Abstract 5311: Integrated approaches for design of precision cancer immunotherapies: Selection of Class I and Class II T cell neo-epitopes and removal of Treg epitopes

Next-generation sequencing has opened the door to precision cancer therapies targeting mutations expressed by tumor cells. However, most neo-epitopes selected by traditional T cell epitope prediction algorithms prove to be non-immunogenic. Poor predictive performance may partially be due to inclusion of mutated epitopes cross-conserved with self-epitopes recognized by the T cell receptor of regulatory (Treg), anergic or deleted T cells. Vaccination with self-epitopes can lead to weak effector responses, active immune suppression, and toxicity due to immune-mediated adverse effects. We have developed Ancer, an advanced cancer T cell epitope identification and characterization tool, that streamlines the selection of Class I and Class II T cell neo-epitopes. Ancer leverages EpiMatrix and JanusMatrix, state-of-the-art predictive algorithms that have been extensively validated in prospective vaccine studies for infectious diseases [Moise et al., Hum. Vaccines Immunother 2015; Wada et al., Sci. Rep. 2017]. Distinctive features of Ancer are its ability to accurately predict Class II HLA ligands with EpiMatrix and its 82% positive predictive value, as estimated in previous prospective studies. Additionally, the application of JanusMatrix allows for the prioritization of neo-epitopes with reduced potential for Treg induction, that is responsible for diminished efficacy of current cancer therapies. We validated Ancer's predictive accuracy using datasets of HLA-bound peptides detected by mass spectrometry, which are independent of training sequence data used in model development. Analysis of sequences from Abelin et al., Immunity 2017 shows a 96% agreement between Ancer predictions and peptides eluted from common Class I HLAs, while only 86% of these sequences are accurately predicted by NetMHC or NetMHCpan. An additional retrospective analysis of a cancer immunogenicity study [Strønen et al., Science 2016] demonstrates that Ancer selects immunogenic neo-epitopes with 72% accuracy, as compared to 21% accuracy when using public prediction tools. These results demonstrate that Ancer may focus epitope candidate selection on higher value sequences than conventional algorithms. Class I and Class II neo-epitopes with low Treg activation potential may then be used to support the development of safer and more effective vaccines.

Citation Format: Guilhem Richard, Lenny Moise, Matthew Ardito, Frances Terry, Gad Berdugo, William Martin, Anne De Groot. Integrated approaches for design of precision cancer immunotherapies: Selection of Class I and Class II T cell neo-epitopes and removal of Treg epitopes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5311.

Abstract A018: High-value T cell epitope selection for mutanome-directed cancer immunotherapy using an innovative cancer neo-epitope classification system

T cell epitopes bearing tumor-specific mutations discovered using whole-exomic and transcriptomic sequencing of tumor-normal pairs stimulate T cell-mediated processes that lead to tumor regression. Although neo-epitope prediction using computational methods rapidly identifies epitope candidates in the mutanome, a large proportion of neo-epitopes prove to be non-immunogenic. Innovative computational tools validated for infectious disease targets can be applied to enhance design of personalized cancer immunotherapies by classification of predicted epitopes by potential for mounting a tumor-specific response. Tumor-specific epitopes with potential to stimulate naïve T cells and epitopes that may cross-react with antigen-experienced T cells raised in infection are valuable targets. Epitopes with potential to activate regulatory T cells trained on self and commensal antigens are counter-indicated.

We developed the JanusMatrix algorithm that parses query sequences into MHC-facing and T cell receptor (TCR)-facing sequences and screens sequence databases to identify MHC ligands that share TCR faces with host-related proteins. A database of human protein sequences is available to identify tumor-specific epitopes that may reduce anti-tumor activity by sequences that activate regulatory T cells (Tregs) trained in the thymus on self-antigens. Similarly, tumor-specific epitope candidates are screened using databases composed of antigens derived from human commensals or pathogens to identify epitopes that, respectively, may detrimentally or beneficially cross-react with T cells raised over the course of an individual's immune history. Neo-epitope candidates are ranked according to MHC binding potential, TCR face homology.

We conducted retrospective analyses of cancer vaccine efficacy studies performed in mice [Kreiter et al. 2015 Nature 520, 692–696] showing that mutanome-directed vaccines effective at preventing tumor growth contained higher numbers of class I and II MHC neo-epitopes, as identified by EpiVax's iVAX platform, and had lower potential to cross-react with other murine proteins. An evaluation of mutanomes derived from non-small cell lung cancer patients [Rizvi et al. 2014 Science 348, 124-128] confirmed these findings. Improved clinical outcomes were observed in patients with mutanomes enriched in class I MHC neo-epitopes with TCR faces distinct from other human-derived epitopes.

These results highlight the benefits of using in silico prediction tools for the selection of neo-epitopes and how they can improve the design and efficacy of future cancer vaccines. While retrospective in nature, the suite of tools used for these analyses have been extensively validated in prospective vaccine studies for infectious disease. Removal of Treg epitopes, identified by JanusMatrix, has led to the development of more immunogenic vaccine antigens. EpiVax's H7N9 influenza Treg epitope-depleted vaccine is scheduled for Phase I clinical trial. Direct application of JanusMatrix to the neo-epitope-driven cancer vaccine discovery and design pipeline will focus candidate selection on higher-value sequences than what conventional T cell epitope mapping algorithms generate. Neo-epitopes with low Treg activation potential may then be used to support development of personalized therapies including vaccination and in vitro expansion of tumor infiltrating lymphocytes for adoptive cell transfer.

Citation Format: Lenny Moise, Guilhem Richard, Frances Terry, William Martin, Anne De Groot. High-value T cell epitope selection for mutanome-directed cancer immunotherapy using an innovative cancer neo-epitope classification system [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A018.

VaxCelerate: the use of MTBhsp70-avidin as an adjuvant to rapidly generate self-assembling vaccines with biotinylated, antigen-specific peptides targeting emerging pathogens. (VAC6P.941)

Development of effective vaccines against emerging infectious diseases can take years to progress from pathogen isolation/identification to clinical approval. As a result, conventional approaches fail to produce field-ready vaccines before the EID has spread extensively. The VaxCelerate Project’s goal is to create a platform capable of generating and pre-clinically testing a new vaccine against specific pathogen targets in less than 120 days. A self-assembling vaccine, consisting of a fusion protein M. tuberculosis MTBhsp70 and avidin (MAV), is at the core of the approach. Mixing the MAV with biotinylated pathogen specific immunogenic peptides yields a self-assembled vaccine (SAV). To minimize the time required, we used a distributed R&D model involving experts in protein engineering, bioinformatics, peptide synthesis/design and GMP/GLP manufacturing and testing. This approach was first tested using ovalbumin in C57Bl/6 mice, Flu (H1N1) specific peptides, and ultimately a Lassa fever virus (LFV) specific vaccine in transgenic HLA DR3 mice. Using a GLP validated assay we demonstrated that the MAV assembled LFV induced significantly increased class II peptide specific interferon-CD4+ T cell responses in transgenic mice compared to peptide or MAV alone controls. The use of an identical design for each vaccine may facilitate accelerated regulatory review and by developing safety assessment tools that are more relevant to human vaccine responses than current preclinical models.

Improved GAA activity in tregitope-treated pompe disease: preclinical studies (TECH1P.864)

“Tregitopes” are immunoglobulin-derived regulatory T-cell (Treg) epitopes that lead to suppression of inflammation and, when administered with a target antigen, adaptive tolerance. One potential application of Tregitopes is mitigating immune responses to therapeutic proteins, manifest when a protein appears foreign either because it is derived from a different species or because patients express a genetic deletion or modification. In Pompe disease, genetic deficiencies in acid alpha-glucosidase (GAA) result in lysosomal glycogen accumulation throughout the body. Life-saving treatment with fully human recombinant GAA can trigger high titer anti-drug-antibodies (ADA) that interfere with drug efficacy. We report here our efforts to apply Tregitopes to provide GAA-specific tolerance induction. Therapeutic GAA protein was expressed in GAA-deficient mice by administering AAV-GAA under conditions known to induce ADA +/- Tregitopes, also delivered by AAV expression vectors. Tregitope administration inhibited ADA formation compared to vehicle-treated controls. In addition, a significant increase in GAA activity was observed for Tregitope, consistent with Tregitope inhibition of glycogen buildup in muscle. Current experiments are designed to refine the Tregitope treatment regimen to achieve clinically-relevant ADA inhibition and to evaluate cellular immune responses towards the goal of providing effective and lasting Tregitope-mediated tolerance to GAA for Pompe patients.

Tregitope-mediated antigen-specific tolerance induction in autoimmune and allergic disease in vivo. (THER5P.831)

Tregitopes are a novel class of therapeutic compounds that harness the activity of regulatory T cells (Tregs) and represent a promising new approach for the treatment of autoimmune and inflammatory diseases. Tregitopes are Treg epitopes found in IgG that provide beneficial immunomodulatory effects, paralleling those attributed to intravenous immunoglobulin (IVIG), in vitro and in vivo. When APCs present Tregitopes to Tregs, APC expression of MHC II, CD80, and CD86 are decreased; expression of the tolerance-associated marker ILT3 is increased. These results are consistent with reported effects of IVIG (Bayry et al. Blood, 2003, 101:758) and the IgG-derived peptide hCDR1 (Sela et al. Immunology, 2009, 128:395). Tregitopes also cause CD4+CD25+FoxP3+ Treg to expand and produce IL-10 in vitro. Evaluation of Tregitope effects in mouse models of MS (EAE), OVA-induced allergic airway disease, and AAV-mediated gene transfer show that effector T cells are modified in the presence of Tregitopes. In OVA-induced allergic airway disease, we observed significant and reproducible expansion of Tregs in conjunction with decreased airway reactivity comparable to, if not greater than, IVIG. We have additional unpublished evidence demonstrating the antigen specificity of tolerance induction using Tregitopes in conjunction with target antigens. Formulated with or without the target antigen, Tregitopes represent a promising new treatment for human immune-mediated disease.

Immunogenic biologics: validation of screening, deimmunization and tolerization approaches (P3251)

Immune responses directed against protein therapeutics can directly impact drug pharmacology, safety and efficacy. While many factors contribute to protein immunogenicity, T cell-dependent responses play a critical role. Tools to predict and reduce T cell responses to protein therapeutics present benefits at every stage of drug development. We provide evidence for two different approaches to mitigate therapeutic protein immunogenicity: epitope modification and antigen-specific tolerance induction. Following a systematic process of in silico epitope mapping applied to either Factor VIII or botulinum toxin, rational epitope modification resulted in reduced immunogenicity. In vitro and in vivo validation of computational predictions and iterative in silico modification of immunogenic epitopes were experimentally validated for selected modified sequences. Tolerance induction is achieved by co-delivery or by chemical or recombinant linkage of regulatory T cell epitopes (Tregitopes) to therapeutic proteins. We have demonstrated that Tregitope incorporation leads to lower immune responses against target epitopes identified in insulin, Factor VIII and botulinum toxin. Analysis, prediction, and modification of T cell-mediated immunogenicity of therapeutic proteins expands the available strategies for mitigating therapeutic protein immunogenicity, enables quality by design for drugs in development and improvement of licensed biologics to create biobetters.

iVAX: a sophisticated suite of online vaccine design tools (P3269)

Emerging and re-emerging infectious diseases represent a significant challenge for next-generation vaccine design and bioterror preparedness. We have composed a suite of online immunoinformatics tools for accelerated design of genome-derived, epitope-driven vaccines generated from protein sequences. Using the Conservatrix algorithm, even the most mutable pathogenic genomes may be probed for highly conserved segments, which are then mapped for T cell epitopes and regions of high epitope density using EpiMatrix and ClustiMer. Pathogen sequences which could potentially elicit an undesired autoimmune or T-regulatory response due to homology with sequences encoded by the human genome are screened out using BlastiMer and JanusMatrix, an improved homology analysis tool examining pathogen/host sequence similarity with respect to the HLA and TCR faces of an epitope. Immunogenic Consensus Sequences are created by EpiAssembler, a tool which optimizes the balance between pathogen and population coverage. VaccineCAD links potential vaccine candidate epitopes into a string-of-beads design while minimizing non-specific junctional epitopes that may be created in the linking process. With proof of principle established in animal models for vaccines against Tularemia, Vaccinia and H. pylori, the iVAX toolkit exemplifies a rapid, efficient, easily accessible and broadly applicable solution to accelerate the development of critically important vaccines for human health and biodefense.

Antigen-specific tolerance induction by Tregitopes in vivo (P4202)

Modulation of T cell responses provide of new opportunities in the treatment of autoimmune and inflammatory diseases. Tregitopes are regulatory T cell (Treg) epitopes found in IgG that provide beneficial immunomodulatory effects, paralleling effects attributed to IVIG. In this presentation, we will provide evidence that Tregitopes derived from human IgG can reproduce immunomodulatory effects of IVIG in vitro and in vivo. Tregitopes cause CD4+CD25+FoxP3+ Treg to expand and produce IL-10 in vitro, and iTreg are induced in vivo. Induction and functions of Tregs have been examined in in vivo model systems such as D011.10 TCR transgenic mice, transplant of BM12 to C57BL/6, AAV-mediated gene transfer and EAE. Together, the data show that effector T cells, Th17, and Th9 cells are modified in the presence of Tregitopes. In OVA-induced allergic airway disease, we observed significant and reproducible expansion of Tregs in conjunction with decreased airway reactivity comparable to, if not greater than IVIG. We will provide additional unpublished evidence demonstrating the antigen specificity of tolerance induction using Tregitopes in conjunction with target antigens, and discuss the relevance of Tregitopes to the treatment of human immune-mediated diseases. Additionally, Treg epitopes (Tregitopes?) have been identified in other common serum proteins, suggesting that peripheral control of inflammatory signals may in part be due to intrinsic self-protein “off switches".

Highly immunogenic vaccine for prevention and therapy of malignant mesothelioma (P4437)

Malignant mesothelioma (MM) is a deadly cancer with increasing incidence and no effective treatment options. We have previously constructed recombinant Fowlpox virus (FP) vectors encoding full-length survivin protein (FP-surv), which induced complete tumor regression in 40% of mice bearing subcutaneous MM. Macro- and microscopic evaluation of the tumor tissue showed that the tumors in vaccinated mice had large necrotic cores resulting from enhanced survivin-specific cytotoxic T lymphocyte (CTL). We aim to refine our novel FP vaccine by focusing on the most immunodominant survivin epitopes, thus enhancing its efficacy. We have identified additional high quality antigenic targets specifically upregulated in MM that will increase the breadth of T cell responses. We have used the EpiMatrix system to identify CD4+ and CD8+ T cell epitopes for synthesis and testing. Following T cell assays, highly immunogenic peptides will be selected that specifically stimulate CTLs, without activating T regulatory cells (Treg) that interfere with anti-cancer immune responses. We will include the selected peptides in the next-generation vaccine, FP-surv.2, which we expect to be more effective for inducing an immune response against MM cells than FP carrying the entire survivin gene (FP-surv). In addition, we anticipate that this response may include a higher number of long-lived memory T cells that can be exploited to prevent MM development in high-risk predisposed subjects.

The two-faced T cell epitope: examining the host-microbe interface with JanusMatrix (P4399)

To explore the intersection of commensals, pathogens, and the human genome at the T cell epitope level, we leveraged the vast genomic sequence information available in databases of microorganisms to which humans are exposed. We developed the JanusMatrix immunoinformatic tool that identifies potentially cross-reactive T cell epitopes from both HLA binding and TCR-facing sides to allow comparison across large genome sequence databases including common human pathogens (HP), the human gut microbiome (HGM), the human genome (HG), and the human plasma proteome (HPP). Initial studies reveal different levels of HPP/HG, HGM, and HP cross-reactivity (XR) for known Treg and Teff epitopes. In Hand Foot Mouth Disease (HFMD), extensive XR with HGM seems to predict immunodominance; more limited XR with enteroviruses (e.g., polio) may protect against severe HFMD. For common Teff epitopes, HPP/HG XR is more limited than HGM XR. For Treg epitopes defined in HCV disease and for Tregitopes (De Groot et al, Blood, 2008), HPP/HG XR is more extensive. Overall, greater XR with HPP/HG compared to HGM seems to distinguish known Treg and Teff epitopes. While predicting all influences on immune responses may be impossible, the vast availability of human pathogen and commensal organism sequences now allows T cell epitope comparisons in these large datasets. Startling discoveries relevant to vaccine development and T cell response phenotype understanding are emerging as we apply this powerful technology.

In silico high throughput pre-clinical determination of monoclonal antibody immunogenicity (P3391)

One of the great surprises of the biologics revolution has been the discovery that recombinant human proteins, including humanized and fully-human monoclonal antibodies (MAb), can be immunogenic when administered to immune-competent subjects. Preclinical and clinical evaluations of the immunogenic potential for biologic drugs primarily focus on humoral immune responses; as a result, the critical contribution of T cells to the development of anti-drug antibodies (ADA) has been somewhat overlooked. Using the EpiMatrix T cell epitope mapping system, we have developed an interactive in silico screening and optimization platform that evaluates the overall immunogenic potential of a biologic as well as identifies individual T cell epitope clusters contributing to its immunogenicity. In contrast to other immunogenicity prediction tools, our platform considers the contribution of regulatory T cell epitopes (Tregitopes) to immunogenic potential. Tregitopes are highly conserved T cell epitopes derived from IgG that we and others have shown activate regulatory T cells and promote tolerance induction to associated antigens. Here we demonstrate the correlation of available clinical immunogenicity data with Tregitope-adjusted immunogenicity scoring for twenty approved MAbs. Further, we present a high-throughput platform from which these scores can be used to triage large pools of candidate MAbs during the discovery phase of antibody development.

Tregitopes: The active ingredient in IVIG-mediated tolerance induction? (P5224)

In the course of screening IgG sequences for T cell epitopes, we identified Treg epitope peptides, now called Tregitopes, contained in conserved framework regions of Fab and Fc. Tregitopes may provide one explanation for the expansion and stimulation of Treg following intravenous immunoglobulin (IVIg) therapy. Their distinguishing characteristics include in silico signatures of high-affinity binding to multiple human HLA class II DR, and conservation across IgG isotypes as well as mammalian species. Tregitopes induce expansion of CD4+/CD25hi/FoxP3+ T cells and suppress immune responses to co-incubated antigens in vitro. Comparing human Tregitopes (hTregitopes) to murine sequences, we identified class II-restricted murine Tregitope homologs (mTregitopes). We provide evidence that when APCs present Tregitopes to natural (n) Treg, APC expression of MHC II, CD80, and CD86 are decreased. Moreover, Tregitopes increase proportions of IL-10-producing nTreg. We propose the mechanism of Tregitope-mediated tolerance induction to be as follows: 1) APC present Tregitopes to nTreg, 2) nTreg are activated, proliferate and produce IL-10, 3) nTreg provide tolerogenic feedback signals to APC, modulating the APC phenotype, and 4) nTreg and tolerogenic APC together suppress antigen-specific T cell responses. The discovery of Tregitopes in IgG and other autologous proteins may lead to the development of new insights as to the role of Tregs in autoimmune diseases.

Cross-reactive influenza H1N1 T cell epitopes identified by immunoinformatic methods stimulate CD4+ T cell responses (P4303)

Immune responses to cross-conserved T cell epitopes in novel H1N1 influenza might explain reports of diminished influenza-like illnesses and confirmed infection among older adults, in the absence of cross-reactive humoral immunity, during the 2009 pandemic. We set out to identify and characterize cross-conserved H1N1 T cell epitopes to develop a universal H1N1 influenza vaccine. An immunoinformatic analysis was conducted using all available pandemic and pre-pandemic HA-H1 and NA-N1 sequences dating back to 1980. From 5,738 HA-H1 and 5,396 NA-N1 sequences, 13 HA and 4 NA immunogenic consensus sequences (ICS) were selected that each cover >84% of pre-pandemic and pandemic H1N1 influenza strains, bear EpiMatrix scores ≥95th percentile and cover ≥4 HLA Class II archetypal alleles. HLA binding assays for 6 Class II archetypal alleles showed that immunoinformatic predictions were 78% accurate. Individual ICS peptides were immunoreactive in cultured human IFNy ELISpot assays after antigen-specific in vitro expansion. Intracellular cytokine staining showed the magnitude of IL-2, IFNy and/or TNFa expressing CD4+ T cells was boosted by 2011 seasonal trivalent influenza immunization for vaccine-matched and ICS HA peptide pools. Immunoinformatic methods identify cross-reactive influenza H1N1-specific CD4+ T cell epitopes. This approach can be applied to other influenza subtypes to develop a universal influenza vaccine that will protect against antigenically novel influenza viruses.

Regulating immune responses to biologics: Epitope prediction and applications (58.23)

Immune responses directed against protein therapeutics can directly impact drug safety and efficacy. The ability to predict and reduce immunogenicity of a potential protein therapeutic presents tremendous benefits at every stage of drug development. While many factors contribute to protein immunogenicity, T cell-dependent responses play a critical role. We report two approaches to mitigate therapeutic protein immunogenicity, one involving epitope modification and the other inducing antigen-specific tolerance induction. Rational epitope modification applied to either Factor VIII or botulinum toxin demonstrates reduced immunogenicity when following a systematic process of in silico epitope mapping, in vitro and in vivo validation of computational predictions, iterative in silico modification of immunogenic epitopes and experimental validation of carefully selected modified sequences. Tolerance induction involves co-delivery, chemical or recombinant linkage of regulatory T cell epitopes (Tregitopes) to therapeutic proteins. We have demonstrated that Tregitope incorporation leads to lower immune responses against target epitopes identified in insulin, Factor VIII and botulinum toxin. The ability to analyze, predict, and modify the immunogenicity of a protein expands the available strategies for mitigating therapeutic protein immunogenicity, enables quality by design for drugs in development and improvement of licensed biologics to create biobetters.

Tregitope mechanism of action and applications for tolerance induction. (116.8)

Tregitopes are T cell epitopes naturally located in immunoglobulins that bind to multiple MHC Class II alleles and induce regulatory T cell (Treg) responses. Harnessing tolerogenic effects of Tregitopes provides a novel tool to suppress unwanted immune responses and maintain antigen-specific tolerance, thus changing treatment paradigms in autoimmunity. We have now demonstrated that APCs present Tregitopes to natural (n) Treg, engage feedback mechanisms promoting a tolerogenic APC phenotype, induce Treg expansion, and modulate antigen-specific effector T cell responses. Proportions of APC expressing MHC II, CD80, and CD86 are suppressed, consistent with reported effects of IVIG (Bayry et al. Blood, 2003, 101:758) and of the IgG-derived peptide hCDR1 (Sela et al. Immunology, 2009, 128:395). Moreover, we observed significant increases in proportions of IL-10-producing CD4+CD25+ FoxP3-expressing nTreg in the presence of Tregitopes. These studies are an exciting first step towards understanding the basic mechanism of Tregitope tolerance induction that we propose to be as follows: 1) APC present Tregitopes to nTreg, 2) nTreg are activated to proliferate and produce IL-10, 3) nTreg provide tolerogenic feedback signals to APC, modulating the APC phenotype, and 4) nTreg and tolerogenic APC together suppress antigen-specific T cell responses. These data suggest a role for Tregitopes in the mechanism of action for IVIG, and provide insight critical for future therapeutic applications.

Tregitope applications to tolerance induction in autoimmune diseases. (116.10)

Modulation of T cell responses may contribute to the design of new approaches for the treatment of autoimmune and inflammatory diseases. IVIG is one example of a therapy with this effect, and evidence is accumulating that Tregitopes (De Groot et al. Blood, 2008, 112:3303; natural T regulatory epitopes derived from IgG) provide beneficial immunomodulatory effects that parallel the effects of IVIG. In this presentation, we will provide evidence that Tregitope sequences derived from human IgG can reproduce immunomodulatory effects of IVIG in vitro and in vivo. In vitro, Tregitopes activate CD4+CD25+FoxP3+ natural regulatory T cells (nTreg). In vitro and in vivo, Tregitopes cause Tregs to produce IL-10, and to expand, and iTreg are induced. Induction and functions of nTregs have been examined in model systems such as D011.10 TCR transgenic mice, transplant of BM12 to C57BL/6, AAV-mediated gene transfer and EAE. Together, the data show that effector T cells, Th17, and Th9 cells are modified in the presence of Tregitopes. In OVA-induced allergic airway disease, we observed significant and reproducible expansion of Tregs in conjunction with decreased airway reactivity that was comparable to, if not greater than IVIG. We will provide additional unpublished evidence demonstrating the antigen specificity of tolerance induction using Tregitopes in conjunction with target antigens, and discuss the relevance of Tregitopes to the treatment of human immune-mediated diseases.

Preclinical design of less immunogenic biologics: Tregitopes and Tolerance (144.28)

The contributions of effector T cell epitopes to autoimmunity and to the clinical immunogenicity of protein therapeutics are now broadly accepted. In allergy and autoimmunity, efforts are directed at broad suppression of cell-mediated immune responses. We have explored the effects of pre-treatment with natural regulatory T cell epitopes (Tregitopes) in murine models of autoimmune disease and protein therapeutics treatment. These natural Tregitopes are promiscuous MHC Class II T cell epitopes identified in IgG. The effect of Tregitopes has been studied in vitro and in vivo. Investigations using standard animal models of allergy (OVA), transplantation (MLR, cardiac transplant), protein therapeutics (OVA, FVIII) and autoimmunity (EAE, NOD) have demonstrated that tolerance to a range of antigens can be induced by co-administration of the Tregitopes. Tregitopes specifically activate CD4+CD25+FoxP3+ natural regulatory T cells. In vitro, co-incubation of antigens with Tregitopes leads to suppression of effector cytokine and chemokine secretion, reduced proliferation, and expansion of antigen-specific adaptive Tregs. In vivo, co-administration leads to suppression of T cell and antibody responses to the test antigens. These corroborating studies have now validated the original finding published by De Groot et al. (Blood 2008). Regulatory T cell induction by Tregitopes represents a paradigm shift for the treatment of autoimmune disease and the design of protein therapeutics.

Greater CD8+ TCR heterogeneity and functional flexibility in HIV-2 compared to HIV-1 infection

Virus-specific CD8(+) T cells are known to play an important role in the control of HIV infection. In this study we investigated whether there may be qualitative differences in the CD8(+) T cell response in HIV-1- and HIV-2-infected individuals that contribute to the relatively efficient control of the latter infection. A molecular comparison of global TCR heterogeneity showed a more oligoclonal pattern of CD8 cells in HIV-1- than HIV-2-infected patients. This was reflected in restricted and conserved TCR usage by CD8(+) T cells recognizing individual HLA-A2- and HLA-B57-restricted viral epitopes in HIV-1, with limited plasticity in their response to amino acid substitutions within these epitopes. The more diverse TCR usage observed for HIV-2-specific CD8(+) T cells was associated with an enhanced potential for CD8 expansion and IFN-gamma production on cross-recognition of variant epitopes. Our data suggest a mechanism that could account for any possible cross-protection that may be mediated by HIV-2-specific CD8(+) T cells against HIV-1 infection. Furthermore, they have implications for HIV vaccine development, demonstrating an association between a polyclonal, virus-specific CD8(+) T cell response and an enhanced capacity to tolerate substitutions within T cell epitopes.