An immunodominant epitope of the human immunodeficiency virus envelope glycoprotein gp160 recognized by class I major histocompatibility complex molecule-restricted murine cytotoxic T lymphocytes

Japanese Kampo Medicine Juzentaihoto Improves Antiviral Cellular Immunity in Tumour-Bearing Hosts

Global and antigen-independent immunosuppression by growing tumours can cause life-threating damage when concurrent with an infection in tumour-bearing hosts. In the present study, we investigated whether the oral administration of the Japanese traditional herbal (Kampo) medicine, juzentaihoto (JTT), plays a role in the improvement of antiviral cellular immunity in tumour-bearing hosts. Female BALB/c mice subcutaneously injected with murine colorectal cancer CT26 cells fed a control or JTT diet were inoculated with recombinant vaccinia virus expressing human immunodeficiency virus-1 glycoprotein 160 (vSC25). At 7 days postinfection, anti-vSC25 cellular immunity was evaluated by measuring the abundance of splenic virus-specific CD8⁺ T cells. JTT had no impact on CT26 tumour growth in vivo. Surprisingly, JTT augmented anti-vSC25 cellular immunity in CT26-bearing mice. Depletion of either CD25⁺ regulatory T (Treg) cells or myeloid-derived suppressor cells (MDSCs) also enhanced anti-vSC25 cellular immunity in tumour-bearing mice but had no therapeutic benefit against tumour growth. However, JTT had no impact on the abundance of these immunosuppressive cells. Overall, our data indicates that JTT contributes to the improvement of anti-vSC25 cellular immunity in tumour-bearing hosts possibly via a mechanism independent of CD25⁺ Treg cells and MDSCs, suggesting that this Kampo medicine can act as a promising antiviral adjuvant in an immunosuppressive state caused by tumours.

Expression of Chimeric HPV-HIV Protein L1P18 in Pichia pastoris; Purification and Characterization of the Virus-like Particles

Currently, three human papillomavirus (HPV) vaccines are already licensed and all of them are based on virus-like particles (VLPs) of HPV L1 capsid protein but not worldwide accessible. While about 38.0 million people were living with HIV in 2019, only 68% of HIV-infected individuals were accessing antiretroviral therapy as of the end of June 2020 and there is no HIV vaccine yet. Therefore, safe, effective, and affordable vaccines against those two viruses are immediately needed. Both HPV and HIV are sexually transmitted infections and one of the main access routes is the mucosal genital tract. Thus, the development of a combined vaccine that would protect against HPV and HIV infections is a logical effort in the fight against these two major global pathogens. In this study, a recombinant Pichia pastoris producing chimeric HPV-HIV L1P18 protein intracellularly was constructed. After cell disruption, the supernatant was collected, and the VLPs were purified by a combination of ammonium sulfate precipitation, size exclusion chromatography, ultracentrifugation, and ultrafiltration. At the end of purification process, the chimeric VLPs were recovered with 96% purity and 9.23% overall yield, and the morphology of VLPs were confirmed by transmission electron microscopy. This work contributes towards the development of an alternative platform for production of a bivalent vaccine against HPV and HIV in P. pastoris.

Japanese Kampo Medicine Juzentaihoto Enhances Antitumor Immunity in CD1d-/- Mice Lacking NKT Cells

Although the Japanese traditional herbal medicine (Kampo), Juzentaihoto (JTT), has been reported to have antitumor effects in several tumor models, its role in tumor immunology remains controversial. In the present study, we tested whether oral administration of JTT enhances antitumor immunity in CD1d^−/− mice, in which immunosuppression was partially relieved due to the lack of NKT cells. In a subcutaneous murine syngeneic CT26 colorectal tumor model, JTT had no impact on tumor growth in wild type (WT) BALB/c mice. However, the growth rate of tumors was significantly slower in CD1d^−/− mice than in WT mice. Surprisingly, JTT significantly delayed tumor growth in such CD1d^−/− mice. In vivo depletion of CD8⁺ T cells revealed that CD8⁺ T cells are required for JTT’s antitumor activity. Moreover, tumor-reactive cytotoxic T-lymphocytes were detected exclusively in JTT-treated mice with well-controlled tumors. JTT did not affect the number of tumor-infiltrating CD4⁺ regulatory T cells. On the contrary, JTT increased the degranulation marker CD107a⁺ CD8⁺ T cells and decreased Ly6G⁺ Ly6C^lo polymorphonuclear myeloid-derived suppressor cells in tumor-infiltrating lymphocytes, most probably contributing to the suppression of tumor growth in JTT-treated mice. Nonetheless, JTT had no impact on the proportion of monocytic myeloid-derived suppressor cells. In conclusion, our results indicate that in the absence of NKT cells, JTT augments antitumor immunity by CD8⁺ T cells, suggesting that this Kampo medicine is a promising anticancer adjuvant when negative immune regulation is partially relieved.

Trimeric HIV-1 gp140 fused with APRIL, BAFF, and CD40L on the mucosal gp140-specific antibody responses in mice

HIV-1 envelope (Env)-specific antibody present at mucosal surfaces can block entry of HIV-1 into these portals and thus should be elicited by an HIV-1 preventive vaccine. Since three molecules of tumor necrosis factor superfamily (TNFSF), APRIL, BAFF, and CD40L, could promote mucosal antibody responses, we made fusion constructs of them with an HIV-1 gp140 trimer and tested the mucosal gp140-specific antibody elicited by the fusion constructs in mice using a DNA prime-protein boost vaccination regimen. The fusion constructs formed trimers and displayed both broadly neutralizing antibody epitopes and non-broadly neutralizing antibody epitopes. Compared with the control construct, trimeric gp140, trimeric gp140-APRIL and gp140-BAFF fusion proteins mildly promoted B cell proliferation in vitro, enhanced HIV-1 gp140-binding IgG responses in vaginal lavage or fecal pellets, respectively, and decreased HIV-1 gp140-binding IgA in sera. Gp140-APRIL also augmented HIV-1 gp140-binding IgG in sera. Surprisingly, gp140-CD40L did not promote B cell proliferation in vitro and inhibited mucosal and systemic HIV-1 gp140-binding IgG or IgA. These results suggest that APRIL and BAFF should be further explored as molecular adjuvants for HIV-1 vaccines to enhance mucosal antibody responses, but covalent fusion of TNFSFs to gp140 may hinder their adjuvancy due to steric interactions.

Effects of Cross-Presentation, Antigen Processing, and Peptide Binding in HIV Evasion of T Cell Immunity

Unlike cytosolic processing and presentation of viral Ags by virus-infected cells, Ags first expressed in infected nonprofessional APCs, such as CD4⁺ T cells in the case of HIV, are taken up by dendritic cells and cross-presented. This generally requires entry through the endocytic pathway, where endosomal proteases have first access for processing. Thus, understanding virus escape during cross-presentation requires an understanding of resistance to endosomal proteases, such as cathepsin S (CatS). We have modified HIV-1_MN gp120 by mutating a key CatS cleavage site (Thr³²²Thr³²³) in the V3 loop of the immunodominant epitope IGPGRAFYTT to IGPGRAFYVV to prevent digestion. We found this mutation to facilitate cross-presentation and provide evidence from MHC binding and X-ray crystallographic structural studies that this results from preservation of the epitope rather than an increased epitope affinity for the MHC class I molecule. In contrast, when the protein is expressed by a vaccinia virus in the cytosol, the wild-type protein is immunogenic without this mutation. These proof-of-concept results show that a virus like HIV, infecting predominantly nonprofessional presenting cells, can escape T cell recognition by incorporating a CatS cleavage site that leads to destruction of an immunodominant epitope when the Ag undergoes endosomal cross-presentation.

Vaccination with Combination DNA and Virus-Like Particles Enhances Humoral and Cellular Immune Responses upon Boost with Recombinant Modified Vaccinia Virus Ankara Expressing Human Immunodeficiency Virus Envelope Proteins

Heterologous prime boost with DNA and recombinant modified vaccinia virus Ankara (rMVA) vaccines is considered as a promising vaccination approach against human immunodeficiency virus (HIV-1). To further enhance the efficacy of DNA-rMVA vaccination, we investigated humoral and cellular immune responses in mice after three sequential immunizations with DNA, a combination of DNA and virus-like particles (VLP), and rMVA expressing HIV-1 89.6 gp120 envelope proteins (Env). DNA prime and boost with a combination of VLP and DNA vaccines followed by an rMVA boost induced over a 100-fold increase in Env-specific IgG antibody titers compared to three sequential immunizations with DNA and rMVA. Cellular immune responses were induced by VLP-DNA and rMVA vaccinations at high levels in CD8 T cells, CD4 T cells, and peripheral blood mononuclear cells secreting interferon (IFN)-γ, and spleen cells producing interleukin (IL)-2, 4, 5 cytokines. This study suggests that a DNA and VLP combination vaccine with MVA is a promising strategy in enhancing the efficacy of DNA-rMVA vaccination against HIV-1.

Effects of extracellular pH and hypoxia on the function and development of antigen-specific cytotoxic T lymphocytes

The major effector cells for cellular adaptive immunity are CD8(+) cytotoxic T lymphocytes (CTLs), which can recognize and kill virus-infected cells and tumor cells. Although CTLs exhibit strong cytolytic activity against target cells in vitro, a number of studies have demonstrated that their function is often impaired within tumors. Nevertheless, CTLs can regain their cytotoxic ability after escaping from the tumor environment, suggesting that the milieu created by tumors may affect the function of CTLs. As for the tumor environment, the patho-physiological situation present in vivo has been shown to differ from in vitro experimental conditions. In particular, low pH and hypoxia are the most important microenvironmental factors within growing tumors. In the present study, to determine the effect of these factors on CTL function in vivo, we examined the cytolytic activity of CTLs against their targets using murine CTL lines and the induction of these cells from memory cells under low pH or hypoxic conditions using antigen-primed spleen cells. The results indicated that both cytotoxic activity and the induction of functional CTLs were markedly inhibited under low pH. In contrast, in hypoxic conditions, although cytotoxic activity was almost unchanged, the induction of CTLs in vitro showed a slight enhancement, which was completely abrogated in low pH conditions. Therefore, antigen-specific CTL functions may be more vulnerable to low pH than to the oxygen concentration in vivo. The findings shown here provide new therapeutic approaches for controlling tumor growth by retaining CTL cytotoxicity through the maintenance of higher pH conditions.

A possible origin of emerged HIV-1 after interrupting anti-retroviral therapy

Although HIV-1 can be successfully eradicated from the circulating blood of HIV-1-infected individuals using anti-retroviral therapy (ART), HIV-1 virions emerge immediately after the interruption of ART. This study was aimed to investigate the origin of the emerged HIV-1. After obtaining informed consent, blood samples from nine HIV-1-infected individuals and endoscopic ileum samples from five of the individuals were obtained. Purified peripheral mononuclear cells (PBMCs)and ileum cells were analyzed by flow-cytometry, and the V3 loop sequences of the HIV-1 envelope protein were determined. By comparing the V3 loop sequences of the samples, we confirmed that the provirus hidden in the CD4(+) PBMCs was not the source of the HIV-1 that emerged after the interruption of ART. Although free virus and HIV-1-p24 antigen (p24)-positive cells were not seen in the blood of patients receiving ART, proviral DNA and p24 could be detected in the ileum from the same patient. Among the HIV-1-infected CD4(+) cells in the ileum samples, Vα24(+) natural killer T (NKT) cells were the major p24-positive cells. These results suggest that the innate NKTcells in the mucosal compartment are the most likely candidates for the origin of the HIV-1 that emerged after ART was interrupted.

Characterization of T-cell responses to conserved regions of the HIV-1 proteome in BALB/c mice

A likely requirement for a protective vaccine against human immunodeficiency virus type 1 (HIV-1)/AIDS is, in addition to eliciting antibody responses, induction of effective T cells. To tackle HIV-1 diversity by T-cell vaccines, we designed an immunogen, HIVconsv, derived from the most functionally conserved regions of the HIV-1 proteome and demonstrated its high immunogenicity in humans and rhesus macaques when delivered by regimens combining plasmid DNA, nonreplicating simian (chimpanzee) adenovirus ChAdV-63, and nonreplicating modified vaccinia virus Ankara (MVA) as vectors. Here, we aimed to increase the decision power for iterative improvements of this vaccine strategy in the BALB/c mouse model. First, we found that prolonging the period after the ChAdV63.HIVconsv prime up to 6 weeks increased the frequencies of HIV-1-specific, gamma interferon (IFN-γ)-producing T cells induced by the MVA.HIVconsv boost. Induction of strong responses allowed us to map comprehensively the H-2^d-restricted T-cell responses to these regions and identified 8 HIVconsv peptides, of which three did not contain a previously described epitope and were therefore considered novel. Induced effector T cells were oligofunctional and lysed sensitized targets in vitro. Our study therefore provides additional tools for studying and optimizing vaccine regimens in this commonly used small animal model, which will in turn guide vaccine improvements in more expensive nonhuman primate and human clinical trials.

Engineering new mycobacterial vaccine design for HIV-TB pediatric vaccine vectored by lysine auxotroph of BCG

In this study, we have engineered a new mycobacterial vaccine design by using an antibiotic-free plasmid selection system. We assembled a novel Escherichia coli (E. coli)–mycobacterial shuttle plasmid p2auxo.HIVA, expressing the HIV-1 clade A immunogen HIVA. This shuttle vector employs an antibiotic resistance-free mechanism for plasmid selection and maintenance based on glycine complementation in E. coli and lysine complementation in mycobacteria. This plasmid was first transformed into glycine auxotroph of E. coli strain and subsequently transformed into lysine auxotroph of Mycobacterium bovis BCG strain to generate vaccine BCG.HIVA^2auxo. We demonstrated that the episomal plasmid p2auxo.HIVA was stable in vivo over a 7-week period and genetically and phenotypically characterized the BCG.HIVA^2auxo vaccine strain. The BCG.HIVA^2auxo vaccine in combination with modified vaccinia virus Ankara (MVA). HIVA was safe and induced HIV-1 and Mycobacterium tuberculosis-specific interferon-γ-producing T-cell responses in adult BALB/c mice. Polyfunctional HIV-1-specific CD8+ T cells, which produce interferon-γ and tumor necrosis factor-α and express the degranulation marker CD107a, were induced. Thus, we engineered a novel, safer, good laboratory practice–compatible BCG-vectored vaccine using prototype immunogen HIVA. This antibiotic-free plasmid selection system based on “double” auxotrophic complementation might be a new mycobacterial vaccine platform to develop not only recombinant BCG-based vaccines expressing second generation of HIV-1 immunogens but also other major pediatric pathogens to prime protective response soon after birth.

Immunogenic properties of a lettuce-derived C4(V3)6 multiepitopic HIV protein

Elicitation of broad humoral immune responses is a critical factor in the development of effective HIV vaccines. In an effort to develop low-cost candidate vaccines based on multiepitopic recombinant proteins, this study has been undertaken to assess and characterize the immunogenic properties of a lettuce-derived C4(V3)6 multiepitopic protein. This protein consists of V3 loops corresponding to five different HIV isolates, including MN, IIIB, RF, CC, and RU. In this study, both Escherichia coli and lettuce-derived C4(V3)6 have elicited local and systemic immune responses when orally administered to BALB/c mice. More importantly, lettuce-derived C4(V3)6 has shown a higher immunogenic potential than that of E. coli-derived C4(V3)6. Moreover, when reactivity of sera from mice immunized with C4(V3)6 are compared with those elicited by a chimeric protein carrying a single V3 sequence, broader responses have been observed. The lettuce-derived C4(V3)6 has elicited antibodies with positive reactivity against V3 loops from isolates MN, RF, and CC. In addition, splenocyte proliferation assays indicate that significant T-helper responses are induced by the C4(V3)6 immunogen. Taken together, these findings account for the observed elicitation of broader humoral responses by the C4(V3)6 multiepitopic protein. Moreover, they provide further validation for the production of multiepitopic vaccines in plant cells as this serves not only as a low-cost expression system, but also as an effective delivery vehicle for orally administered immunogens.

Inactivation of tumor-specific CD8⁺ CTLs by tumor-infiltrating tolerogenic dendritic cells

Cancer immunosurveillance failure is largely attributed to the insufficient activation of tumor-specific class I major histocompatibility complex (MHC) molecule (MHC-I)-restricted CD8⁺ cytotoxic T lymphocytes (CTLs). DEC-205⁺ dendritic cells (DCs), having the ability to cross-present, can present captured tumor antigens on MHC-I alongside costimulatory molecules, inducing the priming and activation of tumor-specific CD8⁺ CTLs. It has been suggested that reduced levels of costimulatory molecules on DCs may be a cause of impaired CTL induction and that some tumors may induce the downregulation of costimulatory molecules on tolerogenic DCs. To examine such possibilities, we established two distinct types of murine hepatoma cell lines, named Hepa1-6-1 and Hepa1-6-2 (derived from Hepa1-6 cells), and confirmed that they display similar antigenicities, as well as identical surface expression of MHC-I. We found that Hepa1-6-1 had the ability to grow continuously after subcutaneous implantation into syngeneic C57BL/6 mice and did not prime CD8⁺ CTLs. In contrast, Hepa1-6-2 cells, which display reduced levels of adhesion molecules, such as Intercellular Adhesion Molecule 1 (ICAM-1), failed to grow in vivo and efficiently primed CTLs. Moreover, Hepa1-6-1-derived factors, such as transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF) and α-fetoprotein (AFP), converted CD11c^high MHC-II^high DEC-205⁺ DC subsets into tolerogenic cells, displaying downregulated costimulatory molecules and having impaired cross-presenting capacities. These immunosuppressive tolerogenic DCs appeared to inhibit the induction of tumor-specific CD8⁺ CTLs and suppress their cytotoxic functions within the tumor. Together, the findings presented here provide a new method of cancer immunotherapy using the selective suppression, depletion or alteration of immunosuppressive tolerogenic DCs within tumors.

Priming with recombinant auxotrophic BCG expressing HIV-1 Gag, RT and Gp120 and boosting with recombinant MVA induces a robust T cell response in mice

In previous studies we have shown that a pantothenate auxotroph of Myocbacterium bovis BCG (BCGΔpanCD) expressing HIV-1 subtype C Gag induced Gag-specific immune responses in mice and Chacma baboons after prime-boost immunization in combination with matched rMVA and VLP vaccines respectively. In this study recombinant BCG (rBCG) expressing HIV-1 subtype C reverse transcriptase and a truncated envelope were constructed using both the wild type BCG Pasteur strain as a vector and the pantothenate auxotroph. Mice were primed with rBCG expressing Gag and RT and boosted with a recombinant MVA, expressing a polyprotein of Gag, RT, Tat and Nef (SAAVI MVA-C). Priming with rBCGΔpanCD expressing Gag or RT rather than the wild type rBCG expressing Gag or RT resulted in higher frequencies of total HIV-specific CD8⁺ T cells and increased numbers of T cells specific to the subdominant Gag and RT epitopes. Increasing the dose of rBCG from 10⁵ cfu to 10⁷ cfu also led to an increase in the frequency of responses to subdominant HIV epitopes. A mix of the individual rBCGΔpanCD vaccines expressing either Gag, RT or the truncated Env primed the immune system for a boost with SAAVI MVA-C and generated five-fold higher numbers of HIV-specific IFN-γ-spot forming cells than mice primed with rBCGΔpanCD containing an empty vector control. Priming with the individual rBCGΔpanCD vaccines or the mix and boosting with SAAVI MVA-C also resulted in the generation of HIV-specific CD4⁺ and CD8⁺ T cells producing IFN-γ and TNF-α and CD4⁺ cells producing IL-2. The rBCG vaccines tested in this study were able to prime the immune system for a boost with rMVA expressing matching antigens, inducing robust, HIV-specific T cell responses to both dominant and subdominant epitopes in the individual proteins when used as individual vaccines or in a mix.

Utility of the Sindbis replicon system as an Env-targeted HIV vaccine

Sindbis replicon-based vaccine vectors are designed to combine the immunostimulatory properties of replicating viruses with the superior safety profile of non-replicating systems. In this study we performed a detailed assessment of Sindbis (SIN) replicon vectors expressing HIV-1 envelope protein (Env) for the induction of cell-mediated and humoral immune responses in a small animal model. SIN-derived virus-like particles (VLP) elicited Env-specific antibody responses that were detectable after boosting with recombinant Env protein. This priming effect could be mediated by replicon activity alone but may be enhanced by Env attached to the surface of VLP, offering a potential advantage for this mode of replicon delivery for Env based vaccination strategies. In contrast, the Env-specific CTL responses that were elicited by SIN-VLP were entirely dependent on replicon activity. SIN-VLP priming induced more durable humoral responses than immunization with protein only. This is important from a vaccine perspective, given the intrinsic tendency of Env to induce short-lived antibody responses in the context of vaccination or infection. These results indicate that further efforts to enhance the magnitude and durability of the HIV-1 Env-specific immune responses generated by Sindbis vectors, either alone or as part of prime-boost regimens, are justified.

IL-1 enhances expansion, effector function, tissue localization, and memory response of antigen-specific CD8 T cells

Here, we show that interleukin-1 (IL-1) enhances antigen-driven CD8 T cell responses. When administered to recipients of OT-I T cell receptor transgenic CD8 T cells specific for an ovalbumin (OVA) peptide, IL-1 results in an increase in the numbers of wild-type but not IL1R1^−/− OT-I cells, particularly in spleen, liver, and lung, upon immunization with OVA and lipopolysaccharide. IL-1 administration also results in an enhancement in the frequency of antigen-specific cells that are granzyme B⁺, have cytotoxic activity, and/ or produce interferon γ (IFN-γ). Cells primed in the presence of IL-1 display enhanced expression of granzyme B and increased capacity to produce IFN-γ when rechallenged 2 mo after priming. In three in vivo models, IL-1 enhances the protective value of weak immunogens. Thus, IL-1 has a marked enhancing effect on antigen-specific CD8 T cell expansion, differentiation, migration to the periphery, and memory.

Induction of apoptosis-resistant and TGF-β-insensitive murine CD8(+) cytotoxic T lymphocytes specific for HIV-1 gp160

Although TGF-β and IL-6 would turn CD8(+) T cells to differentiate into non-cytotoxic state, these treated cells were converted to cytolytic phenotypes after re-exposure to their antigenic epitope in vitro. Here, using spleen cells from TCR transgenic mice expressing TCRαβ genes of clone RT1 recognizing an epitope peptide (P18-I10: RGPGRAFVTI) of HIV-1 gp160, we generated CD8(+) cytotoxic T lymphocytes (CTLs) activated by re-exposure to P18-I10 after primarily cultured with TGF-β and IL-6 in vitro to examine their effector function. The CTLs, having strong cytotoxic activity in vitro, were not only resistant to Fas-FasL mediated apoptosis, but also insensitive to the suppression of their cytotoxicity by re-exposure to TGF-β in vitro. Moreover, adoptive transfer experiments indicated that the CTLs are capable of eliminating recombinant vaccinia virus expressing HIV-1 gp160 in vivo. Taken together, our data suggest that TGF-β and IL-6 may play pivotal roles in inducing apoptosis-resistant and TGF-β-insensitive CTLs in vitro.

Chimeric hepatitis E virus-like particle as a carrier for oral-delivery

Oral delivery with virus-like particles (VLPs) is advantageous because of the inherited entry pathway from their parental viral capsids, which enables VLP to withstand the harsh and enzymatic environment associated with human digestive tract. However, the repeat use of this system is challenged by the self-immunity. In order to overcome this problem, we engineered the recombinant capsid protein of hepatitis E virus by inserting p18 peptide, derived from the V3 loop of HIV-1 gp120, into the antibody-binding site. The chimeric VLP resembled the tertiary and quaternary structures of the wild type VLP and specifically reacted with an HIV-1 antibody against V3 loop. Different from the wild type VLP, the chimeric VLP was vulnerable to trypsin cleavage although it appeared as intact particle, suggesting that the intermolecular forces of attraction between the recombinant capsid proteins are strong enough to maintain the VLP icosahedral arrangement. Importantly, this VLP containing the V3 loop did not react with anti-HEV antibodies, in correspondence to the mutation at its antibody-binding site. Therefore, the insertion of peptides at the surface antigenic site could allow VLPs to escape pre-existing anti-HEV humoral immunity.

Pre-clinical development of BCG.HIVA(CAT), an antibiotic-free selection strain, for HIV-TB pediatric vaccine vectored by lysine auxotroph of BCG

In the past, we proposed to develop a heterologous recombinant BCG prime-recombinant modified vaccinia virus Ankara (MVA) boost dual pediatric vaccine platform against transmission of breast milk HIV-1 and Mycobacterium tuberculosis (Mtb). In this study, we assembled an E. coli-mycobacterial shuttle plasmid pJH222.HIVA^CAT expressing HIV-1 clade A immunogen HIVA. This shuttle vector employs an antibiotic resistance-free mechanism based on Operator-Repressor Titration (ORT) system for plasmid selection and maintenance in E. coli and lysine complementation in mycobacteria. This shuttle plasmid was electroporated into parental lysine auxotroph (safer) strain of BCG to generate vaccine BCG.HIVA^CAT. All procedures complied with Good Laboratory Practices (GLPs). We demonstrated that the episomal plasmid pJH222.HIVA^CAT was stable in vivo over a 20-week period, and genetically and phenotypically characterized the BCG.HIVA^CAT vaccine strain. The BCG.HIVA^CAT vaccine in combination with MVA.HIVA induced HIV-1- and Mtb-specific interferon γ-producing T-cell responses in newborn and adult BALB/c mice. On the other hand, when adult mice were primed with BCG.HIVA^CAT and boosted with MVA.HIVA.85A, HIV-1-specific CD8⁺ T-cells producing IFN-γ, TNF-α, IL-2 and CD107a were induced. To assess the biosafety profile of BCG.HIVA^CAT-MVA.HIVA regimen, body mass loss of newborn mice was monitored regularly throughout the vaccination experiment and no difference was observed between the vaccinated and naïve groups of animals. Thus, we demonstrated T-cell immunogenicity of a novel, safer, GLP-compatible BCG-vectored vaccine using prototype immunogen HIVA. Second generation immunogens derived from HIV-1 as well as other major pediatric pathogens can be constructed in a similar fashion to prime protective responses soon after birth.

Superior induction of T cell responses to conserved HIV-1 regions by electroporated alphavirus replicon DNA compared to that with conventional plasmid DNA vaccine

Vaccination using "naked" DNA is a highly attractive strategy for induction of pathogen-specific immune responses; however, it has been only weakly immunogenic in humans. Previously, we constructed DNA-launched Semliki Forest virus replicons (DREP), which stimulate pattern recognition receptors and induce augmented immune responses. Also, in vivo electroporation was shown to enhance immune responses induced by conventional DNA vaccines. Here, we combine these two approaches and show that in vivo electroporation increases CD8(+) T cell responses induced by DREP and consequently decreases the DNA dose required to induce a response. The vaccines used in this study encode the multiclade HIV-1 T cell immunogen HIVconsv, which is currently being evaluated in clinical trials. Using intradermal delivery followed by electroporation, the DREP.HIVconsv DNA dose could be reduced to as low as 3.2 ng to elicit frequencies of HIV-1-specific CD8(+) T cells comparable to those induced by 1 μg of a conventional pTH.HIVconsv DNA vaccine, representing a 625-fold molar reduction in dose. Responses induced by both DREP.HIVconsv and pTH.HIVconsv were further increased by heterologous vaccine boosts employing modified vaccinia virus Ankara MVA.HIVconsv and attenuated chimpanzee adenovirus ChAdV63.HIVconsv. Using the same HIVconsv vaccines, the mouse observations were supported by an at least 20-fold-lower dose of DNA vaccine in rhesus macaques. These data point toward a strategy for overcoming the low immunogenicity of DNA vaccines in humans and strongly support further development of the DREP vaccine platform for clinical evaluation.

Optimizing HIV-1-specific CD8+ T-cell induction by recombinant BCG in prime-boost regimens with heterologous viral vectors

The desire to induce HIV-1-specific responses soon after birth to prevent breast milk transmission of HIV-1 led us to propose a vaccine regimen which primes HIV-1-specific T cells using a recombinant Mycobacterium bovis bacillus Calmette-Guérin (rBCG) vaccine. Because attenuated live bacterial vaccines are typically not sufficiently immunogenic as stand-alone vaccines, rBCG-primed T cells will likely require boost immunization(s). Here, we compared modified Danish (AERAS-401) and Pasteur lysine auxotroph (222) strains of BCG expressing the immunogen HIVA for their potency to prime HIV-1-specific responses in adult BALB/c mice and examined four heterologous boosting HIVA vaccines for their immunogenic synergy. We found that both BCG.HIVA(401) and BCG.HIVA(222) primed HIV-1-specific CD8(+) T-cell-mediated responses. The strongest boosts were delivered by human adenovirus-vectored HAdV5.HIVA and sheep atadenovirus-vectored OAdV7.HIVA vaccines, followed by poxvirus MVA.HIVA; the weakest was plasmid pTH.HIVA DNA. The prime-boost regimens induced T cells capable of efficient in vivo killing of sensitized target cells. We also observed that the BCG.HIVA(401) and BCG.HIVA(222) vaccines have broadly similar immunologic properties, but display a number of differences mainly detected through distinct profiles of soluble intercellular signaling molecules produced by immune splenocytes in response to both HIV-1- and BCG-specific stimuli. These results encourage further development of the rBCG prime-boost regimen.

One-step simple assay to determine antigen-specific cytotoxic activities by single-color flow cytometry

Assays for cytotoxicity of CTLs in vivo using a fluorescent-based dye, 5- (and 6-) carboxyfluorescein diacetate succinimydyl ester (CFSE), have been established and widely used. On the basis of this experience, we applied it to in vitro assay system and established a simpe, highly sensitive flow cytometric assay for CTL activity. In our assay, specific activities of CTLs could be detected by a reduction in sensitive target cell numbers on single-color histogram plot analysis. By using this assay, we could determine the changes in cytotoxic activity by single amino acid substitution within an epitope peptide. Adherent cells were also used as target cells in this assay by treatment with excess EDTA and trypsin reagents after incubation with effector CTLs. Furthermore, when fluorescent calibration beads were used as a control, we could determine the cytotoxicity of CTLs against tumor cells. The results obtained from our assay were almost consistent with those from the conventional ( 51)Cr-release assay.Because our assay uses only a stable non-radioactive reagent, CFSE, this assay is safe, inexpensive and extremely easy. These results indicated that this new assay (FACS-CTL assay) would be sufficiently acceptable alternative to classical (51)Cr-release assay.

Protective efficacy of serially up-ranked subdominant CD8+ T cell epitopes against virus challenges

Immunodominance in T cell responses to complex antigens like viruses is still incompletely understood. Some data indicate that the dominant responses to viruses are not necessarily the most protective, while other data imply that dominant responses are the most important. The issue is of considerable importance to the rational design of vaccines, particularly against variable escaping viruses like human immunodeficiency virus type 1 and hepatitis C virus. Here, we showed that sequential inactivation of dominant epitopes up-ranks the remaining subdominant determinants. Importantly, we demonstrated that subdominant epitopes can induce robust responses and protect against whole viruses if they are allowed at least once in the vaccination regimen to locally or temporally dominate T cell induction. Therefore, refocusing T cell immune responses away from highly variable determinants recognized during natural virus infection towards subdominant, but conserved regions is possible and merits evaluation in humans.

Dual neonate vaccine platform against HIV-1 and M. tuberculosis

Acquired immunodeficiency syndrome and tuberculosis (TB) are two of the world's most devastating diseases. The first vaccine the majority of infants born in Africa receive is Mycobacterium bovis bacillus Calmette-Guérin (BCG) as a prevention against TB. BCG protects against disseminated disease in the first 10 years of life, but provides a variable protection against pulmonary TB and enhancing boost delivered by recombinant modified vaccinia virus Ankara (rMVA) expressing antigen 85A (Ag85A) of M. tuberculosis is currently in phase IIb evaluation in African neonates. If the newborn's mother is positive for human immunodeficiency virus type 1 (HIV-1), the baby is at high risk of acquiring HIV-1 through breastfeeding. We suggested that a vaccination consisting of recombinant BCG expressing HIV-1 immunogen administered at birth followed by a boost with rMVA sharing the same immunogen could serve as a strategy for prevention of mother-to-child transmission of HIV-1 and rMVA expressing an African HIV-1-derived immunogen HIVA is currently in phase I trials in African neonates. Here, we aim to develop a dual neonate vaccine platform against HIV-1 and TB consisting of BCG.HIVA administered at birth followed by a boost with MVA.HIVA.85A. Thus, mMVA.HIVA.85A and sMVA.HIVA.85A vaccines were constructed, in which the transgene transcription is driven by either modified H5 or short synthetic promoters, respectively, and tested for immunogenicity alone and in combination with BCG.HIVA²²². mMVA.HIVA.85A was produced markerless and thus suitable for clinical manufacture. While sMVA.HIVA.85A expressed higher levels of the immunogens, it was less immunogenic than mMVA.HIVA.85A in BALB/c mice. A BCG.HIVA²²²–mMVA.HIVA.85A prime-boost regimen induced robust T cell responses to both HIV-1 and M. tuberculosis. Therefore, proof-of-principle for a dual anti-HIV-1/M. tuberculosis infant vaccine platform is established. Induction of immune responses against these pathogens soon after birth is highly desirable and may provide a basis for lifetime protection maintained by boosts later in life.

Newborn mice vaccination with BCG.HIVA²²² + MVA.HIVA enhances HIV-1-specific immune responses: influence of age and immunization routes

We have evaluated the influence of age and immunization routes for induction of HIV-1- and M. tuberculosis-specific immune responses after neonatal (7 days old) and adult (7 weeks old) BALB/c mice immunization with BCG.HIVA(222) prime and MVA.HIVA boost. The specific HIV-1 cellular immune responses were analyzed in spleen cells. The body weight of the newborn mice was weekly recorded. The frequencies of HIV-specific CD8(+) T cells producing IFN-γ were higher in adult mice vaccinated intradermally and lower in adult and newborn mice vaccinated subcutaneously. In all cases the IFN-γ production was significantly higher when mice were primed with BCG.HIVA(222) compared with BCGwt. When the HIV-specific CTL activity was assessed, the frequencies of specific killing were higher in newborn mice than in adults. The prime-boost vaccination regimen which includes BCG.HIVA(222) and MVA.HIVA was safe when inoculated to newborn mice. The administration of BCG.HIVA(222) to newborn mice is safe and immunogenic and increased the HIV-specific responses induced by MVA.HIVA vaccine. It might be a good model for infant HIV and Tuberculosis bivalent vaccine.

Co-expression of miRNA targeting the expression of PERK, but not PKR, enhances cellular immunity from an HIV-1 Env DNA vaccine

Small non-coding micro-RNAs (miRNA) are important post-transcriptional regulators of mammalian gene expression that can be used to direct the knockdown of expression from targeted genes. We examined whether DNA vaccine vectors co-expressing miRNA with HIV-1 envelope (Env) antigens could influence the magnitude or quality of the immune responses to Env in mice. Human miR-155 and flanking regions from the non-protein encoding gene mirhg155 were introduced into an artificial intron within an expression vector for HIV-1 Env gp140. Using the miR-155-expressing intron as a scaffold, we developed novel vectors for miRNA-mediated targeting of the cellular antiviral proteins PKR and PERK, which significantly down-modulated target gene expression and led to increased Env expression in vitro. Finally, vaccinating BALB/c mice with a DNA vaccine vector delivering miRNA targeting PERK, but not PKR, was able to augment the generation of Env-specific T-cell immunity. This study provides proof-of-concept evidence that miRNA effectors incorporated into vaccine constructs can positively influence vaccine immunogenicity. Further testing of vaccine-encoded miRNA will determine if such strategies can enhance protective efficacy from vaccines against HIV-1 for eventual human use.

Vaccination with Human Induced Pluripotent Stem Cells Creates an Antigen-Specific Immune Response Against HIV-1 gp160

Induced pluripotent stem cells (iPSCs) are artificially derived from somatic cells that have been transduced with defined reprogramming factors. A previous report has indicated the possibility of using iPSCs as an immune stimulator to generate antigen-specific immunity. In our current study, we have investigated whether human iPSCs (hiPSCs) have the ability to enhance specific immune response against a human immunodeficiency virus type 1 (HIV-1) antigen in a xenogenic mouse model. Our results show that BALB/c mice immunized with hiPSCs transduced with an adenoviral vector encoding HIV-1 gp160 exhibited prominent antigen-specific cellular immune responses. We further found that pre-treatment of hiPSCs with ionizing radiation promotes the secretion of pro-inflammatory cytokines such as interleukin-1 alpha (IL-1α), IL-12, and IL-18. These cytokines might promote the activation of antigen-presenting cells and the effective induction of cellular immunity. Our present findings thus demonstrate that a hiPSCs-based vaccine has the potential to generate cellular immunity against viral antigens such as HIV-1 gp160 in a xenogenic condition.

IFNgamma-producing, virus-specific CD8+ effector cells acquire the ability to produce IL-10 as a result of entry into the infected lung environment

It has become clear that T cells with the potential to negatively regulate the immune response are normal constituents of the immune system. These cells often mediate their effects through the production of immunosuppressive factors. At present our understanding of how these cells are generated is limited. Here we report the presence of a population of IL-10-producing, virus-specific CD8+ T cells in the lungs of mice following acute respiratory infection. These cells were only found at minimal levels in the spleen and draining lymph node; instead they were restricted primarily to the infected lung tissue. A major finding from this study is demonstration that the ability to produce IL-10 can be acquired by IFNgamma-producing effector cells following entry into the infected lung. These studies suggest IL-10 production is the result of further differentiation of an antigen-specific CD8+ T cell that is governed by signals present in infected lung tissue.

Novel recombinant Mycobacterium bovis BCG, ovine atadenovirus, and modified vaccinia virus Ankara vaccines combine to induce robust human immunodeficiency virus-specific CD4 and CD8 T-cell responses in rhesus macaques

Mycobacterium bovis bacillus Calmette-Guérin (BCG), which elicits a degree of protective immunity against tuberculosis, is the most widely used vaccine in the world. Due to its persistence and immunogenicity, BCG has been proposed as a vector for vaccines against other infections, including HIV-1. BCG has a very good safety record, although it can cause disseminated disease in immunocompromised individuals. Here, we constructed a recombinant BCG vector expressing HIV-1 clade A-derived immunogen HIVA using the recently described safer and more immunogenic BCG strain AERAS-401 as the parental mycobacterium. Using routine ex vivo T-cell assays, BCG.HIVA(401) as a stand-alone vaccine induced undetectable and weak CD8 T-cell responses in BALB/c mice and rhesus macaques, respectively. However, when BCG.HIVA(401) was used as a priming component in heterologous vaccination regimens together with recombinant modified vaccinia virus Ankara-vectored MVA.HIVA and ovine atadenovirus-vectored OAdV.HIVA vaccines, robust HIV-1-specific T-cell responses were elicited. These high-frequency T-cell responses were broadly directed and capable of proliferation in response to recall antigen. Furthermore, multiple antigen-specific T-cell clonotypes were efficiently recruited into the memory pool. These desirable features are thought to be associated with good control of HIV-1 infection. In addition, strong and persistent T-cell responses specific for the BCG-derived purified protein derivative (PPD) antigen were induced. This work is the first demonstration of immunogenicity for two novel vaccine vectors and the corresponding candidate HIV-1 vaccines BCG.HIVA(401) and OAdV.HIVA in nonhuman primates. These results strongly support their further exploration.

Elimination of helminth infection restores HIV-1C vaccine-specific T cell responses independent of helminth-induced IL-10

HIV-1 prevalence is highest in developing countries; similarly helminth parasites are often highly endemic in these same areas. Helminths are strong immune modulators, and negatively impact the ability of the infected hosts to mount protective vaccine-specific T cell immune responses for HIV-1 and other pathogens. Indeed, previously we found that Schistosoma mansoni infected mice had significantly impaired HIV-1C vaccine-specific T cell responses. Anthelminthics are available and inexpensive; therefore, in this study, we evaluated whether elimination of schistosome infection prior to vaccination with an HIV-1C DNA vaccine would increase recipients vaccine-specific responses. As expected, splenocytes from S. mansoni infected mice produced significantly elevated amounts of interleukin (IL)-4 and IL-10, and significantly lower amounts of interferon (IFN)-gamma than splenocytes from naïve mice. Following elimination of parasites by praziquantel (PZQ) treatment, splenomegaly was significantly reduced, though splenocytes produced similar or higher levels of IL-10 than splenocytes from infected mice. However, we found that PZQ treatment significantly increased levels of IFN-gamma in response to concanavalin A or SEA compared to splenocytes from untreated mice. Importantly, PZQ treatment resulted in complete restoration of HIV-1C vaccine-specific T cell responses at 8 weeks post-PZQ treatment. Restoration of HIV-1C vaccine-specific T cell responses following elimination of helminth infection was time dependent, but surprisingly independent of the levels of IL-4 and IL-10 induced by parasite antigens. Our study shows that elimination of worms offers an affordable and a simple means to restore immune responsiveness to T cell based vaccines for HIV-1 and other infectious diseases in helminth endemic settings.

Elicitation of broad CTL response against HIV-1 by the DNA vaccine encoding artificial multi-component fusion protein MultiHIV--study in domestic pigs

Broad CTL response against HIV-1 is one factor that helps to control the viral replication. We have constructed a DNA vaccine that encodes a large artificial fusion protein (MultiHIV) and shown it to be immunogenic in mice, swine and macaques. Inbred mice revealed CTL response only against two epitopes due to limited MHC class I variability. To assess the quality of the CTL response we addressed this question in domestic swine. Number of presented epitopes varied between 7 and 14 among the five selected animals. Epitopes detected in swine are localised in the same antigenic regions recognised in humans. This can be explained by the fact that swine MHC-I (SLA-I) complex is remarkably similar to human HLA-I. These results also indicate that immunogenicity profile of vaccines in domestic swine may predict the outcome of human immunisation.

Narrowed TCR diversity for immunised mice challenged with recombinant influenza A-HIV Env(311-320) virus

Understanding CD8+ T cell responses generated by live virus vectors is critical for the rational design of next generation HIV CTL-based vaccines. We used recombinant influenza viruses expressing the HIV Env(311-320) peptide in the neuraminidase stalk to study response magnitude, cytokine production and repertoire diversity for the elicited CD8+ D(d)Env(311) CTL set. The insertion of the CD8+ D(d)Env(311) epitope into the NA stalk resulted in a decrease in viral fitness that was reflected in lower lung viral titres. While not affecting the magnitude of endogenous primary influenza-specific responses, the introduction of the D(d)Env(311) CD8+ T cell epitope altered the hierarchy of responses following secondary challenge. The CD8+ K(d)NP(147) response increased 9-fold in the spleen following secondary infection whereas the CD8+ D(d)Env(311) response increased 15-fold in the spleen. Moreover, this study is the first to describe narrowing of CD8+ TCR repertoire diversity in the context of an evolving secondary immune response against influenza A virus. Analysis of Vbeta bias for CD8+ D(d)Env(311) T cell responses showed a narrowing of CD8+ Vbeta8.1/8.2 D(d)Env(311) TCR repertoire diversity. This work further emphasizes the importance of understanding vaccine-induced CD8+ T cell responses.

In silico prediction and immunological validation of common HLA-DRB1-restricted T cell epitopes of Candida albicans secretory aspartyl proteinase 2

ABSTRACT Sap2 is the most abundant virulence factor expressed during Candida infection, and the principal protein known to induce antibody response during Candida infection in humans. Its role in T-cell activation however, has not yet been determined. Sequence analysis revealed that Sap2 contains two variable regions: Var1 and Var2. Computational predictions by the Hotspot Hunter program identified that Var1 contains three candidate T-cell epitopes, whereas Var2 contains four. Thirty-nine overlapping peptides of Sap2 were then synthesized, and tested for their ability to induce proliferation of PBMC from 12 donors. Peptides P11, P17 and P31 exhibited significantly higher proliferative indices when compared with those of other peptides or controls. P17 and P31 are located in the areas of prediction, while P11 is not. There were other peptides outside the prediction areas that could stimulate PBMC proliferation at low levels. Nevertheless, the proliferative noise caused by such peptides was ruled out by IL-2 ELISpot analysis. Only P17 and P31 were shown to induce clonal proliferation of IFN-gamma producing lymphocytes, suggesting that these two peptides contain T cell epitopes. P11, which stimulated IL-2 producing clones, contains a known B-cell epitope. Interestingly, P17 and P31 elicited both Th1 and Th2 cell responses with significant numbers of IL-13 secreting clones in response to stimulation. Taken together, the computer-based T cell epitope prediction method could identify the immunogenic T cell epitopes of C. albicans Sap2 that promiscuously bind to the HLA-DRB1 supertype.

Combining DNA technologies and different modes of immunization for induction of humoral and cellular anti-HIV-1 immune responses

We show here that it is possible to combine two different genetic immunogens, one designed to induce HIV-1 specific humoral immune responses (pKCMVgp160B) and one designed to induce cellular anti-HIV-1 immune responses (Auxo-GTU-MultiHIV), and still retain the major properties of both vaccine constructs. The two different constructs were delivered using two different methods; the gene-gun and the Biojector, which both are needle-free devices. In BALB/c mice we were able to induce high levels of HIV-1-specific T cell responses as well as high levels of anti-gp160 antibodies by co-administrating the vaccine constructs. The cellular immune responses, but not antibody responses, were moderately compromised from the combination. This study shows that it is a feasible strategy to combine different vaccines and modes of delivery, but that interference as to magnitude may occur to certain gene products.

Generation of functionally active HIV-1 specific CD8+ CTL in intestinal mucosa following mucosal, systemic or mixed prime-boost immunization

Gastrointestinal and vaginal mucosa are major sites of entry in natural HIV infection and therefore the preferred sites to elicit high-avidity CD8+ CTL by vaccination. We directly compare systemic and mucosal immunization in mice after DNA priming and boosting with rgp160 env expressed either in MVA or Ad for their ability to induce mucosal as well as systemic HIV-specific CTL. The optimal CTL response in the gut mucosa was observed after priming with the HIV-1 gp160 env DNA vaccine and boosting with rMVA or rAd encoding the same envelope gene all administered intrarectally (IR). Maximum levels of high-avidity CD8+ T cells were seen in intestinal lamina propria following this regimen. When the prime and boost routes were distinct, the delivery site of the boost had a greater impact than the DNA priming. IM DNA prime and IR rMVA boost were more effective than IR DNA prime and IM rMVA boost for eliciting mucosal CD8+ T-cell avidity. A systemic DNA-prime-followed by systemic rMVA boost induced high levels of high-avidity CD8+ T cells systemically, but responses were undetectable in mucosal sites. A single systemic immunization with rMVA was sufficient to induce high-avidity IFN-gamma secreting CD8+ T cells in systemic organs, whereas a single mucosal immunization with rMVA was not sufficient to elicit high-avidity CD8+ T cells in mucosa. Thus, a heterologous mucosal DNA prime-viral vectored boost strategy was needed. The requirement for a heterologous DNA prime-recombinant viral boost strategy for generation of high-avidity CD8+ T cells in mucosal sites in mice may be more stringent than for the induction of high-avidity CD8+ T cells in systemic compartments.

Murine models for HIV vaccination and challenge

HIV-1 only infects humans and chimpanzees. SIV or SHIV are, therefore, used as models for HIV in rhesus, cynomologus and pigtail macaques. Since conducting experiments in primate models does not fully mimic infection or vaccination against HIV-1 and is expensive, there is a great need for small-animal models in which it is possible to study HIV-1 infection, immunity and vaccine efficacy. This review summarizes the available murine models for studying HIV-1 infection with an emphasis on our experience of the HIV-1-infected-cell challenge as a model for evaluating candidate HIV-1 vaccines. In the cell-based challenge model, several important factors that, hopefully, can be related to vaccine efficacy in humans were discovered: the efficiency of combining plasmid DNA representing several of the viral genes originating from multiple clades of HIV-1, the importance of adjuvants activating innate and induced immunity and the enhanced HIV eradication by drug-conjugated antibody.

Estimation of low frequency antigen-presenting cells with a novel RELISPOT assay

Adequate presentation of self and foreign antigens is a key factor for efficient T-cell immunosurveillance against pathogens and tumors. Cells presenting foreign antigens usually comprise a rare population and are difficult to detect even at the peak of infection. Here we demonstrate a CD8(+) T-cell-based approach that allows detection of specific antigen-presenting cells (APC) at a frequency of less than 0.0005%. When T cells are in excess, they form rosettes with rare APCs, which appear as single spots in an IFN-gamma ELISPOT assay. Using this RELISPOT (Rosette ELISPOT) method we demonstrate the dynamic interplay between CD8 T cells and professional and non-professional APCs following virus challenge.

Role of alpha3 domain of class I MHC molecules in the activation of high- and low-avidity CD8+ CTLs

CD8 can serve as a co-receptor or accessory molecule on the surface of CTL. As a co-receptor, CD8 can bind to the alpha3 domain of the same MHC class I molecules as the TCR to facilitate TCR signaling. To evaluate the role of the MHC class I molecule alpha3 domain in the activation of CD8(+) CTL, we have produced a soluble 227 mutant of H-2D(d), with a point mutation in the alpha3 domain (Glu227 --> Lys). 227 mutant class I-peptide complexes were not able to effectively activate H-2D(d)-restricted CD8 T cells in vitro, as measured by IFN-gamma production by an epitope-specific CD8(+) CTL line. However, the 227 mutant class I-peptide complexes in the presence of another MHC class I molecule (H-2K(b)) (that cannot present the peptide) with a normal alpha3 domain can induce the activation of CD8(+) CTL. Therefore, in order to activate CD8(+) CTL, the alpha3 domain of MHC class I does not have to be located on the same molecule with the alpha1 and alpha2 domains of MHC class I. A low-avidity CD8(+) CTL line was significantly less sensitive to stimulation by the 227 mutant class I-peptide complexes in the presence of the H-2K(b) molecule. Thus, low-avidity CTL may not be able to take advantage of the interaction between CD8 and the alpha3 domain of non-presenting class I MHC molecules, perhaps because of a shorter dwell time for the TCR-MHC interaction.

Design and pre-clinical evaluation of a universal HIV-1 vaccine

Background

One of the big roadblocks in development of HIV-1/AIDS vaccines is the enormous diversity of HIV-1, which could limit the value of any HIV-1 vaccine candidate currently under test.

Methodology and Findings

To address the HIV-1 variation, we designed a novel T cell immunogen, designated HIV_CONSV, by assembling the 14 most conserved regions of the HIV-1 proteome into one chimaeric protein. Each segment is a consensus sequence from one of the four major HIV-1 clades A, B, C and D, which alternate to ensure equal clade coverage. The gene coding for the HIV_CONSV protein was inserted into the three most studied vaccine vectors, plasmid DNA, human adenovirus serotype 5 and modified vaccine virus Ankara (MVA), and induced HIV-1-specific T cell responses in mice. We also demonstrated that these conserved regions prime CD8⁺ and CD4⁺ T cell to highly conserved epitopes in humans and that these epitopes, although usually subdominant, generate memory T cells in patients during natural HIV-1 infection.

Significance

Therefore, this vaccine approach provides an attractive and testable alternative for overcoming the HIV-1 variability, while focusing T cell responses on regions of the virus that are less likely to mutate and escape. Furthermore, this approach has merit in the simplicity of design and delivery, requiring only a single immunogen to provide extensive coverage of global HIV-1 population diversity.

HSV-1 amplicon vectors elicit polyfunctional T cell responses to HIV-1 Env, and strongly boost responses to an adenovirus prime

HSV-1 amplicon vectors elicit strong T-cell responses to encoded antigens but the qualitative nature of these responses is poorly understood. Antigen-specific CD4(+) and CD8(+) T-cell responses to amplicon and adenovirus (rAd5) vectors encoding HIV-1 gp120 were assessed following immunization of mice, by performing intracellular cytokine staining for IFNgamma, IL2 and TNFalpha, following stimulation of splenocytes with a HIV-1 Env peptide pool. The quality of the primary T-cell response to amplicon and rAd5 vectors was strikingly similar, but there were qualitative differences in responses to amplicon vectors that incorporated different promoters upstream of gp120 - suggesting that promoters can significantly influence immune response quality. When prime-boost combinations were studied, a rAd5 prime and amplicon boost elicited the highest T-cell response. Furthermore, protocols that incorporated a rAd5 prime consistently elicited a greater proportion of polyfunctional CD4(+) T-cells-regardless of boost. This suggests that initial priming can shape immune response quality after a boost. Overall, these findings provide insight into effective vector combinations for HIV-1 vaccine development.

Short communication: preclinical evaluation of candidate HIV type 1 vaccines in inbred strains and an outbred stock of mice

Outstanding animal immunogenicity is a prerequisite for progression of novel vaccines to clinical trials. The measurement of vaccine immunogenicity is critically dependent on the specificity, accuracy, sensitivity, and precision of the employed assays. This has been greatly aided by the generation of isogenic mouse strains. Here, we identified three novel H-2(d) -restricted CD8+ T cell epitopes derived from the human immunodeficiency virus type 1 and demonstrated a fine evaluation of the vaccine-elicited T cell responses in an inbred mouse strain. However, unlike inbred mice, outbred mouse stock indicated preferential induction of CD4+ T cell responses by a heterologous DNA-prime-recombinant modified vaccinia virus Ankara boost regimen and induction of dominant responses to the env-derived vaccine component, i.e., observations reminiscent of human data. Thus, an outbred mouse stock may provide more rigorous and realistic tests for candidate vaccine evaluation in addition to sensitive assays in a selected, well-responding inbred strain.

Vaccine platform for prevention of tuberculosis and mother-to-child transmission of human immunodeficiency virus type 1 through breastfeeding

Most children in Africa receive their vaccine against tuberculosis at birth. Those infants born to human immunodeficiency virus type 1 (HIV-1)-positive mothers are at high risk of acquiring HIV-1 infection through breastfeeding in the first weeks of their lives. Thus, the development of a vaccine which would protect newborns against both of these major global killers is a logical yet highly scientifically, ethically, and practically challenging aim. Here, a recombinant lysine auxotroph of Mycobacterium bovis bacillus Calmette-Guérin (BCG), a BCG strain that is safer than those currently used and expresses an African HIV-1 clade-derived immunogen, was generated and shown to be stable and to induce durable, high-quality HIV-1-specific CD4(+)- and CD8(+)-T-cell responses. Furthermore, when the recombinant BCG vaccine was used in a priming-boosting regimen with heterologous components, the HIV-1-specific responses provided protection against surrogate virus challenge, and the recombinant BCG vaccine alone protected against aerosol challenge with M. tuberculosis. Thus, inserting an HIV-1-derived immunogen into the scheduled BCG vaccine delivered at or soon after birth may prime HIV-1-specific responses, which can be boosted by natural exposure to HIV-1 in the breast milk and/or by a heterologous vaccine such as recombinant modified vaccinia virus Ankara delivering the same immunogen, and decrease mother-to-child transmission of HIV-1 during breastfeeding.

Requirement for CD4 T Cell Help in Maintenance of Memory CD8 T Cell Responses Is Epitope Dependent

CD4 Th cells play critical roles in stimulating Ab production and in generating primary or maintaining memory CTL. The requirement for CD4 help in generating and maintaining CTL responses has been reported to vary depending on the vector or method used for immunization. In this study, we examined the requirement for CD4 T cell help in generating and maintaining CTL responses to an experimental AIDS vaccine vector based on live recombinant vesicular stomatitis virus (VSV) expressing HIV Env protein. We found that primary CD8 T cell responses and short-term memory to HIV Env and VSV nucleocapsid (VSV N) proteins were largely intact in CD4 T cell-deficient mice. These responses were efficiently recalled at 30 days postinfection by boosting with vaccinia recombinants expressing HIV Env or VSV N. However, by 60 days postinfection, the memory/recall response to VSV N was lost in CD4-deficient mice, while the recall response HIV Env was partially maintained in the same animals for at least 90 days. This result indicates that there are epitope-specific requirements for CD4 help in the maintenance of memory CD8 T cell responses. Our results also suggest that choice of epitopes might be critical in an AIDS vaccine designed to protect against disease in the context of reduced or declining CD4 T cell help.

GTU®-MultiHIV DNA vaccine results in protection in a novel P815 tumor challenge model

A novel animal model for testing the immunogenicity and protective immune response induced by HIV-1 DNA vaccines was developed. DBA/2 mice were immunized with GTU-MultiHIV DNA encoding multigene for Rev, Nef, Tat, optp17/24 and a stretch of Pol/Env epitopes. A single GTU-MultiHIV B-clade specific plasmid or Auxo-GTU-MultiHIV(mix) (mixture of four plasmids with A, B, C and FGH clade specific MultiHIV antigens) were administered via gene gun and cell-mediated and humoral immune responses were analysed. The protective efficacy of the immune response was evaluated by challenging the mice with syngeneic tumor cells (P815) stably transfected with the MultiHIV fusion gene. Our results show that the strong MultiHIV-specific immune response generated by the GTU-MultiHIV vaccines in DBA/2 mice was able to delay the tumor growth substantially, indicating that the CTL response detected in vitro confers protection in vivo. The model described here is a safe and feasible in vivo assay for assessment of the vaccine potency to induce protective cell-mediated immune responses.

Combined single-clade candidate HIV-1 vaccines induce T cell responses limited by multiple forms of in vivo immune interference

We assessed in mice whether broad CD8+ T cell responses capable of efficient recognition of multiple HIV-1 clades could be induced using current single-clade vaccine constructs that were or will be used in clinical trials in Europe and Africa. We found that single-clade A, B and C vaccines applied alone induced only limited cross-clade reactivity and that the epitope hierarchy varied according to the immunizing clade. However, combining single-clade HIV-1 vaccines into multi-clade formulations resulted in multiple forms of in vivo immune interference such as original antigenic sin and antagonism, which dampened or even abrogated induction of responses to epitope variants and reduced the breadth of induced T cell responses. Simultaneous administration of individual clade-specific vaccines into anatomically separated sites on the body alleviated antagonism and increased the number of detectable epitope responses. Although cross-reactivity of murine CD8+ T cells does not directly translate to humans, the molecular interactions involved in triggering T cell responses are the same in mouse and man. Thus, these results have important ramifications for the design of both prophylactic and therapeutic vaccines against HIV-1 and other highly variable pathogens.

Immunogenicity of virus-like particles containing modified human immunodeficiency virus envelope proteins

Extensive glycosylation and variable loops of the HIV envelope protein (Env) are reported to shield some neutralizing epitopes. Here, we investigated the immunogenicity of mutated HIV Envs presented in virus-like particles (VLPs). We immunized mice with simian human immunodeficiency virus (SHIV) VLPs containing mutant HIV Env with reduced glycosylation (3G), variable loop-deleted mutations (dV1V2), or combinations of both types of mutations (3G-dV2-1G), and evaluated immune responses. Immune sera from mice that received VLPs with modified HIV Envs (3G or dV1V2) showed higher neutralizing activities against the homologous HIV 89.6 virus as well as heterologous viruses when compared with wild type SHIV VLP-immunized mice. Lymphocytes from immunized mice produced HIV Env-specific cytokines, with the 3G-dV2-1G mutant producing high levels of cytokines. Interestingly, both dendritic cells and B cells were found to interact with VLPs suggesting that VLPs are effective immunogens. Therefore, this study suggests that VLPs containing modified HIV Env have the potential to be developed as candidate vaccines capable of inducing cellular and humoral immune responses including neutralizing activities.

Molecular analysis of TCR and peptide/MHC interaction using P18-I10-derived peptides with a single D-amino acid substitution

For the structural analysis of T-cell receptor (TCR) and peptide/MHC interaction, a series of peptides with a single amino acid substitution by a corresponding D-amino acid, having the same weight, size, and charge, within P18-I10 (aa318-327: RGPGRAFVTI), an immunodominant epitope of HIV-1 IIIB envelope glycoprotein, restricted by the H-2Dd class I MHC molecule, has been synthesized. Using those peptides, we have observed that the replacement at positions 324F, 325V, 326T, and 327I with each corresponding D-amino acid induced marked reduction of the potency to sensitize targets for P18-I10-specific murine CD8+ cytotoxic T lymphocytes (CTLs), LINE-IIIB, recognition. To analyze further the role of amino acid at position 325, the most critical site for determining epitope specificity, we have developed a CTL line [LINE-IIIB(325D)] and its offspring clones specific for the epitope I-10(325v) having a D-valine (v) at position 325. Taking advantage of two distinct sets of CD8+ CTLs restricted by the same Dd, three-dimensional structural analysis on TCR and peptide/MHC complexes by molecular modeling was performed, which indicates that the critical amino acids within the TCRs for interacting with 325V or 325v appear to belong to the complementarity-determining region 1 but not to the complementarity-determining region 3 of Vbeta chain.

Induction of human immunodeficiency virus type-1-specific immunity with a novel gene transport unit (GTU)-MultiHIV DNA vaccine

A multiHIV fusion gene expressing an antigenic fusion protein composed of regulatory HIV-1 proteins Rev, Nef, and Tat, as well as Gag p17/p24 and a stretch of 11 cytotoxic T lymphocyte (CTL) epitope clusters from Pol and Env, was cloned into a novel DNA vector named the Gene Transport Unit (GTU). A mouse H-2(d)-restricted HIV-1 gp120 epitope (RGPGRAFVTI) was cloned into the fusion gene as well. In addition to the HIV- 1 genes the GTU codes for a nuclear anchoring protein (bovine papilloma virus E2), ensuring the long maintenance of the vector and a high expression level of the selected immunogens. BALB/c mice were immunized with the GTU-MultiHIV DNA construct by different routes and regimens of immunization to assess the immunogenicity of the DNA vaccine in vivo. Mice developed strong CD8(+) CTL responses to HIV-1 Env and Gag measured by an ELISPOT-IFN-gamma assay and chromium release assay. In addition, T cell responses to regulatory proteins Rev, Nef, and Tat were induced. Antibody responses were detected to each of the HIV antigens encoded by the DNA construct. Minimal doses of the GTU-MultiHIV DNA delivered by gene gun were potent in inducing significant HIV-specific CTL responses. The equivalent doses of the conventional plasmid expressing MultiHIV DNA delivered by gene gun failed to do so. An ideal DNA vaccine should yield high expression of the viral antigens for a prolonged period of time, and expression of the multiple viral antigens is probably required for the induction of a broad and protective immune response. The GTU-MultiHIV DNA vaccine described is a good vaccine candidate that meets the above criteria.