A strategy of antigen incorporation into exosomes: comparing cross-presentation levels of antigens delivered by engineered exosomes and by lentiviral virus-like particles

Targeting soluble proteins to exosomes using a ubiquitin tag

As "natural" antigen carriers in the body, exosomes are potential vaccine vectors. A number of animal studies indicate that antigen-containing exosomes can induce a specific immune response which can protect against tumor progression or various infections. Exosomes that carry the protective antigens can be purified from cells that release them including tumor cells, dendritic cells, and macrophages. However, this strategy is restricted to proteins that are naturally targeted to exosomes and is therefore limited in the number of antigens present within exosomes. Therefore, with the goal of developing an exosome-based vaccine that is more flexible in its antigen composition and has the potential to be scalable, we have developed a new approach where recombinant soluble proteins can be packaged into exosomes and released from a transformed cell line. In this study, we determined that a C-terminal fusion of ubiquitin to EGFP, tumor antigenic protein nHer2 and Mycobacterium tuberculosis proteins Ag85B and ESAT6 served as an efficient delivery sequence into exosomes when expressed in a human embryonic kidney (HEK 293) cell line, a cell line widely used in industrial recombinant protein production. Two stably transgenic HEK293 cell lines were generated using a retroviral vector to express the Ag85B-ESAT6 fusion protein either alone or tagged at the C-terminus with ubiquitin. Both transformants released exosomes containing the fusion proteins. However, the concentration of Ag85B and ESAT6 in exosomes was increased approximately 10-fold when they were coupled to ubiquitin. Moreover, when the exosomes were used for immunization, there was a direct correlation between the amount of fusion protein within the exosomes and the number of Ag85B and ESAT6 specific INFɣ-secreting T lymphocytes in the lung and spleen. This suggests that exosomes containing recombinant antigen can be used to elicit a T cell response. In summary our data indicates that a ubiquitin-based exosomal protein delivery strategy could represent a unique approach to generate antigen-specific exosomes with the potential to be used as novel vaccines. Biotechnol. Bioeng. 2016;113: 1315-1324. © 2015 Wiley Periodicals, Inc.

A novel platform for cancer therapy using extracellular vesicles

Extracellular vesicles (EVs) are nanometer-sized membranous vesicles and are involved in cell-to-cell communication. EVs contain several types of functional molecules, such as proteins, mRNAs, and microRNAs (miRNAs). Over the past several years, EVs have emerged as potential tools for a drug delivery system (DDS) that can target organs or cells. EVs have a function of organ tropism and are naturally occurring from cells. Therefore, EVs have expected as naturally DDSs, which have the organ tropism and a low side effect. Actually, some reports showed that EVs delivered drugs to specific organ. However, despite observed the organ tropism, the mechanisms of organ tropism of EVs are still unclear. Moreover, preservation and efficient collection of EVs are desired to be investigated. Here, we provide an overview of the methods for using EVs as DDSs.

Role and future applications of extracellular vesicles in HIV-1 pathogenesis

ABSTRACT 

Extracellular vesicles (EVs) are released naturally in vivo and in vitro from cells and tissues into biological fluids such as plasma, urine, saliva and amniotic fluid, and into culture medium. EV may contain proteins, lipids, mRNA and miRNA significant of the physiological status or of their cellular origin and affect the functions of neighboring cells. The characterization of EVs present in HIV-1-infected individuals provides insight into pathogenesis, inflammation and disease progression. However, the potential of EVs to become reliable research or diagnostic tools is currently limited by the difficulty of distinguishing apoptotic and plasma membrane EVs, exosomes and virions. In spite of this methodological limitation, EVs are expected to become highly useful tools in biomedicine and uncover a research area expected to lead to innovative R&D.

HPV-E7 delivered by engineered exosomes elicits a protective CD8⁺ T cell-mediated immune response

We developed an innovative strategy to induce a cytotoxic T cell (CTL) immune response against protein antigens of choice. It relies on the production of exosomes, i.e., nanovesicles spontaneously released by all cell types. We engineered the upload of huge amounts of protein antigens upon fusion with an anchoring protein (i.e., HIV-1 Nef^mut), which is an inactive protein incorporating in exosomes at high levels also when fused with foreign proteins. We compared the immunogenicity of engineered exosomes uploading human papillomavirus (HPV)-E7 with that of lentiviral virus-like particles (VLPs) incorporating equivalent amounts of the same antigen. These exosomes, whose limiting membrane was decorated with VSV-G, i.e., an envelope protein inducing pH-dependent endosomal fusion, proved to be as immunogenic as the cognate VLPs. It is noteworthy that the immunogenicity of the engineered exosomes remained unaltered in the absence of VSV-G. Most important, we provide evidence that the inoculation in mouse of exosomes uploading HPV-E7 induces production of anti-HPV E7 CTLs, blocks the growth of syngeneic tumor cells inoculated after immunization, and controls the development of tumor cells inoculated before the exosome challenge. These results represent the proof-of-concept about both feasibility and efficacy of the Nef^mut-based exosome platform for the induction of CD8⁺ T cell immunity.

Different immunogenicity but similar antitumor efficacy of two DNA vaccines coding for an antigen secreted in different membrane vesicle-associated forms

The induction of an active immune response to control or eliminate tumours is still an unfulfilled challenge. We focused on plasmid DNA vaccines using an innovative approach whereby the antigen is expressed in association with extracellular vesicles (EVs) to facilitate antigen cross-presentation and improve induced immunity. Our two groups had independently shown previously that DNA vaccines encoding EV-associated antigens are more efficient at inducing cytotoxic T-cell responses than vaccines encoding the non-EV-associated antigen. Here, we compared our two approaches to associate the ovalbumin (OVA) antigen to EVs: (a) by fusion to the lipid-binding domain C1C2 of MFGE8(=lactadherin), which is exposed on the surface of secreted membrane vesicles; and (b) by fusion to retroviral Gag capsid protein, which is incorporated inside membrane-enclosed virus-like particles. Plasmids encoding either form of modified OVA were used as DNA-based vaccines (i.e. injected into mice to allow in vivo expression of the antigen associated to EVs). We show that both DNA vaccines induced, with similar efficiency, OVA-specific CD8(+) T cells and total IgG antibodies. By contrast, each vaccine preferentially stimulated different isotypes of immunoglobulins, and the OVA-C1C2-encoding vaccine favoured antigen-specific CD4(+) T lymphocyte induction as compared to the Gag-OVA vaccine. Nevertheless, both OVA-C1C2 and Gag-OVA vaccines efficiently prevented in vivo outgrowth of OVA-expressing tumours and reduced tumour progression when administered to tumour-bearing mice, although with variable efficacies depending on the tumour models. DNA vaccines encoding EV-associated antigens are thus promising immunotherapy tools in cancer but also potentially other diseases.

Cell activation and HIV-1 replication in unstimulated CD4+ T lymphocytes ingesting exosomes from cells expressing defective HIV-1

Background

A relevant burden of defective HIV-1 genomes populates PBMCs from HIV-1 infected patients, especially during HAART treatment. These viral genomes, although unable to codify for infectious viral particles, can express viral proteins which may affect functions of host cells as well as bystander ones. Cells expressing defective HIV-1 have a lifespan longer than that of cells producing infectious particles. Hence, their interaction with other cell types, including resting lymphocytes, is expected to occur frequently in tissues where HIV actively replicates. We investigated the effects of the expression of a prototype of functionally defective HIV-1 on bystander, unstimulated CD4⁺ T lymphocytes.

Results

We observed that unstimulated human primary CD4⁺ T lymphocytes were activated and became permissive for HIV-1 replication when co-cultivated with cells expressing a functionally defective HIV-1 (F12/Hut-78 cells). This effect depended on the presence in F12/Hut-78 supernatants of nanovesicles we identified as exosomes. By inspecting the underlying mechanism, we found that ADAM17, i.e., a disintegrin and metalloprotease converting pro-TNF-α in its mature form, associated with exosomes from F12/Hut-78 cells, and played a key role in the HIV-1 replication in unstimulated CD4⁺ T lymphocytes. In fact, the treatment with an inhibitor of ADAM17 abolished both activation and HIV-1 replication in unstimulated CD4⁺ T lymphocytes. TNF-α appeared to be the downstream effector of ADAM17 since the treatment of unstimulated lymphocytes with antibodies against TNF-α or its receptors blocked the HIV-1 replication. Finally, we found that the expression of Nef_F12 in exosome-producing cells was sufficient to induce the susceptibility to HIV-1 infection in unstimulated CD4⁺ T lymphocytes.

Conclusions

Exosomes from cells expressing a functionally defective mutant can induce cell activation and HIV-1 susceptibility in unstimulated CD4⁺ T lymphocytes. This evidence highlights the relevance for AIDS pathogenesis of the expression of viral products from defective HIV-1 genomes.

Recent advances in oral vaccine development: yeast-derived β-glucan particles

Oral vaccination is the most challenging vaccination method due to the administration route. However, oral vaccination has socio-economic benefits and provides the possibility of stimulating both humoral and cellular immune responses at systemic and mucosal sites. Despite the advantages of oral vaccination, only a limited number of oral vaccines are currently approved for human use. During the last decade, extensive research regarding antigen-based oral vaccination methods have improved immunogenicity and induced desired immunological outcomes. Nevertheless, several factors such as the harsh gastro-intestinal environment and oral tolerance impede the clinical application of oral delivery systems. To date, human clinical trials investigating the efficacy of these systems are still lacking. This review addresses the rationale and key biological and physicochemical aspects of oral vaccine design and highlights the use of yeast-derived β-glucan microparticles as an oral vaccine delivery platform.

HIV-1-infected cells transiently express lentiviral RNA shuttled by exosomes

ABSTRACT: 

Aims: Exosomes are lipid bilayer vesicles of 50–100 nm released by basically all cell types. We recently reported that full-length HIV-1 RNA and lentiviral vector (LV) genome associate with exosomes through similar mechanisms. Here, we investigated the fate of lentiviral RNA shuttled by exosomes in target cells. Material & methods: Exosomes from cells transduced by a LV expressing green fluorescent protein under the control of an heterologous promoter were purified by iodixanol gradients and used to evaluate the LV expression in target cells. Results: The genome of LV incorporated in exosomes can be expressed in HIV-1-infected cells, but not in those that are uninfected, despite apparently similar levels of exosome internalization. The expression disappeared 2–3 days after challenge, and was blocked by pre-treatment with azidothymidine. Conclusion: Lentiviral genome incorporated in exosomes can be expressed in target cells having reverse transcriptase activity.

Exosomes as intercellular signaling organelles involved in health and disease: basic science and clinical applications

Cell to cell communication is essential for the coordination and proper organization of different cell types in multicellular systems. Cells exchange information through a multitude of mechanisms such as secreted growth factors and chemokines, small molecules (peptides, ions, bioactive lipids and nucleotides), cell-cell contact and the secretion of extracellular matrix components. Over the last few years, however, a considerable amount of experimental evidence has demonstrated the occurrence of a sophisticated method of cell communication based on the release of specialized membranous nano-sized vesicles termed exosomes. Exosome biogenesis involves the endosomal compartment, the multivesicular bodies (MVB), which contain internal vesicles packed with an extraordinary set of molecules including enzymes, cytokines, nucleic acids and different bioactive compounds. In response to stimuli, MVB fuse with the plasma membrane and vesicles are released in the extracellular space where they can interact with neighboring cells and directly induce a signaling pathway or affect the cellular phenotype through the transfer of new receptors or even genetic material. This review will focus on exosomes as intercellular signaling organelles involved in a number of physiological as well as pathological processes and their potential use in clinical diagnostics and therapeutics.