Longitudinal assessment of tumor-infiltrating lymphocytes in primary breast cancer following neoadjuvant radiotherapy

BACKGROUND

Tumor-infiltrating lymphocytes (TILs) have prognostic significance in several cancers, including breast. Despite interest in combining radiotherapy with immunotherapy, little is known about the effect of radiotherapy itself on the tumor-immune microenvironment, including TILs. Here, we interrogated longitudinal dynamics of tumor-infiltrating and systemic lymphocytes in patient samples taken before, during, and after neoadjuvant radiotherapy (NART), from XXX and XXX breast clinical trials.

METHODS

We manually scored stromal TILs (sTILs) from longitudinal tumor samples using standardized guidelines, as well as deep learning-based scores at cell-level (cTIL) and cell- and tissue-level combination analysis (SuperTIL). In parallel, we interrogated absolute lymphocyte counts from routine blood tests at corresponding timepoints during treatment. Exploratory analyses studied the relationship between TILs and pathological complete response (pCR) and long-term outcomes.

RESULTS

Patients receiving NART experienced a significant and uniform decrease in sTILs that did not recover at the time of surgery (P < 0.0001). This lymphodepletive effect was also mirrored in peripheral blood. Our "SuperTIL" deep learning score showed good concordance with manual sTILs, and importantly performed comparably to manual scores in predicting pCR from diagnostic biopsies. Analysis suggested an association between baseline sTILs and pCR, as well as sTILs at surgery and relapse, in patients receiving NART.

CONCLUSIONS

This study provides novel insights into TIL dynamics in the context of NART in breast cancer, and demonstrates the potential for artificial intelligence to assist routine pathology. We have identified trends which warrant further interrogation and have a bearing on future radio-immunotherapy trials.

DNA-PKcs is required for cGAS/STING-dependent viral DNA sensing in human cells

To mount an efficient interferon response to virus infection, intracellular pattern recognition receptors (PRRs) sense viral nucleic acids and activate anti-viral gene transcription. The mechanisms by which intracellular DNA and DNA viruses are sensed are relevant not only to anti-viral innate immunity, but also to autoinflammation and anti-tumour immunity through the initiation of sterile inflammation by self-DNA recognition. The PRRs that directly sense and respond to viral or damaged self-DNA function by signaling to activate interferon regulatory factor (IRF)-dependent type one interferon (IFN-I) transcription. We and others have previously defined DNA-dependent protein kinase (DNA-PK) as an essential component of the DNA-dependent anti-viral innate immune system. Here, we show that DNA-PK is essential for cyclic GMP-AMP synthase (cGAS)- and stimulator of interferon genes (STING)-dependent IFN-I responses in human cells during stimulation with exogenous DNA and infection with DNA viruses.

T-cell receptor determinants of response to chemoradiation in locally-advanced HPV16-driven malignancies

Background

The effect of chemoradiation on the anti-cancer immune response is being increasingly acknowledged; however, its clinical implications in treatment responses are yet to be fully understood. Human papillomavirus (HPV)-driven malignancies express viral oncogenic proteins which may serve as tumor-specific antigens and represent ideal candidates for monitoring the peripheral T-cell receptor (TCR) changes secondary to chemoradiotherapy (CRT).

Methods

We performed intra-tumoral and pre- and post-treatment peripheral TCR sequencing in a cohort of patients with locally-advanced HPV16-positive cancers treated with CRT. An in silico computational pipeline was used to cluster TCR repertoire based on epitope-specificity and to predict affinity between these clusters and HPV16-derived epitopes.

Results

Intra-tumoral repertoire diversity, intra-tumoral and post-treatment peripheral CDR3β similarity clustering were predictive of response. In responders, CRT triggered an increase peripheral TCR clonality and clonal relatedness. Post-treatment expansion of baseline peripheral dominant TCRs was associated with response. Responders showed more baseline clustered structures of TCRs maintained post-treatment and displayed significantly more maintained clustered structures. When applying clustering by TCR-specificity methods, responders displayed a higher proportion of intra-tumoral TCRs predicted to recognise HPV16 peptides.

Conclusions

Baseline TCR characteristics and changes in the peripheral T-cell clones triggered by CRT are associated with treatment outcome. Maintenance and boosting of pre-existing clonotypes are key elements of an effective anti-cancer immune response driven by CRT, supporting a paradigm in which the immune system plays a central role in the success of CRT in current standard-of-care protocols.

Breaking the barriers in cancer care: The next generation of herpes simplex virus-based oncolytic immunotherapies for cancer treatment

Since the US Food and Drug Administration first approved talimogene laherparepvec for the treatment of melanoma in 2015, the field of oncolytic immunotherapy (OI) has rapidly evolved. There are numerous ongoing clinical studies assessing the clinical activity of OIs across a wide range of tumor types. Further understanding of the mechanisms underlying the anti-tumor immune response has led to the development of OIs with improved immune-mediated preclinical efficacy. In this review, we discuss the key approaches for developing the next generation of herpes simplex virus-based OIs. Modifications to the viral genome and incorporation of transgenes to promote safety, tumor-selective replication, and immune stimulation are reviewed. We also review the advantages and disadvantages of intratumoral versus intravenous administration, summarize clinical evidence supporting the use of OIs as a strategy to overcome resistance to immune checkpoint blockade, and consider emerging opportunities to improve OI efficacy in the combination setting.

Updates on radiotherapy-immunotherapy combinations: Proceedings of 6th annual ImmunoRad conference

Focal radiation therapy (RT) has attracted considerable attention as a combinatorial partner for immunotherapy (IT), largely reflecting a well-defined, predictable safety profile and at least some potential for immunostimulation. However, only a few RT-IT combinations have been tested successfully in patients with cancer, highlighting the urgent need for an improved understanding of the interaction between RT and IT in both preclinical and clinical scenarios. Every year since 2016, ImmunoRad gathers experts working at the interface between RT and IT to provide a forum for education and discussion, with the ultimate goal of fostering progress in the field at both preclinical and clinical levels. Here, we summarize the key concepts and findings presented at the Sixth Annual ImmunoRad conference.

Efficacy of Coxsackievirus A21 against drug-resistant neoplastic B cells

Primary drug resistance and minimal residual disease are major challenges in the treatment of B cell neoplasms. Therefore, this study aimed to identify a novel treatment capable of eradicating malignant B cells and drug-resistant disease. Oncolytic viruses eradicate malignant cells by direct oncolysis and activation of anti-tumor immunity, have proven anti-cancer efficacy, and are safe and well tolerated in clinical use. Here, we demonstrate that the oncolytic virus coxsackievirus A21 can kill a range of B cell neoplasms, irrespective of an anti-viral interferon response. Moreover, CVA21 retained its capacity to kill drug-resistant B cell neoplasms, where drug resistance was induced by co-culture with tumor microenvironment support. In some cases, CVA21 efficacy was actually enhanced, in accordance with increased expression of the viral entry receptor ICAM-1. Importantly, the data confirmed preferential killing of malignant B cells and CVA21 dependence on oncogenic B cell signaling pathways. Significantly, CVA21 also activated natural killer (NK) cells to kill neoplastic B cells and drug-resistant B cells remained susceptible to NK cell-mediated lysis. Overall, these data reveal a dual mode of action of CVA21 against drug-resistant B cells and support the development of CVA21 for the treatment of B cell neoplasms.

PEARLS - A multicentre phase II/III trial of extended field radiotherapy for androgen sensitive prostate cancer patients with PSMA-avid pelvic and/or para-aortic lymph nodes at presentation

PEARLS is a multi-stage randomised controlled trial for prostate cancer patients with pelvic and/or para-aortic PSMA-avid lymph node disease at presentation. The aim of the trial is to determine whether extending the radiotherapy field to cover the para-aortic lymph nodes (up to L1/L2 vertebral interspace) can improve outcomes for this patient group.

Dynamic Changes in the NK-, Neutrophil-, and B-cell Immunophenotypes Relevant in High Metastatic Risk Post Neoadjuvant Chemotherapy-Resistant Early Breast Cancers

PURPOSE

To identify potential immune targets in post-neoadjuvant chemotherapy (NAC)-resistant triple-negative breast cancer (TNBC) and ER+HER2- breast cancer disease.

EXPERIMENTAL DESIGN

Following pathology review, 153 patients were identified as having residual cancer burden (RCB) II/III disease (TNBC n = 80; ER+HER2-n = 73). Baseline pre-NAC samples were available for evaluation for 32 of 80 TNBC and 36 of 73 ER+HER2- cases. Bright-field hematoxylin and eosin assessment allowed for tumor-infiltrating lymphocyte (TIL) evaluation in all cases. Multiplexed immunofluorescence was used to identify the abundance and distribution of immune cell subsets. Levels of checkpoints including PD-1/PD-L1 expression were also quantified. Findings were then validated using expression profiling of cancer and immune-related genes. Cytometry by time-of-flight characterized the dynamic changes in circulating immune cells with NAC.

RESULTS

RCB II/III TNBC and ER+HER2- breast cancer were immunologically "cold" at baseline and end of NAC. Although the distribution of immune cell subsets across subtypes was similar, the mRNA expression profiles were both subtype- and chemotherapy-specific. TNBC RCB II/III disease was enriched with genes related to neutrophil degranulation, and displayed strong interplay across immune and cancer pathways. We observed similarities in the dynamic changes in B-cell biology following NAC irrespective of subtype. However, NAC induced changes in the local and circulating tumor immune microenvironment (TIME) that varied by subtype and response. Specifically, in TNBC residual disease, we observed downregulation of stimulatory (CD40/OX40L) and inhibitory (PD-L1/PD-1) receptor expression and an increase in NK cell populations (especially non-cytolytic, exhausted CD56dimCD16-) within both the local TIME and peripheral white cell populations.

CONCLUSIONS

This study identifies several potential immunologic pathways in residual disease, which may be targeted to benefit high-risk patients.

P11.64.A Long-term follow up and translational data from the ReoGlio phase Ib trial of GM-CSF and intravenous pelareorep (Reovirus) alongside standard of care in GBM

BACKGROUND

We previously reported safety data from a phase Ib, open-label study of intravenous oncolytic virus pelareorep with GM-CSF alongside standard chemoradiotherapy in newly diagnosed glioblastoma confirming that the combination is well tolerated. We now report on long-term follow up and analysis of translational samples from tumour and blood in a subset of patients.

METHODS

15 patients with newly diagnosed GBM were treated with GM-CSF 50μg subcutaneously on days 1-3 and intravenous pelareorep on days 4-5 in weeks 1 and 4 of chemoradiotherapy, and subsequently in week 1 of each adjuvant temozolomide course: 7 patients received 1x1010TCID50 (dose level 1); 8 received 3x1010TCID50 (dose level 2). The primary objective was to determine the maximum tolerated dose of pelareorep and GM-CSF with standard chemoradiotherapy. Following a protocol amendment we also collected survival data in all patients up to August 2021. Serial blood samples were taken from three patients, at baseline, during chemoradiotherapy and in the first adjuvant cycle. Peripheral blood mononuclear cells were analysed for immune checkpoint expression by flow cytometry, RNAseq gene expression and T-cell receptor clonality, whilst plasma cytokines were quantified by Luminex.

RESULTS

This combination was well tolerated with 87% of patients completing treatment as planned. Survival data analysis showed that median OS was 12.6 months in dose level 1 and 16.1 months in dose level 2, median OS for all patients was 13.1 months. The 24-month survival estimate for all patients was 25.0%, 16.7% for dose level 1 and 33.3% for dose level 2. One patient in dose level 1 remains alive at 43 months post registration without further treatment. Laboratory data showed that pelareorep infusion resulted in inflammatory cytokine and chemokine secretion, immune checkpoint modulation, and upregulation of inflammatory pathways. There was also increased peripheral clonal tumour-specific T-cell proliferation following pelareorep infusion.

CONCLUSION

Although based on small numbers, these long-term follow up data suggest this may be an active combination in a subset of GBM patients. Translational data confirm that pelareorep potentially activates tumour-targeting immune pathways in GBM, with consequential immune checkpoint modulation. These data support a combination clinical trial of pelareorep, radiotherapy and immune checkpoint blockade in GBM.

Comprehensive characterization of immune landscape of Indian and Western triple negative breast cancers

PURPOSE

Triple-negative breast cancer (TNBC) is a heterogeneous disease with a significant challenge to effectively manage in the clinic worldwide. Immunotherapy may be beneficial to TNBC patients if responders can be effectively identified. Here we sought to elucidate the immune landscape of TNBCs by stratifying patients into immune-specific subtypes (immunotypes) to decipher the molecular and cellular presentations and signaling events of this heterogeneous disease and associating them with their clinical outcomes and potential treatment options.

EXPERIMENTAL DESIGN

We profiled 730 immune genes in 88 retrospective Indian TNBC samples using the NanoString platform, established immunotypes using non-negative matrix factorization-based machine learning approach, and validated them using Western TNBCs (n=422; public datasets). Immunotype-specific gene signatures were associated with clinicopathological features, immune cell types, biological pathways, acute/chronic inflammatory responses, and immunogenic cell death processes. Responses to different immunotherapies associated with TNBC immunotypes were assessed using cross-cancer comparison to melanoma (n=504). Tumor-infiltrating lymphocytes (TILs) and pan-macrophage spatial marker expression were evaluated.

RESULTS

We identified three robust transcriptome-based immunotypes in both Indian and Western TNBCs in similar proportions. Immunotype-1 tumors, mainly representing well-known claudin-low and immunomodulatory subgroups, harbored dense TIL infiltrates and T-helper-1 (Th1) response profiles associated with smaller tumors, pre-menopausal status, and a better prognosis. They displayed a cascade of events, including acute inflammation, damage-associated molecular patterns, T-cell receptor-related and chemokine-specific signaling, antigen presentation, and viral-mimicry pathways. On the other hand, immunotype-2 was enriched for Th2/Th17 responses, CD4⁺ regulatory cells, basal-like/mesenchymal immunotypes, and an intermediate prognosis. In contrast to the two T-cell enriched immunotypes, immunotype-3 patients expressed innate immune genes/proteins, including those representing myeloid infiltrations (validated by spatial immunohistochemistry), and had poor survival. Remarkably, a cross-cancer comparison analysis revealed the association of immunotype-1 with responses to anti-PD-L1 and MAGEA3 immunotherapies.

CONCLUSION

Overall, the TNBC immunotypes identified in TNBCs reveal different prognoses, immune infiltrations, signaling, acute/chronic inflammation leading to immunogenic cell death of cancer cells, and potentially distinct responses to immunotherapies. The overlap in immune characteristics in Indian and Western TNBCs suggests similar efficiency of immunotherapy in both populations if strategies to select patients according to immunotypes can be further optimized and implemented.

Abstract CT569: Combination of reovirus (pelareorep) and granulocyte-macrophage colony-stimulating factor (GM-CSF) alongside standard chemoradiotherapy and adjuvant chemotherapy (temozolomide) for patients with glioblastoma multiforme (GBM): Long term follow up results of the ReoGlio phase Ib trial

Background: Oncolytic viruses are of increasing interest as an immunologic approach to treating glioma. We previously reported safety data from a phase Ib, open-label study of intravenous pelareorep with GM-CSF alongside standard chemoradiotherapy in newly diagnosed glioblastoma and confirmed that the combination is tolerable. Following agreement from the relevant ethics authorities we have now completed long term follow up data on all patients treated in the study to investigate whether there is a signal of impact on survival. METHODS: 15 patients with newly diagnosed GBM were treated with GM-CSF 50μg subcutaneously on days 1-3 and pelareorep on days 4-5 in weeks 1 and 4 of chemoradiotherapy, and subsequently in week 1 of each adjuvant temozolomide course: 7 patients received 1x1010TCID50 (dose level 1); 8 received 3x1010TCID50 (dose level 2). The primary objective was to determine the maximum tolerated dose of pelareorep and GM-CSF with standard chemoradiotherapy. Following end of study patients were followed up as per institutional practice. Ethical approval was granted to collect survival data in all patients who survived beyond study closure up to June 2021.

Results: We showed that using intravenous pelareorep with GM-CSF alongside standard chemoradiotherapy in patients with GBM was tolerable with 87% of patients completing treatment as planned. Survival data analysis showed that median OS was 12.6 months for patients in dose level 1 and 16.1 months in dose level 2, giving median OS for all patients 13.1 months. It was notable however that a small number of patients survived beyond 24 months. The 24-month survival estimate for all patients was 33%, 16.7% for dose level 1 and 50% for dose level 2. One patient in dose level 2 remains alive at 42 months.

Conclusion: We previously reported that intravenous delivery of pelareorep with standard chemoradiotherapy is tolerable in newly diagnosed GBM. Although based on small numbers, these long-term follow up data suggest that this may be an active combination in a subset of GBM patients and further randomized studies are warranted.

Citation Format: Susan C. Short, Jessica Kendall, Anthony Chalmers, Catherine McBain, Alan Melcher, Adel Samson, Rachel Phillip, Sarah Brown. Combination of reovirus (pelareorep) and granulocyte-macrophage colony-stimulating factor (GM-CSF) alongside standard chemoradiotherapy and adjuvant chemotherapy (temozolomide) for patients with glioblastoma multiforme (GBM): Long term follow up results of the ReoGlio phase Ib trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT569.

IMMU-12. Exploring and modulating the tumour immune microenvironment to facilitate the selection of immunotherapies for paediatric-type diffuse high-grade glioma

Immune cells have the potential to selectively eradicate high-risk brain tumours such as paediatric-type diffuse high-grade glioma (PDHGG). We aim to characterize the tumour immune microenvironment (TIME) of intra-cranial syngeneic mouse models of diffuse hemispheric glioma, H3G34 (DHG-H3G34) and diffuse midline glioma, H3K27 (DMG-H3K27). We also demonstrate how an oncolytic reovirus (Reolysin) can “heat-up” the TIME of our syngeneic models. Orthotopic immunocompetent mouse models of DHG-H3G34 (C57BL/6, NRASG12V + shp53 + shATRX +/- H3.3G34R) and DMG-H3K27 (Nestin-Tv-a/p53fl/fl, RCAS-ACVR1R206H + RCAS-H3.1K27M) were profiled using single-cell RNA-sequencing (scRNA-seq) (10x genomics), a 22-colour custom flow cytometry immune panel and spatial transcriptomics. Differential marker expression was validated with immunohistochemistry and immunofluorescence in tissue sections. Syngeneic mouse tumours treated systemically with Reolysin were also profiled to evaluate the effects of the oncolytic virus on the TIME. Cell type predictions in scRNA-seq using singleR, ssGSEA and expression of individual marker genes suggested that the predominant immune cell types within hemispheric tumours were monocytes (11-21%) and macrophages (10-19%) with much smaller proportions of CD4+ and CD8+ T-cells (4-10%). By contrast, much smaller proportions of monocytes (2%) and macrophages (3%) were observed in the H3.1K27M pontine model. Flow cytometry, immunohistochemistry and immunofluorescence validated scRNA-seq immune profiles and characterised signalling of the PD-1/PD-L1 checkpoint pathway. Spatial transcriptomics allowed immune cell populations to be positioned within tumour sections and showed significant co-localization of CD4+ and CD8+ lymphocytes at tumour margins. Treatment of syngeneic mouse tumours with Reolysin resulted in reduced tumour volumes and altered the TIME, in particular increasing cytotoxic T-cell tumour infiltration. Our results highlight immunological heterogeneity within molecular subgroups of PDHGG and demonstrate ability of a systemically delivered oncolytic virus, Reolysin, to “heat-up” the TIME, contributing to a more immune actionable profile. Future work will help to identify optimal combinations for the next generation of immunotherapies in PDHGG.

Oncolytic virus-mediated expansion of dual-specific CAR T cells improves efficacy against solid tumors in mice

Oncolytic viruses (OVs) encoding a variety of transgenes have been evaluated as therapeutic tools to increase the efficacy of chimeric antigen receptor (CAR)-modified T cells in the solid tumor microenvironment (TME). Here, using systemically delivered OVs and CAR T cells in immunocompetent mouse models, we have defined a mechanism by which OVs can potentiate CAR T cell efficacy against solid tumor models of melanoma and glioma. We show that stimulation of the native T cell receptor (TCR) with viral or virally encoded epitopes gives rise to enhanced proliferation, CAR-directed antitumor function, and distinct memory phenotypes. In vivo expansion of dual-specific (DS) CAR T cells was leveraged by in vitro preloading with oncolytic vesicular stomatitis virus (VSV) or reovirus, allowing for a further in vivo expansion and reactivation of T cells by homologous boosting. This treatment led to prolonged survival of mice with subcutaneous melanoma and intracranial glioma tumors. Human CD19 CAR T cells could also be expanded in vitro with TCR reactivity against viral or virally encoded antigens and was associated with greater CAR-directed cytokine production. Our data highlight the utility of combining OV and CAR T cell therapy and show that stimulation of the native TCR can be exploited to enhance CAR T cell activity and efficacy in mice.

Virally programmed extracellular vesicles sensitize cancer cells to oncolytic virus and small molecule therapy

Recent advances in cancer therapeutics clearly demonstrate the need for innovative multiplex therapies that attack the tumour on multiple fronts. Oncolytic or “cancer-killing” viruses (OVs) represent up-and-coming multi-mechanistic immunotherapeutic drugs for the treatment of cancer. In this study, we perform an in-vitro screen based on virus-encoded artificial microRNAs (amiRNAs) and find that a unique amiRNA, herein termed amiR-4, confers a replicative advantage to the VSVΔ51 OV platform. Target validation of amiR-4 reveals ARID1A, a protein involved in chromatin remodelling, as an important player in resistance to OV replication. Virus-directed targeting of ARID1A coupled with small-molecule inhibition of the methyltransferase EZH2 leads to the synthetic lethal killing of both infected and uninfected tumour cells. The bystander killing of uninfected cells is mediated by intercellular transfer of extracellular vesicles carrying amiR-4 cargo. Altogether, our findings establish that OVs can serve as replicating vehicles for amiRNA therapeutics with the potential for combination with small molecule and immune checkpoint inhibitor therapy.

RNA-based viruses can be engineered to express artificial microRNAs (amiRNAs). Here, the authors identify a candidate amiRNA that confers a replicative advantage to oncolytic viruses, enhancing their anticancer potency, and show that intercellular transfer of extracellular vesicles carrying the amiRNA promotes bystander killing of uninfected cancer cells.

CD4 T cell dynamics shape the immune response to combination oncolytic herpes virus and BRAF inhibitor therapy for melanoma

BACKGROUND

Combination herpes simplex virus (HSV) oncolytic virotherapy and BRAF inhibitors (BRAFi) represent promising immunogenic treatments for BRAF mutant melanoma, but an improved understanding of the immunobiology of combinations is needed to improve on the benefit of immune checkpoint inhibitors (ICI).

METHODS

Using a BRAFV600E-driven murine melanoma model, we tested the immunogenicity of HSV/BRAFi in immunocompetent C57BL mice. In addition to standard FACS analysis, we used the 'Timer of Cell Kinetics and Activity' system, which can analyze the temporal dynamics of different T cell subsets. This immune data was used to inform the selection of ICI for triple combination therapy, the effects of which were then further characterized using transcriptomics.

RESULTS

Adding BRAFi treatment to HSV improved anti-tumor effects in vivo but not in vitro. Immune characterization showed HSV or dual therapy led to fewer intratumoral Treg, although with a more activated phenotype, together with more effector CD8 +T cells. Tocky analysis further showed that HSV/BRAFi dual treatment reduced the Tocky signal (reflecting engagement with cognate antigen), in both Treg and conventional subsets of CD4+, but not in CD8 +cells. However, a higher percentage of Treg than of conventional CD4 +maintained frequent engagement with antigens on treatment, reflecting a predominance of suppressive over effector function within the CD4 +compartment. The only T cell subset which correlated with a reduction in tumor growth was within Tocky signal positive conventional CD4+, supporting their therapeutic role. Targeting CD25 high, antigen-engaged Treg with a depleting anti-CD25 ICI, achieved complete cures in 100% of mice with triple therapy. Transcriptomic analysis confirmed reduction in Foxp3 on addition of anti-CD25 to HSV/BRAFi, as well as increases in expression of genes reflecting interferon signaling and cytotoxic activity.

CONCLUSIONS

Combination HSV/BRAFi is an immunogenic therapy for BRAF mutant melanoma, but cannot fully control tumors. Dual therapy results in changes in T cell dynamics within tumors, with relatively maintained antigen signaling in Treg compared with conv CD4+. Antigen-engaged CD4 +effectors correlate with tumor growth control, and depletion of Treg by addition of an anti-CD25 ICI, releasing suppression of conventional CD4 +effectors by Treg, enhances survival and activates immune signaling within tumors.

PEARLS: A multicenter phase II/III trial of extended field radiotherapy for androgen-sensitive prostate cancer patients with PSMA‐avid pelvic and para-aortic lymph nodes at presentation

TPS199

Background: Optimal management for lymph node (LN) positive prostate cancer has not yet been determined. With the emerging role of PSMA-PET/CT in diagnostic staging, identification of this disease status is increasing. The superior border for prostate nodal radiotherapy is variable across different centres. PEARLS (CRUK/19/016) aims to show that extending the radiotherapy field to cover the para-aortic LN (up to L1/L2 vertebral interspace) can improve outcomes for prostate cancer patients with PSMA-avid pelvic LN at presentation. The trial is registered: ISRCTN36344989. Methods: PEARLS is a multi‐stage randomised controlled trial. Men with histologically confirmed prostate cancer with PSMA‐avid nodal disease within the pelvis +/‐ para‐aortic region receiving androgen deprivation therapy +/‐ androgen receptor targeted therapy or docetaxel chemotherapy are eligible. Two cohorts defined by extent of LN disease determined by PSMA‐PET/CT will be recruited: cohort A (pelvic LN at or below the L4/L5 vertebral interspace) and cohort B (para-aortic LN below L1/L2 vertebral interspace). Patients are randomly allocated (1:1) to standard field (dependent on cohort) intensity modulated radiotherapy (IMRT) (control) or extended-field IMRT (experimental) in 20 fractions over 4 weeks. In the control group, cohort A will receive 60Gy to the prostate and 44Gy to the pelvis with an integrated boost of 51Gy to PSMA-avid LN and cohort B will receive 60Gy to the prostate only. In the experimental group, participants in both cohorts will receive 60Gy to the prostate and 44Gy to the pelvis and para‐aortic region with an integrated boost of 51Gy to involved LN. In phase II, the primary endpoint is lower gastrointestinal RTOG grade 2+ toxicity at week 18 from start of radiotherapy. Assuming acceptable toxicity in the first 75 participants receiving extended-field IMRT, the study will move to phase III where the primary endpoint is metastasis‐free survival. The trial aims to recruit 714 patients with pelvic LN to detect a hazard ratio of 0.62 in favour of extended-field IMRT and a further 179 patients with para‐aortic LN disease. The trial was launched in the UK on 25 June 2021. Phase II will be conducted in 20 NHS Trusts across the UK. Clinical trial information: ISRCTN36344989.

Phase I trial of sargramostim/pelareorep therapy in pediatric patients with recurrent or refractory high-grade brain tumors

Background

Brain tumors are the leading cause of cancer death for pediatric patients. Pelareorep, an immunomodulatory oncolytic reovirus, has intravenous efficacy in preclinical glioma models when preconditioned with GM-CSF (sargramostim). We report a phase I trial with the primary goal of evaluating the safety of sargramostim/pelareorep in pediatric patients with recurrent or refractory high-grade brain tumors and a secondary goal of characterizing immunologic responses.

Methods

The trial was open to pediatric patients with recurrent or refractory high-grade brain tumors (3 + 3 cohort design). Each cycle included 3 days of subcutaneous sargramostim followed by 2 days of intravenous pelareorep. Laboratory studies and imaging were acquired upon recruitment and periodically thereafter.

Results

Six patients participated, including three glioblastoma, two diffuse intrinsic pontine glioma, and one medulloblastoma. Two pelareorep dose levels of 3 × 10⁸ and 5 × 10⁸ tissue culture infectious dose 50 (TCID₅₀) were assessed. One patient experienced a dose limiting toxicity of persistent hyponatremia. Common low-grade (1 or 2) adverse events included transient fatigue, hypocalcemia, fever, flu-like symptoms, thrombocytopenia, and leukopenia. High-grade (3 or 4) adverse events included neutropenia, lymphopenia, leukopenia, hypophosphatemia, depressed level of consciousness, and confusion. All patients progressed on therapy after a median of 32.5 days and died a median of 108 days after recruitment. Imaging at progression did not show evidence of pseudoprogression or inflammation. Correlative assays revealed transient but consistent changes in immune cells across patients.

Conclusions

Sargramostim/pelareorep was administered to pediatric patients with recurrent or refractory high-grade brain tumors. Hyponatremia was the only dose limiting toxicity (DLT), though maximum tolerated dose (MTD) was not determined.

Oncolytic virotherapy as immunotherapy

[Figure: see text].

Kickstarting Immunity in Cold Tumours: Localised Tumour Therapy Combinations With Immune Checkpoint Blockade

Cancer patients with low or absent pre-existing anti-tumour immunity ("cold" tumours) respond poorly to treatment with immune checkpoint inhibitors (ICPI). In order to render these patients susceptible to ICPI, initiation of de novo tumour-targeted immune responses is required. This involves triggering of inflammatory signalling, innate immune activation including recruitment and stimulation of dendritic cells (DCs), and ultimately priming of tumour-specific T cells. The ability of tumour localised therapies to trigger these pathways and act as in situ tumour vaccines is being increasingly explored, with the aspiration of developing combination strategies with ICPI that could generate long-lasting responses. In this effort, it is crucial to consider how therapy-induced changes in the tumour microenvironment (TME) act both as immune stimulants but also, in some cases, exacerbate immune resistance mechanisms. Increasingly refined immune monitoring in pre-clinical studies and analysis of on-treatment biopsies from clinical trials have provided insight into therapy-induced biomarkers of response, as well as actionable targets for optimal synergy between localised therapies and ICB. Here, we review studies on the immunomodulatory effects of novel and experimental localised therapies, as well as the re-evaluation of established therapies, such as radiotherapy, as immune adjuvants with a focus on ICPI combinations.

Immune landscape, evolution, hypoxia-mediated viral mimicry pathways and therapeutic potential in molecular subtypes of pancreatic neuroendocrine tumours

OBJECTIVE

A comprehensive analysis of the immune landscape of pancreatic neuroendocrine tumours (PanNETs) was performed according to clinicopathological parameters and previously defined molecular subtypes to identify potential therapeutic vulnerabilities in this disease.

DESIGN

Differential expression analysis of 600 immune-related genes was performed on 207 PanNET samples, comprising a training cohort (n=72) and two validation cohorts (n=135) from multiple transcriptome profiling platforms. Different immune-related and subtype-related phenotypes, cell types and pathways were investigated using different in silico methods and were further validated using spatial multiplex immunofluorescence.

RESULTS

The study identified an immune signature of 132 genes segregating PanNETs (n=207) according to four previously defined molecular subtypes: metastasis-like primary (MLP)-1 and MLP-2, insulinoma-like and intermediate. The MLP-1 subtype (26%-31% samples across three cohorts) was strongly associated with elevated levels of immune-related genes, poor prognosis and a cascade of tumour evolutionary events: larger hypoxic and necroptotic tumours leading to increased damage-associated molecular patterns (viral mimicry), stimulator of interferon gene pathway, T cell-inflamed genes, immune checkpoint targets, and T cell-mediated and M1 macrophage-mediated immune escape mechanisms. Multiplex spatial profiling validated significantly increased macrophages in the MLP-1 subtype.

CONCLUSION

This study provides novel data on the immune microenvironment of PanNETs and identifies MLP-1 subtype as an immune-high phenotype featuring a broad and robust activation of immune-related genes. This study, with further refinement, paves the way for future precision immunotherapy studies in PanNETs to potentially select a subset of MLP-1 patients who may be more likely to respond.

Quantitative Assessment and Prognostic Associations of the Immune Landscape in Ovarian Clear Cell Carcinoma

Ovarian clear cell carcinoma (OCCC) is a rare subtype of epithelial ovarian cancer characterised by a high frequency of loss-of-function ARID1A mutations and a poor response to chemotherapy. Despite their generally low mutational burden, an intratumoural T cell response has been reported in a subset of OCCC, with ARID1A purported to be a biomarker for the response to the immune checkpoint blockade independent of micro-satellite instability (MSI). However, assessment of the different immune cell types and spatial distribution specifically within OCCC patients has not been described to date. Here, we characterised the immune landscape of OCCC by profiling a cohort of 33 microsatellite stable OCCCs at the genomic, gene expression and histological level using targeted sequencing, gene expression profiling using the NanoString targeted immune panel, and multiplex immunofluorescence to assess the spatial distribution and abundance of immune cell populations at the protein level. Analysis of these tumours and subsequent independent validation identified an immune-related gene expression signature associated with risk of recurrence of OCCC. Whilst histological quantification of tumour-infiltrating lymphocytes (TIL, Salgado scoring) showed no association with the risk of recurrence or ARID1A mutational status, the characterisation of TILs via multiplexed immunofluorescence identified spatial differences in immunosuppressive cell populations in OCCC. Tumour-associated macrophages (TAM) and regulatory T cells were excluded from the vicinity of tumour cells in low-risk patients, suggesting that high-risk patients have a more immunosuppressive microenvironment. We also found that TAMs and cytotoxic T cells were also excluded from the vicinity of tumour cells in ARID1A-mutated OCCCs compared to ARID1A wild-type tumours, suggesting that the exclusion of these immune effectors could determine the host response of ARID1A-mutant OCCCs to therapy. Overall, our study has provided new insights into the immune landscape and prognostic associations in OCCC and suggest that tailored immunotherapeutic approaches may be warranted for different subgroups of OCCC patients.

Antiviral antibody responses to systemic administration of an oncolytic RNA virus: the impact of standard concomitant anticancer chemotherapies

Background

Oncolytic reovirus therapy for cancer induces a typical antiviral response to this RNA virus, including neutralizing antibodies. Concomitant treatment with cytotoxic chemotherapies has been hypothesized to improve the therapeutic potential of the virus. Chemotherapy side effects can include immunosuppression, which may slow the rate of the antiviral antibody response, as well as potentially make the patient more vulnerable to viral infection.

Method

Reovirus neutralizing antibody data were aggregated from separate phase I clinical trials of reovirus administered as a single agent or in combination with gemcitabine, docetaxel, carboplatin and paclitaxel doublet or cyclophosphamide. In addition, the kinetics of individual antibody isotypes were profiled in sera collected in these trials.

Results

These data demonstrate preserved antiviral antibody responses, with only moderately reduced kinetics with some drugs, most notably gemcitabine. All patients ultimately produced an effective neutralizing antibody response.

Conclusion

Patients’ responses to infection by reovirus are largely unaffected by the concomitant drug treatments tested, providing confidence that RNA viral treatment or infection is compatible with standard of care treatments.

Abstract 1960: Mechanisms of therapeutic synergy between pattern recognition response agonists and cdk4 inhibitors

Cytoplasmic nucleic acid sensors for double-stranded (ds) RNA (RIG-I/MDA5) and DNA (cGAS-STING) are pattern recognition receptors (PRRs) key to intracellular anti-viral responses. Recent research has highlighted roles for PRR agonists, including oncolytic virotherapy agents, in anti-tumor immunotherapy. Reovirus type 3 Dearing (Rt3D) is an oncolytic dsRNA virus with limited single-agent activity in clinical studies, but potential for use in combination regimens. We sought synergistic drug-virotherapy combinations using an unbiased screening approach that highlighted the CDK4/6 inhibitor, palbociclib, as a leading hit. We found that, when combined with Rt3D, palbociclib augmented oncolytic virus-induced endoplasmic reticulum (ER) stress/unfolded protein response (UPR) signaling. Combined Rt3D-palbociclib treatment potently increased interferon signaling and endogenous retroviral transcripts. Knockdown (siRNA) studies indicated key UPR proteins and the RNA sensor, RIG-I, were essential to the phenotype observed. Mechanistically independent experiments, using canonical RIG-I agonists and the ER stress inducer (thapsigargin), confirmed cross-talk between RNA sensing and ER stress pathways that augment cancer cell death and interferon production. Combined Rt3D-palbociclib increased innate immune activation and effector function. Our findings demonstrate that UPR signaling and innate immune RNA sensor crosstalk can be exploited to enhance anti-cancer efficacy with pro-immunogenic consequences. This has implications for future clinical development of PRR agonists and oncolytic viruses, as well as broadening the therapeutic remit of CDK4/6 inhibitors to include their role as ER stress sensitizers.

Citation Format: Victoria Roulstone, Joan Kyula, Richard Elliot, Christopher J. Lord, Nik Matthews, Vicki Jennings, Harriet Whittock, David Mansfield, Jyoti Choudhary, James Wright, Lu Yu, Alan Melcher, Richard Vile, Matt Coffey, Martin McLaughlin, Kevin Harrington. Mechanisms of therapeutic synergy between pattern recognition response agonists and cdk4 inhibitors [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 1960.

Abstract 1932: Talazoparib interacts with oncolytic reovirus to enhance death-inducing signaling complex (DISC)-mediated apoptosis and immune response

Reovirus (RT3D) is a naturally occurring double-stranded RNA oncolytic virus that has shown preclinical efficacy in a wide range of tumor types. Early phase clinical studies have shown that this agent has modest monotherapy efficacy and can safely be combined with cytotoxic chemotherapy regimens. In the current studies, we used a high-throughput drug screen approach of different targeted therapeutic agents with the aim of looking for potential viral sensitizers that could enhance RT3D tumor killing. BMN-673 (talazoparib), a clinically approved poly(ADP)-ribose polymerase 1 (PARP-1) inhibitor was identified as a top hit and found to sensitize profoundly to RT3D both in vitro and in vivo in human xenograft tumors in a nude mouse model. We found that RT3D activated cellular PARP1 and was associated with PARylation of cellular proteins, including components of the DISC-associated cell death machinery. Combined treatment with RT3D and talazoparib enhanced extrinsic apoptosis (amplified by autocrine/paracrine TNF-α and TRAIL signaling), NF-κB pathway activity and pro-inflammatory cytokine production (CCL5/RANTES, CXCL8/IL8, CXCL1/GRO and CXCL10/IP10). Signaling was shown to be dependent on nucleic acid sensing mechanisms mediated by RIG-I and TLR3. We also found anti-tumour efficacy in an immunocompetent mouse model and this correlated with an increase in an immune response following combination treatment of RT3D and talazoparib. Our data provide a strong rationale for the combination of oncolytic RT3D with PARP1 inhibitors to exploit immunogenic response in cancer treatment.

Citation Format: Joan N. Kyula, Victoria Roulstone, Richard Elliott, Harriet Whittock, Galabina Bozhanova, Martin McLaughlin, Malin Pedersen, Dragomir Krastev, Stephen Pettitt, Arnaud Legrand, Tencho Tenev, James Wright, Lu Yu, Jyoti Choudhary, Pascal Meier, Christopher J. Lord, Alan Melcher, Grey Wilkinson, Matt Coffey, Kevin J. Harrington. Talazoparib interacts with oncolytic reovirus to enhance death-inducing signaling complex (DISC)-mediated apoptosis and immune response [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 1932.

Computational Image Analysis of T-Cell Infiltrates in Resectable Gastric Cancer: Association with Survival and Molecular Subtypes

Background

Gastric and gastro-esophageal junction cancers (GCs) frequently recur after resection, but markers to predict recurrence risk are missing. T-cell infiltrates have been validated as prognostic markers in other cancer types, but not in GC because of methodological limitations of past studies. We aimed to define and validate the prognostic role of major T-cell subtypes in GC by objective computational quantification.

Methods

Surgically resected chemotherapy-naïve GCs were split into discovery (n = 327) and validation (n = 147) cohorts. CD8 (cytotoxic), CD45RO (memory), and FOXP3 (regulatory) T-cell densities were measured through multicolor immunofluorescence and computational image analysis. Cancer-specific survival (CSS) was assessed. All statistical tests were two-sided.

Results

CD45RO-cell and FOXP3-cell densities statistically significantly predicted CSS in both cohorts. Stage, CD45RO-cell, and FOXP3-cell densities were independent predictors of CSS in multivariable analysis; mismatch repair (MMR) and Epstein–Barr virus (EBV) status were not statistically significant. Combining CD45RO-cell and FOXP3-cell densities into the Stomach Cancer Immune Score showed highly statistically significant (all P ≤ .002) CSS differences (0.9 years median CSS to not reached). T-cell infiltrates were highest in EBV-positive GCs and similar in MMR-deficient and MMR-proficient GCs.

Conclusion

The validation of CD45RO-cell and FOXP3-cell densities as prognostic markers in GC may guide personalized follow-up or (neo)adjuvant treatment strategies. Only those 20% of GCs with the highest T-cell infiltrates showed particularly good CSS, suggesting that a small subgroup of GCs is highly immunogenic. The potential for T-cell densities to predict immunotherapy responses should be assessed. The association of high FOXP3-cell densities with longer CSS warrants studies into the biology of regulatory T cells in GC.

APOBEC and Cancer Viroimmunotherapy: Thinking the Unthinkable

The apolipoprotein B mRNA editing enzyme catalytic polypeptide (APOBEC) family protects against infection by degrading incoming viral genomes through cytosine deamination. Here, we review how the potential to unleash these potent DNA mutagens comes at a price as APOBEC DNA mutagenesis can contribute to development of multiple types of cancer. In addition, because viral infection induces its expression, APOBEC is seen as the enemy of oncolytic virotherapy through mutation of the viral genome and by generating virotherapy-resistant tumors. Therefore, overall APOBEC in cancer has received very poor press. However, we also speculate how there may be silver linings to the storm clouds (kataegis) associated with APOBEC activity. Thus, although mutagenic genomic chaos promotes emergence of ever more aggressive subclones, it also provides significant opportunity for cytotoxic and immune therapies. In particular, the superpower of cancer immunotherapy derives in part from mutation, wherein generation of tumor neoantigens-neoantigenesis-exposes tumor cells to functional T-cell repertoires, and susceptibility to immune checkpoint blockade. Moreover, APOBECs may be able to induce suprathreshold levels of cellular mutation leading to mitotic catastrophe and direct tumor cell killing. Finally, we discuss the possibility that linking predictable APOBEC-induced mutation with escape from specific frontline therapies could identify mutated molecules/pathways that can be targeted with small molecules and/or immunotherapies in a Trap and Ambush strategy. Together, these considerations lead to the counterintuitive hypothesis that, instead of attempting to expunge and excoriate APOBEC activity in cancer therapy, it might be exploited-and even, counterintuitively, encouraged.

On-treatment immune prognostic score for patients with relapsed and/or metastatic head and neck squamous cell carcinoma treated with immunotherapy

BACKGROUND

Previous studies have suggested that inflammatory markers (neutrophil-to-lymphocyte ratio (NLR), lactate dehydrogenase (LDH) and fibrinogen) are prognostic biomarkers in patients with a variety of solid cancers, including those treated with immune checkpoint inhibitors (ICIs). We aimed to develop a model that predicts response and survival in patients with relapsed and/or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) treated with immunotherapy.

METHODS

Analysis of 100 consecutive patients with unresectable R/M HNSCC who were treated with ICI. Baseline and on-treatment (day 28) NLR, fibrinogen and LDH were calculated and correlated with response, progression-free survival (PFS) and overall survival (OS) using univariate and multivariate analyses. The optimal cut-off values were derived using maximally selected log-rank statistics.

RESULTS

Low baseline NLR and fibrinogen levels were associated with response. There was a statistically significant correlation between on-treatment NLR and fibrinogen and best overall response. On-treatment high NLR and raised fibrinogen were significantly associated with poorer outcome. In multivariate analysis, on-treatment NLR (≥4) and on-treatment fibrinogen (≥4 ng/mL) showed a significant negative correlation with OS and PFS. Using these cut-off points, we generated an on-treatment score for OS and PFS (0-2 points). The derived scoring system shows appropriate discrimination and suitability for OS (HR 2.4, 95% CI 1.7 to 3.4, p<0.0001, Harrell's C 0.67) and PFS (HR 1.8, 95% CI 1.4 to 2.3, p<0.0001, Harrell's C 0.68). In the absence of an external validation cohort, results of fivefold cross-validation of the score and evaluation of median OS and PFS on the Kaplan-Meier survival distribution between trained and test data exhibited appropriate accuracy and concordance of the model.

CONCLUSIONS

NLR and fibrinogen levels are simple, inexpensive and readily available biomarkers that could be incorporated into an on-treatment scoring system and used to help predict survival and response to ICI in patients with R/M HNSCC.

Oncolytic virotherapy induced CSDE1 neo-antigenesis restricts VSV replication but can be targeted by immunotherapy

In our clinical trials of oncolytic vesicular stomatitis virus expressing interferon beta (VSV-IFNβ), several patients achieved initial responses followed by aggressive relapse. We show here that VSV-IFNβ-escape tumors predictably express a point-mutated CSDE1P5S form of the RNA-binding Cold Shock Domain-containing E1 protein, which promotes escape as an inhibitor of VSV replication by disrupting viral transcription. Given time, VSV-IFNβ evolves a compensatory mutation in the P/M Inter-Genic Region which rescues replication in CSDE1P5S cells. These data show that CSDE1 is a major cellular co-factor for VSV replication. However, CSDE1P5S also generates a neo-epitope recognized by non-tolerized T cells. We exploit this predictable neo-antigenesis to drive, and trap, tumors into an escape phenotype, which can be ambushed by vaccination against CSDE1P5S, preventing tumor escape. Combining frontline therapy with escape-targeting immunotherapy will be applicable across multiple therapies which drive tumor mutation/evolution and simultaneously generate novel, targetable immunopeptidomes associated with acquired treatment resistance.

Oncolytic Reovirus-Mediated Recruitment of Early Innate Immune Responses Reverses Immunotherapy Resistance in Prostate Tumors

Prostate cancers are considered "cold" tumors characterized by minimal T cell infiltrates, absence of a type I interferon (IFN) signature, and the presence of immunosuppressive cells. This non-inflamed phenotype is likely responsible for the lack of sensitivity of prostate cancer patients to immune checkpoint blockade (ICB) therapy. Oncolytic virus therapy can potentially overcome this resistance to immunotherapy in prostate cancers by transforming cold tumors into "hot," immune cell-infiltrated tumors. We investigated whether the combination of intratumoral oncolytic reovirus, followed by targeted blockade of Programmed cell death protein 1 (PD-1) checkpoint inhibition and/or the immunomodulatory CD73/Adenosine system can enhance anti-tumor immunity. Treatment of subcutaneous TRAMP-C2 prostate tumors with combined intratumoral reovirus and anti-PD-1 or anti-CD73 antibody significantly enhanced survival of mice compared with reovirus or either antibody therapy alone. Only combination therapy led to rejection of pre-established tumors and protection from tumor re-challenge. This therapeutic effect was dependent on CD4+ T cells and natural killer (NK) cells. NanoString immune profiling of tumors confirmed that reovirus increased tumor immune cell infiltration and revealed an upregulation of the immune-regulatory receptor, B- and T-lymphocyte attenuator (BTLA). This expression of BTLA on innate antigen-presenting cells (APCs) and its ligand, Herpesvirus entry mediator (HVEM), on T cells from reovirus-infected tumors was in keeping with a role for the HVEM-BTLA pathway in promoting the potent anti-tumor memory response observed.

Reovirus-induced cell-mediated immunity for the treatment of multiple myeloma within the resistant bone marrow niche

BACKGROUND

Multiple myeloma (MM) remains an incurable disease and oncolytic viruses offer a well-tolerated addition to the therapeutic arsenal. Oncolytic reovirus has progressed to phase I clinical trials and its direct lytic potential has been extensively studied. However, to date, the role for reovirus-induced immunotherapy against MM, and the impact of the bone marrow (BM) niche, have not been reported.

METHODS

This study used human peripheral blood mononuclear cells from healthy donors and in vitro co-culture of MM cells and BM stromal cells to recapitulate the resistant BM niche. Additionally, the 5TGM1-Kalw/RijHSD immunocompetent in vivo model was used to examine reovirus efficacy and characterize reovirus-induced immune responses in the BM and spleen following intravenous administration. Collectively, these in vitro and in vivo models were used to characterize the development of innate and adaptive antimyeloma immunity following reovirus treatment.

RESULTS

Using the 5TGM1-Kalw/RijHSD immunocompetent in vivo model we have demonstrated that reovirus reduces both MM tumor burden and myeloma-induced bone disease. Furthermore, detailed immune characterization revealed that reovirus: (i) increased natural killer (NK) cell and CD8+ T cell numbers; (ii) activated NK cells and CD8+ T cells and (iii) upregulated effector-memory CD8+ T cells. Moreover, increased effector-memory CD8+ T cells correlated with decreased tumor burden. Next, we explored the potential for reovirus-induced immunotherapy using human co-culture models to mimic the myeloma-supportive BM niche. MM cells co-cultured with BM stromal cells displayed resistance to reovirus-induced oncolysis and bystander cytokine-killing but remained susceptible to killing by reovirus-activated NK cells and MM-specific cytotoxic T lymphocytes.

CONCLUSION

These data highlight the importance of reovirus-induced immunotherapy for targeting MM cells within the BM niche and suggest that combination with agents which boost antitumor immune responses should be a priority.

Hematopoietic stem cell gene therapy targeting TGFβ enhances the efficacy of irradiation therapy in a preclinical glioblastoma model

Patients with glioblastoma (GBM) have a poor prognosis, and inefficient delivery of drugs to tumors represents a major therapeutic hurdle. Hematopoietic stem cell (HSC)-derived myeloid cells efficiently home to GBM and constitute up to 50% of intratumoral cells, making them highly appropriate therapeutic delivery vehicles. Because myeloid cells are ubiquitously present in the body, we recently established a lentiviral vector containing matrix metalloproteinase 14 (MMP14) promoter, which is active specifically in tumor-infiltrating myeloid cells as opposed to myeloid cells in other tissues, and resulted in a specific delivery of transgenes to brain metastases in HSC gene therapy. Here, we used this novel approach to target transforming growth factor beta (TGFβ) as a key tumor-promoting factor in GBM. Transplantation of HSCs transduced with lentiviral vector expressing green fluorescent protein (GFP) into lethally irradiated recipient mice was followed by intracranial implantation of GBM cells. Tumor-infiltrating HSC progeny was characterized by flow cytometry. In therapy studies, mice were transplanted with HSCs transduced with lentiviral vector expressing soluble TGFβ receptor II-Fc fusion protein under MMP14 promoter. This TGFβ-blocking therapy was compared with the targeted tumor irradiation, the combination of the two therapies, and control. Tumor growth and survival were quantified (statistical significance determined by t-test and log-rank test). T cell memory response was probed through a repeated tumor challenge. Myeloid cells were the most abundant HSC-derived population infiltrating GBM. TGFβ-blocking HSC gene therapy in combination with irradiation significantly reduced tumor burden as compared with monotherapies and the control, and significantly prolonged survival as compared with the control and TGFβ-blocking monotherapy. Long-term protection from GBM was achieved only with the combination treatment (25% of the mice) and was accompanied by a significant increase in CD8+ T cells at the tumor implantation site following tumor rechallenge. We demonstrated a preclinical proof-of-principle for tumor myeloid cell-specific HSC gene therapy in GBM. In the clinic, HSC gene therapy is being successfully used in non-cancerous brain disorders and the feasibility of HSC gene therapy in patients with glioma has been demonstrated in the context of bone marrow protection. This indicates an opportunity for clinical translation of our therapeutic approach.

Differential and longitudinal immune gene patterns associated with reprogrammed microenvironment and viral mimicry in response to neoadjuvant radiotherapy in rectal cancer

BACKGROUND

Rectal cancers show a highly varied response to neoadjuvant radiotherapy/chemoradiation (RT/CRT) and the impact of the tumor immune microenvironment on this response is poorly understood. Current clinical tumor regression grading systems attempt to measure radiotherapy response but are subject to interobserver variation. An unbiased and unique histopathological quantification method (change in tumor cell density (ΔTCD)) may improve classification of RT/CRT response. Furthermore, immune gene expression profiling (GEP) may identify differences in expression levels of genes relevant to different radiotherapy responses: (1) at baseline between poor and good responders, and (2) longitudinally from preradiotherapy to postradiotherapy samples. Overall, this may inform novel therapeutic RT/CRT combination strategies in rectal cancer.

METHODS

We generated GEPs for 53 patients from biopsies taken prior to preoperative radiotherapy. TCD was used to assess rectal tumor response to neoadjuvant RT/CRT and ΔTCD was subjected to k-means clustering to classify patients into different response categories. Differential gene expression analysis was performed using statistical analysis of microarrays, pathway enrichment analysis and immune cell type analysis using single sample gene set enrichment analysis. Immunohistochemistry was performed to validate specific results. The results were validated using 220 pretreatment samples from publicly available datasets at metalevel of pathway and survival analyses.

RESULTS

ΔTCD scores ranged from 12.4% to -47.7% and stratified patients into three response categories. At baseline, 40 genes were significantly upregulated in poor (n=12) versus good responders (n=21), including myeloid and stromal cell genes. Of several pathways showing significant enrichment at baseline in poor responders, epithelial to mesenchymal transition, coagulation, complement activation and apical junction pathways were validated in external cohorts. Unlike poor responders, good responders showed longitudinal (preradiotherapy vs postradiotherapy samples) upregulation of 198 immune genes, reflecting an increased T-cell-inflamed GEP, type-I interferon and macrophage populations. Longitudinal pathway analysis suggested viral-like pathogen responses occurred in post-treatment resected samples compared with pretreatment biopsies in good responders.

CONCLUSION

This study suggests potentially druggable immune targets in poor responders at baseline and indicates that tumors with a good RT/CRT response reprogrammed from immune "cold" towards an immunologically "hot" phenotype on treatment with radiotherapy.

A blood transcriptome-based analysis of disease progression, immune regulation, and symptoms in coronavirus-infected patients

COVID-19 patients show heterogeneity in clinical presentation and outcomes that makes pandemic control and strategy difficult; optimizing management requires a systems biology approach of understanding the disease. Here we sought to potentially understand and infer complex disease progression, immune regulation, and symptoms in patients infected with coronaviruses (35 SARS-CoV and 3 SARS-CoV-2 patients and 57 samples) at two different disease progression stages. Further, we compared coronavirus data with healthy individuals (n = 16) and patients with other infections (n = 144; all publicly available data). We applied inferential statistics (the COVID-engine platform) to RNA profiles (from limited number of samples) derived from peripheral blood mononuclear cells (PBMCs). Compared to healthy individuals, a subset of integrated blood-based gene profiles (signatures) distinguished acute-like (mimicking coronavirus-infected patients with prolonged hospitalization) from recovering-like patients. These signatures also hierarchically represented multiple (at the system level) parameters associated with PBMC including dysregulated cytokines, genes, pathways, networks of pathways/concepts, immune status, and cell types. Proof-of-principle observations included PBMC-based increases in cytokine storm-associated IL6, enhanced innate immunity (macrophages and neutrophils), and lower adaptive T and B cell immunity in patients with acute-like disease compared to those with recovery-like disease. Patients in the recovery-like stage showed significantly enhanced TNF, IFN-γ, anti-viral, HLA-DQA1, and HLA-F gene expression and cytolytic activity, and reduced pro-viral gene expression compared to those in the acute-like stage in PBMC. Besides, our analysis revealed overlapping genes associated with potential comorbidities (associated diabetes) and disease-like conditions (associated with thromboembolism, pneumonia, lung disease, and septicemia). Overall, our COVID-engine inferential statistics platform and study involving PBMC-based RNA profiling may help understand complex and variable system-wide responses displayed by coronavirus-infected patients with further validation.

CTIM-14. PELAREOREP AND GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF) WITH STANDARD CHEMORADIOTHERAPY/ADJUVANT TEMOZOLOMIDE FOR GLIOBLASTOMA MULTIFORME (GBM) PATIENTS: REOGLIO PHASE I TRIAL RESULTS

BACKGROUND

Oncolytic viruses represent a novel treatment approach in GBM through oncolytic targeting as well as local immune activation. We designed a phase Ib, open-label study of intravenous reovirus (pelareorep) with GM-CSF alongside standard chemoradiotherapy to assess safety and tolerability.

METHODS

15 patients with newly diagnosed GBM were treated with GM-CSF 50mg subcutaneously (days 1–3) and pelareorep (days 4–5) in weeks 1 and 4 of chemoradiotherapy, and week 1 of adjuvant temozolomide course: 7 patients received 1x1010TCID50 (dose level 1); 8 received 3x1010TCID50 (dose level 2). The primary objective was to determine the maximum tolerated dose of pelareorep and GM-CSF with standard chemoradiotherapy. Secondary objectives were to gain preliminary assessment of the activity of the combination and assess treatment compliance.

RESULTS

1 dose limiting toxicity (DLT) and 20 SAEs were experienced overall; median number of SAEs per patient was 2. Commonest SAEs were nervous system disorders, predominantly seizures. SARs included fever/flu-like episodes (n=5), fall (n=1) and headache (n=1). Two SUSARs occurred in dose level 2, classed as vascular disorders manifesting as hypotension episodes – one was a DLT. Suspected relationship of SARs: pelareorep (n=6); temozolomide (n=1); radiotherapy (n=1); all study drugs (n=1). 87% of patients (n=13) completed chemoradiotherapy without unplanned delays. Adjuvant treatment was delayed in 21% of cycles overall, with the majority due to inadequate haematology/biochemistry values (44% of delays). Pelareorep was omitted in 4 instances in 4 patients during chemoradiotherapy and omitted in 4 instances in 3 patients during adjuvant treatment.

CONCLUSION

We present the first clinical data using intravenous pelareorep with GM-CSF alongside standard chemoradiotherapy in patients with GBM, suggesting that the combination is tolerable. Further analysis is underway and efficacy results will be ready for presentation at the conference. This work was supported by CRUK, The Brain Tumour Charity, Yorkshire Cancer Research and Oncolytics Biotech Inc.

Abstract 3415: Mutant BRAF small molecule inhibition enhances oncolytic herpes virus immunotherapy through increased immune cell recruitment and activation in melanoma

Small molecule inhibitors of the MAPK pathway have demonstrated rapid responses in melanoma patients, but their use is hindered by the frequent development of acquired resistance. Oncolytic viruses are a novel class of immunotherapeutics which selectively replicate inside cancer cells, causing lysis and subsequent activation of anti-tumor immunity. BRAF and MEK inhibitors have previously been shown to synergise with oncolytic viruses to kill melanoma cells, but the consequences of these interactions on immune responses have not been assessed. Here, we show that the combination of PLX4720 (BRAFV600E inhibitor) and intratumoral oncolytic herpes virus HSV1716 led to a significant tumor reduction and improved survival over single-agent treatment in a murine BRAFV600E melanoma model. The combination led to a significant increase of PD-L1+ neutrophils and monocytes at an early time point following therapy administration, suggesting an inflammatory switch in the tumor microenvironment. Importantly, the combination led to a significant increase in cytotoxic CD8+ cells at a later time point, which was accompanied by an increase in CD25+ Foxp3+ T-regulatory (Treg) cells. Addition of an anti-CD25 antibody to the PLX4720/HSV1716 doublet led to complete eradication of melanoma tumors in vivo. Current efforts are focused on deciphering T-cell dynamics during this therapy using a novel technology, Timer of cell kinetics and activity (Tocky). Tocky uses a fluorescent Timer protein which spontaneously changes its emission spectrum from blue to red, reporting real-time activation of the T-cell receptor and subsequent activation of immune cells in vivo. Using Tocky, we are identifying specific immune subsets that are stimulated following therapy and the real-time dynamics of antigen recognition and subsequent cell activation. These findings form the basis of future testing of drug-virus combinations in an effort to identify potent cytotoxic, as well as immuno-modulatory, strategies and their detailed mechanism of action.

Citation Format: Galabina Bozhanova, Victoria Jennings, Malin Pedersen, Joan Kyula, Emmanuel Patin, Jehanne Hassan, Masahiro Ono, Kevin Harrington, Alan Melcher. Mutant BRAF small molecule inhibition enhances oncolytic herpes virus immunotherapy through increased immune cell recruitment and activation in melanoma [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 3415.

STING and IRF3 in stromal fibroblasts enable sensing of genomic stress in cancer cells to undermine oncolytic viral therapy

Cancer-associated fibroblasts (CAFs) perform diverse roles and can modulate therapy responses1. The inflammatory environment within tumours also influences responses to many therapies, including the efficacy of oncolytic viruses2; however, the role of CAFs in this context remains unclear. Furthermore, little is known about the cell signalling triggered by heterotypic cancer cell-fibroblast contacts and about what activates fibroblasts to express inflammatory mediators1,3. Here, we show that direct contact between cancer cells and CAFs triggers the expression of a wide range of inflammatory modulators by fibroblasts. This is initiated following transcytosis of cytoplasm from cancer cells into fibroblasts, leading to the activation of STING and IRF3-mediated expression of interferon-β1 and other cytokines. Interferon-β1 then drives interferon-stimulated transcriptional programs in both cancer cells and stromal fibroblasts and ultimately undermines the efficacy of oncolytic viruses, both in vitro and in vivo. Further, targeting IRF3 solely in stromal fibroblasts restores oncolytic herpes simplex virus function.

Author Correction: STING and IRF3 in stromal fibroblasts enable sensing of genomic stress in cancer cells to undermine oncolytic viral therapy

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Combination therapy with oncolytic viruses and immune checkpoint inhibitors

Introduction: Immune checkpoint inhibitors (ICI) have dramatically improved the outcome for cancer patients across multiple tumor types. However the response rates to ICI monotherapy remain relatively low, in part due to some tumors cultivating an inherently 'cold' immune microenvironment. Oncolytic viruses (OV) have the capability to promote a 'hotter' immune microenvironment which can improve the efficacy of ICI.Areas covered: In this article we conducted a literature search through Pubmed/Medline to identify relevant articles in both the pre-clinical and clinical settings for combining OVs with ICIs and discuss the impact of this approach on treatment as well as changes within the tumor microenvironment. We also explore the future directions of this novel combination strategy.Expert opinion: The imminent results of the Phase 3 study combining pembrolizumab with or without T-Vec injection are eagerly awaited. OV/ICI combinations remain one of the most promising avenues to explore in the success of cancer immunotherapy.

Impact of antibiotic use during curative treatment of locally advanced head and neck cancers with chemotherapy and radiotherapy

BACKGROUND

Pre-clinical evidence suggests reduced efficacy of anticancer treatment in patients exposed to broad-spectrum antibiotics. It is hypothesised that this phenomenon may be explained by the effects of antibiotics on the composition of the microbiota. To assess this in a clinical setting, we analysed the impact of antibiotics in patients with locally advanced head and neck cancer (LAHNC) treated with curative intent with chemotherapy and radiotherapy (RT).

MATERIAL AND METHODS

Retrospective data for LAHNC patients treated with curative intent (245 induction chemotherapy followed by chemoradiation [CRT], 17 surgery followed by post-operative CRT, six CRT, three RT alone and one RT with concurrent cetuximab) were analysed. We evaluated the impact of antibiotics prescribed during primary anti-cancer treatment on progression-free survival (PFS), overall survival (OS) and disease-specific survival (DSS) rates by multivariate Kaplan-Meier and Cox proportional hazards regression analysis.

RESULTS

Among 272 patients, those receiving antibiotics between within 1 week before and 2 weeks after treatment (N = 124) progressed significantly earlier and had lower OS and DSS rates. In the multivariate analysis, administration of antibiotics was independently associated with reduced PFS (hazards ratio [HR] 1.98, P = 0.001), OS (HR 1.85, P = 0.001) and DSS (HR 1.95, P = 0.004). This effect was maintained with independence of reason for prescription, type and time of antibiotic prescription. The negative impact was greater for patients who received two or more courses of antibiotics. Antibiotic treatment was correlated with increased risk of locoregional relapse.

CONCLUSIONS

Our data suggest a negative impact of antibiotic therapy on treatment outcomes following CRT with curative intent in patients with LAHNC. This potential harm should be considered when prescribing broad-spectrum and prophylactic antibiotics for such patients.

Abstract PR19: Utilizing novel oncolytic vaccinia virus for selective expression of immunotherapeutic payloads in metastatic tumors

The treatment paradigm for patients with metastatic cancer has evolved rapidly with the approval of agents targeting CTLA-4 and the PD-1/L1 immune checkpoint axis. Despite the profound impact these agents have had, they are minimally effective in the majority of cancer patients. Rational combinations of complementary immune-modulating agents have thus far not led to clear patient benefit, and newer technologies that are better able to safely combine multiple modes of action could well prove to be vital. Oncolytic viruses (OVs) have the capacity to be the ideal therapeutic partner for immune checkpoint therapeutics in several ways. First, on their own OVs can “heat up” immunologically “cold” tumors by initiating a proinflammatory infection within the tumor microenvironment (TME). Second, some OVs can be engineered to strategically express one or more immune-modulating molecules. Finally, certain OVs have the capacity to be delivered systemically and thus enhance immune cell recruitment and activation in all metastatic sites. We have selected a novel vaccinia virus as our therapeutic OV platform and are using it to engineer multi-mechanistic cancer therapeutics. Previously it has been demonstrated that oncolytic vaccinia viruses can be delivered systemically and spread within metastatic lesions. These clinical candidates, however, contain multiple potent immune-suppressive genes. Furthermore, in clinical studies some of these therapeutics exhibited off-tumor infections (e.g., pox lesions), which may ultimately limit their ability to be used to deliver potent immune modulators. We used a combination of functional genomics and bio-selection strategies to generate a novel oncolytic vaccinia backbone (termed SKV) containing a large genome deletion that exhibited augmented oncolytic activity and improved tumor selectivity. Our new best-in-class vaccinia robustly stimulates anti-immune responses, rapidly spreads within and between tumors, and has a substantially improved preclinical safety profile when compared to other vaccinia clinical candidates. As predicted, SKV synergizes well with immune checkpoint inhibitor antibodies and potently activates human immune cells. Due to the exquisite tumor selectivity of SKV, we have been able to engineer and express three potent immune modulators that are safest and most effective when expressed within the TME: anti-CTLA4 antibody, membrane tethered IL-12, and the antigen-presenting cell-activating ligand FLT-3L. Tumor-selective transgene expression has been demonstrated in murine tumor models in which therapeutic payload concentrations (e.g., &gt;1 ug/ml IL-12) were achieved within the TME without any detectable transgene product in the systemic circulation (serum). Expression of the therapeutic payloads increased survival versus the SKV backbone control in an immunocompetent, syngeneic tumor model. Ongoing toxicity and efficacy studies are being carried out prior to clinical evaluation of the novel virus construct.

This abstract is also being presented as Poster A02.

Citation Format: Adrian Pelin, Mike Huh, Matt Tang, Fabrice LeBouef, Brian Keller, Jessie Duong, Katherine Knowles, Julia Petryk, Vicki Jennings, Alan Melcher, Ragunath Singaravelu, Mathieu Crupi, Larissa Pikor, Caroline Breitbach, Steven Bernstein, Michael Burgess, John C. Bell. Utilizing novel oncolytic vaccinia virus for selective expression of immunotherapeutic payloads in metastatic tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR19.

APOBEC3B-mediated corruption of the tumor cell immunopeptidome induces heteroclitic neoepitopes for cancer immunotherapy

APOBEC3B, an anti-viral cytidine deaminase which induces DNA mutations, has been implicated as a mediator of cancer evolution and therapeutic resistance. Mutational plasticity also drives generation of neoepitopes, which prime anti-tumor T cells. Here, we show that overexpression of APOBEC3B in tumors increases resistance to chemotherapy, but simultaneously heightens sensitivity to immune checkpoint blockade in a murine model of melanoma. However, in the vaccine setting, APOBEC3B-mediated mutations reproducibly generate heteroclitic neoepitopes in vaccine cells which activate de novo T cell responses. These cross react against parental, unmodified tumors and lead to a high rate of cures in both subcutaneous and intra-cranial tumor models. Heteroclitic Epitope Activated Therapy (HEAT) dispenses with the need to identify patient specific neoepitopes and tumor reactive T cells ex vivo. Thus, actively driving a high mutational load in tumor cell vaccines increases their immunogenicity to drive anti-tumor therapy in combination with immune checkpoint blockade.

ATR Inhibition Potentiates the Radiation-induced Inflammatory Tumor Microenvironment

PURPOSE

ATR inhibitors (ATRi) are in early phase clinical trials and have been shown to sensitize to chemotherapy and radiotherapy preclinically. Limited data have been published about the effect of these drugs on the tumor microenvironment.Experimental Design: We used an immunocompetent mouse model of HPV-driven malignancies to investigate the ATR inhibitor AZD6738 in combination with fractionated radiation (RT). Gene expression analysis and flow cytometry were performed posttherapy.

RESULTS

Significant radiosensitization to RT by ATRi was observed alongside a marked increase in immune cell infiltration. We identified increased numbers of CD3+ and NK cells, but most of this infiltrate was composed of myeloid cells. ATRi plus radiation produced a gene expression signature matching a type I/II IFN response, with upregulation of genes playing a role in nucleic acid sensing. Increased MHC I levels were observed on tumor cells, with transcript-level data indicating increased antigen processing and presentation within the tumor. Significant modulation of cytokine gene expression (particularly CCL2, CCL5, and CXCL10) was found in vivo, with in vitro data indicating CCL3, CCL5, and CXCL10 are produced from tumor cells after ATRi + RT.

CONCLUSIONS

We show that DNA damage by ATRi and RT leads to an IFN response through activation of nucleic acid-sensing pathways. This triggers increased antigen presentation and innate immune cell infiltration. Further understanding of the effect of this combination on the immune response may allow modulation of these effects to maximize tumor control through antitumor immunity.

PD-1 Blockade Following Isolated Limb Perfusion with Vaccinia Virus Prevents Local and Distant Relapse of Soft-tissue Sarcoma

PURPOSE

The prevention and treatment of metastatic sarcoma are areas of significant unmet need. Immune checkpoint inhibitor monotherapy has shown little activity in sarcoma and there is great interest in identifying novel treatment combinations that may augment responses. In vitro and in vivo, we investigated the potential for an oncolytic vaccinia virus (GLV-1h68) delivered using isolated limb perfusion (ILP) to promote antitumor immune responses and augment response to PD-1 blockade in sarcoma.Experimental Design: In an established animal model of extremity sarcoma, we evaluated the potential of locoregional delivery of a vaccinia virus (GLV-1h68) alongside biochemotherapy (melphalan/TNFα) in ILP. Complementary in vitro assays for markers of immunogenic cell death were performed in sarcoma cell lines.

RESULTS

PD-1 monotherapy had minimal efficacy in vivo, mimicking the clinical scenario. Pretreatment with GLV-1h68 delivered by ILP (viral ILP) significantly improved responses. Furthermore, when performed prior to surgery and radiotherapy, viral ILP and PD-1 blockade prevented both local and distant relapse, curing a previously treatment-refractory model. Enhanced therapy was associated with marked modulation of the tumor microenvironment, with an increase in the number and penetrance of intratumoral CD8+ T cells and expansion and activation of dendritic cells. GLV-1h68 was capable of inducing markers of immunogenic cell death in human sarcoma cell lines.

CONCLUSIONS

Viral ILP augments the response to PD-1 blockade, transforming this locoregional therapy into a potentially effective systemic treatment for sarcoma and warrants translational evaluation.

Suboptimal T-cell Therapy Drives a Tumor Cell Mutator Phenotype That Promotes Escape from First-Line Treatment

Antitumor T-cell responses raised by first-line therapies such as chemotherapy, radiation, tumor cell vaccines, and viroimmunotherapy tend to be weak, both quantitatively (low frequency) and qualitatively (low affinity). We show here that T cells that recognize tumor-associated antigens can directly kill tumor cells if used at high effector-to-target ratios. However, when these tumor-reactive T cells were present at suboptimal ratios, direct T-cell-mediated tumor cell killing was reduced and the ability of tumor cells to evolve away from a coapplied therapy (oncolytic or suicide gene therapy) was promoted. This T-cell-mediated increase in therapeutic resistance was associated with C to T transition mutations that are characteristic of APOBEC3 cytosine deaminase activity and was induced through a TNFα and protein kinase C-dependent pathway. Short hairpin RNA inhibition of endogenous APOBEC3 reduced rates of tumor escape from oncolytic virus or suicide gene therapy to those seen in the absence of antitumor T-cell coculture. Conversely, overexpression of human APOBEC3B in tumor cells enhanced escape from suicide gene therapy and oncolytic virus therapy both in vitro and in vivo Our data suggest that weak affinity or low frequency T-cell responses against tumor antigens may contribute to the ability of tumor cells to evolve away from first-line therapies. We conclude that immunotherapies need to be optimized as early as possible so that, if they do not kill the tumor completely, they do not promote treatment resistance.