Co-immunization of mice with a retroviral DNA vaccine and GITRL-encoding plasmid augments vaccine-induced protection against retrovirus infection

Immune suppression of vaccine-induced CD8+ T-cell responses by gamma retrovirus envelope is mediated by interleukin-10-producing CD4+ T cells

Retroviral envelope (Env) proteins have long been recognized to exhibit immunosuppressive properties, which affect the CD8⁺ T-cell response to an infection but also to immunization. Interestingly, we previously showed in the Friend murine leukemia virus (F-MuLV) model that the surface Env protein gp70 also plays a role in immunosuppression, in addition to the immunosuppressive function attributed to the transmembrane Env protein. We now demonstrate that immunization with F-MuLV Env leads to a significant increase in interleukin-10 (IL-10)-producing CD4⁺ T cells and that the induction of CD8⁺ T-cell responses in the presence of Env is rescued if the capacity of CD4⁺ T cells to produce IL-10 is abrogated, indicating a mechanistic role of IL-10-producing CD4⁺ T cells in mediating the Env-induced suppression of CD8⁺ T-cell responses in Env co-immunization. We found that CD8⁺ T-cell responses against different immunogens are not all equally affected. On the other hand, suppression of immunity was observed not only in co-immunization experiments but also for immune control of subcutaneous tumor growth after an Env immunization. Finally, we show that suppression of CD8⁺ T cells by the surface Env protein is observed not only for Friend MuLV Env but also for the Env proteins of other gamma retroviruses. Taken together, our results show that IL-10-producing CD4⁺ T cells mechanistically underlie the Env-mediated suppression of CD8⁺ T-cell responses and suggest the presence of an immunosuppressive motif in the surface Env protein of gamma retroviruses.

A detailed analysis of F-MuLV- and SFFV-infected cells in Friend virus-infected mice reveals the contribution of both F-MuLV- and SFFV-infected cells to the interleukin-10 host response

BACKGROUND

Friend virus (FV) is a complex of the Friend murine leukemia virus (F-MuLV) and the replication-defective, pathogenic spleen focus forming virus (SFFV). In the past, we used a fluorescently labeled F-MuLV to analyze FV target cells. To build on these findings, we have now created a double-labeled FV that contains a Katushka-labeled F-MuLV and an mTagBFP-labeled SFFV, which we have used to study the infection by the two individual viruses in the FV infection of highly susceptible BALB/c mice.

RESULTS

Our data show that the target cells of SFFV largely mirror those of F-MuLV, with the highest virus loads in erythroblasts, B cells and myeloid cells. The early phase of infection was dominated by cells infected by either SFFV or F-MuLV, whereas double-infected cells became dominant later in the course of infection with increasing viral loads. In the late phase of infection, the frequency of double-infected cells was similarly high as the frequencies of SFFV or F-MuLV single-infected cells, and single- and double-infected cells outnumbered the uninfected cells in the most highly infected cell populations such as erythroblasts. FV and retroviruses in general have been shown to induce interleukin 10 (IL-10) as a means of suppressing immune responses. Interestingly, we found in infected IL-10-eGFP reporter mice that SFFV-infected cells contributed to the IL-10-producing cell pool much more significantly than F-MuLV-infected cells, suggesting that the truncated SFFV envelope protein gp55 might play a role in IL-10 induction. Even though BALB/c mice mount notoriously weak immune responses against FV, infection of mice with an ablation of IL-10 expression in T cells showed transiently lower viral loads and stronger T cell activation, suggesting that IL-10 induction by FV and by SFFV in particular may contribute to a suppressed immune response in BALB/c mice.

CONCLUSION

Our data provide detailed information about both F-MuLV- and SFFV-infected cells during the course of FV infection in highly susceptible mice and imply that the pathogenic SFFV contributes to immune suppression.

Immunization with a murine cytomegalovirus based vector encoding retrovirus envelope confers strong protection from Friend retrovirus challenge infection

Immunization vectors based on cytomegalovirus (CMV) have attracted a lot of interest in recent years because of their high efficacy in the simian immunodeficiency virus (SIV) macaque model, which has been attributed to their ability to induce strong, unusually broad, and unconventionally restricted CD8⁺ T cell responses. To evaluate the ability of CMV-based vectors to mediate protection by other immune mechanisms, we evaluated a mouse CMV (MCMV)-based vector encoding Friend virus (FV) envelope (Env), which lacks any known CD8⁺ T cell epitopes, for its protective efficacy in the FV mouse model. When we immunized highly FV-susceptible mice with the Env-encoding MCMV vector (MCMV.env), we could detect high frequencies of Env-specific CD4⁺ T cells after a single immunization. While the control of an early FV challenge infection was highly variable, an FV infection applied later after immunization was tightly controlled by almost all immunized mice. Protection of mice correlated with their ability to mount a robust anamnestic neutralizing antibody response upon FV infection, but Env-specific CD4⁺ T cells also produced appreciable levels of interferon γ. Depletion and transfer experiments underlined the important role of antibodies for control of FV infection but also showed that while no Env-specific CD8⁺ T cells were induced by the MCMV.env vaccine, the presence of CD8⁺ T cells at the time of FV challenge was required. The immunity induced by MCMV.env immunization was long-lasting, but was restricted to MCMV naïve animals. Taken together, our results demonstrate a novel mode of action of a CMV-based vaccine for anti-retrovirus immunization that confers strong protection from retrovirus challenge, which is conferred by CD4⁺ T cells and antibodies.

CMV-based vectors have attracted a lot of attention in the vaccine development field, since they were shown to induce unconventionally restricted CD8⁺ T cell responses and strong protection in the SIV rhesus macaque model. In a mouse retrovirus model, we show now that immunization with a mouse CMV-based vector encoding retrovirus envelope conferred very strong protection, even though it was not designed to induce any CD8⁺ T cell responses. In this MCMV.env immunization, protection relied on the induction of CD4⁺ T cells and the ability to mount a strong anamnestic neutralizing antibody response upon retrovirus infection, but it was restricted to MCMV pre-naïve mice. In our model system, the MCMV based vector shows very high efficacy that is comparable to an attenuated retrovirus-based vaccine, and encourages the pursuit of this vaccination strategy.

Interference of retroviral envelope with vaccine-induced CD8+ T cell responses is relieved by co-administration of cytokine-encoding vectors

Background

Retroviral envelope (Env) proteins are known to exhibit immunosuppressive properties, which become apparent not only in retroviral infections, but also in gene-based immunizations using retroviral immunogens, where envelope interferes with the induction of CD8⁺ T cell responses towards another, simultaneously or subsequently delivered, immunogen.

Results

In the Friend retrovirus mouse model, immunization with a plasmid encoding the Friend murine leukemia virus (F-MuLV) Leader-Gag protein resulted in induction of a strong GagL_85–93-specific CD8⁺ T cell response, while the response was completely abrogated by co-immunization with an F-MuLV Env-encoding plasmid. In order to overcome this interference of retroviral envelope, we employed plasmids encoding the cytokines interleukin (IL) 1β, IL2, IL12, IL15, IL21, IL28A or granulocyte–macrophage colony-stimulating factor (GM-CSF) as genetic adjuvants. Co-application of plasmids encoding IL2, IL12, IL21, IL28A and especially GM-CSF rescued the induction of GagL_85–93-specific CD8⁺ T cells in mice vaccinated with FV Leader-Gag and Env. Mice that were immunized with plasmids encoding Leader-Gag and Env and the cytokines IL1β, IL12, IL15, IL28A or GM-CSF, but not Leader-Gag and Env without any cytokine, showed significantly reduced viral loads upon a high-dose Friend virus challenge infection.

Conclusions

Our data demonstrate the potency of cytokine-encoding vectors as adjuvants and immune modulators in composite vaccines for anti-retroviral immunization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0352-7) contains supplementary material, which is available to authorized users.

Induction of complex immune responses and strong protection against retrovirus challenge by adenovirus-based immunization depends on the order of vaccine delivery

Background

In the Friend retrovirus mouse model we developed potent adenovirus-based vaccines that were designed to induce either strong Friend virus GagL_85–93-specific CD8⁺ T cell or antibody responses, respectively. To optimize the immunization outcome we evaluated vaccination strategies using combinations of these vaccines.

Results

While the vaccines on their own confer strong protection from a subsequent Friend virus challenge, the simple combination of the vaccines for the establishment of an optimized immunization protocol did not result in a further improvement of vaccine effectivity. We demonstrate that the co-immunization with GagL_85–93/leader-gag encoding vectors together with envelope-encoding vectors abrogates the induction of GagL_85–93-specific CD8⁺ T cells, and in successive immunization protocols the immunization with the GagL_85–93/leader-gag encoding vector had to precede the immunization with an envelope encoding vector for the efficient induction of GagL_85–93-specific CD8⁺ T cells. Importantly, the antibody response to envelope was in fact enhanced when the mice were adenovirus-experienced from a prior immunization, highlighting the expedience of this approach.

Conclusions

To circumvent the immunosuppressive effect of envelope on immune responses to simultaneously or subsequently administered immunogens, we developed a two immunizations-based vaccination protocol that induces strong immune responses and confers robust protection of highly Friend virus-susceptible mice from a lethal Friend virus challenge.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0336-7) contains supplementary material, which is available to authorized users.

Enhancing immunogenicity and cross-reactivity of HIV-1 antigens by in vivo targeting to dendritic cells

Current retroviral treatments have reduced AIDS to a chronic disease for most patients. However, given drug-related side effects, the emergence of drug-resistant strains and the persistence of viral replication, the development of alternative treatments is a pressing need. This review focuses on recent developments in HIV immunotherapy treatments, with particular emphasis on current vaccination strategies for optimizing the induction of an effective immune response by the recruitment of dendritic cells. In addition to cell-based therapies, targeted strategies aiming to deliver synthetic HIV peptides to dendritic cell-specific receptors in vivo will be discussed.

Modification of one epitope-flanking amino acid allows for the induction of friend retrovirus-specific CD8+ T cells by Adenovirus-based immunization

While Friend retrovirus-infected mice readily mount a vigorous CD8(+) T cell response to the leader-gag-derived peptide GagL(85-93), no GagL(85-93)-specific T cells were detectable in mice immunized against Friend virus (FV) with viral vectors or DNA vaccines. By exchanging one epitope-flanking amino acid or using a scaffold protein we were able to demonstrate for the first time the induction of GagL(85-93)-specific CD8(+) T cells by genetic vaccination and show their high protective effect against FV challenge infection.

Pharmacological modulation of GITRL/GITR system: therapeutic perspectives

Glucocorticoid-induced TNFR-related (gitr) is a gene coding for a member of the TNF receptor superfamily. GITR activation by its ligand (GITRL) influences the activity of effector and regulatory T cells, thus participating in the development of immune response against tumours and infectious agents, as well as in autoimmune and inflammatory diseases. Notably, treating animals with GITR-Fc fusion protein ameliorates autoimmune/inflammatory diseases while GITR triggering, by treatment with anti-GITR mAb, is effective in treating viral, bacterial and parasitic infections, as well in boosting immune response against tumours. GITR modulation has been indicated as one of the top 25 most promising research areas by the American National Cancer Institute, and a clinical trial testing the efficacy of an anti-GITR mAb in melanoma patients has been started. In this review, we summarize results regarding: (i) the mechanisms by which GITRL/GITR system modulates immune response; (ii) the structural and functional studies clearly demonstrating differences between GITRL/GITR systems of mice and humans; (iii) the molecules with pharmacological activities including anti-GITR mAbs, GITR-Fc and GITRL-Fc fusion proteins, GITRL in monomer or multimer conformation; and (iv) the possible risks deriving from GITRL/GITR system pharmacological modulation. In conclusion, GITR triggering and inhibition could be useful in treating tumours, infectious diseases, as well as autoimmune and inflammatory diseases. However, differences between mouse and human GITRL/GITR systems suggest that further preclinical studies are needed to better understand how safe therapeutic results can be obtained and to design appropriate clinical trials.

Tregs in infection and vaccinology: heroes or traitors?

The development of effective vaccines against life-threatening pathogens in human diseases represents one of the biggest challenges in biomedical science. Vaccines traditionally make use of the body's own immune armoury to combat pathogens. Yet, while our immune system is mostly effective in eliminating or controlling a diverse range of microorganisms, its responses are incomplete or somewhat limited in several other cases. How immune responses are restrained during certain infections has been a matter of debate for many years. The discovery of regulatory T cells (Tregs), an immune cell type that plays a central role in maintaining immune homeostasis and controlling appropriate immune responses, has shed light into many questions. Indeed, it has been proposed that while Tregs might be beneficial in preventing excessive tissue damage during infection, they might also favour pathogen persistence by restraining effector immune responses. In addition, Tregs are believed to limit immune responses upon vaccination. Different strategies have been pursued to circumvent Treg activity during immunization, but the lack of specific tools for their study has led sometimes to controversial conclusions. With the advent of novel mouse models that allow specific depletion and/or tracking of Treg populations in vivo, novel aspects of Treg biology during infection have been unravelled. In this review, we describe the new advances in understanding Treg biology during infection and evaluate Treg depletion as a novel adjuvant strategy for vaccination.

T-cell intrinsic effects of GITR and 4-1BB during viral infection and cancer immunotherapy

GITR [glucocorticoid inducible tumor necrosis factor receptor (TNFR)-related protein] and 4-1BB are costimulatory TNFR family members that are expressed on regulatory and effector T cells as well as on other cells of the immune system. Here we discuss the role of GITR and 4-1BB on T cells during viral infections and in cancer immunotherapy. Systemic treatment with agonistic anti-4-1BB antibody leads to a number of immune system abnormalities, and clinical trials of anti-4-1BB have been terminated. However, other modes of 4-1BB ligation may be less toxic. To date, similar toxicities have not been reported for anti-GITR treatment of mice, although anti-GITR antibodies can exacerbate mouse autoimmune models. Intrinsic effects of GITR and 4-1BB on effector T cells appear to predominate over their effects on other cell types in some models. Despite their similarities in enhancing T-cell survival, 4-1BB and GITR are clearly not redundant, and both pathways are required for maximal CD8(+) T-cell responses and mouse survival following severe respiratory influenza infection. GITR uses TNFR-associated factor (TRAF) 2 and TRAF5, whereas 4-1BB recruits TRAF1 and TRAF2 to mediate survival signaling in T cells. The differential use of signaling adapters combined with their differential expression may explain the non-redundant roles of GITR and 4-1BB in the immune system.

Lowering the threshold of lung innate immune cell activation alters susceptibility to secondary bacterial superinfection

BACKGROUND

Previous studies have shown that the interaction of CD200R, a myeloid inhibitory receptor, with its ligand, CD200, is critical in the control of innate immune activation in the lung.

METHODS AND RESULTS

Using a mouse model of bacterial superinfection following influenza, we show that an absence of CD200R (a negative regulator highly expressed by macrophages and dendritic cells), restricts commensal and exogenous bacterial invasiveness and completely prevents the mortality observed in wild-type mice. This benefit is due to a heightened innate immune response to influenza virus in cd200r knockout mice that limits immune pathogenesis and viral load. In wild-type mice, apoptotic cells expressing CD200 that we believe contribute to the suppressed innate immune response to bacteria dominate during the resolution phase of influenza-induced inflammation. We also show for the first time the presence of a variety of previously unidentified bacterial species in the lower airways that are significantly adjusted by influenza virus infection and may contribute to the pathophysiology of disease.

CONCLUSIONS

The interaction of CD200 with CD200R therefore contributes to the hyporesponsive innate immune state following influenza virus infection that predisposes to secondary bacterial infection, a phenomenon that has the potential for immune modulation.

Th2 responses to helminth parasites can be therapeutically enhanced by, but are not dependent upon, GITR-GITR ligand costimulation in vivo

The immune suppression that characterizes human helminth infections can hinder the development of protective immunity or help to reduce pathogenic inflammation. Signaling through the T cell costimulator glucocorticoid-induced TNFR-related protein (GITR) counteracts immune downregulation by augmenting effector T cell responses and abrogating suppression by Foxp3(+) regulatory T cells. Thus, superphysiological Ab-mediated GITR costimulation represents a novel therapy for promoting protective immunity toward parasitic helminths, whereas blocking physiological GITR-GITR ligand (GITRL) interactions may provide a mechanism for dampening pathogenic Th2 inflammation. We investigated the superphysiological and physiological roles of the GITR-GITRL pathway in the development of protective and pathogenic Th2 responses in murine infection models of filariasis (Litomosoides sigmodontis) and schistosomiasis (Schistosoma mansoni). Providing superphysiological GITR costimulation using an agonistic anti-GITR mAb over the first 12 d of L. sigmodontis infection initially increased the quantity of Th2 cells, as well as their ability to produce Th2 cytokines. However, as infection progressed, the Th2 responses reverted to normal infection levels, and parasite killing remained unaffected. Despite the Th2-promoting role of superphysiological GITR costimulation, Ab-mediated blockade of the GITR-GITRL pathway did not affect Th2 cell priming or maintenance during L. sigmodontis infection. Blockade of GITR-GITRL interactions during the acute egg phase of S. mansoni infection resulted in reduced Th2 responses, but this effect was confined to the spleen and did not lead to changes in liver pathology. Thus, although superphysiological GITR costimulation can therapeutically enhance Th2 responses, physiological GITR-GITRL interactions are not required for the development of Th2-mediated resistance or pathology in murine models of filariasis and schistosomiasis.

Tumor necrosis factor receptor/tumor necrosis factor family members in antiviral CD8 T-cell immunity

CD8 memory T cells can play a critical role in protection against repeated exposure to infectious agents such as viruses, yet can also contribute to the immunopathology associated with these pathogens. Understanding the mechanisms that control effective memory responses has important ramifications for vaccine design and in the management of adverse immune reactions. Recent studies have implicated several members of the tumor necrosis factor receptor (TNFR) family as key stimulatory and inhibitory molecules involved in the regulation of CD8 T cells. In this review, we discuss their control of the generation, persistence, and reactivation of CD8 T cells during virus infection.

Cortistatin vaccination--a solution to growth hormone deficiency

Cortistatin and somatostatin are neuropeptides which have inhibitory effects on growth hormone through common five receptors. Although, both have inhibitory effects but, only cortistatin has direct inhibitory effects on growth hormone secretagogue and is more potent inhibitor of growth hormone than somatostatin. This control of growth hormone can be manipulated through immunoneutralization of cortistatin through cortistatin DNA vaccine rather than antibodies application. A DNA vaccine of cortistatin can be produced using recombinant DNA technology in a eukaryotic expression system and will serve as a tool not to only alleviate the growth hormone deficiency problems in human but, can also be used to improve growth rate in farm animals.