Antitumor Cytotoxic T Lymphocytes Research Articles

Intratumoral delivery of a highly active form of XCL1 enhances antitumor CTL responses through recruitment of CXCL9-expressing conventional type-1 dendritic cells.

Conventional type 1 dendritic cells (cDC1s) play a crucial role in antitumor immunity through the induction and activation of tumor-specific CD8+ cytotoxic T cells (CTLs). The chemokine XCL1 is a major chemotactic factor for cDC1s and its receptor XCR1 is selectively expressed on cDC1s. Here, we investigated the effect of intratumoral delivery of a highly active form of murine XCL1 (mXCL1-V21C/A59C) on cDC1-mediated antitumor immunity using a hydrophilic gel patch. The hydrophilic gel patch containing mXCL1-V21C/A59C increased cDC1 accumulation in the tumor masses and promoted their migration to the regional lymph nodes, resulting in enhanced induction of tumor-specific CTLs. Tumor-infiltrating cDC1s not only expressed XCR1 but also produced CXCL9, a ligand for CXCR3 which is highly expressed on CTLs and NK cells. Consequently, CTLs and NK cells were increased in the tumor masses of mice treated with mXCL1-V21C/A59C, while immunosuppressive cells such as monocyte-derived suppressive cells and regulatory T cells were decreased. We also confirmed that anti-CXCL9 treatment decreased the tumor infiltration of CTLs. The intratumoral delivery of mXCL1-V21C/A59C significantly decreased tumor growth and prolonged survival in E.G7-OVA and B16-F10 tumor-bearing mice. Furthermore, the antitumor effect of mXCL1-V21CA59C was enhanced in combination with anti-programmed cell death protein 1 treatment. Finally, using The Cancer Genome Atlas database, we found that XCL1 expression was positively correlated with tumor-infiltrating cDC1s and a better prognosis in melanoma patients. Collectively, our findings provide a novel therapeutic approach to enhance tumor-specific CTL responses through the selective recruitment of CXCL9-expressing cDC1s into the tumor masses.

C/EBPα mediates the maturation and antitumor functions of macrophages in human hepatocellular carcinoma

Recent studies have suggested that therapeutic upregulation of CCAAT/enhancer binding protein α (C/EBPα) prevents hepatocellular carcinoma (HCC) progression. However, the mechanisms underlying this outcome are not fully understood. In this study, we investigated the expression and functional roles of C/EBPα in human HCC, with a focus on monocytes/macrophages (Mφs). Paraffin-embedded tissues were used to visualize C/EBPα expression and analyze the prognostic value of C/EBPα+ monocytes/Mφs in HCC patients. The underlying regulatory mechanisms were examined using human monocyte-derived Mφs. The results showed that the expression of C/EBPα on monocytes/Mφs was significantly decreased in intra-tumor tissues compared to the corresponding peri-tumor tissues. C/EBPα+ monocytes/Mφs displayed well-differentiation and antitumor capacities, and the accumulation of these cells in tissue was associated with antitumor immune responses and predicted longer overall survival (OS) of HCC patients. Mechanistic studies demonstrated that C/EBPα was required for Mφ maturation and HLA-DR, CD169 and CD86 expression, which initiates antitumor cytotoxic T-cell responses; however, these effects were inhibited by monocyte autocrine IL-6- and IL-1β-induced suppression of mTOR1 signaling. Reprogramming Mφs via the upregulation of C/EBPα may provide a novel strategy for cancer immunotherapy in patients with HCC.

P07.09.B A RANDOMIZED PHASE 2B STUDY OF SURVIVIN VACCINE SURVAXM PLUS ADJUVANT TEMOZOLOMIDE FOR NEWLY-DIAGNOSED GLIOBLASTOMA (SURVIVE)

Abstract BACKGROUND Newly-diagnosed glioblastoma (nGBM) has a dismal prognosis with a median overall survival (OS) of nearly 16 months. nGBM cells have high expression of tumor-associated survivin protein. Survivin, localized to the cell surface through presentation by MHC class I molecules, is recognized by antibodies and cytotoxic T-lymphocytes (CTLs). A Phase 2a trial (NCT02455557) showed that a 15-amino acid-peptide-conjugate vaccine (SurVaxM) stimulates the production of survivin-directed antibodies and anti-tumor CTL in nGBM patients, resulting in a median OS of 25.9 months. This Phase 2b randomized controlled trial (RCT) aims to further investigate the efficacy of SurVaxM and adjuvant temozolomide for nGBM. METHODS This multicenter, placebo-controlled, investigator- and patient-blinded, in-progress RCT randomizes nGBM patients receiving standard of care to either SurVaxM (arm A) or saline placebo (arm B) in a 3:2 ratio at 15 sites. Included patients have age ≥18 years, normal organ function, Karnofsky Performance Status (KPS) ≥70, surgical resection, residual MRI contrast enhancement of ≤1 cm3 within 72 hours of resection, and adjuvant temozolomide (TMZ) therapy. Patients with recurrent, multicentric, brainstem- or cerebellar-origin GBM are excluded, as well as patients on tumor-treating fields or other immunotherapies. All patients undergo 3 phases: (1) vaccine priming (VP) phase, starting within 4 weeks after completion of chemoradiation, where 4 doses of SurVaxM or Placebo are administered every 2 weeks; (2) adjuvant TMZ phase, started after ≥1 VP dose; and (3) vaccine maintenance phase, started 8 weeks after VP, with SurVaxM or placebo given every 8 weeks. TMZ phase overlaps with VP and VM phases. The primary endpoint is median OS. Assuming a 1-year survival rate of 75% in the SurVaxM arm, comparable to the median OS in early phase trials, and 60% in the control arm, the study will enroll 265 patients, 159 in arm A and 106 in arm B. A log-rank test stratified by KPS (70-80 and 90-100), MGMT status (methylated and unmethylated), and IDH status (mutant and wild-type) will be used for analysis. Secondary endpoints per study arm are survival at 15, 18, and 24 months, median progression-free survival, toxicity, and progression-free survival at 3, 6, and 12 months. A single sequential OS-driven interim analysis is planned when 50% of OS events (deaths) occur. The study is expected to take 35 months, with ongoing accrual. RESULTS 69 patients have been enrolled as of April 11, 2023. CONCLUSION Findings from this trial will demonstrate the safety and efficacy of survivin vaccine in GBM (Clinical trial information: NCT05163080).

The levels of serum soluble CD86 are correlated with the expression of CD86 variant 3 gene and are prognostic indicators in patients with myeloma

We previously showed that cell-surface CD86 expressed on multiple myeloma (MM) cells contributed to not only tumor growth but also antitumor cytotoxic T-lymphocyte responses mediated by induction of IL-10-producing CD4+ T cells. The soluble form of CD86 (sCD86) was also detected in serum from patients with MM. Thus, to determine whether sCD86 levels are a useful prognostic factor, we investigated the association of serum sCD86 levels with disease progression and prognosis in 103 newly diagnosed patients with MM. Serum sCD86 was detected in 71% of the patients with MM but was only rarely detected in patients with monoclonal gammopathy of undetermined significance and healthy controls, and the level was significantly increased in patients with advanced-stage MM. When we examined differences in clinical characteristics according to the level of serum sCD86, those in the high (≥2.18 ng/mL, n = 38) group exhibited more aggressive clinical characteristics, with shorter overall survival times compared with those in the low (<2.18 mg/mL, n = 65) group. On the other hand, it was difficult to stratify the patients with MM into different risk groups based on the expression levels of cell-surface CD86. The levels of serum sCD86 were significantly correlated with the expression levels of the messenger RNA (mRNA) transcripts of CD86 variant 3, which lack exon 6, resulting in a truncated transmembrane region, and its variant transcripts were upregulated in the high group. Thus, our findings suggest that sCD86 can be easily measured in peripheral blood samples and is a useful prognostic marker in patients with MM.

Mutant and non-mutant neoantigen-based cancer vaccines: recent advances and future promises.

Major advances in cancer treatment have emerged with the introduction of immunotherapies using blocking antibodies that target T-cell inhibitory receptors, such as programmed death-1 (PD-1) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), known as immune checkpoints. However, most cancer patients do not respond to immune checkpoint blockade (ICB) therapies, suggesting the development of resistance mechanisms associated with either an insufficient number of preexisting tumor-specific T-cell precursors and/or inappropriate T-cell reactivation. To broaden clinical benefit, anti-PD-1/PD-1 ligand (PD-L1) neutralizing antibodies have been combined with therapeutic cancer vaccines based on non-mutant and/or mutant tumor antigens, to stimulate and expand tumor-specific T lymphocytes. Although these combination treatments achieve the expected goal in some patients, relapse linked to alterations in antigen presentation machinery (APM) of cancer cells often occurs leading to tumor escape from CD8 T-cell immunity. Remarkably, an alternative antigenic peptide repertoire, referred to as T-cell epitopes associated with impaired peptide processing (TEIPP), arises on these malignant cells with altered APM. TEIPP are derived from ubiquitous non-mutant self-proteins and represent a unique resource to target immune-edited tumors that have acquired resistance to cytotoxic T lymphocytes (CTLs) related to defects in transporter associated with antigen processing (TAP) and possibly also to ICB. The present review discusses tumor-associated antigens (TAAs) and mutant neoantigens and their use as targets in peptide- and RNA-based therapeutic cancer vaccines. Finally, this paper highlights TEIPP as a promising immunogenic non-mutant neoantigen candidates for active cancer immunotherapy and combination with TAA and mutant neoantigens. Combining these polyepitope cancer vaccines with ICB would broaden T-cell specificity and reinvigorate exhausted antitumor CTL, resulting in the eradication of all types of neoplastic cells, including immune-escaped subtypes.

Anti-Programmed Cell Death-1 Antibody and Dasatinib Combination Therapy Exhibits Efficacy in Metastatic Colorectal Cancer Mouse Models.

In this study, we investigated the in vivo metastasis suppression effects of the platelet-derived growth factor receptor inhibitor dasatinib, which targets cancer-associated fibroblasts (CAFs), in combination with an anti-programmed cell death-1 (PD-1) antibody. We classified clinical CRC cases as inflamed, excluded, or desert using immunohistochemical analysis and evaluated the tumor stroma. The excluded type was the most common, and cases with high-volume stroma in the primary lesions also had a high stromal volume in the liver metastatic lesions. Liver-metastasis mouse models with different stromal volumes were established and treatment-induced changes in the tumor immune microenvironment were evaluated. The anti-PD-1 antibody alone exhibited a therapeutic effect for the liver metastases with low stromal volumes but not for the liver metastases with high stromal volumes. In contrast, antitumor effects were observed with anti-PD-1 antibody/dasatinib combination therapy even in the liver metastases with high stromal volumes. Combination therapy reduced the stromal volume, promoted immune cell infiltration, induced antitumor cytotoxic T-cell responses, activated antitumor immunity, and promoted tumor regression. These results suggest that CAFs play an important role in the immune evasion of CRC and that anti-PD-1 antibody/dasatinib combination therapy has potential as a treatment option for patients with metastatic CRC for whom immunotherapy alone is ineffective.

Anti-PD-1 antibody-activated Th17 cells subvert re-invigoration of antitumor cytotoxic T-lymphocytes via myeloid cell-derived COX-2/PGE2.

Anti-PD-1 antibody-mediated activation of type 17T-cells undermines checkpoint inhibitor therapy in the LSL-KrasG12D murine lung cancer model. Herein, we establish that the Th17 subset is the primary driver of resistance to therapy demonstrate that the ontogeny of dysplasia-associated Th17 cells is driven by microbiota-conditioned macrophages; and identify the IL-17-COX-2-PGE2 axis as the mediator of CD8+ cytotoxic T-lymphocyte de-sensitization to checkpoint inhibitor therapy. Specifically, anti-PD-1 treatment of LSL-KrasG12D mice, in which CD4+ T-cells were deficient for RORc, resulted in a 60% increase in CTL cytotoxicity and a 2.5-fold reduction in tumor burden confirming the critical role of Th17 cells in resistance to therapy. Lung-specific depletion of microbiota reduced Th17 cell prevalence and tumor burden by 5- and 2.5-fold, respectively; establishing a link between microbiota and Th17 cell-driven tumorigenesis. Importantly, lung macrophages from microbiota sufficient, but not from microbiota-deficient, mice polarized naïve CD4+ T-cells to a Th17 phenotype, highlighting their role in bridging microbiota and Th17 immunity. Further, treatment with anti-PD-1 enhanced COX-2 and PGE2 levels, whereas neutralization of IL-17 diminished this effect. In contrast, inhibition of COX-2 rescued CTL activity and restored tumor suppression in anti-PD-1-treated mice, revealing the molecular basis of IL-17-mediated resistance to checkpoint blockade. Clinical implications of these findings are discussed.

Selected Articles from This Issue

Currently, there is no approved targeted therapy option for treatment naïve patients with AML harboring a FLT3 mutation ineligible for intensive therapy. Konopleva and colleagues investigated the efficacy of venetoclax plus azacitidine in an FLT3-mutated AML population and reported that the remission rates and OS among patients with or without FLT3 mutation were similar, suggesting that venetoclax and azacitidine maybe be used for treatment naïve AML patients who are ineligible for intensive chemotherapy regimens irrespective of FLT3 mutations. They also observed higher remission rates among patients exhibiting both FLT3-ITD and TKD mutations; however, the impact on OS warrants further investigation.Approximately 20% of patients with AML have IDH mutations. Preliminary data suggests they have better responses to venetoclax-based regimens. Pollyea and colleagues investigated the efficacy of venetoclax plus azacitidine in patients harboring IDH1/2 mutations. The responses and OS among these patients were superior compared to azacitidine alone. Furthermore, patients with IDH2 mutations had better outcomes than patients with IDH1 mutations. Finally, cytogenetic risk was not prognostic of OS in patients with IDH1/2 mutations treated with venetoclax plus azacitidine, while it was in IDH1/2 wild-type patients. This suggests that IDH status can overcome the prognostic significance of cytogenetics in some circumstances.Damage to the major salivary glands is a leading permanent side effect of radiation therapy for head and neck cancers, and no adequate treatment exists. Preclinical studies indicate that mesenchymal stem/stromal cell therapy may restore radiation-induced salivary gland damage. Duch Lynggaard and colleagues conducted a first-in-human investigator-initiated, randomized, placebo-controlled phase I/II trial to investigate the long-term safety of intraglandular injections of autologous adipose tissue-derived mesenchymal stem/stromal cells (ASCs) into the submandibular glands of patients previously treated for HPV+ oropharyngeal squamous cell carcinoma. This study demonstrates that autologous ASC therapy is safe and that it significantly reduced xerostomia related symptoms.Immunotherapeutic strategies hold great promise for malignant brain tumors, yet the determinants of an effective anti-tumor cytotoxic T-cell response are unclear. To explore what factors may be important, Kumar and colleagues performed multiomic profiling of a MAPK-activated glioma subtype with a robust CD8+ T cell and microglia/macrophage response. Increased CXCL14 secretion from tumor cells promoted CD8+ T cell chemotaxis, recruited brain tumor-infiltrating CD8+ T cells in vivo, and prolonged overall survival in a cytotoxic T cell-dependent manner. Together, these findings elucidate a novel mechanism of immune regulation in glioma.

Immunovirotherapy Based on Recombinant Vesicular Stomatitis Virus: Where Are We?

Vesicular stomatitis virus (VSV), a negative-strand RNA virus of the Vesiculovirus genus, has demonstrated encouraging anti-neoplastic activity across multiple human cancer types. VSV is particularly attractive as an oncolytic agent because of its broad tropism, fast replication kinetics, and amenability to genetic manipulations. Furthermore, VSV-induced oncolysis can elicit a potent antitumor cytotoxic T-cell response to viral proteins and tumor-associated antigens, resulting in a long-lasting antitumor effect. Because of this multifaceted immunomodulatory property, VSV was investigated extensively as an immunovirotherapy alone or combined with other anticancer modalities, such as immune checkpoint blockade. Despite these recent opportunities to delineate synergistic and additive antitumor effects with existing anticancer therapies, FDA approval for the use of oncolytic VSV in humans has not yet been granted. This mini-review discusses factors that have prompted the use of VSV as an immunovirotherapy in human cancers and provides insights into future perspectives and research areas to improve VSV-based oncotherapy.

A phase I/II study of LOAd703, a TMZ-CD40L/4-1BBL-armed oncolytic adenovirus, combined with nab-paclitaxel and gemcitabine in advanced pancreatic cancer.

4138 Background: Due to its low tumor immunogenicity and immunosuppressive microenvironment, pancreatic ductal adenocarcinoma (PDAC) remains an immunotherapeutic challenge. LOAd703, an oncolytic adenovirus with transgenes encoding TMZ-CD40L and 4-1BBL, has been shown to lyse tumor cells selectively, induce anti-tumor cytotoxic T-cell responses, reduce myeloid-derived suppressor cell (MDSC) infiltration, and induce tumor regression in preclinical studies. Methods: In this phase I/II trial, patients with unresectable or metastatic PDAC were treated with intratumoral injections of LOAd703 and standard intravenous nab-paclitaxel/gemcitabine (nPG) chemotherapy. Starting on cycle 1 day 15 of nPG, LOAd703 was injected with image guidance into the primary pancreatic tumor or a metastasis every 2 weeks for 6 injections. In the event of sustained tumor control, subjects were eligible to receive up to 6 more injections. Three dose levels of LOAd703 were investigated using a BOIN dose escalation design. Primary endpoints were safety and feasibility. Results: Of the 22 subjects enrolled, 21 received at least 1 LOAd703 injection, and 18 received at least 3 LOAd703 injections (the a priori definitions of evaluability for dose limiting toxicity [DLT] and efficacy, respectively). Of the 21 subjects injected, median age was 61, 81% had stage IV disease, and 57% had already received chemotherapy for advanced disease. Median CA 19-9 was 1494. Of the 18 response evaluable subjects, 3 were treated at dose level 1 (5x10e10 VP), 4 at dose level 2 (1x10e11 VP), and 11 at dose level 3 (5x10e11 VP). The most common adverse events (AEs) attributable to LOAd703 were fever, chills, nausea, and increased liver enzymes. AEs were short-lived and grade 1/2, except for a grade 3 transaminase elevation in one subject receiving dose level 3 (the only DLT). Objective response rate (ORR) among those treated at the highest dose level was 55% (5/11 subjects), thus meeting the predefined criterion for efficacy. Among all response evaluable patients, overall response rate (ORR) was 44%, and disease control rate (DCR) was 94%. CA 19-9 decreased by ≥50% in 61% of evaluable patients. Median overall survival (OS) among the 21 subjects receiving at least 1 LOAd703 injection was 8.7 months. The proportion of T effector memory cells increased after initiation of on-protocol treatment (p = 0.0232) while the proportion of T regulatory cells and myeloid-derived suppressor cells decreased (p = 0.0410, p = 0.0256, respectively). Conclusions: Combining intratumoral injections of LOAd703 with standard nPG chemotherapy was safe and feasible. The target response rate at the highest dose level was met, and treatment-emergent immune responses were observed. A follow-up clinical trial combining LOAd703, nPG, and the anti-PDL-1 inhibitor atezolizumab is underway. Clinical trial information: NCT02705196.

Combination of CTLA-4 blockade with MUC1 mRNA nanovaccine induces enhanced anti-tumor CTL activity by modulating tumor microenvironment of triple negative breast cancer

The immunosuppressive tumor microenvironment (TME) is the main reason for the failure of many immunotherapies that directly stimulate anti-tumor immune response. Anti-CTLA-4 antibody may reduce effector regulatory T (Treg) cell numbers and their suppressive activity in the TME. We have previously reported that combination of anti-CTLA-4 antibody with MUC1 mRNA nanovaccine may mutually enhance each single treatment. But the enhancement mechanism of therapeutic efficacy of MUC1 mRNA nanovaccine plus anti-CTLA-4 monoclonal antibody (mAb) is unknown. In this study, anti-tumor CTL activity induced by combination of CTLA-4 Blockade with MUC1 mRNA nanovaccine and immunosuppressive factors in the TME of triple negative breast cancer were investigated. The results demonstrated that combined therapy with nanovaccine and anti-CTLA-4 mAb could induce stronger anti-tumor CTL response than each monotherapy, result in significantly decreased numbers of myeloid-derived suppressor cells (MDSC), Treg cells, tumor-associated fibroblasts (TAFs) and tumor vasculature in the TME, downregulated levels of interleukin-6, tumor necrosis factor-α and transforming growth factor-β, and significantly upregulated levels of IFN-γ and interleukin-12 as well as increased number of CD8+ T cell, and appear more effective than either nanovaccine or anti-CTLA-4 mAb alone at increasing level of apoptosis in tumor cells. In addition, combination immunotherapy could significantly downregulated the signal transducer and activator of transcription 3 (STAT3) signal pathway. Therefore, it can be concluded that combination of CTLA-4 blockade with MUC1 mRNA nanovaccine enhances anti-tumor cytotoxic T-lymphocyte activity by reducing immunosuppressive TME and inhibiting tumor-promoting STAT3 signaling pathway.

Neoantigen vaccine: An emerging immunotherapy for hepatocellular carcinoma.

Tumor-specific neoantigens, which are expressed on tumor cells, can induce an effective antitumor cytotoxic T-cell response and mediate tumor regression. Among tumor immunotherapies, neoantigen vaccines are in early human clinical trials and have demonstrated substantial efficiency. Compared with more neoantigens in melanoma, the paucity and inefficient identification of effective neoantigens in hepatocellular carcinoma (HCC) remain enormous challenges in effectively treating this malignancy. In this review, we highlight the current development of HCC neoantigens in its generation, screening, and identification. We also discuss the possibility that there are more effective neoantigens in hepatitis B virus (HBV)-related HCC than in non-HBV-related HCC. In addition, since HCC is an immunosuppressive tumor, strategies that reverse immunosuppression and enhance the immune response should be considered for the practical exploitation of HCC neoantigens. In summary, this review offers some strategies to solve existing problems in HCC neoantigen research and provide further insights for immunotherapy.

A phase I/II study combining a TMZ-CD40L/4-1BBL-armed oncolytic adenovirus and nab-paclitaxel/gemcitabine chemotherapy in advanced pancreatic cancer: An interim report.

716 Background: Pancreatic ductal adenocarcinoma (PDAC) has been highly resistant to immunotherapeutics to date. LOAd703, an oncolytic adenovirus with transgenes encoding TMZ-CD40L and 4-1BBL, has been shown to lyse tumor cells selectively, induce anti-tumor cytotoxic T-cell responses, reduce myeloid-derived suppressor cell (MDSC) infiltration, and induce tumor regression in preclinical studies. Methods: In this phase I/II trial, patients with unresectable or metastatic PDAC are treated with LOAd703 intratumoral injections and standard nab-paclitaxel/gemcitabine (nab-P/G) chemotherapy. Starting on cycle 1 day 15 of nab-P/G, LOAd703 is injected with image guidance into the primary pancreatic tumor or a metastasis every 2 weeks for 6 injections. In the event of sustained tumor control, subjects are eligible to receive 6 more injections. Three dose levels of LOAd703 are being investigated using a BOIN dose escalation design. Primary endpoints are safety and feasibility. Secondary endpoints include response rate and overall survival. Results: To date, 13 subjects are evaluable for safety and feasibility. Three patients were treated at dose 1 (5x10e10 VP), 4 subjects at dose 2 (1x10e11 VP), and 6 subjects at dose 3 (5x10e11 VP). The most common adverse events (AEs) attributed to LOAd703 have been fever, chills, nausea, and increased transaminases. AEs have been transient and grade 1-2, with the exception of a grade 3 transaminase elevation in 1 subject receiving dose 3 (the only dose-limiting toxicity observed thus far). During protocol treatment, circulating MDSCs decreased in 8/13 subjects while effector memory T-cells increased in 10/13. ELISPOT analyses showed a rise in tumor antigen-specific T-cells in 10/13 subjects. At the lowest dose level, best response was stable disease, and 6/10 patients who received higher LOAd703 doses have had partial responses. Only 1 patient has had progressive disease as best response. Conclusions: Adding LOAd703 to nab-P/G has been safe and feasible. Treatment-emergent immune responses have been demonstrated in most subjects, with a notable proportion having objective anti-tumor responses. Clinical trial information: NCT02705196.

HSV-TK Expressing Mesenchymal Stem Cells Exert Inhibitory Effect on Cervical Cancer Model.

A growing area of research is focused on cancer therapy, and new therapeutic approaches are welcomed. Mesenchymal stem cell (MSC)-based gene therapy is a promising strategy in oncology. Intrinsic tropism and migration to tumor microenvironment with off lights are attractive features of this type of cell carrier. In this way, suicide genes have also found a good platform for better performance and have shown a stronger anti-tumor mechanism by riding on mesenchymal cells. In this study, we investigated the anti-tumor activity of intratumoral injected MSCs transduced with a lentivector expressing the HSV/TK in a mouse cervical cancer model. Following the injection of MSCs transduced with lentivector carrying TK, MSCs alone or PBS into the mice tumor, ganciclovir was administered intraperitoneally during 14 days, and tumor size, survival time, natural killer (NK) cells and cytotoxic T lymphocyte (CTL) activities were assessed. We demonstrated that combination of suicide therapy and cell therapy leading m,to successful tumor inhibition. Significant reduction in tumor size was detected in test group in comparison with controls. Also, potent antitumor NK and CTL activity was seen in treatment group in comparison with controls. Our data demonstrated that the mesenchymal cells expressing TK had inhibitory effect on cervical cancer model.

Abstract TMIM-072: COMBINATIONAL TARGETING OF HDAC6 AND PD-1/PD-L1 IMMUNE CHECKPOINT IN ARID1A-MUTATED OVARIAN CANCERS

Abstract Ovarian clear cell carcinoma (OCCC) typically has a low response rate to platinum-based standard of care, and has no effective therapy for advanced stage disease. About 50% OCCCs harbor a mutation in ARID1A, a subunit of a SWI/SNF chromatin remodeling complex. We have previously demonstrated the dependence of ARID1A-mutated OCCCs on HDAC6 activity. In addition, ARID1A inactivation impairs mismatch repair, thus sensitizing ARID1A-mutated tumors to checkpoint blockade. However, anti-PD-L1 treatment only marginally improved the survival of ARID1A-deficient mice. We sought to determine whether combinational approach will improve efficacy of checkpoint blockade therapy in ARID1A-mutated OCCC. We combined HDAC6 inhibitor ACY1215 and PD-1/PD-L1 immune checkpoint blockade utilizing Arid1a-/-/Pik3caH1047R genetic ovarian clear cell model. Combination further prolonged mice survival as compared to single treatments and observed effects correlated with an increase in the activity of anti-tumor cytotoxic T-cells. In addition, we observed increase in dendritic cell infiltration following HDAC6 inhibition, suggesting of an increase in antigen presentation. Our findings indicate that combination of HDAC6 inhibition with PD-L1 checkpoint blockade could be a potential strategy for ARID1A-mutated OCCCs, not only eliminating ARID1A-mutated tumor cells but also restoring anti-tumor immunity. Citation Format: Nail Fatkhutdinov, Takeshi Fukumoto, and Rugang Zhang. COMBINATIONAL TARGETING OF HDAC6 AND PD-1/PD-L1 IMMUNE CHECKPOINT IN ARID1A-MUTATED OVARIAN CANCERS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-072.

Machine-Learning Prediction of Tumor Antigen Immunogenicity in the Selection of Therapeutic Epitopes.

Current tumor neoantigen calling algorithms primarily rely on epitope/major histocompatibility complex (MHC) binding affinity predictions to rank and select for potential epitope targets. These algorithms do not predict for epitope immunogenicity using approaches modeled from tumor-specific antigen data. Here, we describe peptide-intrinsic biochemical features associated with neoantigen and minor histocompatibility mismatch antigen immunogenicity and present a gradient boosting algorithm for predicting tumor antigen immunogenicity. This algorithm was validated in two murine tumor models and demonstrated the capacity to select for therapeutically active antigens. Immune correlates of neoantigen immunogenicity were studied in a pan-cancer data set from The Cancer Genome Atlas and demonstrated an association between expression of immunogenic neoantigens and immunity in colon and lung adenocarcinomas. Lastly, we present evidence for expression of an out-of-frame neoantigen that was capable of driving antitumor cytotoxic T-cell responses. With the growing clinical importance of tumor vaccine therapies, our approach may allow for better selection of therapeutically relevant tumor-specific antigens, including nonclassic out-of-frame antigens capable of driving antitumor immunity.

Abstract CT167: A Phase Ib study to assess safety, tolerability, pharmacokinetics, and preliminary antitumor activity of sitravatinib in combination with tislelizumab in patients with advanced solid tumors

Abstract Background: Sitravatinib is an investigative, orally bioavailable, spectrum-selective receptor tyrosine kinase (RTK) inhibitor with potential antitumor activity that has been shown to potently inhibit split kinase receptors (eg, VEGFR2, KIT) and TAM receptors (eg, AXL, MER). Inhibition of RTKs by sitravatinib may also modulate effects on the tumor microenvironment to overcome resistance to checkpoint inhibitors, including enhanced M1/suppressed M2 macrophage cytokine response, abrogated negative regulation of antitumor NK cell activity, and depleted regulatory T- and myeloid-derived suppressor cells with enhanced antitumor cytotoxic T-cell activity. Tislelizumab is an investigational, humanized IgG4 monoclonal antibody that has been shown to have high affinity and binding specificity for programmed cell death receptor-1 (PD-1). Combining an agent that has both immune modulatory and antitumor properties with an immunotherapeutic PD-1 checkpoint inhibitor could enhance the antitumor efficacy observed with either agent alone. The primary objective of this trial is to examine the safety and tolerability of sitravatinib combined with tislelizumab in patients with advanced solid tumors. Methods: Adult patients with histologically or cytologically confirmed, locally advanced or metastatic, non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), or ovarian cancer (OC) are enrolling in the open-label, multicenter, nonrandomized, phase 1b clinical trial. Entry criteria include Eastern Cooperative Oncology Group Performance Status ≤ 1 and adequate end-organ function. All patients will receive sitravatinib 120 mg PO QD in combination with tislelizumab 200 mg IV Q3W until progressive disease, unacceptable toxicity, death, withdrawal of consent, or study termination by the sponsor. Approximately 100 patients are expected to be enrolled in 5 cohorts (n=20 patients per cohort): Cohort A: anti-PD-(L)1 antibody-refractory/-resistant, metastatic, nonsquamous NSCLC; Cohort B: anti-PD-1(L)1 antibody-naive, metastatic, nonsquamous NSCLC; Cohort C: anti-PD-(L)1 antibody-refractory/-resistant, metastatic, clear cell RCC; Cohort D (China only): metastatic or advanced RCC without prior therapy; Cohort E: anti-PD-(L)1 antibody-naive, recurrent, platinum-resistant, epithelial OC. The primary endpoint is to assess safety and tolerability of the combination by monitoring adverse events (AEs) and serious AEs. Secondary endpoints include overall response rate, duration of response, disease control rate, progression-free survival assessed by RECIST version 1.1, and plasma concentrations and derived pharmacokinetic parameters of single- and repeated-dose sitravatinib. Seven patients have enrolled as of 3 January 2019 at the sites in Australia and China. Clinical trial registry number: NCT03666143 Citation Format: Jeffrey Goh, Ben Gao, Ben Markman, Hui Gan, Mark Voskoboynik, Yi-Long Wu, Jun Guo, Qing Zhou, Jun Zhao, Cheng Chen, Jingjun Qiu, Yingying Xu, Liu Yang, Michael Millward. A Phase Ib study to assess safety, tolerability, pharmacokinetics, and preliminary antitumor activity of sitravatinib in combination with tislelizumab in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT167.

A lipid-soluble extract of Pinellia pedatisecta Schott enhances antitumor T cell responses by restoring tumor-associated dendritic cell activation and maturation

Ethnopharmacological relevancePinellia pedatisecta Schott (PPS)is a traditional Chinese medicine functioning as reducing swelling and drying dampness. Pinellia pedatisecta Schott extract (PE) has been confirmed to suppress cervical tumor growth and modulate the antitumor CD4+T helper immunity towards Th1. AimsTo explore the roles of PE in modulating tumor-associated dendritic cell (TADC) activation and function. MethodsFor in vivo studies, HPV+TC-1 mouse tumor models were conducted and treated with PE for 3 weeks (10 mg/kg/d or 20 mg/kg/day). The immune profiles of spleen, tumor-draining lymph nodes (TDLNs), tumor and serum were analyzed by flow cytometry and multiplexed bead-based immunoassay. For in vitro studies, TADCs were generated by tumor-conditioned medium and treated with PE solution. The maturation and function of TADCs were evaluated by flow cytometry, ELISA, mixed lymphocyte reaction (MLR) and cytotoxic T lymphocyte (CTL) assay. Furthermore, the effect of PE on SOCS1 pathway was examined by western blotting and real time PCR. ResultsPE upregulated the expression of major histocompatibility complex class II (MHCII) and costimulatory molecules CD80 and CD86 on TADCs and promoted IL-12 secretion from TADCs. In addition, PE-treated TADCs promoted the proliferation of CD4+ and CD8+ T cells and induced the differentiation of IFN-γ+CD4+ and GZMB+CD8+ T cells. PE-treated TADCs also elicited a more powerful antigen-specific cytotoxic T lymphocyte (CTL) response. Furthermore, PE treatment in vivo enhanced the proliferation, activated the functional ability (increased Ki67, CD137, GZMB or IFN-γ, TNF-α expression) and reversed the exhaustion (impaired CD95 or PD-1 expression) of antitumor T cells. Mechanistically, PE inhibited SOCS1-restrained JAK2 activation in TADCs. ConclusionsPE efficiently restored the immature status of TADCs and enhanced their function as antigen-presenting cells to further elicit antitumor Th1 and CTL responses, suggesting that PE may be a potential immunomodulatory drug for cancer treatment.

A phase Ib clinical trial on intratumoral administration of autologous CD1c (BDCA-1)+ myeloid dendritic cells (myDC) in combination with ipilimumab (IPI) and avelumab (AVE) plus intravenous low-dose nivolumab (NIVO) in patients with advanced solid tumors.

e14012 Background: Intratumoral (IT) myDC play a pivotal role in initiating antitumor immune responses and "re-licensing” of antitumor cytotoxic T-lymphocytes within the tumor microenvironment. IT injection of anti-PD-L1 IgG1 mAb AVE and anti-CTLA-4 IgG1 mAb IPI may reduce the number of regulatory T cells and lyse PD-L1+ tumor cells, thereby releasing tumor antigens that can be captured and processed by IT co-administered CD1c (BDCA-1)+ myDC, reinvigorating the cancer immunity cycle. Methods: Patients (pts) with advanced solid tumors who failed standard therapy were eligible for IT injections of ≥1 non-visceral metastasis with IPI (max total dose of 10 mg) and AVE (max total dose of 40 mg) plus IV NIVO (10 mg) on day 1 followed by IT injection of autologous, non-substantially manipulated CD1c (BDCA-1)+ myDC on day 2. Administration of AVE, IPI, and NIVO was repeated every 14 days thereafter. Primary endpoints were safety and feasibility. Repetitive FNA cytology/IHC of treated lesions was performed. Results: In this ongoing trial, 6 pts (3x melanoma, 1x epithelial ovarian carcinoma, 2x triple negative breast carcinoma) were treated with IT injection of a median of 27,2x106 (range 10-43x106) CD1c (BDCA-1)+ myDC and a median of 5 (range 2-10) study drug administrations. At time of this analysis 3 pts are evaluable for response: an ongoing PR ( &gt; 8 months) was documented in a melanoma pt who previously progressed on PD-1 and CTLA-4 inhibitors. In 2 other melanoma pts regression of the injected metastases coincided with progression of non-injected metastases. Adverse events consisted of transient grade(G)2 local pain at injection site in 2 pts, G1 pruritus in 2 pts, G2 pneumonitis in 1 pt, G1 rash in 1 pt, and pruritus and redness of the skin overlaying the injected lesion in 1 pt. Analysis of cytology/IHC results is ongoing. Conclusions: IT injection of autologous CD1c (BDCA-1)+ myDC with IT co-injection of AVE and IPI plus IV low-dose NIVO is feasible and tolerable and resulted in encouraging early signs of anti-tumor activity in injected as well as non-injected lesions. Clinical trial information: NCT03707808.

Monocytes outperform ex vivo generated dendritic cells as cellular vaccines to trigger cytotoxic T lymphocyte responses against cancer in pre-clinical models

Abstract Conventional dendritic cell (DC) vaccines using ex vivo generated DC have been widely tested in clinical trials in the treatment of human cancers. These DC vaccines have often displayed limited efficacy despite a complex manufacturing process. Although the efficacy of DC vaccines is generally thought to depend on their antigen-presenting cell function, several lines of evidence suggest that, instead of directly presenting antigen (Ag) to naïve T cells, administered DC trigger cytotoxic T lymphocyte (CTL) responses in vivo mainly by transferring Ag to lymphoid-resident conventional DC (cDC). We tested here whether monocytes, known to transfer Ag to cDC in vivo, can be directly loaded with tumor Ag to trigger robust anti-tumor CTL responses. We found that IV administered monocytes loaded with protein or peptide Ag triggered stronger Ag-specific CTL responses than conventional adjuvant-based and DC vaccines. In several murine cancer models, including intra-cranial glioblastoma, we showed that monocyte vaccination suppressed tumor growth better than conventional adjuvant-based, GVAX and DC vaccines. Such anti-tumor activities could be further enhanced with immune checkpoint inhibition. Ag-loaded monocytes did not directly activate naïve CD8+T cells. Instead, they formed stable physical contacts with and transferred Ag to splenic CD8+cDC. This Ag transfer required the formation of connexin 43-containing gap junctions between monocytes and CD8+cDC. Our findings demonstrated that gap junctions are an efficient Ag transfer pathway in vivo between monocytes and splenic CD8+cDC and suggested that IV administered Ag-loaded monocytes may serve as a simple and efficacious cellular vaccine platform for the treatment of human cancers.