Control of Tumors by Antigen-Specific CD8+ T Cells through PDL1-Targeted Delivery of Antigenic Peptide

Tumor antigen-specific T cell function is limited by immune tolerance in the tumor microenvironment. In the tumor microenvironment, tumor cells upregulate PD-L1 expression to promote T cell exhaustion by PD-1/PD-L1 interactions and undergo mutations to avoid being targeted by tumor antigen-specific T cells. Thus, tumor cells escape the immune surveillance by causing immune tolerance. We reason that a chimeric molecule made of a PD-L1-specific antibody linked to a cleavable antigenic peptide can target the antigenic peptide to the tumor microenvironment, resulting in the blockade of the PD-1/PD-L1 pathway and killing tumor cells through the coating of antigenic peptide. Here, we have generated a therapeutic chimeric protein containing the PD-L1 single-chain variable fragment (scFv) linked to a cleavable model cytotoxic T lymphocyte (CTL) epitope: E7 CTL peptide. Our study demonstrated that our chimeric protein (named PDL1-scFv-Fc-RE7) can target PD-L1-expressing tumor cells and enable E7 presentation by releasing cleavable E7 CTL peptide to coat tumor cells, resulting in tumor clearance by E7-specific CD8+ T cells. The presentation of the E7 peptide by cancer cells can then render tumor cells susceptible to the killing of preexisting E7-specific CD8+ T cells and contribute to tumor clearance. Our finding suggests a synergistic approach to not only enhance antigen-specific tumor clearance but also bypass immune tolerance.

Efficient targeting of NY-ESO-1 tumor antigen to human cDC1s by lymphotactin results in cross-presentation and antigen-specific T cell expansion

Type 1 conventional dendritic cells (cDC1s) are characterized by their ability to induce potent CD8+ T cell responses. In efforts to generate novel vaccination strategies, notably against cancer, human cDC1s emerge as an ideal target to deliver antigens. cDC1s uniquely express XCR1, a seven transmembrane G protein-coupled receptor (GPCR). Due to its restricted expression and endocytic nature, XCR1 represents an attractive receptor to mediate antigen-delivery to human cDC1s. To explore tumor antigen delivery to human cDC1s, we used an engineered version of XCR1-binding lymphotactin (XCL1), XCL1(CC3). Site-specific sortase-mediated transpeptidation was performed to conjugate XCL1(CC3) to an analog of the HLA-A*02:01 epitope of the cancer testis antigen New York Esophageal Squamous Cell Carcinoma-1 (NY-ESO-1). While poor epitope solubility prevented isolation of stable XCL1-antigen conjugates, incorporation of a single polyethylene glycol (PEG) chain upstream of the epitope-containing peptide enabled generation of soluble XCL1(CC3)-antigen fusion constructs. Binding and chemotactic characteristics of the XCL1-antigen conjugate, as well as its ability to induce antigen-specific CD8+ T cell activation by cDC1s, was assessed. PEGylated XCL1(CC3)-antigen conjugates retained binding to XCR1, and induced cDC1 chemoattraction in vitro. The model epitope was efficiently cross-presented by human cDC1s to activate NY-ESO-1-specific CD8+ T cells. Importantly, vaccine activity was increased by targeting XCR1 at the surface of cDC1s. Our results present a novel strategy for the generation of targeted vaccines fused to insoluble antigens. Moreover, our data emphasize the potential of targeting XCR1 at the surface of primary human cDC1s to induce potent CD8+ T cell responses.

An all-in-one adjuvanted therapeutic cancer vaccine targeting dendritic cell cytosol induces long-lived tumor suppression through NLRC4 inflammasome activation

Therapeutic cancer vaccines (TCVs) should induce robust tumor-specific T cell responses. To achieve this, TCVs incorporate T cell epitopes and strong adjuvants. Here, we report an all-in-one adjuvanted cancer vaccine platform, which targets intracellular compartment of antigen presenting cells and subsequently induces effective cytotoxic T cell responses. We screened a novel peptide (DCpep6) that specifically binds and tranmits into CD11c+ cells through in vivo phage biopanning. We then engineered a protein-based TCV (DEF) consisting of DCpep6 (D), an optimized HPV E7 tumor antigen (E), and a built-in flagellin adjuvant (F) as a single molecule. DEF was stably expressed and each component was functional. In vivo administered DEF rapidly biodistributed in draining LNs and internalized into CD11c+ cells. DEF immunization elicited strong anti-tumor T cell responses and provided long-term survival of TC-1 tumor implanted mice. The DEF-mediated anti-tumor effect was abolished in NLRC4−/− mice. Taken together, we propose a protein-based all-in-one TCV platform that intracellularly co-delivers tumor antigen and inflammasome activator to DCs to induce long-lasting anti-tumor T cell responses.

Adoptive Chimeric Antigen Receptor T Cell (CAR-T) and Treg Cell-Based Immunotherapies: Frontier Therapeutic Aspects in Cancers

Based on this point that some cancers do not appropriately respond to conventional therapy, and there is the possibility of relapse, immunotherapy is currently under investigation. Cancer immunotherapies are widely recognized as transformational for several cancers and enable to move to the front-line therapy with few side effects. One of its new branches is treatment with T-cells that have been changed their receptor. The research on these cells is generally according to the design of a receptor against a specific tumor antigen. Also, manipulation of regulatory T-cell (Tregs), as the barriers to proper immune responses in the tumor microenvironment, will promote Tregs-targeted therapeutic opportunities and improve the efficacy of the current cancer treatment, such as radiation and chemotherapy. This review attempts to show novel insights into the roles of Tregs in cancer which can be considered a promising anticancer therapeutic strategy for targeting them and approaches for the generation of tumor antigen-specific T lymphocytes (AST) using chimeric antigen receptors.

Sensitive identification of neoantigens and cognate TCRs in human solid tumors

The identification of patient-specific tumor antigens is complicated by the low frequency of T cells specific for each tumor antigen. Here we describe NeoScreen, a method that enables the sensitive identification of rare tumor (neo)antigens and of cognate T cell receptors (TCRs) expressed by tumor-infiltrating lymphocytes. T cells transduced with tumor antigen-specific TCRs identified by NeoScreen mediate regression of established tumors in patient-derived xenograft mice.

EXTH-44. SYSTEMIC CCL3 TREATMENT ENHANCES IMMUNOTHERAPY EFFICACY THROUGH IMPROVED DENDRITIC CELL MIGRATION

INTRODUCTION Dendritic cell (DC) vaccines have shown marginal success in treating glioblastoma (GBM), with inefficient vaccine migration a major limitation. Prior evidence from our clinical trials demonstrated that tetanus diphtheria (Td) preconditioning produced greater DC migration to vaccine draining lymph nodes (VDLNs) and long-term survival. Greater DC numbers reaching VDLNs was also associated with long-term survival. We found from preclinical studies and our patients that increased DC migration was dependent upon the chemokine (C-C motif) ligand 3 (CCL3). METHODS The effect of systemic CCL3 treatment on DC vaccine migration (n=5), antigen-specific T cell responses (n=5) and efficacy against orthotopic GL261-OVA and SMA560 tumors (n=10) was studied in C57Bl/6 and VMdK mice. DCs were electroporated with OVA-mRNA or pulsed with ODC1 neoantigen peptide. Median overall survival (mOS) was measure in days (d) post-intracranial implantation. RESULTS Intravenous CCL3 at the time of intradermal DC vaccination resulted in a dose-dependent increase in migration to VDLN (10ug p=0.036, 20ug p< 0.0001, 50ug p< 0.0001). Mean migration levels following CCL3 treatment were similar to Td-preconditioning (p=0.52) but showed significantly less variability between mice. Combined CCL3 and DC vaccination generated more tumor antigen-specific CD8+IFNγ+ T cells 7 days compared to DC vaccine alone (p=0.0045). CCL3+OVA-DC treatment resulted in significantly greater survival compared to OVA-DC alone (mOS 37 vs 19.5 d; p=0.0174) in established GL261-OVA. CCL3 treatment increased survival in mice with established SMA560 tumors treated with neoantigen ODC1 peptide-pulsed DCs (Tumor alone mOS: 21d, DCvac: 25d, CCL3+DCvac: 48d, p=0.002). CONCLUSIONS These data combined with previous success of our DC vaccine clinical trials reflect the potency of CCL3 to enhance DC vaccine-specific migration, immune responses and survival. CCL3 is a novel and safe adjuvant to overcome prior limitations in DC vaccine therapy and may be translatable to increase heterogeneous tumor antigen presentation following vaccine-targeted tumor killing.

IMMU-32. IDENTIFICATION OF TUMOR-ANTIGEN SPECIFIC T CELLS AND THE EFFICACY OF IMMUNOTHERAPY VACCINES FOR GLIOBLASTOMA ANTIGENS DETERMINED USING CANCER IMMUNOGENOMICS APPROACH

BACKGROUND Glioblastoma multiforme (GBM) remains a disease with debilitating survival outcomes. Owing to the heterogeneous nature and low mutation burden, identifying multiple antigens inherent to GBM that may serve as targets for immune-based therapies is attractive. Our aim is to develop a personalized immunotherapy approach using cancer immunogenomics for prospectively identifying neoantigens and uniquely expressed tumor proteins and then selectively expanding T cells against these truly tumor-specific antigens and dendritic cell vaccines to boost the T cell responses. METHODS RNAseq and WES was performed for murine KR158-luc GBM tumor. Using a cancer immunogenomics approach that we developed, called the O pen R eading Frame A ntigen N etwork (O.R.A.N.), we identified the immunogenic neoantigens and tumor-associated antigens (TAAs) including cancer testis and developmental antigens, that are aberrantly over-expressed in KR158-luc tumor. All predicted genes were subjected to a gene enrichment strategy and an mRNA library was generated containing predominantly only the target genes but had some background non-specific genes (validated by RNAseq). KR158-luc tumor bearing animals were then treated with dendritic cells loaded with the tumor antigen specific mRNA library. Tumor volume and thus progress was determined using in vivo luciferase imaging technique. Additionally, tetramers specific to several of the predicted antigens were manufactured and the frequency of antigen specific T cells was determined using flow cytometry. RESULTS The dendritic cell vaccines were effective in delaying the progression of KR158-luc tumors and we identified T cells targeting several of our predicted antigens in the tumor bearing animals. The antigen specific T cells were detected in the tumor infiltrating lymphocytes as well as in the peripheral lymph organs. CONCLUSION We developed a dendritic cell-based vaccination approach targeting all neoantigens and TAAs identified as being tumor-specific and validated our developed immunogenomics pipeline by identifying antigen-specific T cells in the tumor bearing animals against novel GBM antigens.