Peripheral Tolerance Mechanisms Research Articles

Breakdown and Repair of Peripheral Immune Tolerance in Type 1 Diabetes.

Failures in peripheral immune tolerance mechanisms create a permissive environment for autoimmune diabetes initiation and disease progression. Biomarker analyses provide tools that allow recognition of this loss of tolerance, reflecting a serial acquisition of pathogenic characteristics causally linked to islet β-cell dysfunction and death. Autoimmune effector cell activation and expansion, ineffective immune regulation, and tissue response to injury during active disease each represent challenges to homeostasis; however, they also represent targets for therapeutic intervention, with the potential for restoration of tolerance. Limited success in recent clinical trials demonstrates that tolerance in type 1 diabetes (T1D) is achievable, but currently occurs in few subjects and is not durable in most. Combining therapeutic agents to rebuild multiple immune components to restore tolerance, particularly addressing both effector and regulatory T-cell dysfunction, is needed.

Understanding Autoimmunity: Mechanisms, Predisposing Factors, and Cytokine Therapies.

Autoimmunity refers to an organism's immune response against its own healthy cells, tissues, or components, potentially leading to irreversible damage to vital organs. Central and peripheral tolerance mechanisms play crucial roles in preventing autoimmunity by eliminating self-reactive T and B cells. The disruption of immunological tolerance, characterized by the failure of these mechanisms, results in the aberrant activation of autoreactive lymphocytes that target self-tissues, culminating in the pathogenesis of autoimmune disorders. Genetic predispositions, environmental exposures, and immunoregulatory disturbances synergistically contribute to the susceptibility and initiation of autoimmune pathologies. Within the realm of immune therapies for autoimmune diseases, cytokine therapies have emerged as a specialized strategy, targeting cytokine-mediated regulatory pathways to rectify immunological imbalances. Proinflammatory cytokines are key players in inducing and propagating autoimmune inflammation, highlighting the potential of cytokine therapies in managing autoimmune conditions. This review discusses the etiology of autoimmune diseases, current therapeutic approaches, and prospects for future drug design.

Abstract 3985: Immune-competent “NoGlow” transgenic mice overcome restrictive tolerance to multiple xenoantigens and simultaneously permit identification, tracking, and temporal gene expression in tumor cells

Abstract The ability to temporally regulate gene expression and track labeled cells make animal models powerful biomedical tools. However, sudden exposure to xenobiotic genes (e.g. GFP, luciferase (luc), or rtTA3) triggers inadvertent immune responses that can significantly suppress foreign gene expression or result in complete rejection of transplanted cells. Although germline expression of foreign genes somewhat addresses these challenges, native fluorescence and bioluminescence abrogates their utility as cellular reporters and spatiotemporally restricted expression can lead to suboptimal xenoantigen tolerance. Even in endogenous cancer models, we find that the means of tissue-directed expression of the same foreign gene yield significant differences in overall tolerance. Thus, the degree of tolerance to foreign genes strongly impacts the utility of different genetic modification and can strongly influence experimental outcomes and interpretations. To overcome these unwanted immune responses and enable reliable cell tracking/gene regulation, we developed a novel mouse model that selectively expresses antigen-intact but non-functional forms of GFP, luc, and rtTA3. These "NoGlow" mice possess no detectable background fluorescence or luminescence and mount limited adaptive immune responses against transgenic xenoantigens even after vaccination. Furthermore, we demonstrate that NoGlow mice allow tracking and tetracycline inducible gene regulation of triple-transgenic cells expressing GFP/luc/rtTA3, in contrast to transgene-negative immune competent mice which completely eliminate these cells. Notably, this model enables de novo metastasis from orthotopically implanted, triple-transgenic tumor cells, despite high xenoantigen expression. Finally, we observed model and sex-based differences in immune tolerance to the encoded xenoantigens after activation by different tissue-specific CREs, illustrating the obstacles of tolerizing animals to foreign genes and validating the utility of NoGlow mice to dissect the mechanisms of central and peripheral tolerance. Altogether, the NoGlow model provides a critical resource for in vivo studies across multiple disciplines, including oncology, developmental biology, infectious disease, autoimmunity, and transplantation. Citation Format: Timothy N. Trotter, Andrea Wilson, Jason McBane, Carina Dagotto, Xiao Yang, Junping Wei, Gangjun Lei, Hannah Thrash, H. Kim Lyerly, Zachary Hartman. Immune-competent “NoGlow” transgenic mice overcome restrictive tolerance to multiple xenoantigens and simultaneously permit identification, tracking, and temporal gene expression in tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3985.

How persistent infection overcomes peripheral tolerance mechanisms to cause T cell-mediated autoimmune disease.

T cells help orchestrate immune responses to pathogens, and their aberrant regulation can trigger autoimmunity. Recent studies highlight that a threshold number of T cells (a quorum) must be activated in a tissue to mount a functional immune response. These collective effects allow the T cell repertoire to respond to pathogens while suppressing autoimmunity due to circulating autoreactive T cells. Our computational studies show that increasing numbers of pathogenic peptides targeted by T cells during persistent or severe viral infections increase the probability of activating T cells that are weakly reactive to self-antigens (molecular mimicry). These T cells are easily re-activated by the self-antigens and contribute to exceeding the quorum threshold required to mount autoimmune responses. Rare peptides that activate many T cells are sampled more readily during severe/persistent infections than in acute infections, which amplifies these effects. Experiments in mice to test predictions from these mechanistic insights are suggested.

T Cell Repertoire in Lupus: Autoreactive T Cells in Central and Peripheral Selection

Systemic lupus erythematosus (SLE) is an immune disorder characterized by the presence of T and B cells which drive a pathogenic autoimmune response. Autoreactive T effector cells naturally arise during the process of development in the thymus, but most are removed by several self-tolerance mechanisms. Self-antigen recognizing T cells emigrating from the thymus are normally prevented from causing cellular or tissue damage by peripheral tolerance mechanisms. While we understand much about how self-antigens are presented to T cells and the mechanisms to remove those T cells or convert them into regulatory T cells in thymus and peripheral lymphoid organs, we understand much less about the derivation of potentially pathogenic self-reactive T cells in autoimmune disease. It is not clear whether individuals with autoreactive T cell activation have an altered T cell receptor repertoire of naïve T cells that have matured to immunocompetence as effector cells or whether the pathogenic process involves altered activation of immunocompetent T cells in the periphery. There is increasing evidence that the autoantibodies that characterize SLE result from an interaction of B cells with self-reactive T cells. Here we summarize the evidence for autoreactive T cells in both lupus mouse models and in patients with SLE and discuss the evidence for either altered T cell selection or altered T cell activation in SLE, which has implications for both pathogenesis and treatment

Dosage and organic acid residue of MOG35-55 peptide influences immunopathology and development of BCG induced experimental autoimmune encephalomyelitis (EAE).

Experimental autoimmune encephalomyelitis (EAE) serves as a model for studying multiple sclerosis, with immunization strategies utilizing MOG35-55 peptide, emulsified in adjuvant enriched with mycobacterium tuberculosis (Mtb). This study examined the effects of Bacillus Calmette-Guérin (BCG) as an adjuvant, alongside the impact of MOG35-55 peptide doses and their residual counter ions on EAE development. We found that BCG can be effectively used to induce EAE with similar incidence and severity as heat-killed H37Ra, contingent upon the appropriate MOG35-55 peptide dose. Different immunization doses of MOG35-55 peptide significantly affect EAE development, with higher doses leading to a paradoxical reduction in disease activity, probably due to peripheral tolerance mechanisms. Furthermore, doses of MOG35-55 peptides with acetate showed a more pronounced effect on disease development compared to those containing trifluoroacetic acid (TFA), suggesting the potential influence of residual counter ions on EAE activity. We highlighted the feasibility of applying BCG to the establishment of EAE for the first time. Our findings emphasized the importance of MOG peptide dosage and composition in modulating EAE development, offering insights into the mechanisms of autoimmunity and tolerance. This could have implications for autoimmune disease research and the design of therapeutic strategies.

Establishment of CD8+ T Cell Thymic Central Tolerance to Tissue-Restricted Antigen Requires PD-1.

Highly self-reactive T cells are censored from the repertoire by both central and peripheral tolerance mechanisms upon receipt of high-affinity TCR signals. Clonal deletion is considered a major driver of central tolerance; however, other mechanisms such as induction of regulatory T cells and functional impairment have been described. An understanding of the interplay between these different central tolerance mechanisms is still lacking. We previously showed that impaired clonal deletion to a model tissue-restricted Ag did not compromise tolerance. In this study, we determined that murine T cells that failed clonal deletion were rendered functionally impaired in the thymus. Programmed cell death protein 1 (PD-1) was induced in the thymus and was required to establish cell-intrinsic tolerance to tissue-restricted Ag in CD8+ thymocytes independently of clonal deletion. In bone marrow chimeras, tolerance was not observed in PD-L1-deficient recipients, but tolerance was largely maintained following adoptive transfer of tolerant thymocytes or T cells to PD-L1-deficient recipients. However, CRISPR-mediated ablation of PD-1 in tolerant T cells resulted in broken tolerance, suggesting different PD-1 signaling requirements for establishing versus maintaining tolerance. Finally, we showed that chronic exposure to high-affinity Ag supported the long-term maintenance of tolerance. Taken together, our study identifies a critical role for PD-1 in establishing central tolerance in autoreactive T cells that escape clonal deletion. It also sheds light on potential mechanisms of action of anti-PD-1 pathway immune checkpoint blockade and the development of immune-related adverse events.

Neoantigens: The Novel Precision Cancer Immunotherapy

The past few decades have witnessed the remarkable progress of cancer immunotherapy. Neoantigens, also known as tumor-specific antigens, are novel antigens originating from tumor-specific alterations such as genomic mutations, dysregulated RNA splicing, and post-translational modifications. Neoantigens, recognized as non-self entities, trigger immune responses that evade central and peripheral tolerance mechanisms. With the notable strides in cancer genomics facilitated by next-generation sequencing technologies, neoantigens have emerged as a promising avenue for tumor-specific immunotherapy grounded in genomic profiling-based precision medicine. Furthermore, a growing number of preclinical and clinical investigations are harnessing the potential synergies between neoantigens and other immunotherapies such as adoptive cell therapy and immune checkpoint inhibitors. In this review, we will provide a comprehensive perspective encompassing the trajectory of neoantigens, neoantigen design strategies, and the diverse array of clinical applications inherent in immunotherapy strategies centered around neoantigens. Moreover, we delve into the inherent prospects and challenges that accompany the clinical adoption of neoantigen-based immunotherapies while also putting forth potential solutions to address these challenges.

P-352 Evaluation of CD25 and CD69 activation markers expression on peripheral blood cells subpopulations in endometriosis patients

Abstract Study question We aim to determine the percentages of CD25-positive and CD69-positive lymphocytes in peripheral blood of endometriosis (EMS) patients. Summary answer Higher percentages of lymphocytes expressing CD69 and CD25 markers in EMS and their correlation with the severity of the disease, indicate persistent activation of lymphocytes What is known already Exposure to antigens causes activation markers to appear on the surface of lymphocytes. Among them, we can distinguish early and late activation markers. The earliest one is CD69, which is expressed upon activation by the TCR receptor. CD69 plays a role in the proliferation and survival of activated T lymphocytes. CD25 is a moderate late activation marker, considered the most important marker of cellular response activation. The significance of CD69 and CD25 expression by T cells in endometriosis has not yet been determined. Increased CD69 expression on various lymphocyte subsets in peritoneal fluid in EMS has been reported. Study design, size, duration Within this prospective study between January 2016 and August 2018 immune diagnostics of the number of CD25-positive and CD69-positive lymphocytes in peripheral blood of EMS patients (firstly diagnosed during laparoscopy and confirmed histopatologically) and non-EMS controls were performed using flow cytometry analysis. Total number of 74 subjects were included in the study. All patients signed written informed consent before their enrollment in the study. Participants/materials, setting, methods We enrolled 54 subjects with previously untreated endometriosis and 20 healthy age-matched controls. Peripheral blood was collected from control patients to assess the immunophenotype of lymphocytes and measure expression of activation markers Cd25 and CD69 on several subtypes B and T lymphocytes. Diagnosis and assessment of the stage of the EMS was established during laparoscopy using rASRM score. Differences were considered statistically significant with a p < 0.05. Main results and the role of chance Significantly higher expression of the CD25 and CD69 antigen was found in both CD3+ T, CD4+ T and CD8+ T cells as well as CD19+ B cells. In each of the studied groups, a significance level of p < 0.001 was obtained. There was a weak positive correlation between the percentage of CD4+CD25+ T cells and the stage of endometriosis (R = 0.357; p = 0.008) and negative correlations between the percentage of endometriosis and the percentage of CD3+CD69+ T cells (R = −0.554; p < 0.001), T CD4+CD69 + (R = −0.554, p < 0.001) and T CD8+CD69 + (R = −0.553, p < 0.001). The expression of activation markers, CD25 and CD69 antigens in patients suffering from endometriosis with accompanying clinical symptoms was also evaluated. n the group of patients with endometriosis accompanied by infertility or pelvic pain, no statistical differences in the expression of CD25 and CD69 antigens were observed. The only clinical condition coexisting with statistically different expression of activation markers is adhesion disease accompanying endometriosis - a statistically significantly lower percentages of T CD3+CD69 + (p = 0.002), T CD4+CD69 + (p = 0.002) and T CD8+CD69 + (p = 0.002). Limitations, reasons for caution Small sample size is an important limitation of this study. In addition, evaluating immunological analysis only in serum samples does not let us drive any conclusions on the local changes of endometriosis lesions. Wider implications of the findings Clinical interpretation of changed expression of CD69 and CD25 in EMS could be useful in evaluating mechanisms of cellular activation, peripheral tolerance and immune imbalance involved in pathogenesis of endometriosis. Further studies to understand mechanisms underlying correlation between stage of the disease and expression of CD69 should be considered. Trial registration number not applicable

Lung injury induces preferential expansion of Foxp3 +regulatory T cells over conventional T cells in self-antigen specific CD4 +T cell repertoire.

Abstract Self antigen-specific T cells are prevalent in the mature adaptive immune repertoire. At steady state, these T cells are regulated by various mechanisms of peripheral tolerance. Characterizing the activation of these self antigen-specific T cells during inflammation may shed crucial insights into the pathogenesis of autoimmunity. Utilizing an experimental animal model where mice express three model T cell epitopes (2W, gp66, and OVA) in a tissue restricted manner, we detect the exclusive expansion of autoreactive regulatory T cells (Tregs) following acute lung injury that is dependent on recognition of their cognate self antigen and IL-2 signaling. Conversely, conventional T cells of the same self antigen-specificity did not expand during inflammation, even following the depletion of endogenous Tregs. Therefore, our findings suggest that the self-antigen specific T cell repertoire may serve a regulatory function during acute tissue damage to regulate the ongoing immune response and limit the possibility of autoimmunity.

Tuning peptide specificity for T cell tolerance in Type 1 diabetes

Abstract Type 1 Diabetes (T1D) is a classical T-cell mediated autoimmune disease, and fundamental data have implicated insulin as the dominant autoantigen in T1D disease. In the NOD mouse model of T1D, notable studies have found that mice lacking native insulin expression but with an altered insulin sequence to maintain blood glucose levels are protected from insulitis and diabetes. Growing evidence also indicates how the insulin peptide is bound within MHC Class II (peptide register) is essential in determining the strength of interactions and recognition of autoreactive T-cells. We have uncovered a unique peptide binding characterized by the dominant insulin epitope InsB:9–23. The majority of InsB:9–23-specific CD4 T-cells in the periphery recognize insulin bound in the unusual register 3, and knocking in this single amino acid variation into just one copy of the insulin gene in NOD mice, confers protection against T1D. In addition, these mice were protected from T1D, even when treated with checkpoint inhibitor blockade, unlike their wild-type littermates. Introducing this superagonist epitope into the NOD mouse has allowed us to address several key questions surrounding pathways of peptide generation, presentation by MHC molecules, and recognition by auto-reactive pathogenic T cells. In addition, we have been able to model how central and peripheral tolerance mechanisms can be altered when major epitopes in the Insulin gene are mutated, allowing us to explore means of dominant tolerance to understand the potential for translation into treatments for T1D. Supported by grants from NIH (R01 DK133443-01A)

Regulation of CD8 T-cell signaling, metabolism, and cytotoxic activity by extracellular lysophosphatidic acid.

Lysophosphatidic acid (LPA) is an endogenous bioactive lipid that is produced extracellularly and signals to cells via cognate LPA receptors, which are G-protein coupled receptors (GPCRs). Mature lymphocytes in mice and humans express three LPA receptors, LPA2 , LPA5, and LPA6 , and work from our group has determined that LPA5 signaling by T lymphocytes inhibits specific antigen-receptor signaling pathways that ultimately impair lymphocyte activation, proliferation, and function. In this review, we discuss previous and ongoing work characterizing the ability of an LPA-LPA5 axis to serve as a peripheral immunological tolerance mechanism that restrains adaptive immunity but is subverted during settings of chronic inflammation. Specifically, LPA-LPA5 signaling is found to regulate effector cytotoxic CD8 T cells by (at least) two mechanisms: (i) regulating the actin-microtubule cytoskeleton in a manner that impairs immunological synapse formation between an effector CD8 T cell and antigen-specific target cell, thus directly impairing cytotoxic activity, and (ii) shifting T-cell metabolism to depend on fatty-acid oxidation for mitochondrial respiration and reducing metabolic efficiency. The in vivo outcome of LPA5 inhibitory activity impairs CD8 T-cell killing and tumor immunity in mouse models providing impetus to consider LPA5 antagonism for the treatment of malignancies and chronic infections.

Abstract 4060: Selective Neoantigens Peptide TILs (snapTILs): A next generation tumor infiltrating lymphocytes (TIL) therapy platform

Abstract Background: Immunotherapies using autologous tumor infiltrating lymphocytes (TILs) have become effective treatment modalities for several patients with solid tumors, yielding a response rate of around 49% in patients with metastatic melanoma. Most clinical centers utilize bulk, randomly isolated TILs from the tumor tissue for ex vivo expansion and infusion. Only a minor fraction of these administered TILs recognize tumor antigens and most are non-mutated public antigens. Moreover, expression of these antigens on normal cells can trigger central and peripheral tolerance mechanisms. Against this background, cancer neoantigens derived from private mutations represent an ideal class of cancer antigens to target because they are highly tumor specific by nature, therefore reducing the potential induction of central and peripheral tolerance. We recently developed a new technology to enrich TILs with predefined neoantigen specificities, which we termed Selective Neo Antigens Peptides TILs (snapTILs). Here we describe the efficacy studies of a melanoma and pancreatic cancer patient’s snapTILs done in autologous settings both ex vivo and in vivo. Methods: Our workflow consisted of a multistep process performed on a patient-specific basis. Briefly, mutations were called by whole-exome sequencing of tumor vs. normal DNA to generate a peptide library. The peptides were further filtered using an in-silico prediction algorithm and our proprietary peptide-MHC binding assay. Selected peptides were then incubated with TILs isolated from the patient’s tumor biopsy, resulting in TIL population enriched of T cells that recognize the neopeptides (snapTILs). After rapid expansion, snapTIL efficacy was tested by checking their ability to infiltrate in patient-derived tumor organoids, their activation status (IFNγ), cytotoxicity (Granzyme B), and T-cell exhaustion markers. Lastly, snapTILs in vivo efficacy was tested in human melanoma and pancreatic cancer xenograft models using hIL-2 transgenic mice. Results: Our initial data showed that the levels of infiltration of snapTILs into tumor organoids was significantly higher compared to IL2-stimulated TILs in both cancer models. Also, snapTILs recognized tumors with great specificity as they showed significantly less infiltration in organoids generated from generally uninvolved tissues from the same patients. Moreover, snapTILs were found to be more cytotoxic in nature than the IL2-stimulated TILs in terms of IFNγ and Granzyme B secretion after coculture with autologous tumor cells. Our in vivo data confirmed these observations by showing 70% tumor growth inhibition in highly immunogenic melanoma and 50% tumor growth restriction in a poorly immunogenic pancreatic tumor model. In conclusion, our approach proves the potential for personally tailored immunotherapies to yield more effective and safer cancer treatments using snapTILs. Citation Format: Tithi Ghosh Halder, Shelby Rheinschmidt, Sydney Adamson, Anna Larson, Taylor Bargenquast, Ryan Rodriguez del Villar, Serina Ng, Kate Gutowsky, Alexis Weston, Trason Thode, Mohan Kaadige, Erin Kelley, Jorge Soria-Bustos, Jorge Giron, John Altin, Raffaella Soldi, Sunil Sharma. Selective Neoantigens Peptide TILs (snapTILs): A next generation tumor infiltrating lymphocytes (TIL) therapy platform. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4060.

A single-amino acid substitution in the adaptor LAT accelerates TCR proofreading kinetics and alters T-cell selection, maintenance and function

Mature T cells must discriminate between brief interactions with self-peptides and prolonged binding to agonists. The kinetic proofreading model posits that certain T-cell antigen receptor signaling nodes serve as molecular timers to facilitate such discrimination. However, the physiological significance of this regulatory mechanism and the pathological consequences of disrupting it are unknown. Here we report that accelerating the normally slow phosphorylation of the linker for activation of T cells (LAT) residue Y136 by introducing an adjacent Gly135Asp alteration (LATG135D) disrupts ligand discrimination in vivo. The enhanced self-reactivity of LATG135D T cells triggers excessive thymic negative selection and promotes T-cell anergy. During Listeria infection, LATG135D T cells expand more than wild-type counterparts in response to very weak stimuli but display an imbalance between effector and memory responses. Moreover, despite their enhanced engagement of central and peripheral tolerance mechanisms, mice bearing LATG135D show features associated with autoimmunity and immunopathology. Our data reveal the importance of kinetic proofreading in balancing tolerance and immunity.

Maturation of circulating Ly6ChiCCR2+ monocytes by mannan-MOG induces antigen-specific tolerance and reverses autoimmune encephalomyelitis.

Autoimmune diseases affecting the CNS not only overcome immune privilege mechanisms that protect neural tissues but also peripheral immune tolerance mechanisms towards self. Together with antigen-specific T cells, myeloid cells are main effector cells in CNS autoimmune diseases such as multiple sclerosis, but the relative contributions of blood-derived monocytes and the tissue resident macrophages to pathology and repair is incompletely understood. Through the study of oxidized mannan-conjugated myelin oligodendrocyte glycoprotein 35-55 (OM-MOG), we show that peripheral maturation of Ly6ChiCCR2+ monocytes to Ly6ChiMHCII+PD-L1+ cells is sufficient to reverse spinal cord inflammation and demyelination in MOG-induced autoimmune encephalomyelitis. Soluble intradermal OM-MOG drains directly to the skin draining lymph node to be sequestered by subcapsular sinus macrophages, activates Ly6ChiCCR2+ monocytes to produce MHC class II and PD-L1, prevents immune cell trafficking to spinal cord, and reverses established lesions. We previously showed that protection by OM-peptides is antigen specific. Here, using a neutralizing anti-PD-L1 antibody in vivo and dendritic cell-specific Pdl1 knockout mice, we further demonstrate that PD-L1 in non-dendritic cells is essential for the therapeutic effects of OM-MOG. These results show that maturation of circulating Ly6ChiCCR2+ monocytes by OM-myelin peptides represents a novel mechanism of immune tolerance that reverses autoimmune encephalomyelitis.

Abstract 1376: Dysfunctional and tolerant CD8 T cell persistence in premalignant lesions

Abstract T cells have the potential to carry out potent anti-tumor responses. Most studies examining T cell-cancer interactions have been directed toward late-stage tumors, but much less is known about how T cells respond to premalignant lesions. Using a clinically relevant liver cancer mouse model (Albumin-Stop-Large T Antigen; AST) in which the SV40 Large T Antigen (TAG) serves as oncogene and tumor neoantigen, we previously demonstrated that TAG-specific CD8 T cells (TCR-TAG) rapidly become dysfunctional (unable to produce cytokines and cytolytic molecules) after entering premalignant liver lesions, although they persist long-term. We hypothesized that peripheral tolerance mechanisms, which prevent autoimmunity against self-antigens, drive T cell dysfunction in premalignant lesions. To test this, we compared CD8 T cell (TCR-GAG) responses to a liver self-antigen (GAG) to TCR-TAG responses to the TAG neoantigen in premalignant hepatocytes. We found that liver-reactive TCR-GAG were unable to produce cytokines, similar to neoantigen-specific TCR-TAG; however, in contrast, they failed to persist. To test whether oncogenic transformation of hepatocytes promoted T cell persistence, we crossed Alb-GAG and AST mice to generate a model in which GAG and TAG was expressed in premalignant hepatocytes (ASTxAlb-GAG). We found that both TCR-GAG and TCR-TAG transferred into ASTxAlb-GAG mice bearing premalignant lesions driven by the TAG oncogene rapidly lost the ability to produce cytokines; however, only TCR-TAG persisted while TCR-GAG quickly disappeared. To understand why the TCR-GAG failed to persist, we assessed proliferation and cell cycling after T cells encountered their cognate antigen. While both TCR-GAG and TCR-TAG were rapidly activated and began proliferating, TCR-GAG exited cell cycle and began decreasing in number after four cell divisions, while TCR-TAG continued to divide and increase in number. Antigen amount and localization may regulate T cell proliferation and persistence. We found much higher levels of TAG-encoding versus GAG-encoding mRNA in the liver, suggesting that higher antigen expression may be required for T cell persistence. T cell responses can be directed against both shared tumor self-antigens and neoantigens. By dissecting the determinants of CD8 T cell function and persistence in response to self and non-self-antigens, these studies could inform strategies to boost anti-tumor CD8 T cell responses in cancer patients. Citation Format: Jessica J. Roetman, Megan M. Erwin, Minna K. Apostolova, Mary Philip. Dysfunctional and tolerant CD8 T cell persistence in premalignant lesions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1376.

The activation of self-antigen specific T cell repertoire during acute tissue injury.

Abstract Self-antigen specific T cells are prevalent in the mature adaptive immune repertoire. At steady state, these self-antigen specific T cells appear to be regulated through a combination of central and peripheral mechanisms of tolerance. Understanding how these self-antigen specific T cells escape tolerance to mediate autoimmune disease remains of significant scientific and clinical interest. Importantly, the mechanisms that determine whether the self-reactivity will exacerbate or regulate the ongoing immune response are unknown. Utilizing an experimental animal model where mice express a complex of three model T cell epitopes (2W, gp66, and OVA) in a tissue restricted manner, we identified and tracked the activation of endogenous polyclonal T cells that recognize these transgenic epitopes as self-antigens. Interestingly, in the context of acute injury to lung tissue of mice expressing the epitopes in the alveolar epithelium, we detect an asymmetric expansion of the self-antigen specific regulatory T cell (Treg) compartment while the conventional T cell populations remained static. These findings suggest that the self-antigen specific T cell repertoire is uniquely programmed to generate a protective response to acute tissue injury.

Abstract 245: Antibody Responses To ApoA-I Rely On An Interplay Between B And T Cells

Apolipoprotein A-I (ApoA-I), the major protein of high-density lipoprotein (HDL), has been investigated as the target and regulatory element of immune responses in both patients and mice susceptible to atherosclerosis. Previous work by our lab has focused on investigating the immune responses to ApoA-I in wild-type mice as a strategy to understand their role in models of atherosclerosis and other inflammatory conditions. We hypothesize that peripheral immunologic tolerance is responsible for regulating the dynamic immune response to ApoA-I. To examine this, we first evaluated antibody profiles to ApoA-I in both wild-type C57BL/6 and LDL receptor knockout mice and found that anti-ApoA-I antibodies naturally develop to the protein. To determine whether this response was T cell dependent or independent, we examined whether nu/nu mice on a BALB/c background, and the parent strain, displayed the phenotype. These studies showed that both nu/nu, or wild type BALB/c mice fail to mount antibody responses to ApoA-I suggesting a regulatory mechanism might be responsible for suppressing this antibody response. Ex vivo stimulation of immune cells with ApoA-I provide evidence of both B cell and T cell activation, suggesting that peripheral tolerance mechanisms may be responsible for regulating the humoral and cellular immune response to ApoA-I. These findings agree with previous studies where ApoA-I has been shown to regulate T cell activity in the context of atherosclerosis by inducing the development of regulatory T cells, which assist in suppressing the development of plaque formation; as well as studies showing a higher propensity toward Treg development in BALB/c mice. Ongoing experiments, which more clearly characterize the role of B cells and T cells in response to ApoA-I, will be presented with the goal of clarifying the immune mechanisms responsible for anti-ApoA-I autoimmunity. These data will help guide continued understanding of the role of immune responses to ApoA-I in atherosclerotic disease progression.

Serum autoantibodyome reveals that healthy individuals share common autoantibodies

SUMMARYAutoantibodies are a hallmark of both autoimmune disease and cancer, but they also occur in healthy individuals. Here, we perform a meta-analysis of nine datasets and focus on the common autoantibodies shared by healthy individuals. We report 77 common autoantibodies based on the protein microarray data obtained from probing 182 healthy individual sera on 7,653 human proteins and an additional 90 healthy individual sera on 1,666 human proteins. There is no gender bias; however, the number of autoantibodies increase with age, plateauing around adolescence. We use a bioinformatics pipeline to determine possible molecular-mimicry peptides that can contribute to the elicitation of these common autoantibodies. There is enrichment of intrinsic properties of proteins like hydrophilicity, basicity, aromaticity, and flexibility for common autoantigens. Subcellular localization and tissue-expression analysis reveal that several common autoantigens are sequestered from the circulating autoantibodies.

Liver metastasis restrains immunotherapy efficacy via macrophage-mediated T cell elimination

Abstract Metastasis is the primary cause of cancer mortality, and cancer frequently metastasizes to the liver. It is not clear whether liver immune tolerance mechanisms contribute to cancer outcomes. We report that liver metastases diminish immunotherapy efficacy systemically in patients and preclinical models. Patients with liver metastases derive limited benefit from immunotherapy independent of other established biomarkers of response. In multiple mouse models, we show that liver metastases siphon activated CD8+ T cells from systemic circulation. Within the liver, activated antigen-specific Fas+CD8+ T cells undergo apoptosis following their interaction with FasL+CD11b+F4/80+ monocyte-derived macrophages. Consequently, liver metastases create a systemic immune desert in preclinical models. Similarly, patients with liver metastases have reduced peripheral T cell numbers and diminished tumoral T cell diversity and function. In preclinical models, liver-directed radiotherapy eliminates immunosuppressive hepatic macrophages, increases hepatic T cell survival and reduces hepatic siphoning of T cells. Thus, liver metastases co-opt host peripheral tolerance mechanisms to cause acquired immunotherapy resistance through CD8+ T cell deletion, and the combination of liver-directed radiotherapy and immunotherapy could promote systemic antitumor immunity. This work was supported in part by research grants from the NIH/NCI grants for WZ (CA248430, CA123088, CA099985, CA193136, and CA152470); AC (1UM1HG006508); TSL (U01CA216449); IEN (CA233487); FW (S10OD020053); MAM (CA240515) and the NIH through the University of Michigan Rogel Cancer Center Support Grant (P30CA46592).