Intracellular 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.

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.

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.

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.

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.

Antigen-shift in varicella-zoster virus-specific T-cell immunity over the course of Fingolimod-treatment in relapse-remitting multiple sclerosis patients

Fingolimod (FTY) applied as treatment regimen of relapsing-remitting multiple sclerosis (RRMS) induces downregulation of sphingosine-1-phosphate receptors on the lymphocytes. As a result CC chemokine receptor type 7 (CCR7) expressing lymphocytes are retained within the peripheral lymph nodes thus suppressing their accumulation into the cerebrospinal fluid of multiple sclerosis (MS) patients and hampering disease progress. Unfortunately, MS patients treated with FTY suffer from an increased incidence of varicella-zoster virus (VZV) infections which has been associated with a decrease of VZV immediate early 63 (IE63)-specific T-cell immunity. To elucidate VZV-specific T-cell immunity over the course of FTY-treatment, we analyzed T-cell immunity for immediate early, early and late VZV-antigens. T-cell immune responses were detected via intracellular IFN-γ staining after stimulation with VZV-specific peptide mixes for IE62 and IE63 and recombinant proteins for open reading frame 26 (ORF26), ORF9 and glycoprotein E (gE) using flow cytometry. Analyzed samples comprised of different groups including 18 patients with RRMS at baseline (BL), 6 and 12 months after FTY-treatment start, 12 patients with long-term (LT) FTY-treatment, one FTY-treated patient, before and after VZV-reactivation. In addition, VZV-specific IgG and IgM titers were assessed by ELISA. After FTY-treatment start, absolute numbers of CCR7 expressing CD4+ T cells and CD8+T cells dropped rapidly. However, VZV-specific immunity could be detected in the majority of RRMS patients throughout FTY-treatment with increasing prevalence after 6 months of treatment. We found an increase in the prevalence of VZV-specific IFN-γ+CD8+ T-cell immunity in FTY-treated patients after six months of therapy, while in parallel VZV-specific IFN-γ+CD4+ T cells declined dramatically. Additionally, a strong correlation between VZV-specific IgG serum titers and the percentage of RRMS patients with detectable VZV-specific T cells was observed (r = 0.985). Most remarkably, FTY-treated RRMS patients presented a shift in the predominant CD8+ T cell-mediated antigen-response from immediate early (IE62) to early virus antigens (ORF26) six months after treatment in parallel to a decrease of VZV-specific CD4+ T-cell immunity. ORF26-specific CD8+ T cells still dominated the VZV-specific cellular immunity at month 12 after FTY-treatment start and in LT FTY-treated MS patients. In a RRMS patient an increase of VZV-specific CD4+ T cells at VZV-reactivation accompanied with a four-fold increase of a VZV-specific IgG titer was detected which might indicate an important role in cellular immune control of VZV-infections. Monitoring VZV-specific T-cell immunity might provide a valuable tool to RRMS patient risk management during FTY-treatment.

Repertoire of Cytomegalovirus-Specific T Cells Is Focused on the Immunodominant Epitopes in Fixed Hierarchy Dependent on HLA Genotype of the Donor

Background: Cytomegalovirus (HCMV) infection is one of the major complications and causes of mortality in patients receiving immunosuppressive therapy following hematopoietic stem cell transplantation (HSCT). Antiviral drugs have limited efficacy and high toxicity while using CMV-specific T cells from healthy individuals as a cellular vaccine had proven to be safe and efficient. Conventional protocols rely on expanding virus-specific cells ex vivo while more recently it was proposed to transfuse relatively small numbers of minimally manipulated cells and allow them to expand in vivo. To isolate virus-specific cell one could use either the stimulation with overlapping pools of peptides covering the whole immunogenic viral protein followed by isolation of INFγ-producing cells, or direct isolations of cells bound to MHC-multimer loaded with known immunodominant peptides. Both methods have their advantages. The former approach isolates all activated clones irrespective of their MHC-restriction and supplements CD8+ cells with CD4+ fraction, while the latter method is faster and simpler, besides it captures cells irrespective of their ability to produce IFNγ. The efficiency of the two methods was not directly compared and it is currently unknown to what extent T-cell populations isolated by these two approaches are different in terms of absolute quantity and clonal composition. Aims: to compare the quantity and T-cell receptor repertoire composition of T cells specific to pp65 CMV and to pp65-derived immunodominant epitopes NLV restricted by HLA-A*02, TPR and RPH restricted both by HLA-B*07. Methods: PBMC of healthy donors with different combination of HLA-A*02 and HLA-B*07 alleles were stimulated with peptides of immunodominant epitopes or overlapping peptide pool covering the entire pp65 CMV (Miltenyi Biotec, Cat.-130-093-435). Antigen-specific T cells were detected by the intracellular staining for IFNγ and flow cytometry. We obtained fractions of virus-specific T cells from PBMC either by MHC-tetramer staining or IFNγ secretion assay followed by fluorescent activated cell sorting. Then we prepared cDNA libraries of TCR α- and β-chains and sequenced them using NGS. Characterization of TCR repertories was performed by proprietary bioinformatic pipeline. Results: T-cell response to pp65 CMV is strongly focused on immunodominant pp65-derived epitopes. In donors having HLA-A*02 and/or HLA-B*07 absolute majority of pp65-reactive cells are specific to one of the three immunodominant epitopes - NLV, TPR and RPH. Immunodominant antigens are structured in a fixed hierarchy. TPR and RPH are superior to NLV. When HLA-B*07 is present response to the NLV epitope is drastically reduced, most of the pp65-specific cells recognize either TPR or RPH epitopes. TCR repertoire of the NLV-specific T cells is highly skewed and consists of few large dominant clones. TPR and RPH-specific T cells are more clonally diverse. Substantial share of the cells belonging to the large clones specific to the immunodominant antigens do not secrete IFNγ upon antigenic stimulation. Nevertheless, they may be therapeutically valuable, as they might secrete other cytokines. Conclusion: In summary, CMV-specific response in donors positive for HLA-A*02 and/or HLA-B*07 is focused to the combination of three immunodominant epitopes - NLV, TPR and RPH. Substantial share of the cells are not IFNγ-producers. For the patients having these alleles it might be beneficial to use MHC-multimers for isolation of the therapeutic lymphocytes. Figure 1: A - Healthy donors with different combination of HLA-A*02 and HLA-B*07 B - Intracellular staining for IFNγ of CD8+ T cells after stimulation with pp65-derived peptides C - NGS to identify clonally diverse of pp65-sprcific T cells on combination of HLA-A*02 and HLA-B*07 Figure 1 Disclosures No relevant conflicts of interest to declare.

TNF-α/IFN-γ profile of HBV-specific CD4 T cells is associated with liver damage and viral clearance in chronic HBV infection

The role of hepatitis B virus (HBV)-specific CD4 T cells in patients with chronic HBV infection is not clear. Thus, we aimed to elucidate this in patients with chronic infection, and those with hepatitis B flares. Through intracellular IFN-γ and TNF-α staining, HBV-specific CD4 T cells were analyzed in 68 patients with chronic HBV infection and alanine aminotransferase (ALT) <2x the upper limit of normal (ULN), and 28 patients with a hepatitis B flare. HBV-specific HLA-DRB1*0803/HLA-DRB1*1202-restricted CD4 T cell epitopes were identified. TNF-α producing cells were the dominant population in patients' HBV-specific CD4 T cells. In patients with ALT <2xULN, both the frequency and the dominance of HBV-specific IFN-γ producing CD4 T cells increased sequentially in patients with elevated levels of viral clearance: HBV e antigen (HBeAg) positive, HBeAg negative, and HBV surface antigen (HBsAg) negative. In patients with a hepatitis B flare, the frequency of HBV core-specific TNF-α producing CD4 T cells was positively correlated with patients' ALT and total bilirubin levels, and the frequency of those cells changed in parallel with the severity of liver damage. Patients with HBeAg/HBsAg loss after flare showed higher frequency and dominance of HBV-specific IFN-γ producing CD4 T cells, compared to patients without HBeAg/HBsAg loss. Both the frequency and the dominance of HBV S-specific IFN-γ producing CD4 T cells were positively correlated with the decrease of HBsAg during flare. A differentiation process from TNF-α producing cells to IFN-γ producing cells in HBV-specific CD4 T cells was observed during flare. Eight and 9 HBV-derived peptides/pairs were identified as HLA-DRB1*0803 restricted epitopes and HLA-DRB1*1202 restricted epitopes, respectively. HBV-specific TNF-α producing CD4 T cells are associated with liver damage, while HBV-specific IFN-γ producing CD4 T cells are associated with viral clearance in patients with chronic HBV infection. TNF-α producing cells are the dominant population of hepatitis B virus (HBV)-specific CD4 T cells in patients with chronic HBV infection. This population of cells might contribute to the aggravation of liver damage in patients with a hepatitis B flare. HBV-specific IFN-γ producing CD4 T cells are associated with HBV viral clearance. Differentiation from HBV-specific TNF-α producing CD4 T cells into HBV-specific IFN-γ producing CD4 T cells might favor HBV viral clearance.

Restored and Enhanced Memory T Cell Immunity in Rheumatoid Arthritis After TNFα Blocker Treatment.

TNFα inhibitors have shaped the landscape of rheumatoid arthritis (RA) therapy with high clinical efficiency. However, their impact on T cell recall responses is not well-elucidated. We aimed to analyze the immune profiles of memory T cells in RA patients undergoing TNFα inhibitor Golimumab (GM) treatment. Frequencies of peripheral T cell subsets and cytokine expression profiles in memory T cells (TM) upon PMA/Ionomycine stimulation were determined by flow cytometry. Antigen-specific CD8 T cell immunity was analyzed through stimulating PBMCs with CMV-EBV-Flu (CEF) viral peptide pool and subsequent intracellular IFNγ staining. Both peripheral CD8 and CD4 T cells from GM treated patients had a shift pattern characterized by an enlarged effector TM and a reduced central TM cell population when compared to GM untreated group. An increase in the frequencies of TNFα+, IL-2+, and IL-17+ CD8 TM cells was observed whereas only TNFα+CD4 TM cells increased in GM treated patients. Moreover, GM treated patients contained more peripheral IFNγ-producing CD8 T cells specific to CEF viral peptides. Together, these results show a distinct T cell subset pattern and enhanced memory T cell immunity upon GM treatment, suggesting an immunoregulatory effect of TNF inhibitor Golimumab on peripheral memory T cell responses.

OMIP-052: An 18-Color Panel for Measuring Th1, Th2, Th17, and Tfh Responses in Rhesus Macaques.

This 18-color panel was designed to measure vaccine-induced T cell responses in rhesus macaques by intracellular cytokine staining (ICS). It detects seven cytokines, IFN-γ, IL-2, IL-4, IL-5, IL-13, IL-17, and IL-21, two memory markers, CD45RA and CCR7, and four follicular helper T cell (Tfh) markers, CXCR3, CXCR5, ICOS, and PD-1 (Figure 1). While this panel was optimized for use on cryopreserved rhesus macaque peripheral blood mononuclear cells (PBMC) (Table 1), it can also be used on rhesus macaque tissue samples and human PBMC and tissue samples. Experimental vaccines are often tested in nonhuman primates (NHP) for immunogenicity and protection in preclinical trials before proceeding to clinical trials in humans. Historically, vaccine-induced T cell responses have been measured by IFN-γ ELISpot or intracellular cytokine staining (ICS) for IFN-γ, IL-2, and TNF. However, antibody levels, rather than Th1 responses, correlate with protection for many vaccines including the HIV vaccine used in the RV144 clinical trial 1. As such, measuring only Th1 responses may not be adequate for determining T cell correlates of protection or risk in vaccine studies. Therefore, we expanded our 11-color intracellular cytokine staining (ICS) panel, described in OMIP-005, to 18 colors in order to assess a fuller spectrum of T cell responses (Table 2). IL-17 To decrease the variability of the assay due to age-related differences in T cell differentiation, cytokine measurements can be reported as a frequency of memory T cells using the markers CD45RA and CCR7 2. Similarly, IL-21 can be reported as a frequency of Tfh using a combination of the markers CXCR3, CXCR5, ICOS, and PD-1. This combination of markers allows for the delineation of Tfh cells by all currently accepted methods 3-5. This 18-color rhesus macaque panel is an extension of the 11-color panel described in OMIP-005. The cytokines IL-4, IL-5, IL-13, IL-17, and IL-21 were added as well as the Tfh subset markers CXCR3, CXCR5, ICOS, and PD-1. To accommodate these additional markers, CD28 and TNF were removed. It is similar to the following human panels also used to measure antigen-specific responses by intracellular staining: OMIP-001, OMIP-008, OMIP-009, OMIP-14, OMIP-16, OMIP-22, OMIP-25. However, this panel is designed for staining rhesus macaque PBMC (using NHP cross-reactive antibody clones) and includes additional Tfh markers, as well as IL-5 and IL-13. It is also the only panel with this combination of seven cytokines. We thank Mario Roederer and Pratip K. Chattopadhyay for advice and help in developing and optimizing this panel. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Identification of Novel Respiratory Syncytial Virus CD4+ and CD8+ T Cell Epitopes in C57BL/6 Mice.

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection and hospitalization in infants. It is well established that both CD4+ and CD8+ T cells are critical for mediating viral clearance but also contribute to the induction of immunopathology following RSV infection. C57BL/6 mice are often used to study T cell responses following RSV infection given the wide variety of genetically modified animals available. To date, few RSV-derived CD4+ and CD8+ T cell epitopes have been identified in C57BL/6 mice. Using an overlapping peptide library spanning the entire RSV proteome, intracellular cytokine staining for IFN-γ was performed to identify novel CD4+ and CD8+ T cell epitopes in C57BL/6 mice. We identified two novel CD4+ T cell epitopes and three novel CD8+ T cell epitopes located within multiple RSV proteins. Additionally, we characterized the newly described T cell epitopes by determining their TCR Vβ expression profiles and MHC restriction. Overall, the novel RSV-derived CD4+ and CD8+ T cell epitopes identified in C57BL/6 mice will aid in future studies of RSV-specific T cell responses.

Abstract A13: Optimization of a dendritic cell-targeting MIP3α-antigen fusion vaccine in the B16F10 mouse melanoma model

Abstract Background: The chemokine MIP-3α (CCL20) binds to CCR6 found on immature dendritic cells. Vaccines fusing MIP-3α to gp100 have been shown to be effective in therapeutically alleviating melanoma in mouse models. However, that protection was not complete. To optimize the therapy, our laboratory is exploring two avenues. First, we added agents designed to modulate the tolerogenic tumor microenvironment. Here, we report that neutralizing IL-10 at the tumor site enhances the therapeutic anti-melanoma efficacy of a MIP-3α-gp100 DNA vaccine. Secondly, we are optimizing the antigenic profile of the vaccine to help reduce the probability of immunoediting processes leading to tumor therapy escape. Methods: The current studies utilize the B16F10 syngeneic, transplantable, mouse melanoma model system. The MIP-3α-antigen DNA vaccine is administered intramuscularly (i.m.) into the tibialis muscle, followed immediately by i.m. electroporation. Constructs utilized include MIP-3α fused to gp100 alone or in addition to TRP-2. Vaccinations are given therapeutically, beginning at day 3 or 5 post challenge. Tumor sizes, growth, and survival were all assessed. Treatment responses were characterized by flow cytometric analysis of tumor infiltrate. Vaccine-specific T-cells were delineated by gp10025-33 stimulation followed by intracellular cytokine staining for IFN-γ and assessment by flow cytometry. The mechanism of αIL-10 efficacy was explored by RT-PCR and confirmed with a knockout mouse model. Results: With this therapeutic protocol, we demonstrate for the first time that by either neutralizing IL-10 or adding a second antigen to our construct, we are able to enhance the antitumor efficacy of a MIP-3α-gp100 vaccine, leading to significantly smaller tumors, slower growing tumors, and overall increases in mouse survival. Surprisingly, the additive effects of αIL-10 were not shown to be directly mediated by any T-cell parameter tested, including vaccine-specific tumor infiltrating lymphocytes (TILs), total TILs of either CD4+ or CD8+ subset, regulatory T-cells, granzyme positive T-cells, and others. We discovered, however, that IFNα-4 transcripts in the tumor were significantly upregulated in mice given vaccine and αIL-10 compared to vaccine alone. A mouse model with IFNαR1 knocked out eliminated the protection provided by αIL-10, demonstrating that the additional therapeutic value of αIL-10 is primarily mediated by type-I interferons. The immunologic details of the added TRP2 antigen are currently being explored. Conclusions: Efficient targeting of antigen to immature dendritic cells with a chemokine fusion vaccine offers a potential alternative approach to the ex vivo dendritic cell antigen loading protocols currently undergoing clinical investigation. Adding multiple antigens or combining this approach with an IL-10 neutralizing antibody therapy that modulates the tolerogenic tumor microenvironment both enhance vaccine efficacy. Further potential therapy optimization currently undergoing investigation offers promise for this line of investigation to become a novel melanoma therapy. Citation Format: James T. Gordy, Kun Luo, Richard B. Markham. Optimization of a dendritic cell-targeting MIP3α-antigen fusion vaccine in the B16F10 mouse melanoma model [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A13.