TLR5). This interaction evokes a pro-inflammatory state that impacts upon both innate and adaptive immunity. While pathogen associated molecular patterns (PAMPs) like flagellin have been used as stand-alone adjuvants that are co-delivered with antigen, some investigators have demonstrated a distinct advantage to incorporating antigen epitopes within the structure of flagellin itself. This approach has been particularly effective in enhancing humoral immune responses. We sought to use flagellin as both scaffold and adjuvant for HIV gp41 with the aim of eliciting antibodies to the membrane proximal external region (MPER). Accordingly, we devised a straightforward step-wise approach to select flagellin-antigen fusion proteins for gene-based vaccine development. Using plasmid DNA vector-based expression in mammalian cells, we demonstrate robust expression of codon-optimized full length and hypervariable region-deleted constructs of Salmonella enterica subsp. enterica serovar Typhi flagellin (FliC). An HIV gp41 derived sequence including the MPER (gp41607-683) was incorporated into various positions of these constructs and the expressed fusion proteins were screened for effective secretion, TLR5 agonist activity and adequate MPER antigenicity. We show that incorporation of gp41607-683 into a FliC-based scaffold significantly augments gp41607-683 immunogenicity in a TLR5 dependent manner and elicits modest MPER-specific humoral responses in a mouse model.

Immunologic Insights on the Membrane Proximal External Region: A Major Human Immunodeficiency Virus Type-1 Vaccine Target

Broadly neutralizing antibodies (bNAbs) targeting conserved regions within the human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein (Env) can be generated by the human immune system and their elicitation by vaccination will be a key point to protect against the wide range of viral diversity. The membrane proximal external region (MPER) is a highly conserved region within the Env gp41 subunit, plays a major role in membrane fusion and is targeted by naturally induced bNAbs. Therefore, the MPER is considered as an attractive vaccine target. However, despite many attempts to design MPER-based immunogens, further study is still needed to understand its structural complexity, its amphiphilic feature, and its limited accessibility by steric hindrance. These particular features compromise the development of MPER-specific neutralizing responses during natural infection and limit the number of bNAbs isolated against this region, as compared with other HIV-1 vulnerability sites, and represent additional hurdles for immunogen development. Nevertheless, the analysis of MPER humoral responses elicited during natural infection as well as the MPER bNAbs isolated to date highlight that the human immune system is capable of generating MPER protective antibodies. Here, we discuss the recent advances describing the immunologic and biochemical features that make the MPER a unique HIV-1 vulnerability site, the different strategies to generate MPER-neutralizing antibodies in immunization protocols and point the importance of extending our knowledge toward new MPER epitopes by the isolation of novel monoclonal antibodies. This will be crucial for the redesign of immunogens able to skip non-neutralizing MPER determinants.