Inhibitory Immune Checkpoint Receptors Research Articles

LRIG1 engages ligand VISTA and impairs tumor-specific CD8+ T cell responses.

Immune checkpoint blockade is a promising approach to activate antitumor immunity and improve the survival of patients with cancer. V-domain immunoglobulin suppressor of T cell activation (VISTA) is an immune checkpoint target; however, the downstream signaling mechanisms are elusive. Here, we identify leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) as a VISTA binding partner, which acts as an inhibitory receptor by engaging VISTA and suppressing T cell receptor signaling pathways. Mice with T cell-specific LRIG1 deletion developed superior antitumor responses because of expansion of tumor-specific cytotoxic T lymphocytes (CTLs) with increased effector function and survival. Sustained tumor control was associated with a reduction of quiescent CTLs (TCF1+ CD62Lhi PD-1low) and a reciprocal increase in progenitor and memory-like CTLs (TCF1+ PD-1+). In patients with melanoma, elevated LRIG1 expression on tumor-infiltrating CD8+ CTLs correlated with resistance to immunotherapies. These results delineate the role of LRIG1 as an inhibitory immune checkpoint receptor and propose a rationale for targeting the VISTA/LRIG1 axis for cancer immunotherapy.

Peripheral-central network analysis of cancer cachexia status accompanied by the polarization of hypothalamic microglia with low expression of inhibitory immune checkpoint receptors

While the excessive inflammation in cancer cachexia is well-known to be induced by the overproduction of inflammatory mediators in the periphery, microflora disruption and brain dysfunction are also considered to contribute to the induction of cancer cachexia. Hypothalamic microglia play a crucial role in brain inflammation and central-peripheral immune circuits via the production of inflammatory mediators. In the present study, we evaluated possible changes in excessive secretion of gut microbiota-derived endotoxin and the expression timeline of several inflammation-regulatory mediators and their inhibiting modulators in hypothalamic microglia of a mouse model of cancer cachexia following transplantation of pancreatic cancer cells. We demonstrated that the plasma level of lipopolysaccharide (LPS) was significantly increased with an increase in anaerobic bacteria, especially Firmicutes, in the gut at the late stage of tumor-bearing mice that exhibited dramatic appetite loss, sarcopenia and severe peripheral immune suppression. At the early stage, in which tumor-bearing mice had not yet displayed “cachexia symptoms”, the mRNA expression of pro-inflammatory cytokines, but not of the neurodegenerative and severe inflammatory modulator lipocalin-2 (LCN2), was significantly increased, whereas at the late “cachexia stage”, the level of LCN2 mRNA was significantly increased along with significant decreases in levels of inhibitory immune checkpoint receptors programmed death receptor-1 (PD-1) and CD112R in hypothalamic microglia. In addition, a high density of activated neurons in the paraventricular nucleus (PVN) of the hypothalamus region and a significant increase in corticosterone secretion were found in cachexia model mice. Related to the cachexia state, released corticosterone was clearly increased in normal mice with specific activation of PVN neurons. A marked decrease in the natural killer cell population was also observed in the spleen of mice with robust activation of PVN neurons as well as mice with cancer cachexia. On the other hand, in vivo administration of LPS in normal mice induced hypothalamic microglia with low expression of inhibitory immune checkpoint receptors. These findings suggest that the induction of cancer cachexia may parallel exacerbation of the hypothalamic inflammatory status with polarization to microglia expressed with low levels of inhibitory immune checkpoint receptors following LPS release from the gut microflora.

Abstract 7539: First-in-class anti-PVR mAb NTX1088 advancing through Phase I: Safe and potent in restoring DNAM1 expression to enhance antitumor immunity

Abstract NTX1088, a first-in-class anti-PVR (CD155) mAb, is currently evaluated in a Phase 1, open-label, multi-center study (NCT05378425). The trial initiated at MD Anderson Cancer Center, and was expanded into additional sites, including City of Hope, Ochsner Health, Sheba Medical Center and Hadassah Medical Center. Study objectives are safety, dose-finding, and efficacy with focus on pharmacokinetics, pharmacodynamics, and biomarker discovery. NTX1088 is investigated as a single agent and in combination with the anti-PD1 mAb, pembrolizumab (Keytruda) in patients with advanced solid malignancies. Ongoing dose escalation demonstrates a safe profile across ascending dose levels. NTX1088 is a high affinity humanized IgG4-S228P mAb that binds PVR and blocks all known interacting receptors at a single nM EC50. PVR, is a highly upregulated membrane protein on numerous tumor cells. PVR expression has been associated with worse patient outcome, due to its central role in immune suppression. PVR’s impact is mediated through interaction with the key stimulatory receptor, DNAM1 (CD226), on T and NK cells, leading to internalization and degradation of DNAM1. PVR also interacts with the inhibitory immune checkpoint receptors, TIGIT, CD96 and KIR2DL5A. Blocking PVR by NTX1088 has multiple immune-stimulating roles, through restoration of DNAM1 immune activation function, while simultaneously neutralizing TIGIT, CD96 and KIR2DL5A inhibitory signals in immune cells. Importantly, DNAM1 downmodulation was recently identified as a key resistance mechanism to approved immune checkpoint inhibitors, and its restoration by NTX1088 is a novel MoA, not demonstrated previously by other therapies.In vitro, as a monotherapy, NTX1088 significantly increased immune cell activation, superior to TIGIT, CD112R, and PD1 antibody blockade, leading to a greater immune-mediated tumor cell killing, IFNγ secretion, and CD137 induction. Importantly, only NTX1088 was able to restore DNAM1 to the surface of immune cells. Synergy was obtained when NTX1088 was combined with PD1 blockers, or with the anti-CD112R mAb, NTX2R13.Syngeneic models of PVRK.O, demonstrated a complete immune-mediated tumor regression. Numerous humanized murine xenograft models were investigated whereby NTX1088 exhibited robust tumor growth inhibition as a standalone and in combination with PD1 blockade.In conclusion, PVR blockade by NTX1088 has a remarkable pre-clinical efficacy, suggesting a potential clinical breakthrough, based on its ability to simultaneously overcome multiple tumor escape mechanisms. First-in-human (FIH) trial is currently ongoing and biomarker analysis is showing initial mechanistic proof of concept for NTX1088 mode of action, including the restoration of DNAM1 surface expression on patients’ immune cells. This is the first case of surface DNAM1 elevation in clinical settings. Citation Format: Anas Atieh, Akram Obeidat, Alon Vitenshtein, Guy Cinamon, Keren Paz, Tihana Roviš, Paola Brilc, Ofer Mandelboim, Stipan Jonjic, Pini Tsukerman. First-in-class anti-PVR mAb NTX1088 advancing through Phase I: Safe and potent in restoring DNAM1 expression to enhance antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7539.

Tumor-immune metaphenotypes orchestrate an evolutionary bottleneck that promotes metabolic transformation.

Metabolism plays a complex role in the evolution of cancerous tumors, including inducing a multifaceted effect on the immune system to aid immune escape. Immune escape is, by definition, a collective phenomenon by requiring the presence of two cell types interacting in close proximity: tumor and immune. The microenvironmental context of these interactions is influenced by the dynamic process of blood vessel growth and remodelling, creating heterogeneous patches of well-vascularized tumor or acidic niches. Here, we present a multiscale mathematical model that captures the phenotypic, vascular, microenvironmental, and spatial heterogeneity which shapes acid-mediated invasion and immune escape over a biologically-realistic time scale. The model explores several immune escape mechanisms such as i) acid inactivation of immune cells, ii) competition for glucose, and iii) inhibitory immune checkpoint receptor expression (PD-L1). We also explore the efficacy of anti-PD-L1 and sodium bicarbonate buffer agents for treatment. To aid in understanding immune escape as a collective cellular phenomenon, we define immune escape in the context of six collective phenotypes (termed "meta-phenotypes"): Self-Acidify, Mooch Acid, PD-L1 Attack, Mooch PD-L1, Proliferate Fast, and Starve Glucose. Fomenting a stronger immune response leads to initial benefits (additional cytotoxicity), but this advantage is offset by increased cell turnover that leads to accelerated evolution and the emergence of aggressive phenotypes. This creates a bimodal therapy landscape: either the immune system should be maximized for complete cure, or kept in check to avoid rapid evolution of invasive cells. These constraints are dependent on heterogeneity in vascular context, microenvironmental acidification, and the strength of immune response. This model helps to untangle the key constraints on evolutionary costs and benefits of three key phenotypic axes on tumor invasion and treatment: acid-resistance, glycolysis, and PD-L1 expression. The benefits of concomitant anti-PD-L1 and buffer treatments is a promising treatment strategy to limit the adverse effects of immune escape.

Identification of rat Vstm1 with conservative anti-inflammatory effect between rat and human homologs

Human VSTM1 (also known as SIRL1) is an inhibitory immune checkpoint receptor involved in leukocyte activation. Identification of the homologous genes in other species, such as mice and rats, will undoubtedly contribute to functional studies and clinical applications. Here, we successfully cloned the Vstm1 gene in rats, as supported by high-throughput sequencing data. However, Vstm1 is degenerated to a pseudogene in the mouse genome. Rat Vstm1 mRNA contains a complete open reading frame (ORF) of 630 nucleotides encoding 209 amino acids. Rat Vstm1 is highly expressed in bone marrow, especially in granulocytes. The expression levels of Vstm1 gradually increase with the development of granulocytes in bone marrow but are downregulated in response to inflammatory stimuli. Rat VSTM1 does not have an immunoreceptor tyrosine-based inhibitory motif (ITIM), however, it shows a conservative function of inflammatory inhibition with human VSTM1, and both are anti-correlated with many inflammatory cytokines, such as IL-1α and TNF-α. In bone marrow-derived macrophages (BMDMs), either rat or human VSTM1 suppressed the secretion of inflammatory cytokines in response to LPS stimulation. Further analysis in lung cancer microenvironment revealed that VSTM1 is mainly expressed in myeloid cells, anti-correlated with inflammatory cytokines and associated with tumor development and metastasis.

The ligand-dependent suppression of TCR signaling by the immune checkpoint receptor LAG3 depends on the cytoplasmic RRFSALE motif.

Lymphocyte activation gene 3 (LAG3) is an inhibitory immune checkpoint receptor that restrains autoimmune and antitumor responses, but its evolutionarily conserved cytoplasmic tail lacks classical inhibitory motifs. Major histocompatibility complex class II (MHC class II) is an established LAG3 ligand, and fibrinogen-like protein 1 (FGL1), lymph node sinusoidal endothelial cell C-type lectin (LSECtin), and Galectin-3 have been proposed as alternative binding partners that play important roles in LAG3 function. Here, we used a fluorescent human T cell reporter system to study the function of LAG3. We found that LAG3 reduced the response to T cell receptor stimulation in the presence of MHC class II molecules to a lesser extent compared with the receptor programmed cell death protein 1. Analysis of deletion mutants demonstrated that the RRFSALE motif in the cytoplasmic tail of LAG3 was necessary and sufficient for LAG3-mediated inhibition. In this system, FGL1, but not LSECtin or Galectin-3, acted as a LAG3 ligand that weakly induced inhibition. LAG3-blocking antibodies attenuated LAG3-mediated inhibition in our reporter cells and enhanced reporter cell activation even in the absence of LAG3 ligands, indicating that they could potentially enhance T cell responses independently of their blocking effect.

AHR, a novel inhibitory immune checkpoint receptor, is a potential therapeutic target for chemoresistant glioblastoma.

This study aims to elucidate the mechanism underlying temozolomide resistance in patients with MGMT promoter hypomethylated glioblastoma, which is correlated with poor prognosis. The objective is to identify therapeutic targets and drugs suitable for temozolomide-resistant glioblastoma patients using big data analysis. In this retrospective study, transcriptome sequencing data from 457 glioblastoma patients, multi-omics data, and single-cell sequencing data were employed to assess the expression pattern, prognostic value, and biological functions of AHR in glioblastoma. The HERB database was utilized to screen for AHR-targeted drugs for glioblastoma treatment. Validation of our findings was conducted using multiplex immunofluorescence staining of clinical samples and T cells and tumor cells co-culture models. Our findings demonstrated that patients with MGMT promoter unmethylation did not benefit from postoperative temozolomide chemotherapy due to resistance arising from DNA repair function and tumor immune response. AHR was found to be expressed in immune cells and exhibited an immunomodulatory role in glioblastoma with MGMT promoter unmethylation. AHR was identified as a potential novel inhibitory immune checkpoint receptor, serving as a therapeutic target for temozolomide-resistant glioblastoma. Furthermore, targeting AHR with Semen aesculi markedly enhanced the cytotoxic effect of T cells on glioma cells. In addition to DNA repair function, the tumor immune response plays a pivotal role in temozolomide resistance of glioblastoma. Herbal compounds targeting AHR may offer an effective treatment for temozolomide-resistant glioblastoma.

TIGIT Expression Delineates T-cell Populations with Distinct Functional and Prognostic Impact in Pancreatic Cancer.

Immunotherapy has led to a fundamental shift in the treatment of several cancers. However, its efficacy in pancreatic ductal adenocarcinoma (PDAC) is limited. Understanding the expression of inhibitory immune checkpoint receptors (ICR) by intratumoral T cells may help to unravel their involvement in insufficient T-cell-mediated antitumor immunity. Using multicolor flow cytometry, we analyzed circulating and intratumoral T cells from blood (n = 144) and matched tumor samples (n = 107) of patients with PDAC. We determined the expression of programmed cell death protein 1 (PD-1) and T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibition motif (ITIM) domains (TIGIT) by CD8+ T-cells, conventional CD4+ T-cells (Tconv) and regulatory T cells (Treg) and their association with T-cell differentiation, tumor reactivity, and cytokine expression. A comprehensive follow-up was used to determine their prognostic value. Intratumoral T cells were characterized by increased PD-1 and TIGIT expression. Both markers delineated distinct T-cell subpopulations. PD-1+TIGIT- T cells highly expressed proinflammatory cytokines and markers of tumor reactivity (CD39, CD103), whereas TIGIT expression was linked to antiinflammatory and exhausted phenotypes. In addition, the enhanced presence of intratumoral PD-1+TIGIT- Tconv was associated with improved clinical outcomes, while high ICR expression on blood T cells was a significant hazard for overall survival (OS). Our results uncover the association between ICR expression and T-cell functionality. PD-1 and TIGIT characterized intratumoral T cells with highly divergent phenotypes linked to clinical outcomes, further underscoring the relevance of TIGIT for immunotherapeutic approaches in PDAC. The prognostic value of ICR expression in patient blood may be a valuable tool for patient stratification.

Restoring T cell function to promote resolution of chronic HBV infection

Abstract An estimated 296 million people worldwide suffer from chronic hepatitis B virus (HBV) infection, with 1.5 million new infections occurring each year despite the availability of an effective vaccine. Chronic HBV infection persists in a dysfunctional immune environment, manifested by an ineffective T cell response to the virus. Patient HBV-specific CD8 +T cells have diminished proliferative capacity and cytokine production, and they exhibit increased and sustained expression of inhibitory immune checkpoint receptors. In mice with persistent HBV replication, reduction of viral antigens can be achieved by therapeutic immunization with alphavirus- and vesiculovirus-based vaccine platforms expressing HBV antigens. However, blocking PD-1 and CTLA-4 signaling may further enhance antiviral effector T cell function and therapeutic efficacy. Using a mouse model of HBV replication in which mice are transduced with adeno-associated virus encoding the HBV genome (AAV-HBV), we investigated the role of these inhibitory receptors in the T cell response to HBV. Antibody-mediated blockade of either PD-1 or CTLA-4 independently in AAV-HBV mice did not promote viral clearance. Likewise, PD-1 and CTLA-4 inhibition combined with therapeutic immunization with VSV expressing an HBV antigen did not improve anti-HBV T cell responses or virus clearance in high-antigen mice with persistent viral replication. However, in mice with lower initial antigen loads, blockade of these receptors along with VSV therapeutic immunization resulted in an enhanced decrease of circulating HBV antigen. These results suggest new methodologies for improving HBV-specific immune responses to promote a functional cure of the infection. Supported by the National Institute of Allergy and Infectious Diseases and the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under award numbers R01AI148354 and R44DK113858. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Evaluation of the immune checkpoint factors in idiopathic membranous nephropathy

Idiopathic membranous nephropathy (IMN), a single-organ autoimmune disease, is recognized by autoantibodies to podocyte proteins and identified as the most frequent cause of nephrotic syndrome in adults. T cells are important contributors in autoimmunity since they promote B–cell development, antibody production, direct inflammation, and organ tissue cytotoxicity. This study investigated the inhibitory immune checkpoint (ICP) receptors expressed on T lymphocytes and other immune cells. Thus, PBMCs from IMN patients were obtained before treatment, and the levels of ICPs such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA4), lymphocyte activation gene-3 (LAG-3), and T cell immunoglobulin-3 (TIM-3) were examined at both gene and protein expression using real time PCR and Western blot tests respectively. The results illustrated that gene expression levels of ICPs reduced significantly in comparison to the control which were verified by related fold changes of protein expression sequentially. Our study revealed that CTLA-4, PD-1, TIM-3, and LAG-3 expression is impaired in IMN patients before treatment which could be a potential target for therapy.

Abstract CT265: Phase 1 dose-escalation study of SGN-TGT monotherapy in patients with advanced malignancies

Abstract Background: T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is an inhibitory immune checkpoint receptor expressed on subsets of T-cells and natural killer (NK) cells. TIGIT inhibits T and NK cell function by binding to CD155 and CD112. SEA-TGT is an investigational human, nonfucosylated monoclonal antibody directed against TIGIT, blocking TIGIT's interaction with CD155 and CD112. SGNTGT-001 (NCT04254107) is a phase 1, open-label, multicenter study of SEA-TGT in patients (pts) with advanced malignancies (solid tumors and lymphomas). In this abstract, we present data from the dose-escalation phase (Part A). Methods: Pts received SEA-TGT ranging from 0.01 to 6.0 mg/kg of body weight intravenously every 3 weeks (Q3W). The primary objectives were to evaluate the safety and tolerability of SEA-TGT and identify the maximum tolerated dose (MTD) or the recommended dose and schedule of SEA-TGT. The optimal biological dose was defined using the Clinical Utility Index. Secondary objectives included the evaluation of antitumor activity, pharmacokinetics (PK) and immunogenicity. Antitumor activity was based on Response Evaluation Criteria in Solid Tumors version 1.1 or the Lugano classification criteria with Lymphoma Response to Immunomodulatory Therapy Criteria. Results: From June 12, 2020, to October 5, 2022, 41 pts were enrolled (2, 4, 5, 11, 12, and 7 pts in the 0.01, 0.1, 0.3, 1, 3, and 6 mg/kg cohorts, respectively). Among the 39 pts who were treated 23 pts had solid tumors and 16 had lymphomas. The median number of prior therapies across all cohorts was 5. Treatment emergent adverse events of any grade were reported in 100% of pts, and treatment-related adverse events (TRAEs) of any grade were reported in 69.2%. TRAEs seen in ≥10% of the pts were infusion-related reaction (38.5%), chills (25.6%), pyrexia (17.9%), fatigue (12.8%), maculopapular rash (12.8%), and rash (10.3%). Seven pts (17.9%) reported TRAEs grade ≥3, and rash (5.1%) was the most frequently reported. No grade 4 or 5 TRAEs were reported. One dose-limiting toxicity, pruritic rash, was observed in 1 pt in the 6 mg/kg cohort, and MTD was not exceeded. Based on the PK and pharmacodynamic data, 1 mg/kg Q3W was selected as the optimal biological dose for the expansion cohorts. One partial response was observed in a pt with gastric cancer, and 2 partial metabolic responses were seen in a pt with Hodgkin’s lymphoma and a pt with diffuse large B-cell lymphoma. Conclusions: Overall, clinical data for SEA-TGT from the SGNTGT-001 trial suggest a manageable and tolerable safety profile. Preliminary antitumor activity warrants further clinical evaluation of SEA-TGT. SGNTGT-001 is ongoing and evaluating monotherapy and combination therapies. Citation Format: Elena Garralda Cabanas, Elisa Fontana, Honey Kumar Oberoi, Nataliya V. Uboha, Ecaterina E. Dumbrava, Emiliano Calvo, Giuseppe Curigliano, Diwakar Davar, Bridget K. Keenan, Vincent K. Lam, Sudhir Manda, Amitkuma Mehta, Anna Minchom, Alison Moskowitz, Ravi Paluri, Vincent Ribrag, Donald Richards, Lillian Siu, Paul Swiecicki, Trisha Wise-Draper, Jasmine Zain, Andres Forero-Torres, Ping Xu, Stephen Ansell. Phase 1 dose-escalation study of SGN-TGT monotherapy in patients with advanced malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT265.

First-in-Human (FIH) Study of the Fully-Human Kappa-Lambda CD19/CD47 Bispecific Antibody TG-1801 in Patients (pts) with B-Cell Lymphoma

Introduction: Cancer cells elude anti-tumor immunity through multiple mechanisms, including upregulated expression of ligands for inhibitory immune checkpoint receptors. Blockade of signal regulatory protein (SIRP)-α on macrophages, or of its ligand CD47 expressed on tumor cells, improves tumor cell elimination however CD47 is a challenging target given its ubiquitous distribution in healthy tissues. Combination of CD47 blockade with the anti-CD20 antibody rituximab has resulted in encouraging clinical activity (Advani 2018), and CD19 is also an established target of multiple B-NHL therapies. TG-1801 is a bispecific agent designed with a CD19 high-affinity arm and a blocking CD47 arm for concurrent target engagement on the tumor cells surface. Herein we report results of the FIH study for the first time. Methods: The primary objectives were to characterize the safety profile and to determine the recommended phase 2 dose (RP2D) of TG-1801. Other objectives included assessment of pharmacokinetics (PK), preliminary antitumor activity (Lugano 2014), and pharmacodynamics (PD: B-cell depletion). Eligible patients must have had relapsed/refractory (R/R) B-cell lymphoma after at least one prior standard therapy. A 3+3 design was utilized to evaluate sequentially higher doses of TG-1801 at the following dose levels: 20 mg, 60 mg, 180 mg, 360 mg, and 500 mg. In the monotherapy arm, treatment consisted of weekly fixed dosing 1h-infusions of TG-1801 in a 4-week cycle: day (D)1, D8, D15, and D22 of cycle (C) 1 and C2. Patients who had at least stable disease after 2 cycles were given the option of receiving TG-1801 once every 4 weeks for an additional 4 infusions. Intra-patient dose escalations were permitted. An additional arm was enrolled with the combination therapy of ublituximab (anti-CD20 mAb) plus TG-1801. Patients received TG-1801 and ublituximab infusions in a 4 week-cycle: D1, D8, and D15 of C1; D1 of C2 thru C6; and D1 of C9 and every 3 cycles thereafter, up to 24 cycles. A 3+3 design was also utilized to evaluate two dose levels of TG-1801 (300 mg and 400 mg) with a standard dose of ublituximab (900 mg). Results: As of May 2022, 14 pts (MZL = 5, DLBCL including Richter's transformation = 5, FL = 4) received monotherapy and 16 pts received combination therapy (DLBCL = 9, FL = 4, MZL = 2, MCL = 1). Patients were heavily pretreated: median 3 prior systemic therapies (range, 1 - 8), all had received ≥1 prior anti-CD20; 14 pts (46%) were refractory to their last prior therapy. Twenty-one (70%) had extranodal disease, and 9 (30%) had bulky disease. One DLT of grade (G) 4 thrombocytopenia occurred at the 500 mg dose level. The most common (>20%) treatment emergent adverse events (TEAEs) at monotherapy doses of 20 mg to 360 mg (n=10) included fatigue, thrombocytopenia, and infusion-related reaction (3 pts each), with no G3/4 TEAE occurring in >20% of pts. Combination therapy was also well tolerated (TG-1801 at 300 mg N=3, 400 mg N=13) without DLT. The most common TEAE (≥20%) for combination therapy were: anemia (31%), headache, abdominal pain, fatigue, and thrombocytopenia (25% each), with no G3/4 TEAE occurring in >20% of pts. There were 2 permanent treatment discontinuations due to TEAE (1 infusion reaction [500 mg monotherapy], 1 rash [360 mg monotherapy]). Three partial responses (PR) were observed on monotherapy (n=14), all at 360 mg TG-1801, including 1 MZL pt with 7 prior lines that included PI3Ki, BTKi, auto transplant, and multiple prior anti-CD20s. All 3 pts completed 6 cycles of treatment and continued to further cycles of re-treatment. In the combination arm (n=16), a 44% response rate was observed with 1 complete response (CR) in a pt with FL and 6 PR (5 pts with DLBCL and 1 pt with FL) for a 56% ORR for DLBCL patients and 50% ORR for FL patients. The median duration of combination therapy exposure was 8.7 mo (range of 1-20 mo). Responses appear durable, with ten pts remaining on study, with 1 pt receiving 360 mg monotherapy and 9 pts receiving combination therapy. Dose dependent increases in exposure were observed and pharmacodynamic analysis demonstrated a >50% depletion of circulating lymphocytes within 7 days of the first infusion in all evaluable pts. Conclusions: TG-1801 monotherapy and combination therapy demonstrates clinical activity, particularly in relapsed and refractory DLBCL, with an acceptable preliminary safety profile. This study (NCT03804996) has completed enrollment. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

CRISPR/Cas9 Gene Editing of Immune Checkpoint Receptor NKG2A Improves the Efficacy of Primary CD33-CAR-NK Cells Against AML

BACKGROUND: CD33-targeting chimeric antigen receptor (CAR)-T cells already showed utility for the treatment of AML. Yet clinical application of CD33-CAR-T cells remains challenging due to potential side effects and its restriction to autologous cell preparations. In contrast, natural killer (NK) cells can be safely administered to HLA-mismatched recipients without severe side effects. Recently, we reported on the successful generation of primary CD33-CAR-NK cells, which are highly effective against AML in vitro and in vivo in AML-xenograft models (Albinger et al., Blood Cancer J 2022). However, CAR-NK cell function can be impaired by high levels of the inhibitory immune checkpoint receptor NKG2A (natural killer group 2A) expressed on NK cells (Bexte et al., Oncoimmunology 2022). By applying a CRISPR/Cas9 gene editing for knockout (KO) of NKG2A, we significantly improved CD33-CAR-NK cell functionality in vitro and in vivo. METHODS: CD33-targeting CAR-NK cells were generated by lentiviral transduction. KO of the NKG2A-encoding killer cell lectin like receptor C1 (KLRC1) locus was performed using CRISPR-Cas9 technology. The CD33-CAR- and NKG2A-expression as well as cytotoxicity were analysed using flow cytometry after feeder cell-free, IL-15/IL-2-based expansion. The in vivo-efficacy was evaluated in OCI-AML2 (GFP+, Luc+) xenografted NSG-SGM3 mouse models. RESULTS: Lentiviral transduction resulted in up to 60% CD33-CAR-positive NK cells, while KLRC1 gene disruption resulted in 50% reduction of NKG2A expression. Cite-Seq and qPCR analysis revealed a distinct gene regulation pattern in CD33-CAR- and CD33-CAR-NKG2A-KO-NK cells and CAR-KO-NK cells showed significantly higher elimination of CD33+/HLA-E+ OCI-AML2 cells in in vitro cytotoxicity assays compared to NKG2A-KO- or CD33-CAR-NK cells. Furthermore, a reduction of leukemic burden was observed in vivo following a single injection of a low dose (3x106 cells) of CAR-KO-NK cells compared to NKG2A-KO or CD33-CAR-NK cell treatment in an AML-xenografted mouse model. A double injection led to a complete elimination of AML and leukemia-initiating cells in the bone marrow of mice treated with CAR-KO NK cells, which was confirmed by bone marrow re-engraftment analysis. CONCLUSION: Removing an inhibitory receptor in CAR-NK cells showed a highly beneficial effect for the treatment of AML. This double genetic modification has the potential to enable NK cells to bypass the suppressive effect not only in the tumor microenvironment in context of AML, but also in a broad range of malignant diseases. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

T helper cell subsets and related target cells in acute COVID-19

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 24 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells basophiles and eosinophils were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased regulatory Tfh1 cell and increased pro-inflammatory Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of nave and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24 plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.

Abstract 3433: Novel dual antagonist anti-LILRB1/LILRB2 antibodies reprogram myeloid cells and potentiate T cells

Abstract Background: Genome-wide association studies have identified HLA-G and LILRB1/2 loci associated with cancer risk. LILRB1 and LILRB2 are distinct inhibitory immune checkpoint receptors that recognize MHC-I ligands, particularly immunosuppressive HLA-G. LILRB1-mediated inhibition can lead to impairment of T-cell cytotoxicity and preventing the efficient engulfment of tumor cells by macrophages as a “don’t eat me” signal. LILRB2 is expressed primarily by myeloid cells, especially in the tumor microenvironment, as an important immunosuppressive signal to inhibit the stimulation of an immune response. A dual antagonist antibody targeting both LILRB1 and LILRB2 could be more effective for cancer immunotherapy than targeting either LILRB1 or LILRB2 individually. Methods: Mice were immunized with recombinant D1-D2 domain of LILRB1 and LILRB2 proteins. Resulted heavy chain and light chain variable regions of IgG were PCR amplified from splenocytes and bone marrow plasma cells. PCR amplicons were built into yeast libraries. Yeast displayed scFv were screened for LILRB1 and LILRB2 binding. The dual binders were converted to effector silent human IgG1 and evaluated for ability to block HLA-G binding to LILRB1/RB2. The dual binder and dual blocker were further assessed in series of assays using human T cells and various primary myeloid cell subsets, including human monocyte-derived macrophages (hMDMs), tumor-associated macrophages (TAMs), dendritic cells (DCs) and monocytes. Results: We have discovered a panel of anti-LILRB1/2 antibodies that bind to both LILRB1 and LILRB2 with high affinity and block the interactions to HLA-G efficiently. The anti-LILRB1/2 antibodies inhibit both LILRB1 and LILRB2 signaling and modulate the function of immune cells. Anti-LILRB1/LILRB2-mediatted LILRB1 blockade: 1) enhances phagocytosis of tumor cells by macrophages; 2) releases HLA-G mediated inhibition on TCR activation in Jurkat T cells over-expressing LILRB1; 3) promotes the activation of human primary T cells stimulated with allogenic DCs. Anti-LILRB1/LILRB2-mediatted LILRB2 blockad:1) enhances TNFα expression and inhibits IL10 expression in LPS-stimulated human PBMC; 2) reprograms both hMDMs and TAMs induced by tumor cells to polarize toward a more inflammatory phenotype, including enhanced T cell responses to stimulation by DCs and macrophages, increased expression of M1 markers and secreted proinflammatory cytokine TNFα, decreased expression of M2 markers and secreted anti-inflammatory cytokine IL10. Conclusions: We have generated dual antagonist anti-LILRB1/LILRB2 antibodies. The anti-LILRB1/LILRB2 can reprogram suppressive myeloid cells to a stimulatory state, enhance phagocytotic function of myeloid cells, and promote the activation of lymphoid cells. The data support further development of anti-LILRB1/LILRB2 as an immunotherapeutic for solid tumor malignancies. Citation Format: Guangan Hu, Quanju Zhao, Lai Shi, Nan Bing, Dong Zhang. Novel dual antagonist anti-LILRB1/LILRB2 antibodies reprogram myeloid cells and potentiate T cells [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 3433.

Semi-automated validation and quantification of CTLA-4 in 90 different tumor entities using multiple antibodies and artificial intelligence

AbstractCTLA-4 is an inhibitory immune checkpoint receptor and a negative regulator of anti-tumor T-cell function. This study is aimed for a comparative analysis of CTLA-4+ cells between different tumor entities. To quantify CTLA-4+ cells, 4582 tumor samples from 90 different tumor entities as well as 608 samples of 76 different normal tissue types were analyzed by immunohistochemistry in a tissue microarray format. Two different antibody clones (MSVA-152R and CAL49) were validated and quantified using a deep learning framework for automated exclusion of unspecific immunostaining. Comparing both CTLA-4 antibodies revealed a clone dependent unspecific staining pattern in adrenal cortical adenoma (63%) for MSVA-152R and in pheochromocytoma (67%) as well as hepatocellular carcinoma (36%) for CAL49. After automated exclusion of non-specific staining reaction (3.6%), a strong correlation was observed for the densities of CTLA-4+ lymphocytes obtained by both antibodies (r = 0.87; p < 0.0001). A high CTLA-4+ cell density was linked to low pT category (p < 0.0001), absent lymph node metastases (p = 0.0354), and PD-L1 expression in tumor cells or inflammatory cells (p < 0.0001 each). A high CTLA-4/CD3-ratio was linked to absent lymph node metastases (p = 0.0295) and to PD-L1 positivity on immune cells (p = 0.0026). Marked differences exist in the number of CTLA-4+ lymphocytes between tumors. Analyzing two independent antibodies by a deep learning framework can facilitate automated quantification of immunohistochemically analyzed target proteins such as CTLA-4.

First-in-human study of SRF388, a first-in-class IL-27 targeting antibody, as monotherapy and in combination with pembrolizumab in patients with advanced solid tumors.

2501 Background: The immunoregulatory cytokine IL-27 upregulates inhibitory immune checkpoint receptors (eg, PD-L1, TIGIT) and downregulates proinflammatory cytokines (eg, IFNγ, TNFα). SRF388 is a fully human IgG1 blocking antibody to IL-27 with potential to promote immune activation in the tumor microenvironment. A phase 1 study was conducted to establish the preliminary safety of SRF388 and to identify recommended phase 2 doses (RP2D) suitable for monotherapy and combination expansions (NCT04374877). Methods: The dose-escalation study (accelerated single patient followed by standard 3+3) enrolled patients (pts) with advanced treatment-refractory solid tumors. Upon RP2D selection, monotherapy and combination expansions opened for treatment-refractory clear cell renal cell cancer (ccRCC), hepatocellular cancer (HCC), and non-small cell lung cancer. SRF388 was administered IV every 4 weeks (wks) as monotherapy and every 3 wks with pembrolizumab. Tumor response was assessed by RECIST1.1. Results: The monotherapy dose-escalation enrolled 29 pts with doses ranging from 0.003 to 20 mg/kg. Median age was 64 years. Most pts were female (62%) with ECOG PS of 1 (72%). Approximately 80% had prior PD-(L)1 blockade, and 48% had ≥4 prior therapies. Treatment-related adverse events (TRAEs) occurred in 21%, and all were low grade. Fatigue was the only TRAE reported in ≥10% (n = 3). No dose-limiting toxicities (DLTs) or Grade ≥3 TRAEs were observed. Median time on study was 9 wks (range 0–59). One patient with highly treatment-refractory NSCLC experienced a confirmed partial response (PR) at 8 wks that was durable for 20 wks. Nine pts (31%) experienced disease stabilization at 8 wks, with 6 of 9 exhibiting durable disease control at 6 months. Of the 7 pts with ccRCC in the dose-escalation portion of the trial, 3 (43%) experienced durable disease control for ≥20 wks (range: 20-32). With doses up to 20 mg/kg, SRF388 PK remain linear with an estimated T1/2 of 10-12 days. PK characteristics and safety profile support dosing every 3 or 4 wks. Based on safety, tolerability, PK, peripheral pSTAT1 inhibition, and preliminary efficacy, 10 mg/kg was selected as the RP2D. Both the pembrolizumab safety cohort (n = 10) and Stage 1 of the ccRCC monotherapy expansion (n = 17) have fully enrolled. Of the 10 evaluable pts with ccRCC, 1 confirmed monotherapy PR has been reported, enabling Stage 2 initiation. Changes in several serum cytokines and chemokines were observed after SRF388 administration, including expected increase in circulating IL-27 levels. Conclusions: Results of IL-27 pathway blockade with a first-in-class therapeutic demonstrates that SRF388 has good tolerability with encouraging preliminary antitumor activity as a monotherapy. Updated data, including safety and clinical outcomes as well as correlative biomarker analyses, will be presented. Clinical trial information: NCT04374877.

Epigenetic regulation of T cell exhaustion.

Chronic antigen stimulation during viral infections and cancer can lead to T cell exhaustion, which is characterized by reduced effector function and proliferation, and the expression of inhibitory immune checkpoint receptors. Recent studies have demonstrated that T cell exhaustion results in wholescale epigenetic remodeling that confers phenotypic stability to these cells and prevents T cell reinvigoration by checkpoint blockade. Here, we review foundational technologies to profile the epigenome at multiple scales, including mapping the locations of transcription factors and histone modifications, DNA methylation and three-dimensional genome conformation. We discuss how these technologies have elucidated the development and epigenetic regulation of exhausted T cells and functional implications across viral infection, cancer, autoimmunity and engineered T cell therapies. Finally, we cover emerging multi-omic and genome engineering technologies, current and upcoming opportunities to apply these to T cell exhaustion, and therapeutic opportunities for T cell engineering in the clinic.

Lymphocytic Thyroiditis Transcriptomic Profiles Support the Role of Checkpoint Pathways and B Cells in Pathogenesis.

Background: Autoimmune thyroid diseases are the most common types of autoimmune diseases, but their physiopathology is still relatively unexplored. Genotype-tissue expression (GTEx) is a publicly available repository containing RNAseq data, including profiles from thyroid. Approximately 14.8% of these glands were affected by focal lymphocytic thyroiditis and 6.3% were annotated as Hashimoto. We interrogated these data to improve the characterization of infiltrating cells and to identify new molecular pathways active in autoimmune thyroiditis. Materials and Methods: Histological GTEx images of 336 thyroid samples were classified into three categories, that is, non-infiltrated thyroid, small focal infiltrated thyroid, and extensive lymphoid infiltrated thyroid. Differentially expressed genes among these categories were identified and subjected to in silico pathway enrichment analysis accordingly. CIBERSORTx deconvolution was used to characterize infiltrating cells. Results: As expected, most of the transcriptional changes were dependent on tissue infiltration. Upregulated genes in tissues include-in addition to lineage-specific B and T cell genes-a broad representation of inhibitory immune checkpoint receptors expressed by B and T lymphocytes. CIBERSORTx analysis identified 22 types of infiltrating cells showed that T cells predominate 3:1 over B cells in glands with small infiltrates, only by 1.7:1 in those with large infiltrates. Follicular helper and memory CD4 T cells were significantly more abundant in glands with large infiltrates (p < 0.0001), but the most prominent finding in these glands was an almost sixfold increase in the number of naive B cells (p < 0.0001). A predominance of M2 macrophages over M1 and M0 macrophages was observed in the three gland categories (p < 0.001). Conclusions: Analysis of transcriptomic RNA-seq profiles constitutes a rich source of information for the analysis of autoimmune tissues. High-resolution transcriptomic data analysis of thyroid glands indicates the following: (a) in all infiltrated glands, active autoimmune response coexists with suppressor counteracting mechanisms involving several inhibitory checkpoint receptor pairs, (b) glands with small infiltrates contain an unexpected relatively high proportion of B lymphocytes, and (c) in highly infiltrated glands, there is a distinct transcriptomic signature of active tertiary lymphoid organs. These results support the concept that the autoimmune response is amplified in the thyroid tissue.

Inhibitory Immune Checkpoint Receptors and Ligands as Prognostic Biomarkers in COVID-19 Patients.

Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2. During T-cell activation, the immune system uses different checkpoint pathways to maintain co-inhibitory and co-stimulatory signals. In COVID-19, expression of immune checkpoints (ICs) is one of the most important manifestations, in addition to lymphopenia and inflammatory cytokines, contributing to worse clinical outcomes. There is a controversy whether upregulation of ICs in COVID-19 patients might lead to T-cell exhaustion or activation. This review summarizes the available studies that investigated IC receptors and ligands in COVID-19 patients, as well as their effect on T-cell function. Several IC receptors and ligands, including CTLA-4, BTLA, TIM-3, VISTA, LAG-3, TIGIT, PD-1, CD160, 2B4, NKG2A, Galectin-9, Galectin-3, PD-L1, PD-L2, LSECtin, and CD112, were upregulated in COVID-19 patients. Based on the available studies, there is a possible relationship between disease severity and increased expression of IC receptors and ligands. Overall, the upregulation of some ICs could be used as a prognostic biomarker for disease severity.