Longitudinal immune characterization of syngeneic tumor models to enable model selection for immune oncology drug discovery

Combination of Bremachlorin PDT and Immune Checkpoint Inhibitor Anti-PD-1 Shows Response in Murine Immunological T-cell-High and T-cell-Low PDAC Models

Pancreatic ductal adenocarcinoma (PDAC) is one of the most challenging types of cancer with little or no response to immune checkpoint inhibitors (ICI). Photodynamic therapy (PDT) has been shown to ablate tumors and induce an immune response. In our study, we investigated the effect of PDT using the photosensitizer Bremachlorin, in its ability to reduce tumor burden and immunologically sensitize T-cell-high and T-cell-low murine PDAC tumors to the ICIs that blocks PD-1 immune checkpoint. In addition, we monitored the effect on survival and investigated if there was a response in PDT-treated and non-PDT-treated distant tumors. Our results showed that Bremachlorin PDT induces direct tumor killing that increased survival in both "hot" T-cell-high and "cold" T-cell-low PDAC tumors and that it can make T-cell-high tumors more sensitive to ICIs blocking PD-1. We found that T-cell-high tumor-bearing mice had an overall greater response to therapy than did T-cell-low tumor-bearing mice. One mouse with T-cell-high tumors exhibited complete tumor regression in both the treated and nontreated distant tumor 90 days after treatment. These results indicate that combining ICIs with Bremachlorin PDT could be a promising therapeutic intervention for enhancing PDAC's response to therapy.

Transcriptomic analysis of the immune response to in vivo gene electrotransfer in colorectal cancer

Gene electrotransfer (GET) has recently emerged as an effective nonviral approach for plasmid DNA (pDNA) delivery in gene therapy for several pathologies, including cancer. Multiple mechanisms have been identified that influence cell biology after GET, as electroporation significantly increases pDNA uptake and immunogenicity, which may directly influence target cell death. However, the molecular effects of in vivo electroporation-mediated DNA delivery have yet to be fully elucidated. In this study, we evaluated the transcriptomes of murine colorectal tumors treated with two protocols, short- and high-voltage (SHV) electric pulses or an adapted high-voltage-low-voltage (HV-LV) pulse protocol, both of which are used for reversible electroporation. Although no significant differences in clinical outcomes were observed, variations in intratumoral macrophage infiltration were reported between the two treatment methods. Transcriptomic analysis revealed that apoptosis is a predominant mode of cell death after GET by SHV pulses, whereas GET by HV-LV pulses is associated with immunogenic necrotic pathways as well as the activation of both the innate and adaptive immune response. We demonstrated that specific pulse parameters can induce distinct immunomodulatory profiles in the tumor microenvironment; therefore, these aspects should be considered carefully when selecting the most suitable GET-based approach for antitumor immunization.

Infiltration of innate and adoptive lymphoid cells in 4T1 and MC4-L2 breast cancer models

Objectives

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes that have vital roles in activating further immune responses. However, due to their tumor-induced diversity, we decided to examine ILCs, T cells, and the associated cytokines in mouse models of breast cancer.

Materials and Methods

4T1 and MC4-L2 cells were used to induce triple-negative and hormone-receptor-positive breast cancer, respectively. Tumor tissue was resected at early and late stages of tumor growth and used for further analysis. Total RNA was extracted and used in Real-Time PCR to analyze the expression of IFN-γ, IL-4, IL-10, IL-13, and IL-22. Tumor tissue was digested and used in a flow cytometric assay. H&E staining was used to examine the pathology of tumor progression.

Results

Both tumor models showed a notable increase in T-cell frequency at the early stage of tumor growth. However, as the tumors progressed, the frequency of T cells significantly decreased, while the ILC component exhibited a significant increase in tumor progression. Gene analysis indicated a significant increase in the inflammatory to anti-inflammatory cytokine ratio during tumor progression in the tumor model. In contrast, this ratio was considerably reduced in advanced MC4-L2 tumors. Both tumor models showed the development of invasive breast carcinoma and lung metastasis in advanced tumors.

Conclusion

Our study highlighted the expansion of ILCs during tumor progression in two distinct breast cancer models with different immunogenicity. These findings suggest that ILCs may actively modulate the tumor microenvironment during the advanced stage of tumor growth.

The Evolving Applications of Bispecific Antibodies: Reaping the Harvest of Early Sowing and Planting New Seeds

After decades of gradual progress from conceptualization to early clinical trials (1960-2000), the therapeutic potential of bispecific antibodies (bisp Abs) is now being fully realized. Insights gained from both successful and unsuccessful trials are helping to identify which mechanisms of action, antibody formats, and targets prove most effective, and which may benefit from further refinement. While T-cell engagers remain the most commonly used class of bisp Abs, current efforts aim to increase their effectiveness by co-engaging costimulatory molecules, reducing escape mechanisms, and countering immunosuppression. Strategies to minimize cytokine release syndrome (CRS) are also actively under development. In addition, novel antibody formats that are selectively activated within tumors are an exciting area of research, as is the precise targeting of specific T-cell subsets. Beyond T cells, the recruitment of macrophages and dendritic cells is attracting increasing interest, with researchers exploring various macrophage receptors to promote phagocytosis or to carry out specialized functions, such as the immunologically silent clearance of amyloid-beta plaques in the brain. While bisp Abs targeting B cells are relatively limited, they are primarily aimed at inhibiting B-cell activity in autoimmune diseases. Another evolving application involves the forced interaction between proteins. Beyond the successful development of Hemlibra for hemophilia, bispecific antibodies that mimic cytokine activity are being explored. Additionally, the recruitment of cell surface ubiquitin ligases and other enzymes represents a novel and promising therapeutic strategy. In regard to antibody formats, some applications such as the combination of T-cell engagers with costimulatory molecules are driving the development of trispecific antibodies, at least in preclinical settings. However, the increasing structural complexity of multispecific antibodies often leads to more challenging development paths, and the number of multispecific antibodies in clinical trials remains low. The clinical success of certain applications and well-established production methods position this therapeutic class to expand its benefits into other therapeutic areas.

OMIP-105: A 30-color full-spectrum flow cytometry panel to characterize the immune cell landscape in spleen and tumor within a syngeneic MC-38 murine colon carcinoma model

This panel was designed to characterize the immune cell landscape in the mouse tumor microenvironment as well as mouse lymphoid tissues (e.g., spleen). As an example, using the MC-38 mouse syngeneic tumor model, we demonstrated that we could measure the frequency and characterize the functional status of CD4 T cells, CD8 T cells, regulatory T cells, NK cells, B cells, macrophages, granulocytes, monocytes, and dendritic cells. This panel is especially useful for understanding the immune landscape in "cold" preclinical tumor models with very low immune cell infiltration and for investigating how therapeutic treatments may modulate the immune landscape.

Validation of the C-X-C chemokine receptor 3 (CXCR3) as a target for PET imaging of T cell activation

PURPOSE

CXCR3 is expressed on activated T cells and plays a crucial role in T-cell recruitment to the tumor microenvironment (TME) during cell-based and immune checkpoint inhibitor (ICI) immunotherapy. This study utilized a 64Cu-labeled NOTA-α-CXCR3 antibody to assess CXCR3 expression in the TME and validate it as a potential T cell activation biomarker in vivo.

PROCEDURES

CXCR3+ cells infiltrating MC38 tumors (B57BL/6 mice, untreated and treated with αPD-1/αCTLA-4 ICI) were quantified using fluorescence microscopy and flow cytometry. A commercial anti-mouse CXCR3 antibody (α-CXCR3) was site-specifically conjugated with 2,2,2-(1,4,7-triazacyclononane-1,4,7-triyl)triacetic acid (NOTA) and radiolabeled with 64Cu. Saturation binding of [64Cu]Cu-NOTA-α-CXCR3 was investigated using CHO cells stably transfected with murine CXCR3. Biodistribution and PET imaging studies both at baseline and after 1 to 3 cycles of ICI, respectively, were carried out using different molar activities (10 GBq/µmol to 300 GBq/µmol) of [64Cu]Cu-NOTA-α-CXCR3.

RESULTS

Flow cytometry analysis at baseline confirmed the presence of CXCR3 + T-cells in MC38 tumors, which was significantly increased at day five after ICI (treated 33.8 ± 17.4 vs. control 8.8 ± 6.2 CD3+CXCR3+ cells/mg). These results were qualitatively and quantitatively confirmed by immunofluorescence of tumor cryoslices. In vivo PET imaging of MC38 tumor bearing mice before, during and after ICI using [64Cu]Cu-NOTA-α-CXCR3 (Kd = 3.3 nM) revealed a strong dependence of CXCR3-specificity of tracer accumulation in secondary lymphoid organs on molar activity. At 300 GBq/µmol (1.5 µg of antibody/mouse), a specific signal was observed in lymph nodes (6.33 ± 1.25 control vs. 3.95 ± 1.23%IA/g blocking) and the spleen (6.04 ± 1.02 control vs. 3.84 ± 0.79%IA/g blocking) at 48 h p.i. Spleen-to-liver ratios indicated a time dependent systemic immune response showing a steady increase from 1.08 ± 0.19 (untreated control) to 1.54 ± 0.14 (three ICI cycles).

CONCLUSIONS

This study demonstrates the feasibility of in vivo imaging of CXCR3 upregulation under immunotherapy using antibodies. However, high molar activities and low antibody doses are essential for sensitive detection in lymph nodes and spleen. Detecting therapy-induced changes in CXCR3+ T cell numbers in tumors was challenging due to secondary antibody-related effects. Nonetheless, CXCR3 remains a promising target for imaging T cell activation, with anticipated improvements in sensitivity using alternative tracers with high affinities and favorable pharmacokinetics.

Mapping the genetic landscape establishing a tumor immune microenvironment favorable for anti-PD-1 response in mice and humans

Identifying host genetic factors modulating immune checkpoint inhibitor (ICI) efficacy has been experimentally challenging because of variations in both host and tumor genomes, differences in the microbiome, and patient life exposures. Utilizing the Collaborative Cross (CC) multi-parent mouse genetic resource population, we developed an approach that fixes the tumor genomic configuration while varying host genetics. With this approach, we discovered that response to anti-PD-1 (aPD1) immunotherapy was significantly heritable in four distinct murine tumor models (H2 between 0.18-0.40). For the MC38 colorectal carcinoma system (H2 = 0.40), we mapped four significant ICI response quantitative trait loci (QTL) localized to mouse chromosomes (mChr) 5, 9, 15 and 17, and identified significant epistatic interactions between specific QTL pairs. Differentially expressed genes within these QTL were highly enriched for immune genes and pathways mediating allograft rejection and graft vs host disease. Using a cross species analytical approach, we found a core network of 48 genes within the four QTLs that showed significant prognostic value for overall survival in aPD1 treated human cohorts that outperformed all other existing validated immunotherapy biomarkers, especially in human tumors of the previously defined immune subtype 4. Functional blockade of two top candidate immune targets within the 48 gene network, GM-CSF and high affinity IL-2/IL-15 signaling, completely abrogated the MC38 tumor transcriptional response to aPD1 therapy in vivo. Thus, we have established a powerful cross species in vivo platform capable of uncovering host genetic factors that establish the tumor immune microenvironment configuration propitious for ICI response.

Exploiting temporal aspects of cancer immunotherapy

Many mechanisms underlying an effective immunotherapy-induced antitumour response are transient and critically time dependent. This is equally true for several immunological events in the tumour microenvironment induced by other cancer treatments. Immune checkpoint therapy (ICT) has proven to be very effective in the treatment of some cancers, but unfortunately, with many cancer types, most patients do not experience a benefit. To improve outcomes, a multitude of clinical trials are testing combinations of ICT with various other treatment modalities. Ideally, those combination treatments should take time-dependent immunological events into account. Recent studies have started to map the dynamic cellular and molecular changes that occur during treatment with ICT, in the tumour and systemically. Here, we overlay the dynamic ICT response with the therapeutic response following surgery, radiotherapy, chemotherapy and targeted therapies. We propose that by combining treatments in a time-conscious manner, we may optimally exploit the interactions between the individual therapies.

Enhanced Proteomic Coverage in Tissue Microenvironment by Immune Cell Subtype Library-Assisted DIA-MS

Immune cells that infiltrate the tumor microenvironment (TME) play crucial roles in shaping cancer development and influencing clinical outcomes and therapeutic responses. However, obtaining a comprehensive proteomic snapshot of tumor-infiltrating immunity in clinical specimens is often hindered by small sample amounts and a low proportion of immune infiltrating cells in the TME. To enable in-depth and highly sensitive profiling of microscale tissues, we established an immune cell-enriched library-assisted strategy for data-independent acquisition mass spectrometry (DIA-MS). Firstly, six immune cell subtype-specific spectral libraries were established from sorted cluster of differentiation markers, CD8+, CD4+ T lymphocytes, B lymphocytes, natural killer cells, dendritic cells, and macrophages in murine mesenteric lymph nodes (MLNs), covering 7815 protein groups with surface markers and immune cell-enriched proteins. The feasibility of microscale immune proteomic profiling was demonstrated on 1 μg tissue protein from the tumor of murine colorectal cancer (CRC) models using single-shot DIA; the immune cell-enriched library increased coverage to quantify 7419 proteins compared to directDIA analysis (6978 proteins). The enhancement enabled the mapping of 841 immune function-related proteins and exclusive identification of many low-abundance immune proteins, such as CD1D1, and CD244, demonstrating high sensitivity for immune landscape profiling. This approach was used to characterize the MLNs in CRC models, aiming to elucidate the mechanism underlying their involvement in cancer development within the TME. Even with a low percentage of immune cell infiltration (0.25-3%) in the tumor, our results illuminate downregulation in the adaptive immune signaling pathways (such as C-type lectin receptor signaling, and chemokine signaling), T cell receptor signaling, and Th1/Th2/Th17 cell differentiation, suggesting an immunosuppressive status in MLNs of CRC model. The DIA approach using the immune cell-enriched libraries showcased deep coverage and high sensitivity that can facilitate illumination of the immune proteomic landscape for microscale samples.

Towards effective CAIX-targeted radionuclide and checkpoint inhibition combination therapy for advanced clear cell renal cell carcinoma

Background: Immune checkpoint inhibitors (ICI) are routinely used in advanced clear cell renal cell carcinoma (ccRCC). However, a substantial group of patients does not respond to ICI therapy. Radiation is a promising approach to increase ICI response rates since it can generate anti-tumor immunity. Targeted radionuclide therapy (TRT) is a systemic radiation treatment, ideally suited for precision irradiation of metastasized cancer. Therefore, the aim of this study is to explore the potential of combined TRT, targeting carbonic anhydrase IX (CAIX) which is overexpressed in ccRCC, using [177Lu]Lu-DOTA-hG250, and ICI for the treatment of ccRCC. Methods: In this study, we evaluated the therapeutic and immunological action of [177Lu]Lu-DOTA-hG250 combined with aPD-1/a-CTLA-4 ICI. First, the biodistribution of [177Lu]Lu-DOTA-hG250 was investigated in BALB/cAnNRj mice bearing Renca-CAIX or CT26-CAIX tumors. Renca-CAIX and CT26-CAIX tumors are characterized by poor versus extensive T-cell infiltration and homogeneous versus heterogeneous PD-L1 expression, respectively. Tumor-absorbed radiation doses were estimated through dosimetry. Subsequently, [177Lu]Lu-DOTA-hG250 TRT efficacy with and without ICI was evaluated by monitoring tumor growth and survival. Therapy-induced changes in the tumor microenvironment were studied by collection of tumor tissue before and 5 or 8 days after treatment and analyzed by immunohistochemistry, flow cytometry, and RNA profiling. Results: Biodistribution studies showed high tumor uptake of [177Lu]Lu-DOTA-hG250 in both tumor models. Dose escalation therapy studies in Renca-CAIX tumor-bearing mice demonstrated dose-dependent anti-tumor efficacy of [177Lu]Lu-DOTA-hG250 and remarkable therapeutic synergy including complete remissions when a presumed subtherapeutic TRT dose (4 MBq, which had no significant efficacy as monotherapy) was combined with aPD-1+aCTLA-4. Similar results were obtained in the CT26-CAIX model for 4 MBq [177Lu]Lu-DOTA-hG250 + a-PD1. Ex vivo analyses of treated tumors revealed DNA damage, T-cell infiltration, and modulated immune signaling pathways in the TME after combination treatment. Conclusions: Subtherapeutic [177Lu]Lu-DOTA-hG250 combined with ICI showed superior therapeutic outcome and significantly altered the TME. Our results underline the importance of investigating this combination treatment for patients with advanced ccRCC in a clinical setting. Further investigations should focus on how the combination therapy should be optimally applied in the future.

Hierarchical cluster analysis and nonlinear mixed-effects modelling for candidate biomarker detection in preclinical models of cancer

BACKGROUND

Preclinical models of cancer can be of translational benefit when assessing how different biomarkers are regulated in response to particular treatments. Detection of molecular biomarkers in preclinical models of cancer is difficult due inter-animal variability in responses, combined with limited accessibility of longitudinal data.

METHODS

Nonlinear mixed-effects modelling (NLME) was used to analyse tumour growth data based on expected tumour growth rates observed 7 days after initial doses (DD7) of Radiotherapy (RT) and Combination of RT with DNA Damage Response Inhibitors (DDRi). Cox regression was performed to confirm an association between DD7 and survival. Hierarchical Cluster Analysis (HCA) was then used to identify candidate biomarkers impacting responses to RT and RT/DDRi and these were validated using NLME.

RESULTS

Cox regression confirmed significant associations between DD7 and survival. HCA of RT treated samples, combined with NLME confirmed significant associations between DD7 and Cluster specific CD8+ Ki67 MFI, as well as DD7 and cluster specific Natural Killer cell density in RT treated mice.

CONCLUSION

Application of NLME, as well as HCA of candidate biomarkers may provide additional avenues to assess the effect of RT in MC38 syngeneic tumour models. Additional studies would need to be conducted to confirm association between DD7 and biomarkers in RT/DDRi treated mice.

PD-1/CD80+ small extracellular vesicles from immunocytes induce cold tumours featured with enhanced adaptive immunosuppression

Only a minority of cancer patients benefit from immune checkpoint blockade therapy. Sophisticated cross-talk among different immune checkpoint pathways as well as interaction pattern of immune checkpoint molecules carried on circulating small extracellular vesicles (sEV) might contribute to the low response rate. Here we demonstrate that PD-1 and CD80 carried on immunocyte-derived sEVs (I-sEV) induce an adaptive redistribution of PD-L1 in tumour cells. The resulting decreased cell membrane PD-L1 expression and increased sEV PD-L1 secretion into the circulation contribute to systemic immunosuppression. PD-1/CD80+ I-sEVs also induce downregulation of adhesion- and antigen presentation-related molecules on tumour cells and impaired immune cell infiltration, thereby converting tumours to an immunologically cold phenotype. Moreover, synchronous analysis of multiple checkpoint molecules, including PD-1, CD80 and PD-L1, on circulating sEVs distinguishes clinical responders from those patients who poorly respond to anti-PD-1 treatment. Altogether, our study shows that sEVs carry multiple inhibitory immune checkpoints proteins, which form a potentially targetable adaptive loop to suppress antitumour immunity.

Applications of Flow Cytometry in Drug Discovery and Translational Research

Flow cytometry is a mainstay technique in cell biology research, where it is used for phenotypic analysis of mixed cell populations. Quantitative approaches have unlocked a deeper value of flow cytometry in drug discovery research. As the number of drug modalities and druggable mechanisms increases, there is an increasing drive to identify meaningful biomarkers, evaluate the relationship between pharmacokinetics and pharmacodynamics (PK/PD), and translate these insights into the evaluation of patients enrolled in early clinical trials. In this review, we discuss emerging roles for flow cytometry in the translational setting that supports the transition and evaluation of novel compounds in the clinic.

Peritoneal carcinomatosis in mouse models

Peritoneal carcinomatosis (PCa) represents a metastatic stage of a disease with unmet therapeutic options. Malignant cells from primary tumors (gastrointestinal or gynecologic malignancies) invade the peritoneal cavity and eventually seed onto peritoneal surfaces, with the omentum being the most common nest area. With a median survival of less than 6 months, PCa has a dismal prognosis that can be improved with treatments only available to a select few individuals with low tumor burden. Thus, the discovery of novel and effective therapies for this disease depends on reliable animal models. Here, we describe a method to generate syngeneic PCa mouse models based on intraperitoneal (i.p.) administration of tumor cells. This model allows to follow-up cancer progression in PCa models from ovarian and colorectal origins monitoring mice bodyweight changes, ascites development and overall survival. Moreover, luciferase-expressing tumor cells can also be used to assess tumor growth after i.p. injection through in vivo bioluminescence quantification. The establishment of reliable, easy-to-monitor and reproducible intraperitoneal syngeneic tumors models, as described here, is the first step to develop cutting-edge therapies against PCa.

A Cancer Nanovaccine for Co-Delivery of Peptide Neoantigens and Optimized Combinations of STING and TLR4 Agonists

Immune checkpoint blockade (ICB) has revolutionized cancer treatment and led to complete and durable responses, but only for a minority of patients. Resistance to ICB can largely be attributed to insufficient number and/or function of antitumor CD8+ T cells in the tumor microenvironment. Neoantigen targeted cancer vaccines can activate and expand the antitumor T cell repertoire, but historically, clinical responses have been poor because immunity against peptide antigens is typically weak, resulting in insufficient activation of CD8+ cytotoxic T cells. Herein, we describe a nanoparticle vaccine platform that can overcome these barriers in several ways. First, the vaccine can be reproducibly formulated using a scalable confined impingement jet mixing method to coload a variety of physicochemically diverse peptide antigens and multiple vaccine adjuvants into pH-responsive, vesicular nanoparticles that are monodisperse and less than 100 nm in diameter. Using this approach, we encapsulated synergistically acting adjuvants, cGAMP and monophosphoryl lipid A (MPLA), into the nanocarrier to induce a robust and tailored innate immune response that increased peptide antigen immunogenicity. We found that incorporating both adjuvants into the nanovaccine synergistically enhanced expression of dendritic cell costimulatory markers, pro-inflammatory cytokine secretion, and peptide antigen cross-presentation. Additionally, the nanoparticle delivery increased lymph node accumulation and uptake of peptide antigen by dendritic cells in the draining lymph node. Consequently, nanoparticle codelivery of peptide antigen, cGAMP, and MPLA enhanced the antigen-specific CD8+ T cell response and delayed tumor growth in several mouse models. Finally, the nanoparticle platform improved the efficacy of ICB immunotherapy in a murine colon carcinoma model. This work establishes a versatile nanoparticle vaccine platform for codelivery of peptide neoantigens and synergistic adjuvants to enhance responses to cancer vaccines.

In vivo C6 glioma models: an update and a guide toward a more effective preclinical evaluation of potential anti-glioblastoma drugs

Glioblastoma multiform (GBM) is the most common primary brain tumor with a poor prognosis and few therapeutic choices. In vivo, tumor models are useful for enhancing knowledge of underlying GBM pathology and developing more effective therapies/agents at the preclinical level, as they recapitulate human brain tumors. The C6 glioma cell line has been one of the most widely used cell lines in neuro-oncology research as they produce tumors that share the most similarities with human GBM regarding genetic, invasion, and expansion profiles and characteristics. This review provides an overview of the distinctive features and the different animal models produced by the C6 cell line. We also highlight specific applications of various C6 in vivo models according to the purpose of the study and offer some technical notes for more convenient/repeatable modeling. This work also includes novel findings discovered in our laboratory, which would further enhance the feasibility of the model in preclinical GBM investigations.

A Bacterial and Ganglioside-based Nanoparticle Initiates Reprogramming of Macrophages and Promotes Antitumor Phenotypes

Macrophages represent the most abundant immune component of the tumor microenvironment and often exhibit protumorigenic (M2-like) phenotypes that contribute to disease progression. Despite their generally accepted protumorigenic role, macrophages can also display tumoricidal (or M1-like) behavior, revealing that macrophages can be functionally reprogrammed, depending on the cues received within the tumor microenvironment. Moreover, such plasticity may be achieved by pharmacologic or biologic interventions. To that end, we previously demonstrated that a novel immunomodulator termed the "very small size particle" (VSSP) facilitates maturation of dendritic cells and differentiation of myeloid-derived suppressor cells to APCs with reduced suppressive activity in cancer models. VSSP was further shown to act in the bone marrow to drive the differentiation of progenitors toward monocytes, macrophages, and dendritic cells during emergency myelopoiesis. However, the underlying mechanisms for VSSP-driven alterations in myeloid differentiation and function remained unclear. In this study, in mouse models, we focused on macrophages and tested the hypothesis that VSSP drives macrophages toward M1-like functional states via IRF8- and PU.1-dependent mechanisms. We further hypothesized that such VSSP-mediated actions would be accompanied by enhanced antitumor responses. Overall, we showed that (1) VSSP drives naive or M2-derived macrophages to M1-like states, (2) the M1-like state induced by VSSP occurs via IRF8- and PU.1-dependent mechanisms, and (3) single-agent VSSP induces an antitumor response that is accompanied by alterations in the intratumoral myeloid compartment. These results provide a deeper mechanistic underpinning of VSSP and strengthen its use to drive M1-like responses in host defense, including cancer.

Engineered IL-7 synergizes with IL-12 immunotherapy to prevent T cell exhaustion and promote memory without exacerbating toxicity

Cancer immunotherapy is moving toward combination regimens with agents of complementary mechanisms of action to achieve more frequent and robust efficacy. However, compared with single-agent therapies, combination immunotherapies are associated with increased overall toxicity because the very same mechanisms also work in concert to enhance systemic inflammation and promote off-tumor toxicity. Therefore, rational design of combination regimens that achieve improved antitumor control without exacerbated toxicity is a main objective in combination immunotherapy. Here, we show that the combination of engineered, tumor matrix-binding interleukin-7 (IL-7) and IL-12 achieves remarkable anticancer effects by activating complementary pathways without inducing any additive immunotoxicity. Mechanistically, engineered IL-12 provided effector properties to T cells, while IL-7 prevented their exhaustion and boosted memory formation as assessed by tumor rechallenge experiments. The dual combination also rendered checkpoint inhibitor (CPI)-resistant genetically engineered melanoma model responsive to CPI. Thus, our approach provides a framework of evaluation of rationally designed combinations in immuno-oncology and yields a promising therapy.

Dysfunctional TLR1 reduces the therapeutic efficacy of chemotherapy by attenuating HMGB1-mediated antitumor immunity in locally advanced colorectal cancer

Regional lymph node metastasis is an important predictor for survival outcome and an indicator for postoperative adjuvant chemotherapy in patients with colorectal cancer. Even with advances in adjuvant chemotherapeutic regimens, 5-year distant metastasis and survival rates are still unsatisfactory. Here, we evaluate the clinical significance of polymorphisms in receptors for HMGB1, which is the hallmark of chemotherapy-induced immunogenic cell death, in patients with stage II-III colon carcinoma (COAD). We found that high cytosolic HMGB1 is elicited in stage III COAD patients who received adjuvant chemotherapy. Patients with the TLR1-N248S polymorphism (rs4833095), which causes loss-of-function in HMGB1-mediated TLR1-TLR2 signaling, may influence the therapeutic efficacy of adjuvant chemotherapy, leading to a high risk of distant metastasis within 5 years [HR = 1.694, 95% CI = 1.063-2.698, p = 0.027], suggesting that TLR1-N248S is an independent prognostic factor for locally advanced colon carcinoma patients. We found that defective TLR1 impaired TLR1/2 signaling during dendritic cell (DC) maturation for the antitumor immune response under immunogenic chemotherapy oxaliplatin (OXP) treatment. Defective TLR1 on DCs impaired their maturation ability by HMGB1 and reduced the secretion of IFNγ from T cells to eradicate tumor cells in vitro. Moreover, systemic inhibition of TLR1/2 dramatically reduced the tumor-infiltrating immune cells by OXP treatment, leading to poor therapeutic response to OXP. In contrast, administration of a TLR1/2 agonist synergistically increased the benefit of OXP treatment and triggered a high density of tumor-infiltrating immune cells. We also observed that fewer tumor-infiltrating cytotoxic T lymphocytes were located within the tumor microenvironment in patients bearing the TLR1-N248S polymorphism. Overall, our results suggest that dysfunctional TLR1 may reduce the therapeutic response to adjuvant chemotherapy by impairing HMGB1-mediated DC maturation and attenuating the antitumor immune response in locally advanced colon carcinoma patients.

Decoding the Complexity of Immune-Cancer Cell Interactions: Empowering the Future of Cancer Immunotherapy

The tumor and tumor microenvironment (TME) consist of a complex network of cells, including malignant, immune, fibroblast, and vascular cells, which communicate with each other. Disruptions in cell-cell communication within the TME, caused by a multitude of extrinsic and intrinsic factors, can contribute to tumorigenesis, hinder the host immune system, and enable tumor evasion. Understanding and addressing intercellular miscommunications in the TME are vital for combating these processes. The effectiveness of immunotherapy and the heterogeneous response observed among patients can be attributed to the intricate cellular communication between immune cells and cancer cells. To unravel these interactions, various experimental, statistical, and computational techniques have been developed. These include ligand-receptor analysis, intercellular proximity labeling approaches, and imaging-based methods, which provide insights into the distorted cell-cell interactions within the TME. By characterizing these interactions, we can enhance the design of cancer immunotherapy strategies. In this review, we present recent advancements in the field of mapping intercellular communication, with a particular focus on immune-tumor cellular interactions. By modeling these interactions, we can identify critical factors and develop strategies to improve immunotherapy response and overcome treatment resistance.

Whole-body bioluminescence imaging of T-cell response in PDAC models

Introduction

The location of T-cells during tumor progression and treatment provides crucial information in predicting the response in vivo.

Methods

Here, we investigated, using our bioluminescent, dual color, T-cell reporter mouse, termed TbiLuc, T-cell location and function during murine PDAC tumor growth and checkpoint blockade treatment with anti-PD-1 and anti-CTLA-4. Using this model, we could visualize T-cell location and function in the tumor and the surrounding tumor microenvironment longitudinally. We used murine PDAC clones that formed in vivo tumors with either high T-cell infiltration (immunologically 'hot') or low T-cell infiltration (immunologically 'cold').

Results

Differences in total T-cell bioluminescence could be seen between the 'hot' and 'cold' tumors in the TbiLuc mice. During checkpoint blockade treatment we could see in the tumor-draining lymph nodes an increase in bioluminescence on day 7 after treatment.

Conclusions

In the current work, we showed that the TbiLuc mice can be used to monitor T-cell location and function during tumor growth and treatment.

Combined therapeutic effect of YHO-1701 with PD-1 blockade is dependent on natural killer cell activity in syngeneic mouse models

The signal transducer and activator of transcription 3 (STAT3) signaling pathway is a key mediator of cancer cell proliferation, survival, and invasion. We discovered YHO-1701 as a small molecule inhibitor of STAT3 dimerization and demonstrated its potent anti-tumor activity using xenograft mouse models as monotherapy and combination therapy with molecular targeted drugs. STAT3 is also associated with cancer immune tolerance; therefore, we used the female CT26 syngeneic mouse model to examine the effect of combining YHO-1701 administration with PD-1/PD-L1 blockade. Pretreatment of the mice with YHO-1701 before starting anti-PD-1 antibody administration resulted in a significant therapeutic effect. In addition, the effect of monotherapy and combination treatment with YHO-1701 was significantly abolished by depleting natural killer (NK) cell activity. YHO-1701 was also found to restore the activity of mouse NK cells under inhibitory conditions in vitro. Furthermore, this combination therapy significantly inhibited tumor growth in an immunotherapy-resistant model of murine CMS5a fibrosarcoma. These results suggest that the combination of YHO-1701 with PD-1/PD-L1 blockade might be a new candidate for cancer immunotherapy involving the enhancement of NK cell activity in the tumor microenvironment.

Systematic elucidation and pharmacological targeting of tumor-infiltrating regulatory T cell master regulators

Due to their immunosuppressive role, tumor-infiltrating regulatory T cells (TI-Tregs) represent attractive immuno-oncology targets. Analysis of TI vs. peripheral Tregs (P-Tregs) from 36 patients, across four malignancies, identified 17 candidate master regulators (MRs) as mechanistic determinants of TI-Treg transcriptional state. Pooled CRISPR-Cas9 screening in vivo, using a chimeric hematopoietic stem cell transplant model, confirmed the essentiality of eight MRs in TI-Treg recruitment and/or retention without affecting other T cell subtypes, and targeting one of the most significant MRs (Trps1) by CRISPR KO significantly reduced ectopic tumor growth. Analysis of drugs capable of inverting TI-Treg MR activity identified low-dose gemcitabine as the top prediction. Indeed, gemcitabine treatment inhibited tumor growth in immunocompetent but not immunocompromised allografts, increased anti-PD-1 efficacy, and depleted MR-expressing TI-Tregs in vivo. This study provides key insight into Treg signaling, specifically in the context of cancer, and a generalizable strategy to systematically elucidate and target MR proteins in immunosuppressive subpopulations.

Evaluation of a CD206-Targeted Peptide for PET Imaging of Macrophages in Syngeneic Mouse Models of Cancer

Tumor-associated macrophages (TAMs) are large phagocytic cells that play numerous roles in cancer biology and are an important component of the relationship between immune system response and tumor progression. The peptide, RP832c, targets the Mannose Receptor (CD206) expressed on M2-like macrophages and is cross-reactive to both human and murine CD206. Additionally, it exhibits therapeutic properties through its ability to shift the population of TAMs from an M2-like (protumor) toward an M1-like phenotype (antitumor) and has demonstrated promise in inhibiting tumor resistance in PD-L1 unresponsive melanoma murine models. In addition, it has shown inhibition in bleomycin-induced pulmonary fibrosis through interactions with CD206 macrophages.1,2 Our work aims to develop a novel CD206 positron emission tomography (PET) imaging probe based on RP832c (Kd = 5.64 μM) as a direct, noninvasive method for the assessment of TAMs in mouse models of cancer. We adapted RP832c to incorporate the chelator DOTA to allow for radiolabeling with the PET isotope 68Ga (t1/2 = 68 min; ß+ = 89%). In vitro stability studies were conducted in mouse serum up to 3 h. The in vitro binding characteristics of [68Ga]RP832c to CD206 were determined by a protein plate binding assay and Surface Plasmon Resonance (SPR). PET imaging and biodistribution studies were conducted in syngeneic tumor models. Stability studies in mouse serum demonstrated that 68Ga remained complexed up to 3 h (less than 1% free 68Ga). Binding affinity studies demonstrated high binding of [68Ga]RP832c to mouse CD206 protein and that the binding of the tracer was able to be blocked significantly when incubated with a blocking solution of native RP832c. PET imaging and biodistribution studies in syngeneic tumor models demonstrated uptake in tumor and CD206 expressing organs of [68Ga]RP832c. A significant correlation was found between the percentage of CD206 present in each tumor imaged with [68Ga]RP832c and PET imaging mean standardized uptake values in a CT26 mouse model of cancer. The data shows that [68Ga]RP832c represents a promising candidate for macrophage imaging in cancer and other diseases.

Late-stage MC38 tumours recapitulate features of human colorectal cancer - implications for appropriate timepoint selection in preclinical studies

Anti-tumour T cell responses play a crucial role in controlling the progression of colorectal cancer (CRC), making this disease a promising candidate for immunotherapy. However, responses to immune-targeted therapies are currently limited to subpopulations of patients and specific types of cancer. Clinical studies have therefore focussed on identifying biomarkers that predict immunotherapy responses and elucidating the immunological landscapes of different cancers. Meanwhile, our understanding of how preclinical tumour models resemble human disease has fallen behind, despite their crucial role in immune-targeted drug development. A deeper understanding of these models is therefore needed to improve the development of immunotherapies and the translation of findings made in these systems. MC38 colon adenocarcinoma is a widely used preclinical model, yet how it recapitulates human colorectal cancer remains poorly defined. This study investigated the tumour-T cell immune landscape of MC38 tumours using histology, immunohistochemistry, and flow cytometry. We demonstrate that early-stage tumours exhibit a nascent TME, lacking important immune-resistance mechanisms of clinical interest, while late-stage tumours exhibit a mature TME resembling human tumours, with desmoplasia, T cell exhaustion, and T cell exclusion. Consequently, these findings clarify appropriate timepoint selection in the MC38 model when investigating both immunotherapies and mechanisms that contribute to immunotherapy resistance. Overall, this study provides a valuable resource that will enable appropriate application of the MC38 model and expedite the development and clinical translation of new immunotherapies.

Activatable near-infrared probes for the detection of specific populations of tumour-infiltrating leukocytes in vivo and in urine

Tracking the immune microenvironment of tumours is essential for understanding the mechanisms behind the effectiveness of cancer immunotherapies. Molecular imaging of tumour-infiltrating leukocytes (TILs) can be used to non-invasively monitor the tumour immune microenvironment, but current imaging agents do not distinguish TILs from leukocytes resident in other tissues. Here we report a library of activatable molecular probes for the imaging, via near-infrared fluorescence, of specific TILs (including M1 macrophages, cytotoxic T lymphocytes and neutrophils) in vivo in real time and also via excreted urine, owing to the probes' renal clearance. The fluorescence of the probes is activated only in the presence of both tumour and leukocyte biomarkers, which allows for the imaging of populations of specific TILs in mouse models of cancers with sensitivities and specificities similar to those achieved via flow-cytometric analyses of biopsied tumour tissues. We also show that the probes enable the non-invasive evaluation of the immunogenicity of different tumours, the dynamic monitoring of responses to immunotherapies and the accurate prediction of tumour growth under various treatments.

Characterization of immune cell populations in syngeneic murine tumor models

Immunocompetent murine models are important tools for preclinical evaluation of immunotherapies. Here, six different immunocompetent tumor models based on four different cell lines were characterized, including metastatic lung cancer (CMT 167), triple-negative breast cancer (4T1), pancreatic cancer (KPCY), and colon cancer (MC38). The tumors were implanted subcutaneously or orthotopically before the animals were treated with anti-PD1 checkpoint inhibitor. A range of innate and adaptive immune cells were then quantified by flow cytometry of single-cell suspensions from the tumors. Furthermore, confocal laser scanning microscopy was used to quantify the density and distribution of T-cells in frozen sections. A model-dependent cellular immune landscape was observed, with variable responsiveness toward anti-PD1, ranging from the most responsive MC38 colon cancer model to the least responsive 4T1 breast cancer model. The study provides an overview of the immune landscape of these tumor models, and a foundation for further elucidation of pro-tumor and anti-tumor mechanisms behind heterogeneous responses towards immunotherapies.

Immunotargeting of Cancer Stem Cells

The generally accepted view is that CSCs hijack the signaling pathways attributed to normal stem cells that regulate the self-renewal and differentiation processes. Therefore, the development of selective targeting strategies for CSC, although clinically meaningful, is associated with significant challenges because CSC and normal stem cells share many important signaling mechanisms for their maintenance and survival. Furthermore, the efficacy of this therapy is opposed by tumor heterogeneity and CSC plasticity. While there have been considerable efforts to target CSC populations by the chemical inhibition of the developmental pathways such as Notch, Hedgehog (Hh), and Wnt/β-catenin, noticeably fewer attempts were focused on the stimulation of the immune response by CSC-specific antigens, including cell-surface targets. Cancer immunotherapies are based on triggering the anti-tumor immune response by specific activation and targeted redirecting of immune cells toward tumor cells. This review is focused on CSC-directed immunotherapeutic approaches such as bispecific antibodies and antibody-drug candidates, CSC-targeted cellular immunotherapies, and immune-based vaccines. We discuss the strategies to improve the safety and efficacy of the different immunotherapeutic approaches and describe the current state of their clinical development.

Inducing mismatch repair deficiency sensitizes immune-cold neuroblastoma to anti-CTLA4 and generates broad anti-tumor immune memory

Immune checkpoint blockade can induce potent and durable responses in patients with highly immunogenic mismatch repair-deficient tumors; however, these drugs are ineffective against immune-cold neuroblastoma tumors. To establish a role for a T cell-based therapy against neuroblastoma, we show that T cell and memory T cell-dependent gene expression are associated with improved survival in high-risk neuroblastoma patients. To stimulate anti-tumor immunity and reproduce this immune phenotype in neuroblastoma tumors, we used CRISPR-Cas9 to knockout MLH1-a crucial molecule in the DNA mismatch repair pathway-to induce mismatch repair deficiency in a poorly immunogenic murine neuroblastoma model. Induced mismatch repair deficiency increased the expression of proinflammatory genes and stimulated T cell infiltration into neuroblastoma tumors. In contrast to adult cancers with induced mismatch repair deficiency, neuroblastoma tumors remained unresponsive to anti-PD1 treatment. However, anti-CTLA4 therapy was highly effective against these tumors. Anti-CTLA4 therapy promoted immune memory and T cell epitope spreading in cured animals. Mechanistically, the effect of anti-CTLA4 therapy against neuroblastoma tumors with induced mismatch repair deficiency is CD4+ T cell dependent, as depletion of these cells abolished the effect. Therefore, a therapeutic strategy involving mismatch repair deficiency-based T cell infiltration of neuroblastoma tumors combined with anti-CTLA4 can serve as a novel T cell-based treatment strategy for neuroblastoma.

TLR5 agonists enhance anti-tumor immunity and overcome resistance to immune checkpoint therapy

Primary and adaptive resistance to immune checkpoint therapies (ICT) represent a considerable obstacle to achieving enhanced overall survival. Innate immune activators have been actively pursued for their antitumor potential. Herein we report that a syngeneic 4T1 mammary carcinoma murine model for established highly-refractory triple negative breast cancer showed enhanced survival when treated intra-tumorally with either the TLR5 agonist flagellin or CBLB502, a flagellin derivative, in combination with antibodies targeting CTLA-4 and PD-1. Long-term survivor mice showed immunologic memory upon tumor re-challenge and a distinctive immune activating cytokine profile that engaged both innate and adaptive immunity. Low serum levels of G-CSF and CXCL5 (as well as high IL-15) were candidate predictive biomarkers correlating with enhanced survival. CBLB502-induced enhancement of ICT was also observed in poorly immunogenic B16-F10 melanoma tumors. Combination immune checkpoint therapy plus TLR5 agonists may offer a new therapeutic strategy to treat ICT-refractory solid tumors.

Impact of mouse model tumor implantation site on acquired resistance to anti-PD-1 immune checkpoint therapy

Introduction

The use of tumor subcutaneous (SC) implantations rather than orthotopic sites is likely to induce a significant bias, in particular, in the field of immunotherapy.

Methods

In this study, we developed and characterized MC38 models, implanted subcutaneously and orthotopically, which were either sensitive or rendered resistant to anti-PD1 therapy. We characterized the tumor immune infiltrate by flow cytometry at baseline and after treatment.

Results and Discussion

Our results demonstrate several differences between SC and orthotopic models at basal state, which tend to become similar after therapy. These results emphasize the need to take into account tumor implantation sites when performing preclinical studies with immunotherapeutic agents.

Cancer-targeted photoimmunotherapy induces antitumor immunity and can be augmented by anti-PD-1 therapy for durable anticancer responses in an immunologically active murine tumor model

The complex immunosuppressive nature of solid tumor microenvironments poses a significant challenge to generating efficacious and durable anticancer responses. Photoimmunotherapy is a cancer treatment strategy by which an antibody is conjugated with a non-toxic light-activatable dye. Following administration of the conjugate and binding to the target tumor, subsequent local laser illumination activates the dye, resulting in highly specific target cell membrane disruption. Here we demonstrate that photoimmunotherapy treatment elicited tumor necrosis, thus inducing immunogenic cell death characterized by the release of damage-associated molecular patterns (DAMPs). Photoimmunotherapy-killed tumor cells activated dendritic cells (DC), leading to the production of proinflammatory cytokines, T cell stimulation, priming antigen-specific T cells, and durable memory T cell responses, which led complete responder mice to effectively reject new tumors upon rechallenge. PD-1 blockade in combination with photoimmunotherapy enhanced overall anticancer efficacy, including against anti-PD-1-resistant tumors. The combination treatment also elicited abscopal anticancer activity, as observed by reduction of distal, non-illuminated tumors, further demonstrating the ability of photoimmunotherapy to harness local and peripheral T cell responses. With this work we therefore delineate the immune mechanisms of action for photoimmunotherapy and demonstrate the potential for cancer-targeted photoimmunotherapy to be combined with other immunotherapy approaches for augmented, durable anticancer efficacy. Moreover, we demonstrate responses utilizing various immunocompetent mouse models, as well as in vitro data from human cells, suggesting broad translational potential.

Attenuated Salmonella potentiate PD-L1 blockade immunotherapy in a preclinical model of colorectal cancer

The use of immune checkpoint inhibitors to treat cancer resulted in unprecedented and durable clinical benefits. However, the response rate among patients remains rather modest. Previous work from our laboratory demonstrated the efficacy of using attenuated bacteria as immunomodulatory anti-cancer agents. The current study investigated the potential of utilizing a low dose of attenuated Salmonella typhimurium to enhance the efficacy of PD-L1 blockade in a relatively immunogenic model of colon cancer. The response of MC38 tumors to treatment with αPD-L1 monoclonal antibody (mAb) was variable, with only 30% of the mice being responsive. Combined treatment with αPD-L1 mAb and Salmonella resulted in 75% inhibition of tumor growth in 100% of animals. Mechanistically, the enhanced response correlated with a decrease in the percentage of tumor-associated granulocytic cells, upregulation in MHC class II expression by intratumoral monocytes and an increase in tumor infiltration by effector T cells. Collectively, these alterations resulted in improved anti-tumor effector responses and increased apoptosis within the tumor. Thus, our study demonstrates that a novel combination treatment utilizing attenuated Salmonella and αPD-L1 mAb could improve the outcome of immunotherapy in colorectal cancer.

Assessment of spatial transcriptomics for oncology discovery

Tumor heterogeneity is a major challenge for oncology drug discovery and development. Understanding of the spatial tumor landscape is key to identifying new targets and impactful model systems. Here, we test the utility of spatial transcriptomics (ST) for oncology discovery by profiling 40 tissue sections and 80,024 capture spots across a diverse set of tissue types, sample formats, and RNA capture chemistries. We verify the accuracy and fidelity of ST by leveraging matched pathology analysis, which provides a ground truth for tissue section composition. We then use spatial data to demonstrate the capture of key tumor depth features, identifying hypoxia, necrosis, vasculature, and extracellular matrix variation. We also leverage spatial context to identify relative cell-type locations showing the anti-correlation of tumor and immune cells in syngeneic cancer models. Lastly, we demonstrate target identification approaches in clinical pancreatic adenocarcinoma samples, highlighting tumor intrinsic biomarkers and paracrine signaling.

Eradication of tumors and development of anti-cancer immunity using STINGa targeted by pHLIP

Despite significant progress in the development of novel STING agonists (STINGa), applications appear to be challenged by the low efficiency and poor selectivity of these agents. A pH Low Insertion Peptide (pHLIP) extends the lifetime of a STINGa in the blood and targets it to acidic cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), myeloid derived suppressor cells (mMDSCs) and dendritic cells (DCs). CAFs constitute 25% of all live cells within CT26 tumors, and M2-type TAMs and mMDSCs are the most abundant among the immune cells. The resulting activation of cytokines within the tumor microenvironment (TME) triggers the eradication of small (100 mm³) and large (400-700 mm³) CT26 tumors in mice after a single dose of pHLIP-STINGa. The tumor stroma was destroyed (the number of CAFs was reduced by 98%), intratumoral hemorrhage developed, and the level of acidity within the TME was reduced. Further, no tumors developed in 20 out of 25 tumor-free mice re-challenged by an additional injection of cancer cells. The therapeutic effect on CT26 tumors was insignificant in nude mice, lacking T-cells. Thus, targeted delivery of STINGa to tumor stroma and TAMs induces activation of signaling, potentially resulting in the recruitment and infiltration of T-cells, which gain access to the tumor core. The cytotoxic activity of T-cells is not impaired by an acidic environment and immune memory is developed.

Machine learning on syngeneic mouse tumor profiles to model clinical immunotherapy response

Most patients with cancer are refractory to immune checkpoint blockade (ICB) therapy, and proper patient stratification remains an open question. Primary patient data suffer from high heterogeneity, low accessibility, and lack of proper controls. In contrast, syngeneic mouse tumor models enable controlled experiments with ICB treatments. Using transcriptomic and experimental variables from >700 ICB-treated/control syngeneic mouse tumors, we developed a machine learning framework to model tumor immunity and identify factors influencing ICB response. Projected on human immunotherapy trial data, we found that the model can predict clinical ICB response. We further applied the model to predicting ICB-responsive/resistant cancer types in The Cancer Genome Atlas, which agreed well with existing clinical reports. Last, feature analysis implicated factors associated with ICB response. In summary, our computational framework based on mouse tumor data reliably stratified patients regarding ICB response, informed resistance mechanisms, and has the potential for wide applications in disease treatment studies.

TNIK Inhibition Has Dual Synergistic Effects on Tumor and Associated Immune Cells

Treatment with checkpoint inhibitors can be extraordinarily effective in a fraction of patients, particularly those whose tumors are pre-infiltrated by T cells. In others, efficacy is considerably lower, which has led to interest in developing strategies for sensitization to immunotherapy. Using various colorectal cancer mouse models, it is shown that the use of Traf2 and Nck-interacting protein kinase inhibitors (TNIKi) unexpectedly increases tumor infiltration by PD-1⁺ CD8⁺ T cells, thus contributing to tumor control. This appears to happen by two independent mechanisms, by inducing immunogenic cell death and separately by directly activating CD8. The use of TNIKi achieves complete tumor control in 50% of mice when combined with checkpoint inhibitor targeting PD-1. These findings reveal immunogenic properties of TNIKi and indicate that the proportion of colorectal cancers responding to checkpoint therapy can be increased by combining it with immunogenic kinase inhibitors.

PARP inhibition is a modulator of anti-tumor immune response in BRCA-deficient tumors

PARP inhibitors are synthetically lethal with BRCA1/2 mutations, and in this setting, accumulation of DNA damage leads to cell death. Because increased DNA damage and subsequent immune activation can prime an anti-tumor immune response, we studied the impact of olaparib ± immune checkpoint blockade (ICB) on anti-tumor activity and the immune microenvironment. Concurrent combination of olaparib, at clinically relevant exposures, with ICB gave durable and deeper anti-tumor activity in the Brca1m BR5 model vs. monotherapies. Olaparib and combination treatment modulated the immune microenvironment, including increases in CD8+ T cells and NK cells, and upregulation of immune pathways, including type I IFN and STING signaling. Olaparib also induced a dose-dependent upregulation of immune pathways, including JAK/STAT, STING and type I IFN, in the tumor cell compartment of a BRCA1m (HBCx-10) but not a BRCA WT (HBCx-9) breast PDX model. In vitro, olaparib induced BRCAm tumor cell–specific dendritic cell transactivation. Relevance to human disease was assessed using patient samples from the MEDIOLA (NCT02734004) trial, which showed increased type I IFN, STING, and JAK/STAT pathway expression following olaparib treatment, in line with preclinical findings. These data together provide evidence for a mechanism and schedule underpinning potential benefit of ICB combination with olaparib.

TGF-β and CIS inhibition overcomes NK cell suppression to restore anti-tumor immunity

Antibodies targeting "immune checkpoints" have revolutionized cancer therapy by reactivating tumor-resident cytotoxic lymphocytes, primarily CD8+ T cells. Interest in targeting analogous pathways in other cytotoxic lymphocytes is growing. Natural killer (NK) cells are key to cancer immunosurveillance by eradicating metastases and driving solid tumor inflammation. NK cell anti-tumor function is dependent on the cytokine interleukin (IL)-15. Ablation of the IL-15 signaling inhibitor CIS (Cish) enhances NK cell anti-tumor immunity by increasing NK cell metabolism and persistence within the tumor microenvironment (TME). The TME has also been shown to impair NK cell fitness via the production of immunosuppressive TGF-β, a suppression which occurs even in the presence of high IL-15 signaling. Here, we identified an unexpected interaction between CIS and the TGF-β signaling pathway in NK cells. Independently, Cish- and Tgfbr2-deficient NK cells are both hyper-responsive to IL-15 and hypo-responsive to TGF-β, with dramatically enhanced anti-tumor immunity. Remarkably, when both these immunosuppressive genes are simultaneously deleted in NK cells, mice are largely resistant to tumor development, suggesting that combining suppression of these two pathways might represent a novel therapeutic strategy to enhance innate anti-cancer immunity.

IN VIVO SYNGENEIC TUMOR MODELS WITH ACQUIRED RESISTANCE TO ANTI-PD-1/PD-L1 THERAPIES

Antibodies targeting PD-1 and PD-L1 have produced durable responses in a subset of cancer patients. However, a majority of these patients will ultimately relapse due to acquired resistance. To explore the underlying mechanisms of this secondary resistance, we developed five syngeneic murine tumor variants with acquired resistance to anti-PD-1 and/or PD-L1 antibodies in vivo. Resistant in vivo models were obtained by serial treatment/reimplantation cycles of the MC38 colorectal, MB49 and MBT2 bladder, TyrNras melanoma and RENCA kidney models. Tumor immune infiltrates were characterized for wild type and resistant tumors using spectral cytometry and their molecular alterations analyzed using RNA-seq analyses. Alterations in the tumor immune microenvironment were strongly heterogeneous amongst resistant models, involving select lymphoid and/or myeloid subpopulations. Molecular alterations in resistant models included previously identified pathways as well as novel candidate genes found to be deregulated in several resistant models. Among these, Serpinf1, coding for Pigment Epithelial Derived Factor was further explored in the MC38 and the MBT2 models. Overexpression of Serpinf1 induced resistance to anti-PD-1 antibodies in the MC38 model, whereas knock-down of Serpinf1 sensitized this model as well as the primarily resistant MBT2 model. Serpinf1 overexpression was associated with increased production of free fatty acids and reduced activation of CD8+ cells, while orlistat, a compound that reduces the production of free fatty acids, reversed resistance to anti-PD-1 therapy. Our results suggest that a panel of syngeneic resistant models constitutes a useful tool to model the heterogeneity of resistance mechanisms encountered in the clinic.

Multiparameter Longitudinal Imaging of Immune Cell Activity in Chimeric Antigen Receptor T Cell and Checkpoint Blockade Therapies

Longitudinal multimodal imaging presents unique opportunities for noninvasive surveillance and prediction of treatment response to cancer immunotherapy. In this work we first designed a novel granzyme B activated self-assembly small molecule, G-SNAT, for the assessment of cytotoxic T lymphocyte mediated cancer cell killing. G-SNAT was found to specifically detect the activity of granzyme B within the cytotoxic granules of activated T cells and engaged cancer cells in vitro. In lymphoma tumor-bearing mice, the retention of cyanine 5 labeled G-SNAT-Cy5 correlated to CAR T cell mediated granzyme B exocytosis and tumor eradication. In colorectal tumor-bearing transgenic mice with hematopoietic cells expressing firefly luciferase, longitudinal bioluminescence and fluorescence imaging revealed that after combination treatment of anti-PD-1 and anti-CTLA-4, the dynamics of immune cell trafficking, tumor infiltration, and cytotoxic activity predicted the therapeutic outcome before tumor shrinkage was evident. These results support further development of G-SNAT for imaging early immune response to checkpoint blockade and CAR T-cell therapy in patients and highlight the utility of multimodality imaging for improved mechanistic insights into cancer immunotherapy.

Direct targeting of FOXP3 in Tregs with AZD8701, a novel antisense oligonucleotide to relieve immunosuppression in cancer

BACKGROUND

The Regulatory T cell (Treg) lineage is defined by the transcription factor FOXP3, which controls immune-suppressive gene expression profiles. Tregs are often recruited in high frequencies to the tumor microenvironment where they can suppress antitumor immunity. We hypothesized that pharmacological inhibition of FOXP3 by systemically delivered, unformulated constrained ethyl-modified antisense oligonucleotides could modulate the activity of Tregs and augment antitumor immunity providing therapeutic benefit in cancer models and potentially in man.

METHODS

We have identified murine Foxp3 antisense oligonucleotides (ASOs) and clinical candidate human FOXP3 ASO AZD8701. Pharmacology and biological effects of FOXP3 inhibitors on Treg function and antitumor immunity were tested in cultured Tregs and mouse syngeneic tumor models. Experiments were controlled by vehicle and non-targeting control ASO groups as well as by use of multiple independent FOXP3 ASOs. Statistical significance of biological effects was evaluated by one or two-way analysis of variance with multiple comparisons.

RESULTS

AZD8701 demonstrated a dose-dependent knockdown of FOXP3 in primary Tregs, reduction of suppressive function and efficient target downregulation in humanized mice at clinically relevant doses. Surrogate murine FOXP3 ASO, which efficiently downregulated Foxp3 messenger RNA and protein levels in primary Tregs, reduced Treg suppressive function in immune suppression assays in vitro. FOXP3 ASO promoted more than 70% reduction in FOXP3 levels in Tregs in vitro and in vivo, strongly modulated Treg effector molecules (eg, ICOS, CTLA-4, CD25 and 4-1BB), and augmented CD8⁺ T cell activation and produced antitumor activity in syngeneic tumor models. The combination of FOXP3 ASOs with immune checkpoint blockade further enhanced antitumor efficacy.

CONCLUSIONS

Antisense inhibitors of FOXP3 offer a promising novel cancer immunotherapy approach. AZD8701 is being developed clinically as a first-in-class FOXP3 inhibitor for the treatment of cancer currently in Ph1a/b clinical trial (NCT04504669).

A novel immunopeptidomic-based pipeline for the generation of personalized oncolytic cancer vaccines

Besides the isolation and identification of major histocompatibility complex I-restricted peptides from the surface of cancer cells, one of the challenges is eliciting an effective antitumor CD8+ T-cell-mediated response as part of therapeutic cancer vaccine. Therefore, the establishment of a solid pipeline for the downstream selection of clinically relevant peptides and the subsequent creation of therapeutic cancer vaccines are of utmost importance. Indeed, the use of peptides for eliciting specific antitumor adaptive immunity is hindered by two main limitations: the efficient selection of the most optimal candidate peptides and the use of a highly immunogenic platform to combine with the peptides to induce effective tumor-specific adaptive immune responses. Here, we describe for the first time a streamlined pipeline for the generation of personalized cancer vaccines starting from the isolation and selection of the most immunogenic peptide candidates expressed on the tumor cells and ending in the generation of efficient therapeutic oncolytic cancer vaccines. This immunopeptidomics-based pipeline was carefully validated in a murine colon tumor model CT26. Specifically, we used state-of-the-art immunoprecipitation and mass spectrometric methodologies to isolate >8000 peptide targets from the CT26 tumor cell line. The selection of the target candidates was then based on two separate approaches: RNAseq analysis and HEX software. The latter is a tool previously developed by Jacopo, 2020, able to identify tumor antigens similar to pathogen antigens in order to exploit molecular mimicry and tumor pathogen cross-reactive T cells in cancer vaccine development. The generated list of candidates (26 in total) was further tested in a functional characterization assay using interferon-γ enzyme-linked immunospot (ELISpot), reducing the number of candidates to six. These peptides were then tested in our previously described oncolytic cancer vaccine platform PeptiCRAd, a vaccine platform that combines an immunogenic oncolytic adenovirus (OAd) coated with tumor antigen peptides. In our work, PeptiCRAd was successfully used for the treatment of mice bearing CT26, controlling the primary malignant lesion and most importantly a secondary, nontreated, cancer lesion. These results confirmed the feasibility of applying the described pipeline for the selection of peptide candidates and generation of therapeutic oncolytic cancer vaccine, filling a gap in the field of cancer immunotherapy, and paving the way to translate our pipeline into human therapeutic approach.

Exosome-mediated genetic reprogramming of tumor-associated macrophages by exoASO-STAT6 leads to potent monotherapy antitumor activity

Effectiveness of checkpoint immunotherapy in cancer can be undermined by immunosuppressive tumor-associated macrophages (TAMs) with an M2 phenotype. Reprogramming TAMs toward a proinflammatory M1 phenotype is a novel approach to induce antitumor immunity. The M2 phenotype is controlled by key transcription factors such as signal transducer and activator of transcription 6 (STAT6), which have been "undruggable" selectively in TAMs. We describe an engineered exosome therapeutic candidate delivering an antisense oligonucleotide (ASO) targeting STAT6 (exoASO-STAT6), which selectively silences STAT6 expression in TAMs. In syngeneic models of colorectal cancer and hepatocellular carcinoma, exoASO-STAT6 monotherapy results in >90% tumor growth inhibition and 50 to 80% complete remissions. Administration of exoASO-STAT6 leads to induction of nitric oxide synthase 2 (NOS2), an M1 macrophage marker, resulting in remodeling of the tumor microenvironment and generation of a CD8 T cell-mediated adaptive immune response. Collectively, exoASO-STAT6 represents the first platform targeting transcription factors in TAMs in a highly selective manner.

A Combination of Chemotherapy and Oncolytic Virotherapy Sensitizes Colorectal Adenocarcinoma to Immune Checkpoint Inhibitors in a cDC1-Dependent Manner

Immune checkpoint therapy has shown great promise in the treatment of cancers with a high mutational burden, such as mismatch repair-deficient colorectal carcinoma (dMMR CRC). However, many patients fail to respond to immune checkpoint therapy. Using a mouse model of dMMR CRC, we demonstrated that tumors can be further sensitized to immune checkpoint therapy by using a combination of low-dose chemotherapy and oncolytic HSV-1. This combination induced the infiltration of CD8+ and CD4+ T cells into the tumor and the upregulation of gene signatures associated with the chemoattraction of myeloid cell subsets. When combined with immune checkpoint therapy, the combination promoted the infiltration of activated type 1 conventional dendritic cells (cDC1s) into the tumor. Furthermore, we found this combination strategy to be dependent on cDC1s, and its therapeutic efficacy to be abrogated in cDC1-deficient Batf3-/- mice. Thus, we demonstrated that the adjuvanticity of dMMR CRCs can be improved by combining low-dose chemotherapy and oncolytic HSV-1 in a cDC1-dependent manner.

CLEC5a-directed bispecific antibody for effective cellular phagocytosis

While antibody-dependent cellular phagocytosis mediated by activating Fcγ receptor is a key mechanism underlying many antibody drugs, their full therapeutic activities can be restricted by the inhibitory Fcγ receptor IIB (FcγRIIB). Here, we describe a bispecific antibody approach that harnesses phagocytic receptor CLEC5A (C-type Lectin Domain Containing 5A) to drive Fcγ receptor-independent phagocytosis, potentially circumventing the negative impact of FcγRIIB. First, we established the effectiveness of such an approach by constructing bispecific antibodies that simultaneously target CLEC5A and live B cells. Furthermore, we demonstrated its in vivo application for regulatory T cell depletion and subsequent tumor regression.

Engineered Bacteria Enhance Immunotherapy and Targeted Therapy through Stromal Remodeling of Tumors

Desmoplastic solid tumors are characterized by the rapid build-up of extracellular matrix (ECM) macromolecules, such as hyaluronic acid (HA). The resulting physiological barrier prevents the infiltration of immune cells and also impedes the delivery of anticancer agents. The development of a hypervesiculating Escherichia coli Nissle (ΔECHy) based tumor targeting bacterial system capable of distributing a fusion peptide, cytolysin A (ClyA)-hyaluronidase (Hy) via outer membrane vesicles (OMVs) is reported. The capability of targeting hypoxic tumors, manufacturing recombinant proteins in situ and the added advantage of an on-site OMV based distribution system makes the engineered bacterial vector a unique candidate for peptide delivery. The HA degrading potential of Hy for stromal modulation is combined with the cytolytic activity of ClyA followed by testing it within syngeneic cancer models. ΔECHy is combined with immune checkpoint antibodies and tyrosine kinase inhibitors (TKIs) to demonstrate that remodeling the tumor stroma results in the improvement of immunotherapy outcomes and enhancing the efficacy of biological signaling inhibitors. The biocompatibility of ΔECHy is also investigated to show that the engineered bacteria are effectively cleared, elicit minimal inflammatory and immune responses, and therefore could be a reliable candidate as a live biotherapeutic.

Immuno-oncology trends: preclinical models, biomarkers, and clinical development

The landscape in immuno-oncology (I-O) has undergone profound changes since its early beginnings up through the rapid advances happening today. The current drug development pipeline consists of thousands of potential I-O therapies and therapy combinations, many of which are being evaluated in clinical trials. The efficient and successful development of these assets requires the investment in and utilization of appropriate tools and technologies that can facilitate the rapid transitions from preclinical evaluation through clinical development. These tools include (i) appropriate preclinical models, (ii) biomarkers of pharmacodynamic, predictive and monitoring utility, and (iii) evolving clinical trial designs that allow rapid and efficient evaluation during the development process. This article provides an overview of how novel discoveries and insights into each of these three areas have the potential to further address the clinical management needs for patients with cancer.