Intestinal tuft cell immune privilege enables norovirus persistence

The persistent murine norovirus strain MNVCR6 is a model for human norovirus and enteric viral persistence. MNVCR6 causes chronic infection by directly infecting intestinal tuft cells, rare chemosensory epithelial cells. Although MNVCR6 induces functional MNV-specific CD8+ T cells, these lymphocytes fail to clear infection. To examine how tuft cells promote immune escape, we interrogated tuft cell interactions with CD8+ T cells by adoptively transferring JEDI (just EGFP death inducing) CD8+ T cells into Gfi1b-GFP tuft cell reporter mice. Unexpectedly, some intestinal tuft cells partially resisted JEDI CD8+ T cell-mediated killing-unlike Lgr5+ intestinal stem cells and extraintestinal tuft cells-despite seemingly normal antigen presentation. When targeting intestinal tuft cells, JEDI CD8+ T cells predominantly adopted a T resident memory phenotype with decreased effector and cytotoxic capacity, enabling tuft cell survival. JEDI CD8+ T cells neither cleared nor prevented MNVCR6 infection in the colon, the site of viral persistence, despite targeting a virus-independent antigen. Ultimately, we show that intestinal tuft cells are relatively resistant to CD8+ T cells independent of norovirus infection, representing an immune-privileged niche that can be leveraged by enteric microbes.

PD-1 maintains CD8 T cell tolerance towards cutaneous neoantigens

The peripheral T cell repertoire of healthy individuals contains self-reactive T cells1,2. Checkpoint receptors such as PD-1 are thought to enable the induction of peripheral tolerance by deletion or anergy of self-reactive CD8 T cells3-10. However, this model is challenged by the high frequency of immune-related adverse events in patients with cancer who have been treated with checkpoint inhibitors11. Here we developed a mouse model in which skin-specific expression of T cell antigens in the epidermis caused local infiltration of antigen-specific CD8 T cells with an effector gene-expression profile. In this setting, PD-1 enabled the maintenance of skin tolerance by preventing tissue-infiltrating antigen-specific effector CD8 T cells from (1) acquiring a fully functional, pathogenic differentiation state, (2) secreting significant amounts of effector molecules, and (3) gaining access to epidermal antigen-expressing cells. In the absence of PD-1, epidermal antigen-expressing cells were eliminated by antigen-specific CD8 T cells, resulting in local pathology. Transcriptomic analysis of skin biopsies from two patients with cutaneous lichenoid immune-related adverse events showed the presence of clonally expanded effector CD8 T cells in both lesional and non-lesional skin. Thus, our data support a model of peripheral T cell tolerance in which PD-1 allows antigen-specific effector CD8 T cells to co-exist with antigen-expressing cells in tissues without immunopathology.

Clonal lineage tracing reveals mechanisms skewing CD8+ T cell fate decisions in chronic infection

Although recent evidence demonstrates heterogeneity among CD8+ T cells during chronic infection, developmental relationships and mechanisms underlying their fate decisions remain incompletely understood. Using single-cell RNA and TCR sequencing, we traced the clonal expansion and differentiation of CD8+ T cells during chronic LCMV infection. We identified immense clonal and phenotypic diversity, including a subset termed intermediate cells. Trajectory analyses and infection models showed intermediate cells arise from progenitor cells before bifurcating into terminal effector and exhausted subsets. Genetic ablation experiments identified that type I IFN drives exhaustion through an IRF7-dependent mechanism, possibly through an IFN-stimulated subset bridging progenitor and exhausted cells. Conversely, Zeb2 was critical for generating effector cells. Intriguingly, some T cell clones exhibited lineage bias. Mechanistically, we identified that TCR avidity correlates with an exhausted fate, whereas SHP-1 selectively restricts low-avidity effector cell accumulation. Thus, our work elucidates novel mechanisms underlying CD8+ T cell fate determination during persistent infection and suggests two potential pathways leading to exhaustion.

Novel Mouse Models for Cancer Immunology

Mouse models for the study of cancer immunology provide excellent systems in which to test biological mechanisms of the immune response against cancer. Historically, these models have been designed to have different strengths based on the current major research questions at the time. As such, many mouse models of immunology used today were not originally developed to study questions currently plaguing the relatively new field of cancer immunology, but instead have been adapted for such purposes. In this review, we discuss various mouse model of cancer immunology in a historical context as a means to provide a fuller perspective of each model's strengths. From this outlook, we discuss the current state of the art and strategies for tackling future modeling challenges.

Neoantigen-driven B cell and CD4 T follicular helper cell collaboration promotes anti-tumor CD8 T cell responses

CD4 T follicular helper (TFH) cells support B cells, which are critical for germinal center (GC) formation, but the importance of TFH-B cell interactions in cancer is unclear. We found enrichment of TFH cell transcriptional signature correlates with GC B cell signature and with prolonged survival in individuals with lung adenocarcinoma (LUAD). We further developed a murine LUAD model in which tumor cells express B cell- and T cell-recognized neoantigens. Interactions between tumor-specific TFH and GC B cells, as well as interleukin (IL)-21 primarily produced by TFH cells, are necessary for tumor control and effector CD8 T cell function. Development of TFH cells requires B cells and B cell-recognized neoantigens. Thus, tumor neoantigens can regulate the fate of tumor-specific CD4 T cells by facilitating their interactions with tumor-specific B cells, which in turn promote anti-tumor immunity by enhancing CD8 T cell effector functions.

A reservoir of stem-like CD8+ T cells in the tumor-draining lymph node preserves the ongoing antitumor immune response

“Stem-like” TCF1+ CD8+ T (TSL) cells are necessary for long-term maintenance of T cell responses and the efficacy of immunotherapy, but, as tumors contain signals that should drive T cell terminal differentiation, how these cells are maintained in tumors remains unclear. In this study, we found that a small number of TCF1+ tumor-specific CD8+ T cells were present in lung tumors throughout their development. Yet, most intratumoral T cells differentiated as tumors progressed, corresponding with an immunologic shift in the tumor microenvironment (TME) from “hot” (T cell inflamed) to “cold” (non–T cell inflamed). By contrast, most tumor-specific CD8+ T cells in tumor-draining lymph nodes (dLNs) had functions and gene expression signatures similar to TSL from chronic lymphocytic choriomeningitis virus infection, and this population was stable over time despite the changes in the TME. dLN T cells were the developmental precursors of, and were clonally related to, their more differentiated intratumoral counterparts. Our data support the hypothesis that dLN T cells are the developmental precursors of the TCF1+ T cells in tumors that are maintained by continuous migration. Last, CD8+ T cells similar to TSL were also present in LNs from patients with lung adenocarcinoma, suggesting that a similar model may be relevant in human disease. Thus, we propose that the dLN TSL reservoir has a critical function in sustaining antitumor T cells during tumor development and in protecting them from the terminal differentiation that occurs in the TME.

Soluble N-Acetylgalactosamine-Modified Antigens Enhance Hepatocyte-Dependent Antigen Cross-Presentation and Result in Antigen-Specific CD8+ T Cell Tolerance Development

Hepatocytes compose up to 80% of the total liver and have been indicated as important players in the induction of immunologic tolerance in this organ. We show that hepatocytes possess the molecular machinery required for the cross-presentation of extracellular antigens. Using a derivative of the model antigen ovalbumin (OVA) covalently modified with a polymer containing multiple N-acetylgalactosamine residues (pGal-OVA) that enhance extracellular antigen uptake by mimicking the glycome of apoptotic debris, we show efficient hepatocyte-dependent induction of cross-tolerance of both adoptively transferred OT-I cells and endogenous OVA-specific CD8+ T lymphocytes, for example inducing tolerance to OVA-expressing skin transplants. Our study confirms that hepatocytes are capable of inducing peripheral tolerogenesis and provides proof of concept that they may be a valuable candidate for in vivo targeted tolerogenic treatments.

Inducible de novo expression of neoantigens in tumor cells and mice

Inducible expression of neoantigens in mice would enable the study of endogenous antigen-specific naïve T cell responses in disease and infection, but has been difficult to generate because leaky antigen expression in the thymus results in central T cell tolerance. Here we develop inversion-induced joined neoantigen (NINJA), using RNA splicing, DNA recombination and three levels of regulation to prevent leakiness and allow tight control over neoantigen expression. We apply NINJA to create tumor cell lines with inducible neoantigen expression, which could be used to study antitumor immunity. We also show that the genetic regulation in NINJA mice bypasses central and peripheral tolerance mechanisms and allows for robust endogenous CD8 and CD4 T cell responses on neoantigen induction in peripheral tissues. NINJA will enable studies of how T cells respond to defined neoantigens in the context of peripheral tolerance, transplantation, autoimmune diseases and cancer.

Abstract PR5: Investigating the mechanisms of immune-related adverse events using engineered animal models

The rise in checkpoint inhibitor (CPI) therapies has revolutionized oncology and informed on the mechanisms regulating natural antitumor immune responses in patients. However, because immunotherapy often results in immune-related adverse events (irAEs), CPIs have also revealed the key role that immune checkpoint receptors play in the active maintenance of immunologic tolerance towards self antigens. irAEs target a variety of organ systems and can have long-term, potentially fatal consequences for treated patients. Little is known about why irAEs occur, how to predict irAEs, or whether it is possible to block irAEs while sustaining CPI-induced antitumor effects. One of the challenges for therapeutically investigating these open questions has been the lack of suitable animal models for systematically studying irAEs in different organs. To address this, we have genetically engineered an animal model called NINJA (iNversion Inducible Joined neoAntigen), which bypasses T-cell tolerance mechanisms and allows us to induce the expression of known neoantigens de novo. Induction of neoantigens in healthy organs with NINJA is achieved by tissue-specific Cre recombinase expression and subsequent administration of doxycycline and tamoxifen (dox/tam), which expresses neoantigens in the Cre+ cells. This allows us to use either tissue-specific infection with Cre-expressing adenoviruses or tissue-specific promoters expressing Cre to control the organ that will express neoantigen after dox/tam treatment. Moreover, NINJA allows us to compare how T cells respond against antigens when presented in different contexts, from self antigens in a peripheral tissue, to neoantigens expressed during a viral infection or developing cancer. In the context of viral infection, the function of neoantigen-specific effector CD8 T cells is highly dependent on the organ expressing the neoantigen, with robust, functional effector T cells observed when antigen is induced in skin or muscle and weak, low-functioning PD-1+ T cells when antigen is induced in liver or lungs. Similarly, in absence of inflammation, neoantigen induction in hepatocytes results in rapid and dominant systemic CD8 T-cell tolerance, while induction in skin leads to effector CD8 T-cell responses. Crucially, in the latter context, CPI treatment results in severe skin irAEs. Finally, because NINJA is on a non-autoimmune-prone C57Bl/6 background, we are testing whether one can block CPI-induced irAEs while allowing CPI-induced antitumor responses. In summary, the NINJA model is demonstrating that tissues have a strong bearing on T-cell function regardless of whether antigens are encountered in the context of infection or as self antigens. Furthermore, there appears to be a hierarchy, where certain tissues (i.e., skin) are programmed to provide stronger immune responses than in others (i.e., liver). This might explain why certain tissues are prone to the development of T cell-mediated irAEs after CPI treatment.

This abstract is also being presented as Poster B1.

Citation Format: Martina Damo, Ivana William, Nikhil S. Joshi. Investigating the mechanisms of immune-related adverse events using engineered animal models [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr PR5.

Improving Efficacy and Safety of Agonistic Anti-CD40 Antibody Through Extracellular Matrix Affinity

CD40 is an immune costimulatory receptor expressed by antigen-presenting cells. Agonistic anti-CD40 antibodies have demonstrated considerable antitumor effects yet can also elicit serious treatment-related adverse events, such as liver toxicity, including in man. We engineered a variant that binds extracellular matrix through a super-affinity peptide derived from placenta growth factor-2 (PlGF-2_123-144) to enhance anti-CD40's effects when administered locally. Peritumoral injection of PlGF-2_123-144-anti-CD40 antibody showed prolonged tissue retention at the injection site and substantially decreased systemic exposure, resulting in decreased liver toxicity. In four mouse tumor models, PlGF-2_123-144-anti-CD40 antibody demonstrated enhanced antitumor efficacy compared with its unmodified form and correlated with activated dendritic cells, B cells, and T cells in the tumor and in the tumor-draining lymph node. Moreover, in a genetically engineered Braf^V600E βCat^STA melanoma model that does not respond to checkpoint inhibitors, PlGF-2_123-144-anti-CD40 antibody treatment enhanced T-cell infiltration into the tumors and slowed tumor growth. Together, these results demonstrate the marked therapeutic advantages of engineering matrix-binding domains onto agonistic anti-CD40 antibody as a therapeutic given by tumori-regional injection for cancer immunotherapy.Implications: Extracellular matrix-binding peptide conjugation to agonistic anti-CD40 antibody enhances antitumor efficacy and reduces treatment-related adverse events. Mol Cancer Ther; 17(11); 2399-411. ©2018 AACR.

The NINJA mouse: a novel model to study tissue-specific peripheral T cell tolerance

T cell inhibitory pathways induce peripheral tolerance and have evolved to avoid pathogenic autoimmunity. Generally, peripheral tolerance either prevents T cell activation or inhibits T cells during chronic responses, but it is not clear whether these functions are orchestrated by the same mechanisms. Moreover, it is not known if these mechanisms have a tissue-specific usage. Persistent viral infections and cancer leverage the T cell inhibitory pathways involved in peripheral tolerance, thus providing translational relevance to the role of these pathways in disease. However, many of the mechanisms of peripheral tolerance remain understudied, in part because few animal models can distinguish these mechanisms from those driving central tolerance. We have generated a novel mouse model (iNversion INduced Joined neoAntigen, NINJA) that bypasses central and peripheral tolerance by using genetic recombination to create a neoantigen-coding gene for de novo neoantigen expression in any tissue of choice. NINJA expresses LCMV-derived GP33–41 and GP61–80 after induction, enabling investigation of tolerance using well established immunologic tools. Prior to recombination, NINJA mice respond robustly to LCMV-Arm infection, indicating absence of tolerance. However, after recombination, LCMV GP-specific responses are significantly impaired, although mice retain the capacity of developing immunity against unrelated LCMV epitopes. PD-1 is upregulated by tolerized endogenous GP33–41-specific CD8+ T cells after hepatocyte-specific NINJA activation, thus suggesting its involvement in hepatic peripheral tolerance. We therefore propose NINJA as a model to investigate tissue-specific mechanisms of peripheral T cell tolerance.

Improving the immunogenicity of dendritic cell-derived exosome-based vaccines for the immunotherapy of melanoma

Dendritic cell (DC)-derived exosomes (Dexo) are promising vaccine candidates for the treatment of cancer.

We aimed at identifying a Dexo formulation with stronger immune stimulatory properties and efficacy as compared to the Dexo vaccines previously tested in pre-clinical and clinical settings of cancer immunotherapy. We therefore produced Dexo from DCs loaded with specific antigens and matured with the Toll-like receptor (TLR)-3 ligand poly(I:C) as danger signal.

In vivo, Dexo produced from DCs loaded with OVA and stimulated with poly(I:C) could induce efficient activation of endogenous OVA-specific CD4+ and CD8+ T cells, leading to pro-inflammatory Th1 immune responses.

We subsequently produced Dexo from DCs matured with poly(I:C) and cultured in the presence of oxidized B16F10 cell lysates (Dexo(B16+pIC)) as a source of B16F10 antigens.

Mice bearing subcutaneous B16F10 tumors were vaccinated intradermally to target tumor-draining lymph nodes (tdLN), resulting in reduced tumor growth, limited metastasis burden and, most importantly, in prolonged survival of the mice vaccinated with Dexo(B16+pIC). Such benefits were associated with increased frequencies of effector CD8+ T cells in the tdLNs, spleen and tumor masses, reduced frequencies of tumor-infiltrating exhausted PD-1+ CD8+ T cells and increased frequencies of tumor-infiltrating NK and NK-T cells obtained upon vaccination with Dexo(B16+pIC) as compared to Dexo(B16), which instead are devoid of poly(I:C) and resemble the Dexo vaccines previously tested in human patients.

Our results demonstrate that poly(I:C) is a promising candidate for the production of Dexo vaccines with improved immune stimulatory properties suitable for the immunotherapy of cancer.

Hepatocyte-dependent cross-presentation of soluble antigens induces antigen-specific CD8+ T cell tolerance

The ability of hepatocytes to cross-present soluble extracellular antigens and the related immunological outcomes remain poorly investigated.

Our work shows that murine primary hepatocytes actively uptake and process extracellular antigens in EEA1+ and TAP1+ phagosomes, which are functionally related to cross-presentation. In fact EEA1+TAP1+ organelles, which are one of the signatures of professional cross-presenting cells, are also found in the cytoplasm of hepatocytes. Moreover, in vitro hepatocyte-dependent cross-presentation of OVA to OT-I cells is sensitive to specific drug inhibitors of endosomal and proteasomal activity, providing direct evidence that endocytosed antigens enter the cross-presentation pathway.

In vivo, cross-presenting hepatocytes induce tolerance of adoptively transferred OT-I cells by clonal deletion, as pro-apoptotic markers are upregulated on hepatocyte-educated OT-I cells. Non-deleted OT-I cells show instead significantly reduced response to vaccination, indicative of anergy. Active engulfment or emperipolesis of antigen cross-presenting hepatocytes by OT-I cells is also detected in vitro, as an additional means of T cell deletion.

PD-1/PD-L1 interactions participate in the induction of hepatocyte-dependent cross-tolerance, as specific blockage of PD-L1 on hepatocytes significantly reduces the development of hepatocyte-dependent cross-tolerance.

Due to their physiologic metabolic functions and their capacity to cross-present extracellular antigens here described, we propose hepatocytes as one of the major players in the establishment of antigen-specific CD8+ T cell peripheral tolerance.

Hepatocyte-targeted expression by integrase-defective lentiviral vectors induces antigen-specific tolerance in mice with low genotoxic risk

Lentiviral vectors are attractive tools for liver-directed gene therapy because of their capacity for stable gene expression and the lack of preexisting immunity in most human subjects. However, the use of integrating vectors may raise some concerns about the potential risk of insertional mutagenesis. Here we investigated liver gene transfer by integrase-defective lentiviral vectors (IDLVs) containing an inactivating mutation in the integrase (D64V). Hepatocyte-targeted expression using IDLVs resulted in the sustained and robust induction of immune tolerance to both intracellular and secreted proteins, despite the reduced transgene expression levels in comparison with their integrase-competent vector counterparts. IDLV-mediated and hepatocyte-targeted coagulation factor IX (FIX) expression prevented the induction of neutralizing antibodies to FIX even after antigen rechallenge in hemophilia B mice and accounted for relatively prolonged therapeutic FIX expression levels. Upon the delivery of intracellular model antigens, hepatocyte-targeted IDLVs induced transgene-specific regulatory T cells that contributed to the observed immune tolerance. Deep sequencing of IDLV-transduced livers showed only rare genomic integrations that had no preference for gene coding regions and occurred mostly by a mechanism inconsistent with residual integrase activity.

CONCLUSION

IDLVs provide an attractive platform for the tolerogenic expression of intracellular or secreted proteins in the liver with a substantially reduced risk of insertional mutagenesis.