Epitope-specific T-cell Responses Research Articles

Synthetic Self-Adjuvanted Lipopeptide Vaccines Conferred Protection against Helicobacter pylori Infection.

Helicobacter pylori(H. pylori) colonizes the stomach epithelium of half the world's population and is responsible for various digestive diseases and even stomach cancer. Vaccine-mediated protection against H. pylori infection depends primarily on the specific mucosal and T-cell responses. In this study, the synthetic lipopeptide vaccines, Hp4 (Pam2 Cys modified UreB T-cell epitope) and Hp10 (Pam2 Cys modified CagA T/B cell combined epitope), not only induce the bone marrow derived dendritic cells (BMDCs) maturation by activating a variety of pattern-recognition receptors (PRRs) such as Toll-like receptor (TLR), Nod-like receptor (NLR), and retinoic acid-inducing gene (RIG) I-like receptor (RLR), and but also stimulate BMDCs to secret cytokines that have the potential to modulate T-cell activation and differentiation. Although intranasal immunization with Hp4 or Hp10 elicits robust epitope-specific T-cell responses in mice, only Hp10 confers protection against H. pylori infection, possibly due to the fact that Hp10 also induces substantial specific sIgA response at mucosal sites. Interestingly, Hp4 elevates the protective response against H. pylori infection of Hp10 when administrated in combination, characterized by better protective effect and enhanced specific T-cell and mucosal antibody responses. The results suggest that synthetic lipopeptide vaccines based on the epitopes derived from the protective antigens are promising candidates for protection against H. pylori infection.

Clonal diversity predicts persistence of SARS-CoV-2 epitope-specific T-cell response.

T cells play a pivotal role in reducing disease severity during SARS-CoV-2 infection and formation of long-term immune memory. We studied 50 COVID-19 convalescent patients and found that T cell response was induced more frequently and persisted longer than circulating antibodies. We identified 756 clonotypes specific to nine CD8+ T cell epitopes. Some epitopes were recognized by highly similar public clonotypes. Receptors for other epitopes were extremely diverse, suggesting alternative modes of recognition. We tracked persistence of epitope-specific response and individual clonotypes for a median of eight months after infection. The number of recognized epitopes per patient and quantity of epitope-specific clonotypes decreased over time, but the studied epitopes were characterized by uneven decline in the number of specific T cells. Epitopes with more clonally diverse TCR repertoires induced more pronounced and durable responses. In contrast, the abundance of specific clonotypes in peripheral circulation had no influence on their persistence.

SARS-CoV-2 Infection in Children Does Not Necessitate Establishment of Adaptive SARS- CoV-2-Specific Immunological Memory

Children are at lower risk of developing severe COVID-19, yet the underlying immune mechanisms are understudied. While children’s innate immunity can drive rapid resolution of SARS-CoV-2 infection, the establishment of SARS-CoV-2-specific T-cell and B-cell memory in COVID-19 children remains unexplored. We recruited a household cohort to understand SARS-CoV-2-specific CD4+ and CD8+ T-cell immune responses at one month after mild or asymptomatic SARS-CoV-2 infection in PCR-positive children in comparison to those found in their mothers. We analysed SARS-CoV-2-specific T-cell responses, together with B-cells, directly ex vivo using six HLA class-I tetramers and one class-II tetramer presenting SARS57 CoV-2 T-cell epitopes (A1/ORF1a1637, A2/S269, A3/N361, A24/S1208, B7/N105, B40/N322 and DPB4/S167), and Spike- and Receptor Binding Domain (RBD)-specific B-cell probes. Our in depth profiling of epitope-specific T-cell responses at quantitative, phenotypic and clonal levels found that only children who seroconverted had prominent memory T-cell and B-cell profiles. These children had a high magnitude of SARS-CoV-2-specific T-cells displaying memory phenotypes and prevalent T-cell receptor motifs, which were not observed in PCR+ RBD but IgG-negative children. This suggests that seroconversion but not PCR-positivity defines establishment of adaptive SARS-CoV-2-specific immunological memory in children. Our study suggests that COVID-19 vaccination of children could be a major advantage in terms of establishing T-cell and B-cell immunological memory, especially in children who did not seroconvert after SARS-CoV-2 infection.

MMP-7 derived peptides with MHC class-I binding motifs from canine mammary tumor tissue elicit strong antigen-specific T-cell responses in BALB/c mice.

Matrix Metalloproteinases (MMPs)-induced altered proteolysis of extracellular matrix proteins and basement membrane holds the key for tumor progression and metastasis. Matrix metalloproteinases-7 (Matrilysin), the smallest member of the MMP family also performs quite alike; thus serves as a potential candidate for anti-tumor immunotherapy. Conversely, being an endogenous tumor-associated antigen (TAA), targeting MMP-7 for immunization is challenging. But MMP-7-based xenovaccine can surmount the obstacle of poor immunogenicity and immunological tolerance, often encountered in TAA-based conventional vaccine for anti-tumor immunotherapy. This paves the way for investigating the potential of MMP-7-derived major histocompatibility complex (MHC)-binding peptides to elicit precise epitope-specific T-cell responses towards their possible inclusion in anti-tumor vaccine formulations. Perhaps it also ushers the path of achieving multiple epitope-based broad and universal cellular immunity. In current experiment, an immunoinformatics approach has been employed to identify the putative canine matrix matelloproteinases-7 (cMMP-7)-derived peptides with MHC class-I-binding motifs which can elicit potent antigen-specific immune responses in BALB/c mice. Immunization with the cMMP-7 DNA vaccine induced a strong CD8+ cytotoxic T lymphocytes (CTLs) and Th1- type response, with high level of gamma interferon (IFN-γ) production in BALB/c mice. The two identified putative MHC-I-binding nonameric peptides (Peptide32-40 and Peptide175-183) from cMMP-7 induced significant lymphocyte proliferation along with the production of IFN-γ from CD8+ T-cells in mice immunized with cMMP-7 DNA vaccine. The current observation has depicted the immunogenic potential of the two cMMP-7-derived nonapeptides for their possible exploitation in xenovaccine-mediated anti-tumor immunotherapy in mouse model.

Tumor lysate particle loaded dendritic cell vaccine: preclinical testing of a novel personalized cancer vaccine.

We developed a novel approach to efficiently deliver autologous tumor antigens to the cytoplasm of dendritic cells (DC) using yeast cell wall particles (YCWP). Loading of YCWP, leakage of protein from loaded YCWP and cytoplasmic delivery of YCWP content was assessed using fluorescent-tagged experiments. Spectrophotometric analysis compared the epitope-specific T-cell responses following antigen presentation via YCWP versus exogenous loading. The in vivo effectiveness of tumor lysate (TL) particle loaded DC (TLPLDC) vaccine was assessed using murine melanoma models. In fluorescence-tagged experiments, YCWP efficiently delivered antigen to the cytoplasm of DC. TLPLDC loading was more effective than conventional exogenous loading of DC. Finally, in murine melanoma models, TLPLDC outperformed an analogous dendritoma vaccine. The TLPLDC vaccine is commercially scalable and holds the potential of producing personalized vaccines.

Epitope specific T-cell responses against influenza A in a healthy population.

Pre-existing human CD4(+) and CD8(+) T-cell-mediated immunity may be a useful correlate of protection against severe influenza disease. Identification and evaluation of common epitopes recognized by T cells with broad cross-reactivity is therefore important to guide universal influenza vaccine development, and to monitor immunological preparedness against pandemics. We have retrieved an optimal combination of MHC class I and class II restricted epitopes from the Immune Epitope Database (www.iedb.org), by defining a fitness score function depending on prevalence, sequence conservancy and HLA super-type coverage. Optimized libraries of CD4(+) and CD8(+) T-cell epitopes were selected from influenza antigens commonly present in seasonal and pandemic influenza strains from 1934 to 2009. These epitope pools were used to characterize human T-cell responses in healthy donors using interferon-γ ELISPOT assays. Upon stimulation, significant CD4(+) and CD8(+) T-cell responses were induced, primarily recognizing epitopes from the conserved viral core proteins. Furthermore, the CD4(+) and CD8(+) T cells were phenotypically characterized regarding functionality, cytotoxic potential and memory phenotype using flow cytometry. Optimized sets of T-cell peptide epitopes may be a useful tool to monitor the efficacy of clinical trials, the immune status of a population to predict immunological preparedness against pandemics, as well as being candidates for universal influenza vaccines.

Vaccine based immunotherapy as a strategy to bypass drug resistance in multiple myeloma

Clonal evolution under therapy leads to drug resistance and relapse in multiple myeloma (MM), requiring new treatment mo- dalities to control disease. Immunotherapy and specifically vacci- nation to induce anti-tumor CD8+ cytotoxic T-cells (CTLs) provides one such strategy, but susceptibility of drug resistant MM cells to CTL attack is as yet not defined. To examine this, a first requirement is identification of tumour-associated antigens in drug refractory MM. To this end, we had previously specifically evaluated cancer testis antigens (CTAs) in MM for retention at relapse post- therapy, and identified SPAG9 and MAGEC1 as frontline antigen targets for vaccines. Of these, SPAG9 is generic to relapse MM (expressed in w100% of cases) and MAGEC1 is essentially tumour-specific (expressed w60% of cases). An optimal strategy for vaccination as therapy is in disease remission to attack re-emerging MM cells that escape drug therapy. A second requirement is to model drug resistance in MM, and accordingly we have now generated derivatives of the XG2 MM cell line that are resistant to melphalan (XG2 M) or Bortezomib (XG2 600R3); the RPMI8226-derivative R5 line with multiple drug resistance was also available. A third requirement is to show effective lysis of drug resistant MM cells by antigen specific CTLs. To generate antigen-specific CTLs, we utilized pDOM-CTAepitope DNA vaccine delivery in HLA-A2 transgenic HHD mice. We examined two epitopes in respective vaccines, pDOM-SPAG9p1 and pDOM-MAGEC1p2. Both vac- cines elicited epitope specific T-cell responses in HHD measured by IFN release assays following prime and boost with electroporation. Significantly, using MM cell lines made chimeric for HHD MHC class I as targets, both vaccines induced CTLs in HHD mice that were able to effectively lyse primary (XG2 and others) and drug resistant MM cell lines (XG2M, XG2 600R3, R5) effectively. These data demonstrate that drug resistant MM cells are susceptible to CTL killing, substantiating a role for vaccination in MM to over- come drug resistance and hence prevent relapse.

Loss of Immunization-Induced Epitope-Specific CD4 T-Cell Response following Anaplasma marginale Infection Requires Presence of the T-Cell Epitope on the Pathogen and Is Not Associated with an Increase in Lymphocytes Expressing Known Regulatory Cell Phenotypes.

We have shown that in cattle previously immunized with outer membrane proteins, infection with Anaplasma marginale induces a functionally exhausted CD4 T-cell response to the A. marginale immunogen. Furthermore, T-cell responses following infection in nonimmunized cattle had a delayed onset and were sporadic and transient during persistent infection. The induction of an exhausted T-cell response following infection presumably facilitates pathogen persistence. In the current study, we hypothesized that the loss of epitope-specific T-cell responses requires the presence of the immunizing epitope on the pathogen, and T-cell dysfunction correlates with the appearance of regulatory T cells. In limited studies in cattle, regulatory T cells have been shown to belong to γδ T-cell subsets rather than be CD4 T cells expressing forkhead box protein P3 (FoxP3). Cattle expressing the DRB3*1101 haplotype were immunized with a truncated A. marginale major surface protein (MSP) 1a that contains a DRB3*1101-restricted CD4 T-cell epitope, F2-5B. Cattle either remained unchallenged or were challenged with A. marginale bacteria that express the epitope or with A. marginale subsp. centrale that do not. Peripheral blood and spleen mononuclear cells were monitored for MSP1a epitope F2-5B-specfic T-cell proliferative responses and were stained for γδ T-cell subsets or CD4(+) CD25(+) FoxP3(+) T cells before and during infection. As hypothesized, the induction of T-cell exhaustion occurred only following infection with A. marginale, which did not correlate with an increase in either CD4(+) CD25(+) FoxP3(+) T cells or any γδ T-cell subset examined.

Frequencies of Gag-restricted T-cell escape “footprints” differ across HIV-1 clades A1 and D chronically infected Ugandans irrespective of host HLA B alleles

Objective(s)We evaluated relationships between critical Gag T-cell escape mutations and concomitant T-cell responses to determine whether HLA-restricted Gag mutations that confer protection, occur at similar rates in a population infected with mixed HIV-1 clades A1 and D viruses. MethodsAssessment of Gag selective pressure, and adaptive T-cell functions to KAFSPEVIPMF (KF11), ISPRTLNAW (ISW9) and TSTLQEQIGW (TW10) Gag epitopes were combined with host HLA to assess correlations with rates of critical epitope escape mutations in clades A1- (n=23) and D- (n=21) infected, untreated subjects. Infecting clades and selection pressure were determined from the gag sequences. ResultsOverall, Gag escape mutations A163X in KF11 were detected in 61% (14/23) A1- infected compared to 5% (1/21) in D-infected subjects (p=0.00015). Gag mutations I147X in the ISW9 epitope were seen in 43%: (10/23) clade A compared to 5%: (1/21) clade D infected subjects, p=0.007, Fisher's Exact test. Both mutations were more frequent in clade A1 infection. Frequencies of the measured epitope-specific T-cell responses were comparable across clades. Peptide binding affinities for the restricting HLA alleles did not differ across clades. Overall, selection pressure on the Gag protein was significantly greater in clade A than in clade D sequences. ConclusionsThese findings imply that HIV-1 vaccine strategies designed to target structurally constrained T-cell epitopes may be further challenged by clade-driven outcomes in specific HLA-restricted Gag epitopes. Equally, the data are line with slower HIV-1 disease progression in clade A infection; and raise hope that increased selective pressure on Gag may be protective irrespective of host HLA alleles.

PLGA nanoparticle-entrapped inactivated porcine reproductive and respiratory syndrome virus vaccine coadministered intranasally with a potent adjuvant elicits cross-protective immunity in the pig respiratory system (VAC7P.981)

Abstract Porcine reproductive and respiratory syndrome (PRRS) is caused by a highly mutagenic RNA virus, PRRS virus (PRRSV). Currently used vaccines have failed to prevent PRRS outbreaks induced losses of estimated one billion dollar annually to the US pig farmers. The PRRSV infects primarily the lung macrophages. Because of safety advantage, we attempted to strengthen the immunogenicity of killed PRRSV vaccine antigens (KAg) in the pig respiratory system. We entrapped the KAg in biodegradable PLGA nanoparticles (NP-KAg) and coadministered the NP-KAg with a potent mucosal adjuvant, whole cell lysate of Mycobacterium tuberculosis (M. tb WCL), twice intranasally to growing pigs and challenged with a heterologous virus. Our results indicated that formulation of NP-KAg and unentrapped soluble M. tb WCL significantly cleared detectable replicating infective PRRSV with a 10-fold reduction in viral RNA load in the lungs, associated with substantially reduced microscopic lung pathology. Immunologically, enhanced virus neutralizing antibody titers by high avidity antibodies and augmented populations of IFN-γ secreting CD4+ and CD8+ lymphocytes, and reduced secretion of TGFbeta was detected in the lungs. Currently, we are in the process of identifying PRRSV epitope-specific T-cell response and frequency of apoptotic/necrotic immune cells in the lungs of vaccinated pigs. In conclusion, our vaccine formulation elicited broadly cross-protective anti-PRRSV immunity in the pig respiratory system.

Immunization with a prostate cancer xenoantigen elicits a xenoantigen epitope-specific T-cell response

Vaccines encoding xenoantigens, “non-self” proteins that are highly homologous to their autologous counterparts, have been investigated as a means to increase immunogenicity and overcome tolerance to “self” antigens. We have previously shown that DNA vaccines encoding native prostatic acid phosphatase (PAP) were able to elicit PAP-specific T cells in both rats and humans, but required multiple immunization courses. In this study, we investigated in a preclinical model whether immunizations with a DNA vaccine encoding a xenoantigen could elicit a cross-reactive immune response to the native protein, potentially requiring fewer immunizations. Lewis rats were immunized with a DNA vaccine encoding human PAP and splenocytes from immunized rats were screened with a human peptide library containing overlapping, 15-mer PAP-derived peptides using T-cell proliferation and interferon γ (IFNγ) release as measures of the immune response. One dominant PAP-specific, RT1.Al-restricted, epitope was identified. Direct immunization with the immunodominant peptide (HP201–215) containing this epitope demonstrated that it included a naturally presented MHC Class I epitope recognized by CD8+ T cells in Lewis rats. However, no cross-reactive immune response was elicited to the corresponding rat peptide despite a difference of only three amino acids. Immunization with DNA vaccines encoding rat PAP (rPAP) in which this foreign dominant epitope was included as well as with DNA vaccines coding for a variant of the xenoantigen from which this epitope was deleted, did not elicit responses to the native antigen. Overall, these results indicate that the immunization with a xenoantigen-coding DNA vaccine can lead to an immune response which potentially favors foreign epitopes and hence limits any cross-reactive response to the native antigen.

1086 IGHV1-69 as a Promising Candidate for the Development of a Shared Immunotherapy to B-cell Lymphomas

B-cell Non-Hodgkin Lymphomas (B-NHL) are a heterogeneous group of cancers, broadly diffused worldwide and often relapsing after standard treatment and rituximab. Therapeutic vaccines targeting B-NHL idiotype (Id) represent a promising approach to maintain the complete response induced by standard treatments. However, customized idiotypic vaccination still remains a non-approved, experimental therapeutic option, mostly due to the personalized use and penalized by the lack of reliable clinical or biological markers of patient eligibility and responsiveness. Nevertheless, the molecular characterization of different lymphoid tumor histotypes revealed a set of stereotyped immunoglobulins among distinct B-cell lymphoma types. On this ground, we focused our attention on the IGHV1-69 protein, frequently expressed in HCV-associated lymphomas, chronic lymphocytic leukaemia, and auto-immunity related lymphoproliferations, and we characterized the ex vivo immunogenicity of this protein. Seventy IGHV1-69 sequences obtained from patients affected by different B-NHLs or pre-malignant lymphoproliferations were compared to design an optimized sequence characterized by the highest degree of similarity among studied cancers, and thus CDR3 hypervariable region free. Within this “immunogenically” optimized sequence, we identified 13 potential HLA class-I cytotoxic T lymphocyte (CTL) epitopes and synthesized the corresponding pentamers (Pent). We assessed by flow cytometry the presence and extent of epitope-specific T-cell responses in peripheral blood of patients with IGHV1-69+ B-cell lymphoproliferative disorders and healthy donors, and validated these data in IFN-γ ELISPOT (Enzyme-linked immunosorbent spot) assays. Finally, we boosted in vitro IGHV1-69-specific responses by stimulating peripheral blood lymphocytes (PBL) from donors and patients with different protocols for the generation of epitope-specific CTL cultures. Interestingly, the IGHV1-69 Pent+ population observed in patients’ samples was generally larger than in donors, supporting the existence of spontaneous memory T-cell responses against IGHV1-69, at least for some HLA-restrictions. Surprisingly, in patients’ samples, IGHV1-69-recognizing T cells displayed higher IFN-γ release in ELISPOT assays compared to viral-specific T cells. Moreover, we obtained peptide-specific CTL lines, which showed a weak but specific lysis against peptide-pulsed targets, especially when derived from patients’ PBLs. In addition, we were able to generate IGHV1-69-epitope specific CTL clones from healthy donors CD8+ T cells, employing synthetic artificial APC, developed to elicit and expand low-avidity tumor-directed human CTL lines. Finally, IGHV1-69-induced CTL lines showed specific lysis also towards an IGHV1-69 naturally expressing cell line, suggesting that IGHV1-69 memory T-cell responses could be boosted for therapeutic purposes. These results show that IGHV1-69 constitutes a potential target for the development of a subset-specific Id vaccine. Furthermore, multimer (tetramers and pentamers) and ELISPOT immune-monitoring may partially overcome the main limitations of current Id-targeting vaccinations and further improve their clinical efficacy.

Salmonella expressing a T-cell epitope from Sendai virus are able to induce anti-infection immunity

Bacterial fimbriae can accept foreign peptides and display them on the cell surface. A highly efficient gene replacement method was used to generate peptide vaccines based on Salmonella enterica subsp. enterica serovar Typhimurium LT2. DNA encoding an epitope from Sendai virus, SV9 (Sendai virus nucleoprotein peptide 324-332, FAPGNYPAL), which is known to induce cytotoxic T lymphocytes, was incorporated into the gene encoding AgfA (the major subunit protein of thin aggregative fimbriae of Salmonella) by replacing an equal length DNA segment. To improve cytotoxic T lymphocyte recognition, both termini of the peptide were flanked by double alanine (AA) or arginine (RR) residues. Western blotting and immunofluorescence microscopy using AgfA-specific antiserum verified the expression of chimeric AgfA; expression was also proved by a Congo red binding assay. Oral immunizations of C57BL/6 mice with the four strains induced an epitope-specific T-cell response (detected by enzyme-linked immunosorbent spot assay). When the mice were challenged with the Sendai virus, the magnitude of the infection was significantly reduced in the immunized groups compared with the controls. The Salmonella fimbrial display system efficiently induces a cellular immune response and anti-infection immunity in vivo, providing a new strategy for the development of efficient peptide vaccination.

IL-17 Is Secreted by T-Cell Clones Isolated Following An Initial Peak Inhibitor Response to Factor VIIII, Suggesting Th17 Cells Play a Role in Inhibitor Development

Some, but not all, hemophilia A patients who receive factor VIII (FVIII) replacement therapy develop antibodies that interfere with FVIII coagulation activity (“inhibitors”), and their development is T-cell dependent. Immune tolerance induction protocols induce longterm tolerance to FVIII in a number of these patients, and although this clinical success is remarkable, its multifactorial molecular basis is still poorly understood. Our laboratory is characterizing protein-protein interactions and subsequent cytokine signaling that occurs when antigen-presenting cells present FVIII-derived peptides to T-cell receptors (TCRs). We previously mapped HLA-DR-restricted T-cell epitopes recognized by T cells from several related individuals with mild hemophilia A due to the missense substitution FVIIIA2201P (James EA, et al. J Thromb Haemost 5:2399, 2007; Ettinger et al., submitted). Two brothers had unambiguous HLA-DRA-DRB1*0101-restricted T-cell responses to the same epitope in the FVIII C2 domain, which included the missense substitution site at FVIII residue 2201. Both had received FVIII infusions but only the proband developed a high-titer inhibitor. Although a standard Bethesda assay indicated the brother did not have an inhibitor, his concentrated IgG showed detectable FVIII inhibition. The present study addresses the question of why a high-titer inhibitor developed in only one of two hemophilic brothers, despite strong recognition of the same HLA-restricted epitope by T cells from both. In other words, why was tolerance to wild-type FVIII broken in the proband? Several antigen-specific T-cell clones were isolated from each subject's CD4+ T cells using MHC Class II tetramers: PE-labeled, tetrameric DR0101 proteins complexed with synthetic peptides containing the relevant FVIII epitope were used to label and then single-cell sort antigen-specific T cells, which were then expanded in culture following standard protocols. The clones from the proband were isolated 19 weeks after his peak inhibitor response, and clones were isolated from a blood sample obtained from his brother two years after his last FVIII exposure. Cloned T cells from both proband and brother showed highly similar tetramer staining and dose-dependent proliferation upon stimulation with the peptide FVIII2194–2213 presented by irradiated HLA-DR-matched peripheral blood mononuclear cells. Cytokine ELISA assays of supernatants following stimulation of these clones with 1 mM FVIII2194–2213 showed the following patterns for the proband:three clones secreted IL-17 (20–600 pg/ml), relatively low levels of IFN-g and TNF-a (0–200 pg/ml) and no IL-4 or IL-10;two clones secreted IL-4 and IL-10 (100–500 pg/ml), relatively low IFN-g and TNF-a (0–200 pg/ml) and no IL-17. In contrast, all six clones from the brother had a similar profile, secreting relatively high levels of IFN-g (500–1500 pg/ml), moderate levels of TNF-a, IL-4, and IL-10 (50–300 pg/ml) and no IL-17. These profiles indicate that FVIII-specific clones from the proband are of the Th17 and Th2 lineage, whereas the brother had a Th1high/Th2low T-cell response.We next sequenced the TCRBV-D-J genes to investigate whether differences in the TCRs correlated with T-cell responses. Four distinct TCRBV-D-J sequences were identified among the 11 clones that correlated with the observed differences in cytokine secretion, suggesting a structural basis for these functional differences. Expression patterns of chemokine receptors considered to be markers of Th1, Th2, and Th17 cells provided additional evidence for the Th lineage designations of the clones. Eight additional clones were isolated from the proband 21 months following his peak inhibitor response, when his inhibitor titer was 5 Bethesda units/mL, and none of them secreted IL-17, suggesting Th17 cells may play a significant role in early stages of anti-FVIII antibody responses. The importance of Th17 cells in various inflammatory as well as autoimmune responses has been recognized only recently. This is the first report of Th17 involvement in epitope-specific T-cell responses to FVIII.

A design aid for determining width of filter strips

<h3>Background</h3> SARS-CoV-2 primarily infects the upper and lower airway system, y<i>et al</i>so endothelial cells and multiple tissues/organ systems. Anti-SARS-CoV-2 directed cellular immune responses may be deleterious or may confer immune protection – more research is needed in order to link epitope-specific T-cell responses with clinically relevant endpoints.¹ Analysis of epitope reactivity in blood from healthy individuals showed pre-existing (CD4+) reactivity most likely due to previous exposure to the common old coronavirus species HCoV-OC43, HCoV-229E, - NL63 or HKU1, or – not mutually exclusive - cross-reactive T-cell responses that would recognize SARS-CoV-2, y<i>et al</i>so other non-SARS-CoV-2 targets.^2,3 Detailed single cell analysis in PBMCs from patients with COVID-19 showed strong T-cell activation and expansion of TCR gamma – delta T-cells in patients with fast recovery or mild clinical symptoms.⁴ Previous studies examining antigen-specific T-cell responses in tumor-infiltrating T-cells (TIL) showed that EBV or CMV-specific cellular immune responses in TIL from patients with melanoma or pancreatic cancer. Such virus -specific T-cells may represent ‘bystander’ T-cell activation, yet they may also impact on the quality and quantity of anti-tumor directed immune responses. We tested therefore TIL expanded from 5 patients with gastrointestinal cancer, who underwent elective tumor surgery during the COVID-19 pandemic for recognition of a comprehensive panel of SARS-CoV-2 T-cell epitopes and compared the reactivity, defined by IFN-gamma production to TIL reactivity in TIL harvested from patients in 2018, prior to the pandemic. <h3>Methods</h3> A set of 187 individual T-cell epitopes were tested for TIL recognition using 100IU IL-2 and 100 IU IL-15. Different peptide epitopes were selected: i) all epitopes were not shared with the 4 common old coronavirus species, ii) some peptides were unique for SARS-CoV-2, and iii) others were shared with SARS-CoV-1. Antigen targets were either 15 mers or 9mers for MHC class II or class I epitopes, respectively, derived from the nucleocapsid, membrane, spike protein, ORF8 or the ORF3a. The amount of IFN-gamma production was reported as pg/10e4 cells/epitope/5 days. Controls included CMV and EBV peptides. <h3>Results</h3> We detected strong IFN-gamma production directed against antigenic ‘hotspots’ including the ORF3a, epitopes from the SARS-CoV-2 nucleocapsid and spike protein with a range of 12 up to 30 targets being recognized/TIL. <h3>Conclusions</h3> SARS-CoV-2 epitope recognition, defined by IFN production, can be readily detected in TIL from patients who underwent surgery during the pandemic, which is not the case for TIL harvested prior to the circulating SARS-CoV-2. This suggests a broader exposure of individuals to SARS-CoV-2 and shows that SARS-CoV-2 responses may shape the quality and quantity of anti-cancer directed cellular immune responses in patients with solid epithelial malignancies. <h3>Acknowledgements</h3> We thank the Surgery, Pathology and Vivarium Units of Champalimaud Clinical Center (N. Figueiredo, A. Brandl, A. Beltran, M. Castillo, C. Silva ). <h3>Ethics Approval</h3> This study was approved by the Champalimaud Foundation Ethics Committee. <h3>Consent</h3> All donors provided written consent and the study was approved by the local ethics committee. The study is in compliance with the Declaration of Helsinki. <h3>References</h3> Grifoni, A., Weiskopf, D., Ramirez, S. I., Mateus, J., Dan, J. M., Moderbacher, C. R., Rawlings, S. A., Sutherland, A., Premkumar, L., Jadi, R. S., Marrama, D., de Silva, A. M., Frazier, A., Carlin, A. F., Greenbaum, J. A., Peters, B., Krammer, F., Smith, D. M., Crotty, S., &amp; Sette, A. ( 2020). Targets of T Cell Responses to SARS-CoV-2 Coronavirus in Humans with COVID-19 Disease and Unexposed Individuals. <i>Cell</i>, 181(7), 1489–1501.e15. https://doi.org/10.1016/j.cell.2020.05.015 Mateus, J., Grifoni, A., Tarke, A., Sidney, J., Ramirez, S. I., Dan, J. M., Burger, Z. C., Rawlings, S. A., Smith, D. M., Phillips, E., Mallal, S., Lammers, M., Rubiro, P., Quiambao, L., Sutherland, A., Yu, E. D., da Silva Antunes, R., Greenbaum, J., Frazier, A., … Weiskopf, D. ( 2020). Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans. <i>Science</i>, eabd3871. https://doi.org/10.1126/science.abd3871 Le Bert, N., Tan, A. T., Kunasegaran, K., Tham, C. Y. L., Hafezi, M., Chia, A., Chng, M. H. Y., Lin, M., Tan, N., Linster, M., Chia, W. N., Chen, M. I.-C., Wang, L.-F., Ooi, E. E., Kalimuddin, S., Tambyah, P. A., Low, J. G.-H., Tan, Y.-J., &amp; Bertoletti, A. ( 2020). SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls. <i>Nature</i>, 584(7821), 457–462. https://doi.org/10.1038/s41586-020-2550-z Zhang, J., Wang, X., Xing, X. et al. Single-cell landscape of immunological responses in patients with COVID-19. Nat Immunol 2020;<b>21</b>:1107–1118. https://doi.org/10.1038/s41590-020-0762-x

Epitope-specific T-cell responses and allergic phenotypes: implications for T-cell peptide therapy

In the 1990s, elucidation of the primary amino acid sequence of several major allergens using molecular cloning techniques opened the door to T-cell epitope mapping studies. Such analyses underscored the complexity of the allergen-specific T-cell repertoire and the challenges to using allergen-derived peptides to identify epitope-specific differences associated with allergic and nonallergic responses. This review highlights important factors that may influence the nature of epitope-specific T-cell responses observed in vitro. These include the properties of the allergen, genetics of the host and selection of patients with defined allergic phenotypes based on serum antibody profiles and skin test reactivity. By taking these factors into account, T-cell epitope-specific differences associated with distinct allergic phenotypes can be identified. Observations at the T-cell epitope level undermine the Th1/Th2 paradigm as a model for the development of allergic versus nonallergic responses. Instead, they support the mounting data that point to a network of interactions between T helper cells and regulatory T cells, which controls the allergic response. The ability of peptides that localize to polypeptide chain 2 of the major cat allergen, Fel d 1, to preferentially induce interleukin-10 and interferon-γ is discussed. Mechanisms whereby specific allergen-derived peptides may modify the T-cell repertoire and influence the immune outcome are also outlined. Further investigation of allergen-derived T-cell epitopes is warranted in order to optimize the design of peptide vaccines for the treatment of allergic disease.

Inactivation of the viral interleukin 1 receptor improves CD8+ T-cell memory responses elicited upon immunization with modified vaccinia virus Ankara

Interleukin 1 (IL1) is an important regulator of inflammatory responses and contributes to host immune defence against infection. Vaccinia virus encodes a viral soluble IL1beta receptor (IL1betaR), which modulates the acute-phase host response to infection and might influence the induction of immune responses against virus-associated antigens. Here, modified vaccinia virus Ankara (MVA) mutants defective in IL1betaR production were produced by insertion of selectable marker gene sequences that precisely deleted the IL1betaR coding sequences from the MVA genome (MVA-DeltaIL1betaR). Analysis of MVA mutants indicated that deletion of the IL1betaR gene did not abrogate the formation of MVA progeny upon tissue culture propagation. After high-dose intranasal infection with MVA-DeltaIL1betaR, mice showed no signs of fever or other illness, suggesting that the avirulent phenotype remained preserved for MVA-DeltaIL1betaR. Following vaccination of mice, MVA-DeltaIL1betaR or non-mutated MVA induced similar acute-phase immune responses. Importantly, when monitored at the memory phase, significantly higher vaccinia virus-specific total CD8(+) and HLA-A*0201-binding peptide epitope-specific T-cell responses were found after vaccination of HLA-A*0201-transgenic and non-transgenic mice with MVA-DeltaIL1betaR. Moreover, 4-6 months after vaccination, MVA-DeltaIL1betaR provided higher levels of protection against lethal respiratory challenge infection with virulent vaccinia virus strain Western Reserve compared with wild-type MVA. These data suggest that deletion of the viral IL1betaR gene may be considered a relevant approach to amplify the virus-specific CD8+ memory T-cell response and duration of protective immunity obtained after MVA vaccination.

The Majority of Currently Circulating Human Immunodeficiency Virus Type 1 Clade B Viruses Fail To Prime Cytotoxic T-Lymphocyte Responses against an Otherwise Immunodominant HLA-A2-Restricted Epitope: Implications for Vaccine Design

Human immunodeficiency virus type 1 (HIV-1) mutates to escape immune selection pressure, but there is little evidence of selection mediated through HLA-A2, the dominant class I allele in persons infected with clade B virus. Moreover, HLA-A2-restricted responses are largely absent in the acute phase of infection as the viral load is being reduced, suggesting that circulating viruses may lack immunodominant epitopes targeted through HLA-A2. Here we demonstrate an A2-restricted epitope within Vpr (Vpr59-67) that is targeted by acute-phase HIV-1-specific CD8+ T cells, but only in a subset of persons expressing HLA-A2. Individuals in the acute stage of infection with viruses containing the most common current sequence within this epitope (consensus sequence) were unable to mount epitope-specific T-cell responses, whereas subjects infected with the less frequent I60L variant all developed these responses. The I60L variant epitope was a stronger binder to HLA-A2 and was recognized by epitope-specific T cells at lower peptide concentrations than the consensus sequence epitope. These data demonstrate that HLA-A2 is capable of contributing to the acute-phase cytotoxic T-lymphocyte response in infected subjects, but that most currently circulating viruses lack a dominant immunogenic epitope presented by this allele, and suggest that immunodominant epitopes restricted by common HLA alleles may be lost as the epidemic matures.

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We evaluated relationships between critical Gag T-cell escape mutations and concomitant T-cell responses to determine whether HLA-restricted Gag mutations that confer protection, occur at similar rates in a population infected with mixed HIV-1 clades A1 and D viruses.Assessment of Gag selective pressure, and adaptive T-cell functions to KAFSPEVIPMF (KF11), ISPRTLNAW (ISW9) and TSTLQEQIGW (TW10) Gag epitopes were combined with host HLA to assess correlations with rates of critical epitope escape mutations in clades A1- (n = 23) and D- (n = 21) infected, untreated subjects. Infecting clades and selection pressure were determined from the gag sequences.Overall, Gag escape mutations A163X in KF11 were detected in 61% (14/23) A1- infected compared to 5% (1/21) in D-infected subjects (p = 0.00015). Gag mutations I147X in the ISW9 epitope were seen in 43%: (10/23) clade A compared to 5%: (1/21) clade D infected subjects, p = 0.007, Fisher's Exact test. Both mutations were more frequent in clade A1 infection. Frequencies of the measured epitope-specific T-cell responses were comparable across clades. Peptide binding affinities for the restricting HLA alleles did not differ across clades. Overall, selection pressure on the Gag protein was significantly greater in clade A than in clade D sequences.These findings imply that HIV-1 vaccine strategies designed to target structurally constrained T-cell epitopes may be further challenged by clade-driven outcomes in specific HLA-restricted Gag epitopes. Equally, the data are line with slower HIV-1 disease progression in clade A infection; and raise hope that increased selective pressure on Gag may be protective irrespective of host HLA alleles.

Delivery of class I and class II MHC-restricted T-cell epitopes of listeriolysin of Listeria monocytogenes by attenuated Salmonella

Using a Salmonella vaccine-Listeria infection model of intracellular infection, we studied the capacity of an attenuated strain of Salmonella carrying T-cell epitopes of listeriolysin (LLO) of L. monocytogenes to elicit epitope-specific T-cell responses. Class II (LLO 215–226) or class I (LLO 91–99) MHC-restricted T-cell epitopes of LLO were inserted within a central, hypervariable domain of the flagellin protein of an attenuated ΔaroA Salmonella dublin strain. T cells from Listeria-immunized mice were activated by lysates or heat-killed preparations of Salmonella construct expressing the LLO 215–226 epitope, indicating that LLO 215–226 is processed and presented to T cells when offered to antigen-presenting cells as part of a flagellin-epitope fusion protein. The chimeric flagellin genes were integrated into the chromosome of the flagellin-negative S. dublin strain to obtain stable expression of the epitopes. Immunication with the living, chromosomally integrated Salmonella construct carrying LLO 215–226 epitope as part of the flagellin protein generated T cells reactive with the corresponding LLO peptide, indicating that this chimera can stimulate a class-specific immune response in vitro. The effect of flanking residues on the processing and presentation of MHC class I LLO 91–99 epitope was studied using Salmonella vaccine strains that express chimeric flagellins containing one of three LLO 91–99 inserts: 91–99 (normal flagellin amino acids as flanking residues); KK91–99KK (Lys-Lys flanking residues); and AAA91–99AAA (Ala-Ala-Ala flanking residues). Spleen cells from mice immunized with the KK91–99KK flagellin chimeric Salmonella strain showed the greater CTL response indicating that Lys-Lys flanking residues are associated with enhanced immunogenicity, possibly by facilitating the proteolytic excision of the epitope in the endosomal compartment of antigen-presenting cells. A statistically significant decrease in the number of hepatic and/or splenic bacteria was achieved after Listeria challenge in mice immunized with Salmonella constructs expressing either MHC class II LLO 215–226 or class I LLO KK91–99KK flagellin chimera, showing that the immunogenicity of these constructs is associated with an epitope-specific increased resistance to infection.