IFN-γ Staining Research Articles

SARS-CoV-2-Specific T Lymphocytes Analysis in mRNA-Vaccinated Patients with B-Cell Lymphoid Malignancies on Active Treatment.

Patients with B-lymphocyte malignancies (BCMs) receiving B-lymphocyte-targeted therapies have increased risk of severe COVID-19 outcomes and impaired antibody response to SARS-CoV-2 mRNA vaccination in comparison to non-hematologic oncologic patients or general population. Consequently, it is vital to explore vaccine-induced T-lymphocyte responses in patients referred for the understanding of immune protection against SARS-CoV2 infections. The objective of the present study was to analyze the recall immune responses carried out by T lymphocytes after two COVID-19 mRNA vaccine doses. We enrolled 40 patients with BCMs and 10 healthy controls (HCs) after 4 weeks from the second mRNA vaccine dose. Spike (S)-specific T-lymphocyte responses were assessed in peripheral blood mononuclear lymphocytes (PBMCs) by intracellular IFN-γ staining combined with flow cytometry. Furthermore, the humoral response was assessed with the measurement of anti-spike antibodies. From March to July 2021, 40 patients (median age 68) received mRNA vaccines. The overall antibody response for BCMs was 52.5% versus 100% for the healthy controls (p = 0.008). The antibody response was different across BCMs: 18.75% for non-Hodgkin lymphoma, 54.5% for chronic lymphocytic leukemia, and 92.3% for multiple myeloma. Responses varied by malignancy type and treatment, with anti-CD20 therapies showing the lowest response (6.7%). T-lymphocyte analysis revealed reduced numbers and altered differentiation stages in patients compared to the controls. However, the vaccine-induced T response was generally robust, with variations in specific T subpopulations. mRNA vaccines induced significant humoral and cellular immune responses in B-cell lymphoid malignancy patients, although responses varied by treatment type and malignancy. Further research is needed to optimize vaccination strategies in this population.

Tumor-associated KLRG1+ Tregs drive a dominant immunosuppressive program in Non-small Cell Lung Cancer

Abstract Killer cell lectin-like receptor G1 (KLRG1) is a co-inhibitory receptor expressed on T and NK cells. While KLRG1’s role in effector T and NK cells has been extensively documented, its impact on regulatory T cells (Tregs) remains poorly understood. This study aims to characterize and compare the immunosuppressive potential of KLRG1+ Tregs in contrast to KLRG1- Tregs and their therapeutic targeting in non-small cell lung cancer (NSCLC). CTV-labelled effector T cells were cultured with TAMs and tumor digests in the presence or absence of each Treg subpopulation for 5 days in a Treg suppression assay. For in vivo studies, T cells with either KLRG1+ or KLRG1- Tregs were adoptively transferred into lung tumor-bearing mice. Intracellular staining for GZB, IFN-γ and TNF-α was performed on the processed tumor cells. Lastly, cohorts of tumor-bearing KP mice were treated with a KLRG1-blocking antibody for 6 weeks. Our study revealed that KLRG1+ Tregs exhibit robust suppressive functions both in vitro and in vivo, contingent upon intact KLRG1 signaling. Blockade of KLRG1 in vitro and in vivo profoundly arrested tumor growth, augmented effector T cell activity, and significantly prolonged the survival of tumor-bearing mice. In conclusion, KLRG1+ Tregs drives immunosuppressive activity in the tumor microenvironment; this provides novel insights into the functional dynamics of KLRG1+ Tregs and underscores their therapeutic potential for boosting anti-tumor T cell responses in NSCLC.

Abstract 2909: ST101, a clinical CEBPβ antagonist peptide, promotes an immune-active tumor microenvironment by multiple cellular mechanisms

Abstract CCAAT/Enhancer Binding Protein β (C/EBPβ) is a transcription factor that is an established driver of cellular transformation in several cancer types with poor prognosis, including glioblastoma (GBM), triple negative breast cancer (TNBC) and non-small cell lung cancer (NSCLC). These cancers’ growth is often supported by an immunosuppressive (IS) tumor microenvironment (TME), characterized by high expression of TAMs, MDSCs, Tregs, and in the case of GBM, IS microglia. In addition to its cell-autonomous role of promoting survival and proliferation in cancer cells, C/EBPβ is also critical for IS M2 macrophage polarization, while its role in other TME populations is less understood. ST101 is a peptide antagonist of C/EBPβ that is being evaluated in a Phase 2 clinical study in patients with recurrent and newly diagnosed glioblastoma (NCT04478279). Here we explored the impact of ST101 on IS TME cell populations and on activation of cytotoxic T-cells in macrophage co-culture systems. ST101 increased the M1:M2 ratio up to 40-fold in hPBMC-derived macrophages cultured under conditions that typically drive M2 polarization. Further, ST101 promoted M2 repolarization to the M1 cell type, demonstrating that C/EBPβ is required for maintenance of the M2 program. When added to co-cultures of T cells with M2 macrophages, ST101 induced a 3-4-fold increase in intracellular IFN-γ staining indicating enhanced T cell activation. Notably, in M1 cultures ST101 further enhanced expression of the immune activity marker CD80 and T cell activation. Similar to its effect on M2 repolarization, ST101 induced activation of iPs-derived IS human microglia cultures toward an M1-like program. ST101 also impacted IS cell populations in vivo, as demonstrated in an orthotopic TNBC model in which ST101 exposure was associated with a reduction of the TAM fraction, increased intratumoral M1/M2 ratios, reduction of Tregs, increase of CD8:Treg fraction, and enhanced activity in combination with anti-PD-1. Similar observations were observed in clinical samples, where following ST101 exposure a significant decrease in expression of factors involved in M2 polarization, including CD209, SIGLEC5, and IL-24, and T cell suppression, including FoxP3 and inhibitory KIR proteins, were observed. Gene expression analysis suggests that ST101 induced a decrease in the intratumoral Treg:TIL ratio, indicating a shift towards a more immune-active TME. Overall, these results provide novel evidence for the contribution of C/EBPβ to the expression of multiple IS cancer-associated cell types and support the use of ST101 to antagonize C/EBPβ and promote an immune-active TME. Further, these data provide rational for evaluating the clinical impact of ST101 in combinations with immune checkpoint inhibitors. Citation Format: Claudio Scuoppo, Julia Diehl, Ricardo Ramirez, Mark Koester, Erin Gallagher, Siok Leong, Jerel Gonzales, Karen Mendelson, Zach Mattes, Lila Ghamsari, Gene Merutka, Abi Vainstein-Haras, Barry J. Kappel, Jim A. Rotolo. ST101, a clinical CEBPβ antagonist peptide, promotes an immune-active tumor microenvironment by multiple cellular mechanisms [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 2909.

Tetanus-diphtheria vaccine can prime SARS-CoV-2 cross-reactive T cells.

Vaccines containing tetanus-diphtheria antigens have been postulated to induce cross-reactive immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which could protect against coronavirus disease (COVID-19). In this work, we investigated the capacity of Tetanus-diphtheria (Td) vaccine to prime existing T cell immunity to SARS-CoV-2. To that end, we first collected known SARS-CoV-2 specific CD8+ T cell epitopes targeted during the course of SARS-CoV-2 infection in humans and identified as potentially cross-reactive with Td vaccine those sharing similarity with tetanus-diphtheria vaccine antigens, as judged by Levenshtein edit distances (≤ 20% edits per epitope sequence). As a result, we selected 25 potentially cross-reactive SARS-CoV-2 specific CD8+ T cell epitopes with high population coverage that were assembled into a synthetic peptide pool (TDX pool). Using peripheral blood mononuclear cells, we first determined by intracellular IFNγ staining assays existing CD8+ T cell recall responses to the TDX pool and to other peptide pools, including overlapping peptide pools covering SARS-CoV-2 Spike protein and Nucleocapsid phosphoprotein (NP). In the studied subjects, CD8+ T cell recall responses to Spike and TDX peptide pools were dominant and comparable, while recall responses to NP peptide pool were less frequent and weaker. Subsequently, we studied responses to the same peptides using antigen-inexperienced naive T cells primed/stimulated in vitro with Td vaccine. Priming stimulations were carried out by co-culturing naive T cells with autologous irradiated peripheral mononuclear cells in the presence of Td vaccine, IL-2, IL-7 and IL-15. Interestingly, naive CD8+ T cells stimulated/primed with Td vaccine responded strongly and specifically to the TDX pool, not to other SARS-CoV-2 peptide pools. Finally, we show that Td-immunization of C57BL/6J mice elicited T cells cross-reactive with the TDX pool. Collectively, our findings support that tetanus-diphtheria vaccines can prime SARS-CoV-2 cross-reactive T cells and likely contribute to shape the T cell responses to the virus.

Abstract B149: Anti-tumor and immunostimulatory properties of ST316, a peptide antagonist of beta-catenin for treatment of cancers with aberrant Wnt pathway activity

Abstract Beta-catenin represents a significant challenge as a therapeutic target due to its multifaceted role in tumor development as well as normal cell homeostasis. Dysregulation of the Wnt/beta-catenin signaling pathway is implicated in various cancers, including colorectal, hepatocellular, breast, ovarian, and pancreatic cancers. We developed ST316 as a peptide antagonist of the interaction of beta-catenin with BCL9, a co-activator implicated in oncogenic beta-catenin signaling. ST316 is currently being evaluated in a Phase 1-2 study (NCT05848739) that is currently enrolling patients with selected advanced solid tumors likely to harbor abnormalities of the Wnt/beta-catenin signaling pathway. In vitro studies indicate that ST316 selectively attenuates Wnt transcriptional activity in beta-catenin-dependent but not -independent cell lines. Gene expression profiling using RNA sequencing in beta-catenin mutant HCT116 cells and APC mutant Colo320DM cells demonstrates a significant downregulation of Wnt pathway target genes, oncogenic signature genes and pro-tumor immunologic gene sets within 24 hours of ST316 treatment. Consequently, ST316 induced a dose-dependent decrease in viability of beta-catenin-dependent cells while beta-catenin-independent cells were resistant, indicating that the anticancer effects of ST316 are mediated by inhibition of the Wnt/beta-catenin pathway. To evaluate the impact of ST316 in vivo, a 4T1 triple negative breast cancer orthotopic tumor model was employed. Once weekly injection of ST316 (5mg/kg SC) over eight weeks suppressed expression of Wnt target genes CDK4 and cMyc and resulted in a significant 84.3% inhibition of tumor growth compared to the control group. In addition to direct anti-tumor activity, ST316 triggers a pro-inflammatory immune microenvironment. ST316 induces polarization of human macrophages derived from peripheral blood mononuclear cells, resulting in >100-fold shift from immunosuppressive M2 macrophages towards the anti-tumor M1 phenotype. Co-cultures of M2 macrophages with T cells treated with ST316 demonstrate a significant three-fold increase in T-cell activation, as indicated by intracellular IFN-γ staining. Finally, ST316 enhances the anti-tumor activity of anti-PD-1 therapy in a syngeneic orthotopic 4T1 mouse model, where combination ST316 and anti-PD-1 antibody results in enhanced tumor growth inhibition compared to either single agent alone (p<0.01). These findings demonstrate the antitumor and immunostimulatory effects of ST316 and highlight its potential as a therapeutic agent for targeting cancers with aberrantly activated Wnt signaling pathways. Citation Format: Lila Ghamsari, Claudio Scuoppo, Erin Gallagher, Siok Leong, Mark Koester, Rick Ramirez, Zachary Mattes, Jerel Gonzales, Gene Merutka, Barry Kappel, Abi Vainstein, Jim Rotolo. Anti-tumor and immunostimulatory properties of ST316, a peptide antagonist of beta-catenin for treatment of cancers with aberrant Wnt pathway activity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B149.

Abstract LB016: Immunotherapeutic potential of ST316, a peptide antagonist of β-catenin

Abstract The transcription factor β-catenin is a key player in many cellular processes, including stem cell renewal, cellular homeostasis and inflammation. Deregulation of β-catenin occurs frequently in several cancer types by mutation or overexpression of the β-catenin gene or mutation of negative regulators such as Adenomatous Polyposis Coli (APC). ST316 is a novel peptide antagonist that specifically interferes with the association of β-catenin with its co-activator BCL9, disrupting β-catenin nuclear localization and attenuating target gene expression. In an orthotopic triple-negative breast cancer (TNBC) model, ST316 demonstrates potent anti-tumor activity, resulting in 84% tumor growth inhibition (TGI) (p<0.001 vs. vehicle control). In addition to its cell-autonomous mechanisms, deregulated Wnt/β-catenin signaling can promote tumorigenesis by impacting the tumor microenvironment. Reprogramming of immunosuppressive M2-like Tumor Associated Macrophages (TAMs) toward an immune-promoting program (M1-like) is an attractive cancer immunotherapeutic strategy. Here we explored ST316 potential for macrophage repolarization toward the M1-like phenotype, activation of cytotoxic T-cells in macrophage/T-cell co-culture assays and cooperation of ST316 with anti-PD-1 to enhance anti-tumor activity in vivo. Initial studies demonstrate that human macrophages derived from Peripheral Blood Mononuclear Cells (hPBMCs) and subsequently committed to the M2-like identity are reprogrammed toward an M1-like phenotype upon ST316 exposure. ST316 treatment dose-dependently suppressed expression of the M2 marker CD163 by flow cytometry and quantitative PCR, resulting in 100-fold increase in the M1/M2 ratio without substantial impact on cell viability. Importantly, T-cell viability and activation markers associated with M1-state (CD80, CD86) were not affected by ST316 at the concentrations used in these studies. Further, in co-cultures of M2 macrophage with T cells, ST316 exposure resulted in a three-fold increase in T-cell activation compared to control M2/T cell co-cultures, as measured by intracellular IFN-γ staining. Finally, in an orthotopic TNBC model in vivo, subtherapeutic ST316 enhanced the anti-tumor activity of anti-PD-1 [85% TGI with combination, compared to 51% TGI with anti-PD1 alone (p<0.01) and -9% TGI with subtherapeutic ST316 alone (p<0.001)]. Anti-tumor activity was accompanied by an increase the M1/M2 ratio. Overall, these results support the immuno-therapeutic potential of ST316 and extend the application range of ST316 to include Wnt-driven cancers with poor clinical response to immune checkpoint blockade and other immunotherapeutic agents. Citation Format: Claudio Scuoppo, Lila Ghamsari, Erin Gallagher, Siok Leong, Mark Koester, Rick Ramirez, Jerel Gonzales, Gene Merutka, Barry Kappel, Abi Vainstein-Haras, Jim Rotolo. Immunotherapeutic potential of ST316, a peptide antagonist of β-catenin [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 LB016.

Abstract 1846: Intratumoral mPH-762, a self-delivering RNAi therapeutic (INTASYL™) targeting mouse PD-1, generates systemic tumor-specific memory CD8 T cells, providing a mechanism for abscopal efficacy toward untreated tumors in a murine hepatocarcinoma model

Abstract Intratumoral (IT) administration of immune checkpoint inhibition (ICI) holds potential to enhance local activity while decreasing systemic toxicity, however, high molecular weight antibodies are not well-suited for this application. PH-762, a self-delivering RNAi compound targeting PD-1 built on proprietary INTASYL™ technology, rapidly enters tissues without need for further formulation or delivery vehicles. In preclinical studies, PH-762 and its murine-targeted analog (mPH-762) provide robust PD-1 silencing, anti-tumor efficacy and associated immunophenotypic changes in the tumor microenvironment (TME). PH-762 is currently under clinical investigation in a Phase 1b study as neoadjuvant therapy for advanced resectable melanoma. We have previously shown that IT mPH-762 provides abscopal efficacy toward untreated distal tumors in a bilateral Hepa1-6 model of murine hepatocellular carcinoma. Here, we identify potential mechanisms underlying this abscopal efficacy in follow-up studies in vivo and ex vivo. Equivalent inoculums of Hepa1-6 cells were subcutaneously implanted into bilateral flanks of C57BL/6J mice (N = 12/group). When tumors reached a mean volume of 150 mm3, vehicle (PBS) or mPH-762 (0.5 mg/dose or 2 mg/dose) were administered to one of the two tumors (the directly treated tumor), on Days 1, 4, 7, 10 and 13. Tumor volumes and body weights were recorded longitudinally. Directly treated (DT) and untreated distal tumors (UT), as well as mesenteric lymph nodes (mLNs) and spleens (SP) were isolated from a satellite group (N = 6) on Day 14. On-target immunomodulatory changes were assessed in DT and UT TME by immunostaining/flow cytometry. Additionally, systemic tumor specific T cells were expanded from bulk mLN and SP by 21-day culture with irradiated Hepa1-6 cells. Tumor specific memory reactivity was assessed by challenge with either intact Hepa1-6 cells; or intact CT26 BALB/c colon cancer cells, PMA/ionomycin, or PBS controls: and assessed by intracellular IFN-γ, TNF-α and surface CD107a staining. IT mPH-762 again provided an abscopal decrease in mean tumor volume of UT tumors compared to IT PBS. On-target immunomodulatory changes to TME appeared primarily confined to the DT only at this timepoint. However, IT mPH-762 increased both the frequency and reactivity of Hepa1-6-specific CD8 T cells expanded from mLN and SP compared to IT PBS. These data indicate that IT mPH-762 generates a systemic immune response of durable tumor-specific reactive memory CD8 T cells in systemic lymphoid organs, providing a mechanism for the abscopal efficacy of mPH-762. These data further support the clinical development of IT PH-762. Citation Format: Benjamin G. Cuiffo, Andrew Boone, Dingxue Yan, Melissa Maxwell, Brianna Rivest, James Cardia, Simon P. Fricker. Intratumoral mPH-762, a self-delivering RNAi therapeutic (INTASYL™) targeting mouse PD-1, generates systemic tumor-specific memory CD8 T cells, providing a mechanism for abscopal efficacy toward untreated tumors in a murine hepatocarcinoma model [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 1846.

BSCI-15 INVESTIGATING CD8 T CELL EXHAUSTION STATES WITHIN THE TME AND DRAINING LYMPH NODE OF PRIMARY BRAIN TUMORS AND BRAIN METASTASES

Abstract Brain metastases affect nearly 20% of all cancer patients. Likewise, glioblastoma (GBM) is the most common primary brain cancer in adults and remains universally lethal. Current immunotherapeutic efficacy is hindered by immunosuppression present in the brain tumor microenvironment (TME). T-cells, critical for tumor clearance, take on a functionally exhausted phenotype. Importantly, two exhaustion states, progenitor (Tpe) and terminal (Tte), have been identified in models of chronic infection and cancer. This distinction is particularly relevant, as Tpe can remain responsive to immune checkpoint blockade (ICB), while Tte cannot. To date, the dynamics and characteristics of these exhausted populations in primary tumors and brain metastases remain unclear. Using intracranially implanted murine models of GBM (CT2A) and metastatic melanoma (B16F10), Tpe and Tte were identified by flow cytometry as PD1+SLAMF6+ and PD1+TIM3+, respectively. Functional differences between subsets were evaluated via intracellular staining of IFNγ, TNFα, IL2, CD107a, and Ki67. To determine the role of antigen, we performed adoptive lymphocyte transfers of tumor-specific and non-tumor-specific transgenic T-cells into a TRP2 or OVA overexpressing intracranial CT2A or B16 tumor, respectively. Tte displayed higher cytotoxic molecule expression than Tte, consistent with chronic infection models. Key exhaustion-associated transcription factors were identified in exhaustion subsets, including Tox, Tcf7, T-bet, and Eomes. Tox and Tcf7 expression identified Tpe within tumor-draining lymph nodes, suggesting a potential origin outside of the tumor, and the capacity for rescued function. We observed a decline in the Tpe population over time, with an associated rise in Tte within both tumor types. Notably, the ratio of Tpe to Tte was higher at all time points in B16F10 compared to CT2A. Tte appeared only in tumor-specific T-cells of the TME, further confirming the tumor-antigen dependence of T cell exhaustion. Tpe may arise outside the TME in tumor-specific T-cells. Further study may reveal a means and time window for rescuing T-cell function with ICB for brain tumors.

Investigation of CD4 and CD8 T cell-mediated protection against influenza A virus in a cohort study

BackgroundThe protective effect of T cell-mediated immunity against influenza virus infections in natural settings remains unclear, especially in seasonal epidemics.MethodsTo explore the potential of such protection, we analyzed the blood samples collected longitudinally in a community-based study and covered the first wave of pandemic H1N1 (pH1N1), two subsequent pH1N1 epidemics, and three seasonal H3N2 influenza A epidemics (H3N2) for which we measured pre-existing influenza virus-specific CD4 and CD8 T cell responses by intracellular IFN-γ staining assay for 965 whole blood samples.ResultsBased on logistic regression, we found that higher pre-existing influenza virus-specific CD4 and CD8 T cell responses were associated with lower infection odds for corresponding subtypes. Every fold increase in H3N2-specific CD4 and CD8 T cells was associated with 28% (95% CI 8%, 44%) and 26% (95% CI 8%, 41%) lower H3N2 infection odds, respectively. Every fold increase in pre-existing seasonal H1N1 influenza A virus (sH1N1)-specific CD4 and CD8 T cells was associated with 28% (95% CI 11%, 41%) and 22% (95% CI 8%, 33%) lower pH1N1 infection odds, respectively. We observed the same associations for individuals with pre-epidemic hemagglutination inhibition (HAI) titers < 40. There was no correlation between pre-existing influenza virus-specific CD4 and CD8 T cell response and HAI titer.ConclusionsWe demonstrated homosubtypic and cross-strain protection against influenza infections was associated with T cell response, especially CD4 T cell response. These protections were independent of the protection associated with HAI titer. Therefore, T cell response could be an assessment of individual and population immunity for future epidemics and pandemics, in addition to using HAI titer.

Ex Vivo Differential Responsiveness to Clostridium perfringens and Lactococcus lactis by Avian Small Intestine Macrophages and T Cells.

Tissue resident immune system cells in the chicken intestine play a significant role in the protection against pathogens. However, very little is known about these cells. The current study was conducted to further characterize chicken intestinal immune system cells. Furthermore, this study aimed to assess the immune modulatory action of a highly virulent Clostridium perfringens, a commonly found chicken intestinal microbe, in comparison with a non-commensal, Lactococcus lactis, on intestine-derived immune system cells. The results demonstrated varying distribution of innate and adaptive immune cells along the avian gut-associated lymphoid tissue (GALT) in the duodenum, jejunum, ileum, and cecal tonsils. In addition, steady-state and tissue-specific presence of CD25+ cells among αβ and γδ T-cell subsets was assessed along the intestine. Ex vivo stimulation with C. perfringens or L. lactis resulted in a significant increase in the frequency of CD25+ T cells (γδ and αβ T cells). In addition, significantly more cell death was observed in ex vivo stimulation with C. perfringens, which was indirectly correlated with a decrease in macrophage activation based on nitric oxide (NO) production with no effect on lymphoid cell responsiveness as per intracellular interferon (IFN)-gamma (γ) staining. Ex vivo stimulation with L. lactis activated γδ T cells and αβ T cells, based on intracellular IFN-γ staining, while it had limited effect on macrophages. However, the ability of γδ and αβ T cells to produce IFN-γ and the ability of macrophages production of NO was rescued in the presence of L. lactis. These results demonstrate the potential application of L. lactis, as a probiotic, against virulent C. perfringens infection in chicken.

IMMU-15. INVESTIGATING CD8 T CELL EXHAUSTION STATES GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma (GBM) is the most common primary brain cancer in adults and remains universally lethal. Median survival remains a bleak 15-17 months from time of diagnosis, and current immunotherapeutic efficacy continues to be hindered by the robust immunosuppression present in the GBM microenvironment. T cells, critical for tumor clearance, are particularly affected, and many take on a functionally exhausted phenotype within the tumor. Importantly, two exhaustion states, progenitor and terminal, have been identified in models of chronic infection and cancer. This distinction is particularly relevant, as progenitor exhausted T cells can respond favorably to immune checkpoint blockade, while terminally exhausted T cells are resistant. To date, the dynamics and characteristics of these exhausted populations in GBM remain unclear. RESULTS In an orthotopic murine model of GBM, progenitor and terminal exhausted CD8 T cells were identified by flow cytometry as PD1+SLAMF6+ and PD1+TIM3+, respectively. Using a time-course approach, we detected progenitor exhaustion by day 8 in the tumor, but not in draining lymph nodes. Additionally, we show that the frequency of progenitor exhaustion is highest during early tumor progression, while terminal exhaustion is the most abundant in more advanced tumors ( &amp;gt;14 days). Functional differences between subsets were evaluated via intracellular staining of IFNγ, TNFα, granzyme B, and Ki67. Terminally exhausted T cells displayed higher cytotoxic molecule expression than progenitor exhausted T cells, similar to what has been documented in melanoma models. CONCLUSIONS Our findings identify T cell exhaustion subsets within GBM that require further investigation and may be relevant to overcome current barriers to immunotherapeutic efficacy.

Profiling CD8+ Tcell epitopes of COVID-19 convalescents reveals reduced cellular immune responses to SARS-CoV-2 variants.

Cellular immunity is important in determining the disease severity of COVID-19 patients. However, current understanding of SARS-CoV-2 epitopes mediating cellular immunity is limited. Here we apply T-Scan, a recently developed method, to identify CD8+ T cell epitopes from COVID-19 patients of four major HLA-A alleles. Several identified epitopes are conserved across human coronaviruses, which might mediate pre-existing cellular immunity to SARS-CoV-2. In addition, we identify and validate four epitopes that were mutated in the newly circulating variants, including the Delta variant. The mutations significantly reduce T cell responses to the epitope peptides in convalescent and vaccinated samples. We further determine the crystal structure of HLA-A∗02:01/HLA-A∗24:02 in complex with the epitope KIA_S/NYN_S, respectively, which reveals the importance of K417 and L452 of the spike protein for binding to HLA. Our data suggest that evading cellular immunity might contribute to the increased transmissibility and disease severity associated with the new SARS-CoV-2 variants.

Abstract 1676: A comprehensive whole blood CyTOF immune monitoring panel with expanded surface and intracellular markers using the Maxpar Direct Immune Profiling Assay

Abstract In-depth monitoring of the immune response to cancer and infection is vital to ascertain disease status and to assess immunotherapeutic options. Time-of-flight technology, the basis of CyTOF® mass cytometry, enables multiplex proteomic cellular phenotyping with 50 or more markers, making it ideal for comprehensive immune profiling. Unlike fluorescence-dependent approaches, which require signal compensation that makes the development of larger panels more challenging, CyTOF utilizes monoisotopic metal-tagged antibodies that exhibit minimal background signal, enabling the highest-resolution multiparametric landscape of a single cell. The Maxpar® Direct™ Immune Profiling Assay™ is a pre-titrated dried-down 30-antibody cocktail preparation for immune profiling of human whole blood or PBMC. This assay is used with Maxpar Pathsetter™ software, which resolves whole blood into 37 immune populations comprising major lineage populations and their subsets, such as CD4 Th subsets and B and T cell memory cells, as well as stratifications of myeloid populations. The resulting system is a simple sample-to-answer solution for immune monitoring studies. Here, we expanded the 30-marker assay with 14 additional antibodies comprising pertinent targets of immunotherapy, including the exhaustion markers PD-1, PD-L1, Tim-3 and CTLA-4, and co-stimulation markers 4-1BB and ICOS. We also demonstrated the compatibility of the assay with downstream intracellular staining for cytoplasmic markers IFN-γ, TNF-α, IL-2, perforin and granzyme B for assessment of cellular function in 4h PMA/ionomycin-stimulated whole blood cultures. Next, we modified the existing Pathsetter model to automate the analysis of whole blood stained with the expanded panel to generate reports on key immune cell populations, percentages of exhausted cells and cell subsets producing cytokines. Last, to demonstrate the ability of this expanded panel to identify antigen-specific T cell subsets accompanied by their in-depth phenotypic assessment, we tested this panel against CMV peptide-stimulated whole blood samples. We demonstrated the flexibility of the Maxpar Direct Immune Profiling Assay in panel customization and a streamlined workflow for automated analysis to enable comprehensive immune profiling of human whole blood. For Research Use Only. Not for use in diagnostic procedures. Citation Format: Shariq Mujib, Stephen K. Li, Nick Zabinyakov, Christina Loh. A comprehensive whole blood CyTOF immune monitoring panel with expanded surface and intracellular markers using the Maxpar Direct Immune Profiling Assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1676.

Profiling and Characterization of Localized Cytokine Response in Congenital Cleft Affected Lip Tissue.

(1) Background: Despite cleft lips and palates belonging to the most common orofacial congenital anomalies, their morphopathogenesis is not yet fully understood. The study aimed to determine the distribution and relation of cytokines interferon-γ (IFN-γ), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-2, IL-7, IL-12, and IL-13 in the cleft affected mucosa of the lip. (2) Materials and Methods: Twenty cleft lip (CL) mucosal samples and seven control tissues of oral cavity mucosa were included in the study. Specimen were obtained during reconstruction surgeries and processed by hematoxylin and eosin staining and immunohistochemistry for IFN-γ, TNF-α, IL-2, IL-7, IL-12, and IL-13. (3) Results: The distribution of cytokines was higher overall in the cleft affected epithelium compared to the connective tissue, with TNF-a, IL-2, and IL-12 displaying the highest number of immunopositive cells. With the exception of IL-2, CL specimen showed higher immunoreactivity. IFN-γ displayed only minor immunoreactivity, with no expression in the control epithelium. Correlation analysis was strongest between CL epithelial IL-13 and IFN-γ (z = 0.71, p < 0.0001). (4) Conclusions: The CLP affected epithelium displays high degrees of plasticity in expressing different cytokines, pointing towards the stimulation of a local adaptive immune response based on consistent inflammatory processes.

Red Blood Cell Released ATP Regulates Systemic Immune Response in Atherosclerosis

Our studies demonstrated that disturbed flow-induced ATP release from red blood cells (RBCs) via pannexin 1 (Panx1) channels plays a significant role in site-specific vascular inflammation and atherosclerosis. This is supported by a 40-60% reduction of atherosclerotic plaque observed in high fat diet (HFD)-fed ApoE-/- mice with RBC panx1 deletion that nearly abolished the release of ATP. Given the interplay of the immune system in atherosclerosis, we hypothesize that disturbed blood flow-induced release of ATP from RBCs at micromolar concentration is a major source of extracellular ATP (orders of magnitude higher than other ATP sources), which plays a crucial role in purinergic signaling-mediated local and systemic immune cell activation, cytokine production, and phenotypic transformation, serving as an important mediator in immune system-mediated initiation and progression of atherosclerosis. To test this hypothesis, we conducted experiments in 3 mouse groups (n = 4 to 12 per group): chow diet-fed wild type control, and 16 weeks HFD-fed ApoE-/- and ApoE-/-/RBC Panx1-/- mice. Plasma inflammatory cytokines were measured via ELISA. Subpopulations of peripheral blood monocytes (PBMCs) were characterized by flow cytometry, and the cytokine secretion capacity of T cells was examined by intracellular interferon-gamma (IFN-γ) staining in isolated splenocytes. Results showed that plasma IFN-γ and interleukin 1 beta (IL-1β) increased 10 and 8 fold, respectively, in HFD ApoE-/- mice when compared to the control group. These increases were reduced to levels close to the control in HFD ApoE-/-/RBC Panx1-/- mice. PBMCs analysis showed a significantly increased pro-inflammatory Ly6Chigh monocytes in HFD ApoE-/- mice from 2.9 ± 0.5% (control) to 19.2 ± 2.0%, while only 7.6 ± 1.0% was found in HFD ApoE-/-/RBC Panx1-/- mice. Intracellular IFN-γ staining of isolated splenocytes from HFD ApoE-/- mice showed a 5-fold increase in IFN-γ+ T cells (%) when compared to the control. In contrast, ApoE-/-/RBC Panx1-/- mice had significantly reduced percentage of IFN-γ+ T cells when compared with ApoE-/- mice (0.12 ± 0.03% vs 1.5 ± 0.48%, p < 0.05), especially in CD4+ T cells (0.06 ± 0.01% vs 0.79 ± 0.21%, p < 0.05). These cells further demonstrated their increased inflammatory potential, as stimulation with phorbol 12-myristate 13-acetate and Ionomycin yielded a markedly higher percentage of IFN-γ+ T cells in the HFD ApoE-/- group (40.4 ± 3.3%) than control (22.7 ± 1.8%) and ApoE-/-/RBC Panx1-/- group (26.6 ± 3.2%), and more prominent differences were found in CD4+ subgroup with values at 29.0 ± 2.5%, 11.1 ± 1.7%, and 14.5 ± 2.9%, respectively (p<0.05). In conclusion, our results indicate that shear stress-induced release of ATP from RBCs via Panx1 channels plays important roles in the immune cell recruitment, activation, and cytokine production, contributing to immune system-mediated vascular inflammation and the initiation and progression of atherosclerosis. Our findings provide novel mechanistic insight into local hemodynamics and systemic risk factor-mediated vascular pathogenesis and disease progression, directly benefiting clinical diagnosis and the prediction of atherosclerosis development.

Droplet-based mRNA sequencing of fixed and permeabilized cells by CLInt-seq allows for antigen-specific TCR cloning

T cell receptors (TCRs) are generated by somatic recombination of V/D/J segments to produce up to 1015 unique sequences. Highly sensitive and specific techniques are required to isolate and identify the rare TCR sequences that respond to antigens of interest. Here, we describe the use of mRNA sequencing via cross-linker regulated intracellular phenotype (CLInt-Seq) for efficient recovery of antigen-specific TCRs in cells stained for combinations of intracellular proteins such as cytokines or transcription factors. This method enables high-throughput identification and isolation of low-frequency TCRs specific for any antigen. As a proof of principle, intracellular staining for TNFα and IFNγ identified cytomegalovirus (CMV)- and Epstein-Barr virus (EBV)-reactive TCRs with efficiencies similar to state-of-the-art peptide-MHC multimer methodology. In a separate experiment, regulatory T cells were profiled based on intracellular FOXP3 staining, demonstrating the ability to examine phenotypes based on transcription factors. We further optimized the intracellular staining conditions to use a chemically cleavable primary amine cross-linker compatible with current single-cell sequencing technology. CLInt-Seq for TNFα and IFNγ performed similarly to isolation with multimer staining for EBV-reactive TCRs. We anticipate CLInt-Seq will enable droplet-based single-cell mRNA analysis from any tissue where minor populations need to be isolated by intracellular markers.

A study of the immune infiltrate and patient outcomes in esophageal cancer.

Cancer patient outcomes and selection for novel therapies are heavily influenced by the immune contexture of the tumor microenvironment. Esophageal cancer is associated with poor outcomes. In contrast to colorectal cancer, where the immunoscore is increasingly used in prognostic staging, little is known about the immune cell populations in esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (SCC), and their clinical significance. Tissue microarrays were constructed from resected tumor tissue of 72 EAC patients and 23 SCC patients. Immunohistochemical staining of CD3, CD8, CD56, CD68, CD45RO, CD69, IFN-γ, IL-10, IL-4, IL-17, TGF-β, FOXP3 and CD107a was performed. Positivity was examined in both the stromal and epithelial compartments. Statistical analysis was performed to identify differences in immune cell infiltration and functional phenotypes between cancer subtypes and tissue compartments. This study identified that esophageal tumors are enriched with CD45RO+ and CD8+ cells and such positivity is significantly higher in SCC compared with EAC. Furthermore, the expression of CD45RO positively correlates with that of CD8 within the tumors of both patient cohorts, suggesting a dominance of memory cytotoxic T cells. This is supported by strong positivity of degranulation marker CD107a in the stromal compartment of EAC and SCC tumors. Cytokine staining revealed a mixed pro- and anti-inflammatory profile within EAC tumors. Esophageal tumors are enriched with memory cytotoxic T cells. Applying these measurements to a larger cohort will ascertain the clinical utility of assessing specific lymphocyte infiltrates in EAC and SCC tumors with regards to future immunotherapy use, patient prognosis and outcomes.

Abstract 895: Coexpression of MHC class I-restricted neoTCRs and ectopic CD8 receptors in precision genome engineered CD4 T cells significantly potentiates antigen-specific effector functions

Abstract Neoepitopes (NeoE) from tumor-exclusive mutations represent compelling targets for personalized neoE-specific autologous TCR-T cell therapies for patients with solid tumors. The imPACT Isolation Technology® is an ultra-sensitive and high-throughput process for capturing neoE-specific CD8 T cells from the blood of patients with solid cancers. Leveraging this technology, neoepitope-specific MHC class I-restricted TCRs (MHC-I neoTCRs) are cloned from individually captured CD8 T cells. Using DNA -mediated (non-viral) gene editing, fresh CD8 and CD4 T cells from the same patient with cancer are engineered to express the MHC-I neoTCR (concomitant with elimination of the endogenous TCR). While naturally occurring MHC-I TCRs are presumed to require concurrent CD8 co-receptor help to stabilize peptide-MHC binding, higher affinity TCRs drive CD8-independent target binding and T cell activation. CD4 T cells, when engineered with high affinity neoTCRs, are thus able to recognize peptide-MHC-I targets and trigger effector T cell functions. However, lower affinity TCRs are dependent on CD8 co-receptors to trigger T cell activation. By precision genome engineering CD8 co-receptor genes together with the neoTCR into CD4 T cells, MHC-I neoTCRs are now competent to trigger antigen-specific effector T cell function. In this study, MHC-I neoTCRs were cloned from neoE-specific T cells captured from the blood of a patient with colorectal cancer. Healthy donor CD8 and CD4 T cells were precision genome engineered to express the cloned MHC-I neoTCRs alone or to include engineering of ectopic CD8 co-receptors in the gene-edited T cells. Flow cytometric analysis was used to evaluate surface expression of neoTCRs and ectopic CD8 co-receptors, respectively. Rescue of neoTCR binding among CD4 T cells for lower affinity, CD8-dependent neoTCRs was observed. Importantly, in response to stimulation with cognate antigen, CD107a and intracellular IFNγ staining revealed 10-100-fold increases in the sensitivity of MHC-I neoTCR-induced effector functions by CD4 T cells, with no effect on specificity. No change in functionality or sensitivity was seen on CD8 T cells by the expression of additional CD8 co-receptor. These results demonstrate that simultaneous precision genome engineering of the CD8 co-receptor together with CD8-dependent MHC-I neoTCRs into CD4 T cells significantly increases their sensitivity to neoE-HLA target recognition as well as triggering pro-inflammatory and cytotoxic function, yet without compromising antigen-specificity. Citation Format: Barbara Sennino, Andrew Conroy, Bhamini Purandare, Kyle Jacoby, Olivier Dalmas, Songming Peng, Alex Franzusoff, Stefanie Mandl. Coexpression of MHC class I-restricted neoTCRs and ectopic CD8 receptors in precision genome engineered CD4 T cells significantly potentiates antigen-specific effector functions [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 895.

A gastric cancer cell derived extracellular compounds suppresses CD161+CD3- lymphocytes and aggravates tumor formation in a syngeneic mouse model

Evasion of the immune system is often associated with malignant tumors. The cancer cell microenvironment plays an important role in tumor progression, but its mechanism is largely unknown. Here we show that an extracellular compound derived from gastric cancer (GC-EC) selectively suppresses CD161+CD3− natural killer (NK) cells. Splenocytes treated with GC-EC showed considerable proliferation and the CD161+CD3− NK cell population was time-dependently suppressed. Intracellular staining of IFN-γ was shown to be down-regulated in concert with granzyme B and perforin. A cytotoxicity assay of splenocytes treated with GC-EC against K-562 cells showed a significant reduction in cytolytic activity. Further, the immune-suppressive effect of GC-EC was more evident in a syngeneic tumor model in C57BL/6 mice. Animals treated with B16 F10 and GC-EC exhibited more aggravated tumor formation than animals treated with B16 F10 only. We demonstrated that inhibition of apoptosis while increasing PI3 K/AKT levels may provoke tumor formation by GC-EC. A cytokine array revealed the presence of several cytokines in GC-EC that negatively regulate immune cytolytic activity and could be potential candidates for immune-suppressive effects.

Clinical and immune responses to anti-CD3 x anti-EGFR bispecific antibody armed activated T cells (EGFR BATs) in pancreatic cancer patients

ABSTRACT Purpose This was a phase I/II adoptive T cell trial in 7 locally advanced and metastatic pancreatic cancer patients using 3–8 infusions of anti-CD3 x anti-EGFR bispecific antibody armed activated T cells (BATs) to determine safety, the maximum tolerated dose (MTD), immune responses, time to progression (TTP), and overall survival (OS). Study Design: T cells obtained by apheresis were expanded and armed with EGFRBi, cryopreserved for infusions. In a phase I dose escalation, five patients received three weekly infusions of 10–40 × 109 BATs/infusion followed by a booster infusion 3 months later, and 2 patients received 8 infusions twice weekly for 4 weeks in a phase II. The trials were registered at http://www.clinicaltrials.gov, NCT01420874 and NCT02620865. Results: There were no dose-limiting toxicities (DLTs), and the targeted dose of 80 × 109 BATs was met. The median TTP is 7 months, and the median OS is 31 months. Two patients had stable disease for 6.5 and 25+ months, and two patients developed complete responses (CRs) after restarting chemotherapy. Infusions of BATs induced anti-pancreatic cancer cytotoxicity, innate immune responses, cytokine responses (IL-12, IP-10), and shifts in CD4 and CD8 Vβ repertoire with enhanced cytoplasmic IFN-γ staining in the Vβ repertoire of the CD8 subset that suggest specific clonal TCR responses. Conclusions: Infusions of BATs are safe, induce endogenous adaptive anti-tumor responses, and may have a potential to improve overall survival.