Selective elimination of HIV-1-infected cells by Env-directed, HIV-1-based virus-like particles

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

Driving DNA transposition by lentiviral protein transduction

Gene vectors derived from DNA transposable elements have become powerful molecular tools in biomedical research and are slowly moving into the clinic as carriers of therapeutic genes. Conventional uses of DNA transposon-based gene vehicles rely on the intracellular production of the transposase protein from transfected nucleic acids. The transposase mediates mobilization of the DNA transposon, which is typically provided in the context of plasmid DNA. In recent work, we established lentiviral protein transduction from Gag precursors as a new strategy for direct delivery of the transposase protein. Inspired by the natural properties of infecting viruses to carry their own enzymes, we loaded lentivirus-derived particles not only with vector genomes carrying the DNA transposon vector but also with hundreds of transposase subunits. Such particles were found to drive efficient transposition of the piggyBac transposable element in a range of different cell types, including primary cells, and offer a new transposase delivery approach that guarantees short-term activity and limits potential cytotoxicity. DNA transposon vectors, originally developed and launched as a non-viral alternative to viral integrating vectors, have truly become viral. Here, we briefly review our findings and speculate on the perspectives and potential advantages of transposase delivery by lentiviral protein transduction.

Protein delivery using engineered virus-like particles

Over the years, researchers have developed several methods to deliver macromolecules into the cytosol and nucleus of living cells. However, there are limitations to all of these methods. The problems include (i) inefficient uptake, (ii) endosomal entrapment, (iii) delivery that is restricted to certain cell types, and (iv) damage to cells in the delivery process. Retroviral vectors are often used for gene delivery; however, integration of the genome of retroviral vector into the host genome can have serious consequences. Here we describe a safe alternative in which virus-like particles (VLPs), derived from an avian retrovirus, are used to deliver protein to cells. We show that these VLPs are a highly adaptable platform that can be used to deliver proteins either as part of Gag fusion proteins (intracellular delivery) or on the surface of VLPs. We generated VLPs that contain Gag-Cre recombinase, Gag-Fcy::Fur, and Gag-human caspase-8 as a proof-of-concept and demonstrated that the encapsidated proteins are active in recipient cells. In addition, we show that murine IFN-γ and human TNF-related apoptosis-inducing ligand can be displayed on the surface of VLPs, and that these modified VLPs can cause the appropriate response in cells, as evidenced by phosphorylation of STAT1 and induction of cell death, respectively.

Engineered lentiviral vectors pseudotyped with a CD4 receptor and a fusogenic protein can target cells expressing HIV-1 envelope proteins

Lentiviral vectors (LVs) derived from human immunodeficiency virus type 1 (HIV-1) are promising vehicles for gene delivery because they not only efficiently transduce both dividing and non-dividing cells, but also maintain long-term transgene expression. Development of an LV system capable of transducing cells in a cell type-specific manner can be beneficial for certain applications that rely on targeted gene delivery. Previously it was shown that an inverse fusion strategy that incorporated an HIV-1 receptor (CD4) and its co-receptor (CXCR4 or CCR5) onto vector surfaces could confer to LVs the ability to selectively deliver genes to HIV-1 envelope-expressing cells. To build upon this work, we aim to improve its relatively low transduction efficiency and circumvent its inability to target multiple tropisms of HIV-1 by a single vector. We investigated a method to create LVs co-enveloped with the HIV-1 cellular receptor CD4 and a fusogenic protein derived from the Sindbis virus glycoprotein and tested its efficiency to selectively deliver genes into cells expressing HIV-1 envelope proteins. The engineered LV system yields a higher level of transduction efficiency and a broader tropism towards cells displaying the HIV-1 envelope protein (Env) than the previously developed system. Furthermore, we demonstrated in vitro that this engineered LV can preferentially deliver suicide gene therapy to HIV-1 envelope-expressing cells. We conclude that it is potentially feasible to target LVs towards HIV-1-infected cells by functional co-incorporation of the CD4 and fusogenic proteins, and provide preliminary evidence for further investigation on a potential alternative treatment for eradicating HIV-1-infected cells that produce drug-resistant viruses after highly active antiretroviral therapy (HAART).

Strong CD8+ T cell antigenicity and immunogenicity of large foreign proteins incorporated in HIV-1 VLPs able to induce a Nef-dependent activation/maturation of dendritic cells

Virus-like particles (VLPs) are excellent tools for vaccines against pathogens and tumors. They can accommodate foreign polypeptides whose incorporation efficiency and immunogenicity however decrease strongly with the increase of their size. We recently described the CD8(+) T cell immune response against a small foreign antigen (i.e., the 98 amino acid long human papilloma virus E7 protein) incorporated in human immunodeficiency virus (HIV)-1 based VLPs as product of fusion with an HIV-1 Nef mutant (Nef(mut)). Here, we extended our previous investigations by testing the antigenic/immunogenic properties of Nef(mut)-based VLPs incorporating much larger heterologous products, i.e., human hepatitis C virus (HCV) NS3 and influenza virus NP proteins, which are composed of 630 and 498 amino acids, respectively. We observed a remarkable cross-presentation of HCV NS3 in dendritic cells challenged with Nef(mut)-NS3 VLPs, as detected using a NS3 specific CD8(+) T cell clone as well as PBMCs from HCV infected patients. On the other hand, when injected in mice, Nef(mut)-NP VLPs elicited strong anti-NP CD8(+) T cell and CTL immune responses. In addition, we revealed the ability of Nef(mut) incorporated in VLPs to activate and mature primary human immature dendritic cells (iDCs). This phenomenon correlated with the activation of Src tyrosine kinase-related intracellular signaling, and can be transmitted from VLP-challenged to bystander iDCs. Overall, these results prove that Nef(mut)-based VLPs represent a rather flexible platform for the design of innovative CD8(+) T cell vaccines.

Role of macrophages in HIV infection and persistence

Current antiretroviral therapy regimens can effectively suppress HIV in patients for prolonged periods of time, but do not constitute a cure, since they are incapable of eradicating viral reservoirs. It is, therefore, necessary for us to refocus on the partially understood pathogenesis of HIV, on the issue of viral persistence, and on the development of strategies for a temporally contained therapy capable of purging HIV from the body. Macrophages play a pivotal role in all three of these scenarios. This review summarizes important aspects of macrophage biology as they relate to HIV and discusses conceptual challenges for virus suppression and eradication in this cell type. We highlight a number of significant recent advances in understanding differences in HIV replication and pharmacotherapy between macrophages and CD4 T cells, as well as the role of macrophages in various aspects of the disease process and in different anatomical compartments. Finally, the importance of infected macrophages in the persistence of HIV, regarding both pathogenesis and advancement of eradication strategies, is discussed.

Lentivirus-based virus-like particles as a new protein delivery tool

Virus Like Particles (VLPs) are self-assembling, nonreplicating, nonpathogenic, genomeless particles similar in size and conformation to intact infectious virions. The possibility of engineering VLPs to incorporate heterologous polypeptides/proteins renders VLPs attractive candidates for vaccine strategies, as well as for protein delivery for basic science. Among the wide number of VLP types, our expertise focused on both retro- and lentivirus based VLPs as protein delivery tools. In particular, here we describe a system relying on the finding that some HIV-1 Nef mutants are incorporated at high levels into both Human Immunodeficiency virus (HIV)-1 and Moloney Leukemia Virus (MLV)-based VLPs. Most importantly, these Nef mutants can efficiently act as anchoring proteins upon fusion with heterologous proteins up to 630 amino acids in length. This chapter describes the preparation of prototypic HIV-1 based VLPs incorporating Nef mutant-GFP fusion molecules. Besides having potential utility in the field of basic virology, these VLPs represent a useful reference model for recovering alternative retro- or lentiviral based VLPs for the cell delivery of polypeptides/proteins of interest.

Inhibition of HIV-1 infection and replication by enhancing viral incorporation of innate anti-HIV-1 protein A3G: a non-pathogenic Nef mutant-based anti-HIV strategy

APOBEC3G (A3G) is a cellular protein that has been identified as an innate anti-human immunodeficiency virus type 1 (HIV-1) factor. One of the major functions of HIV-1 virion infectivity protein (Vif) protein is to target A3G for ubiquitination/proteasome-mediated degradation and, as a result, evade the host innate defense mechanism. Thus, we wished to devise a strategy to restore the anti-HIV activity of A3G by actively targeting it into HIV-1 virions and countering HIV-1 Vif-targeted degradation. In the current study we performed a series of proof-of-concept experiments for this strategy using as a delivery vehicle of A3G, a derivate of non-pathogenic Nef mutant Nef7 that is capable of being efficiently incorporated into HIV-1 virions. We demonstrate that the Nef7.A3G fusion protein retains several important properties of Nef7; that is, the higher virion incorporation efficiency, no PAK-2 (p21-activated kinase 2) activation, and no CD4 and major histocompatibility complex I down-regulation. Meanwhile, we show that virion incorporated Nef7.A3G possesses the anti-HIV infectivity function of A3G. Moreover, we show that virus-like particle-mediated inverse fusion delivery of Nef7.A3G into HIV-infected CD4+ T lymphocytes leads to potent inhibition of HIV-1 replication in these cells. Taken together, these results indicate that Nef7.A3G can effectively restrict HIV infection and replication by restoring the virion incorporation of A3G, even in the presence of Vif.

Virus-like particles-universal molecular toolboxes

Virus-like particles (VLPs) are highly organised spheres that self-assemble from virus-derived structural antigens. These stable and versatile subviral particles possess excellent adjuvant properties capable of inducing innate and cognate immune responses. Commercialised VLP-based vaccines have been successful in protecting humans from hepatitis B virus (HBV) and human papillomavirus (HPV) infection and are currently explored for their potential to combat other infectious diseases and cancer. Much insight into VLP-mediated immune stimulation and optimised VLP design has been gained from human immunodeficiency virus (HIV)-derived VLPs presenting promising components of current AIDS vaccine approaches. Owing to their unique features, VLPs and virosomes, the in vitro-reconstituted VLP counterparts, have recently gained ground in the field of nanobiotechnology as organic templates for the development of new biomaterials.