PD-1 KO Research Articles

Abstract 6367: BSI-507, a first-in-class bispecific antibody targeting PD1 and PVRIG for cancer immunotherapy

Abstract Introduction: Despite the success of anti-PD1/PDL1 therapies, only a small fraction of patients benefit from these checkpoint inhibitors (CPIs). Novel approaches to improve outcomes for patients who are resistant to current CPIs are needed. PVRIG is expressed on CD4+ and CD8+ T cells, NKT and NK cells. PVRIG binds with high affinity with its ligand PVRL2, which is expressed on tumor cells and some myeloid cells. The PVRIG-PVRL2 axis exerts an inhibitory effect on the cytotoxic activity of lymphocytes. Bispecific antibodies that exhibit dual blockade of PD1 and PVRIG provide a promising strategy to enhance anti-tumor immune response. Methods: An anti-PD1 mAb was identified from PD1 KO mice immunized with PD1-ECD-Fc and screened by our proprietary H3 (High-throughput, High-content and High-efficiency) platform. An anti-PVRIG mAb was identified from rats immunized with recombinant PVRIG-ECD-Fc and screened by the H3 platform. Both anti-PD1 and anti-PVRIG antibodies were humanized, and the anti-PD1 scFv was fused to the N-terminus of the heavy chain of the anti-PD1 antibody via a flexible linker. The binding activities and affinities were evaluated by ELISA, FACS and SPR, and the ligand blocking activities were measured by ELISA and FACS. Cell-based reporter assays were used to evaluate the functions of the anti-PD1 and anti-PVRIG mAbs alone and the bispecific antibody. In addition, the activity of the bispecific antibody to reverse PD1 and PVRIG mediated suppression of CMV pp65495-503 antigen specific CD8+ T-cell cytotoxicity was evaluated. Results: BSI-507, an anti-PD1xanti-PVRIG bispecific antibody demonstrated comparable activity to the parental anti-PD1 antibody regarding PD1 binding and PD1/PDL1 blocking. It also exhibited comparable activity to the parental anti-PVRIG antibody in PVRIG binding and PVRIG/PVRL2 blocking. Based on cell-based reporter assays, BSI-507 was able to reverse either PD1 or PVRIG mediated T-cell suppression and exhibited comparable potency to the parental antibodies. BSI-507 was also able to show enhanced reversal of both PD1 and PVRIG mediated T-cell suppression, much better than anti-PD1 or anti-PVRIG alone. In addition, BSI-507 showed the ability to reverse PD1 and PVRIG mediated suppression of CMV pp65495-503 antigen specific CD8+ T-cell cytotoxicity, stronger than either the anti-PD1 or anti-PVRIG monoclonal antibody. Summary: BSI-507 is a first-in-class anti-PD1xanti-PVRIG bispecific antibody for dual blockade of PD-1 and PVRIG pathways to enhance reversal of T cell inhibition. BSI-507 demonstrates favorable biophysical and functional characteristics, supporting the initiation of development activities including manufacturing and IND-enabling studies. Citation Format: Zeyu Peng, Xiaodong F. Liu, Hongyan Li, Wenwen Dai, Jinyu Liu, Xiaoyao Hao, Shukai Xia, Qun Lv, Hugh M. Davis, Mingjiu Chen, Mark Z. Ma. BSI-507, a first-in-class bispecific antibody targeting PD1 and PVRIG for cancer immunotherapy. [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 6367.

Immunotherapy-related cardiovascular toxicity: Development of a preclinical murine model of acute myocarditis

Immunotherapies represent a major advance in oncology and an increasing number of patients will benefit from them. However, activation of the immune system can lead to severe myocarditis with a fatality rate up to 50%. The pathophysiological mechanisms of myocarditis induced by anti-PD-1 and anti-CTLA-4, the most commonly used immune checkpoint inhibitor (ICIs), are poorly understood and require models to study this cardiotoxicity. PD-1 and CTLA-4 KO mouse models do show cardiomyopathy but still do not reflect the immuno-induced myocarditis observed in patients. Our objective is to develop a preclinical mouse model to characterize in vivo the pathophysiological mechanisms of ICIs-induced myocarditis. We used a syngeneic model with adult BALB/c mice grafted with murine melanoma cells. Ten days after graft, mice were treated every 2 days with peritoneal injection of a combination of anti-PD-1 (6.5 mg/kg) and anti-CTLA-4 (20 mg/kg) monoclonal antibodies. A group of ICIs-treated mice with melanoma also received diphtheria toxin to amplify the cardiotoxic response, by depletion of regulatory T cells. To follow-up the cardiac function, an ECG was recorded before each ICIs injection and 1 week after the 3rd injection before euthanasia. A submaxillary blood sample was taken before and after ICIs injection. To investigate inflammation, hearts were dissected for transcriptomic analysis and immunostaining. All transplanted mice developed a palpable melanocytic tumor. They maintained a stable clinical condition (no weight loss or signs of pain). ECG analysis showed some arrhythmias and numerous extrasystoles. Analyses are currently underway to determine the characteristics of the different intervals in each of the groups tested and to verify the significance of the results. qPCR analyzes are in progress to verify the inflammatory state of the myocardium. We are looking for changes in the expression of genes of the JAK/STAT pathway and of the NLRP3 inflammasome, including the GBP5 , GBP6 , and CCDC175 , CXCL9 , CXCL11 genes which have been described in cardiac biopsies from patients. This model of in vivo cardiotoxicity is very important to unravel the mechanisms that lead to immuno-induced myocarditis. The results obtained will be integrated with data from patients followed at the Cardio-Oncology center in Marseille and those from the in vitro hiPSC model in order to better understand the pathology and identify prognosis markers.

Neutrophil Extracellular Traps Promote T Cell Exhaustion in the Tumor Microenvironment.

While neutrophil extracellular traps (NETs) are important for directly promoting cancer growth, little is known about their impact on immune cells within the tumor microenvironment (TME). We hypothesize that NETs can directly interact with infiltrating T cells to promote an immunosuppressive TME. Herein, to induce a NET-rich TME, we performed liver Ischemia/Reperfusion (I/R) in an established cancer metastasis model or directly injected NETs in subcutaneous tumors. In this NET-rich TME, the majority of CD4+ and CD8+ tumor infiltrating lymphocytes expressed multiple inhibitory receptors, in addition these cells showed a functional and metabolic exhausted phenotype. Targeting of NETs in vivo by treating mice with DNAse lead to decreased tumor growth, decreased NET formation and higher levels of functioning T cells. In vitro, NETs contained the immunosuppressive ligand PD-L1 responsible for T cell exhaustion and dysfunction; an effect abrogated by using PD-L1 KO NETs or culturing NETs with PD-1 KO T cells. Furthermore, we found elevated levels of sPDL-1 and MPO-DNA, a NET marker, in the serum of patients undergoing surgery for colorectal liver metastases resection. Neutrophils isolated from patients after surgery were primed to form NETs and induced exhaustion and dysfunction of human CD4+ and CD8+ T cells. We next targeted PD-L1 in vivo by injecting a blocking antibody during liver I/R. A single dose of anti-PD-L1 during surgery lead to diminished tumors at 3 weeks and functional T cells in the TME. Our data thus reveal that NETs have the capability of suppressing T cell responses through metabolic and functional exhaustion and thereby promote tumor growth. Furthermore, targeting of PD-L1 containing NETs at time of surgery with DNAse or anti-PD-L1 lead to diminished tumor growth, which represents a novel and viable strategy for sustaining immune competence within the TME.

PD-1 blockade later but not at post-transplant attenuates chronic graft-versus-host disease

Abstract PD-1 and its ligand PD-L1 are widely appreciated as targets of immune checkpoint blockade. We sought to investigate the role of the PD-1 pathway in the context of chronic graft-versus-host disease (cGVHD). To induce cGVHD, mice are conditioned with Cytoxan and radiation prior to MHC disparate bone marrow (BM) + T cells (70k) and develop multi-organ symptoms with bronchiolitis obliterans lung manifestations. CGHVD mice have high survival rates past 50 days, with <15% weight loss over this period. Anti-PD-1 mAb given to mice with established cGVHD resulted in disease attenuation assessed by significantly improved pulmonary function tests compared to irrelevant mAb controls. PD-1 blockade significantly reduced germinal center (GC)-promoting GC B and T follicular helper (Tfh) cell and increased GC-suppressing T-follicular regulatory (Tfr) cell frequencies. However, in studies with mice given five percent higher T cell dose, resulting in T cell rather than GC-mediated disease, anti-PD-1 mAb dramatically worsened cGVHD severity. To assess GC cell-specific effects, recipients were given PD-1-deficient cells in graft compartments. Mice receiving PD-1 KO T cells predictably exhibited marked escalation of cGVHD severity and lethality, while mice receiving PD-1 KO B cells showed diminished disease, with significant improvement in pulmonary function. Co-culture of isolated B, Tfh and Tfr cells from NP-OVA immunized mice to determine effects of individual GC cell populations on Ig class switching demonstrated significant increase in Tfr suppressive capacity with addition of anti-PD-1 mAb. Together, these data provide evidence for PD-1 support of the GC reaction and identifies the PD-1/PD-L1 axis as a potential target for cGVHD therapy.

Enhancing Human NK Cell Function and Specificity for Cancer Immunotherapy

▪Natural Killer (NK) cells are cytotoxic lymphocytes capable of immune surveillance and represent an excellent source of cells for cancer immunotherapy for numerous reasons: 1) they mediate direct killing of transformed cells with reduced or absent MHC expression, 2) they can carryout antibody-dependent cell-mediated cytotoxicity (ADCC) on cells bound by appropriate antibodies via CD16, 3) they are readily available and easy to isolate from peripheral blood, 4) they can be expanded to clinically relevant numbers in vitro. Moreover, as NK cells do not cause graft versus host disease, they are inherently an off-the-shelf cellular product, precluding the need to use a patient's own NK cells to treat their cancer. In light of these attributes, NK cells have been used in many clinical trials to treat a number of cancer types; however, the results have not been as successful as other cellular based immunotherapies, such as CAR-T. In light of this, many groups have taken approaches to augment NK cell function, such as high dose IL15, CARs and Bi- or Tri-specific killer engagers. A synergistic or even alternative approach to these technologies is the use of CRISPR/Cas9-based genome editing to disrupt or manipulate the function of NK genes to improve their utility as an immunotherapeutic agent.In order to enhance the immunotherapeutic efficacy of NK cells we have implemented the CRISPR/Cas9 system to edit genes and deliver CARs. To this end, we have developed methods for high efficiency nucleic acid delivery to NK cells using electroporation. First, primary human NK cells are immunomagnetically isolated from peripheral blood mononuclear cells (PBMCs) of healthy donors. Purified NK cells are then activated and expanded using artificial antigen presenting cells (aAPCs) expressing membrane bound IL21 and 41BB for 7 days and subsequently electroporated (Figure 1A). Using this approach with EGFP encoding mRNA, we achieve high rates of transfection (>90%) and high viability (>90%) (Figure 1B).We next developed gRNAs targeting PD1, CISH, and ADAM17. PD1 is a negative regulator of NK cell function and its cognate receptor, PD-L1, is upregulated in a number of cancers. ADAM17 mediates CD16 cleavage on NK cells to negatively regulate their ability to perform ADCC. CISH is a recently described negative regulator of NK cell activation and integrates cytokine signals, including IL-15. We consistently achieved high rates (up to 90%) of gene inactivation in primary human NK cells across multiple donors (Figure 1C). Importantly, these gene edits do not affect expansion potential and are stable over several rounds of expansion (Figure 1D, E). Moreover, ADAM17 KO NK cells are highly resistant to CD16 cleavage upon activation (Figure 2A-E) and PD1 KO NK cells demonstrate significantly enhanced function against PD-L1 expressing cancer cell lines in vitro and in vivo (Figure 2F-J). These data demonstrate that high efficiency gene editing of NK cells can significantly enhance their function while maintaining in vitro expansion.In an effort to engineer NK cell specificity for cancer immunotherapy, we recently developed CAR molecules designed for use in NK cells (Li et al., 2018, Cell Stem Cell 23, 1-12). To this end, we engineered and tested 10 mesothelin CAR molecules with NK specific transmembrane domains (CD16, NKp44, NKp46, or NKG2D) and intracellular signaling domains (2B4, DAP10, DAP12, CD3ζ, and/or CD137). Utilizing several cancer models, we identified an architecture that significantly enhanced NK activation compared to T-CAR architectures (CAR4: scFv-NKG2D-2B4-CD3ζ). Moreover, NK-CAR4 cells demonstrated increased in vivo expansion, improved activity, and reduced toxicity compared to CAR-T cell therapy.In our studies to develop novel NK CARs, CARs were delivered to iPSC derived test NK cells (iNKs) using the PiggyBac transposon system. In order to deliver NK-CAR4 to peripheral blood NK cells we developed methods for high frequency, site specific integration. To this end, we utilized CRISPR/Cas9 combined with non-integrating recombinant Adeno-Associated Virus (rAAV) DNA donor for homologous recombination. Using an EGFP reporter we were able to optimize this process and deliver EGFP reporter to the AAVS1 safe harbor site with efficiencies >80% in NK cells. We are now utilizing our optimized gene editing approaches to generate multiplex edited CAR-NK cells and results from these studies will be presented. [Display omitted] DisclosuresWebber:BEAM Therapeutics: Consultancy; B-MoGen Biotechnologies: Employment, Equity Ownership. Felices:GT Biopharma: Research Funding. Moriarity:BEAM Therapeutics: Consultancy; B-MoGen Biotechnologies: Employment, Equity Ownership.

Metabolic Reprogramming of Myeloid Cells in Response to Factors of “Emergency” Myelopoiesis By Myeloid-Specific PD-1 Ablation, Regulates Myeloid Lineage Fate Commitment and Anti-Tumor Immunity

PD-1 is a T cell inhibitor for which blocking agents have achieved success as anti-cancer therapeutics. The current view is that cancer limits host immune responses by upregulating PD-L1 in the tumor microenvironment (TME) thereby causing PD-1 ligation and inactivation of CD8+ Teff cells. However, PD-L1 expression in the TME does not always correlate with therapeutic response. Thus, the mechanism(s) by which PD-1 blockade reverses compromised anti-tumor immunity are poorly understood. The rapid increase in hematopoietic cell output that occurs in response to immunologic stress is known as emergency myelopoiesis. Low-level stimulation by cancer-generated factors induces modest but continuous expansion of myeloid progenitors (MP) (common myeloid progenitors (CMP) and granulocyte/macrophage progenitors (GMP)) albeit with hindered differentiation, leading to output of tumor-promoting myeloid-derived suppressor cells (MDSCs). We determined that myeloid cells expanding during cancer-driven emergency myelopoiesis in tumor-bearing mice express PD-1 and PD-L1. Using PD-1 KO mice we found that PD-1 deletion prevented the accumulation of GMP and stimulated the output of Ly6Chi effector monocytes, macrophages and dendritic cells (DC). To determine whether these outcomes were mediated by a myeloid-intrinsic impact of PD-1 ablation or by the effects of PD-1neg T cells on myeloid cells, we generated mice with conditional targeting of the Pdcd1 gene (PD-1f/f) and selectively eliminated PD-1 in myeloid cells (PD-1f/fLysMcre) or T cells (PD-1f/fCD4cre). Myeloid-specific, but not T cell-specific PD-1 ablation, prevented the accumulation of GMP while promoting the output of effector-like myeloid cells expressing CD80, CD86, CD16/32 (FcRII/III) and CD88 (C5aR). Myeloid cells with PD-1 ablation had elevated expression of IRF8 that drives monocyte and DC differentiation and decreased expression of the MDSC hallmark markers IL-4R, CD206, ARG1 and CD38. Nutrient utilization has a decisive role on the fate of hematopoietic progenitors (HP) and MP. Stemness and pluripotency are regulated by maintenance of glycolysis whereas switch to mitochondrial metabolism is associated with differentiation. To examine whether PD-1 ablation affected these metabolic proceces, bone marrow (BM) from PD-1f/f and PD-1f/fLysMcre mice was cultured with G-CSF/GM-CSF/IL-6, key drivers of emergency myelopoiesis. MP differentiation was documented by decrease of Linneg and increase of Linpos cells, which was more prominent in PD-1f/fLysMcre BM cultures. This coincided with increase of CD45+CD11b+ and dominance of Ly6C+ monocytic cells consistent with a cell-intrinsic mechanism of monocytic lineage commitment. PD-1f/fLysMcre MP had elevated mTORC1, Erk1/2 and Stat1 activation, and enhanced glucose uptake and mitochondrial biogenesis. Bioenergetics studies showed robust development of a mitochondrial-dominant profile, consistent with metabolism-driven enhanced differentiation of MP. Mass spectrometry revealed enhanced intermediates of glycolysis, PPP and TCA cycle, but the most prominent difference was the increased cholesterol. Because mTORC1 signaling, which was enhanced in PD-1f/fLysMcre MP, activates de novo lipid and cholesterol synthesis via SREBP1, we examined the mevalonate pathway of cholesterol synthesis. mRNA for genes mediating cholesterol synthesis and uptake was increased whereas mRNA for genes mediating cholesterol metabolism was decreased. Cholesterol induces a proinflammatory program in myeloid cells, drives differentiation of monocytes, macrophages and DC and promotes antigen-presenting function. We examined how such changes in myeloid cells might affect the function of T cells, which are key anti-tumor mediators. Compared to tumor-bearing PD-1f/f mice, PD-1f/fLysMcre tumor-bearers had no quantitative T cell differences but had an increase in IFNγ- IL-17-, and IL-10-expressing CD8+ Teff-mem and IL-2-expressing Tcentral-mem cells, consistent with superior functionality. These changes correlated with enhanced anti-tumor protection despite preserved PD-1 expression in T cells. Our findings reveal a previously unidentified role of PD-1 in metabolism-driven myeloid cell lineage fate commitment and differentiation and suggest that switch to effector myeloid cells might be a key mechanism by which PD-1 blockade mediates systemic anti-tumor immunity. DisclosuresNo relevant conflicts of interest to declare.

PD-1 deficiency augments bone marrow failure in a minor-histocompatibility antigen mismatch lymphocyte infusion model

Although PD-1 blockade has revolutionized cancer immunotherapy, immune-related adverse events (irAEs) present life-threatening complications. Recent reports of aplastic anemia (AA) as irAEs implicate PD-1/PD-L1 as important in preventing immune-mediated destruction of the hematopoietic niche. Infusion of PD-1-deficient (PD-1 knockout [KO]) lymph node (LN) cells into minor-antigen mismatched mice resulted in early mortality, as well as more severe bone marrow (BM) hypoplasia, anemia, and BM microarchitecture disruption in PD-1 KO LN-infused mice relative to mice that received B6 LN cell infusion. Mice that received PD-1 KO LN cells had more CD8+ T-cell infiltration of the BM and greater expansion of H60-specific CD8+ T cells than did their B6 LN-infused counterparts. In the spleen, CD8+ T cells were skewed to an effector memory phenotype, suggesting accelerated differentiation of PD-1 KO T cells. Our data suggest that PD-1 dysregulation has a role in murine BM failure and vigilance in irAE monitoring may be desirable to treat early AA and related cytopenias.

Nitrosative damage during retrovirus infection-induced neuropathic pain

BackgroundPeripheral neuropathy is currently the most common neurological complication in HIV-infected individuals, occurring in 35–50% of patients undergoing combination anti-retroviral therapy. Data have shown that distal symmetric polyneuropathy develops in mice by 6 weeks following infection with the LP-BM5 retrovirus mixture. Previous work from our laboratory has demonstrated that glial cells modulate antiviral T-cell effector responses through the programmed death (PD)-1: PD-L1 pathway, thereby limiting the deleterious consequences of unrestrained neuroinflammation.MethodsUsing the MouseMet electronic von Frey system, we assessed hind-paw mechanical hypersensitivity in LP-BM5-infected wild-type (WT) and PD-1 KO animals. Using multi-color flow cytometry, we quantitatively assessed cellular infiltration and microglial activation. Using real-time RT-PCR, we assessed viral load, expression of IFN-γ, iNOS, and MHC class II. Using western blotting, we measured protein nitrosylation within the lumbar spinal cord (LSC) and dorsal root ganglion (DRG). Histochemical staining was performed to analyze the presence of CD3, ionized calcium binding adaptor molecule (Iba)-1, MHCII, nitrotyrosine, isolectin B4 (IB4) binding, and neurofilament 200 (NF200). Statistical analyses were carried out using graphpad prism.ResultsHind-paw mechanical hypersensitivity observed in LP-BM5-infected animals was associated with significantly increased lymphocyte infiltration into the spinal cord and DRG. We also observed elevated expression of IFN-γ (in LSC and DRG) and MHC II (on resident microglia in LSC). We detected elevated levels of 3-nitrotyrosine within the LSC and DRG of LP-BM5-infected animals, an indicator of nitric oxide (NO)-induced protein damage. Moreover, we observed 3-nitrotyrosine in both small (IB4+) and large (NF200+) DRG sensory neurons. Additionally, infected PD-1 KO animals displayed significantly greater mechanical hypersensitivity than WT or uninfected mice at 4 weeks post-infection (p.i.). Accelerated onset of hind-paw hypersensitivity in PD-1 KO animals was associated with significantly increased infiltration of CD4+ and CD8+ T lymphocytes, macrophages, and microglial activation at early time points. Importantly, we also observed elevated levels of 3-nitrotyrosine and iNOS in infected PD-1 KO animals when compared with WT animals.ConclusionsResults reported here connect peripheral immune cell infiltration and reactive gliosis with nitrosative damage. These data may help elucidate how retroviral infection-induced neuroinflammatory networks contribute to nerve damage and neuropathic pain.

PD-1 blockade alters fate commitment of myeloid progenitors during tumor-mediated “emergency” myelopoiesis

Abstract PD-1 is an immune inhibitory receptor for which blocking agents have achieved significant success as anti-cancer therapeutics. The mechanism(s) of the how PD-1 compromises anti-tumor function and how such effect is reversed by PD-1 blockade remain poorly understood. The rapid change in hematopoietic output that occurs in response to immunologic stress is known as “emergency” myelopoiesis. This process is co-opted by tumors to enhance the generation of tumor-promoting myeloid cells, mostly undifferentiated myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). We analyzed the myeloid compartment of tumor-bearing mice and determined that myeloid cells express PD-1 and PD-L1. Using PD-1 KO mice or WT mice treated with PD-1 blocking antibody in cancer-driven myelopoiesis experiments we determined a cell-switch fate from MDSCs to effector myeloid cells. PD-1 deletion or blockade, which impaired tumor growth and metastases, stimulated the differentiation of hematopoietic progenitor cells and resulted in increase of Ly6Chimonocytes and monocyte-derived DC (mo-DC). Abrogation of PD-1 signaling enhanced the maturation of MDSCs by inducing the lineage commitment transcription factors IRF8, IRF4 and RORC1. IRF8 and IRF4 promote monocytes/macrophage and hinder granulocyte differentiation, whereas RORC1 is required for expansion of Ly6Chi monocytes and resolution of inflammation. These results reveal a role of the PD-1:PD-L1 pathway in the differentiation of lineage-committed myeloid progenitors to promote undifferentiated MDSCs and suppress effector monocytes/DCs. Switch of myeloid progenitor fate commitment might be a key mechanism by which PD-1 blockade mediates anti-tumor function.

PD-1 is not required for natural or peripherally induced regulatory T cells: Severe autoimmunity despite normal production of regulatory T cells.

The expression of the coinhibitor PD-1 on T cells is important for the establishment of immune homeostasis. We previously found that PD-1 is particularly critical for the control of self-tolerance during lymphopenia-induced proliferation of recent thymic emigrants (RTEs). Previous studies suggested that PD-1 modulates the generation of Treg cells, particularly peripherally induced Treg (pTreg) cells, and controls Th17 cells. However, these conclusions were derived indirectly from studies on the ligand PD-L1, and not PD-1 itself. Herein we directly tested whether T-cell PD-1 expression was needed for Treg cell generation and examined if a paucity of Treg cells or enhanced Th17 cells could explain the severe lymphopenia-potentiated autoimmunity caused by PD-1 KO RTEs. Employing the murine FoxP3(EGFP) reporter system to simultaneously monitor conversion of WT and PD-1 KO T cells to pTreg cells in the same animal, we found that PD-1 deficiency did not inhibit pTreg cell generation or lead to Th17-cell-mediated autoimmunity. Surprisingly, pTreg cell numbers were increased in PD-1 KO versus WT cell populations. Furthermore, we noted an increased conversion to pTreg cells by RTEs. Our data suggest that the primary role for PD-1 is to restrain T-cell activation/proliferation to self-Ags rather than promote generation of Treg cells.

Ideal Timing of Immunotherapy With Radiation in Murine Tumor Models

218 mm (p Z 0.028). Similarly, anti-PD-1 therapy with RT resulted in significantly longer survival than PD-1 blockade therapy alone (29 days vs 19 days; p Z 0.021). The mean tumor size on day 19 at the primary site was 103 mm (anti-PD-1) and 26.2 mm (anti-PD-1 + RT) (p Z 0.043). Secondary tumor growth was 197.8 mm and 88.4 mm for PD-1 therapy alone or with RT (p Z 0.037). RT alone to the primary tumor had no suppressive effect on the distant tumor growth. Flow analysis confirmed the presence of anti-melanoma PD-1+ CD8+ effector T cells in both primary and distant tumor sites. Conclusions: In our preclinical models, the addition of RT to PD-1 blockade (PD-1 KO and anti-PD-1 antibody) suppressed tumor growth at both radiated and non-radiated sites, and successfully recapitulated the clinical abscopal effect of RT. Two mice developed anti-melanoma immunity and did not exhibit melanoma growth upon rechallenge. These results provide a rationale for testing RT and PD-1 blockade combination therapy in a clinical setting. Author Disclosure: S.S. Park: A. Employee; Mayo Clinic. E. Research Grant; RSNA Research Scholar Grant Recipient. H. Dong: A. Employee; Mayo Clinic. W. Zhao: A. Employee; Mayo Clinic. M.P. Grams: A. Employee; Mayo Clinic. X. Liu: A. Employee; Mayo Clinic. S.M. Harrington: A. Employee; Mayo Clinic. K.M. Furutani: A. Employee; Mayo Clinic. C.J. Krco: A. Employee; Mayo Clinic. K.R. Olivier: A. Employee; Mayo Clinic. S.N. Markovic: A. Employee; Mayo Clinic. E.D. Kwon: A. Employee; Mayo Clinic.

Negative role of inducible PD-1 on survival of activated dendritic cells

PD-1 is a well-established negative regulator of T cell responses by inhibiting proliferation and cytokine production of T cells via interaction with its ligands, B7-H1 (PD-L1) and B7-DC (PD-L2), expressed on non-T cells. Recently, PD-1 was found to be expressed in innate cells, including activated DCs, and plays roles in suppressing production of inflammatory cytokines. In this study, we demonstrate that PD-1 KO DCs exhibited prolonged longevity compared with WT DCs in the dLNs after transfer of DCs into hind footpads. Interestingly, upon LPS stimulation, WT DCs increased the expression of PD-1 and started to undergo apoptosis. DCs, in spleen of LPS-injected PD-1 KO mice, were more resistant to LPS-mediated apoptosis in vivo than WT controls. Moreover, treatment of blocking anti-PD-1 mAb during DC maturation resulted in enhanced DC survival, suggesting that PD-1:PD-L interactions are involved in DC apoptosis. As a result, PD-1-deficient DCs augmented T cell responses in terms of antigen-specific IFN-γ production and proliferation of CD4 and CD8 T cells to a greater degree than WT DCs. Moreover, PD-1 KO DCs exhibited increased MAPK1 and CD40-CD40L signaling, suggesting a possible mechanism for enhanced DC survival in the absence of PD-1 expression. Taken together, our findings further extend the function of PD-1, which plays an important role in apoptosis of activated DCs and provides important implications for PD-1-mediated immune regulation.

PD-1 controls effectors but not the generation or function of natural or induced regulatory T-cells (P1011)

Abstract During T cell activation, the balance of co-stimulatory and co-inhibitory interactions plays an important role in shaping the resulting T cell response. Co-inhibitory signals help maintain peripheral immune tolerance, and thus animals with defective co-inhibitory molecules, such as PD-1 KO mice, are predisposed to autoimmunity. Unlike PD-1 KO mice, which develop mild autoimmunity, adult Rag KO recipients of PD-1 KO hematopoietic stem cells (HSC) succumb to rapid and severe multi-organ autoimmune disease soon after T cells first emerge from the thymus, implicating PD-1 as a critical factor in the control of T cell self-reactivity during lymphopenia induced homeostatic proliferation (LIP). While we have found no reduction in the absolute number of FoxP3+ regulatory T cells (Treg) in diseased PD-1 KO vs. wild type (WT) HSC recipients, some studies have indirectly suggested that PD-1 deficiency may inhibit the development of induced Treg (iTreg) cells from conventional T cells in the periphery. We therefore investigated whether PD-1 deficiency results in an intrinsic inability of T cells to convert to iTreg in vivo, which could lead to disease in PD-1 KO HSC recipients. Surprisingly, our findings suggest that PD-1 deficiency does not inhibit the development of iTreg nor does it affect Treg suppressive function, and that in the context of LIP, co-inhibitor deficient effector T cells cause disease primarily by expanding beyond the ability of Treg to control them.

PD-1, B7-H1 and IL-10 in protection from kidney ischemia reperfusion injury (P1022)

Abstract Regulatory T cells (Tregs) protect the kidney from inflammation, tissue damage and loss of function induced by ischemia-reperfusion (IR) in an IL-10 and PD-1 dependent manner, but the mechanisms of action for Tregs in IR are not completely understood. We hypothesized that Treg PD-1 is engaged by its ligand B7-H1, leading to increased IL-10 production by Tregs, which suppresses inflammation and protects from kidney IR. Similar to our previous observation that WT Tregs lose their ability to protect mice from kidney IR if treated with a PD-1 blocking antibody (ex vivo, prior to adoptive transfer), PD-1 KO Tregs did not offer any protection from kidney IR. In a model of mild renal IR that does not result in significant renal dysfunction in isotype control antibody-treated mice (plasma creatinine (PCr) level: 0.5±0.1, n=5 vs. sham PCr: 0.3±0.1, n=3) blockade of B7-H1 prior to IR causes a marked reduction in renal function (PCr: 1.3±0.3, n=6) accompanied by increased acute tubular necrosis and accumulation of neutrophils in the kidney. Stimulation of isolated WT Tregs with plate-bound anti-CD3, in the presence of IL-2, resulted in significant production of IL-10. In contrast to our hypothesis, addition of plate-bound B7-H1 Ig fusion protein dose-dependently inhibited IL-10 production by WT Tregs. Taken together these results suggest PD-1 and its ligand B7-H1 interact to protect from ischemic kidney injury, but argue against enhanced IL-10 production by Tregs as the mechanism.

Peripheral tolerance induced by apoptotic cells and PD-1+ CD8 T cells

Self tolerization in peripheral is critical to prevent autoimmune diseases including arthritis and here we focus on the role of PD-1 in tolerance induction against the antigen associated with apoptotic cellsdelivered intravenously (i.v.). We accessed delayed type hypersensitivity (DTH) reaction against hapten (TNP) as antigen specific immune response, in which the injection of TNP-apoptotic cells i.v. suppressed DTH in wild type mice but we found not in PD-1 KO mice (Figure ​(Figure1).1). Adaptive transfer of CD8 T cells into PD-1 KO mouse from wild type mice tolerated with TNP-apoptotic cells suppresses DTH. This result shows PD-1 functions on CD8 T cells for immune suppression. Additionally we neutralized the PD-1 with antibody to determine the phase when PD-1 functions for immune tolerance by apoptotic cells, and identified PD-1 functions particularly at the initial phase of antigen specific immune response. We are further studying the mechanism of suppressive role of PD-1+ CD8 T cells that should be activated with apoptotic cells. Figure 1 PD-1 is essential for tolerance induced by apoptotic cells. TNP-apoptotic cells were injected intravenously into PD-1 hetero- or homo- deficient mice. The mice were immunized with TNP (Filled bar) or preconditioned with apoptotic cells before immunization ...

788 Development of a New Mouse Model of Fatal Autoimmune Hepatitis

Background: An aberrant regulation of autoreactive T cells against liver antigens appears to initiate development of autoimmune hepatitis (AIH), characterized by mononuclear-cell infiltration and autoantibody production. Because of the lack of animal models developing spontaneous autoimmune liver disease resembling AIH, molecular mechanisms involved in development of AIH are still unclear. Although Con A-induced acute hepatic injury is considered to be an experimental model of AIH, Con A-induced acute hepatic injury does not produce circulating autoAbs and a single intravenous injection of Con A in mice induces rapid injury of hepatocytes with a striking increase in plasma transaminase levels within 24 h. Thus, this model is not likely to provide the clues for resolving molecular mechanisms of how an aberrant regulation of autoreactive T cells against liver antigens is initiated In Vivo. Aim: The aim of this study is to develop a new mouse model of spontaneous AIH and to examine molecular mechanisms involved in development of AIH. Methods: Using a negative co-stimulatory molecule, programmed cell death 1, deficient mice (PD-1 KO mice), we performed depletion of naturally arising CD4+CD25+ regulatory T cells (Treg cells). After Treg-cell depletion In Vivo, we monitored histological findings of the liver and production of autoantibody, and performed immunohistological analysis, flow cytometry examination and adoptive transfer experiments. Results: Neither Treg-cell depleted wild-type mice nor PD1 KO mice showed inflammation of the liver. However, age-matched Treg-cell depleted PD1 KO (Treg-dep-PD-1 KO mice) produced anti-hepatocyte antibodies and developed fatal hepatitis. The fatal hepatitis showed severe CD4+ and CD8+ T-cell infiltration invading parenchyma and massive lobular necrosis without bile duct destruction and fibrosis. Transfer of total splenocytes from Treg-dep-PD-1 KOmice into immunodeficient host, RAG2 deficient mice developed hepatitis. However, transfer of CD4+ T-cell-depleted splenocytes into RAG2 deficient recipient mice did not induce any inflammation of the liver. These data indicate that hepatitis in Treg-dep-PD-1 KO mice is a bona fide T cell-mediated autoimmune disease and that CD4+ T cells plays an essential role in the induction of AIH. Conclusion: This study indicates that Treg-dep-PD-1 KO mice are the first mouse model of spontaneous fatal AIH, and that immune dysregulation by concurrent loss of Treg cells and PD-1-mediated signaling can trigger activation of autoreactive T cells to induce fatal AIH.