Multivalent display of engineered HIV-1 envelope trimers on silica nanoparticles for targeting and in vitro activation of germline VRC01 B cells

Phytochemical-based nanosystems: recent advances and emerging application in antiviral photodynamic therapy

Phytochemicals are typically natural bioactive compounds or metabolites produced by plants. Phytochemical-loaded nanocarrier systems, designed to overcome bioavailability limitations and enhance therapeutic effects, have garnered significant attention in recent years. The coronavirus disease 2019 (COVID-19) pandemic has intensified interest in the therapeutic application of phytochemicals to combat viral infections. This review explores nanoparticle-based treatment strategies incorporating phytochemicals for antiviral application, highlighting their demonstrated antiviral mechanisms. It specifically examines the antiviral activities of phytochemical-loaded nanosystems against (i) influenza virus (IAV), respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); (ii) mosquito-borne viruses [dengue (DENV), Zika (ZIKV), and Chikungunya (CHIKV)]; and (iii) sexually transmitted/blood borne viruses [e.g. herpes simplex virus (HSV), human papillomavirus (HPV), and human immunodeficiency virus (HIV)]. Furthermore, this review highlights the emerging role of these nanosystems in photodynamic therapy (PDT)-mediated attenuation of viral proliferation, and offers a perspective on the future directions of research in this promising area of multimodal therapeutic approach.

Prolonged delivery of HIV-1 vaccine nanoparticles from hydrogels

Immunization is a straightforward concept but remains for some pathogens like HIV-1 a challenge. Thus, new approaches towards increasing the efficacy of vaccines are required to turn the tide. There is increasing evidence that antigen exposure over several days to weeks induces a much stronger and more sustained immune response compared to traditional bolus injection, which usually leads to antigen elimination from the body within a couple of days. Therefore, we developed a poly(ethylene) glycol (PEG) hydrogel platform to investigate the principal feasibility of a sustained release of antigens to mimic natural infection kinetics. Eight-and four-armed PEG macromonomers of different MWs (10, 20, and 40 kDa) were end-group functionalized to allow for hydrogel formation via covalent cross-linking. An HIV-1 envelope (Env) antigen in its trimeric (Envtri) or monomeric (Envmono) form was applied. The soluble Env antigen was compared to a formulation of Env attached to silica nanoparticles (Env-SiNPs). The latter are known to have a higher immunogenicity compared to their soluble counterparts. Hydrogels were tunable regarding the rheological behavior allowing for different degradation times and release timeframes of Env-SiNPs over two to up to 50 days. Affinity measurements of the VCR01 antibody which specifically recognizes the CD4 binding site of Env, revealed that neither the integrity nor the functionality of Envmono-SiNPs (Kd = 2.1 ± 0.9 nM) and Envtri-SiNPs (Kd = 1.5 ± 1.3 nM), respectively, were impaired after release from the hydrogel (Kd before release: 2.1 ± 0.1 and 7.8 ± 5.3 nM, respectively). Finally, soluble Env and Env-SiNPs which are two physico-chemically distinct compounds, were co-delivered and shown to be sequentially released from one hydrogel which could be beneficial in terms of heterologous immunization or single dose vaccination. In summary, this study presents a tunable, versatile applicable, and effective delivery platform that could improve vaccination effectiveness also for other infectious diseases than HIV-1.

Oriented display of HIV-1 Env trimers by a novel coupling strategy enhances B cell activation and phagocytosis

Introduction

Conformationally stabilized Env trimers have been developed as antigens for the induction of neutralizing antibodies against HIV-1. However, the non-glycosylated immunodominant base of these soluble antigens may compete with the neutralizing antibody response. This has prompted attempts to couple Env trimers to organic or inorganic nanoparticles with the base facing towards the carrier. Such a site-directed coupling could not only occlude the base of the trimer, but also enhance B cell activation by repetitive display.

Methods

To explore the effect of an ordered display of HIV-1 Env on microspheres on the activation of Env-specific B cells we used Bind&Bite, a novel covalent coupling approach for conformationally sensitive antigens based on heterodimeric coiled-coil peptides. By engineering a trimeric HIV-1 Env protein with a basic 21-aa peptide (Peptide K) extension at the C-terminus, we were able to covalently biotinylate the antigen in a site-directed fashion using an acidic complementary peptide (Peptide E) bearing a reactive site and a biotin molecule. This allowed us to load our antigen onto streptavidin beads in an oriented manner.

Results

Microspheres coated with HIV-1 Env through our Bind&Bite system showed i) enhanced binding by conformational anti-HIV Env broadly neutralizing antibodies (bNAbs), ii) reduced binding activity by antibodies directed towards the base of Env, iii) higher Env-specific B cell activation, and iv) were taken-up more efficiently after opsonization compared to beads presenting HIV-1 Env in an undirected orientation.

Discussion

In comparison to site-directed biotinylation via the Avi-tag, Bind&Bite, offers greater flexibility with regard to alternative covalent protein modifications, allowing selective modification of multiple proteins via orthogonal coiled-coil peptide pairs. Thus, the Bind&Bite coupling approach via peptide K and peptide E described in this study offers a valuable tool for nanoparticle vaccine design where surface conjugation of correctly folded antigens is required.

Potency and durability of T and B cell immune responses after homologous and heterologous vector delivery of a trimer-stabilized, membrane-displayed HIV-1 clade ConC Env protein

Introduction

The generation of an HIV-1 vaccine able to induce long-lasting protective immunity remains a main challenge. Here, we aimed to modify next-generation soluble, prefusion-stabilized, close-to-native, glycan-engineered clade C gp140 envelope (Env) trimers (sC23v4 KIKO and ConCv5 KIKO) for optimal display on the cell surface following homologous or heterologous vector delivery.

Methods

A combination of the following modifications scored best regarding the preservation of closed, native-like Env trimer conformation and antigenicity when using a panel of selected broadly neutralizing (bnAb) and non-neutralizing (nnAb) monoclonal antibodies for flow cytometry: i) replacing the natural cleavage site with a native flexible linker and introducing a single amino acid substitution to prevent CD4 binding (*), ii) fusing a heterologous VSV-G-derived transmembrane moiety to the gp140 C-terminus, and iii) deleting six residues proximal to the membrane.

Results

When delivering membrane-tethered sC23v4 KIKO* and ConCv5 KIKO* via DNA, VSV-GP, and NYVAC vectors, the two native-like Env trimers provide differential antigenicity profiles. Whereas such patterns were largely consistent among the different vectors for either Env trimer, the membrane-tethered ConCv5 KIKO* trimer adopted a more closed and native-like structure than sC23v4 KIKO*. In immunized mice, VSV-GP and NYVAC vectors expressing the membrane-tethered ConCv5 KIKO* administered in prime/boost combination were the most effective regimens for the priming of Env-specific CD4 T cells among all tested combinations. The subsequent booster administration of trimeric ConCv5 KIKO* Env protein preserved the T cell activation levels between groups. The evaluation of the HIV-1-specific humoral responses induced in the different immunization groups after protein boosts showed that the various prime/boost protocols elicited broad and potent antibody responses, preferentially of a Th1-associated IgG2a subclass, and that the obtained antibody levels remained high at the memory phase.

Discussion

In summary, we provide a feasible strategy to display multiple copies of native-like Env trimers on the cell surface, which translates into efficient priming of sustained CD4+ T cell responses after vector delivery as well as broad, potent, and sustained antibody responses following booster immunizations with the homologous, prefusion-stabilized, close-to-native ConCv5 KIKO* gp140 Env trimer.

Immunogenicity of a silica nanoparticle-based SARS-CoV-2 vaccine in mice

Safe and effective vaccines have been regarded early on as critical in combating the COVID-19 pandemic. Among the deployed vaccine platforms, subunit vaccines have a particularly good safety profile but may suffer from a lower immunogenicity compared to mRNA based or viral vector vaccines. In fact, this phenomenon has also been observed for SARS-CoV-2 subunit vaccines comprising the receptor-binding domain (RBD) of the spike (S) protein. Therefore, RBD-based vaccines have to rely on additional measures to enhance the immune response. It is well accepted that displaying antigens on nanoparticles can improve the quantity and quality of vaccine-mediated both humoral and cell-mediated immune responses. Based on this, we hypothesized that SARS-CoV-2 RBD as immunogen would benefit from being presented to the immune system via silica nanoparticles (SiNPs). Herein we describe the preparation, in vitro characterization, antigenicity and in vivo immunogenicity of SiNPs decorated with properly oriented RBD in mice. We found our RBD-SiNP conjugates show narrow, homogeneous particle distribution with optimal size of about 100 nm for efficient transport to and into the lymph node. The colloidal stability and binding of the antigen was stable for at least 4 months at storage- and in vivo-temperatures. The antigenicity of the RBD was maintained upon binding to the SiNP surface, and the receptor-binding motif was readily accessible due to the spatial orientation of the RBD. The particles were efficiently taken up in vitro by antigen-presenting cells. In a mouse immunization study using an mRNA vaccine and spike protein as benchmarks, we found that the SiNP formulation was able to elicit a stronger RBD-specific humoral response compared to the soluble protein. For the adjuvanted RBD-SiNP we found strong S-specific multifunctional CD4+ T cell responses, a balanced T helper response, improved auto- and heterologous virus neutralization capacity, and increased serum avidity, suggesting increased affinity maturation. In summary, our results provide further evidence for the possibility of optimizing the cellular and humoral immune response through antigen presentation on SiNP.