Complex antigen presentation pathway for an HLA-A*0201-restricted epitope from Chikungunya 6K protein.

BACKGROUND: The adaptive cytotoxic T lymphocyte (CTL)-mediated immune response is critical for clearance of many viral infections. These CTL recognize naturally processed short viral antigenic peptides bound to human leukocyte antigen (HLA) class I molecules on the surface of infected cells. This specific recognition allows the killing of virus-infected cells. The T cell immune T cell response to Chikungunya virus (CHIKV), a mosquito-borne Alphavirus of the Togaviridae family responsible for severe musculoskeletal disorders, has not been fully defined; nonetheless, the importance of HLA class I-restricted immune response in this virus has been hypothesized. METHODOLOGY/PRINCIPAL FINDINGS: By infection of HLA-A*0201-transgenic mice with a recombinant vaccinia virus that encodes the CHIKV structural polyprotein (rVACV-CHIKV), we identified the first human T cell epitopes from CHIKV. These three novel 6K transmembrane protein-derived epitopes are presented by the common HLA class I molecule, HLA-A*0201. One of these epitopes is processed and presented via a complex pathway that involves proteases from different subcellular locations. Specific chemical inhibitors blocked these events in rVACV-CHIKV-infected cells. CONCLUSIONS/SIGNIFICANCE: Our data have implications not only for the identification of novel Alphavirus and Togaviridae antiviral CTL responses, but also for analyzing presentation of antigen from viruses of different families and orders that use host proteinases to generate their mature envelope proteins.

The viral transcription group determines the HLA class I cellular immune response against human respiratory syncytial virus.

The cytotoxic T-lymphocyte-mediated killing of virus-infected cells requires previous recognition of short viral antigenic peptides bound to human leukocyte antigen class I molecules that are exposed on the surface of infected cells. The cytotoxic T-lymphocyte response is critical for the clearance of human respiratory syncytial virus infection. In this study, naturally processed viral human leukocyte antigen class I ligands were identified with mass spectrometry analysis of complex human leukocyte antigen-bound peptide pools isolated from large amounts of human respiratory syncytial virus-infected cells. Acute antiviral T-cell response characterization showed that viral transcription determines both the immunoprevalence and immunodominance of the human leukocyte antigen class I response to human respiratory syncytial virus. These findings have clear implications for antiviral vaccine design.

Evaluating CD8⁺ T cell responses in vitro.

The (51)Cr-release assay described in the 1960s has been for decades the gold standard cytolytic assay and remains in use in many laboratories. Whereas other radioactive tests were later on described, they never fully replaced the (51)Cr-release assay. More thorough understanding of CTL biology and killing pathways has more recently resulted in the design of reliable nonradioactive tests to analyze CD8(+) T cell responses which are likely to supplant in a close future the (51)Cr-release assay.

Cloning CD8⁺ cytolytic T lymphocytes.

CD8(+) T lymphocyte cloning has resulted in many fundamental advances: structural elucidation of peptide-MHC recognition, spatiotemporal dissection of the thymic positive and negative selection processes and is further expected, TCRs being the key molecules controlling T cell activation, to provide us with molecular tools of immuno-therapeutical interest for infectious, tumor, and autoimmune diseases. However, cloning CD8(+) T lymphocytes remains a relatively difficult enterprise. Cloning mouse CD8(+) T lymphocytes that will be first consider is to some extend facilitated by our complete control of the in vivo priming process and the unlimited access we usually have to perfectly suited (syngeneic) antigen presenting cells. Cloning human CD8(+) T lymphocytes is more difficult largely but not exclusively for ethical reasons.

Role of metalloproteases in vaccinia virus epitope processing for transporter associated with antigen processing (TAP)-independent human leukocyte antigen (HLA)-B7 class I antigen presentation.

The transporter associated with antigen processing (TAP) translocates the viral proteolytic peptides generated by the proteasome and other proteases in the cytosol to the endoplasmic reticulum lumen. There, they complex with nascent human leukocyte antigen (HLA) class I molecules, which are subsequently recognized by the CD8(+) lymphocyte cellular response. However, individuals with nonfunctional TAP complexes or tumor or infected cells with blocked TAP molecules are able to present HLA class I ligands generated by TAP-independent processing pathways. Herein, using a TAP-independent polyclonal vaccinia virus-polyspecific CD8(+) T cell line, two conserved vaccinia-derived TAP-independent HLA-B*0702 epitopes were identified. The presentation of these epitopes in normal cells occurs via complex antigen-processing pathways involving the proteasome and/or different subsets of metalloproteinases (amino-, carboxy-, and endoproteases), which were blocked in infected cells with specific chemical inhibitors. These data support the hypothesis that the abundant cellular proteolytic systems contribute to the supply of peptides recognized by the antiviral cellular immune response, thereby facilitating immunosurveillance. These data may explain why TAP-deficient individuals live normal life spans without any increased susceptibility to viral infections.

Design of a HIV-1-derived HLA-B07.02-restricted polyepitope construct.

OBJECTIVE: To design a vaccine construct containing various but conserved HIV-1-derived epitopes and generating broad CD8 T cell responses. METHODS: HLA-B7 transgenic H-2KD KO transgenic mice were used to identify potential new HLA-B07.02-restricted HIV-1-derived epitopes. Immunological recognition of these epitopes was confirmed by IFN-gamma ELISpot assays with PBMCs from HLA-B*0702 HIV-1-infected individuals. For these peptides as well as others previously identified, the capacity to induce cross-reactive responses against their frequent allelic variants was evaluated in the mouse model. A set of epitopes inducing strong T cell responses against various and conserved regions of HIV-1 was selected. A DNA vaccine was designed to express them as a unique antigen with or without a three amino acid ARY extension flanking each epitope. The spectrum of CD8 T responses generated by polyepitope constructs was tested in HLA-B7 transgenic mice. RESULTS: Five new epitopes were identified in accessory and regulatory HIV-1 proteins. Twelve HLA-B07.02-restricted epitopes were selected on the basis of their structural conservation and cross-reactive immunogenicity. The ARY N-terminal extension flanking each epitope markedly increases their affinity for TAP and the use of this flanking extension in polyepitope vaccine has a sizable advantage to induce CD8 T cell cytotoxic responses in mice following DNA immunization. CONCLUSION: The HLA-B7 mouse model allows to rapidly identify various HIV-1-derived epitopes of vaccine interest. Grouped in a polyepitope construct designed to increase their processing, this vaccine may be suitable for inducing multiple and relevant HIV-1-specific CTL responses in humans.

Immunosuppressive effect of angiotensin receptor blocker on stimulation of mice CTLs by angiotensin II.

While angiotensin II, which is produced by the renin-angiotensin-aldosterone system, is considered to be the major regulator molecule that controls both the blood pressure and fluid system, there is an increasing body of evidence that this bioactive peptide and its receptor might also contribute to the immune system. However, there are few details known about the direct effect that angiotensin type I receptors (AT1R) have on the cytotoxic T cell (CTL). To clarify the relationship between angiotensin II and its CTL receptor, we used murine splenic and antigen-specific CTLs. Murine CTLs constantly expressed AT1R, with the activation of the AT1R expression strengthened by both anti-CD3 Ab and the use of an antigen-specific methodology. Moreover, the production of IFN-gamma and TNF-alpha through CTL stimulation can be inhibited by the selective AT1R inhibitor, Losartan. In particular, the TNF-alpha production from activated CTL that had been magnified by angiotensin II, was nullified by the AT1R inhibitor. However, a cytotoxic assay indicated it did not have any effect on the cognate interaction of the CTLs. In addition, the antigen-specific CTL induction by immunization with the CTL antigenic peptide was reduced by angiotensin II type 1 receptor blocker (ARB) in vivo. These findings suggest that ARBs might have the ability to suppress excessive antigen-specific activation and induction of CTLs promoted by angiotensin II.

Role of class I human leukocyte antigen molecules in early steps of echovirus infection of rhabdomyosarcoma cells.

Several echoviruses use decay accelerating factor (DAF) as a cell surface receptor. However, most of them require additional cell surface coreceptors. We investigated the respective roles of DAF and class I human leukocyte antigen (HLA) molecules in the early steps of the echovirus 11 (EV11) lifecycle in rhabdomyosarcoma (RD) cells. EV11 infection was inhibited at an early stage by anti-beta2-microglobulin (beta2m) and anti-HLA monoclonal antibodies and by a soluble monochain HLA class I molecule. Expression of class I HLA molecules restored the early steps of the EV11 lifecycle, but its expression was not sufficient for EV11 replication and particle production. Expression of HLA class I molecules was associated with leukocyte cell line permissiveness to EV11 infection. In conclusion, HLA class I molecules are involved in the early steps of EV11 infection of RD cells and appear to participate in a complex interplay of surface molecules acting as coreceptors, including DAF.

An SV40 VP1-derived epitope recognized by CD8+ T cells is naturally processed and presented by HLA-A*0201 and cross-reactive with human polyomavirus determinants.

The CD8+ T cell responses directed toward the VP1 antigens of human polyomaviruses JC and BK recently were shown to be cross-reactive. Two HLA-A0201-restricted determinants from each virus have been defined and include JCp100-108 (ILMWEAVTL) and BKp108-116 (LLMWEAVTV) as well as JCp36-44 (SITEVECFL) and BKp44-52 (AITEVECFL). We asked whether VP1 from the related SV40 contains similar HLA-A0201-restricted determinants. In this study, we demonstrate that CD8+ T cells specific for SV40 VP1 p110-118 (ILMWEAVTV), but not p46-54 (SFTEVECFL), can be induced in HLA-A0201-transgenic mice and that these CD8+ T cells cross-react with the corresponding determinants from JC and BK virus. The SV40 p110 determinant was found to be processed and presented in SV40-infected cells. These results indicate that the JCp36/BKp44 determinants are distinctive for the human polyomaviruses while the JCp100/BKp108/SVp110 determinants are shared by all three viruses, providing a target for CD8+ T cell cross-reactivity.

A polyepitope DNA vaccine targeted to Her-2/ErbB-2 elicits a broad range of human and murine CTL effectors to protect against tumor challenge.

A cDNA vaccine (pVax1/pet-neu) was designed to encode 12 different Her-2/ErbB-2-derived, HLA-A*0201-restricted dominant and high-affinity heteroclitic cryptic epitopes. Vaccination with pVax1/pet-neu triggered multiple and ErbB-2-specific CTL responses in HLA-A*0201 transgenic HHD mice and in HLA-A*0201 healthy donors in vitro. Human and murine CTL specific for each one of the 12 ErbB-2 peptides recognized in vitro both human and murine tumor cells overexpressing endogenous ErbB-2. Furthermore, vaccination of HHD mice with pVax1/pet-neu significantly delayed the in vivo growth of challenged ErbB-2-expressing tumor (EL4/HHD/neu murine thymoma) more actively when compared with vaccination with the empty vector (pVax1) or vehicle alone. These data indicate that the pVax1/pet-neu cDNA vaccine coding for a poly-ErbB-2 epitope is able to generate simultaneous ErbB-2-specific antitumor responses against dominant and cryptic multiple epitopes.

HAGE, a cancer/testis antigen with potential for melanoma immunotherapy: identification of several MHC class I/II HAGE-derived immunogenic peptides.

There remains a need to identify novel epitopes of potential tumour target antigens for use in immunotherapy of cancer. Here, several melanoma tissues and cell lines but not normal tissues were found to overexpress the cancer-testis antigen HAGE at the mRNA and protein level. We identified a HAGE-derived 15-mer peptide containing a shorter predicted MHC class I-binding sequence within a class II-binding sequence. However, only the longer peptide was found to be both endogenously processed and immunogenic for T cells in transgenic mice in vivo, as well as for human T cells in vitro. A different class I-binding peptide, not contained within a longer class II sequence, was subsequently found to be both immunogenic and endogenously processed in transgenic mice, as was a second class II epitope. These novel HAGE-derived epitopes may contribute to the range of immunotherapeutic targets for use in cancer vaccination programs.

Induction of multiple CD8+ T cell responses against the inducible Hsp70 employing an Hsp70 oligoepitope peptide.

The inducible heat shock protein Hsp70 has been described as a tumour antigen being frequently overexpressed in tumours of various histologic origins, with a role in tumourigenicity, as a critical event in tumour progression. A strategy to enhance the immune response to an antigen is the identification of multiple epitopes and the induction of a polyspecific response. Applied to tumour vaccination, such a polyspecific response should lead to a more robust antitumour efficacy. The long peptide Hsp70380-402 encompasses three nonamer peptides with a high affinity for HLA-A *0201. In a previous paper, we have shown that two of these nonamer peptides, p391 and p393, can raise CTL to recognize tumour cells overexpressing Hsp70. In the present paper, we demonstrate that the third nonamer peptide, p380, is a new epitope efficient in raising an antitumour immune response. The p380-402 polypeptide was able to induce an immune response against each of the three constituent epitopes both in vivo in HLA-A *0201 transgenic mice and in vitro with human PBMC. This polypeptide therefore constitutes an interesting candidate for the induction of multiple HLA-A *0201-restricted anti-Hsp70 antitumour CTL responses.

Expression of iron transport proteins divalent metal transporter-1, Ferroportin-1, HFE and transferrin receptor-1 in human monocyte-derived dendritic cells.

Iron is essential for cell survival and regulates many cell functions. In the context of the immune response, iron-related metabolism is tightly controlled in activated lymphocytes as well as in cells of the innate immunity. More precisely, for dendritic cells (DCs), which are the key cell type in the development of a specific immune response, the importance of iron absorption was recently unravelled by showing that depletion of iron inhibits the maturation of DCs. On this basis, we studied in detail the expression of iron transport proteins and HFE in DCs. We found that iron uptake in this cell type is mediated by divalent-metal transporter 1 (DMT1) and transferrin receptor-1 (TfR) whereas Ferroportin-1 is very weakly expressed. HFE that regulates TfR's activity is also detected at the mRNA level. The expression of DMT1 and HFE barely varies upon endotoxin-induced maturation but TfR is up-regulated and the iron export molecule Ferroportin-1 is down-regulated. As opposed to MHC class II molecules, the intracellular localization of TfR is not changed during maturation. Our results indicate that the uptake of iron during DCs development and maturation is mediated by a strong expression of iron-uptake molecules such as DMT1 and TfR as well as a down-regulation of iron export molecules such as Ferroportin-1.

Identification of novel HLA-DR1-restricted epitopes from the hepatitis B virus envelope protein in mice expressing HLA-DR1 and vaccinated human subjects.

Helper T lymphocytes that control CD8(+) T-cell and antibody responses are key elements for the resolution of infection by the hepatitis B virus and for the development of effective immunological memory after hepatitis B vaccination. We have used H-2 class II-deficient mice that express the human MHC class II molecule, HLA-DR1, to identify novel hepatitis B virus envelope-derived T helper epitopes. We confirmed the immunogenicity of a previously described HLA-DR1-restricted epitope, and identified three novel epitopes. CD4(+) T-cell immune responses against these epitopes were detected in peripheral blood mononuclear cells from HLA-DR1(+) individuals vaccinated against hepatitis B. We showed that subjects receiving the currently available hepatitis B vaccines do not develop cross-reactive T helper responses against one of the novel epitopes which are structurally variable between different hepatitis B virus subtypes. These findings highlight the need for developing vaccines against a wider range of viral subtypes, and establish humanized mice as a convenient tool for identifying new immunogenic epitopes from pathogens.

STEAP, a prostate tumor antigen, is a target of human CD8+ T cells.

STEAP is a recently identified protein shown to be particularly overexpressed in prostate cancer and also present in numerous human cancer cell lines from prostate, pancreas, colon, breast, testicular, cervical, bladder and ovarian carcinoma, acute lymphocytic leukemia and Ewing sarcoma. This expression profile renders STEAP an appealing candidate for broad cancer immunotherapy. In order to investigate if STEAP is a tumor antigen that can be targeted by specific CD8(+) T cells, we identified two high affinity HLA-A*0201 restricted peptides (STEAP(86-94) and STEAP(262-270)). These peptides were immunogenic in vivo in HLA-A*0201 transgenic HHD mice. Peptide specific murine CD8 T cells recognized COS-7 cells co-transfected with HHD (HLA-A*0201) and STEAP cDNA constructs and also HLA-A*0201(+) STEAP(+) human tumor cells. Furthermore, STEAP(86-94) and STEAP(262-270) stimulated specific CD8(+) T cells from HLA-A*0201(+) healthy donors, and these peptide specific CD8(+) T cells recognized STEAP positive human tumor cells in an HLA-A*0201-restricted manner. Importantly, STEAP(86-94)-specific T cells were detected and reactive in the peripheral blood mononuclear cells in NSCLC and prostate cancer patients ex vivo. These results show that STEAP can be a target of anti-tumor CD8(+) T cells and that STEAP peptides can be used for a broad-spectrum-tumor immunotherapy.

Determination of cellularly processed HLA-A2402-restricted novel CTL epitopes derived from two cancer germ line genes, MAGE-A4 and SAGE.

PURPOSE: For identification of CTL epitopes useful for cancer vaccines, it is crucial to determine whether cognate epitopes are presented on the cell surface of target cancer cells through natural processing of endogenous proteins. For this purpose, we tried to use the cellular machinery of both mice and human to define naturally processed CTL epitopes derived from two "cancer germ line" genes, MAGE-A4 and SAGE. EXPERIMENTAL DESIGN: We vaccinated newly produced HLA-A2402 transgenic mice with DNA plasmids encoding target antigens. Following screening of synthesized peptides by splenic CD8(+) T cells of vaccinated mice, we selected candidate epitopes bound to HLA-A2402. We then examined whether human CD8(+) T cells sensitized with autologous CD4(+) PHA blasts transduced by mRNA for the cognate antigens could react with these selected peptides in an HLA-A2402-restricted manner. RESULTS: After DNA vaccination, murine CD8(+) T cells recognizing MAGE-A4(143-151) or SAGE(715-723) in an HLA-A2402-restricted manner became detectable. Human CTLs specific for these two peptides were generated after sensitization of HLA-A2402-positive CD8(+) T cells with autologous CD4(+) PHA blasts transduced with respective mRNA. CTL clones were cytotoxic toward tumor cell lines expressing HLA-A2402 and cognate genes. Taken together, these CTL epitopes defined in HLA-A24 transgenic mice are also processed and expressed with HLA-A2402 in human cells. The presence of SAGE(715-723)-specific precursors was observed in HLA-A2402-positive healthy individuals. CONCLUSIONS: Two novel HLA-A2402-restricted CTL epitopes, MAGE-A4(143-151) and SAGE(715-723), were identified. Our approach assisted by cellular machinery of both mice and human could be widely applicable to identify naturally processed CTL epitopes.

A single amino acid substitution improves the in vivo immunogenicity of the HPV16 oncoprotein E7(11-20) cytotoxic T lymphocyte epitope.

One of the few and most extensively studied human papilloma virus (HPV) type 16 oncoprotein E7-derived cytotoxic T lymphocyte (CTL) epitopes is YMLDLQPETT, presented to CTL by HLA-A2.1. We previously identified an altered peptide ligand (APL) of this epitope with increased binding affinity for HLA-A2.1, YMLDLQPETV. Herein, the in vivo immunogenicity of this APL was investigated in HLA-A2.1 transgenic HHD mice. Both in vitro and direct ex vivo analysis, performed using newly generated HHD tetramers, showed a significant increase in the number of specific CD8+ T cells upon vaccination with the APL as compared to its unmodified counterpart. Improved immunogenicity of the APL was also observed in functional analyses, including antigen-specific lytic activity and cytokine production of primed CD8+ T cells. Consequently, the YMLDLQPETV peptide may prove useful when included in vaccination strategies against HPV16-induced cervical carcinoma.

Enhanced multiepitope-based vaccines elicit CD8+ cytotoxic T cells against both immunodominant and cryptic epitopes.

A frequent issue in vaccinology is to elicit balanced T cell responses against both immunodominant and cryptic T cell epitopes, from one or several antigens presented at the same time to the immune system. Using HLA-A2.1.1 restricted epitopes from the Melan A/MART-1 or gp 100 melanoma-associated antigens as a model, we engineered a series of constructs in the ALVAC canarypox vector system: T cell epitopes were expressed either as linear polyepitopes (with or without spacers), or as minigenes encoding a single epitope. The latter were found to allow the best processing and presentation of most T cell epitopes, following infection by ALVAC recombinants of the HLA A2+ bladder carcinoma cell line and stimulation of epitope-specific human TIL lines. These various constructs were also used to immunize HLA-A2.1.1 HHD transgenic mice to compare their capacity to elicit T cells responses. Polyepitopes but also minigenes encoding wild-type epitopes could not elicit in a reliable manner balanced CTL responses against all target epitopes from gp100. We could rescue T cells responses against poorly immunogenic epitopes after introducing appropriate point mutations to enhance their interaction with MHC Class I molecules. Epitope enhancement within either polyepitope, multiepitopes (i.e. minigenes expressed under the control of separate promoters) or full length immunogens should be systematically considered when designing vaccines containing both cryptic and immunodominant target epitopes.

The non-classical HLA class I molecule HFE does not influence the NK-like activity contained in fresh human PBMCs and does not interact with NK cells.

In humans, four beta2-microglobulin-associated non-classical class I molecules are encoded in the MHC: HLA-E, -F, -G and -H. Three of them (HLA-E, -F and -G) were shown to inhibit NK activity. On the contrary, the fourth one, HLA-H, named HFE after it was found to be mutated in patients suffering from inherited hemochromatosis, has been shown to be involved only in the regulation of iron uptake. We tested the capacity of HFE to affect (enhance or reduce) specifically the NK activity contained in non-manipulated fresh human PBMCs. We showed that HFE expression by target cells does not affect their killing by the NK-like activity contained in PBMCs. Moreover, using fluorescent HFE tetramers, we could confirm that blood NK cells as well as blood gammadelta T cells do not bind HFE. Altogether, our data indicate that HFE does not affect the NK activity contained in the PBMCs.