A2-restricted Epitopes Research Articles

HLA-A2-Restricted Epitopes Identified from MTA1 Could Elicit Antigen-Specific Cytotoxic T Lymphocyte Response.

Overexpression of metastasis-associated protein 1 (MTA1) has been observed in many human malignancies and is significantly related to tumor invasion and metastasis, therapeutic resistance to radiation and chemotherapy, making MTA1 an ideal candidate tumor antigen. We identified several human leukocyte antigen- (HLA-) A2-restricted epitopes in MTA1 and evaluated their binding ability to HLA-A∗0201 molecules. Subsequently, a recombinant fragment encompassing the dominant epitopes, MTA1(1–283), was expressed, and the abilities of the selected epitopes of MTA1 and the MTA1(1–283) fragment to induce cytotoxic T lymphocytes (CTLs) were examined. Our results indicated that the epitopes and MTA1(1–283) fragment elicited HLA-A2-restricted and antigen-specific CTL responses both in vitro and in vivo. The new epitopes identified here may help promote the development of new therapeutic vaccines for HLA-A2+ patients expressing MTA1.

Abstract A51: High-throughput method identifies rare, high-affinity, thymus-vetted T cell receptors (TCRs) for clinical translation

Abstract Adoptive T cell therapy is a promising therapeutic approach with the potential to eradicate otherwise incurable cancers. Through T cell receptor (TCR) gene therapy, donor- or patient-derived T cells can be reprogrammed to recognize tumor-associated antigens (Ags); the ability of these engineered T cells to eliminate tumor cells is largely dictated by the affinity of the transferred TCR. As thymic selection eliminates T cells with high avidity for self, most tumor-reactive T cells in the native repertoire have limited antitumor efficacy. While TCRs can be mutated to enhance affinity, such TCRs carry the clinically-validated risk of off-target or on-target/off-tissue toxicity. Therefore, one of the key challenges of T cell-based immunotherapies is to identify TCRs with sufficient affinity to mediate effective anti-tumor activity without compromising safety. Based on the premise that a wide variability in thymus-vetted, tumor/self antigen-specific T cell avidity exists among individuals, we established a high-throughput method to simultaneously affinity rank and quickly retrieve the highest affinity TCRs from any number of pooled matched donors. We hypothesized high-affinity clonotypes would be preferentially enriched by binding to limiting concentrations of antigen-specific peptide/major histocompatibility complex (pMHC) multimers, such that TCR clonotype enrichment under increasingly stringent conditions would identify the highest affinity TCRs from within heterogenous T cell populations. Using this approach, we isolated TCRs specific for HLA A2-restricted epitopes of over-expressed self Ags (Wilms’ Tumor Antigen 1 [WT1], Mesothelin, Melanoma Antigen Recognized by T cells 1 [MART1]), cancer testis (CT) Ags (Melanoma-associated antigen 1 [MAGE A1]), as well as for viruses, including HIV and the Merkel cell polyoma virus. High-throughput TCRα/β chain pairing was obtained by PairedSeq (Adaptive Biotechnologies) or by single-cell sequencing (10X Genomics). Our results show that 1) clonotype Enrichment Ratios positively correlated with TCR affinity, thus validating our method; 2) the highest affinity T cell clones targeting self-Ags (but not viral Ags) were present at very low frequencies in native TCR repertoires, suggesting impaired antigen-driven expansion in vitro and precluding detection by conventional cloning methods; 3) many of the highest-affinity TCRs targeting viral, CT or self Ags bound pMHC complexes independent of CD8 co-receptor, confirming that tumor/self Ag-specific T cells are not entirely deleted by negative selection in healthy donors; and 4) select class I TCRs thus identified activated CD4+ (class II HLA-restricted) T cells to produce cytokines and lyse cells expressing cognate antigen. This method is poised to rapidly (~6 weeks) identify for clinical translation rare, native, high-affinity tumor-reactive TCRs with the potential to engage CD4+ T cells and enhance anti-tumor CD8+ T cell activity, but that have a low likelihood of off-target toxicity. Citation Format: Thomas M. Schmitt, Megan McAfee, Harlan Robins, Lara Kropp, Philip D. Greenberg, Aude G. Chapuis. High-throughput method identifies rare, high-affinity, thymus-vetted T cell receptors (TCRs) for clinical translation [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A51.

Dual Molecular Mechanisms Govern Escape at Immunodominant HLA A2-Restricted HIV Epitope.

Serial accumulation of mutations to fixation in the SLYNTVATL (SL9) immunodominant, HIV p17 Gag-derived, HLA A2-restricted cytotoxic T lymphocyte epitope produce the SLFNTIAVL triple mutant “ultimate” escape variant. These mutations in solvent-exposed residues are believed to interfere with TCR recognition, although confirmation has awaited structural verification. Here, we solved a TCR co-complex structure with SL9 and the triple escape mutant to determine the mechanism of immune escape in this eminent system. We show that, in contrast to prevailing hypotheses, the main TCR contact residue is 4N and the dominant mechanism of escape is not via lack of TCR engagement. Instead, mutation of solvent-exposed residues in the peptide destabilise the peptide–HLA and reduce peptide density at the cell surface. These results highlight the extraordinary lengths that HIV employs to evade detection by high-affinity TCRs with a broad peptide-binding footprint and necessitate re-evaluation of this exemplar model of HIV TCR escape.

Glypican-3-specific cytotoxic T lymphocytes induced by human leucocyte antigen-A*0201-restricted peptide effectively kill hepatocellular carcinoma cells in vitro

To investigate potential human leucocyte antigen (HLA)-A2-restricted epitope peptides of glypican-3 (GPC3) and determine the cytotoxicity of peptide-specific cytotoxic T lymphocytes (CTLs) against hepatocellular carcinoma (HCC) cells. The potential HLA-A*0201-restricted GPC3 peptides were screened using computer algorithms, T2 cell-binding affinity and stability of peptide/HLA-A*0201 complex assay. The peptide-specific CTLs were generated and their cytotoxicity against GPC3+ SMMC 7721 and HepG2 cells was detected using IFN-γ based enzyme-linked immunospot and lactate dehydrogenase release assays invitro. A total of six peptides were identified for bindings to HAL-A2 and the GPC3 522-530 and GPC3 229-237 peptides with HLA-A*0201 molecules displayed high binding affinity and stability. The CTLs induced by the GPC3 522-530 or positive control GPC3 144-152 peptide responded to the peptide by producing IFN-γ, which were abrogated by treatment with anti-HLA-A2 antibody. The GPC3 522-530-specific CTLs responded to and killed SMMC 7721 and HepG2 cells, instead of GPC3-silenced SMMC 7721 or HepG2 cells. GPC3 522-530-specific CTLs response to HCC cells was blocked by anti-HLA-A2 antibody. The GPC3 522-530 peptide contains antigen-determinant and its specific CTLs can effectively kill HCC in a HLA-A2-restricted and peptide-dependent manner. Our findings suggest that this peptide may be valuable for development of therapeutic vaccine.

HLA-Restricted CTL That Are Specific for the Immune Checkpoint Ligand PD-L1 Occur with High Frequency in Cancer Patients

PD-L1 (CD274) contributes to functional exhaustion of T cells and limits immune responses in patients with cancer. In this study, we report the identification of an human leukocyte antigen (HLA)-A2-restricted epitope from PD-L1, and we describe natural, cytolytic T-cell reactivity against PD-L1 in the peripheral blood of patients with cancer and healthy individuals. Notably, PD-L1-specific T cells were able not only to recognize and kill tumor cells but also PD-L1-expressing dendritic cells in a PD-L1-dependent manner, insofar as PD-L1 ablation rescued dendritic cells from killing. Furthermore, by incubating nonprofessional antigen-presenting cells with long peptides from PD-L1, we found that PD-L1 was rapidly internalized, processed, and cross-presented by HLA-A2 on the cell surface. Apparently, this cross-presentation was TAP-independent, as it was conducted not only by B cells but in addition by TAP-deficient T2-cells. This is intriguing, as soluble PD-L1 has been detected in the sera from patients with cancer. PD-L1-specific CTL may boost immunity by the killing of immunosuppressive tumor cells as well as regulatory cells. However, PD-L1-specific CTLs may as well suppress immunity by the elimination of normal immune cells especially PD-L1 expressing mature dendritic cells.

Abstract A7: TARP-TCR-engineered T cells specifically kill HLA-A2 positive prostate and breast cancer cells.

Abstract In order to produce genetically engineered T cells directed against prostate and breast cancer cells we have cloned the T cell receptor recognizing the human leukocyte antigen (HLA)-A2-restricted TARP4-13 epitope. TARP is a protein exclusively expressed in normal prostate epithelium and in adenocarcinomas of the prostate and breast. Peripheral blood T cells transduced with a lentiviral vector encoding the TARP-TCR proliferated well when exposed to peptide-specific stimuli. They exerted peptide-specific interferon-γ production and cytotoxic activity. Importantly, HLA-A2+ prostate and breast cancer cells expressing TARP were also killed, demonstrating that the TARP4-13 epitope is a physiologically relevant target for T cell therapy of prostate and breast cancer. In conclusion, we present the cloning of a TCR directed against a physiologically relevant HLA-A2 epitope of TARP. To our knowledge this is the first report on engineering of T cells with a TCR directed against an antigen specifically expressed by prostate cells. Citation Format: Victoria Hillerdal, Berith Nilsson, Bjorn Carlsson, Fredrik Eriksson, Magnus Essand.TARP-TCR-engineered T cells specifically kill HLA-A2 positive prostate and breast cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr A7.

Cyclin-A1 expression in acute myeloid leukemia stem cells and its representation as an immunogenic antigen that can be targeted by cytotoxic T cells.

2523 Background: Targeted T-cell therapy represents a more specific and less toxic alternative to allogeneic stem cell transplantation for providing a cytotoxic anti-leukemic response to eliminate the leukemic stem cell (LSC) compartment in acute myeloid leukemia (AML). The aim of this study was to identify a leukemia-associated antigen that is both immunogenic and exhibits selective high expression in AML LSCs. Methods: Expression microarrays of leukemic and normal cells were used to identify suitable candidate genes. Cyclin-A1 appeared to be differentially expressed, and was further analyzed by quantitative RT-PCR, intracellular FACS staining, and immunofluorescence microscopy. T-cell clones specific for cyclin-A1 were generated by stimulation in vitro with an overlapping peptide library, followed by cloning of responding cells. Specificity of the clones was documented by intracellular IFNg and tetramer staining. Cytotoxicity was determined by chromium release and caspase-3 cleavage assays. Results: To identify target candidates with a suitable expression pattern, microarray data from LSCs, hematopoietic cells and healthy tissues were compared. Cyclin-A1 was found to be selectively expressed in LSCs of >50% of AML patients, but minimally expressed in normal tissues with exception of testis. Using dendritic cells and monocytes pulsed with a cyclin-A1 peptide library, T-cells were generated against eight cyclin-A1 oligopeptides. Two HLA A2-restricted epitopes were further characterized, and specific T-cell clones recognized both peptide-pulsed target cells and the HLA A2-positive AML line THP-1. Furthermore, cyclin-A1-specific CD8 T-cells lysed primary AML cells. Conclusions: Cyclin-A1, known to be important in meiosis, is expressed in AML LSCs and testis and can be targeted by T-cells. Thus, cyclin-A1 is the first prototypic LSC-associated leukemia-testis-antigen. Cyclin-A1 already has been shown to be leukemogenic in mice and to promote proliferation and survival in AML blasts. This pro-oncogenic activity, together with high expression levels and a multitude of immunogenic epitopes, make it a promising target for T-cell based therapy approaches.

Comparison of Human Memory CD8 T Cell Responses to Adenoviral Early and Late Proteins in Peripheral Blood and Lymphoid Tissue

Treatment of invasive adenovirus (Ad) disease in hematopoietic stem cell transplant (SCT) recipients with capsid protein hexon-specific donor T cells is under investigation. We propose that cytotoxic T cells (CTLs) targeted to the late protein hexon may be inefficient in vivo because the early Ad protein E3-19K downregulates HLA class I antigens in infected cells. In this study, CD8+ T cells targeted to highly conserved HLA A2-restricted epitopes from the early regulatory protein DNA polymerase (P-977) and late protein hexon (H-892) were compared in peripheral blood (PB) and tonsils of naturally infected adults. In tonsils, epitope-specific pentamers detected a significantly higher frequency of P-977+CD8+ T cells compared to H-892+CD8+ T cells; this trend was reversed in PB. Tonsil epitope-specific CD8+ T cells expressed IFN-γ and IL-2 but not perforin or TNF-α, whereas PB T cells were positive for IFN-γ, TNF-α, and perforin. Tonsil epitope-specific T cells expressed lymphoid homing marker CCR7 and exhibited lower levels of the activation marker CD25 but higher proliferative potential than PB T cells. Finally, in parallel with the kinetics of mRNA expression, P-977-specific CTLs lysed targets as early as 8 hrs post infection. In contrast, H-892-specific CTLs did not kill unless infected fibroblasts were pretreated with IFN-γ to up regulate HLA class I antigens, and cytotoxicity was delayed until 16–24 hours. These data show that, in contrast to hexon CTLs, central memory type DNA polymerase CTLs dominate the lymphoid compartment and kill fibroblasts earlier after infection without requiring exogenous IFN-γ. Thus, use of CTLs targeted to both early and late Ad proteins may improve the efficacy of immunotherapy for life-threatening Ad disease in SCT recipients.

EDDR1 is a Potential Immunotherapeutic Antigen in Ovarian, Breast, and Prostate Cancer

Selection of suitable antigens, preferably targets for cell mediated and humoral immune response is a critical step in the development of cancer vaccines. Cell surface proteins that are over-expressed in cancer cells thus constitute a very attractive class of antigens that can be targeted for effective cancer immunotherapy. Toward this goal, we characterized the relevance of Epithelial Discoidin Domain Receptor 1 (EDDR1) for such targeted therapeutics. EDDR1, a membrane expressed protein associated with adhesion, has recently emerged as a new therapeutic target in several tumor types. In the present study, we analyzed the expression profile of EDDR1 in a variety of normal and cancer cells of human origin by flow cytometry as well as immunohistochemistry. EDDR1 was found to be abundantly expressed on the surface of ovarian, prostate and breast cancer cells but not on the normal counterparts, making it a suitable candidate for antibody mediated therapy. Furthermore, a Human Leukocyte Antigen (HLA) A2-restricted epitope derived from EDDR1 was efficiently presented by various cancer cells to EDDR1 epitope-specific T cells. Collectively, our data present evidence that EDDR1 could be a potential target antigen for immunotherapy.

ADAM metallopeptidase domain 17 (ADAM17) is naturally processed through major histocompatibility complex (MHC) class I molecules and is a potential immunotherapeutic target in breast, ovarian and prostate cancers

Selection of suitable antigens is critical for the development of cancer vaccines. Most desirable are over-expressed cell surface proteins that may serve as targets for both antibodies and T cells, thus maximizing a concerted immune response. Towards this goal, we characterized the relevance of tumour necrosis factor-α-converting enzyme (ADAM17) for such targeted therapeutics. ADAM17 is one of the several metalloproteinases that play a key role in epidermal growth factor receptor (EGFR) signalling and has recently emerged as a new therapeutic target in several tumour types. In the present study, we analysed the expression profile of ADAM17 in a variety of normal and cancer cells of human origin and found that this protein is over-expressed on the surface of several types of cancer cells compared to the normal counterparts. Furthermore, we analysed the presentation of a human leucocyte antigen (HLA)-A2-restricted epitope from ADAM17 protein to specific T cells established from normal donors as well as ovarian cancer patients. Our analysis revealed that the HLA-A2-restricted epitope is processed efficiently and presented by various cancer cells and not by normal cells. Tumour-specific T cell activation results in the secretion of both interferon-γ and granzyme B that can be blocked by HLA-A2 specific antibodies. Collectively, our data present evidence that ADAM17 can be a potential target antigen to devise novel immunotherapeutic strategies against ovarian, breast and prostate cancer.

Vaccine generated immunity targets an HPV16 E7 HLA-A2.1-restricted CD8+ T cell epitope relocated to an early gene or a late gene of the cottontail rabbit papillomavirus (CRPV) genome in HLA-A2.1 transgenic rabbits

The newly established HLA-A2.1 transgenic rabbit model has proven useful for testing the immunogenicity of well known and computer-predicted A2-restricted epitopes. In the current study we compared the protective immunity induced to a preferred HPV16 E7 A2-restricted epitope that has been relocated to positions within the CRPV E7 gene and the CRPV L2 gene. Epitope expression from both the E7 protein and the L2 protein resulted in increased protection against viral DNA challenge of the HLA-A2.1 transgenic rabbits as compared to control-vaccinated rabbit groups. These data indicate that proteins expressed at both early and late time points during a natural papillomavirus infection can be targeted by epitope-specific immunity and indicate this immunity is increased to early rather than late expressed proteins of papillomaviruses. This study also highlights the broad utility of the HLAA2.1 transgenic rabbit model for testing numerous immunological factors involved in vaccine generated protective immunity.

Processing and cross-presentation of individual HLA-A, -B, or -C epitopes from NY-ESO-1 or an HLA-A epitope for Melan-A differ according to the mode of antigen delivery

AbstractThe ability of dendritic cells (DCs) to cross-present protein tumor antigens to cytotoxic T lymphocytes (CTLs) underpins the success of therapeutic cancer vaccines. We studied cross-presentation of the cancer/testis antigen, NY-ESO-1, and the melanoma differentiation antigen, Melan-A by human DC subsets. Monocyte-derived DCs (MoDCs) efficiently cross-presented human leukocyte associated (HLA)–A2-restricted epitopes from either a formulated NY-ESO-1/ISCOMATRIX vaccine or when either antigen was mixed with ISCOMATRIX adjuvant. HLA-A2 epitope generation required endosomal acidification and was proteasome-independent for NY-ESO-1 and proteasome-dependent for Melan-A. Both MoDCs and CD1c+ blood DCs cross-presented NY-ESO-1–specific HLA-A2157-165–, HLA-B760-72–, and HLA-Cw392-100–restricted epitopes when formulated as an NY-ESO-1/ISCOMATRIX vaccine, but this was limited when NY-ESO-1 and ISCOMATRIX adjuvant were added separately to the DC cultures. Finally, cross-presentation of NY-ESO-1157-165/HLA-A2, NY-ESO-160-72/HLA-B7, and NY-ESO-192-100/HLA-Cw3 epitopes was proteasome-dependent when formulated as immune complexes (ICs) but only proteasome-dependent for NY-ESO-160-72/HLA-B7–restricted cross-presentation facilitated by ISCOMATRIX adjuvant. We demonstrate, for the first time, proteasome-dependent and independent cross-presentation of HLA-A–, B–, and C–restricted epitopes within the same full-length tumor antigen by human DCs. Our findings identify important differences in the capacities of human DC subsets to cross-present clinically relevant, full-length tumor antigens and how vaccine formulation impacts CTL responses in vivo.

MM–GBSA binding free energy decomposition and T cell receptor engineering

Recognition by the T-cell receptor (TCR) of immunogenic peptides (p) presented by class I major histocompatibility complexes (MHC) is the key event in the immune response against virus infected cells or tumor cells. The major determinant of T cell activation is the affinity of the TCR for the peptide-MHC complex, though kinetic parameters are also important. A study of the 2C TCR/SIYR/H-2Kb system using a binding free energy decomposition (BFED) based on the MM-GBSA approach had been performed to assess the performance of the approach on this system. The results showed that the TCR-p-MHC BFED including entropic terms provides a detailed and reliable description of the energetics of the interaction (Zoete and Michielin, 2007). Based on these results, we have developed a new approach to design sequence modifications for a TCR recognizing the human leukocyte antigen (HLA)-A2 restricted tumor epitope NY-ESO-1. NY-ESO-1 is a cancer testis antigen expressed not only in melanoma, but also on several other types of cancers. It has been observed at high frequencies in melanoma patients with unusually positive clinical outcome and, therefore, represents an interesting target for adoptive transfer with modified TCR. Sequence modifications of TCR potentially increasing the affinity for this epitope have been proposed and tested in vitro. T cells expressing some of the proposed TCR mutants showed better T cell functionality, with improved killing of peptide-loaded T2 cells and better proliferative capacity compared to the wild type TCR expressing cells. These results open the door of rational TCR design for adoptive transfer cancer therapy.

Dependence of T Cell Antigen Recognition on T Cell Receptor-Peptide MHC Confinement Time

SummaryT cell receptor (TCR) binding to diverse peptide-major histocompatibility complex (pMHC) ligands results in various degrees of T cell activation. Here we analyze which binding properties of the TCR-pMHC interaction are responsible for this variation in pMHC activation potency. We have analyzed activation of the 1G4 cytotoxic T lymphocyte clone by cognate pMHC variants and performed thorough correlation analysis of T cell activation with 1G4 TCR-pMHC binding properties measured in solution. We found that both the on rate (kon) and off rate (koff) contribute to activation potency. Based on our results, we propose a model in which rapid TCR rebinding to the same pMHC after chemical dissociation increases the effective half-life or “confinement time” of a TCR-pMHC interaction. This confinement time model clarifies the role of kon in T cell activation and reconciles apparently contradictory reports on the role of TCR-pMHC binding kinetics and affinity in T cell activation.

Natural epitope variants of the hepatitis C virus impair cytotoxic T lymphocyte activity

To understand how interactions between hepatitis C virus (HCV) and the host's immune system might lead to viral persistence or effective elimination of HCV. Nucleotides 3519-3935 of the non-structural 3 (NS3) region were amplified by using reverse transcription polymerase chain reaction (PCR). PCR products of the HCV NS3 regions were integrated into a PCR((R)) T7TOPO((R)) TA vector and then sequenced in both directions using an automated DNA sequencer. Relative major histocompatibility complex binding levels of wild-type and variant peptides were performed by fluorescence polarization-based peptide competition assays. Peptides with wild type and variant sequences of NS3 were synthesized locally using F-moc chemistry and purified by high-performance liquid chromatography. Specific cytotoxic T lymphocytes (CTLs) clones toward HCV NS3 wild-type peptides were generated through limiting dilution cloning. The CTL clones specifically recognizing HCV NS3 wild-type peptides were tested by tetramer staining and flow cytometry. Cytolytic activity of CTL clones was measured using target cells labeled with the fluorescence enhancing ligand, DELFIA EuTDA. The pattern of natural variants within three human leukocyte antigen (HLA)-A2-restricted NS3 epitopes has been examined in one patient with chronic HCV infection at 12, 28 and 63 mo post-infection. Results obtained may provide convincing evidence of immune selection pressure for all epitopes investigated. Statistical analysis of the extensive sequence variation found within these NS3 epitopes favors a Darwinian selection model of variant viruses. Mutations within the epitopes coincided with the decline of CTL responses, and peptide-binding studies suggested a significant impact of the mutation on T cell recognition rather than peptide presentation by HLA molecules. While most variants were either not recognized or elicited low responses, such could antagonize CTL responses to target cells pulsed with wild-type peptides. Cross-recognition of CTL epitopes from wild-type and naturally-occurring HCV variants may lead to impaired immune responses and ultimately contribute to viral persistence.

Melan-A/MART1 Analog Peptide Triggers Anti-myeloma T-cells Through Crossreactivity With HM1.24

The Melan-A(aa26-35) (EAAGIGILTV) peptide is a human leukocyte antigen (HLA)-A2-restricted T-cell epitope within the Melan-A/MART-1 tumor antigen expressed on malignant melanoma cells. Melan-A and Melan-A analog (ELAGIGILTV, Melan-A(aa26-35*A27L)) specific T-cells can be expanded reliably for immunotherapeutic approaches in vitro. We studied the ability of Melan-A analog (ELAGIGILTV, Melan-A(aa26-35*A27L)) specific T-cells to recognize the HM1.24(aa22-30) (LLLGIGILV) peptide within the HM1.24 antigen presented by normal and malignant plasma cells. Peripheral blood mononuclear cells from HLA-A2+ healthy donors and HLA-A2+ multiple myeloma (MM) patients were stimulated with Melan-A analog peptide-loaded autologous dendritic cells, and expanded in vitro. T-cell activation was assessed by interferon-gamma specific enzyme-linked immunosorbent spot and cytotoxicity by (51)Chromium-release-assays. The frequency of Melan-A analog specific CD8+ T-cells was detected by using tetramers. Melan-A analog specific T-cells from HLA-A2+ healthy donors and HLA-A2+ MM patients showed a interferon-gamma secretion mediated by HM1.24(aa22-30) peptide-pulsed T2 cells and lysed the HLA-A2+ HM1.24+ U266 and XG-1 human myeloma derived cell-lines as well as the B-lymphoblastoid cell-line IM-9. Melan-A analog specific T-cells from MM patients specifically lysed autologous MM cells. The current data demonstrate that Melan-A analog specific T-cells crossreact with HM1.24(aa22-30). They might be a tool for the future use in immunotherapy against MM.

Induction of Multiepitopic and Long‐Lasting Immune Responses Against Tumour Antigens by Immunization with Peptides, DNA and Recombinant Adenoviruses Expressing Minigenes

The development of immunization strategies to induce strong and multiepitopic T-cell responses against tumour antigens is needed for anti-tumour immunotherapy. However, a common finding after immunization with complex antigens is the preferential induction of immune responses against immunodominant epitopes. In this study, with the aim of inducing multiepitopic responses against several common tumour antigens, we have designed a minigene construct encoding four human leucocyte antigen (HLA)-A2-restricted epitopes belonging to tumour antigens CEA (CEA-691 and CEA-571), MAGE2 (MAGE2-157) and MAGE3 (MAGE3-112), as well as the universal PADRE epitope recognized by T helper lymphocytes. To optimize the activation of immune responses against these epitopes, we have used different antigen formats (short peptides encompassing individual epitopes and DNA plasmids or adenoviral constructs expressing the minigene) in single or combined immunization schedules. A single immunization with either DNA plasmid or recombinant adenovirus induced a monospecific immune response against the immunodominant epitope CEA-571, whereas immunization with the peptide pool induced responses against all epitopes. Combination of peptide priming followed by a boost with the plasmid and the recombinant adenovirus expressing the minigene induced stronger, multi-specific and long-lasting immune responses, overcoming the immunodominance imposed by the main T-cell epitope. Moreover, these combined immunization strategies were able to induce responses that were able to recognize Mel624 HLA-A2+ tumour cells expressing MAGE2. These results suggest that heterologous immunization strategies combining peptides and DNA or recombinant adenoviruses can be useful to broaden the specificity and enhance the efficacy of subunit vaccines.

Cellular and Humoral Immunogenicity of Hamster Polyomavirus-Derived Virus-Like Particles Harboring a Mucin 1 Cytotoxic T-Cell Epitope

In this study, we examined hamster polyomavirus (HaPyV) major capsid protein VP1-derived virus-like particles (VLPs) as a carrier for a human tumor-associated cytotoxic T lymphocyte (CTL) epitope. The VP1 tolerated the insertion of an HLA-*A2-restricted CTL epitope from human mucin 1 (MUC1) into two sites independently and simultaneously, without interfering with assembly of chimeric VLPs. Chimeric VLPs did not differ in the entry pathway or maturation potential of human dendritic cells (hDCs) compared to unmodified VLPs. Recently we demonstrated that immunization of BALB/c mice with chimeric VLPs harboring two MUC1 insertions resulted in the generation of MUC1-specific monoclonal antibodies. Here we demonstrate that the monoclonal antibodies generated react specifically with human tumor cells. Co-cultivation of chimeric VLP-primed hDCs with autologous peripheral blood leukocytes resulted in the activation of MUC1 epitope-specific CD8(+) T cells. This was evidenced by IFN-gamma secretion of an expanded MUC1-specific CD8(+) T-cell pool. The induction of epitope-specific T cells in a human in vitro model and of murine MUC1-reactive antibodies in vivo indicate the potential of chimeric HaPyV VP1-derived VLPs as a delivery vehicle for immunotherapeutic targets.

HCV-Specific T-Cell Response in Relation to Viral Kinetics and Treatment Outcome (DITTO-HCV Project)

The second slope of viral decline induced by interferon treatment has been suggested to be influenced mainly by the hepatitis C virus (HCV)-specific T-cell response; however, this hypothesis needs to be validated by results derived from experimental studies. To address this issue, the HCV-specific T-cell response of 32 genotype-1-infected patients of the 270 patients enrolled in the dynamically individualized treatment of hepatitis C infection and correlates of viral/host dynamics phase III, open-label, randomized, multicenter trial was studied in relation to viral kinetics and treatment outcome. Greater proliferative responses by HCV-specific CD8 cells were found before treatment in patients with a fast viral decline and with a sustained viral response. However, no significant improvement of HCV-specific CD8 responses was observed in the first weeks of therapy in both rapid viral responder and non-rapid viral responder patients. A mild enhancement of proliferative T-cell responses and a partial restoration of the cytotoxic T-cell potential was expressed only late during treatment, likely favored by HCV clearance. Early restoration of an efficient T-cell response does not seem to be an essential requirement for a rapid viral decline in the first weeks of treatment. However, patients presenting a better HCV-specific CD8 cell proliferative potential at baseline are more likely to present a rapid and sustained viral response. Therefore, future treatment protocols should consider the development of strategies aimed at improving HCV-specific T-cell responses.

A Complete Mutational Fitness Map of the Hepatitis C Virus Nonstructural 3 Protease: Relation to Recognition by Cytotoxic T Lymphocytes

The hepatitis C virus nonstructural (NS) 3/4A protease sequence is highly conserved for reasons not fully understood. We determined the protease activity in 181 NS3/4A gene products in which each protease residue was replaced by alanine or glycine. Unexpectedly, most (87%) protease residues could be replaced and protease activity would be retained. Using these data, we were able to identify a human leukocyte antigen A2-restricted epitope in which substitutions at 5 of 9 residues destroyed the protease. The NS3 protease shows an unexpectedly high plasticity, and it is therefore important to identify target sequences in which the appearance of mutations is restricted by viral fitness.