Microbes are an integral component of the tumor microenvironment. However, determinants of microbial presence remain ill-defined. Here, using spatial-profiling technologies, we show that bacterial and immune cell heterogeneity are spatially coupled. Mouse models of pancreatic cancer recapitulate the immune-microbial spatial coupling seen in humans. Distinct intra-tumoral niches are defined by T cells, with T cell-enriched and T cell-poor regions displaying unique bacterial communities that are associated with immunologically active and quiescent phenotypes, respectively, but are independent of the gut microbiome. Depletion of intra-tumoral bacteria slows tumor growth in T cell-poor tumors and alters the phenotype and presence of myeloid and B cells in T cell-enriched tumors but does not affect T cell infiltration. In contrast, T cell depletion disrupts the immunological state of tumors and reduces intra-tumoral bacteria. Our results establish a coupling between microbes and T cells in cancer wherein spatially defined immune-microbial communities differentially influence tumor biology.

Abstract Microbes play a crucial role in the tumor microenvironment, yet the factors governing their presence within tumors remain poorly understood. In this study, we employed advanced in situ spatial-profiling technologies to investigate the relationship between microbial and immune cell heterogeneity in human lung and pancreas cancers. We observed a spatial coupling between microbes and immune cells, which was also replicated in mouse models of pancreatic cancer. Within the tumor, distinct niches characterized by T cell abundance or scarcity exhibited varied microbial diversity and compositions associated with immunologically active and quiescent phenotypes. Interestingly, gut microbiome are similar between mice bearing T cell- enriched or T cell-poor pancreas tumors. Depletion of intra-tumoral bacteria resulted in reduced tumor growth specifically in T cell-poor tumors and altered the phenotype and presence of myeloid and B cells in T cell-enriched tumors, without affecting T cell infiltration. Conversely, depletion of T cells disrupted the immunological state of tumors and led to a decrease in intra-tumoral bacteria. Our findings highlight a tight interplay between microbes and T cells in the tumor microenvironment, where spatially defined immune-microbial communities differentially influence tumor biology. Citation Format: Yan Li, Renee B. Chang, Meredith L. Stone, Yuqing Xue, Heather Coho, Kelly Markowitz, Dhruv Patel, Veronica M. Herrera, Joey H. Li, Devora Delman, Liti Zhang, Shaanti Choi-Bose, Michael Giannone, Jae W. Lee, Gregory Beatty. Spatial coupling of microbes and immune cells shapes the tumor microenvironment in human cancers [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B030.

Metal Conjugated Antibodies for Mass Cytometry Analysis

Pancreatic ductal adenocarcinoma (PDA) is characterized by a robust myeloid cell infiltrate. Although myeloid cells in PDA most commonly associate with immunosuppression, they also show plasticity and possess the capacity to engage productive anti-tumor immunity, thereby providing a potential therapeutic vulnerability. Here, we show that distinct myeloid cell subsets infiltrating human PDA express non-redundant activating receptors. Among the most highly expressed receptors was the pattern recognition receptor CLEC7A, which was expressed by macrophages, monocytes, and immature myeloid cells. In contrast, the TNF superfamily member CD40, was expressed by dendritic cells (DC) and SPP1+ macrophages. We hypothesized that combinatory targeting of myeloid activating receptors might be needed to restore productive immunosurveillance in PDA. In immune checkpoint blockade-resistant mouse models of PDA, pharmacologic activation of CLEC7A, using beta glucan (BG) therapy was associated with upregulation of the CXCL2/3-CXCR2 axis and triggered increases in intra-tumoral macrophages and granulocytes. Conversely, CD40 agonist therapy induced activity of the CXCL9-CXCR3 axis and drove conventional DC type 1-dependent infiltration of CD4+ and CD8+ T cells into tumors. Neither myeloid agonist alone, though, was sufficient to trigger durable anti-tumor immunity. By contrast, induction of both myeloid and lymphoid immunosurveillance by co-activation of CLEC7A/CD40 pathways caused tumor eradication, durable tumor control and T cell dependent immunological memory. Depletion of CSF1R+ myeloid cells or T cells significantly reduced the anti-tumor activity of treatment thereby highlighting the cooperativity of innate and adaptive immunity for anti-tumor activity. Moreover, the efficacy of CLEC7A and CD40 co-activation was independent of immune checkpoint blockade. Thus, beyond inhibitory checkpoint molecules on T cells, combinatory activation of non-redundant myeloid signaling pathways can be leveraged to trigger durable anti-tumor immunity, suggesting a new immunotherapy paradigm. A clinical trial of CLEC7A and CD40 agonist therapy for the treatment of patients with PDA is under development. Citation Format: Max M. Wattenberg, Heather Coho, Veronica M. Herrera, Kathleen Graham, Meredith L. Stone, Yuqing Xue, Renee B. Chang, Christopher Cassella, Mingen Liu, Shaanti Choi-Bose, Stacy K. Thomas, Hana Choi, Yan Li, Lauren Melendez, Michael Giannone, Nandita Bose, Gregory L. Beatty. Co-activation of myeloid signaling pathways for pancreatic cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C018.

Abstract TGFβ is a pleiotropic cytokine with immunosuppressive activity. In preclinical models, blockade of TGFβ enhances the activity of radiation and invokes T-cell antitumor immunity. Here, we combined galunisertib, an oral TGFβ inhibitor, with stereotactic body radiotherapy (SBRT) in patients with advanced hepatocellular carcinoma (HCC) and assessed safety, efficacy, and immunologic correlatives. Patients (n = 15) with advanced HCC who progressed on, were intolerant of, or refused sorafenib were treated with galunisertib (150 mg orally twice a day) on days 1 to 14 of each 28-day cycle. A single dose of SBRT (18-Gy) was delivered between days 15 to 28 of cycle 1. Site of index lesions treated with SBRT included liver (9 patients), lymph node (4 patients), and lung (2 patients). Blood for high-dimensional single cell profiling was collected. The most common treatment-related adverse events were fatigue (53%), abdominal pain (46.6%), nausea (40%), and increased alkaline phosphatase (40%). There were two instances of grade 2 alkaline phosphatase increase and two instances of grade 2 bilirubin increase. One patient developed grade 3 achalasia, possibly related to treatment. Two patients achieved a partial response. Treatment with galunisertib was associated with a decrease in the frequency of activated T regulatory cells in the blood. Distinct peripheral blood leukocyte populations detected at baseline distinguished progressors from nonprogressors. Nonprogressors also had increased CD8+PD-1+TIGIT+ T cells in the blood after treatment. We found galunisertib combined with SBRT to be well tolerated and associated with antitumor activity in patients with HCC. Pre- and posttreatment immune profiling of the blood was able to distinguish patients with progression versus nonprogression.

Agonist CD40 antibodies are under clinical development in combination with chemotherapy as an approach to prime for antitumor T cell immunity. However, treatment with anti-CD40 is commonly accompanied by both systemic cytokine release and liver transaminase elevations, which together account for the most common dose-limiting toxicities. Moreover, anti-CD40 treatment increases the potential for chemotherapy-induced hepatotoxicity. Here, we report a mechanistic link between cytokine release and hepatotoxicity induced by anti-CD40 when combined with chemotherapy and show that toxicity can be suppressed without impairing therapeutic efficacy. We demonstrate in mice and humans that anti-CD40 triggers transient hepatotoxicity marked by increased serum transaminase levels. In doing so, anti-CD40 sensitizes the liver to drug-induced toxicity. Unexpectedly, this biology is not blocked by the depletion of multiple myeloid cell subsets, including macrophages, inflammatory monocytes, and granulocytes. Transcriptional profiling of the liver after anti-CD40 revealed activation of multiple cytokine pathways including TNF and IL-6. Neutralization of TNF, but not IL-6, prevented sensitization of the liver to hepatotoxicity induced with anti-CD40 in combination with chemotherapy without impacting antitumor efficacy. Our findings reveal a clinically feasible approach to mitigate toxicity without impairing efficacy in the use of agonist CD40 antibodies for cancer immunotherapy.

Agonistic anti-CD40 monoclonal antibody (mAb) therapy in combination with chemotherapy (chemoimmunotherapy) shows promise for the treatment of pancreatic ductal adenocarcinoma (PDA). To gain insight into immunological mechanisms of response and resistance to chemoimmunotherapy, we analyzed blood samples from patients (n = 22) with advanced PDA treated with an anti-CD40 mAb (CP-870,893) in combination with gemcitabine. We found a stereotyped cellular response to chemoimmunotherapy characterized by transient B cell, CD56+CD11c+HLA-DR+CD141+ cell, and monocyte depletion and CD4+ T cell activation. However, these cellular pharmacodynamics did not associate with outcomes. In contrast, we identified an inflammatory network in the peripheral blood consisting of neutrophils, cytokines (IL-6 and IL-8), and acute phase reactants (C-reactive protein and serum amyloid A) that was associated with outcomes. Furthermore, monocytes from patients with elevated plasma IL-6 and IL-8 showed distinct transcriptional profiles, including upregulation of CCR2 and GAS6, genes associated with regulation of leukocyte chemotaxis and response to inflammation. Patients with systemic inflammation, defined by neutrophil/lymphocyte ratio (NLR) greater than 3.1, had a shorter median overall survival (5.8 vs. 12.3 months) as compared with patients with NLR less than 3.1. Taken together, our findings identify systemic inflammation as a potential resistance mechanism to a CD40-based chemoimmunotherapy and suggest biomarkers for future studies.

4575 Background: TGF-β is a pleiotropic cytokine with immunosuppressive activity. In mouse models, blockade of TGF-β signaling enhances the activity of radiation and invokes T cell dependent anti-tumor immunity. We previously reported preliminary safety and efficacy results from a pilot study combining galunisertib (LY2157299), an oral TGF-β inhibitor, with SBRT for the treatment of patients with advanced HCC. Here, we investigate immunological mechanisms and potential biomarkers associated with therapeutic activity. Methods: Patients with advanced HCC who had progressed on or refused sorafenib were treated with galunisertib (150 mg PO BID) on days 1-14 of each 28-day cycle. SBRT (18 Gy) was delivered in a single dose between days 15-28 of cycle 1. Blood was collected at baseline, following two weeks of galunisertib and following SBRT for high-dimensional analysis using a 37-marker CyTOF panel. Patients were dichotomized based on best response as either progressor (PD) or non-progressor (PR+SD). The frequency of immune subsets was compared between groups. Results: Fifteen patients were enrolled and treated. One patient was not evaluable. The most common adverse event was grade 1 or 2 fatigue in 53% of patients. The only possibly-related grade 3 event was achalasia in one patient which coincided with disease progression. Two patients achieved a PR and six patients had SD (DCR 57%) with a median progression-free survival of 3.7 months and a median overall survival of 9.0 months. For most patients, regardless of outcome, galunisertib treatment was associated with a decrease in activated Ki67+ Treg cells. However, pre-treatment immune composition within the blood of progressors and non-progressors was distinct. At baseline, progressors had an increased frequency of naive-like CD8+ T cells, whereas non-progressors had an increased frequency of non-classical monocytes. After combination therapy, only non-progressors showed a significant increase in CD8+PD1+TIGIT+ T cells. Conclusions: Galunisertib combined with SBRT was well-tolerated with modest efficacy. Immune profiling of the blood revealed distinct pre- and post-treatment signatures that differentiated patients with progression versus non-progression. These findings show that the combination of anti-TGF-β therapy with radiation can mediate disease control and identify potential correlates of efficacy. Clinical trial information: NCT02906397 .