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Pancreatic ductal adenocarcinoma (PDA) is a lethal and metastatic malignancy resistant to therapy. Elucidating how pancreatic tumor-specific T cells differentiate and are maintained in vivo could inform novel therapeutic avenues to promote T cell antitumor activity. Here, we show that the spleen is a critical site harboring tumor-specific CD8 T cells that functionally segregate based on differential Cxcr3 and Klrg1 expression. Cxcr3+ Klrg1- T cells express the memory stem cell marker Tcf1, whereas Cxcr3-Klrg1 + T cells express GzmB consistent with terminal differentiation. We identify a Cxcr3+ Klrg1+ intermediate T cell subpopulation in the spleen that is highly enriched for tumor specificity. However, tumor-specific T cells infiltrating primary tumors progressively downregulate both Cxcr3 and Klrg1 while upregulating exhaustion markers PD-1 and Lag-3. We show that antigen-specific T cell infiltration into PDA is Cxcr3 independent. Further, Cxcr3-deficiency results in enhanced antigen-specific T cell IFNγ production in primary tumors, suggesting that Cxcr3 promotes loss of effector function. Ultimately, however, Cxcr3 was critical for mitigating cancer cell dissemination following immunotherapy with CD40 agonist + anti-PD-L1 or T cell receptor engineered T cell therapy targeting mesothelin. In the absence of Cxcr3, splenic Klrg1 + GzmB + antitumor T cells wain while pancreatic cancer disseminates suggesting a role for these cells in eliminating circulating metastatic tumor cells. Intratumoral myeloid cells are poised to produce Cxcl10, whereas splenic DC subsets produce Cxcl9 following immunotherapy supporting differential roles for these chemokines on T cell differentiation. Together, our study supports that Cxcr3 mitigates tumor cell dissemination by impacting peripheral T cell fate rather than intratumoral T cell trafficking.

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Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy resistant to therapies, including immune-checkpoint blockade. We investigated two distinct strategies to modulate tumor-associated macrophages (TAM) to enhance cellular therapy targeting mesothelin in an autochthonous PDA mouse model. Administration of an antibody to colony-stimulating factor (anti-Csf1R) depleted Ly6Clow protumorigenic TAMs and significantly enhanced endogenous T-cell intratumoral accumulation. Despite increasing the number of endogenous T cells at the tumor site, as previously reported, TAM depletion had only minimal impact on intratumoral accumulation and persistence of T cells engineered to express a murine mesothelin-specific T-cell receptor (TCR). TAM depletion interfered with the antitumor activity of the infused T cells in PDA, evidenced by reduced tumor cell apoptosis. In contrast, TAM programming with agonistic anti-CD40 increased both Ly6Chigh TAMs and the intratumoral accumulation and longevity of TCR-engineered T cells. Anti-CD40 significantly increased the frequency and number of proliferating and granzyme B+ engineered T cells, and increased tumor cell apoptosis. However, anti-CD40 failed to rescue intratumoral engineered T-cell IFNγ production. Thus, although functional modulation, rather than TAM depletion, enhanced the longevity of engineered T cells and increased tumor cell apoptosis, ultimately, anti-CD40 modulation was insufficient to rescue key effector defects in tumor-reactive T cells. This study highlights critical distinctions between how endogenous T cells that evolve in vivo, and engineered T cells with previously acquired effector activity, respond to modifications of the tumor microenvironment.

SummaryPancreatic ductal adenocarcinoma (PDA) is a lethal malignancy resistant to immunotherapy. The pancreatic tumor microenvironment is shaped and maintained by myeloid cells that outnumber tumor cells. Here, using monocyte fate-mapping PDA mouse models and human tumor tissues, we identify monocytes give rise to most heterogeneous macrophage subpopulations in PDA. We show that monocyte differentiation is governed by the local presence of CD4, but not CD8, T cells. We demonstrate that tumor specific CD4 T cells induce monocyte differentiation into antitumor MHCIIhiproinflammatory macrophages dependent on non-redundant IFNγ and CD40 signaling pathways that suppress tumor growth. Pancreatic tissue-resident macrophages exhibit an immunosuppressive pro-tumor state that is refractory to the modulatory effects of antitumor CD4 T cells. Intratumoral monocytes adopt a pro-tumor fate indistinguishable from tissue-resident macrophages following CD4 T cell depletion. Thus, tumor-specific CD4 T cell governance of monocyte fate promotes immune-mediated control of solid tumors.Highlights▪Circulating monocytes are progenitors to most heterogeneous macrophage subsets in PDA▪Monocyte-derived macrophage acquisition of an MHCIIhiphenotype is dependent on tumor-specific CD4 T cells▪In the absence of CD4 T cells, monocyte-derived macrophages acquire tissue resident macrophage traits and tumors rapidly progress▪IFNγ and CD40 signaling are nonredundant and critical determinants of intratumoral monocyte fate

Ageing of the immune system, or immunosenescence, contributes to the morbidity and mortality of the elderly(1,2). To define the contribution of immune system ageing to organism ageing, here we selectively deleted Ercc1, which encodes a crucial DNA repair protein(3,4), in mouse haematopoietic cells to increase the burden of endogenous DNA damage and thereby senescence(5–7) in the immune system only. We show that Vav-iCre(+/−);Ercc1(−/fl) mice were healthy into adulthood, then displayed premature onset of immunosenescence characterized by attrition and senescence of specific immune cell populations and impaired immune function, similar to changes that occur during ageing in wild-type mice(8–10). Notably, non-lymphoid organs also showed increased senescence and damage, which suggests that senescent, aged immune cells can promote systemic ageing. The transplantation of splenocytes from Vav-iCre(+/−);Ercc1(−/fl) or aged wild-type mice into young mice induced senescence in trans, whereas the transplantation of young immune cells attenuated senescence. The treatment of Vav-iCre(+/−);Ercc1(−/fl) mice with rapamycin reduced markers of senescence in immune cells and improved immune function(11,12). These data demonstrate that an aged, senescent immune system has a causal role in driving systemic ageing and therefore represents a key therapeutic target to extend healthy ageing.

BackgroundAchieving robust responses with adoptive cell therapy for the treatment of the highly lethal pancreatic ductal adenocarcinoma (PDA) has been elusive. We previously showed that T cells engineered to express a mesothelin-specific T cell receptor (TCRMsln) accumulate in autochthonous PDA, mediate therapeutic antitumor activity, but fail to eradicate tumors in part due to acquisition of a dysfunctional exhausted T cell state.MethodsHere, we investigated the role of immune checkpoints in mediating TCR engineered T cell dysfunction in a genetically engineered PDA mouse model. The fate of engineered T cells that were either deficient in PD-1, or transferred concurrent with antibodies blocking PD-L1 and/or additional immune checkpoints, were tracked to evaluate persistence, functionality, and antitumor activity at day 8 and day 28 post infusion. We performed RNAseq on engineered T cells isolated from tumors and compared differentially expressed genes to prototypical endogenous exhausted T cells.ResultsPD-L1 pathway blockade and/or simultaneous blockade of multiple coinhibitory receptors during adoptive cell therapy was insufficient to prevent engineered T cell dysfunction in autochthonous PDA yet resulted in subclinical activity in the lung, without enhancing anti-tumor immunity. Gene expression analysis revealed that ex vivo TCR engineered T cells markedly differed from in vivo primed endogenous effector T cells which can respond to immune checkpoint inhibitors. Early after transfer, intratumoral TCR engineered T cells acquired a similar molecular program to prototypical exhausted T cells that arise during chronic viral infection, but the molecular programs later diverged. Intratumoral engineered T cells exhibited decreased effector and cell cycle genes and were refractory to TCR signaling.ConclusionsAbrogation of PD-1 signaling is not sufficient to overcome TCR engineered T cell dysfunction in PDA. Our study suggests that contributions by both the differentiation pathways induced during the ex vivo T cell engineering process and intratumoral suppressive mechanisms render engineered T cells dysfunctional and resistant to rescue by blockade of immune checkpoints.

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy resistant to therapies, including immune-checkpoint blockade. We investigated two distinct strategies to modulate tumor-associated macrophages (TAM) to enhance cellular therapy targeting mesothelin in an autochthonous PDA mouse model. Administration of an antibody to colony-stimulating factor (anti-Csf1R) depleted Ly6Clow protumorigenic TAMs and significantly enhanced endogenous T-cell intratumoral accumulation. Despite increasing the number of endogenous T cells at the tumor site, as previously reported, TAM depletion had only minimal impact on intratumoral accumulation and persistence of T cells engineered to express a murine mesothelin-specific T-cell receptor (TCR). TAM depletion interfered with the antitumor activity of the infused T cells in PDA, evidenced by reduced tumor cell apoptosis. In contrast, TAM programming with agonistic anti-CD40 increased both Ly6Chigh TAMs and the intratumoral accumulation and longevity of TCR-engineered T cells. Anti-CD40 significantly increased the frequency and number of proliferating and granzyme B+ engineered T cells, and increased tumor cell apoptosis. However, anti-CD40 failed to rescue intratumoral engineered T-cell IFNγ production. Thus, although functional modulation, rather than TAM depletion, enhanced the longevity of engineered T cells and increased tumor cell apoptosis, ultimately, anti-CD40 modulation was insufficient to rescue key effector defects in tumor-reactive T cells. This study highlights critical distinctions between how endogenous T cells that evolve in vivo, and engineered T cells with previously acquired effector activity, respond to modifications of the tumor microenvironment.

Genocea’s ATLAS platform is an empirical bioassay that uses patient autologous immune cells to identify both true neoantigens and Inhibigens࣪ for inclusion in or exclusion from neoantigen-targeted vaccines and cell therapies, respectively. In ATLAS, patient-derived antigen-presenting cells (APCs) are pulsed with E. coli expressing individual mutations identified from the patient mutanome ± listeriolysin O, enabling interrogation of both CD8+ and CD4+ T cell recognition. True neoantigens induce T cell activation and cytokine release, while Inhibigens lead to a downregulation of T cell responses and thus can promote tumor growth. Previous ATLAS screening of CD8+ T cells from mice carrying B16F10 mouse melanoma tumors identified both neoantigens and Inhibigens. Upon therapeutic vaccination, adjuvanted neoantigens generated immunogenicity and anti-tumor efficacy1. In contrast, therapeutic vaccination with multiple ATLAS-identified Inhibigens, alone or in combination with an otherwise-protective vaccine, led to accelerated tumor growth, impaired T cell responses, and abrogated tumor immune infiltration. Our current study further explores the mechanism of Inhibigen-specific responses through adoptive transfer of vaccine-experienced T cells into tumor-bearing recipient mice, as well as through analysis of T cell gene expression. Additionally, in order to determine whether Inhibigen identification and treatment translates into pro-tumor effects universally across tumor models, we performed ATLAS screening on CD4+ and CD8+ T cells isolated from mice bearing orthotopic KPC pancreatic cancer. Out of 73 total non-synonymous mutations, we successfully identified 14 CD4+ and 15 CD8+ true neoantigens, and 16 CD4+ and 18 CD8+ Inhibigens. This is the first known comprehensive characterization of endogenous antigens in this model. Therapeutic administration of neoantigens as adjuvanted peptide vaccines in KPC tumor-bearing mice led to smaller tumor sizes and reduced ascites volumes, whereas Inhibigen vaccination accelerated tumor growth. Mouse studies are ongoing and additional data will be presented. Taken together, our data from human cancer patients and two mouse cancer models support the importance of appropriate neoantigen selection and Inhibigen identification and exclusion from cancer therapies. Genocea’s GEN-011 neoantigen-targeted peripheral T cell (NPT) therapy candidate, designed using ATLAS-identified neoantigens and omitting Inhibigens, is being evaluated in an ongoing clinical trial (NCT04596033). Continued exploration of mechanisms of action of Inhibigen-specific responses may reveal new paradigms of cancer immune evasion. 1H Lam et al, Cancer Discov 2021;11:1-18 Citation Format: Hanna S. Starobinets, Victoria L. DeVault, Zoe C. Schmiechen, Ebony A. Miller, Eduardo Cruz, Meagan R. Rollins, Adam L. Burrack, Stephanie J. Rinaldi, Julie Arnold, Emily Tjon, Kyle Gonzalez, Dimitry Lineker, Hubert Lam, Ingunn M. Stromnes, Jessica B. Flechtner. ATLAS-identified Inhibigen-specific responses accelerate tumor growth in mouse melanoma and pancreatic cancer [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 2088.

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy that is currently the third leading cause of cancer related deaths. PDA creates a suppressive fibroinflammatory tumor microenvironment (TME) composed of stromal and immune cells that inhibit anti-tumor immune responses. Tumor associated macrophages (TAMs) account for a large percentage of the TME and have remarkably heterogeneous functions, with some subsets promoting anti-tumor responses while others suppress tumor specific T-cells. While many studies have highlighted macrophage heterogeneity in PDA, it remains unclear mechanisms regulating monocyte differentiation into pro vs anti-tumor populations. To understand monocyte differentiation in PDA, we performed trajectory analysis on scRNA-seq data from mouse and human tumors and identified predicted monocyte differentiation pathways toward either MHCII-hi anti-tumor TAMs or Trem2-hi pro-tumor TAMs. Using a newly designed monocyte tracking mouse (CCR2CreER x R26tdTomato) implanted with orthotopic tumors that express the click beetle luciferase (CB) neoantigen, we temporally tracked monocyte differentiation within tumors into TAM populations. Furthermore, using antibody depletion, we found that CD4 depletion led to increased monocyte differentiation into pro-tumor macrophages and a dramatic downregulation of PDL1 on monocyte derived TAMs. Finally, using Ifngr1−/− mice implanted with CB+ tumors, we identify that polarization toward anti-tumor macrophages was driven by IFNy, but TAM PDL1 expression was IFNy independent. Together these data are the first to address monocyte differentiation within PDA and identify previously unexpected role for CD4 T cells governing TAM differentiation program.

Pancreatic ductal adenocarcinoma (PDA) is the 4th leading cause of cancer related deaths and has a dismal 5-year survival rate of 10 percent. PDA lethality is attributed to late diagnosis, early metastasis, and therapeutic resistance. Metastasis can occur before the development of histologically detectable tumors and is a leading cause of cancer-related deaths. We identified that pancreatic tumor cells derived from mice that resist immunotherapy (e.g., tumor escape variants, TEV) and re-implanted into the pancreas of syngeneic and immunocompetent mice rapidly metastasize, reflecting the pathogenesis of human PDA. We show that TEVs retain the targeted tumor antigen, and despite a defect in IFNgamma-inducible MHC class I upregulation, TEVs remain sensitive to tumor antigen specific T cell-mediated lysis in vitro, suggesting TEVs may confer unique qualities in vivo to resist T cell killing. Using a peptide:MHC tetramer to identify the tumor-specific CD8 T cells, we identified that intratumoral T cells in EV tumors have increased Granzyme B production and a reduction in prototypical exhaustion markers PD1, Lag3, and Tox, perhaps due to reduced MHC class I signaling. Notably, primary tumors from TEVs were significantly enriched for Foxp3+ Tregs as compared to parental tumors. Using a genetic model, we identified that Treg depletion resulted in a drastic reduction in tumor burden and metastasis and improved tumor-specific T cell function in TEV tumors. Tumor-cell intrinsic changes driving Treg accumulation in TEVs will be discussed. In summary, Tregs are key drivers of both T cell exhaustion and immunosuppression in pancreatic cancer and may prove a valuable clinical target for tumors that evade immune checkpoint blockade. Supported by grants from NIH (R01 CA249393)

Pancreatic cancer is a particularly lethal malignancy that resists immunotherapy. In this study, using a preclinical pancreatic cancer murine model, we demonstrate a progressive decrease in IFN-γ and granzyme B and a concomitant increase in Tox and IL-10 in intratumoral tumor-specific T cells. Intratumoral myeloid cells produced elevated IL-27, a cytokine that correlates with poor patient outcome. Abrogating IL-27 signaling significantly decreased intratumoral Tox+ T cells and delayed tumor growth yet was not curative. Agonistic αCD40 decreased intratumoral IL-27–producing myeloid cells, decreased IL-10–producing intratumoral T cells, and promoted intratumoral Klrg1+Gzmb+ short-lived effector T cells. Combination agonistic αCD40+αPD-L1 cured 63% of tumor-bearing animals, promoted rejection following tumor rechallenge, and correlated with a 2-log increase in pancreas-residing tumor-specific T cells. Interfering with Ifngr1 expression in nontumor/host cells abrogated agonistic αCD40+αPD-L1 efficacy. In contrast, interfering with nontumor/host cell Tnfrsf1a led to cure in 100% of animals following agonistic αCD40+αPD-L1 and promoted the formation of circulating central memory T cells rather than long-lived effector T cells. In summary, we identify a mechanistic basis for T cell exhaustion in pancreatic cancer and a feasible clinical strategy to overcome it.

BackgroundPancreatic ductal adenocarcinoma (PDA) is a lethal malignancy characterized by a highly suppressive tumor microenvironment. Despite this, engineered T cell therapy has promise for effectively targeting PDA. To identify the underlying mechanisms of antigen-specific engineered T cell immunosuppression in PDA, we create novel TCR knock-in mouse models for a robust and standardized source of naïve mesothelin (Msln)-specific T cells.MethodsSpecifically, we integrate two murine mesothelin-specific TCRs into the physiologic Trac locus in primary murine T cells and zygotes using CRISPR/Cas9 and rAAV expressing the TCR DNA. Simultaneously using CRISPR/Cas9, Msln was disrupted to circumvent T cell tolerance.ResultsThis strategy resulted in the rapid generation of homozygous TCR Trac knock-in mice and with homozygous null mutations in Msln. In these TCR-exchanged (TRex) mice, most T cells expressed the 1045 (high affinity) or 7431 (low affinity) as determined by tetramer staining. TRex T cells exhibit a naïve phenotype and rapidly differentiate into effector T cells upon antigenic stimulation. While the high affinity 1045 TCR elicits function in CD4 T cells, the lower affinity 7431 T cells exhibit a higher functional avidity and less TCR downregulation when antigen is limiting. Historical TCR transgenic T cells, in which the TCR is randomly integrated into the genome, exhibit increased PD1, CD25, and CD69, decreased functionality, and a bias to CD25-Foxp3+ Treg as compared to T cells from TRex mice. Further, TCR Trac integration in primary T cells retain superior function following repetitive antigenic stimulations retrovirally transduced T cells. Adoptive transfer of 1045 TRex T cells significantly prolongs survival of mice bearing autochthonous PDA. When combined with a vaccine, 1045 TRex T cells cause involution of the fibroinflammatory tumor stroma.ConclusionsIn sum, we rapidly generate mice that physiologically express the desired TCR, circumventing the shortcomings of standard T cell engineering strategies and TCR transgenic models.Ethics ApprovalUniversity of Minnesota Institutional Animal Care and Use Committee approved all animal studies to Dr. Ingunn Stromnes (2005-38115A.) Generation of TCR knockin (KI) animals was performed in the Mouse Genetic Laboratory at the University of Minnesota.

Background: Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy that is resistant to conventional therapies including monotherapy using PD-1 or PD-L1 inhibition. Combination agonistic anti-CD40 and PD-1/PD-L1 blockade have clinical promise in advanced cancer patients including PDA. The underlying mechanism(s) driving the therapeutic effects of this combination are ill-defined. Here, we create a syngeneic PDA animal model and utilize various genetic tools to assess how CD40 agonist, PD-L1 blockade or the combination impact tumor antigen-specific T cells using fluorescently-labeled peptide:MHC tetramers and cells in the tumor microenvironment. Molecular analyses of tumor cell escape variants is also performed. Methods: We recently developed a high-throughput orthotopic syngeneic KPC pancreatic cancer mouse model that expresses a novel model neoantigen in B6 mice described in Burrack et al., Cell Reports, 2019. We create fluorescently labeled peptide:H-2Db tetramers to track the fate of endogenous pancreatic tumor-antigen specific CD8+ T cells over time. Here, we use this model alone or mixed at a 1:1 ratio of KPC tumor cells that do not express the neoantigen to examine how agnostic anti-CD40 (a single dose, clone FGK145), anti-PDL1 (3 doses, clone 10F.932), or the combination impact tumor growth in the pancreas over time using bioluminescent imaging and high-resolution ultrasound. We use multiparameter flow cytometry to investigate how anti-CD40 +/- PD-L1 blockade impacts the phenotype, longevity and functionality of tetramer-binding T cells over time. We assess how other immune cell lineages are altered systemically and in the tumor microenvironment by quantifying myeloid subpopulations, B cells, NK cells and regulatory T cells following therapy. We use Batf3-/- mice and XCR1VenusDTR mice to assess the role of conventional type I dendritic cells (cDC1s) on therapeutic efficacy. We employ both cytokine and chemokine reporter strains to identify how anti-CD40 +/- PD-L1 blockade impacts inflammatory gene expression in immune cells enriched the tumor microenvironment. We examine the persistence and location of tetramer-binding T cells in the pancreas, lung and liver of mice following tumor eradication. Additionally, we re-derive resistant tumor cells from mice and evaluate the integrity of MHC class I antigen processing and presentation pathways. Finally, single cell sequencing is performed to assess the traits of subpopulations of tumor-antigen specific T cells that correlate with enhanced antitumor activity following therapy. Results: We show that anti-CD40 or anti-PD-L1 monotherapy have significant yet transient antitumor effects in mice with neoantigen+ PDA with distinct effects on tumor specific T cells. Objective responses occur in 100% of the monotherapy treated mice and survival is significantly prolonged. However, tumors recur in 100% of these animals. Tumor escape variants defective in MHC class I protein and Tap1 gene expression following IFN-gamma treatment ultimately emerge. In contrast, combination agonistic anti-CD40 + PD-L1 blockade synergize therapeutically resulting in cures in 60% of the animals and formation of pancreas resident memory T cells that specifically bind tetramer and express CD49a and CD103 following tumor eradication. Mechanistically, the combination selectively expands conventional type 1 dendritic cells (cDC1s) in the spleens and tumors of tumor-bearing animals. cDC1s in PDA are CD11c+MHCII+ and express CD8, CD103 and Xcr1. Using Batf3-/- mice or an Xcr1venusDTR transient cDC1 depletion model, we demonstrate a striking dependency on cDC1s for therapeutic benefit with anti-CD40 or PD-L1 blockade. Unexpectedly, we find that the expansion of cDC1s in pancreatic tumor-bearing animals is partially dependent on Xcr1 expression by DCs. Anti-CD40+PD-L1 blockade significantly expand the number of tetramer-binding T cells that express KLRG1 in PDA. The tetramer-binding T cells remain PD-1+ yet have lower expression of Lag3 and have heightened polyfunctionality as measured by cytokine production. Further studies using chemokine and cytokine reporter models, we uncover key differences in how anti-CD40 and anti-PD-L1 impact inflammatory gene expression by antigen presenting cells in PDA. Finally, we demonstrate the requirement for tumor neoantigen expression for efficacy because in mice that have tumors containing a 50:50 mixture of neoantigen+ pancreatic tumor cells with neoantigen- pancreatic tumor cells, combination anti-CD40 + PD-L1 blockade results in elimination of predominantly those tumor cells that express the neoantigen. Further single cell sequencing data on how this combination impacts tumor-antigen specific T cell subpopulations as well as epitope spreading will be discussed. Conclusions: These findings reveal for the first time to our knowledge that anti-CD40 + PD-L1 blockade synergize via the expansion of cDC1s in pancreatic tumor-bearing animals. Instead of anti-CD40 promoting priming of neoantigen-specific T cells, we find that this combination promotes the systemic expansion and intratumoral accumulation of KLRG1+ tumor-specific T cells that eradicate PDA and form pancreas resident CD49a+CD103+ memory T cells. Citation Format: Adam L. Burrack, Meagan R. Rollins, Ellen J. Spartz, Jackson F. Raynor, Iris Wang, Jason Mitchell, Tsuneyasu Kaisho, Brian Fife, Ross Kedl, Stephen Shen, Ingunn M. Stromnes. Mechanisms governing efficacy of combination CD40 agonist and anti-PD-L1 in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr NG12.

Type 1 diabetes is caused by autoreactive T cell-mediated β cell destruction. Even though co-inhibitory receptor programmed death-1 (PD-1) restrains autoimmunity, the expression and regulation of its cognate ligands on β cell remains unknown. Here, we interrogated β cell-intrinsic programmed death ligand-1 (PD-L1) expression in mouse and human islets. We measured a significant increase in the level of PD-L1 surface expression and the frequency of PD-L1+ β cells as non-obese diabetic (NOD) mice aged and developed diabetes. Increased β cell PD-L1 expression was dependent on T cell infiltration, as β cells from Rag1-deficient mice lacked PD-L1. Using Rag1-deficient NOD mouse islets, we determined that IFN-γ promotes β cell PD-L1 expression. We performed analogous experiments using human samples, and found a significant increase in β cell PD-L1 expression in type 1 diabetic samples compared to type 2 diabetic, autoantibody positive, and non-diabetic samples. Among type 1 diabetic samples, β cell PD-L1 expression correlated with insulitis. In vitro experiments with human islets from non-diabetic individuals showed that IFN-γ promoted β cell PD-L1 expression. These results suggest that insulin-producing β cells respond to pancreatic inflammation and IFN-γ production by upregulating PD-L1 expression to limit self-reactive T cells.

The autoimmune condition is a primary obstacle to inducing tolerance in type 1 diabetes patients receiving allogeneic pancreas transplants. It is unknown how autoreactive T cells that recognize self-MHC molecules contribute to MHC-disparate allograft rejection. In this report, we show the presence and accumulation of dual-reactive, that is autoreactive and alloreactive, T cells in C3H islet allografts that were transplanted into autoimmune diabetic NOD mice. Using high-throughput sequencing, we discovered that T cells prevalent in allografts share identical TCRs with autoreactive T cells present in pancreatic islets. T cells expressing TCRs that are enriched in allograft lesions recognized C3H MHC molecules, and five of six cell lines expressing these TCRs were also reactive to NOD islet cells. These results reveal the presence of autoreactive T cells that mediate cross-reactive alloreactivity, and indicate a requirement for regulating such dual-reactive T cells in tissue replacement therapies given to autoimmune individuals.

Organ transplants are rapidly rejected because T cells in the recipient attack the foreign MHC molecules on the graft. The robustness of the T cell response to histoincompatible tissue is not understood. We found that mice have many small T cell populations with Ag receptors specific for a foreign MHC class II molecule type loaded with peptides from leukocytes from the graft. These T cells proliferated modestly after skin transplantation and underwent relatively weak functional differentiation compared with T cells stimulated by a vaccine. Thus, the potency of the T cell response to histoincompatible tissue is likely due to many small T cell populations responding weakly to hundreds of MHC-bound peptides from graft-derived leukocytes.

Type 1 diabetes (T1D) results from destruction of pancreatic beta cells by T cells of the immune system. Despite improvements in insulin analogs and continuous blood glucose level monitoring, there is no cure for T1D, and some individuals develop life-threatening complications. Pancreas and islet transplantation have been attractive therapeutic approaches; however, transplants containing insulin-producing cells are vulnerable to both recurrent autoimmunity and conventional allograft rejection. Current immune suppression treatments subdue the immune system, but not without complications. Ideally a successful approach would target only the destructive immune cells and leave the remaining immune system intact to fight foreign pathogens. This review discusses the autoimmune diabetes disease process, diabetic complications that warrant a transplant, and alloimmunity. First, we describe the current understanding of autoimmune destruction of beta cells including the roles of CD4 and CD8 T cells and several possibilities for antigen-specific tolerance induction. Second, we outline diabetic complications necessitating beta cell replacement. Third, we discuss transplant recognition, potential sources for beta cell replacement, and tolerance-promoting therapies under development. We hypothesize that a better understanding of autoreactive T cell targets during disease pathogenesis and alloimmunity following transplant destruction could enhance attempts to re-establish tolerance to beta cells.

Type 1 diabetes (T1D) results from T cell–mediated destruction of insulin-producing β-cells. Insulin represents a key self-antigen in disease pathogenesis, as recent studies identified proinsulin-responding T cells from inflamed pancreatic islets of organ donors with recent-onset T1D. These cells respond to an insulin B-chain (InsB) epitope presented by the HLA-DQ8 molecule associated with high T1D risk. Understanding insulin-specific T-cell frequency and phenotype in peripheral blood is now critical. We constructed fluorescent InsB10–23:DQ8 tetramers, stained peripheral blood lymphocytes directly ex vivo, and show DQ8+ patients with T1D have increased tetramer+ CD4+ T cells compared with HLA-matched control subjects without diabetes. Patients with a shorter disease duration had higher frequencies of insulin-reactive CD4+ T cells, with most of these cells being antigen experienced. We also demonstrate that the number of insulin tetramer+ effector memory cells is directly correlated with insulin antibody titers, suggesting insulin-specific T- and B-cell interactions. Notably, one of four control subjects with tetramer+ cells was a first-degree relative who had insulin-specific cells with an effector memory phenotype, potentially representing an early marker of T-cell autoimmunity. Our results suggest that studying InsB10–23:DQ8 reactive T-cell frequency and phenotype may provide a biomarker of disease activity in patients with T1D and those at risk.

Immune checkpoint blockade has been largely ineffective for treating pancreatic ductal adenocarcinoma (PDA). Here, we develop a novel model of pancreatic cancer to investigate reasons for response and failure to immune checkpoint blockade in this lethal malignancy. Primary tumor epithelial cell clones from the genetically engineered KPC mouse model transduced to express a specific luciferase antigen, commonly used for bioluminescent in mice, rapidly establish tumors similar to parental cells after orthotopic implantation into syngeneic mice. Unexpectedly, αPD-L1 or αPD-1, which fail to elicit responses to luciferase- KPC parental cells, induce objective responses to luciferase+ KPC clones and prolong animal survival. We identify the immunodominant luciferase H- 2Db-restricted epitope and generate a fluorescently labeled peptide:MHC tetramer that specifically binds PDA-specific CD8 T cells. Up to 40% of tumor-infiltrating T cells bind this tetramer, yet most of these cells co-express PD-1 and Lag-3 and are dysfunctional. αPD-L1 enhances the systemic expansion of tetramer+ T cells and induced the accumulation of PD-1+ Ki67+ and Ki67- tetramer+ T cells in PDA. αPD-L1 significantly reduced the frequency of intra-tumoral tetramer+ T cells that expressed Lag-3 resulting in enhanced ex vivo peptide-specific cytokine production. However, tumors rapidly returned despite T cell infiltration and prolonged immunotherapy. Current efforts are underway to study the evolution of PDA-specific T cells and tumor clones using single cell technologies to inform clinical immunotherapy design.

Chikungunya virus (CHIKV) and Ross River virus (RRV) cause a debilitating, and often chronic, musculoskeletal inflammatory disease in humans. Macrophages constitute the major inflammatory infiltrates in musculoskeletal tissues during these infections. However, the precise macrophage effector functions that affect the pathogenesis of arthritogenic alphaviruses have not been defined. We hypothesized that the severe damage to musculoskeletal tissues observed in RRV- or CHIKV-infected mice would promote a wound-healing response characterized by M2-like macrophages. Indeed, we found that RRV- and CHIKV-induced musculoskeletal inflammatory lesions, and macrophages present in these lesions, have a unique gene-expression pattern characterized by high expression of arginase 1 and Ym1/Chi3l3 in the absence of FIZZ1/Relmα that is consistent with an M2-like activation phenotype. Strikingly, mice specifically deleted for arginase 1 in neutrophils and macrophages had dramatically reduced viral loads and improved pathology in musculoskeletal tissues at late times post-RRV infection. These findings indicate that arthritogenic alphavirus infection drives a unique myeloid cell activation program in inflamed musculoskeletal tissues that inhibits virus clearance and impedes disease resolution in an arginase 1-dependent manner.

Type 1 diabetes (T1D) results from T cell-mediated destruction of insulin-producing pancreatic β cells. Individuals with long-term disease are at risk of developing life-threatening complications. β cell replacement is a therapy for T1D but is limited by recurrent autoreactive T cell targeted β cell death. Thus, β cells better equipped to inhibit local T cell responses may survive longer in autoimmune recipients. Programmed-death 1 (PD-1) signaling through its ligand PD-L1 inhibits T cells, and may serve as a prominent defense in T1D. Using flow cytometric analysis, in the absence of T cells in NOD.RAG−/− mice we do not detect β cell PD-L1 expression. However, with T cells, we observed an increased proportion of β cells expressing PD-L1 in female non-obese diabetic (NOD) mice which had not developed diabetes. In addition, the majority of remaining live β cells at diabetes onset in NOD mice continue to express high levels of PD-L1. These three situations suggest that islet β cells may increase PD-L1 expression as a last line of defense to limit infiltrating T cell mediated destruction. To manipulate β cell PD-L1 expression prior to transplantation, we screened a panel of diabetes-related cytokines and found that IFN-γ enhances β cell PD-L1 expression. Unfortunately, islet transplant survival was not prolonged, which we hypothesized was due to enhanced MHC class I expression, facilitating CD8+ T cell-mediated killing. We therefore de-coupled PD-L1 from enhanced MHC I expression. Using this approach, enforced β cell PD-L1 expression delays disease recurrence. These data support our hypothesis that β cells expressing T cell co-inhibitory molecules, like PD-L1, can locally inhibit autoreactive T cells which may prevent transplant destruction.

More than one-half of the ~50 human chemokines have been associated with or implicated in the pathogenesis of type 1 diabetes, yet their actual expression patterns in the islet environment of type 1 diabetic patients remain, at present, poorly defined. Here, we have integrated a human islet culture system, murine models of virus-induced and spontaneous type 1 diabetes, and the histopathological examination of pancreata from diabetic organ donors with the goal of providing a foundation for the informed selection of potential therapeutic targets within the chemokine/receptor family. Chemokine (C-C motif) ligand (CCL) 5 (CCL5), CCL8, CCL22, chemokine (C-X-C motif) ligand (CXCL) 9 (CXCL9), CXCL10, and chemokine (C-X3-C motif) ligand (CX3CL) 1 (CX3CL1) were the major chemokines transcribed (in an inducible nitric oxide synthase–dependent but not nuclear factor-κB–dependent fashion) and translated by human islet cells in response to in vitro inflammatory stimuli. CXCL10 was identified as the dominant chemokine expressed in vivo in the islet environment of prediabetic animals and type 1 diabetic patients, whereas CCL5, CCL8, CXCL9, and CX3CL1 proteins were present at lower levels in the islets of both species. Of importance, additional expression of the same chemokines in human acinar tissues emphasizes an underappreciated involvement of the exocrine pancreas in the natural course of type 1 diabetes that will require consideration for additional type 1 diabetes pathogenesis and immune intervention studies.