Rapid functional impairment of natural killer cells following tumor entry limits anti-tumor immunity

Immune cell dysfunction within the tumor microenvironment (TME) undermines the control of cancer progression. Established tumors contain phenotypically distinct, tumor-specific natural killer (NK) cells; however, the temporal dynamics, mechanistic underpinning and functional significance of the NK cell compartment remains incompletely understood. Here, we use photo-labeling, combined with longitudinal transcriptomic and cellular analyses, to interrogate the fate of intratumoral NK cells. We reveal that NK cells rapidly lose effector functions and adopt a distinct phenotypic state with features associated with tissue residency. NK cell depletion from established tumors did not alter tumor growth, indicating that intratumoral NK cells cease to actively contribute to anti-tumor responses. IL-15 administration prevented loss of function and improved tumor control, generating intratumoral NK cells with both tissue-residency characteristics and enhanced effector function. Collectively, our data reveals the fate of NK cells after recruitment into tumors and provides insight into how their function may be revived.

Tumour-retained activated CCR7+ dendritic cells are heterogeneous and regulate local anti-tumour cytolytic activity

Tumour dendritic cells (DCs) internalise antigen and upregulate CCR7, which directs their migration to tumour-draining lymph nodes (dLN). CCR7 expression is coupled to an activation programme enriched in regulatory molecule expression, including PD-L1. However, the spatio-temporal dynamics of CCR7+ DCs in anti-tumour immune responses remain unclear. Here, we use photoconvertible mice to precisely track DC migration. We report that CCR7+ DCs are the dominant DC population that migrate to the dLN, but a subset remains tumour-resident despite CCR7 expression. These tumour-retained CCR7+ DCs are phenotypically and transcriptionally distinct from their dLN counterparts and heterogeneous. Moreover, they progressively downregulate the expression of antigen presentation and pro-inflammatory transcripts with more prolonged tumour dwell-time. Tumour-residing CCR7+ DCs co-localise with PD-1+CD8+ T cells in human and murine solid tumours, and following anti-PD-L1 treatment, upregulate stimulatory molecules including OX40L, thereby augmenting anti-tumour cytolytic activity. Altogether, these data uncover previously unappreciated heterogeneity in CCR7+ DCs that may underpin a variable capacity to support intratumoural cytotoxic T cells.

Age-induced changes in anti-tumor immunity alter the tumor immune infiltrate and impact response to immuno-oncology treatments

Introduction

Immuno-oncology (IO) research relies heavily on murine syngeneic tumor models. However, whilst the average age for a cancer diagnosis is 60 years or older, for practical purposes the majority of preclinical studies are conducted in young mice, despite the fact that ageing has been shown to have a significant impact on the immune response.

Methods

Using aged (60-72 weeks old) mice bearing CT26 tumors, we investigated the impact of ageing on tumor growth as well as the immune composition of the tumor and peripheral lymphoid organs.

Results

We found many differences in the immune cell composition of both the tumor and tumor-draining lymph node between aged and young mice, such as a reduction in the naïve T cell population and a decreased intratumoral CD8/Treg ratio in aged animals. We hypothesized that these differences may contribute to impaired anti-cancer immune responses in aged mice and therefore assessed the anti-tumor efficacy of different IO therapies in aged mice, including both co-stimulation (using an anti-OX40 antibody) and immune checkpoint blockade (using anti-PD-L1 and anti-CTLA-4 antibodies). Whilst aged mice retained the capacity to generate anti-tumor immune responses, these were significantly attenuated when compared to the responses observed in young mice.

Discussion

These differences highlight the importance of age-related immunological changes in assessing and refining the translational insights gained from preclinical mouse models.

Defining the spatial distribution of extracellular adenosine revealed a myeloid-dependent immunosuppressive microenvironment in pancreatic ductal adenocarcinoma

BACKGROUND

The prognosis for patients with pancreatic ductal adenocarcinoma (PDAC) remains extremely poor. It has been suggested that the adenosine pathway contributes to the ability of PDAC to evade the immune system and hence, its resistance to immuno-oncology therapies (IOT), by generating extracellular adenosine (eAdo).

METHODS

Using genetically engineered allograft models of PDAC in syngeneic mice with defined and different immune infiltration and response to IOT and autochthonous tumors in KPC mice we investigated the impact of the adenosine pathway on the PDAC tumor microenvironment (TME). Flow cytometry and imaging mass cytometry (IMC) were used to characterize the subpopulation frequency and spatial distribution of tumor-infiltrating immune cells. Mass spectrometry imaging (MSI) was used to visualize adenosine compartmentalization in the PDAC tumors. RNA sequencing was used to evaluate the influence of the adenosine pathway on the shaping of the immune milieu and correlate our findings to published data sets in human PDAC.

RESULTS

We demonstrated high expression of adenosine pathway components in tumor-infiltrating immune cells (particularly myeloid populations) in the murine models. MSI demonstrated that extracellular adenosine distribution is heterogeneous in tumors, with high concentrations in peri-necrotic, hypoxic regions, associated with rich myeloid infiltration, demonstrated using IMC. Protumorigenic M2 macrophages express high levels of the Adora2a receptor; particularly in the IOT resistant model. Blocking the in vivo formation and function of eAdo (Adoi), using a combination of anti-CD73 antibody and an Adora2a inhibitor slowed tumor growth and reduced metastatic burden. Additionally, blocking the adenosine pathway improved the efficacy of combinations of cytotoxic agents or immunotherapy. Adoi remodeled the TME, by reducing the infiltration of M2 macrophages and regulatory T cells. RNA sequencing analysis showed that genes related to immune modulation, hypoxia and tumor stroma were downregulated following Adoi and a specific adenosine signature derived from this is associated with a poorer prognosis in patients with PDAC.

CONCLUSIONS

The formation of eAdo promotes the development of the immunosuppressive TME in PDAC, contributing to its resistance to conventional and novel therapies. Therefore, inhibition of the adenosine pathway may represent a strategy to modulate the PDAC immune milieu and improve therapy response in patients with PDAC.

Small gene networks delineate immune cell states and characterize immunotherapy response in melanoma

Single-cell technologies have elucidated mechanisms responsible for immune checkpoint inhibitor (ICI) response, but are not amenable to a clinical diagnostic setting. In contrast, bulk RNA sequencing (RNA-seq) is now routine for research and clinical applications. Our workflow uses transcription factor (TF)-directed co-expression networks (regulons) inferred from single-cell RNA-seq data to deconvolute immune functional states from bulk RNA-seq data. Regulons preserve the phenotypic variation in CD45+ immune cells from metastatic melanoma samples (n=19, discovery dataset) treated with ICIs, despite reducing dimensionality by > 100-fold. Four cell states, termed exhausted T cells, monocyte lineage cells, memory T cells, and B cells were associated with therapy response; and were characterized by differentially active and cell-state specific regulons. Clustering of bulk RNA-seq melanoma samples from four independent studies (n=209, validation dataset) according to regulon-inferred scores identified four groups with significantly different response outcomes (p < 0.001). An intercellular link was established between exhausted T cells and monocyte lineage cells, whereby their cell numbers were correlated, and exhausted T cells predicted prognosis as a function of monocyte lineage cell number. The ligand-receptor expression analysis suggested that monocyte lineage cells drive exhausted T cells into terminal exhaustion through programs that regulate antigen presentation, chronic inflammation, and negative co-stimulation. Together, our results demonstrate how regulon-based characterization of cell states provide robust and functionally informative markers that can deconvolve bulk RNA-seq data to identify ICI responders.

Strategies for clinical dose optimization of T cell-engaging therapies in oncology

Innovative approaches in the design of T cell-engaging (TCE) molecules are ushering in a new wave of promising immunotherapies for the treatment of cancer. Their mechanism of action, which generates an in trans interaction to create a synthetic immune synapse, leads to complex and interconnected relationships between the exposure, efficacy, and toxicity of these drugs. Challenges thus arise when designing optimal clinical dose regimens for TCEs with narrow therapeutic windows, with a variety of dosing strategies being evaluated to mitigate key side effects such as cytokine release syndrome, neurotoxicity, and on-target off-tumor toxicities. This review evaluates the current approaches to dose optimization throughout the preclinical and clinical development of TCEs, along with perspectives for improvement of these strategies. Quantitative approaches used to aid the understanding of dose-exposure-response relationships are highlighted, along with opportunities to guide the rational design of next-generation TCE molecules, and optimize their dose regimens in patients.

Characterization of a novel potency endpoint for the evaluation of immune checkpoint blockade in humanized mice

Introduction

Humanized mice are emerging as valuable models to experimentally evaluate the impact of different immunotherapeutics on the human immune system. These immunodeficient mice are engrafted with human cells or tissues, that then mimic the human immune system, offering an alternative and potentially more predictive preclinical model. Immunodeficient NSG mice engrafted with human CD34+ cord blood stem cells develop human T cells educated against murine MHC. However, autoimmune graft versus host disease (GvHD), mediated by T cells, typically develops 1 year post engraftment.

Methods

Here, we have used the development of GvHD in NSG mice, using donors with HLA alleles predisposed to autoimmunity (psoriasis) to weight in favor of GvHD, as an endpoint to evaluate the relative potency of monoclonal and BiSpecific antibodies targeting PD-1 and CTLA-4 to break immune tolerance.

Results

We found that treatment with either a combination of anti-PD-1 & anti-CTLA-4 mAbs or a quadrivalent anti-PD-1/CTLA-4 BiSpecific (MEDI8500), had enhanced potency compared to treatment with anti-PD-1 or anti-CTLA-4 monotherapies, increasing T cell activity both in vitro and in vivo. This resulted in accelerated development of GvHD and shorter survival of the humanized mice in these treatment groups commensurate with their on target activity.

Discussion

Our findings demonstrate the potential of humanized mouse models for preclinical evaluation of different immunotherapies and combinations, using acceleration of GvHD development as a surrogate of aggravated antigenic T-cell response against host.

Targeting DNA damage response components induces enhanced STING-dependent type-I IFN response in ATM deficient cancer cells and drives dendritic cell activation

The concept of exploiting tumor intrinsic deficiencies in DNA damage repair mechanisms by inhibiting compensatory DNA repair pathways is well established. For example, ATM-deficient cells show increased sensitivity to the ATR inhibitor ceralasertib. DNA damage response (DDR)-deficient cells are also more sensitive to DNA damaging agents like the DNA crosslinker pyrrolobenzodiazepine (PBD) SG-3199. However, additional antitumor benefits from targeting the DDR pathways, which could operate through the activation of the innate immune system are less well studied. DNA accumulation in the cytosol acts as an immunogenic danger signal, inducing the expression of type-I interferon (IFN) stimulated genes (ISGs) by the activation of the cGAS-STING pathway. Here, we demonstrate that ATM ^−/− FaDu tumor cells have higher basal expression of ISGs when compared to WT cells and respond to ceralasertib and PBD SG-3199 by inducing higher levels of ISGs in a cGAS-STING-dependent manner. We show that sensitive tumor cells treated with ceralasertib and PBD SG-3199 activate dendritic cells (DCs) via a type-I IFN-dependent mechanism. However, STING deficiency in tumor cells does not prevent DC activation, suggesting that transactivation of the STING pathway occurs within DCs. Furthermore, depletion of the cytosolic DNA exonuclease TREX1 in tumor cells increases DC activation in response to PBD SG-3199-treated tumor cells, indicating that an increase in tumor-derived cytosolic DNA may further enhance DC activation. In summary, in this study, we show that ceralasertib and PBD SG-3199 treatment not only intrinsically target tumor cells but also extrinsically increase tumor cell immunogenicity by inducing DC activation, which is enhanced in ATM-deficient cells.

Impact of CTLA-4 checkpoint antibodies on ligand binding and Transendocytosis

Anti-CTLA-4 antibodies have pioneered the field of tumour immunotherapy. However, despite impressive clinical response data, the mechanism by which anti-CTLA-4 antibodies work is still controversial. Two major checkpoint antibodies (ipilimumab and tremelimumab) have been trialled clinically. Both have high affinity binding to CTLA-4 and occupy the ligand binding site, however recently it has been suggested that in some settings such antibodies may not block ligand-CTLA-4 interactions. Here we evaluated blocking capabilities of these antibodies in a variety of settings using both soluble and cell bound target proteins. We found that when ligands (CD80 or CD86) were expressed on cells, soluble CTLA-4-Ig bound in line with affinity expectations and that this interaction was effectively disrupted by both ipilimumab and tremelimumab antibodies. Similarly, cellular CTLA-4 binding to soluble ligands was comparably prevented. We further tested the ability of these antibodies to block transendocytosis, whereby CTLA-4 captures ligands from target cells during a cognate cell-cell interaction. Once again ipilimumab and tremelimumab were similar in preventing removal of ligand by transendocytosis. Furthermore, even once transendocytosis was ongoing and cell contact was fully established, the addition of these antibodies could prevent further ligand transfer. Together these data indicate that the above checkpoint inhibitors performed in-line with predictions based on affinity and binding site data and are capable of blocking CTLA-4-ligand interactions in a wide range of settings tested.

Abstract 6103: Reshaping the myeloid-dependent pro-tumorigenic microenvironment in PDAC by targeting the extracellular adenosine pathway: A therapeutic opportunity

The prognosis for patients with pancreatic adenocarcinoma (PDAC) remains extremely poor. PDAC is resistant to both conventional therapies and emerging immunotherapies (IOT), apart from tumors with mismatch repair deficiency. This may be explained in part by its low tumor mutational burden (TMB) but also by its immunosuppressive tumor microenvironment (TME). It has been suggested that CD73, a member of the adenosine pathway, expressed on cancer cells contributes to immune escape and resistance to cytotoxic/radiotherapy treatment. The adenosine pathway converts the immune activator ATP, released by dying cells during cell turnover or after treatment, to extracellular Adenosine (eAdo), which is immunosuppressive.

Using syngeneic, in vivo models by s.c. implantation of KPC-derived cell lines (courtesy of Ben Stanger, UPenn) with differential immune infiltration and response to IOT [resistant (IOTResi) or responsive (IOTResp)], we showed by flow cytometry that the adenosine pathway is enriched in the tumor-infiltrating immune cells (in particular myeloid populations) which co-express CD39 and CD73, enabling the formation of eAdo. Mass Spec Imaging (MSI) revealed that adenosine distribution is heterogeneous in the tumors with high concentrations in the hypoxic margins that surround necrotic areas. Subpopulations of myeloid cells infiltrating the lesions are a target for eAdo, expressing high levels of adenosine receptor Adora2a. We discovered that pro-tumorigenic M2 macrophages have the highest expression of the receptor and significantly higher in the IOTResi model. Blocking the in vivo formation and function of eAdo in IOTResi tumors, using a combination of anti-CD73 antibody (2C5, murine IgG1-Fc) and an inhibitor of Adora2a (AZD4635) reduced the presence of eAdo, slowed tumor growth and reduced the lung metastatic burden. The combination remodeled the TME, reducing the infiltration by M2 macrophages, particularly those that are PD-L1 positive and diminished the frequency of infiltrating Tregs. Bulk RNAseq analysis demonstrated a profound dependency of the TME on the presence of eAdo. Genes related to cytokine/chemokine signaling, immunosuppression/inflammation, hypoxia, metastasis and collagen production are strongly downregulated following administration of anti-CD73Ab/Adora2ai. In addition, blocking the adenosine pathway improved the efficacy of combinations of cytotoxics (gemcitabine/ATR inhibitor) and immunotherapy (aCD40/anti-PDL1Ab).

The formation of eAdo appears to be a factor in the development of the immunosuppressive TME in PDAC, contributing to its resistance to conventional and novel therapies. Therefore, inhibition of the adenosine pathway using a CD73Ab and an Adora2ai may represent a strategy to modulate the PDAC stroma and improve therapy response in patients with PDAC.

Citation Format: Vincenzo Graziano, Andreas Dannhorn, Kate Williamson, Heather Hulme, Hannah Buckley, Sheng Y. Lee, Sabita Islam, James E. Thaventhiran, Richard Goodwin, Rebecca Brais, Simon J. Dovedi, Alwin Schuller, Jim Eyles, Duncan I. Jodrell. Reshaping the myeloid-dependent pro-tumorigenic microenvironment in PDAC by targeting the extracellular adenosine pathway: A therapeutic opportunity [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 6103.

In vivo labeling reveals continuous trafficking of TCF-1+ T cells between tumor and lymphoid tissue

Improving the efficacy of immune checkpoint therapies will require a better understanding of how immune cells are recruited and sustained in tumors. Here, we used the photoconversion of the tumor immune cell compartment to identify newly entering lymphocytes, determine how they change over time, and investigate their egress from the tumor. Combining single-cell transcriptomics and flow cytometry, we found that while a diverse mix of CD8 T cell subsets enter the tumor, all CD8 T cells retained within this environment for more than 72 h developed an exhausted phenotype, revealing the rapid establishment of this program. Rather than forming tumor-resident populations, non-effector subsets, which express TCF-1 and include memory and stem-like cells, were continuously recruited into the tumor, but this recruitment was balanced by concurrent egress to the tumor-draining lymph node. Thus, the TCF-1+ CD8 T cell niche in tumors is highly dynamic, with the circulation of cells between the tumor and peripheral lymphoid tissue to bridge systemic and intratumoral responses.

Deep phenotyping of surface stimulatory and inhibitory co-receptors on cancer-resident T and NK cells reveals cell subsets within the tumor-reactive CTL population that are uniquely defined by NKG2A expression

The field of Immuno-Oncology (IO) is evolving to utilise novel antibody backbones that can co-target multiple cell-surface stimulatory and inhibitory co-receptors (SICR). This approach necessitates a better understanding of SICR co-expression at the single-cell level on IO-relevant tumor-infiltrating leukocyte (TIL) cell types such as T and natural killer (NK) cells. Using high-dimensional flow cytometry we established a comprehensive SICR profile for tumor-resident T and NK cells across a range of human solid tumors where there is a clear need for improved immunotherapeutic intervention. Leveraging the power of our large flow panel, we performed deep-phenotyping of the critical CD8⁺CD39⁺ Cytotoxic T Lymphocyte (CTL) population that is enriched for tumor-reactive cytotoxic cells, revealing subsets that are differentiated by their SICR profile, including three that are uniquely defined by NKG2A expression. This study establishes a comprehensive SICR phenotype for human TIL T and NK cells, providing insights to guide the design and application of the next generation of IO molecules.

Cyton2: A Model of Immune Cell Population Dynamics That Includes Familial Instructional Inheritance

Lymphocytes are the central actors in adaptive immune responses. When challenged with antigen, a small number of B and T cells have a cognate receptor capable of recognising and responding to the insult. These cells proliferate, building an exponentially growing, differentiating clone army to fight off the threat, before ceasing to divide and dying over a period of weeks, leaving in their wake memory cells that are primed to rapidly respond to any repeated infection. Due to the non-linearity of lymphocyte population dynamics, mathematical models are needed to interrogate data from experimental studies. Due to lack of evidence to the contrary and appealing to arguments based on Occam’s Razor, in these models newly born progeny are typically assumed to behave independently of their predecessors. Recent experimental studies, however, challenge that assumption, making clear that there is substantial inheritance of timed fate changes from each cell by its offspring, calling for a revision to the existing mathematical modelling paradigms used for information extraction. By assessing long-term live-cell imaging of stimulated murine B and T cells in vitro, we distilled the key phenomena of these within-family inheritances and used them to develop a new mathematical model, Cyton2, that encapsulates them. We establish the model’s consistency with these newly observed fine-grained features. Two natural concerns for any model that includes familial correlations would be that it is overparameterised or computationally inefficient in data fitting, but neither is the case for Cyton2. We demonstrate Cyton2’s utility by challenging it with high-throughput flow cytometry data, which confirms the robustness of its parameter estimation as well as its ability to extract biological meaning from complex mixed stimulation experiments. Cyton2, therefore, offers an alternate mathematical model, one that is, more aligned to experimental observation, for drawing inferences on lymphocyte population dynamics.

Recombinant Newcastle Disease Virus Immunotherapy Drives Oncolytic Effects and Durable Systemic Antitumor Immunity

A recombinant Newcastle Disease Virus (NDV), encoding either a human (NDVhuGM-CSF, MEDI5395) or murine (NDVmuGM-CSF) GM-CSF transgene, combined broad oncolytic activity with the ability to significantly modulate genes related to immune functionality in human tumor cells. Replication in murine tumor lines was significantly diminished relative to human tumor cells. Nonetheless, intratumoral injection of NDVmuGM-CSF conferred antitumor effects in three syngeneic models in vivo; with efficacy further augmented by concomitant treatment with anti-PD-1/PD-L1 or T-cell agonists. Ex vivo immune profiling, including T-cell receptor sequencing, revealed profound immune-contexture changes consistent with priming and potentiation of adaptive immunity and tumor microenvironment (TME) reprogramming toward an immune-permissive state. CRISPR modifications rendered CT26 tumors significantly more permissive to NDV replication, and in this setting, NDVmuGM-CSF confers immune-mediated effects in the noninjected tumor in vivo Taken together, the data support the thesis that MEDI5395 primes and augments cell-mediated antitumor immunity and has significant utility as a combination partner with other immunomodulatory cancer treatments.

Inhibition of DNA-PK with AZD7648 Sensitizes Tumor Cells to Radiotherapy and Induces Type I IFN-Dependent Durable Tumor Control

PURPOSE

Combining radiotherapy (RT) with DNA damage response inhibitors may lead to increased tumor cell death through radiosensitization. DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break repair via the nonhomologous end joining (NHEJ) pathway. We hypothesized that in addition to a radiosensitizing effect from the combination of RT with AZD7648, a potent and specific inhibitor of DNA-PK, combination therapy may also lead to modulation of an anticancer immune response.

EXPERIMENTAL DESIGN

AZD7648 and RT efficacy, as monotherapy and in combination, was investigated in fully immunocompetent mice in MC38, CT26, and B16-F10 models. Immunologic consequences were analyzed by gene expression and flow-cytometric analysis.

RESULTS

AZD7648, when delivered in combination with RT, induced complete tumor regressions in a significant proportion of mice. The antitumor efficacy was dependent on the presence of CD8+ T cells but independent of NK cells. Analysis of the tumor microenvironment revealed a reduction in T-cell PD-1 expression, increased NK-cell granzyme B expression, and elevated type I IFN signaling in mice treated with the combination when compared with RT treatment alone. Blocking of the type I IFN receptor in vivo also demonstrated a critical role for type I IFN in tumor growth control following combined therapy. Finally, this combination was able to generate tumor antigen-specific immunologic memory capable of suppressing tumor growth following rechallenge.

CONCLUSIONS

Blocking the NHEJ DNA repair pathway with AZD7648 in combination with RT leads to durable immune-mediated tumor control.

Abstract 1695: Activation of B cells by CD73 blocking antibodies

The catabolism of ATP into immunosuppressive adenosine contributes to the dysfunction of tumor infiltrating leukocytes (TIL). CD73 is an ectonucleotidase which catabolizes conversion of AMP to adenosine and is expressed on a range of immune cells including B cells. Oleclumab (MEDI9447) is a monoclonal antibody specific for human CD73 and is currently in clinical development for the treatment of cancer. B cells constitute a significant proportion of human TIL; however, their importance to Immuno-Oncology (IO) treatments remains unclear. Recent publications demonstrate that B cells sustain inflammation and predict response to immune checkpoint blockade in human melanoma, their presence within the tumor microenvironment is correlated with improved prognosis in several human tumor types, and CD73 expression has been shown to vary on different human B cell subtypes. Further investigations into the role of CD73 in control of human B cell function are therefore warranted. We show that blockade of CD73 by oleclumab and other monoclonal antibodies on peripheral blood B cells from healthy human donors upregulates expression of CD69, CD83 and CD86, and induces secretion of IL-6, MIP-1α and MIP-1β. Activation is mediated by antibodies that block and internalize CD73 and is reduced by pharmacological inhibition of BTK, thus highlighting involvement of the canonical B-cell receptor signaling pathway. Furthermore, our analyses highlight a differential effect of CD73 blockade on individual B-cell populations, with the most robust increases in activation marker expression being observed on naïve subsets that retain expression of IgD. Our research has identified that oleclumab activates human peripheral blood B cells. Given the renewed interest in B-cell biology in IO, this is an area we believe warrants further clinical investigation.

Citation Format: James Hair, Fabien Garcon, Michelle Hsueh, Laura Dallaway, Elena Bibikova, Maria Letizia Giardino Torchia, Gordon Moody, Alwin Schuller, Simon J. Dovedi, Zachary A. Cooper, Kris Sachsenmeier, Rakesh Kumar, Jim Eyles, Robert W. Wilkinson. Activation of B cells by CD73 blocking antibodies [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 1695.

Abstract 2768: A novel non-terminal tumor sampling procedure using fine needle aspiration supports biomarker discovery

Immunotherapy is part of the standard of care for oncology however, durable objective responses remain limited to a subset of patients. As such there is a crucial need to identify biomarkers that can predict/enrich for treatment response. So far, the majority of proposed biomarkers consist of features of the tumor microenvironment (TME). However, in preclinical mouse models, the collection of tumor tissue for this type of analysis is a terminal procedure obviating the ability to directly link potential biomarkers to response/outcome following treatment. Therefore, we have developed and validated a novel non-terminal tumor sampling method to biopsy the TME in mouse models based on fine needle aspiration. We show that this technique enables repeated in-life sampling of subcutaneous flank tumors without impacting tumor growth or animal welfare. This method yields sufficient sample for flow cytometric analysis of tumor-infiltrating immune cells and we demonstrate that it is able to recapitulate results obtained with the current methodology of whole tumor analysis. We propose that this method represents a simple, fast, minimally invasive technique to enable analysis of the TME, reduction in the number of animals used for preclinical oncology studies and refinement of pharmacodynamic analysis. Additionally, its unique ability to provide longitudinal TME sampling can support investigation of biomarkers of response to treatment.

Citation Format: Suzanne I. Sitnikova, Sophie Munnings-Tomes, Stacy R. Kentner, Kathy Mulgrew, Judit Espana-Agusti, Tianhui Zhang, Kristina M. Ilieva, Hormas M. Ghadially, Matthew J. Robinson, Robert W. Wilkinson, Simon J. Dovedi. A novel non-terminal tumor sampling procedure using fine needle aspiration supports biomarker discovery [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 2768.

Novel non-terminal tumor sampling procedure using fine needle aspiration supports immuno-oncology biomarker discovery in preclinical mouse models

Background

Immuno-oncology therapies are now part of the standard of care for cancer in many indications. However, durable objective responses remain limited to a subset of patients. As such, there is a critical need to identify biomarkers that can predict or enrich for treatment response. So far, the majority of putative biomarkers consist of features of the tumor microenvironment (TME). However, in preclinical mouse models, the collection of tumor tissue for this type of analysis is a terminal procedure, obviating the ability to directly link potential biomarkers to long-term treatment outcomes.

Methods

To address this, we developed and validated a novel non-terminal tumor sampling method to enable biopsy of the TME in mouse models based on fine needle aspiration.

Results

We show that this technique enables repeated in-life sampling of subcutaneous flank tumors and yields sufficient material to support downstream analyses of tumor-infiltrating immune cells using methods such as flow cytometry and single-cell transcriptomics. Moreover, using this technique we demonstrate that we can link TME biomarkers to treatment response outcomes, which is not possible using the current method of terminal tumor sampling.

Conclusion

Thus, this minimally invasive technique is an important refinement for the pharmacodynamic analysis of the TME facilitating paired evaluation of treatment response biomarkers with outcomes and reducing the number of animals used in preclinical research.

A LAT-Based Signaling Complex in the Immunological Synapse as Determined with Live Cell Imaging Is Less Stable in T Cells with Regulatory Capability

Peripheral immune regulation is critical for the maintenance of self-tolerance. Here we have investigated signaling processes that distinguish T cells with regulatory capability from effector T cells. The murine Tg4 T cell receptor recognizes a peptide derived from the self-antigen myelin basic protein. T cells from Tg4 T cell receptor transgenic mice can be used to generate effector T cells and three types of T cells with regulatory capability, inducible regulatory T cells, T cells tolerized by repeated in vivo antigenic peptide exposure or T cells treated with the tolerogenic drug UCB9608 (a phosphatidylinositol 4 kinase IIIβ inhibitor). We comparatively studied signaling in all of these T cells by activating them with the same antigen presenting cells presenting the same myelin basic protein peptide. Supramolecular signaling structures, as efficiently detected by large-scale live cell imaging, are critical mediators of T cell activation. The formation of a supramolecular signaling complex anchored by the adaptor protein linker for activation of T cells (LAT) was consistently terminated more rapidly in Tg4 T cells with regulatory capability. Such termination could be partially reversed by blocking the inhibitory receptors CTLA-4 and PD-1. Our work suggests that attenuation of proximal signaling may favor regulatory over effector function in T cells.

Design and Efficacy of a Monovalent Bispecific PD-1/CTLA4 Antibody That Enhances CTLA4 Blockade on PD-1+ Activated T Cells

The clinical benefit of PD-1 blockade can be improved by combination with CTLA4 inhibition but is commensurate with significant immune-related adverse events suboptimally limiting the doses of anti-CTLA4 mAb that can be used. MEDI5752 is a monovalent bispecific antibody designed to suppress the PD-1 pathway and provide modulated CTLA4 inhibition favoring enhanced blockade on PD-1⁺ activated T cells. We show that MEDI5752 preferentially saturates CTLA4 on PD-1⁺ T cells versus PD-1^- T cells, reducing the dose required to elicit IL2 secretion. Unlike conventional PD-1/CTLA4 mAbs, MEDI5752 leads to the rapid internalization and degradation of PD-1. Moreover, we show that MEDI5752 preferentially localizes and accumulates in tumors providing enhanced activity when compared with a combination of mAbs targeting PD-1 and CTLA4 in vivo. Following treatment with MEDI5752, robust partial responses were observed in two patients with advanced solid tumors. MEDI5752 represents a novel immunotherapy engineered to preferentially inhibit CTLA4 on PD-1⁺ T cells. SIGNIFICANCE: The unique characteristics of MEDI5752 represent a novel immunotherapy engineered to direct CTLA4 inhibition to PD-1⁺ T cells with the potential for differentiated activity when compared with current conventional mAb combination strategies targeting PD-1 and CTLA4. This molecule therefore represents a step forward in the rational design of cancer immunotherapy.See related commentary by Burton and Tawbi, p. 1008.This article is highlighted in the In This Issue feature, p. 995.

PD-1 suppresses the maintenance of cell couples between cytotoxic T cells and target tumor cells within the tumor

The killing of tumor cells by CD8⁺ T cells is suppressed by the tumor microenvironment, and increased expression of inhibitory receptors, including programmed cell death protein-1 (PD-1), is associated with tumor-mediated suppression of T cells. To find cellular defects triggered by tumor exposure and associated PD-1 signaling, we established an ex vivo imaging approach to investigate the response of antigen-specific, activated effector CD8⁺ tumor-infiltrating lymphocytes (TILs) after interaction with target tumor cells. Although TIL-tumor cell couples readily formed, couple stability deteriorated within minutes. This was associated with impaired F-actin clearing from the center of the cellular interface, reduced Ca²⁺ signaling, increased TIL locomotion, and impaired tumor cell killing. The interaction of CD8⁺ T lymphocytes with tumor cell spheroids in vitro induced a similar phenotype, supporting a critical role of direct T cell-tumor cell contact. Diminished engagement of PD-1 within the tumor, but not acute ex vivo blockade, partially restored cell couple maintenance and killing. PD-1 thus contributes to the suppression of TIL function by inducing a state of impaired subcellular organization.

Opportunities for Quantitative Translational Modeling in Oncology

A 2-day meeting was held by members of the UK Quantitative Systems Pharmacology Network () in November 2018 on the topic of Translational Challenges in Oncology. Participants from a wide range of backgrounds were invited to discuss current and emerging modeling applications in nonclinical and clinical drug development, and to identify areas for improvement. This resulting perspective explores opportunities for impactful quantitative pharmacology approaches. Four key themes arose from the presentations and discussions that were held, leading to the following recommendations: Evaluate the predictivity and reproducibility of animal cancer models through precompetitive collaboration. Apply mechanism of action (MoA) based mechanistic models derived from nonclinical data to clinical trial data. Apply MoA reflective models across trial data sets to more robustly quantify the natural history of disease and response to differing interventions. Quantify more robustly the dose and concentration dependence of adverse events through mathematical modelling techniques and modified trial design.

Abstract 2152: Characterisation of co-expression of CD39 with other IO-relevant markers on major T/NK cell TIL subsets

CD39 has recently been identified as critically differentiating tumour-reactive from bystander tumour-infiltrating leukocyte (TIL) CD8+ T cells. CD39 is an ectonucleotidase that degrades immunostimulatory ATP to ADP and AMP. CD73 then further metabolises AMP to generate immunosuppressive adenosine in the tumor microenvironment. To facilitate our understanding of CD39 as a therapeutic target we established a detailed receptor co-expression profile for CD39 with other immuno-oncology (IO)-relevant targets on TIL T/NK cells. TIL samples from three diseases (NSCLC, Renal cancer [RC] and Melanoma) were profiled, via the creation and use of a single large flow cytometry panel, combined with computational analysis.

Unbiased clustering identified the expected major T and NK cell populations, however one of the most striking findings was that CD39 was highly differentially expressed across the different cell subsets. Almost all TREG cells were CD39 positive, whereas CD8+ T cells and NK cells were highly variable in their degree of expression of CD39. CD4+CD8+ T cells predominantly did not express cell surface CD39 and only very few CD4+ TCONV cells expressed CD39.

The co-expression profile for TREG, TCONV and NK cells is presented, but we have also defined a detailed phenotype of the critical tumour-specific CD39+CD8+ T cell population. Our analyses show that CD39+CD8+ T cells express more markers associated with antigen-experienced T cells versus CD39-CD8+ T cells; a significantly greater proportion of CD39+CD8+ T cells expressed TIM3, CTLA-4, PD-1, TIGIT, CD137 and GITR versus CD39-CD8+ T cells. Significantly fewer CD39+CD8+ T cells than CD39-CD8+ T cells expressed CD28, a receptor known to be downregulated on antigen-experienced cytotoxic CD8+ T cells.

These data reveal the detailed co-expression patterns of key IO-relevant receptors across TIL T and NK cell subsets and are consistent with recent reports identifying CD39 as a key marker differentiating the critical tumor-specific, antigen-experienced tumor infiltrating CD8+ T cells.

Citation Format: Jim Hair, Nadia Luheshi, Simon J. Dovedi, Robert W. Wilkinson. Characterisation of co-expression of CD39 with other IO-relevant markers on major T/NK cell TIL subsets [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 2152.

Developing an Arrayed CRISPR-Cas9 Co-Culture Screen for Immuno-Oncology Target ID

Immunotherapies including PD-L1 blockade have shown remarkable increases in the T cell-directed antitumor response; however, efficacy is seen only in a minority of patients. Recently, pooled CRISPR-Cas9 knockout (CRISPRn) screens in tumor/immune co-culture systems have identified a number of genes that confer resistance to T cell killing in pathways including antigen presentation and cytokine signaling, providing insight into tumor mechanisms that cause resistance to immunotherapies. The development of an arrayed CRISPRn screen in a tumor/immune co-culture system would allow the identification of novel targets for immuno-oncology, characterization of hits from pooled screens, and multiple assay endpoints to be measured per gene. Here, a small-scale arrayed CRISPRn screen was successfully developed to investigate the effects on a co-culture of T cells and Cas9-expressing PC9 lung adenocarcinoma cells modified to express anti-CD3 antibody on the cell surface (PC9-OKT3 T cell system). A focused CRISPRn library was designed to target genes involved in known resistance mechanisms (including antigen presentation, cytokine signaling, and apoptosis) as well as genes involved in immune synapse interactions. The viability of PC9 cells was assessed in two-dimensional adherent co-cultures via longitudinal imaging analysis. Knockout of epidermal growth factor receptor (EGFR) and PLK1 in tumor cells cultured alone or with T cells resulted in increased tumor cell death, as expected, whereas knockout of the test gene ICAM1 showed subtle donor-specific resistance to T cell killing. Taken together, these data provide proof of concept for arrayed CRISPRn screens in tumor/immune co-culture systems and warrant further investigation of in vitro co-culture models.

Developing an Arrayed CRISPR-Cas9 Co-Culture Screen for Immuno-Oncology Target ID

Immunotherapies including PD-L1 blockade have shown remarkable increases in the T cell-directed antitumor response; however, efficacy is seen only in a minority of patients. Recently, pooled CRISPR-Cas9 knockout (CRISPRn) screens in tumor/immune co-culture systems have identified a number of genes that confer resistance to T cell killing in pathways including antigen presentation and cytokine signaling, providing insight into tumor mechanisms that cause resistance to immunotherapies. The development of an arrayed CRISPRn screen in a tumor/immune co-culture system would allow the identification of novel targets for immuno-oncology, characterization of hits from pooled screens, and multiple assay endpoints to be measured per gene. Here, a small-scale arrayed CRISPRn screen was successfully developed to investigate the effects on a co-culture of T cells and Cas9-expressing PC9 lung adenocarcinoma cells modified to express anti-CD3 antibody on the cell surface (PC9-OKT3 T cell system). A focused CRISPRn library was designed to target genes involved in known resistance mechanisms (including antigen presentation, cytokine signaling, and apoptosis) as well as genes involved in immune synapse interactions. The viability of PC9 cells was assessed in two-dimensional adherent co-cultures via longitudinal imaging analysis. Knockout of epidermal growth factor receptor (EGFR) and PLK1 in tumor cells cultured alone or with T cells resulted in increased tumor cell death, as expected, whereas knockout of the test gene ICAM1 showed subtle donor-specific resistance to T cell killing. Taken together, these data provide proof of concept for arrayed CRISPRn screens in tumor/immune co-culture systems and warrant further investigation of in vitro co-culture models.

Intratumoral immunotherapy with TLR7/8 agonist MEDI9197 modulates the tumor microenvironment leading to enhanced activity when combined with other immunotherapies

Background

Immune checkpoint blockade (ICB) promotes adaptive immunity and tumor regression in some cancer patients. However, in patients with immunologically “cold” tumors, tumor-resident innate immune cell activation may be required to prime an adaptive immune response and so exploit the full potential of ICB. Whilst Toll-like receptor (TLR) agonists have been used topically to successfully treat some superficial skin tumors, systemic TLR agonists have not been well-tolerated.

Methods

The response of human immune cells to TLR7 and 8 agonism was measured in primary human immune cell assays. MEDI9197 (3M-052) was designed as a novel lipophilic TLR7/8 agonist that is retained at the injection site, limiting systemic exposure. Retention of the TLR7/8 agonist at the site of injection was demonstrated using quantitative whole-body autoradiography, HPLC-UV, and MALDI mass spectrometry imaging. Pharmacodynamic changes on T cells from TLR7/8 agonist treated B16-OVA tumors was assessed by histology, quantitative real time PCR, and flow cytometry. Combination activity of TLR7/8 agonism with immunotherapies was assessed in vitro by human DC-T cell MLR assay, and in vivo using multiple syngeneic mouse tumor models.

Results

Targeting both TLR7 and 8 triggers an innate and adaptive immune response in primary human immune cells, exemplified by secretion of IFNα, IL-12 and IFNγ. In contrast, a STING or a TLR9 agonist primarily induces release of IFNα. We demonstrate that the TLR7/8 agonist, MEDI9197, is retained at the sight of injection with limited systemic exposure. This localized TLR7/8 agonism leads to Th1 polarization, enrichment and activation of natural killer (NK) and CD8⁺ T cells, and inhibition of tumor growth in multiple syngeneic models. The anti-tumor activity of this TLR7/8 agonist is enhanced when combined with T cell-targeted immunotherapies in pre-clinical models.

Conclusion

Localized TLR7/8 agonism can enhance recruitment and activation of immune cells in tumors and polarize anti-tumor immunity towards a Th1 response. Moreover, we demonstrate that the anti-tumor effects of this TLR7/8 agonist can be enhanced through combination with checkpoint inhibitors and co-stimulatory agonists.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0724-8) contains supplementary material, which is available to authorized users.

Abstract 4987: Age-induced changes in anti-tumor immunity alter the tumor immune infiltrate and reduce response to immuno-oncology treatments

Immuno-oncology research relies heavily on murine syngeneic tumor models. However, whilst the median age for a cancer diagnosis is 65 years or older, for practical purposes the majority of preclinical studies are conducted in young mice, despite the fact that aging has been shown to have a significant impact on the immune response. Using aged mice bearing CT26 tumors, we analysed how aging impacts the immune composition of the tumor, spleen and tumor-draining lymph nodes by flow cytometry. We found many age-related changes between aged (60-72 weeks old) and young (6-8 weeks old) mice, such as a reduction in the naïve T cell population and a decreased CD8/Treg ratio in aged animals. Profiling of co-inhibitory and co-stimulatory receptor expression levels on immune cells in aged versus young mice also identified altered expression profiles in both the periphery and tumor. We hypothesised that these differences may contribute to impaired anti-cancer immune responses in aged mice. To investigate this, we compared the anti-tumor efficacy of immune checkpoint blockade (PD-L1 and CTLA-4) and T-cell costimulation (OX-40) in aged versus young mice. Our data demonstrate that aged mice retained their capacity to generate effective anti-tumor immune responses, albeit often attenuated when compared to the responses observed in young mice. These differences highlight the potential importance of age-related immunological changes in assessing and refining the translational insights gained from preclinical mouse models.

Citation Format: Suzanne I. Sitnikova, Michelle Morrow, Viia Valge-Archer, Robert W. Wilkinson, Simon J. Dovedi, Matthew J. Robinson. Age-induced changes in anti-tumor immunity alter the tumor immune infiltrate and reduce response to immuno-oncology treatments [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4987.

A cell-engineered system to assess tumor cell sensitivity to CD8+ T cell-mediated cytotoxicity

In vitro assays that evaluate CD8+ T cell-mediated cytotoxicity are important to aid in the development of novel therapeutic approaches to enhance anti-tumor immune responses. Here, we describe a novel cytotoxicity co-culture assay that circumvents the problem of highly variable allogeneic responses and obviates the constraints of HLA-restriction between effector and target cells. We show that this assay can be easily applied to a panel of tumor cell lines to provide additional insights into intrinsic drivers of sensitivity/resistance to T cell-mediated killing, and to evaluate the impact of targeted therapies on both tumor and T cell compartments.

Radiation and PD-(L)1 treatment combinations: immune response and dose optimization via a predictive systems model

BACKGROUND

Numerous oncology combination therapies involving modulators of the cancer immune cycle are being developed, yet quantitative simulation models predictive of outcome are lacking. We here present a model-based analysis of tumor size dynamics and immune markers, which integrates experimental data from multiple studies and provides a validated simulation framework predictive of biomarkers and anti-tumor response rates, for untested dosing sequences and schedules of combined radiation (RT) and anti PD-(L)1 therapies.

METHODS

A quantitative systems pharmacology model, which includes key elements of the cancer immunity cycle and the tumor microenvironment, tumor growth, as well as dose-exposure-target modulation features, was developed to reproduce experimental data of CT26 tumor size dynamics upon administration of RT and/or a pharmacological IO treatment such as an anti-PD-L1 agent. Variability in individual tumor size dynamics was taken into account using a mixed-effects model at the level of tumor-infiltrating T cell influx.

RESULTS

The model allowed for a detailed quantitative understanding of the synergistic kinetic effects underlying immune cell interactions as linked to tumor size modulation, under these treatments. The model showed that the ability of T cells to infiltrate tumor tissue is a primary determinant of variability in individual tumor size dynamics and tumor response. The model was further used as an in silico evaluation tool to quantitatively predict, prospectively, untested treatment combination schedules and sequences. We demonstrate that anti-PD-L1 administration prior to, or concurrently with RT reveal further synergistic effects, which, according to the model, may materialize due to more favorable dynamics between RT-induced immuno-modulation and reduced immuno-suppression of T cells through anti-PD-L1.

CONCLUSIONS

This study provides quantitative mechanistic explanations of the links between RT and anti-tumor immune responses, and describes how optimized combinations and schedules of immunomodulation and radiation may tip the immune balance in favor of the host, sufficiently to lead to tumor shrinkage or rejection.

Distinct patterns of infiltrating CD8+ T cells in HPV+ and CD68 macrophages in HPV- oropharyngeal squamous cell carcinomas are associated with better clinical outcome but PD-L1 expression is not prognostic

Immunotherapies are beginning to revolutionise treatment paradigms in oncology with monoclonal antibodies (mAb) targeting T-cell co-inhibitory (e.g. PD-1/PD-L1) and co-stimulatory pathways (e.g. CTLA-4/CD28) demonstrating clinical utility. Some clinical studies demonstrate that responsiveness to PD-1/PD-L1 mAb therapy is greater in patients with expression of PD-L1 in the tumour microenvironment. However, robust responses have also been observed in patients with low or absent expression of PD-L1. Using multiplex immuno-fluorescent labelling we sought to determine how infiltration of tumours by CD8⁺ T-cells, their expression of PD-1, and the expression of PD-L1 on both tumours and CD68 cells (macrophages) correlated with HPV status and outcome in a cohort of 124 oropharyngeal squamous cell carcinomas (OPSCC).

A TLR7 agonist enhances the antitumor efficacy of obinutuzumab in murine lymphoma models via NK cells and CD4 T cells

This corrects the article DOI: 10.1038/leu.2016.352.

Fractionated Radiation Therapy Stimulates Antitumor Immunity Mediated by Both Resident and Infiltrating Polyclonal T-cell Populations when Combined with PD-1 Blockade

Purpose: Radiotherapy is a highly effective anticancer treatment forming part of the standard of care for the majority of patients, but local and distal disease recurrence remains a major cause of mortality. Radiotherapy is known to enhance tumor immunogenicity; however, the contribution and mechanisms of radiotherapy-induced immune responses are unknown.Experimental Design: The impact of low-dose fractionated radiotherapy (5 × 2 Gy) alone and in combination with αPD-1 mAb on the tumor microenvironment was evaluated by flow cytometry and next-generation sequencing of the T-cell receptor (TCR) repertoire. A dual-tumor model was used, with fractionated radiotherapy delivered to a single tumor site to enable evaluation of the local and systemic response to treatment and ability to induce abscopal responses outside the radiation field.Results: We show that fractionated radiotherapy leads to T-cell infiltration at the irradiated site; however, the TCR landscape remains dominated by polyclonal expansion of preexisting T-cell clones. Adaptive resistance via the PD-1/PD-L1 pathway restricts the generation of systemic anticancer immunity following radiotherapy, which can be overcome through combination with αPD-1 mAb leading to improved local and distal tumor control. Moreover, we show that effective clearance of tumor following combination therapy is dependent on both T cells resident in the tumor at the time of radiotherapy and infiltrating T cells.Conclusions: These data provide evidence that radiotherapy can enhance T-cell trafficking to locally treated tumor sites and augment preexisting anticancer T-cell responses with the capacity to mediate regression of out-of-field tumor lesions when delivered in combination with αPD-1 mAb therapy. Clin Cancer Res; 23(18); 5514-26. ©2017 AACR.

The MEK inhibitor selumetinib complements CTLA-4 blockade by reprogramming the tumor immune microenvironment

Background

T-cell checkpoint blockade and MEK inhibitor combinations are under clinical investigation. Despite progress elucidating the immuno-modulatory effects of MEK inhibitors as standalone therapies, the impact of MEK inhibition on the activity of T-cell checkpoint inhibitors remains incompletely understood. Here we sought to characterize the combined effects of MEK inhibition and anti-CTLA-4 mAb (anti-CTLA-4) therapy, examining effects on both T-cells and tumor microenvironment (TME).

Methods

In mice, the effects of MEK inhibition, via selumetinib, and anti-CTLA-4 on immune responses to keyhole limpet haemocyanin (KLH) immunization were monitored using ex vivo functional assays with splenocytes. In a KRAS-mutant CT26 mouse colorectal cancer model, the impact on the tumor microenvironment (TME) and the spleen were evaluated by flow cytometry. The TME was further examined by gene expression and immunohistochemical analyses. The combination and sequencing of selumetinib and anti-CTLA-4 were also evaluated in efficacy studies using the CT26 mouse syngeneic model.

Results

Anti-CTLA-4 enhanced the generation of KLH specific immunity following KLH immunization in vivo; selumetinib was found to reduce, but did not prevent, this enhancement of immune response by anti-CTLA-4 in vivo. In the CT26 mouse model, anti-CTLA-4 treatment led to higher expression levels of the immunosuppressive mediators, Cox-2 and Arg1 in the TME. Combination of anti-CTLA-4 with selumetinib negated this up-regulation of Cox-2 and Arg1, reduced the frequency of CD11⁺ Ly6G⁺ myeloid cells, and led to the accumulation of differentiating monocytes at the Ly6C⁺ MHC⁺ intermediate state in the tumor. We also report that MEK inhibition had limited impact on anti-CTLA-4-mediated increases in T-cell infiltration and T-cell activation in CT26 tumors. Finally, we show that pre-treatment, but not concurrent treatment, with selumetinib enhanced the anti-tumor activity of anti-CTLA-4 in the CT26 model.

Conclusion

These data provide evidence that MEK inhibition can lead to changes in myeloid cells and immunosuppressive factors in the tumor, thus potentially conditioning the TME to facilitate improved response to anti-CTLA-4 treatment. In summary, the use of MEK inhibitors to alter the TME as an approach to enhance the activities of immune checkpoint inhibitors warrants further investigation in clinical trials.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0268-8) contains supplementary material, which is available to authorized users.

A TLR7 agonist enhances the antitumor efficacy of obinutuzumab in murine lymphoma models via NK cells and CD4 T cells

Anti-CD20 monoclonal antibodies (mAb) such as rituximab have been proven to be highly effective at improving outcome in B-cell malignancies. However, many patients ultimately relapse and become refractory to treatment. The glycoengineered anti-CD20 mAb obinutuzumab was developed to induce enhanced antibody-dependent cellular cytotoxicity, antibody-dependent phagocytosis and direct cell death and was shown to lead to improved outcomes in a randomized study in B-CLL. We hypothesized that immune stimulation through Toll-like receptor 7 (TLR7) agonism in combination with obinutuzumab would further enhance lymphoma clearance and the generation of long-term antitumor immune responses. Here we demonstrate, in syngeneic human CD20 (hCD20)-expressing models of lymphoma, that systemic administration of a TLR7 agonist (R848) increases responses when administered in combination with obinutuzumab and protects against disease recurrence. Depletion studies demonstrate that primary antitumor activity is dependent on both NK cells and CD4+ T cells but not on CD8+ T cells. However, both CD4+ and CD8+ T cells appear necessary for the generation of protective immunological memory. Importantly, increased tumor-free survival post obinutuzumab and R848 combination therapy was seen in hCD20 transgenic mice, which express hCD20 on normal B cells. These findings provide a rationale for clinical testing of obinutuzumab in combination with systemically administered TLR7 agonists to further improve outcome.

Rational Selection of Syngeneic Preclinical Tumor Models for Immunotherapeutic Drug Discovery

Murine syngeneic tumor models are critical to novel immuno-based therapy development, but the molecular and immunologic features of these models are still not clearly defined. The translational relevance of differences between the models is not fully understood, impeding appropriate preclinical model selection for target validation, and ultimately hindering drug development. Across a panel of commonly used murine syngeneic tumor models, we showed variable responsiveness to immunotherapies. We used array comparative genomic hybridization, whole-exome sequencing, exon microarray analysis, and flow cytometry to extensively characterize these models, which revealed striking differences that may underlie these contrasting response profiles. We identified strong differential gene expression in immune-related pathways and changes in immune cell-specific genes that suggested differences in tumor immune infiltrates between models. Further investigation using flow cytometry showed differences in both the composition and magnitude of the tumor immune infiltrates, identifying models that harbor "inflamed" and "non-inflamed" tumor immune infiltrate phenotypes. We also found that immunosuppressive cell types predominated in syngeneic mouse tumor models that did not respond to immune-checkpoint blockade, whereas cytotoxic effector immune cells were enriched in responsive models. A cytotoxic cell-rich tumor immune infiltrate has been correlated with increased efficacy of immunotherapies in the clinic, and these differences could underlie the varying response profiles to immunotherapy between the syngeneic models. This characterization highlighted the importance of extensive profiling and will enable investigators to select appropriate models to interrogate the activity of immunotherapies as well as combinations with targeted therapies in vivo Cancer Immunol Res; 5(1); 29-41. ©2016 AACR.

Antitumor Efficacy of Radiation plus Immunotherapy Depends upon Dendritic Cell Activation of Effector CD8+ T Cells

Tumor cells dying after cytotoxic therapy are a potential source of antigen for T-cell priming. Antigen-presenting cells (APC) can cross-present MHC I-restricted peptides after the uptake of dying cells. Depending on the nature of the surrounding environmental signals, APCs then orchestrate a spectrum of responses ranging from immune activation to inhibition. Previously, we had demonstrated that combining radiation with either agonistic monoclonal antibody (mAb) to CD40 or a systemically administered TLR7 agonist could enhance CD8 T-cell-dependent protection against syngeneic murine lymphoma models. However, it remains unknown how individual APC populations affect this antitumor immune response. Using APC depletion models, we now show that dendritic cells (DC), but not macrophages or B cells, were responsible for the generation of long-term immunologic protection following combination therapy with radiotherapy and either agonistic CD40 mAb or systemic TLR7 agonist therapy. Novel immunotherapeutic approaches that augment antigen uptake and presentation by DCs may further enhance the generation of therapeutic antitumor immune responses, leading to improved outcomes after radiotherapy. Cancer Immunol Res; 4(7); 621-30. ©2016 AACR.

Intravenous administration of the selective toll-like receptor 7 agonist DSR-29133 leads to anti-tumor efficacy in murine solid tumor models which can be potentiated by combination with fractionated radiotherapy

Strategies to augment anti-cancer immune responses have recently demonstrated therapeutic utility. To date clinical success has been achieved through targeting co-inhibitory checkpoints such as CTLA-4, PD-1, and PD-L1. However, approaches that target co-activatory pathways are also being actively being developed. Here we report that the novel TLR7-selective agonist DSR-29133 is well tolerated in mice and leads to acute immune activation. Administration of DSR-29133 leads to the induction of IFNα/γ, IP-10, TNFα, IL-1Ra and IL-12p70, and to a reduction in tumor burden in syngeneic models of renal cancer (Renca), metastatic osteosarcoma (LM8) and colorectal cancer (CT26). Moreover, we show that the efficacy of DSR-29133 was significantly improved when administered in combination with low-dose fractionated radiotherapy (RT). Effective combination therapy required weekly administration of DSR-29133 commencing on day 1 of a fractionated RT treatment cycle, whereas no enhancement of radiation response was observed when DSR-29133 was administered at the end of the fractionated RT cycle. Combined therapy resulted in curative responses in a high proportion of mice bearing established CT26 tumors which was dependent on the activity of CD8+ T-cells but independent of CD4+ T-cells and NK/NKT cells. Moreover, long-term surviving mice originally treated with DSR-29133 and RT were protected by a tumor-specific memory immune response which could prevent tumor growth upon rechallenge. These results demonstrate that DSR-29133 is a potent selective TLR7 agonist that when administered intravenously can induce anti-tumor immune responses that can be further enhanced through combination with low-dose fractionated RT.

Pre-treatment lymphocytopaenia is an adverse prognostic biomarker in muscle-invasive and advanced bladder cancer

BACKGROUND

Pre-treatment lymphocytopaenia may result from cytokines secreted by the tumour microenvironment in association with aggressive tumour biology. We sought to establish the prognostic significance of lymphocytopaenia in muscle-invasive and advanced bladder cancer.

PATIENTS AND METHODS

Seventy-four patients with muscle-invasive bladder cancer treated with radical chemoradiotherapy and 131 patients with advanced bladder cancer treated with palliative chemotherapy were included in the study. The absolute lymphocyte count on the first day of treatment was recorded. Invasive local or systemic recurrence in the muscle-invasive bladder cancer cohort and all-cause mortality in the advanced bladder cancer cohort were defined as survival end points. Receiver operating characteristic (ROC) curve analysis was utilized to determine the cut-off for defining lymphocytopaenia in the muscle-invasive bladder cancer cohort followed by multivariable analysis in a model evaluating the following variables: anaemia, neutrophilia, tumour stage, hydronephrosis and neoadjuvant chemotherapy. Subsequently, lymphocytopaenia was assessed in a multivariable model of the advanced bladder cancer cohort analysing the following prognostic variables: neutrophilia, anaemia, performance status and presence of bone or visceral metastases. A further analysis was carried out evaluating absolute lymphocyte count as a continuous variable.

RESULTS

An absolute lymphocyte count of 1.5 × 10(9)/l was determined as the cut-off on ROC curve analysis in the muscle-invasive bladder cancer cohort, and multivariate analysis revealed that only lymphocytopaenia was predictive for inferior outcome in this cohort. In the advanced bladder cancer cohort, lymphocytopaenia [hazard ratio (HR) 1.6, 95% confidence interval (CI) 1.1-2.4; P = 0.02] and performance status (HR 1.7, 95% CI 1.0-2.7; P = 0.047) were adverse prognostic factors in the binary variable multivariate model. Absolute lymphocyte count was the sole significant factor when analysed as a continuous variable (HR 0.66, 95% CI 0.5-0.87; P = 0.003).

CONCLUSION

Pre-treatment lymphocytopaenia is an independent adverse prognostic factor in both muscle-invasive and advanced bladder cancer. It may be a manifestation of cancer-induced immune suppression driving tumour progression.

TLR7 tolerance is independent of the type I IFN pathway and leads to loss of anti-tumor efficacy in mice

Systemic administration of small molecule toll-like receptor (TLR)-7 agonists leads to potent activation of innate immunity and to the generation of anti-tumor immune responses. However, activation of TLRs with small molecule agonists may lead to the induction of TLR tolerance, defined as a state of hyporesponsiveness to subsequent agonism, which may limit immune activation, the generation of anti-tumor responses and clinical response. Our data reveal that dose scheduling impacts on the efficacy of systemic therapy with the selective TLR7 agonist, 6-amino-2-(butylamino)-9-((6-(2-(dimethylamino)ethoxy)pyridin-3-yl)methyl)-7,9-dihydro-8H-purin-8-one (DSR-6434). In a preclinical model of renal cell cancer, systemic administration of DSR-6434 dosed once weekly resulted in a significant anti-tumor response. However, twice weekly dosing of DSR-6434 led to the induction of TLR tolerance, and no anti-tumor response was observed. We show that TLR7 tolerance was independent of type I interferon (IFN) negative feedback because induction of TLR7 tolerance was also observed in IFN-α/β receptor knockout mice treated with DSR-6434. Moreover, our data demonstrate that treatment of bone marrow-derived plasmacytoid dendritic cells (BM-pDC) with DSR-6434 led to downregulation of TLR7 expression. From our data, dose scheduling of systemically administered TLR7 agonists can impact on anti-tumor activity through the induction of TLR tolerance. Furthermore, TLR7 expression on pDC may be a useful biomarker of TLR7 tolerance and aid in the optimization of dosing schedules involving systemically administered TLR7 agonists.

Immuno-regulatory antibodies for the treatment of cancer

INTRODUCTION

After years of limited success, progress of anti-cancer immuno-therapeutics has been considerable over the past decade. Key to this progress has been the application of new biological insights around the importance and nature of immune checkpoints that are able to reverse down-regulation of anti-tumor immunity.

AREAS COVERED

An overview of the preclinical and recent clinical trial data on key immuno-regulatory agents currently in development, including antibody targeting of cytotoxic T-lymphocyte antigen 4 (CTLA-4), programmed death receptor 1 (PD-1) on T-lymphocytes and its principal ligand (PD-L1) on tumor cells as well as immune agonists (e.g., anti-CD40).

EXPERT OPINION

Durable long-term responses in some patients with advanced melanoma, initially with ipilimumab (anti-CTLA-4) and more recently antibodies targeting either PD-1 or PD-L1 in patients with melanoma and renal cancer, non-small-cell lung, bladder and head and neck cancers with less toxicity, have provided real optimism that immunotherapeutic approaches can improve outcomes in a wide range of cancer. The manageable tolerability of PD-1-pathway blockers and their unique mechanism of action are encouraging combination approaches. Current efforts focus on registration trials of single agents plus combinations in many different tumor types and treatment settings and identifying and developing predictive biomarkers of immunological response.

The antitumor immune response generated by fractionated radiation therapy may be limited by tumor cell adaptive resistance and can be circumvented by PD-L1 blockade

Fractionated radiation therapy (RT) leads to adaptive changes in the tumor microenvironment that may limit the generation of an antitumor immune response. We demonstrated that fractionated RT led to increased tumor cell expression of programmed cell death ligand 1 (PD-L1) in response to CD8⁺ T cell production of interferon gamma. Our data reveal that the efficacy of fractionated RT can be significantly improved through the generation of durable systemic immune responses when combined with concurrent, but not sequential, blockade of the PD-1/PD-L1 pathway.

Abstract 2567: Enhancement of antitumor activity of DSP-6434, a novel TLR7 agonist through reduction of TLR tolerance

Introduction: Systemic administration of the small molecule Toll-like receptor (TLR)-7 agonist DSR-6434 leads to potent activation of innate immunity and to the generation of anti-tumor immune responses. However, clinical responses with systemically administered TLR7 agonists have been underwhelming, in part because activation of TLRs with small-molecule agonists can induce TLR tolerance; defined as a state of hyporesponsiveness to subsequent agonism. This study is undertaken to identify conditions to overcome TLR tolerance.

Experimental procedures: To confirm the anti-tumor effect of DSR-6434, mice were inoculated with the mouse renal cell carcinoma cell line, Renca, at day 0, and then administrated DSR-6434 weekly from day 1, or twice weekly from day 6. To examine tolerance, wild-type or IFN-α/β receptor knockout (IFN-AR KO) mice were intravenously administrated DSR-6434 at intervals of 3, 7 or 10 days. Plasma samples were taken 2 hours after the second administration of DSR-6434 and IFN-α levels were measured. Splenocytes were isolated 24 hours following either single or sequential i.v. doses. To measure lymphocyte activation, CD69 expression was assessed and splenocyte-mediated cytotoxicity against YAC-1 target cells was determined. Bone-marrow derived pDC (BM-pDC) were also treated with DSR-6434 for 5 or 48 hours. Expression of TLR7 signaling-related genes was determined by real-time quantitative RT-PCR.

Results: Weekly administration of DSR-6434 significantly reduced tumor burden when compared to vehicle-treated mice. By contrast, pre-inoculation and 2qw administration of DSR-6434 completely abolished anti-tumor activity. IFN-α induction was completely impaired following the second administration of DSR-6434 after 3 days, partially impaired after 7 days, and fully functional when the dosing interval was extended to 10 days. Sequential dosing of DSR-6434 reduced the frequency of activated splenocytes (defined as CD69+) and the level of cytotoxicity, compared with a single administration of DSR-6434. TLR7 tolerance was also observed in IFN-AR KO mice, suggesting this effect was independent of IFN signaling. Interestingly, TLR7 down-regulation was only observed after DSR-6434 dosing, while the expression of other TLR7-signaling related genes was unaltered.

Conclusion: The dosing schedule of systemically administered TLR7 agonists significantly affect TLR tolerance and antitumor activity, offering a potential solution to overcome TLR tolerance . Furthermore, TLR7 expression on BM-pDC cells may serve as a useful biomarker of TLR7 tolerance and aid in the optimization of dosing schedules involving systemically administered TLR7 agonists.

Citation Format: Erina Koga-Yamakawa, Masashi Murata, Simon J. Dovedi, Robert W. Wilkinson, Hiroki Umehara, Eiji Sugaru, Yuko Hirose, Hideyuki Harada, David T. Robinson, Philip J. Jewsbury, Setsuko Yamamoto, Chiang J. Li. Enhancement of antitumor activity of DSP-6434, a novel TLR7 agonist through reduction of TLR tolerance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2567. doi:10.1158/1538-7445.AM2014-2567

Acquired resistance to fractionated radiotherapy can be overcome by concurrent PD-L1 blockade

Radiotherapy is a major part in the treatment of most common cancers, but many patients experience local recurrence with metastatic disease. In evaluating response biomarkers, we found that low doses of fractionated radiotherapy led to PD-L1 upregulation on tumor cells in a variety of syngeneic mouse models of cancer. Notably, fractionated radiotherapy delivered in combination with αPD-1 or αPD-L1 mAbs generated efficacious CD8(+) T-cell responses that improved local tumor control, long-term survival, and protection against tumor rechallenge. These favorable outcomes were associated with induction of a tumor antigen-specific memory immune response. Mechanistic investigations showed that IFNγ produced by CD8(+) T cells was responsible for mediating PD-L1 upregulation on tumor cells after delivery of fractionated radiotherapy. Scheduling of anti-PD-L1 mAb was important for therapeutic outcome, with concomitant but not sequential administration with fractionated radiotherapy required to improve survival. Taken together, our results reveal the mechanistic basis for an adaptive response by tumor cells that mediates resistance to fractionated radiotherapy and its treatment failure. With attention to scheduling, combination immunoradiotherapy with radiotherapy and PD-1/PD-L1 signaling blockade may offer an immediate strategy for clinical evaluation to improve treatment outcomes.

Abstract 5034: The antitumor immune response generated by radiation therapy may be limited by tumor cell adaptive resistance and can be circumvented by PD-L1 blockade

Radiation therapy (RT) is administered to around 50% of all cancer patients making it one of the most important cancer treatments. In addition to the direct cytoreductive effect of RT there is increasing evidence that radiation-induces immunogenic tumor cell death. Despite the immunogenicity of RT-induced tumor cell death, RT delivered to tumours in the clinic rarely generates therapeutic systemic anti-cancer immune responses or ‘abscopal effects’.

Here we show that tumor infiltrating CD8+ cytotoxic T lymphocytes (CTL) have increased expression of PD-1 following RT in vivo. Moreover, our data demonstrate that treatment of established syngeneic tumors with RT leads to upregulation of tumor cell expression of PD-L1 in vivo but not when cells are irradiated in vitro. Using depleting antibodies we determined that the depletion of CD8+ T cells but not CD4+ T cells or NK cells could abrogate this RT-induced increase in tumor cell expression of PD-L1 in vivo. Furthermore, silencing of IFNγR1 using ShRNA confirmed that this process was dependent on CD8+ T cell production of IFNγ suggesting an adaptive upregulation of PD-L1 following RT occurs in response to CTL activation. This novel finding suggests that the immunogenicity of RT may be limited via the PD-L1/PD-1 signalling axis and may contribute to treatment failure.

We next sought to determine whether blockade of the PD-1/PD-L1 signalling axis could enhance the therapeutic response to RT. Our study demonstrates that administration of either an anti-PD-1 or anti-PD-L1 mAb in combination with RT leads to substantially improved survival when compared to either monotherapy alone with approximately 60% of treated mice undergoing a complete response. In addition, our data reveal that combination therapy generates long-term immunological memory in mice that have undergone complete response protecting against tumor rechallenge.

This is the first report to our knowledge that demonstrates adaptive resistance through the upregulation of tumour cell PD-L1 expression in response to an RT-induced CTL response. This study demonstrates the potential for enhancing the efficacy of conventional RT through blockade of the PD-1/PD-L1 axis and warrants clinical evaluation.

Citation Format: Simon J. Dovedi, Graznya Lipowska-Bhalla, Eleanor Cheadle, Edmund Poon, Michelle Morrow, Ross Stewart, Robert Wilkinson, Jamie Honeychurch, Timothy Illidge. The antitumor immune response generated by radiation therapy may be limited by tumor cell adaptive resistance and can be circumvented by PD-L1 blockade. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5034. doi:10.1158/1538-7445.AM2014-5034

A novel systemically administered Toll-like receptor 7 agonist potentiates the effect of ionizing radiation in murine solid tumor models

Although topical TLR7 therapies such as imiquimod have proved successful in the treatment of dermatological malignancy, systemic delivery may be required for optimal immunotherapy of nondermatological tumors. We report that intravenous delivery of the novel small molecule TLR7 agonist, DSR-6434, leads to the induction of type 1 interferon and activation of T and B lymphocytes, NK and NKT cells. Our data demonstrate that systemic administration of DSR-6434 enhances the efficacy of ionizing radiation (IR) and leads to improved survival in mice bearing either CT26 or KHT tumors. Of the CT26 tumor-bearing mice that received combined therapy, 55% experienced complete tumor resolution. Our data reveal that these long-term surviving mice have a significantly greater frequency of tumor antigen specific CD8(+) T cells when compared to age-matched tumor-naïve cells. To evaluate therapeutic effects on spontaneous metastases, we showed that combination of DSR-6434 with local IR of the primary tumor significantly reduced metastatic burden in the lung, when compared to time-matched cohorts treated with IR alone. The data demonstrate that systemic administration of the novel TLR7 agonist DSR-6434 in combination with IR primes an antitumor CD8(+) T-cell response leading to improved survival in syngeneic models of colorectal carcinoma and fibrosarcoma. Importantly, efficacy extends to sites outside of the field of irradiation, reducing metastatic load. Clinical evaluation of systemic TLR7 therapy in combination with IR for the treatment of solid malignancy is warranted.

Immunogenic potential of irradiated lymphoma cells is enhanced by adjuvant immunotherapy and modulation of local macrophage populations

The aim of this study was to assess the immunogenic potential of irradiated lymphoma cells in vivo and determine whether immunogenicity can be enhanced by modulation of the host immune system. Syngeneic murine lymphoma models irradiated ex vivo were used as an orthotopic cellular vaccination prior to challenge with viable tumor cells. We demonstrate that irradiated lymphoma cells are poorly immunogenic and that protective anti-tumor CD8 T-cell responses require the addition of immunostimulatory monoclonal antibody as an immune adjuvant, and increased frequency of antigen exposure by multiple vaccinations. Furthermore, we show the potential importance of macrophages in regulating immunogenicity of irradiated lymphoma cells and demonstrate that depletion of macrophages using clodronate-encapsulated liposomes considerably enhances primary vaccination efficacy in the presence of adjuvant anti-CD40 antibody. Our results demonstrate that the immunogenic potential of poorly immunogenic lymphoma cells dying after radiation therapy can be improved by modulation of the host immune system.

Intratracheal and oral administration of SM-276001: a selective TLR7 agonist, leads to antitumor efficacy in primary and metastatic models of cancer

Topical TLR7 agonists such as imiquimod are highly effective for the treatment of dermatological malignancies; however, their efficacy in the treatment of nondermatological tumors has been less successful. We report that oral administration of the novel TLR7-selective small molecule agonist; SM-276001, leads to the induction of an inflammatory cytokine and chemokine milieu and to the activation of a diverse population of immune effector cells including T and B lymphocytes, NK and NKT cells. Oral administration of SM-276001 leads to the induction of IFNα, TNFα and IL-12p40 and a reduction in tumor burden in the Balb/c syngeneic Renca and CT26 models. Using the OV2944-HM-1 model of ovarian cancer which spontaneously metastasizes to the lungs following subcutaneous implantation, we evaluated the efficacy of intratracheal and oral administration of SM-276001 in an adjuvant setting following surgical resection of the primary tumor. We show that both oral and intratracheal TLR7 therapy can reduce the frequency of pulmonary metastasis, and metastasis to the axillary lymph nodes. These results demonstrate that SM-276001 is a potent selective TLR7 agonist that can induce antitumor immune responses when dosed either intratracheally or orally.