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Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 enters the host by infecting nasal ciliated cells. The virus then spreads toward the oropharyngeal cavity, and, in most severe cases, the pulmonary tissues. The antiviral adaptive response is promptly induced in response to virus detection, with virus-specific T lymphocytes appearing before antiviral antibodies. Both breadth and potency of the antiviral CD8+ T cell immunity have a key role in containing viral spread and disease severity. However, how much the spread of infecting SARS-CoV-2 into the respiratory tracts influences the potency of the antiviral CD8+ T-cell immunity is still largely unknown. To fill the gap, we checked the CD8+ T cell immunity induced after infection of K18-hACE2 transgenic mice in conditions where the virus spread is impeded. In detail, mice were infected with SARS-CoV-2 both 3 weeks and 3 months after anti-Spike vaccinations, and virus-specific CD8+ T cell immunity was monitored both before and after infection. We noticed a strong increase of the Spike-specific CD8+ T cell immunity in vaccinated mice six days after infection despite a nearly-full inhibition of the viral replication. Most important, both kinetics and efficiency of the induction of SARS-CoV-2 N-and M-specific CD8+ T cell immunity in vaccinated mice appeared not inferior to those induced in control mice. These results support the idea that the SARS-CoV-2 replication in the lungs does not relevantly influence the generation of virus-specific CD8+ T cell immunity.

Induction of effective immunity in lungs should be a pre-requisite for any vaccine designed to control the severe pathogenic effects generated by respiratory infectious agents. In the case of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 infection, vaccination is expected to associate with significant inhibition of viral replication in lungs. We recently provided evidence that the generation of endogenous extracellular vesicles (EVs) engineered for the incorporation of SARS-CoV-2 Nucleocapsid (N) protein can protect K18-hACE2 transgenic mice from the lethal intranasal infection with the ancestral Wuhan isolate. Actually, it was widely demonstrated that these transgenic mice succumb to SARS-CoV-2 intranasal infection mainly as a consequence of the viral invasiveness of central nervous system, a pathogenetic mechanism almost absent in humans. On the other hand, K18-hACE2 transgenic mice support viral replication in lungs, an event strictly mirroring the major pathogenic signature linked to the severe disease in humans. However, nothing is known about the ability of N-specific CD8+ T cell immunity induced by engineered EVs in controlling viral replication in lungs. To fill the gap, we investigated the immunity generated in lungs by N-engineered EVs in terms of induction of N-specific effectors and resident memory CD8+ T lymphocytes before and after virus challenge carried out three weeks and three months after boosting. At the same time points, viral replication extents in lungs were evaluated. We found that three weeks after second immunization, virus replication was reduced in mice best responding to vaccination by more than 3-logs compared to control group. The impaired viral replication matched with a reduced induction of Spike-specific CD8+ T lymphocytes. The antiviral effect appeared similarly strong when the viral challenge was carried out 3 months after boosting. This inhibitory effect associated with the persistence of a N-specific CD8+ T-resident memory lymphocytes in lungs of N-immunized mice. In view of the quite conserved sequence of the N protein among SARS-CoV-2 variants, these results support the idea that a vaccine strategy focused on the induction of anti-N CD8+ T cell immunity in lungs has the potential to control the replication of emerging variants

Induction of effective immunity in lungs should be a pre-requisite for any vaccine designed to control the severe pathogenic effects generated by respiratory infectious agents. In the case of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 infection, vaccination is expected to associate with significant inhibition of viral replication in lungs. We recently provided evidence that the generation of endogenous extracellular vesicles (EVs) engineered for the incorporation of SARS-CoV-2 Nucleocapsid (N) protein can protect K18-hACE2 transgenic mice from the lethal intranasal infection with the ancestral Wuhan isolate. Actually, it was widely demonstrated that these transgenic mice succumb to SARS-CoV-2 intranasal infection mainly as a consequence of the viral invasiveness of central nervous system, a pathogenetic mechanism almost absent in humans. On the other hand, K18-hACE2 transgenic mice support viral replication in lungs, an event strictly mirroring the major pathogenic signature linked to the severe disease in humans. However, nothing is known about the ability of N-specific CD8+T cell immunity induced by engineered EVs in controlling viral replication in lungs. To fill the gap, we investigated the immunity generated in lungs by N-engineered EVs in terms of induction of N-specific effectors and resident memory CD8+T lymphocytes before and after virus challenge carried out three weeks and three months after boosting. At the same time points, viral replication extents in lungs were evaluated. We found that three weeks after second immunization, virus replication was reduced in mice best responding to vaccination by more than 3-logs compared to control group. The impaired viral replication matched with a reduced induction of Spike-specific CD8+T lymphocytes. The antiviral effect appeared similarly strong when the viral challenge was carried out 3 months after boosting. This inhibitory effect associated with the persistence of a N-specific CD8+T-resident memory lymphocytes in lungs of N-immunized mice. In view of the quite conserved sequence of the N protein among SARS-CoV-2 variants, these results support the idea that a vaccine strategy focused on the induction of anti-N CD8+T cell immunity in lungs has the potential to control the replication of emerging variants.

Extracellular vesicles (EVs) are membranous particles released by all cells in the external milieu. Depending on their origin, they are given different names: exosomes are nanovesicles that originate from the endosomal compartment, whereas microvesicles bud from plasma membrane. Both contain molecules that are crucial for the onset and spreading of different pathologies, from neurodegenerative diseases to cancer, and are considered promising disease markers. On the other hand, EVs are often used as therapeutic tools, and can be engineered to carry drugs and chemicals. This chapter describes a method to produce EVs, mainly exosomes, containing the green fluorescent protein (GFP) linked to an exosome anchoring protein (Nef

We propose an innovative anti-SARS-CoV-2 immune strategy based on extracellular vesicles (EVs) inducing an anti-SARS-CoV-2 N CD8+ T cytotoxic lymphocyte (CTL) immune response. We previously reported that the SARS-CoV-2 N protein can be uploaded at high levels in EVs upon fusion with Nefmut, i.e., a biologically inactive HIV-1 Nef mutant incorporating into EVs at quite high levels. Here, we analyze the immunogenic properties in human cells of EVs engineered with SARS-CoV-2 N fused at the C-terminus of either Nefmut or a deletion mutant of Nefmut referred to as NefmutPL. The analysis of in vitro-produced EVs has supported the uploading of N protein when fused with truncated Nefmut. Mice injected with DNA vectors expressed each fusion protein developed robust SARS-CoV-2 N-specific CD8+ T cell immune responses. When ex vivo human dendritic cells were challenged with EVs engineered with either fusion products, the induction of a robust N-specific CTL activity, as evaluated by both CD107a and trogocytosis assays, was observed. Through these data we achieved the proof-of-principle that engineered EVs can be instrumental to elicit anti-SARS-CoV-2 CTL immune response in human cells. This achievement represents a mandatory step towards the upcoming experimentations in pre-clinical models focused on intranasal administration of N-engineered EVs.

Purpose Single-chain variable fragments (scFvs) are one of the smallest antigen-binding units having the invaluable advantage to be expressed by a unique short open reading frame (ORF). Despite their reduced size, spontaneous cell entry of scFvs remains inefficient, hence precluding the possibility to target intracellular antigens. Here, we describe an original strategy to deliver scFvs inside target cells through engineered extracellular vesicles (EVs). This approach relies on the properties of a Human Immunodeficiency Virus (HIV)-1 Nef mutant protein referred to as Nefmut. It is a previously characterized Nef allele lacking basically all functions of wt Nef, yet strongly accumulating in the EV lumen also when fused at its C-terminus with a foreign protein. To gain the proof-of-principle for the efficacy of the proposed strategy, the tumor-promoting Human Papilloma Virus (HPV)16-E7 protein was considered as a scFv-specific intracellular target. The oncogenic effect of HPV16-E7 relies on its binding to the tumor suppressor pRb protein leading to a dysregulated cell duplication. Interfering with this interaction means impairing the HPV16-E7-induced cell proliferation. Methods The Nefmut gene was fused in frame at its 3'-terminus with the ORF coding for a previously characterized anti-HPV16-E7 scFv. Interaction between the Nefmut-fused anti-HPV16-E7 scFv and the HPV16-E7 protein was tested by both confocal microscope and co-immunoprecipitation analyses on co-transfected cells. The in cis anti-proliferative effect of the Nefmut/anti-HPV16-E7 scFv was assayed by transfecting HPV16-infected cells. The anti-proliferative effect of EVs engineered with Nefmut/anti-HPV16-E7 scFv on HPV16-E7-expressing cells was evaluated in two ways: i) through challenge with purified EVs by a Real-Time Cell Analysis system and ii) in transwell co-cultures by an MTS-based assay. Results The Nefmut/anti-HPV16-E7 scFv chimeric product is efficiently uploaded in EVs, binds HPV16-E7, and inhibits the proliferation of HPV16-E7-expressing cells. Most important, challenge with cell-free EVs incorporating the Nefmut/anti-HPV16-E7 scFv led to the inhibition of proliferation of HPV16-E7-expressing cells. The proliferation of these cells was hindered also when they were co-cultured in transwells with cells producing EVs uploading Nefmut/anti-HPV16-E7 scFv. Conclusion Our data represent the proof-of-concept for the possibility to target intracellular antigens through EV-mediated delivery of scFvs. This finding could be relevant to design novel methods of intracellular therapeutic interventions.

Most advanced vaccines against severe acute respiratory syndrome coronavirus (SARS-CoV)-2 are designed to induce antibodies against spike (S) protein. Differently, we developed an original strategy to induce CD8+ T cytotoxic lymphocyte (CTL) immunity based on in vivo engineering of extracellular vesicles (EVs). This is a new vaccination approach based on intramuscular injection of DNA expression vectors coding for a biologically inactive HIV-1 Nef protein (Nefmut) with an unusually high efficiency of incorporation into EVs, even when foreign polypeptides are fused to its C-terminus. Nanovesicles containing Nefmut-fused antigens released by muscle cells can freely circulate into the body and are internalized by antigen-presenting cells. Therefore, EV-associated antigens can be cross-presented to prime antigen-specific CD8+ T-cells. To apply this technology to a strategy of anti-SARS-CoV-2 vaccine, we designed DNA vectors expressing the products of fusion between Nefmut and different viral antigens, namely N- and C-terminal moieties of S (referred to as S1 and S2), M, and N. We provided evidence that all fusion products are efficiently uploaded in EVs. When the respective DNA vectors were injected in mice, a strong antigen-specific CD8+ T cell immunity became detectable in spleens and, most important, in lung airways. Co-injection of DNA vectors expressing the diverse SARS-CoV-2 antigens resulted in additive immune responses in both spleen and lungs. Hence, DNA vectors expressing Nefmut-based fusion proteins can be proposed for new anti-SARS-CoV-2 vaccine strategies.

Simple Summary The induction of an effective immune response against tumor cells is of a great benefit in the battle against cancers. We recently characterized a novel, safe, and cost-effective strategy to induce an efficient CD8+ T cell immune response against potentially whatever antigen. This technique is based on in vivo engineering of exosomes/extracellular vesicles (EVs), i.e., nanovesicles constitutively released by all healthy cells. Immunogenic EVs are generated by intramuscular injection of a DNA vector expressing an EV-anchoring protein fused with the antigen of interest. In this paper, we applied our vaccine platform to counteract the growth of tumors expressing antigens of Human Papilloma Virus (HPV). We demonstrated that this method is instrumental in curing mice already developing HPV-related tumors. In addition, cured mice were shown to resist a second tumor cell implantation. These results could be of relevance for a possible translation into the clinic of our technology. Abstract We developed an innovative method to induce antigen-specific CD8+ T cytotoxic lymphocyte (CTL) immunity based on in vivo engineering of extracellular vesicles (EVs). This approach employs a DNA vector expressing a mutated HIV-1 Nef protein (Nefmut) deprived of the anti-cellular effects typical of the wild-type isoform, meanwhile showing an unusual efficiency of incorporation into EVs. This function persists even when foreign antigens are fused to its C-terminus. In this way, Nefmut traffics large amounts of antigens fused to it into EVs spontaneously released by the recipient cells. We previously provided evidence that mice injected with a DNA vector expressing the Nefmut/HPV16-E7 fusion protein developed an E7-specific CTL immune response as detected 2 weeks after the second immunization. Here, we extended and optimized the anti-HPV16 CD8+ T cell immune response induced by the endogenously engineered EVs, and evaluated the therapeutic antitumor efficacy over time. We found that the co-injection of DNA vectors expressing Nefmut fused with E6 and E7 generated a stronger anti-HPV16 immune response compared to that observed in mice injected with the single vectors. When HPV16-E6 and -E7 co-expressing tumor cells were implanted before immunization, all mice survived at day 44, whereas no mice injected with either void or Nefmut-expressing vectors survived until day 32 after tumor implantation. A substantial part of immunized mice (7 out of 12) cleared the tumor. When the cured mice were re-challenged with a second tumor cell implantation, none of them developed tumors. Both E6- and E7-specific CD8+ T immunities were still detectable at the end of the observation time. We concluded that the immunity elicited by engineered EVs, besides counteracting and curing already developed tumors, was strong enough to guarantee the resistance to additional tumor attacks. These results can be of relevance for the therapy of both metastatic and relapsing tumors.

Intramuscular injection of DNA vectors expressing the extracellular vesicle (EV)-anchoring protein Nefmut fused at its C-terminus to viral and tumor antigens elicits a potent, effective, and anti-tolerogenic CD8+ T cell immunity against the heterologous antigen. The immune response is induced through the production of EVs incorporating Nefmut-derivatives released by muscle cells. In the perspective to a possible translation into the clinic of the Nefmut-based vaccine platform, we aimed at increasing its safety profile by identifying the minimal part of Nefmut retaining the EV-anchoring protein property. We found that a C-terminal deletion of 29-amino acids did not affect the ability of Nefmut to associate with EVs. Furthermore, the EV-anchoring function was preserved when antigens from both HPV16 (i.e., E6 and E7) and SARS-CoV-2 (i.e., S1 and S2) were fused to its C-terminus. By analyzing the immune responses induced after intramuscular injection of DNA vectors expressing fusion products based on the four viral antigens, we found that the Nefmut C-terminal deletion did not impact on the levels of antigen –specific CD8+ T lymphocytes as evaluated by IFN-γ EliSpot analysis and intracellular cytokine staining. In addition, immune responses at distal sites remained unaffected, as indicated by the similar percentages of SARS-CoV-2 S1- and S2-specific CD8+ T cells detected in spleens and lung airways of mice injected with DNA vectors expressing the viral antigens fused with either Nefmut or NefmutPL.We concluded that the C-terminal Nefmut truncation does not affect stability, EV-anchoring, and CD8+ T cell immunogenicity of the fused antigen. Hence, NefmutPL represents a safer alternative to full-length Nefmut for the design of CD8+ T cell vaccines for humans.

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is spreading rapidly in the absence of validated tools to control the growing epidemic besides social distancing and masks. Many efforts are ongoing for the development of vaccines against SARS-CoV-2 since there is an imminent need to develop effective interventions for controlling and preventing SARS-CoV-2 spread. Essentially all vaccines in most advanced phases are based on the induction of antibody response against either whole or part of spike (S) protein. Differently, we developed an original strategy to induce CD8+ T cytotoxic lymphocyte (CTL) immunity based on in vivo engineering of extracellular vesicles (EVs). We exploited this technology with the aim to identify a clinical candidate defined as DNA vectors expressing SARS-CoV-2 antigens inducing a robust CD8+ T-cell response. This is a new vaccination approach employing a DNA expression vector encoding a biologically inactive HIV-1 Nef protein (Nefmut) showing an unusually high efficiency of incorporation into EVs even when foreign polypeptides are fused to its C-terminus. Nanovesicles containing Nefmut-fused antigens released by muscle cells are internalized by antigen-presenting cells leading to cross-presentation of the associated antigens thereby priming of antigen-specific CD8+ T-cells. To apply this technology to a design of anti-SARS-CoV-2 vaccine, we recovered DNA vectors expressing the products of fusion between Nefmut and four viral antigens, namely N- and C-terminal moieties of S (referred to as S1 and S2), M, and N. All fusion products are efficiently uploaded in EVs. When the respective DNA vectors were injected in mice, a strong antigen-specific CD8+ T cell immunity was generated. Most important, high levels of virus-specific CD8+ T cells were found in bronchoalveolar lavages of immunized mice. Co-injection of DNA vectors expressing the diverse SARS-CoV-2 antigens resulted in additive immune responses in both spleen and lung. EVs engineered with SARS-CoV-2 antigens proved immunogenic also in the human system through cross-priming assays carried out with ex vivo human cells. Hence, DNA vectors expressing Nefmut-based fusion proteins can be proposed as anti-SARS-CoV-2 vaccine candidates.

Neurodegenerative diseases are commonly generated by intracellular accumulation of misfolded/aggregated mutated proteins. These abnormal protein aggregates impair the functions of mitochondria and induce oxidative stress, thereby resulting in neuronal cell death. In turn, neuronal damage induces chronic inflammation and neurodegeneration. Thus, reducing/eliminating these abnormal protein aggregates is a priority for any anti-neurodegenerative therapeutic approach. Although several antibodies against mutated neuronal proteins have been already developed, how to efficiently deliver them inside the target cells remains an unmet issue. Extracellular vesicles/exosomes incorporating intrabodies against the pathogenic products would be a tool for innovative therapeutic approaches. In this review/perspective article, we identify and describe the major molecular targets associated with neurodegenerative diseases, as well as the antibodies already developed against them. Finally, we propose a novel targeting strategy based on the endogenous engineering of extracellular vesicles/exosomes constitutively released by cells of the central nervous system.

HIV-1 infection is efficiently controlled by combination anti-retroviral therapy (cART). However, despite preventing disease progression, cART does not eradicate virus infection which persists in a latent form for an individual’s lifetime. The latent reservoir comprises memory CD4+ T lymphocytes, macrophages, and dendritic cells; however, for the most part, the reservoir is generated by virus entry into activated CD4+ T lymphocytes committed to return to a resting state, even though resting CD4+ T lymphocytes can be latently infected as well. The HIV-1 reservoir is not recognized by the immune system, is quite stable, and has the potential to re-seed systemic viremia upon cART interruption. Viral rebound can occur even after a long period of cART interruption. This event is most likely a consequence of the extended half-life of the HIV-1 reservoir, the maintenance of which is not clearly understood. Several recent studies have identified extracellular vesicles (EVs) as a driving force contributing to HIV-1 reservoir preservation. In this review, we discuss recent findings in the field of EV/HIV-1 interplay, and then propose a mechanism through which EVs may contribute to HIV-1 persistence despite cART. Understanding the basis of the HIV-1 reservoir maintenance continues to be a matter of great relevance in view of the limitations of current strategies aimed at HIV-1 eradication.

Eukaryotic cells constitutively produce nanovesicles of 50-150nm of diameter, referred to as exosomes, upon release of the contents of multivesicular bodies (MVBs). We recently characterized a novel, exosome-based way to induce cytotoxic T lymphocyte (CTL) immunization against full-length antigens. It is based on DNA vectors expressing products of fusion between the exosome-anchoring protein Nef mutant (Nefmut) with the antigen of interest. The strong efficiency of Nefmut to accumulate in MVBs results in the production of exosomes incorporating huge amounts of the desired antigen. When translated in animals, the injection of Nefmut-based DNA vectors generates engineered exosomes whose internalization in antigen-presenting cells induces cross-priming and antigen-specific CTL immunity. Here, we describe the molecular strategies we followed to produce DNA vectors aimed at generating immunogenic exosomes potentially useful to elicit a CTL immune response against antigens expressed by the etiologic agents of major chronic viral infections, i.e., HIV-1, HBV, and the novel tumor-associated antigen HOXB7. Unique methods intended to counteract intrinsic RNA instability and nuclear localization of the antigens have been developed. The success we met with the production of these engineered exosomes opens the way towards pre-clinic experimentations devoted to the optimization of new vaccine candidates against major infectious and tumor pathologies.

Paola Di Bonito,1 Chiara Chiozzini,2 Claudia Arenaccio,2 Simona Anticoli,2 Francesco Manfredi,2 Eleonora Olivetta,2 Flavia Ferrantelli,2 Emiliana Falcone,3 Anna Ruggieri,3 Maurizio Federico2 1Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanità, Rome, Italy; 2National AIDS Center, Istituto Superiore di Sanità, Rome, Italy; 3Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy Abstract: We recently proved that exosomes engineered in vitro to deliver high amounts of HPVE7 upon fusion with the Nefmut exosome-anchoring protein elicit an efficient anti-E7 cytotoxic T lymphocyte immune response. However, in view of a potential clinic application of this finding, our exosome-based immunization strategy was faced with possible technical difficulties including industrial manufacturing, cost of production, and storage. To overcome these hurdles, we designed an as yet unproven exosome-based immunization strategy relying on delivery by intramuscular inoculation of a DNA vector expressing Nefmut fused with HPVE7. In this way, we predicted that the expression of the Nefmut/E7 vector in muscle cells would result in a continuous source of endogenous (ie, produced by the inoculated host) engineered exosomes able to induce an E7-specific immune response. To assess this hypothesis, we first demonstrated that the injection of a Nefmut/green fluorescent protein-expressing vector led to the release of fluorescent exosomes, as detected in plasma of inoculated mice. Then, we observed that mice inoculated intramuscularly with a vector expressing Nefmut/E7 developed a CD8+ T-cell immune response against both Nef and E7. Conversely, no CD8+ T-cell responses were detected upon injection of vectors expressing either the wild-type Nef isoform of E7 alone, most likely a consequence of their inefficient exosome incorporation. The production of immunogenic exosomes in the DNA-injected mice was formally demonstrated by the E7-specific CD8+ T-cell immune response we detected in mice inoculated with exosomes isolated from plasma of mice inoculated with the Nefmut/E7 vector. Finally, we provide evidence that the injection of Nefmut/E7 DNA led to the generation of effective antigen-specific cytotoxic T lymphocytes whose activity was likely part of the potent, therapeutic antitumor effect we observed in mice implanted with TC-1 tumor cells. In summary, we established a novel method to generate immunogenic exosomes in vivo by the intramuscular inoculation of DNA vectors expressing the exosome-anchoring protein Nefmut and its derivatives. Keywords: nanovesicles, cytotoxic T lymphocytes, HIV-1 Nef, DNA vectors

Purpose Single-chain variable fragments (scFvs) are one of the smallest antigen-binding units having the invaluable advantage to be expressed by a unique short open reading frame (ORF). Despite their reduced size, spontaneous cell entry of scFvs remains inefficient, hence precluding the possibility to target intracellular antigens. Here, we describe an original strategy to deliver scFvs inside target cells through engineered extracellular vesicles (EVs). This approach relies on the properties of a Human Immunodeficiency Virus (HIV)-1 Nef mutant protein referred to as Nefmut. It is a previously characterized Nef allele lacking basically all functions of wt Nef, yet strongly accumulating in the EV lumen also when fused at its C-terminus with a foreign protein. To gain the proof-of-principle for the efficacy of the proposed strategy, the tumor-promoting Human Papilloma Virus (HPV)16-E7 protein was considered as a scFv-specific intracellular target. The oncogenic effect of HPV16-E7 relies on its binding to the tumor suppressor pRb protein leading to a dysregulated cell duplication. Interfering with this interaction means impairing the HPV16-E7-induced cell proliferation. Methods The Nefmut gene was fused in frame at its 3ʹ-terminus with the ORF coding for a previously characterized anti-HPV16-E7 scFv. Interaction between the Nefmut-fused anti-HPV16-E7 scFv and the HPV16-E7 protein was tested by both confocal microscope and co-immunoprecipitation analyses on co-transfected cells. The in cis anti-proliferative effect of the Nefmut/anti-HPV16-E7 scFv was assayed by transfecting HPV16-infected cells. The anti-proliferative effect of EVs engineered with Nefmut/anti-HPV16-E7 scFv on HPV16-E7-expressing cells was evaluated in two ways: i) through challenge with purified EVs by a Real-Time Cell Analysis system and ii) in transwell co-cultures by an MTS-based assay. Results The Nefmut/anti-HPV16-E7 scFv chimeric product is efficiently uploaded in EVs, binds HPV16-E7, and inhibits the proliferation of HPV16-E7-expressing cells. Most important, challenge with cell-free EVs incorporating the Nefmut/anti-HPV16-E7 scFv led to the inhibition of proliferation of HPV16-E7-expressing cells. The proliferation of these cells was hindered also when they were co-cultured in transwells with cells producing EVs uploading Nefmut/anti-HPV16-E7 scFv. Conclusion Our data represent the proof-of-concept for the possibility to target intracellular antigens through EV-mediated delivery of scFvs. This finding could be relevant to design novel methods of intracellular therapeutic interventions.

Background:Eukaryotic cells release vesicles of different sizes under both physiological and pathological conditions. On the basis of the respective biogenesis, extracellular vesicles are classified as apoptotic bodies, microvesicles, and exosomes. Among these, exosomes are considered tools for innovative therapeutic interventions, especially when engineered with effector molecules. The delivery functions of exosomes are favored by a number of typical features. These include their small size (i.e., 50-200 nm), the membrane composition tightly similar to that of producer cells, lack of toxicity, stability in serum as well as other biological fluids, and accession to virtually any organ and tissue including central nervous system. However, a number of unresolved questions still affects the possible use of exosomes in therapy. Among these are the exact identification of both in vitro and ex vivo produced vesicles, their large-scale production and purification, the uploading efficiency of therapeutic macromolecules, and the characterization of their pharmacokinetics. Objective: Here, we discuss two key aspects to be analyzed before considering exosomes as a tool of delivery for the desired therapeutic molecule, i.e., techniques of engineering, and their in vivo biodistribution/ pharmacokinetics. In addition, an innovative approach aimed at overcoming at least part of the obstacles towards a safe and efficient use of exosomes in therapy will be discussed.Conclusion:Several biologic features render exosomes an attractive tool for the delivery of therapeutic molecules. They will surely be a part of innovative therapeutic interventions as soon as few still unmet technical hindrances will be overcome.

Intrinsic genetic instability of tumor cells leads to continuous production of mutated proteins referred to as tumor-specific neoantigens. Generally, they are recognized as nonself products by the host immune system. However, an effective adaptive response clearing neoantigen-expressing cells is lost in tumor diseases. Most advanced therapeutic strategies aim at inducing neoantigen-specific immune activation through personalized approaches. They include tumor cell exome sequencing, human leukocyte antigen (HLA) typing, synthesis, and injection of peptides/RNA with adjuvants. Here, we propose an innovative method to induce a CD8+ T cytotoxic lymphocyte (CTL) immune response against tumor neoantigens bypassing the steps needed in current therapeutic strategies of personalized vaccination. We assumed that tumor cells can be the most efficient and precise factory of major histocompatibility complex (MHC) class I-associated, tumor neoantigen-derived peptides. Hence, endowing tumor cells with professional antigen-presenting functions would prime CD8+ T lymphocytes towards a response against nonself tumor antigens. To explore this possibility, both adenocarcinoma and melanoma human cells were engineered to express both CD80 and CD86 costimulatory molecules. HLA-matched lymphocytes were then primed through cocultivation with the engineered tumor cells. The generation of tumor-specific CD8+ T lymphocytes was tested through the combined analysis of cell activation markers, formation of immunologic synapses, generation of tumor antigen-specific CD8+ T lymphocytes, and cytotoxic activity. Our data consistently indicate that tumor cells endowed with professional antigen-presenting functions can generate an effective tumor-specific CTL immune response. This finding may open avenues towards the development of innovative antitumor immunotherapies. Key messages: We established a novel method to induce antitumor CTLs without a need to identify TAAs and/or tumor neoantigens.This strategy relies on transducing tumor cells with a retroviral vector expressing both CD80 and CD86.In this way, tumor cells prime naïve CD8+ T lymphocytes in a way that CTLs killing the same tumor cells are generated.These findings open the way towards preclinical assays in the perspective to introduce this antitumor immunotherapy strategy in clinic.

Intramuscular injection of DNA vectors expressing the extracellular vesicle (EV)-anchoring protein Nefmut fused at its C-terminus to viral and tumor antigens elicit a potent, effective, and anti-tolerogenic CD8+ T cell immunity against the heterologous antigen. The immune response is induced through the production of EVs incorporating Nefmut-derivatives released by muscle cells. In the perspective of a possible translation into the clinic of the Nefmut-based vaccine platform, we aimed at increasing its safety profile by identifying the minimal part of Nefmut retaining the EV-anchoring protein property. We found that a C-terminal deletion of 29-amino acids did not affect the ability of Nefmut to associate with EVs. The EV-anchoring function was also preserved when antigens from both HPV16 (i.e., E6 and E7) and SARS-CoV-2 (i.e., S1 and S2) were fused to its C-terminus. Most important, the Nefmut C-terminal deletion did not affect levels, quality, and diffusion at distal sites of the antigen-specific CD8+ T immunity. We concluded that the C-terminal Nefmut truncation does not influence stability, EV-anchoring, and CD8+ T cell immunogenicity of the fused antigen. Hence, the C-terminal deleted Nefmut may represent a safer alternative to the full-length isoform for vaccines in humans.

Immunosuppression at tumor microenvironment (TME) is one of the major obstacles to be overcome for an effective therapeutic intervention against solid tumors. Tumor-associated macrophages (TAMs) comprise a sub-population that plays multiple pro-tumoral roles in tumor development including general immunosuppression, which can be identified in terms of high expression of mannose receptor (MR or CD206). Immunosuppressive TAMs, like other macrophage sub-populations, display functional plasticity that allows them to be re-programmed to inflammatory macrophages. In order to mitigate immunosuppression at the TME, several efforts are ongoing to effectively re-educate pro-tumoral TAMs. Extracellular vesicles (EVs), released by both normal and tumor cells types, are emerging as key mediators of the cell to cell communication and have been shown to have a role in the modulation of immune responses in the TME. Recent studies demonstrated the enrichment of high mannose glycans on the surface of small EVs (sEVs), a subtype of EVs of endosomal origin of 30–150 nm in diameter. This characteristic renders sEVs an ideal tool for the delivery of therapeutic molecules into MR/CD206-expressing TAMs. In this review, we report the most recent literature data highlighting the critical role of TAMs in tumor development, as well as the experimental evidences that has emerged from the biochemical characterization of sEV membranes. In addition, we propose an original way to target immunosuppressive TAMs at the TME by endogenously engineered sEVs for a new therapeutic approach against solid tumors.

We recently described a cytotoxic CD8+ T lymphocyte (CTL) vaccine platform based on the intramuscular (i.m.) injection of DNA eukaryotic vectors expressing antigens of interest fused at the C-terminus of HIV-1 Nefmut, i.e., a functionally defective mutant that is incorporated at quite high levels into exosomes/extracellular vesicles (EVs). This system has been proven to elicit strong CTL immunity against a plethora of both viral and tumor antigens, as well as inhibit both transplantable and orthotopic tumors in mice. However, a number of open issues remain regarding the underlying mechanism. Here we provide evidence that hindering the uploading into EVs of Nefmut-derived products by removing the Nefmut N-terminal fatty acids leads to a dramatic reduction of the downstream antigen-specific CD8+ T-cell activation after i.m. injection of DNA vectors in mice. This result formally demonstrates that the generation of engineered EVs is part of the mechanism underlying the in vivo induced CD8+ T-cell immunogenicity. Gaining new insights on the EV-based vaccine platform can be relevant in view of its possible translation into the clinic to counteract both chronic and acute infections as well as tumors.

We recently described a novel biotechnological platform for the production of unrestricted cytotoxic T lymphocyte (CTL) vaccines. It relies on in vivo engineering of exosomes, i.e., nanovesicles constitutively released by all cells, with full-length antigens of choice upon fusion with an exosome-anchoring protein referred to as Nefmut. They are produced upon intramuscular injection of a DNA vector and, when uploaded with a viral tumor antigen, were found to elicit an immune response inhibiting the tumor growth in a model of transplantable tumors. However, for a possible application in cancer immunotherapy, a number of key issues remained unmet. Among these, we investigated: (i) whether the immunogenic stimulus induced by the engineered exosomes can break immune tolerance, and (ii) their effectiveness when applied in human system. As a model of immune tolerance, we considered mice transgenic for the expression of activated rat HER2/neu which spontaneously develop adenocarcinomas in all mammary glands. When these mice were injected with a DNA vector expressing the product of fusion between Nefmut and the extracellular domain of HER2/neu, antigen-specific CD8+ T lymphocytes became readily detectable. This immune response associated with a HER2-directed CTL activity and a significant delay in tumor development. On the other hand, through cross-priming experiments, we demonstrated the effectiveness of the engineered exosomes emerging from transfected human primary muscle cells in inducing antigen-specific CTLs. We propose our CTL vaccine platform as part of new immunotherapy strategies against tumors expressing self-antigens, i.e., products highly expressed in oncologic lesions but tolerated by the immune system.

Intact HIV-1 and exosomes can be internalized by dendritic cells (DCs) through a common pathway leading to their transmission to CD4

Intact HIV-1 and exosomes can be internalized by dendritic cells (DCs) through a common pathway leading to their transmission to CD4+ T lymphocytes by means of mechanisms defined as trans-infection and trans-dissemination, respectively. We previously reported that exosomes from HIV-1-infected cells activate both uninfected quiescent CD4+ T lymphocytes, which become permissive to HIV-1, and latently infected cells, with release of HIV-1 particles. However, nothing is known about the effects of trans-dissemination of exosomes produced by HIV-1-infected cells on uninfected or latently HIV-1-infected CD4+ T lymphocytes. Here, we report that trans-dissemination of exosomes from HIV-1-infected cells induces cell activation in resting CD4+ T lymphocytes, which appears stronger with mature than immature DCs. Using purified preparations of both HIV-1 and exosomes, we observed that mDC-mediated trans-dissemination of exosomes from HIV-1-infected cells to resting CD4+ T lymphocytes induces efficient trans-infection and HIV-1 expression in target cells. Most relevant, when both mDCs and CD4+ T lymphocytes were isolated from combination anti-retroviral therapy (ART)-treated HIV-1-infected patients, trans-dissemination of exosomes from HIV-1-infected cells led to HIV-1 reactivation from the viral reservoir. In sum, our data suggest a role of exosome trans-dissemination in both HIV-1 spread in the infected host and reactivation of the HIV-1 reservoir.

Some human papillomavirus (HPV) genotypes are universally recognized as major etiological agents not only of ano-genital tumors but also of head and neck cancers, which show increasing incidence. The evaluation of current and future therapeutic approaches against HPV-induced tumors is a global health priority, despite an effective prophylactic vaccine against 7 of the 12 genotypes involved in the etiology of tumors being currently available. In this review, we present the main anti-HPV therapeutic approaches in clinical experimentation, with a focus on a novel tumor antigen delivery method using engineered exosomes, that we recently developed. Our system allows the induction of an efficient unrestricted cytotoxic T lymphocyte (CTL) immune response against the HPV16-E7 tumor-associated antigen, with the formation of endogenously engineered exosomes, i.e., nanovesicles spontaneously released by all cell types. Immunogenic exosomes are uploaded with HPV16-E7 due to the fusion with a unique exosome-anchoring protein referred to as Nefmut. Intramuscular injection of a DNA vector expressing the fusion protein generates exosomes sufficiently immunogenic to elicit a potent anti-16E7 CTL immune response. The approach is described here and the advantages over other existing methodologies are reported.

Mauritian cynomolgus macaques (MCM) are widely used in human immunodeficiency virus research because of their restricted major histocompatibility complex (MHC) diversity which provides the opportunity to address the influence of host factors on vaccine studies. We herein report the impact of MHC haplotype on the outcome of 21 MCM infections with the CCR5-tropic simian/human immunodeficiency virus (SHIV)(SF162P4cy). MCM were susceptible to SHIV(SF162P4cy) infection as shown by viremia and loss of CD4+ T cells. A significant association between haplotype M7 (class IA, IB, II) and persistent viremia was observed in chronic phase, whereas recombinant class IA haplotype was associated with a reduction of viral RNA during acute infection. Class IB M4 haplotype displayed significantly lower acute phase provirus copy numbers. In addition, statistical analysis indicated a detrimental effect of haplotype M4 (class IA, IB) on the course of infection as indicated by lower CD4+ T-cell levels during chronic infection. A decrease in post-acute phase CD4+ T-cell numbers was also observed in haplotype M2 animals. This is the first report that documents the effects of host MHC class I and II molecules on the SHIV(SF162P4cy) infection in MCM, particularly with regard to the association between recombinant class IA, M4, and M7 haplotypes and the dynamic of viral replication and level of CD4+ T cells.

HIV native Tat and V2 loop-deleted Env (EnvΔV2) proteins already proved safe and immunogenic in phase I clinical testing as single vaccine components. Further, a phase II vaccine trial with Tat showed intensification of the therapeutic effects of HAART in successfully treated HIV-infected individuals. Here a pilot study assessed the immunogenicity and protective efficacy of an HIV/AIDS vaccine based on the combination of Tat and EnvΔV2 proteins in cynomolgus macaques against homologous intrarectal challenge with 35 MID(50) (monkey infectious dose 50) of an R5 simian-human immunodeficiency virus (SHIV(SF162P4cy)). Upon challenge, three of four macaques immunized with Tat and EnvΔV2, and two of three monkeys immunized with EnvΔV2 alone were protected from infection. In contrast, all three control animals, which had been either administered with the adjuvants only or left untreated, and an additional monkey immunized with Tat alone became systemically infected. Protection of the macaques vaccinated with EnvΔV2 or Tat/EnvΔV2 correlated with higher peak titers of pre-challenge neutralizing antibodies obtained during the immunization period (between 70 and 3 weeks before challenge) and with anti-Env V3 loop binding antibodies assessed 3 weeks before challenge. Compared to EnvΔV2 alone, the Tat and EnvΔV2 combined vaccine elicited faster antibody responses (IgM) with a trend, early in the vaccination schedule, after the second immunization including EnvΔV2, towards broader anti-Env IgG epitope specificity and a higher ratio of neutralizing to Env-binding antibody titers. As the number of immunizations increased, vaccination with EnvΔV2 approached the immune response assessed after two inocula with the Tat/EnvΔV2 combined vaccine, even though some differences remained between groups, as indicated by anti-Env IgG epitope mapping. In fact, three weeks before challenge, plasma IgG of animals in the EnvΔV2 group showed a trend towards stronger specificity for the V1 loop and V5 loop-C5 regions of Env, whereas the Tat/EnvΔV2 group displayed an overall higher reactivity for epitopes within the Env V3 loop throughout the immunization period. Although differences in terms of protection rate were not found between the EnvΔV2 or Tat/EnvΔV2 vaccination groups in this pilot study, vaccination with Tat/EnvΔV2 appeared to accelerate the induction of potentially protective antibody responses to Env. In particular, antibodies to the Env V3 loop, whose levels at pre-challenge correlated with protection, were already higher early in the vaccination schedule in monkeys immunized with Tat/EnvΔV2 as compared to EnvΔV2 alone. Further studies including larger vaccination groups and fewer immunizations with these two vaccine candidates are needed to confirm these findings and to assess whether the Tat/EnvΔV2 vaccine may afford superior protection against infection.

The induction of both cellular and humoral immunity is an important goal for vaccine development against HIV. As a step towards the development of an efficacious vaccine against HIV clade C, the world's most prevalent strain, a combination DNA prime/protein boost immunization strategy was tested. A DNA expression vector was prepared encoding a codon-optimized env gene derived from a pediatric HIV clade C isolate, 1084i. Mice were immunized with HIV1084i env-encoding DNA, then boosted with homologous 1084i gp160. HIV1084i Env-specific T-cell responses were induced with DNA vaccination alone, but the strongest cellular immune responses were seen after boosting with gp160. Immunization with gp160 alone induced high-titer antibodies but required two inoculations. In contrast, high-titer antibodies were seen after a single 1084i gp160 boost in DNA-primed animals. All animals given gp160 inoculations, whether DNA primed or not, developed neutralizing antibodies reactive with HIV1084i and a macaque-passaged simian/human immunodeficiency construct, SHIV-1084ip. The results demonstrate the utility of this DNA prime/protein boost approach to generate cellular immunity, as well as neutralizing antibodies, against HIV clade C env antigens.

Earlier primate studies revealed that oral transmission of immunodeficiency viruses can occur at all ages [R. M. Ruprecht et al., J. Infect. Dis.179(Suppl. 3):S408-S412, 1999]. Using a stock of pathogenic simian-human immunodeficiency virus, SHIV89.6P, we compared the 50% animal infectious dose needed to achieve systemic infection after oral challenge in newborn and older infant or juvenile rhesus macaques. Unexpectedly, the older monkeys required a 150-fold-lower virus challenge dose than the neonates (P= 3.3 × 10−5). In addition, at least 60,000 times more virus was needed to achieve systemic infection in neonates by the oral route than by the intravenous route (P< 1 × 10−5). Thus, route of inoculation and age are important determinants of SHIV89.6P infectivity in rhesus macaques.

Because milk-borne transmission of human immunodeficiency virus (HIV) diminishes the benefits of perinatal antiviral drug therapy in developing countries, we have developed a new strategy to prevent postnatal and, possibly, intrapartum virus transmission in a primate model. Eight neonatal rhesus macaques were exposed orally to pathogenic simian-human immunodeficiency virus (SHIV); 4 neonates were then given intramuscular postexposure prophylaxis with 3 anti-HIV human neutralizing monoclonal antibodies (nMAbs) with potent cross-clade and cross-group neutralization activity. Untreated infants experienced high viral RNA levels and CD4(+) T-cell losses and died (median survival time, 5.5 weeks). In contrast, all 4 nMAb-treated neonates were protected from infection (P=.028); their plasma, peripheral blood mononuclear cells, and lymph nodes remained virus negative for >1 year. These data are important for designing clinical trials in human neonates and have general implications for AIDS vaccine development, as the epitopes recognized by the 3 nMAbs are conserved among diverse primary isolates.

We have established models for intrapartum and milk-borne HIV transmission by orally challenging neonatal macaques with chimeric simian-human immunodeficiency viruses (SHIVs). This allowed us to test safety and efficacy of passive immunization with human neutralizing monoclonal antibodies (nmAbs), which had been isolated from HIV clade B-infected individuals and which target conserved, functionally important epitopes. The nmAbs studied were F105 or IgG1b12, b12 for short (directed against the CD4 binding site), 2G12 (anti-gp120), 2F5 and 4E10 (both anti-gp41). Out of 16 newborn macaques challenged orally with different SHIV strains, 11 were completely protected by triple or quadruple nmAb combinations, even by post-exposure prophylaxis. In vitro, the combination of b12, 2G12, 2F5 and 4E10 potently neutralized primary HIV isolates of clades A, B, C, and D. Our data suggest that passive immunization with currently available anti-HIV clade B nmAbs could play a role in preventing transmission of non-clade B isolates through breastfeeding. We furthermore conclude that the epitopes recognized by the nmAbs in our successful passive immunization studies are important determinants for protection and provide targets for developing neutralizing antibody-response-based, active AIDS vaccines.

BACKGROUND: The majority of infants infected through maternal transmission acquire the virus during birth or postpartum through breastfeeding: mucosal exposure is considered to be a major route of infection. OBJECTIVES: To develop passive immunization with human neutralizing monoclonal antibodies (mAbs) against mother-to-child transmission of HIV during delivery and through breastfeeding. DESIGN: An oral challenge model in newborn rhesus macaques mimicked peri- and postpartum virus transmission. METHODS: Neonatal rhesus macaques were challenged orally with the highly pathogenic, chimeric simian-human immunodeficiency virus SHIV89.6P and given post-exposure prophylaxis with a quadruple combination of neutralizing human mAbs, IgG1b12, 2G12, 2F5, and 4E10, directed against conserved epitopes of HIV envelope glycoproteins. Control animals were virus challenged but left untreated. All infants were followed prospectively for signs of viremia and immunodeficiency. RESULTS: Two out of four macaque infants treated with neutralizing mAbs showed no evidence of infection; the other two maintained normal CD4 T cell counts. In contrast, all control animals became highly viremic and had profound CD4 T cell losses; three out of four died from AIDS within 1.5-6 weeks of the challenge. CONCLUSIONS: Passive immunization with this quadruple neutralizing mAbs combination may represent a promising approach to prevent peri- and postnatal HIV transmission. Furthermore, the epitopes recognized by the four neutralizing mAbs are key determinants to achieve complete protection and represent important targets against which to develop active, antibody-response-based AIDS vaccines.

Little is known about the effects of Major Histocompatibility Complex (MHC) haplotypes on immunity to primate lentiviruses involving both acquired and innate immune responses. We present statistical evidence of the influence of MHC polymorphism on antiviral immunity of Mauritian cynomolgus macaques (MCM) following simian/human immunodeficiency virus SHIVSF162P4cy infection, involving the production of pro- and anti-inflammatory cytokines and α-defensins, which may modulate acquired immune responses. During the acute phase of infection, IL-10 correlated positively with viral load and negatively with CD4+T cell counts. Furthermore, α-defensins production was directly correlated with plasma viral RNA, particularly at peak of viral load. When the effects of the MHC were analyzed, a significant association between lower anti-Env binding and neutralizing antibody levels with class IB M4 haplotype and with class IA, IB M4 haplotype, respectively, was observed in the post-acute phase. Lower antibody responses may have resulted into a poor control of infection thus explaining the previously reported lower CD4 T cell counts in these monkeys. Class II M3 haplotype displayed significantly lower acute and post-acute IL-10 levels. In addition, significantly lower levels of α-defensins were detected in class IA M3 haplotype monkeys than in non-M3 macaques, in the post-acute phase of infection. These data indicate that the MHC could contribute to the delicate balance of pro-inflammatory mechanisms, particularly with regard to the association between IL-10 and α-defensins in lentivirus infection. Our results show that host genetic background, virological and immunological parameters should be considered for the design and interpretation of HIV-1 vaccine efficacy studies.

Here we describe a prime-boost regimen of vaccination in Macaca fascicularis that combines priming with novel anionic microspheres designed to deliver the biologically active HIV-1 Tat protein and boosting with Tat in Alum. This regimen of immunization modulated the IgG subclass profile and elicited a balanced Th1-Th2 type of humoral and cellular responses. Remarkably, following intravenous challenge with SHIV89.6P(cy243), vaccinees significantly blunted acute viremia, as compared to control monkeys, and this control was associated with significantly lower CD4(+) T cell depletion rate during the acute phase of infection and higher ability to resume the CD4(+) T cell counts in the post-acute and chronic phases of infection. The long lasting control of viremia was associated with the persistence of high titers anti-Tat antibodies whose profile clearly distinguished vaccinees in controllers and viremics. Controllers, as opposed to vaccinated and viremic cynos, exhibited significantly higher pre-challenge antibody responses to peptides spanning the glutamine-rich and the RGD-integrin-binding regions of Tat. Finally, among vaccinees, titers of anti-Tat IgG1, IgG3 and IgG4 subclasses had a significant association with control of viremia in the acute and post-acute phases of infection. Altogether these findings indicate that the Tat/H1D/Alum regimen of immunization holds promise for next generation vaccines with Tat protein or other proteins for which maintenance of the native conformation and activity are critical for optimal immunogenicity. Our results also provide novel information on the role of anti-Tat responses in the prevention of HIV pathogenesis and for the design of new vaccine candidates.

To develop prophylaxis against mother-to-child human immunodeficiency virus (HIV) transmission, we established a simian-human immunodeficiency virus (SHIV) infection model in neonatal macaques that mimics intrapartum mucosal virus exposure (T. W. Baba et al., AIDS Res. Hum. Retroviruses 10:351–357, 1994). Using this model, neonates were protected from mucosal SHIV-vpu+challenge by pre- and postnatal treatment with a combination of three human neutralizing monoclonal antibodies (MAbs), F105, 2G12, and 2F5 (Baba et al., Nat. Med. 6:200–206, 2000). In the present study, we used this MAb combination only postnatally, thereby significantly reducing the quantity of antibodies necessary and rendering their potential use in humans more practical. We protected two neonates with this regimen against oral SHIV-vpu+challenge, while four untreated control animals became persistently infected. Thus, synergistic MAbs protect when used as immunoprophylaxis without the prenatal dose. We then determined in vitro the optimal MAb combination against the more pathogenic SHIV89.6P, a chimeric virus encodingenvof the primary HIV89.6. Remarkably, the most potent combination included IgG1b12, which alone does not neutralize SHIV89.6P. We administered the combination of MAbs IgG1b12, 2F5, and 2G12 postnatally to four neonates. One of the four infants remained uninfected after oral challenge with SHIV89.6P, and two infants had no or a delayed CD4+T-cell decline. In contrast, all control animals had dramatic drops in their CD4+T cells by 2 weeks postexposure. We conclude that our triple MAb combination partially protected against mucosal challenge with the highly pathogenic SHIV89.6P. Thus, combination immunoprophylaxis with passively administered synergistic human MAbs may play a role in the clinical prevention of mother-to-infant transmission of HIV type 1.

The HIV epidemic continues to represent one of the major problems worldwide, particularly in the Asia and Sub-Saharan regions of the world, with social and economical devastating effects. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals that have access to treatment, it has had a negligible impact on the global epidemic. Hence, the inexorable spreading of the HIV pandemic and the increasing deaths from AIDS, especially in developing countries, underscore the urgency for an effective vaccine against HIV/AIDS. However, the generation of such a vaccine has turned out to be extremely challenging. Here we provide an overview on the rationale for the use of non-structural HIV proteins, such as the Tat protein, alone or in combination with other HIV early and late structural HIV antigens, as novel, promising preventative and therapeutic HIV/AIDS vaccine strategies.

According to recent estimates, 39.5 million people have been infected with HIV and 2.9 million have already died. The effect of HIV infection on individuals and communities is socially and economically devastating. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals who have access to treatment, it has had a negligible impact on the global epidemic. Therefore, the need for an efficacious HIV/AIDS vaccine remains the highest priority of the world HIV/AIDS agenda. The generation of a vaccine against HIV/AIDS has turned out to be extremely challenging, as indicated by20 years of unsuccessful attempts. This review discusses the major challenges in the field and key experimental evidence providing a rationale for the use of non-structural HIV proteins, such as Rev, Tat and Nef, either in the native form or expressed by viral vectors such as a replicating adeno-vector. These non-structural proteins alone or in combination with modified structural HIV-1 Env proteins represent a novel strategy for both preventative and therapeutic HIV/AIDS vaccine development.

The need for an effective HIV/AIDS vaccine is imperative to halt a pandemic that involves more than 40 million individuals worldwide as of 2005 and is causing enormous socio-economic losses, especially in developing countries (DC). The overall failure of more than two decades of HIV vaccine research justifies the demands for a concerted effort for the rapid development of new and efficacious vaccines against HIV/AIDS. In this context, building international collaborative networks is a must for speeding up scientific research and optimizing the use of funding in a synergistic fashion, as resources for HIV/AIDS are limited and do not involve most of the biggest Pharmas that are more interested in drug discovery. The AIDS Vaccine Integrated Project (AVIP) consortium is an example of synergistic partnership of international European Union and DC experts with a common research goal. AVIP is a European Commission-funded (FP-6), consortium-based, 5-year program directed to the fast development of new HIV/AIDS vaccine candidates to be tested in phase I clinical trials in Europe for future advancement to phase II/III testing in DC. To ensure their rapid development, AVIP novel combined vaccines include both regulatory and structural HIV antigens, which have already been tested, as single components, in phase I clinical trials. In particular, such combination vaccines may be superior to earlier vaccine candidates, the vast majority of which are based only on either structural or regulatory HIV products. In fact, the generation of immune responses to both types of viral antigens expressed either early (regulatory products) or late (structural products) during the viral life cycle can maximize immune targeting of both primary or chronic viral infection. Further, the rational design of combined vaccines allows exploitation of immunomodulatory functions of HIV regulatory proteins, which can improve immunity against structural vaccine components. The building of the AVIP consortium and its scientific strategy will be reviewed in this paper as an example of the establishment of a consortium regulated by a specific intellectual property agreement.

The promising results obtained with the HIV-1 Tat-based vaccines in mice, monkeys and humans, a better understanding of Tat immunomodulatory functions, as well as evidence that vaccination with trimeric V2 loop-deleted HIV-1 Env induces cross-clade neutralizing antibodies led to the rational design of a novel vaccine based on the combination of Tat and V2-deleted Env.