Live Imaging to Quantify Cellular Radiosensitivity in Patient-Derived Tumor Organoids

Radiation therapy (RT) is one of the mainstays of modern clinical cancer management. However, not all cancer types are equally sensitive to irradiation, often (but not always) because of differences in the ability of malignant cells to repair oxidative DNA damage as elicited by ionizing rays. Clonogenic assays have been employed for decades to assess the sensitivity of cultured cancer cells to ionizing irradiation, largely because irradiated cancer cells often die in a delayed manner that is difficult to quantify with short-term flow cytometry- or microscopy-assisted techniques. Unfortunately, clonogenic assays cannot be employed as such for more complex tumor models, such as patient-derived tumor organoids (PDTOs). Indeed, irradiating established PDTOs may not necessarily abrogate their growth as multicellular units, unless their stem-like compartment is completely eradicated. Moreover, irradiating PDTO-derived single-cell suspensions may not properly recapitulate the sensitivity of malignant cells to RT in the context of established PDTOs. Here, we detail an adaptation of conventional clonogenic assays that involves exposure of established PDTOs to ionizing radiation, followed by single-cell dissociation, replating in suitable culture conditions and live imaging. Non-irradiated (control) PDTO-derived stem-like cells reform growing PDTOs with a PDTO-specific efficiency, which is negatively influenced by irradiation in a dose-dependent manner. In these conditions, PDTO-forming efficiency and growth rate can be quantified as a measure of radiosensitivity on time-lapse images collected until control PDTOs achieve a predefined space occupancy.

The Next Chapter in Immunotherapy and Radiation Combination Therapy: Cancer-Specific Perspectives

Immunotherapeutic agents have revolutionized cancer treatment over the past decade. However, most patients fail to respond to immunotherapy alone. A growing body of preclinical studies highlights the potential for synergy between radiation therapy and immunotherapy, but the outcomes of clinical studies have been mixed. This review summarizes the current state of immunotherapy and radiation combination therapy across cancers, highlighting existing challenges and promising areas for future investigation.

Tumor-Associated Lymphocytes and Breast Cancer Survival in Black and White Women

This case series evaluates whether differences in immune filtration are associated with breast cancer risk in Black vs White women.

Image-based multiplex immune profiling of cancer tissues: translational implications. A report of the International Immuno-oncology Biomarker Working Group on Breast Cancer

Recent advances in the field of immuno-oncology have brought transformative changes in the management of cancer patients. The immune profile of tumours has been found to have key value in predicting disease prognosis and treatment response in various cancers. Multiplex immunohistochemistry and immunofluorescence have emerged as potent tools for the simultaneous detection of multiple protein biomarkers in a single tissue section, thereby expanding opportunities for molecular and immune profiling while preserving tissue samples. By establishing the phenotype of individual tumour cells when distributed within a mixed cell population, the identification of clinically relevant biomarkers with high-throughput multiplex immunophenotyping of tumour samples has great potential to guide appropriate treatment choices. Moreover, the emergence of novel multi-marker imaging approaches can now provide unprecedented insights into the tumour microenvironment, including the potential interplay between various cell types. However, there are significant challenges to widespread integration of these technologies in daily research and clinical practice. This review addresses the challenges and potential solutions within a structured framework of action from a regulatory and clinical trial perspective. New developments within the field of immunophenotyping using multiplexed tissue imaging platforms and associated digital pathology are also described, with a specific focus on translational implications across different subtypes of cancer. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The crosstalk between DNA repair and immune responses

In recent years, increasing evidence has highlighted the profound connection between DNA damage repair and the activation of immune responses. We spoke with researchers about their mechanistic interplays and the implications for cancer and other diseases.

Immunologically relevant effects of radiation therapy on the tumor microenvironment

Focal radiation therapy (RT) has been successfully employed to clinically manage multiple types of cancer for more than a century. Besides being preferentially cytotoxic for malignant cells over their nontransformed counterparts, RT elicits numerous microenvironmental alterations that appear to factor into its therapeutic efficacy. Here, we briefly discuss immunostimulatory and immunosuppressive microenvironmental changes elicited by RT and their impact on tumor recognition by the host immune system.

CD40 agonism improves anti-tumor T cell priming induced by the combination of radiation therapy plus CTLA4 inhibition and enhances tumor response

Radiation therapy (RT) combined with CTLA4 blockers converts immunosuppressed (cold) mouse triple negative breast cancers (TNBCs) into immune infiltrated (hot) lesions. We have recently shown that targeting the myeloid compartment to improve dendritic cell activation is required for most TNBC-bearing mice to achieve superior therapeutic responses to RT plus CTLA4 inhibitors.

Immunotherapy targeting different immune compartments in combination with radiation therapy induces regression of resistant tumors

Radiation therapy (RT) increases tumor response to CTLA-4 inhibition (CTLA4i) in mice and in some patients, yet deep responses are rare. To identify rational combinations of immunotherapy to improve responses we use models of triple negative breast cancer highly resistant to immunotherapy in female mice. We find that CTLA4i promotes the expansion of CD4+ T helper cells, whereas RT enhances T cell clonality and enriches for CD8+ T cells with an exhausted phenotype. Combination therapy decreases regulatory CD4+ T cells and increases effector memory, early activation and precursor exhausted CD8+ T cells. A combined gene signature comprising these three CD8+ T cell clusters is associated with survival in patients. Here we show that targeting additional immune checkpoints expressed by intratumoral T cells, including PD1, is not effective, whereas CD40 agonist therapy recruits resistant tumors into responding to the combination of RT and CTLA4i, indicating the need to target different immune compartments.

Multi-Institutional Evaluation of Pathologists' Assessment Compared to Immunoscore

BACKGROUND

The Immunoscore (IS) is a quantitative digital pathology assay that evaluates the immune response in cancer patients. This study reports on the reproducibility of pathologists' visual assessment of CD3+- and CD8+-stained colon tumors, compared to IS quantification.

METHODS

An international group of expert pathologists evaluated 540 images from 270 randomly selected colon cancer (CC) cases. Concordance between pathologists' T-score, corresponding hematoxylin-eosin (H&E) slides, and the digital IS was evaluated for two- and three-category IS.

RESULTS

Non-concordant T-scores were reported in more than 92% of cases. Disagreement between semi-quantitative visual assessment of T-score and the reference IS was observed in 91% and 96% of cases before and after training, respectively. Statistical analyses showed that the concordance index between pathologists and the digital IS was weak in two- and three-category IS, respectively. After training, 42% of cases had a change in T-score, but no improvement was observed with a Kappa of 0.465 and 0.374. For the 20% of patients around the cut points, no concordance was observed between pathologists and digital pathology analysis in both two- and three-category IS, before or after training (all Kappa < 0.12).

CONCLUSIONS

The standardized IS assay outperformed expert pathologists' T-score evaluation in the clinical setting. This study demonstrates that digital pathology, in particular digital IS, represents a novel generation of immune pathology tools for reproducible and quantitative assessment of tumor-infiltrated immune cell subtypes.

Pitfalls in machine learning-based assessment of tumor-infiltrating lymphocytes in breast cancer: A report of the International Immuno-Oncology Biomarker Working Group on Breast Cancer

The clinical significance of the tumor-immune interaction in breast cancer is now established, and tumor-infiltrating lymphocytes (TILs) have emerged as predictive and prognostic biomarkers for patients with triple-negative (estrogen receptor, progesterone receptor, and HER2-negative) breast cancer and HER2-positive breast cancer. How computational assessments of TILs might complement manual TIL assessment in trial and daily practices is currently debated. Recent efforts to use machine learning (ML) to automatically evaluate TILs have shown promising results. We review state-of-the-art approaches and identify pitfalls and challenges of automated TIL evaluation by studying the root cause of ML discordances in comparison to manual TIL quantification. We categorize our findings into four main topics: (1) technical slide issues, (2) ML and image analysis aspects, (3) data challenges, and (4) validation issues. The main reason for discordant assessments is the inclusion of false-positive areas or cells identified by performance on certain tissue patterns or design choices in the computational implementation. To aid the adoption of ML for TIL assessment, we provide an in-depth discussion of ML and image analysis, including validation issues that need to be considered before reliable computational reporting of TILs can be incorporated into the trial and routine clinical management of patients with triple-negative breast cancer. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Spatial analyses of immune cell infiltration in cancer: current methods and future directions: A report of the International Immuno-Oncology Biomarker Working Group on Breast Cancer

Modern histologic imaging platforms coupled with machine learning methods have provided new opportunities to map the spatial distribution of immune cells in the tumor microenvironment. However, there exists no standardized method for describing or analyzing spatial immune cell data, and most reported spatial analyses are rudimentary. In this review, we provide an overview of two approaches for reporting and analyzing spatial data (raster versus vector-based). We then provide a compendium of spatial immune cell metrics that have been reported in the literature, summarizing prognostic associations in the context of a variety of cancers. We conclude by discussing two well-described clinical biomarkers, the breast cancer stromal tumor infiltrating lymphocytes score and the colon cancer Immunoscore, and describe investigative opportunities to improve clinical utility of these spatial biomarkers. © 2023 The Pathological Society of Great Britain and Ireland.

The interplay between the DNA damage response and ectonucleotidases modulates tumor response to therapy

The extracellular nucleoside adenosine reduces tissue inflammation and is generated by irreversible dephosphorylation of adenosine monophosphate (AMP) mediated by the ectonucleotidase CD73. The pro-inflammatory nucleotides adenosine triphosphate, nicotinamide adenine dinucleotide, and cyclic guanosine -monophosphate-AMP (cGAMP), which are produced in the tumor microenvironment (TME) during therapy-induced immunogenic cell death and activation of innate immune signaling, can be converted into AMP by ectonucleotidases CD39, CD38, and CD203a/ENPP1. Thus, ectonucleotidases shape the TME by converting immune-activating signals into an immunosuppressive one. Ectonucleotidases also hinder the ability of therapies including radiation therapy, which enhance the release of pro-inflammatory nucleotides in the extracellular milieu, to induce immune-mediated tumor rejection. Here, we review the immunosuppressive effects of adenosine and the role of different ectonucleotidases in modulating antitumor immune responses. We discuss emerging opportunities to target adenosine generation and/or its ability to signal via adenosine receptors expressed by immune and cancer cells in the context of combination immunotherapy and radiotherapy.

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.

Pipeline to identify neoantigens exposed by radiation

Mutation-associated neoantigens are key targets of tumor-specific T cells and thus play a major role in driving responses to immune checkpoint blockade (ICB) therapy in tumors with high mutational burden. However, only a small number of mutated peptides are actually presented by MHC molecules and only a minority can induce T cell responses. In addition, the recognition of these neoantigens by T cells is limited by the level of expression of the mutated gene product in the tumor cells. Preclinical studies have shown that radiation can convert the irradiated tumor into an in situ vaccine, leading to the priming of tumor-specific T cells and to the rejection of otherwise ICB-resistant tumors. There is now preclinical and clinical evidence that radiation can upregulate the expression of genes containing immunogenic mutations and expose them to the immune system. Therefore, the identification of neoantigens upregulated by radiation could help to predict which patients might benefit from treatment with combinations of radiotherapy and ICB and could also be incorporated into personalized neoantigen vaccination strategies. In this chapter, we present the pipeline that we used to identify relevant radiation-upregulated neoantigens in a poorly immunogenic mouse model of metastatic breast cancer.

Facts and Perspectives: Implications of tumor glycolysis on immunotherapy response in triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive disease that is difficult to treat and portends a poor prognosis in many patients. Recent efforts to implement immune checkpoint inhibitors into the treatment landscape of TNBC have led to improved outcomes in a subset of patients both in the early stage and metastatic settings. However, a large portion of patients with TNBC remain resistant to immune checkpoint inhibitors and have limited treatment options beyond cytotoxic chemotherapy. The interplay between the anti-tumor immune response and tumor metabolism contributes to immunotherapy response in the preclinical setting, and likely in the clinical setting as well. Specifically, tumor glycolysis and lactate production influence the tumor immune microenvironment through creation of metabolic competition with infiltrating immune cells, which impacts response to immune checkpoint blockade. In this review, we will focus on how glucose metabolism within TNBC tumors influences the response to immune checkpoint blockade and potential ways of harnessing this information to improve clinical outcomes.

Abstract 1309: Patient-derived tumor organoids as a platform to study radiation-exposed neoantigens

Focal radiation therapy (RT) can increase tumor immunogenicity and T cell-mediated tumor rejection when combined with immune checkpoint blockade (ICB). Our prior findings in patients and in preclinical studies suggest that one mechanism whereby RT increases tumor immunogenicity is by enhancing the expression of neoantigens.1,2 In response to RT, cells rapidly transcribe and translate hundreds of genes associated with the DNA damage response (DDR), protein turnover and cellular stress. Genes in these pathways are frequently mutated in cancer. Thus, we hypothesized that the presence of immunogenic mutations in genes upregulated by radiation could help predict the benefits of RT used in combination with ICB. In order to develop such a predictor, we built an in vitro system to study the RT-induced transcriptional response of primary human tumors cultured as patient-derived tumor organoids (PDO). PDOs were established from 2 breast cancer (BC), 4 non-small cell lung cancer (NSCLC) and 3 colorectal cancer (CRC) patients. PDOs were irradiated with doses of 5 to 8 Gy daily for 3 days (n=4) or left untreated (UT, n=4) and cultured for 24h prior to RNA extraction. RNA sequencing was carried out using a NovaSeq6000 sequencer (Illumina) to a depth of 30 million reads. Differential expression analysis between RT and UT samples was performed using DESeq2 and significantly perturbed genes were defined as genes with fold change greater than 1.5 and adjusted p-value cutoff of 0.05. In total we detected an average of 15,000+/-800 protein coding genes per sample and the number of genes modulated by RT was found to vary with cancer type. This ranged from an average of 3.9+/-1.6% genes upregulated by RT in NSCLC to 12.1+/-2.5% in CRC organoids. There were 104 and 490 genes commonly upregulated by RT in NSCLC and CRC, respectively. One of the BC PDOs is a triple-negative BC and the other HR+ and despite this difference, we identified 24 commonly upregulated genes. Gene Set Enrichment Analysis (GSEA), revealed enrichments in DDR and pro-inflammatory signaling pathways among the upregulated genes. Whole exome sequencing and paired normal tissue was used to determine the variants and predicted neoantigens for these PDOs. In one of the EGFR mutated NSCLC PDOs we found that among the genes transcriptionally upregulated by RT, 18 carried somatic mutations predicted to be antigenic. The presentation of these neoantigens is being investigated by mass spectrometry analysis of the immunopeptidome eluted from surface MHC-I molecules. Similar investigations are being carried out in the other models. Overall, results support the feasibility of identifying a common signature of RT upregulated genes in PDOs. This will provide a system to predict RT- exposed neoantigens. [1] Formenti et al. Nat. Med. 2018;24(12):1845-1851, [2] Lhuillier et al. J. Clin. Invest. 2021;131(5):e138740

Citation Format: Samantha J. Van Nest, Jared Capuano, Bhavneet Bhinder, Martin G. Klatt, Tuo Zhang, M. Laura Martin, Silvia C. Formenti, Olivier Elemento, Nils-Petter Rudqvist, Sandra Demaria. Patient-derived tumor organoids as a platform to study radiation-exposed neoantigens [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 1309.

Perspectives in Immunotherapy: meeting report from the Immunotherapy Bridge, December 1st-2nd, 2021

Over the past decade, immunotherapy has become an increasingly fundamental modality in the treatment of cancer. The positive impact of immune checkpoint inhibition, especially anti-programmed death (PD)-1/PD-ligand (L)1 blockade, in patients with different cancers has focused attention on the potential for other immunotherapeutic approaches. These include inhibitors of additional immune checkpoints, adoptive cell transfer (ACT), and therapeutic vaccines. Patients with advanced cancers who previously had limited treatment options available may now benefit from immunotherapies that can offer durable responses and improved survival outcomes. However, despite this, a significant proportion of patients fail to respond to immunotherapy, especially those with less immunoresponsive cancer types, and there remains a need for new treatment strategies.The virtual Immunotherapy Bridge (December 1st-2nd, 2021), organized by the Fondazione Melanoma Onlus, Naples, Italy in collaboration with the Society for Immunotherapy of Cancer addressed several areas of current research in immunotherapy, including lessons learned from cell therapies, drivers of immune response, and trends in immunotherapy across different cancers, and these are summarised here.

ATM Modulates Nuclear Mechanics by Regulating Lamin A Levels

Ataxia-telangiectasia mutated (ATM) is one of the three main apical kinases at the crux of DNA damage response and repair in mammalian cells. ATM activates a cascade of downstream effector proteins to regulate DNA repair and cell cycle checkpoints in response to DNA double-strand breaks. While ATM is predominantly known for its role in DNA damage response and repair, new roles of ATM have recently begun to emerge, such as in regulating oxidative stress or metabolic pathways. Here, we report the surprising discovery that ATM inhibition and deletion lead to reduced expression of the nuclear envelope protein lamin A. Lamins are nuclear intermediate filaments that modulate nuclear shape, structure, and stiffness. Accordingly, inhibition or deletion of ATM resulted in increased nuclear deformability and enhanced cell migration through confined spaces, which requires substantial nuclear deformation. These findings point to a novel connection between ATM and lamin A and may have broad implications for cells with ATM mutations—as found in patients suffering from Ataxia Telangiectasia and many human cancers—which could lead to enhanced cell migration and increased metastatic potential.

The "Great Debate" at Melanoma Bridge 2021, December 2nd-4th, 2021

The Great Debate session at the 2021 Melanoma Bridge virtual congress (December 2-4) featured counterpoint views from experts on seven important issues in melanoma. The debates considered the use of adoptive cell therapy versus use of bispecific antibodies, mitogen-activated protein kinase (MAPK) inhibitors versus immunotherapy in the adjuvant setting, whether the use of corticosteroids for the management of side effects have an impact on outcomes, the choice of programmed death (PD)-1 combination therapy with cytotoxic T-lymphocyte-associated antigen (CTLA)-4 or lymphocyte-activation gene (LAG)-3, whether radiation is needed for brain metastases, when lymphadenectomy should be integrated into the treatment plan and then the last debate, telemedicine versus face-to-face. As with previous Bridge congresses, the debates were assigned by meeting Chairs and positions taken by experts during the debates may not have necessarily reflected their respective personal view. Audiences voted both before and after each debate.

Expression of the mono-ADP-ribosyltransferase ART1 by tumor cells mediates immune resistance in non-small cell lung cancer

Most patients with non-small cell lung cancer (NSCLC) do not achieve durable clinical responses from immune checkpoint inhibitors, suggesting the existence of additional resistance mechanisms. Nicotinamide adenine dinucleotide (NAD)-induced cell death (NICD) of P2X7 receptor (P2X7R)-expressing T cells regulates immune homeostasis in inflamed tissues. This process is mediated by mono-adenosine 5'-diphosphate (ADP)-ribosyltransferases (ARTs). We found an association between membranous expression of ART1 on tumor cells and reduced CD8 T cell infiltration. Specifically, we observed a reduction in the P2X7R⁺ CD8 T cell subset in human lung adenocarcinomas. In vitro, P2X7R⁺ CD8 T cells were susceptible to ART1-mediated ADP-ribosylation and NICD, which was exacerbated upon blockade of the NAD⁺-degrading ADP-ribosyl cyclase CD38. Last, in murine NSCLC and melanoma models, we demonstrate that genetic and antibody-mediated ART1 inhibition slowed tumor growth in a CD8 T cell-dependent manner. This was associated with increased infiltration of activated P2X7R⁺CD8 T cells into tumors. In conclusion, we describe ART1-mediated NICD as a mechanism of immune resistance in NSCLC and provide preclinical evidence that antibody-mediated targeting of ART1 can improve tumor control, supporting pursuit of this approach in clinical studies.

The tale of TILs in breast cancer: A report from The International Immuno-Oncology Biomarker Working Group

The advent of immune-checkpoint inhibitors (ICI) in modern oncology has significantly improved survival in several cancer settings. A subgroup of women with breast cancer (BC) has immunogenic infiltration of lymphocytes with expression of programmed death-ligand 1 (PD-L1). These patients may potentially benefit from ICI targeting the programmed death 1 (PD-1)/PD-L1 signaling axis. The use of tumor-infiltrating lymphocytes (TILs) as predictive and prognostic biomarkers has been under intense examination. Emerging data suggest that TILs are associated with response to both cytotoxic treatments and immunotherapy, particularly for patients with triple-negative BC. In this review from The International Immuno-Oncology Biomarker Working Group, we discuss (a) the biological understanding of TILs, (b) their analytical and clinical validity and efforts toward the clinical utility in BC, and (c) the current status of PD-L1 and TIL testing across different continents, including experiences from low-to-middle-income countries, incorporating also the view of a patient advocate. This information will help set the stage for future approaches to optimize the understanding and clinical utilization of TIL analysis in patients with BC.

Something Old and Something New to Unleash the Power of Natural Killer Cells Against Metastases

Single-agent immunotherapy has improved outcomes for patients with cancer, but only a minority of patients respond, necessitating investigation of combinations of immunotherapy agents. In this issue of Cancer Immunology Research, Milling and colleagues show that neoadjuvant therapy with an intratumoral stimulator of interferon genes agonist combined with systemic IL2 and anti-PD-1 results in clearance of lung metastases mediated by natural killer cells in mouse models of triple-negative breast cancer.See related article by Milling et al. (4).

560 Immunotherapeutic and antimetastatic activity of LTX-315 in preclinical models of ICI-resistant breast cancer

Background

Oncolytic peptides are attractive tools for the development of novel anticancer regimens [1]. LTX-315 is a synthetic peptide with a marked capacity to elicit tumor-targeting immunity in preclinical cancer models [2]. Indeed, LTX-315 has been shown to elicit immunogenic cell death (ICD) in malignant cells [3, 4] and to deplete immunosuppressive cells such as CD4+CD25+FOXP3+ TREG cells and myeloid-derived suppressor cells (MDSCs) from the tumor microenvironment (TME) [5]. Accordingly, LTX-315 synergized with immunogenic chemotherapeutics or immune checkpoint inhibitors (ICIs) in preclinical tumor models [5, 6]. Moreover, recent findings from a Phase I clinical trial in patients with advanced solid tumors (NCT01986426) indicate that intratumoral LTX-315 is safe, clinically active, and elicits alterations in the TME that support the initiation of anticancer immunity [7, 8]. However, the dependency of LTX-315 therapeutic effects on the immune system in preclinical models of breast cancer has not been mechanistically investigated.

Methods

We harnessed three distinct mouse models of ICI-resistant breast cancer, namely hormone receptor (HR)-positive TS/A established and triple-negative breast cancer (TNBC) 4T1 cells established in immunocompetent syngeneic BALB/c mice, as well as medroxyprogesterone acetate (MPA, M)-initiated, 7,12-dimethylbenz[a]anthracene (DMBA, D)-driven mammary carcinomas evolving in C57BL/6 mice to assess the immunotherapeutic effects of LTX-315 optionally combined with radiation therapy (RT), based on the primary tumor growth, metastatic dissemination and overall survival (depending on model). Multilesion models, rechallenge assays, antibody-mediated depletion experiments as well as experiments in Rag1-/- mice were employed to elucidate the mechanistic involvement of the immune system.

Results

In the multilesion TS/A models, intratumoral LTX-315 to one lesion combined with hypofractionated RT to another lesion resulted in superior systemic disease control as manifested by eradication of a 3rd untreated lesion in up to 50% of mice, which were protected from a subsequent rechallenge with living TS/A cells. In the single lesion 4T1 model, LTX-315 mediated enable robust local and metastatic disease control, which could be enhanced (only locally) with RT and dependent on natural killer (NK) cells, but less so on T lymphocytes (as determined with anti-asialo GM1 antibodies and Rag1-/- hosts). In the M/D-driven model, LTX-315 considerably controlled the growth of primary tumors and delayed relapse, an effect that depended on NK cells (as demonstrated with anti-NK1.1 antibodies).

Conclusions

LTX-315, alone and combined with RT, mediates robust immunotherapeutic effects in multiple models of ICI-resistant breast cancer. Intriguingly, NK cells appear to be required for such effects, potentially linked to the emergence of immunological memory.

Acknowledgements

We are indebted to Dr. Fred Miller (Karmanos Cancer Center, Detroit, MI) for the kind gift of 4T1 cells, as well as to Dr. Karsten A. Pilones (Weill Cornell Medicine, New York, NY) and Maria E. Rodriguez-Ruiz (University of Navarra, Pamplona, Spain) for help with clonogenic assays. This work has been sponsored by a research grant by Lytix Biopharma (Oslo, Norway) to S.D. and L.G.

References

Kepp, O. et al. (2020) Oncolysis without viruses - inducing systemic anticancer immune responses with local therapies. Nat Rev Clin Oncol 17 (1), 49–64.

Vitale, I. et al. (2021) Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides. Trends Cancer 7 (6), 557–572.

Eike, L.M. et al. (2015) The oncolytic peptide LTX-315 induces cell death and DAMP release by mitochondria distortion in human melanoma cells. Oncotarget 6 (33), 34910–23.

Zhou, H. et al. (2016) The oncolytic peptide LTX-315 triggers immunogenic cell death. Cell Death Dis 7 (3), e2134.

Yamazaki, T. et al. (2016) The oncolytic peptide LTX-315 overcomes resistance of cancers to immunotherapy with CTLA4 checkpoint blockade. Cell Death Differ 23 (6), 1004–15.

Camilio, K.A. et al. (2019) Combining the oncolytic peptide LTX-315 with doxorubicin demonstrates therapeutic potential in a triple-negative breast cancer model. Breast Cancer Res 21 (1), 9.

Jebsen, N.L. et al. (2019) Enhanced T-lymphocyte infiltration in a desmoid tumor of the thoracic wall in a young woman treated with intratumoral injections of the oncolytic peptide LTX-315: a case report. J Med Case Rep 13 (1), 177.

Spicer, J. et al. (2021) Safety, Antitumor Activity, and T-cell Responses in a Dose-Ranging Phase I Trial of the Oncolytic Peptide LTX-315 in Patients with Solid Tumors. Clin Cancer Res 27 (10), 2755–2763.

Ethics Approval

This study was approved by Weill Cornell Medical College’s Ethics Board; approval number 2015-0028, 2018-0002.

264 SIRPa blockade synergizes with radiation therapy in murine breast cancer models

Background

Focal tumor radiation-therapy (RT) induces an immunogenic cell-death associated with endogenous adjuvants that promote uptake of cancer antigens by conventional dendritic cells (cDCs). The expression of CD47 is markedly increased in a high proportion of breast cancers (BC) and correlates with poor-prognosis molecular subtypes. CD47 interaction with SIRPα on cDCs and macrophages provides a negative signal that inhibits phagocytosis of dying cancer cells, hindering cross-presentation of tumor-derived antigens and activation of anti-tumor T cells. Thus, we hypothesized that the ”don’t-eat-me” signal mediated by CD47/SIRPα acts as a barrier to RT-induced anti-tumor immunity. Using two mouse BC models refractory to immune-checkpoint blockade, we investigated the effects of RT combined with SIRPα blockade on the development of anti-tumor immunity.

Methods

BALB/c or C57BL/6 mice were inoculated subcutaneously in one or both flanks with respectively TSA and AT-3 BC cells. RT was delivered to one tumor, 8Gy on 3 consecutive days once tumor volume reached 60–80mm3. SIRPα-blocking (MY1,1) or isotype antibodies were given one day prior to RT and every 3 days thereafter. Some mice received PD-L1-blocking Abs (BioXcell) every 3 days starting one day after RT completion. cDC depletion experiments were performed on AT-3 bearing C57BL/6 mice using the inducible diphtheria toxin-dependent CD11c-DTR model.2

Results

SIRPα-blockade alone did not inhibit TSA tumor growth, but significantly improved tumor response to RT (p<0.05), leading to complete regression of the irradiated tumor in 50–60% of the mice. In addition, SIRPα-blockade + RT combination significantly inhibited the growth (p<0.05) of contralateral non-irradiated tumors (abscopal response), suggesting that it induced a systemic anti-tumor immune response. Consistent with systemic immune activation, the percentage of PD1+CD4 T cells was increased in the spleen of mice treated with anti-SIRPα compared to control Abs (p<0.01), regardless of RT. In the myeloid compartment, cDC1 and macrophages showed increased PD-L1 expression. However, addition of anti-PD-L1 to RT + anti-SIRPα did not further improve abscopal responses. In the AT-3 model, SIRPα blockade significantly improved tumor control induced by RT (p<0.01) but no complete regression was observed. Depletion of cDC in AT-3 bearing mice abrogated the benefit of the combination of SIRPα blockade to RT.

Conclusions

Overall, our results support the hypothesis that SIRPα-blockade potentiates the ability of RT to induce anti-tumor T cell responses and improve local and systemic tumor control. We are currently investigating the mechanisms of RT interaction with SIRPα blockade to provide the rationale for translating these findings to the clinic

References

Noel Verjan Garcia, et al. SIRPα/CD172a regulates eosinophil homeostasis. The Journal of Immunology September 1, 2011;187(5):2268–2277.

Jung S, et al. In vivo depletion of CD11c+ dendritic cells abrogates priming of CD8+ T cells by exogenous cell-associated antigens. Immunity 2002;17(2):211–20.

LTX-315-enabled, radiotherapy-boosted immunotherapeutic control of breast cancer by NK cells

LTX-315 is a nonameric oncolytic peptide in early clinical development for the treatment of solid malignancies. Preclinical and clinical evidence indicates that the anticancer properties of LTX-315 originate not only from its ability to selectively kill cancer cells, but also from its capacity to promote tumor-targeting immune responses. Here, we investigated the therapeutic activity and immunological correlates of intratumoral LTX-315 administration in three syngeneic mouse models of breast carcinoma, with a focus on the identification of possible combinatorial partners. We found that breast cancer control by LTX-315 is accompanied by a reconfiguration of the immunological tumor microenvironment that supports the activation of anticancer immunity and can be boosted by radiation therapy. Mechanistically, depletion of natural killer (NK) cells compromised the capacity of LTX-315 to limit local and systemic disease progression in a mouse model of triple-negative breast cancer, and to extend the survival of mice bearing hormone-accelerated, carcinogen-driven endogenous mammary carcinomas. Altogether, our data suggest that LTX-315 controls breast cancer progression by engaging NK cell-dependent immunity.

Abstract LB168: Blocking SIRPα on myeloid cells synergizes with radiation therapy in mouse breast cancer models

Focal tumor radiation therapy (RT) induces an immunogenic cell death associated with endogenous adjuvants that promote uptake of cancer antigens by conventional dendritic cells (cDCs). The expression of CD47 is markedly increased in a high proportion of breast cancers (BC) and correlates with poor-prognosis molecular subtypes. CD47 interaction with SIRPα expressed at the surface of cDCs and macrophages provides a negative signal that inhibits phagocytosis of dying cancer cells, hindering cross-presentation of tumor-derived antigens and activation of anti-tumor T cells. Thus, we hypothesized that the “don't-eat-me” signal mediated by CD47/SIRPα acts as a barrier to RT-induced anti-tumor immunity. Using two mouse BC models refractory to immune checkpoint blockade, we investigated the effects of RT combined with SIRPα; blockade on the development of anti-tumor immunity. BALB/c mice were inoculated subcutaneously in one or both flanks with the syngeneic TSA BC cells. RT was delivered to one tumor in 8 Gy doses on three consecutive days once tumor volume reached 60-80 mm3. SIRPα; blocking (MY1, OSAKA University [Garcia, et al. J Immunol. 2011;187:2268]) or isotype control antibodies (Abs) were given one day prior to RT and every 3 days thereafter. Some mice also received PD-L1 blocking Abs (BioXcell) every 3 days starting one day after RT completion. Mice were followed for tumor growth and splenic immune cells were analyzed by flow cytometry. Similar experiments were performed in the AT-3 mouse model of triple-negative BC (C57BL/6 background). SIRPα; blockade alone did not inhibit TSA tumor growth, but it significantly improved tumor response to RT (p&lt;0.05), leading to complete regression of the irradiated tumor in 50-60% of the mice. In addition, the combination of SIRPα; blockade with RT significantly inhibited the growth (p&lt;0.05) of a contralateral non-irradiated tumor (abscopal response), suggesting that it induced a systemic anti-tumor immune response. Consistent with systemic immune activation induced by SIRPα; blockade, the percentage of PD1+ CD4 T cells was increased in the spleen of mice treated with SIRPα; Abs compared to control Abs (p&lt;0.01), regardless of RT. In the myeloid compartment, SIRPα; blockade led to a reduction in PD-L1 expression on type 2 conventional DC (cDC2) whereas cDC1 and macrophages showed increased PD-L1 expression. However, addition of anti-PD-L1 to RT+anti-SIRPα; did not further improve abscopal responses. The ability of SIRPα; blockade to significantly improve tumor control induced by RT was also seen in the AT-3 model (p&lt;0.01).Overall, obtained results support the hypothesis that SIRPα; blockade potentiates the ability of RT to induce anti-tumor T cell responses and improve local and systemic tumor control. We are currently investigating the mechanisms of RT interaction with SIRPα; blockade to provide the rationale for translating these findings to the clinic.

Citation Format: Claire Lhuillier, Maud Charpentier, Sergio Trombetta, Sandra Demaria. Blocking SIRPα on myeloid cells synergizes with radiation therapy in mouse breast cancer models [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 LB168.

Perspectives in immunotherapy: meeting report from the immunotherapy bridge (December 2nd-3rd, 2020, Italy)

Improved understanding of tumor immunology has enabled the development of therapies that harness the immune system and prevent immune escape. Numerous clinical trials and real-world experience has provided evidence of the potential for long-term survival with immunotherapy in various types of malignancy. Recurring observations with immuno-oncology agents include their potential for clinical application across a broad patient population with different tumor types, conventional and unconventional response patterns, durable responses, and immune-related adverse events. Despite the substantial achievements to date, a significant proportion of patients still fail to benefit from current immunotherapy options, and ongoing research is focused on transforming non-responders to responders through the development of novel treatments, new strategies to combination therapy, adjuvant and neoadjuvant approaches, and the identification of biomarkers of response. These topics were the focus of the virtual Immunotherapy Bridge (December 2nd-3rd, 2020), organized by the Fondazione Melanoma Onlus, Naples, Italy, in collaboration with the Society for Immunotherapy of Cancer and are summarised in this report.

Abstract PO-051: Radiation therapy enhances the presentation of phosphopeptides by MHC-I on cancer cells

Background: Cancer immunotherapy relies on presentation of immunogenic peptides on major histocompatibility complex class-I (MHC-I) by the cancer cells that are recognized by cytotoxic CD8+ T cells. We have shown that radiation therapy (RT) enhances the presentation of immunogenic mutations in a lung cancer patient with complete response to RT and ipilimumab.1 In addition to the cancer mutanome, neoantigens generated by post-translational modifications like phosphorylation have been shown to be the targets of tumor-specific T cells.2,3 RT elicits changes in many signaling pathways involved in the response to DNA damage. Thus, we tested the hypothesis that the RT-modulated cellular phosphoproteome will result in qualitative and quantitative changes in the phosphopeptides (pPeptides) presented by MHC-I of cancer cells. Methods: Human breast adenocarcinoma MDA-MB-231 cells were irradiated daily with 8 Gy in three consecutive days (8 Gyx3) or left untreated. At 24 hours following the last RT dose, cells were harvested and MHC-I bound peptides were affinity-purified using the human MHC-I (A, B and C allele) specific W-6/32 antibody. High resolution LC-MS/MS was used to analyze the immunopeptidome according to established protocols.4 Pathway analysis of peptides was carried out in Qiagen Ingenuity Pathway Analysis. Results: Radiation increased the expression of MHC-I on the surface of MDA-MB-231 cells and the number of unique MHC-I bound peptides presented by the cells (mean 1918 in control vs 6180 in RT, n=3, p=0.0008). The total number of phosphorylated MHC-I ligands was increased 11-fold, representing, on average, 0.17% of ligands in untreated cells and 0.61% in irradiated cells (p=0.005). Phosphorylation usually occurred on serine or threonine residues and was found predominantly in position 4 or 5 of the peptide. The phosphorylated amino acid was often followed by proline, and stabilized by positively charged amino acids at either the +3 or -3 position relative to the phosphorylation site. The pPeptides presented only by the irradiated cells (and identified in at least 2 out of 3 samples) were derived from proteins belonging to pathways activated by radiation, including p53 and hypoxia signaling (HIF1a, JUN), regulation of cell proliferation (TGFl1, BCAR3) and senescence (CDC25B, JUN). Conclusions: Our results show, for the first time, that RT enhances the presentation of pPeptides by MHC-I. RT enhanced both the number and repertoire of pPeptides bound to surface MHC-I of cancer cells. Given the ability of pPeptides to serve as cancer antigens that are recognized by T cells, our data suggests that one way RT increases tumor immunogenicity may be through inducing the presentation of novel pPeptides. This hypothesis is being tested in ongoing studies.

References: 1.Formenti SC, et al. Nat Med 2018;24. 2.Engelhard VH, et al. J Immunother Cancer 2020;8. 3.Zarling AL, et al. J Exp Med 2000;192:1755-62. 4.Klatt MG, et al. J Proteomics 2020;228:103921.

Citation Format: Samantha J. Van Nest, Tomer M. Yaron, Martin G. Klatt, Noah E. Dephoure, Gad Getz, Laura Santambrogio, Olivier Elemento, David Scheinberg, Sandra Demaria, Lewis C. Cantley. Radiation therapy enhances the presentation of phosphopeptides by MHC-I on cancer cells [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-051.

The role of radiotherapy in the age of immunotherapy

With the development of immune checkpoint inhibitors, the efficacy of immunotherapy as a cancer treatment that is effective against multiple tumor types has been established, and this modality came to be considered as the fourth pillar of cancer therapy. The clinical success of immunotherapy greatly changed the field of oncology by highlighting the importance of the immune system in cancer control and elimination. It has now become clear that research into, and the clinical application of, the immune response are important for effective cancer treatment. Moreover, it has become apparent that conventional cancer treatments, such as radiotherapy and chemotherapy, can modulate the cross-talk between the tumor and the immune system, and their efficacy depends, in part, on the ability to elicit antitumor immune response. The ability of radiotherapy to induce an immune response has become relevant in the immunotherapy age. Radiotherapy has been redefined as a partner for cancer immunotherapy, based on evidence indicating the potential synergistic effect of the combination of these therapeutic modalities. This review outlines the major findings reported to date on the immune response induced by radiotherapy and discusses the role of radiotherapy in combination with immunotherapy. Furthermore, we introduce research aimed at the clinical application of combination therapy and discuss its potential in clinical practice and future issues.

Radiation dose and fraction in immunotherapy: one-size regimen does not fit all settings, so how does one choose?

Recent evidence indicates that ionizing radiation can enhance immune responses to tumors. Advances in radiation delivery techniques allow hypofractionated delivery of conformal radiotherapy. Hypofractionation or other modifications of standard fractionation may improve radiation’s ability to promote immune responses to tumors. Other novel delivery options may also affect immune responses, including T-cell activation and tumor-antigen presentation changes. However, there is limited understanding of the immunological impact of hypofractionated and unique multifractionated radiotherapy regimens, as these observations are relatively recent. Hence, these differences in radiotherapy fractionation result in distinct immune-modulatory effects. Radiation oncologists and immunologists convened a virtual consensus discussion to identify current deficiencies, challenges, pitfalls and critical gaps when combining radiotherapy with immunotherapy and making recommendations to the field and advise National Cancer Institute on new directions and initiatives that will help further development of these two fields.

This commentary aims to raise the awareness of this complexity so that the need to study radiation dose, fractionation, type and volume is understood and valued by the immuno-oncology research community. Divergence of approaches and findings between preclinical studies and clinical trials highlights the need for evaluating the design of future clinical studies with particular emphasis on radiation dose and fractionation, immune biomarkers and selecting appropriate end points for combination radiation/immune modulator trials, recognizing that direct effect on the tumor and potential abscopal effect may well be different. Similarly, preclinical studies should be designed as much as possible to model the intended clinical setting. This article describes a conceptual framework for testing different radiation therapy regimens as separate models of how radiation itself functions as an immunomodulatory ‘drug’ to provide alternatives to the widely adopted ‘one-size-fits-all’ strategy of frequently used 8 Gy×3 regimens immunomodulation.

Preventive efficacy of a tenofovir alafenamide fumarate nanofluidic implant in SHIV-challenged nonhuman primates

Pre-exposure prophylaxis (PrEP) using antiretroviral oral drugs is effective at preventing HIV transmission when individuals adhere to the dosing regimen. Tenofovir alafenamide (TAF) is a potent antiretroviral drug, with numerous long-acting (LA) delivery systems under development to improve PrEP adherence. However, none has undergone preventive efficacy assessment. Here we show that LA TAF using a novel subcutaneous nanofluidic implant (nTAF) confers partial protection from HIV transmission. We demonstrate that sustained subcutaneous delivery through nTAF in rhesus macaques maintained tenofovir diphosphate concentration at a median of 390.00 fmol/106 peripheral blood mononuclear cells, 9 times above clinically protective levels. In a non-blinded, placebo-controlled rhesus macaque study with repeated low-dose rectal SHIVSF162P3 challenge, the nTAF cohort had a 62.50% reduction (95% CI: 1.72% to 85.69%; p=0.068) in risk of infection per exposure compared to the control. Our finding mirrors that of tenofovir disoproxil fumarate (TDF) monotherapy, where 60.00% protective efficacy was observed in macaques, and clinically, 67.00% reduction in risk with 86.00% preventive efficacy in individuals with detectable drug in the plasma. Overall, our nanofluidic technology shows potential as a subcutaneous delivery platform for long-term PrEP and provides insights for clinical implementation of LA TAF for HIV prevention.

Radiotherapy-exposed CD8+ and CD4+ neoantigens enhance tumor control

Neoantigens generated by somatic nonsynonymous mutations are key targets of tumor-specific T cells, but only a small number of mutations predicted to be immunogenic are presented by MHC molecules on cancer cells. Vaccination studies in mice and patients have shown that the majority of neoepitopes that elicit T cell responses fail to induce significant antitumor activity, for incompletely understood reasons. We report that radiotherapy upregulates the expression of genes containing immunogenic mutations in a poorly immunogenic mouse model of triple-negative breast cancer. Vaccination with neoepitopes encoded by these genes elicited CD8+ and CD4+ T cells that, whereas ineffective in preventing tumor growth, improved the therapeutic efficacy of radiotherapy. Mechanistically, neoantigen-specific CD8+ T cells preferentially killed irradiated tumor cells. Neoantigen-specific CD4+ T cells were required for the therapeutic efficacy of vaccination and acted by producing Th1 cytokines, killing irradiated tumor cells, and promoting epitope spread. Such a cytotoxic activity relied on the ability of radiation to upregulate class II MHC molecules as well as the death receptors FAS/CD95 and DR5 on the surface of tumor cells. These results provide proof-of-principle evidence that radiotherapy works in concert with neoantigen vaccination to improve tumor control.

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.

Liver Metastasis Irradiation Can Restore Immunotherapeutic Responsiveness

Allogeneic liver transplants tolerize the immune system, preventing organ rejection from the same donor. A recent article by Yu et al. shows that liver metastases can likewise prevent tumor rejection in immunotherapy-treated murine and human hosts. Furthermore, radiation can reprogram the liver microenvironment to restore systemic tumor rejection.

Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides

Accumulating preclinical and clinical evidence indicates that high degrees of heterogeneity among malignant cells constitute a considerable obstacle to the success of cancer therapy. This calls for the development of approaches that operate - or enable established treatments to operate - despite such intratumoral heterogeneity (ITH). In this context, oncolytic peptides stand out as promising therapeutic tools based on their ability to drive immunogenic cell death associated with robust anticancer immune responses independently of ITH. We review the main molecular and immunological pathways engaged by oncolytic peptides, and discuss potential approaches to combine these agents with modern immunotherapeutics in support of superior tumor-targeting immunity and efficacy in patients with cancer.

Activin A Promotes Regulatory T-cell-Mediated Immunosuppression in Irradiated Breast Cancer

Increased regulatory T cells (Treg) after radiotherapy have been reported, but the mechanisms of their induction remain incompletely understood. TGFβ is known to foster Treg differentiation within tumors and is activated following radiotherapy. Thus, we hypothesized that TGFβ blockade would result in decreased Tregs within the irradiated tumor microenvironment. We found increased Tregs in the tumors of mice treated with focal radiotherapy and TGFβ blockade. This increase was mediated by upregulation of another TGFβ family member, activin A. In vitro, activin A secretion was increased following irradiation of mouse and human breast cancer cells, and its expression was further enhanced upon TGFβ blockade. In vivo, dual blockade of activin A and TGFβ was required to decrease intratumoral Tregs in the context of radiotherapy. This resulted in an increase in CD8⁺ T-cell priming and was associated with a reduced tumor recurrence rate. Combination of immune checkpoint inhibitors with the dual blockade of activin A and TGFβ led to the development of tumor-specific memory responses in irradiated breast cancer. Supporting the translational value of activin A targeting to reduce Treg-mediated immunosuppression, retrospective analysis of a public dataset of patients with breast cancer revealed a positive correlation between activin A gene expression and Treg abundance. Overall, these results shed light on an immune escape mechanism driven by activin A and suggest that dual targeting of activin A and TGFβ may be required to optimally unleash radiation-induced antitumor immunity against breast cancer.

Converging focal radiation and immunotherapy in a preclinical model of triple negative breast cancer: contribution of VISTA blockade

Antibodies targeting the co-inhibitory receptor programmed cell death 1 (PDCD1, best known as PD-1) or its main ligand CD274 (best known as PD-L1) have shown some activity in patients with metastatic triple-negative breast cancer (TNBC), especially in a recent Phase III clinical trial combining PD-L1 blockade with taxane-based chemotherapy. Despite these encouraging findings, however, most patients with TNBC fail to derive significant benefits from PD-L1 blockade, calling for the identification of novel therapeutic approaches. Here, we used the 4T1 murine mammary cancer model of metastatic and immune-resistant TNBC to test whether focal radiation therapy (RT), a powerful inducer of immunogenic cell death, in combination with various immunotherapeutic strategies can overcome resistance to immune checkpoint blockade. Our results suggest that focal RT enhances the therapeutic effects of PD-1 blockade against primary 4T1 tumors and their metastases. Similarly, the efficacy of an antibody specific for V-set immunoregulatory receptor (VSIR, another co-inhibitory receptor best known as VISTA) was enhanced by focal RT. Administration of cyclophosphamide plus RT and dual PD-1/VISTA blockade had superior therapeutic effects, which were associated with activation of tumor-infiltrating CD8⁺ T cells and depletion of intratumoral granulocytic myeloid-derived suppressor cells (MDSCs). Overall, these results demonstrate that RT can sensitize immunorefractory tumors to VISTA or PD-1 blockade, that this effect is enhanced by the addition of cyclophosphamide and suggest that a multipronged immunotherapeutic approach may also be required to increase the incidence of durable responses in patients with TNBC.

Viral load Reduction in SHIV-Positive Nonhuman Primates via Long-Acting Subcutaneous Tenofovir Alafenamide Fumarate Release from a Nanofluidic Implant

HIV-1 is a chronic disease managed by strictly adhering to daily antiretroviral therapy (ART). However, not all people living with HIV-1 have access to ART, and those with access may not adhere to treatment regimens increasing viral load and disease progression. Here, a subcutaneous nanofluidic implant was used as a long-acting (LA) drug delivery platform to address these issues. The device was loaded with tenofovir alafenamide (TAF) and implanted in treatment-naïve simian HIV (SHIV)-positive nonhuman primates (NHP) for a month. We monitored intracellular tenofovir-diphosphate (TFV-DP) concentration in the target cells, peripheral blood mononuclear cells (PBMC). The concentrations of TFV-DP were maintained at a median of 391.0 fmol/106 cells (IQR, 243.0 to 509.0 fmol/106 cells) for the duration of the study. Further, we achieved drug penetration into lymphatic tissues, known for persistent HIV-1 replication. Moreover, we observed a first-phase viral load decay of -1.14 ± 0.81 log10 copies/mL (95% CI, -0.30 to -2.23 log10 copies/mL), similar to -1.08 log10 copies/mL decay observed in humans. Thus, LA TAF delivered from our nanofluidic implant had similar effects as oral TAF dosing with a lower dose, with potential as a platform for LA ART.

Perspectives in melanoma: meeting report from the "Melanoma Bridge" (December 5th-7th, 2019, Naples, Italy)

The melanoma treatment landscape changed in 2011 with the approval of the first anti-cytotoxic T-lymphocyte-associated protein (CTLA)-4 checkpoint inhibitor and of the first BRAF-targeted monoclonal antibody, both of which significantly improved overall survival (OS). Since then, improved understanding of the tumor microenvironment (TME) and tumor immune-evasion mechanisms has resulted in new approaches to targeting and harnessing the host immune response. The approval of new immune and targeted therapies has further improved outcomes for patients with advanced melanoma and other combination modalities are also being explored such as chemotherapy, radiotherapy, electrochemotherapy and surgery. In addition, different strategies of drugs administration including sequential or combination treatment are being tested. Approaches to overcome resistance and to potentiate the immune response are being developed. Increasing evidence emerges that tissue and blood-based biomarkers can predict the response to a therapy. The latest findings in melanoma research, including insights into the tumor microenvironment and new biomarkers, improved understanding of tumor immune response and resistance, novel approaches for combination strategies and the role of neoadjuvant and adjuvant therapy, were the focus of discussions at the Melanoma Bridge meeting (5-7 December, 2019, Naples, Italy), which are summarized in this report.

Emerging technologies for local cancer treatment

The fundamental limitations of systemic therapeutic administration have prompted the development of local drug delivery platforms as a solution to increase effectiveness and reduce side effects. By confining therapeutics to the site of disease, local delivery technologies can enhance therapeutic index. This review highlights recent advances and opportunities in local drug delivery strategies for cancer treatment in addition to challenges that need to be addressed to facilitate clinical translation. The benefits of local cancer treatment combined with technological advancements and increased understanding of the tumor microenvironment, present a prime breakthrough opportunity for safer and more effective therapies.

Abstract 2158: ART1 tumor expression mediates immune resistance in non-small cell lung cancer by elimination of P2 × 7R+ CD8 tissue resident memory T cells and conventional type I dendritic cells

Extracellular NAD+ (eNAD) is released from stressed and dying cells where it acts as a proinflammatory mediator. However, in the presence of mono-ADP-ribosyltransferases (ARTs) eNAD serves as a substrate for ADP-ribosylation of the P2 × 7 receptor (P2RX7), resulting in NAD-induced cell death (NICD). P2RX7 is expressed on several immune cells including CD103+ conventional type I dendritic cells (cDC1s) which are essential for initiation of tumor-specific immune responses as well as on tissue resident memory T cells (TRMs), of which high tumor infiltration has been associated with improved survival in non-small cell lung cancer (NSCLC) [1]. NICD of P2 × 7R+ TRMs was recently identified as a regulator of TRM tissue homeostasis [2]. CD38 is expressed on activated immune cells and can reduce eNAD levels by converting eNAD into ADPR. We tested the hypothesis that ART1 expression in NSCLC constitutes a mechanism of immune resistance by mediating NICD of P2 × 7R+ TRMs and P2 × 7R+ cDC1s.

ART1 expression in human NSCLC samples was determined by immunohistochemistry scoring of NSCLC tumors using a tissue microarray (TMA) (n=493). In addition, matched tumor and adjacent normal lung tissue samples were analyzed for ART1 expression by qPCR (n=40) and for infiltration of TRM and cDC1s by flow cytometry. A mouse KP1 lung tumor cell line with high ART1 expression was established from KRASG12D/P53−/− mice and transduced with a doxycycline-inducible shRNA targeting ART1 (ART1KD). KP1 cells and their derivatives were intravenously injected into syngeneic C57BL/6 mice to generate orthotopic lung tumors. Lung tumor nodules were enumerated two weeks after tumor inoculation using H&E-stained FFPE lung sections and lung-derived cell suspensions were analyzed by flow cytometry for infiltration of T cell and DC subsets.

Increased expression of ART1 in tumor compared to normal lung was observed in 55% of NSCLC samples by TMA analysis, and confirmed by qPCR. The frequency of P2RX7+ CD8 TRMs (p&lt;0.05) and P2 × 7R+ cDC1s (p&lt;0.01) were reduced in ART1+ tumors compared to matched normal lung tissue. In line with the hypothesis that CD38 protects P2 × 7R+ cells from ART1-mediated NICD, P2 × 7R+ CD8 TRMs and P2 × 7R+ cDC1s present within ART1+ tumors had elevated expression of CD38. In mice, knockdown of ART1 in KP1 tumors resulted in significantly delayed growth in immunocompetent mice (p&lt;0.001) but not in nude or CD8-depeleted mice. In an orthotopic lung model, ART1KD resulted in a 75% decrease in lung metastatic nodules (p&lt;0.01) and was associated with increased infiltration of CD8 T cells (P&lt;0.0001) and cDC1s (p&lt;0.01). In vitro experiments confirmed that CD38- P2RX7+ CD8 T cells were susceptible to ADP-ribosylation and NICD when co-cultured with ART1high lung tumor cells, while P2 × 7R+ CD8 T cells that co-expressed CD38 were resistant to NICD.

In conclusion, we show that ART1 is overexpressed in NSCLC and identify ART1-mediated NICD of P2 × 7R+ TRMs and cDC1s as a possible novel immune escape mechanism in NSCLC.

Furthermore, we describe a novel role of CD38 expression on immune cells in its protection against NICD.

1. Nizard, M., et al., Induction of resident memory T cells enhances the efficacy of cancer vaccine. Nat Commun, 2017. 8: p. 15221.

2. Stark, R., et al., T RM maintenance is regulated by tissue damage via P2RX7. Sci Immunol, 2018. 3(30).

Citation Format: Erik Wennerberg, Clarey Hung, Amanda Valeta, Timothy McGraw, Sandra Demaria, Brendon Stiles. ART1 tumor expression mediates immune resistance in non-small cell lung cancer by elimination of P2 × 7R+ CD8 tissue resident memory T cells and conventional type I dendritic cells [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 2158.

Abstract 2263: Characteristics of the interferon-stimulatory DNA cargo of exosomes produced by irradiated breast cancer cells

Radiation therapy (RT) used at immunogenic doses (8GyX3) leads to cytosolic accumulation of DNA that binds to the DNA sensor cGAS and activates the cGAMP synthesis, resulting in STING activation and downstream interferon type I (IFN-I) production by cancer cells [1-3]. RT-induced IFN-I is critical for effective anti-tumor immune responses in combination with immune-checkpoint blockade therapy [1]. We have recently demonstrated that tumor-derived exosomes (TEX) secreted by irradiated (8GyX3) TSA murine carcinoma cells (RT-TEX) contain more DNA compared to TEX produced by untreated cells (UT-TEX). Interestingly, only the DNA carried by RT-TEX is capable of STING-dependent activation of recipient dendritic cells (DCs) resulting in CD40, CD80 and CD86 upregulation and IFN-I production. Mice vaccination with RT-TEX, but not UT-TEX, elicits tumor-specific CD8+ T-cell responses that protect mice from tumor development [4]. Here, we tested the hypothesis that not only quantitative but also qualitative differences between the DNA cargo of RT-TEX and UT-TEX may explain its differential ability to activate DCs. To this end, internal DNA purified from TEX and from the cytosolic fraction of the parent TSA cells was characterized for length using Agilent Bioanalyzer. Furthermore, DNA TEX was analyzed by whole-genome sequencing (WGS) and by whole-genome bisulfite sequencing for methylation status. In addition, the percentage of global methylation of DNA of the TSA cells was quantified by 5-methyl cytosine DNA Elisa kit. All experiments were performed in biological triplicates. DNA size analysis revealed an enrichment of DNA fragments with size between 60 and 250 bp in RT-TEX compared to UT-TEX, and in the cytosolic fraction of irradiated compared to untreated TSA cells. The WGS showed that the entire genome was represented in DNA contained within TEX, regardless of the treatment of the parent cells. More than 99% of TEX DNA was of nuclear origin, but mitochondrial DNA was increased in RT-TEX (6.2 fold change, p=0.006). Interestingly, the RT treatment increases the DNA abundance of several regions (median p=0.006). Interestingly, we found reduced levels of methylation in exosomal and total DNA purified from irradiated compared to untreated TSA cells. Our data support the hypothesis that there are potentially important qualitative differences in the DNA cargo of TEX derived from irradiated compared to untreated cancer cells that reflect molecular changes occurring in parent cells. For instance, the enrichment in DNA fragments with size between 60-250 bp in RT-TEX is especially intriguing in light of the recent report that cGAS is optimally activated by this DNA length range [5]. The impact of these qualitative differences in the cargo DNA on activation of the IFN-I pathway in innate immune cells that uptake TEX is under investigation. Identification of DNA signature associated with TEX ability to activate the cGAS/STING pathway could provide a blood-based biomarker for the immunogenic tumor response to radiotherapy.

Citation Format: Sheila Spada, Paul Zumbo, Doron Betel, Tuo Zhang, Nils-Petter Rudqvist, Sandra Demaria. Characteristics of the interferon-stimulatory DNA cargo of exosomes produced by irradiated breast cancer cells [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 2263.

IL15 synergizes with radiotherapy to reprogram the tumor immune contexture through a dendritic cell connection

IL15 is a key cytokine for the activation and survival of anti-tumor effectors CD8⁺ T and NK cells. Recently published preclinical studies demonstrate that the therapeutic activity of IL15 requires conventional dendritic cells type 1 (cDC1). Radiotherapy cooperates with IL15 by enhancing cDC1 tumor infiltration via interferon type 1 activation.

Radiation-induced Adaptive Response: New Potential for Cancer Treatment

Radiotherapy is highly effective due to its ability to physically focus the treatment to target the tumor while sparing normal tissue and its ability to be combined with systemic therapy. This systemic therapy can be utilized before radiotherapy as an adjuvant or induction treatment, during radiotherapy as a radiation "sensitizer," or following radiotherapy as a part of combined modality therapy. As part of a unique concept of using radiation as "focused biology," we investigated how tumors and normal tissues adapt to clinically relevant multifraction (MF) and single-dose (SD) radiation to observe whether the adaptations can induce susceptibility to cell killing by available drugs or by immune enhancement. We identified an adaptation occurring after MF (3 × 2 Gy) that induced cell killing when AKT-mTOR inhibitors were delivered following cessation of radiotherapy. In addition, we identified inducible changes in integrin expression 2 months following cessation of radiotherapy that differ between MF (1 Gy × 10) and SD (10 Gy) that remain targetable compared with preradiotherapy. Adaptation is reflected across different "omics" studies, and thus the range of possible molecular targets is not only broad but also time, dose, and schedule dependent. While much remains to be studied about the radiation adaptive response, radiation should be characterized by its molecular perturbations in addition to physical dose. Consideration of the adaptive effects should result in the design of a tailored radiotherapy treatment plan that accounts for specific molecular changes to be targeted as part of precision multimodality cancer treatment.