Impact of the ileal microbiota on colon cancer.

Besides tumor cell-intrinsic oncogenic pathways, host and environmental factors have a major impact on cancer immunosurveillance and the efficacy of immunotherapeutics. Several modalities of anticancer treatments including immunogenic chemotherapies and immune checkpoint inhibitors lose their efficacy in patients treated with broad-spectrum antibiotics, pointing to a key role for the gut microbiota. The complex interactions between intestinal microbes, gut immunity and anti-tumor responses constitute an emerging field of investigation. In this work, we revise key primary literature, with an emphasis on recent mechanistic insights, unraveling the interplay between the immunosurveillance of colon cancers and ileal factors including the local microbiota, tissue architecture and immune system.

Prevalence of human herpesviruses in biliary fluid and their association with biliary complications after liver transplantation.

BACKGROUND: Beta-herpesviruses are common opportunistic pathogens that cause morbidity after liver transplantation (LT). METHODS: Objective of the study was to evaluate the prevalence and correlation of herpesviruses in bile, blood and liver tissue and to investigate their association with biliary complications and retransplantation (re-LT) free survival after LT. The study design is a single-center case-control study. We performed quantative polymerase chain reaction (qPCR) for herpesvirus 1-8 DNA in bile, blood and liver tissue of 73 patients after first LT and analyzed their clinical courses retrospectively. RESULTS: The median follow-up was 48 months (range 2-102), during which a total of 16 patients underwent re-LT and 11 patients died. Of the patients, 46.5% received valganciclovir prophylaxis at the time of bile sample acquisition. Cytomegalovirus (CMV) (18.3%), human herpesvirus 6 (HHV-6) (34.2%), human herpesvirus 7 (HHV-7) (20.5%) and Epstein-Barr virus (EBV) (16.4%) were highly prevalent in bile after LT, while herpes simpex virus 1 and 2 (HSV-1, HSV-2), varicella-zoster virus (VZV) and human herpesvirus 8 (HHV-8) were not or rarely detected in bile. Valganciclovir prophylaxis did not reduce the prevalence of HHV-6 and HHV-7 in bile, but it did reduce the presence of CMV and EBV. The presence of HHV-6 in bile was associated with non-anastomotic biliary strictures (NAS) and acute cellular rejection (ACR). CONCLUSIONS: CMV, EBV, HHV-6 and HHV-7 are more prevalent in biliary fluid than in liver biopsy or blood serum after LT. HHV-6 and HHV-7 might be associated with biliary complications after LT. Biliary fluids might be an attractive target for routine herpesvirus detection.

Hypercalcemia, necrotizing pancreatitis and bone lesions: a benign cause.

Primary Hyperparathyroidism is asymptomatic in most patients (PHPT). We report a case of PHPT in a young male patient. He presented with severe pancreatitis due to hypercalcemia and multiple bone lesions resulting in pathological fractures. The patients recovered rapidly after parathyroidectomy.

Exacerbation of Myopathy in Glycogen Debrancher Deficiency After Liver Transplantation: Case Report and Review of the Literature.

BACKGROUND: Glycogen storage disorder (GSD) type IIIa is a rare inherited genetic disorder affecting liver and muscle tissue. Liver transplantation (LT) improves metabolic control, but muscle involvement persists. CASE: We report the case of a 31-year-old man who underwent orthotopic LT for end-stage liver disease caused by GSD type IIIa. After LT, he developed worsening clinical signs of myopathy, along with exponentially increasing levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and creatine kinase. Liver-related elevations of AST and ALT were excluded through liver biopsy and endoscopic cholangiography; consequently, AST and ALT elevations were attributed to the underlying muscle involvement. Exacerbation of muscle disease after LT could be attributed to restoration of liver glycogen metabolism after LT, leading to increased glucose accumulation in muscle cells, where the gene defect persists. A dietary intervention with a high-protein, ketogenic diet was initiated but did not lead to significant improvement of myalgia. CONCLUSION: LT exacerbated muscle disease in a patient with GSD type IIIa. Patients should be counseled about this possible side effect of LT in GSD type IIIa.

Durvalumab Plus Gemcitabine and Cisplatin in Patients with Advanced Biliary Tract Cancer: An Exploratory Analysis of Real-World Data.

BACKGROUND: The combination of gemcitabine and cisplatin (gem/cis) with the anti-PD-L1-antibody durvalumab was recently approved as first line therapy for biliary tract cancer (BTC) based on the results of the TOPAZ-1 trial. OBJECTIVE: We aim to analyse the feasibility and efficacy of the triple combination therapy in patients with BTC in a real-world setting and in correspondence with the genetic alterations of the cancer. METHODS: In this single-centre retrospective analysis, all patients with BTC and treated with durvalumab plus gem/cis from April 2022 to September 2023 were included. Survival and treatment response were investigated, within the context of the inclusion and exclusion criteria of TOPAZ-1 and in correspondence with genetic alterations of the cancer. RESULTS: In total, 35 patients, of which 51% met the inclusion criteria of the TOPAZ-1 trial, were analysed. Patients treated within TOPAZ-1 criteria did not have a significantly different median overall survival and progression free survival than the rest of the patients (10.3 versus 9.7 months and 5.3 versus 5 months, respectively). The disease control rate of patients within the TOPAZ-1 criteria was 61.1%, in comparison to 58.8% in the rest of patients. A total of 51 grade 3 and 4 adverse events were observed without significant differences in the subgroups. No specific correlating patterns of genetic alterations with survival and response were observed. CONCLUSIONS: The treatment of advanced patients with BTC with durvalumab and gem/cis, even beyond the inclusion criteria of the TOPAZ-1 trial, shows promising safety.

A microbiota-modulated checkpoint directs immunosuppressive intestinal T cells into cancers.

Antibiotics (ABX) compromise the efficacy of programmed cell death protein 1 (PD-1) blockade in cancer patients, but the mechanisms underlying their immunosuppressive effects remain unknown. By inducing the down-regulation of mucosal addressin cell adhesion molecule 1 (MAdCAM-1) in the ileum, post-ABX gut recolonization by Enterocloster species drove the emigration of enterotropic α4ß7+CD4+ regulatory T 17 cells into the tumor. These deleterious ABX effects were mimicked by oral gavage of Enterocloster species, by genetic deficiency, or by antibody-mediated neutralization of MAdCAM-1 and its receptor, α4ß7 integrin. By contrast, fecal microbiota transplantation or interleukin-17A neutralization prevented ABX-induced immunosuppression. In independent lung, kidney, and bladder cancer patient cohorts, low serum levels of soluble MAdCAM-1 had a negative prognostic impact. Thus, the MAdCAM-1-α4ß7 axis constitutes an actionable gut immune checkpoint in cancer immunosurveillance.

Immune system and intestinal microbiota determine efficacy of androgen deprivation therapy against prostate cancer.

BACKGROUND: Prostate cancer (PC) responds to androgen deprivation therapy (ADT) usually in a transient fashion, progressing from hormone-sensitive PC (HSPC) to castration-resistant PC (CRPC). We investigated a mouse model of PC as well as specimens from PC patients to unravel an unsuspected contribution of thymus-derived T lymphocytes and the intestinal microbiota in the efficacy of ADT. METHODS: Preclinical experiments were performed in PC-bearing mice, immunocompetent or immunodeficient. In parallel, we prospectively included 65 HSPC and CRPC patients (Oncobiotic trial) to analyze their feces and blood specimens. RESULTS: In PC-bearing mice, ADT increased thymic cellularity and output. PC implanted in T lymphocyte-depleted or athymic mice responded less efficiently to ADT than in immunocompetent mice. Moreover, depletion of the intestinal microbiota by oral antibiotics reduced the efficacy of ADT. PC reduced the relative abundance of Akkermansia muciniphila in the gut, and this effect was reversed by ADT. Moreover, cohousing of PC-bearing mice with tumor-free mice or oral gavage with Akkermansia improved the efficacy of ADT. This appears to be applicable to PC patients because long-term ADT resulted in an increase of thymic output, as demonstrated by an increase in circulating recent thymic emigrant cells (sjTRECs). Moreover, as compared with HSPC controls, CRPC patients demonstrated a shift in their intestinal microbiota that significantly correlated with sjTRECs. While feces from healthy volunteers restored ADT efficacy, feces from PC patients failed to do so. CONCLUSIONS: These findings suggest the potential clinical utility of reversing intestinal dysbiosis and repairing acquired immune defects in PC patients.

SARS-CoV-2 Seroprevalence and Clinical Features of COVID-19 in a German Liver Transplant Recipient Cohort: A Prospective Serosurvey Study.

BACKGROUND: In liver transplant (LT) recipients with severe coronavirus disease 2019 (COVID-19), fatal outcome has been reported in a substantial subset of patients. Whether LT recipients are at increased risk for severe COVID-19 compared with the general population is controversial. Here we report the results of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serosurvey in a large LT recipient cohort. METHODS: A total of 219 LT recipients were enrolled between May 5, 2020, and August 6, 2020, at the University Hospital Heidelberg. Serum blood samples were collected and tested for anti-SARS-CoV-2 IgG. SARS-CoV-2 RNA was detected in nasopharyngeal swabs using reverse transcription-polymerase chain reaction assays. RESULTS: Taking into account known risk factors of arterial hypertension, obesity, diabetes, or leukopenia, LT recipients a priori represented a high-risk cohort for severe COVID-19 with 101 of 219 (46.1%) presenting with more than 2 risk factors for severe COVID-19. Out of 219 LT recipients, 8 (3.7%) either had a positive test result for nasopharyngeal SARS-CoV-2 RNA or anti-SARS-CoV-2 serum IgG. Five of eight (62.5%) did not show any clinical signs of infection, three of eight (37.5%) had self-limited disease, and none required hospitalization for COVID-19. Two of eight (25%) had known exposure to infected health care staff as the probable source of infection. CONCLUSIONS: In summary, LT recipients showed a SARS-CoV-2 seroconversion rate similar to that of the general population with a substantial percentage of unrecognized infections.

Dysregulated Host Response in Severe Acute Respiratory Syndrome Coronavirus 2-Induced Critical Illness.

BACKGROUND: Impaired immune response has been reported to be the cause of the development of coronavirus disease 2019 (COVID-19)-related respiratory failure. Further studies are needed to understand the immunopathogenesis and to enable an improved stratification of patients who are at risk for critical illness. METHODS: Thirty-two severely ill patients hospitalized with COVID-19 were recruited in our center at the University Hospital Heidelberg. We performed a comprehensive analysis of immune phenotype, cytokine, and chemokine profiling and leukocyte transcripts in patients with severe COVID-19 and compared critically ill patients who required mechanical ventilation and high-flow oxygen therapy and noncritically ill patient who received low-flow oxygen therapy. RESULTS: Critically ill patients exhibited low levels of CD8 T cells and myeloid dendritic cells. We noted a pronounced CCR6+ TH17 phenotype in CD4 central memory cells and elevated circulating levels of interleukin-17 in the critical group. Gene expression of leukocytes derived from critically ill patients was characterized by an upregulation of proinflammatory cytokines and reduction of interferon (IFN)-responsive genes upon stimulation with Toll-like receptor 7/8 agonist. When correlating clinical improvement and immune kinetics, we found that CD8 T-cell subsets and myeloid dendritic cells significantly increased after disconnection from the ventilator. CONCLUSION: Critical illness was characterized by a TH17-mediated response and dysfunctional IFN-associated response, indicating an impaired capacity to mount antiviral responses during severe acute respiratory syndrome coronavirus 2 severe infection.

Ketogenic diet and ketone bodies enhance the anticancer effects of PD-1 blockade.

Limited experimental evidence bridges nutrition and cancer immunosurveillance. Here, we show that ketogenic diet (KD) - or its principal ketone body, 3-hydroxybutyrate (3HB), most specifically in intermittent scheduling - induced T cell-dependent tumor growth retardation of aggressive tumor models. In conditions in which anti-PD-1 alone or in combination with anti-CTLA-4 failed to reduce tumor growth in mice receiving a standard diet, KD, or oral supplementation of 3HB reestablished therapeutic responses. Supplementation of KD with sucrose (which breaks ketogenesis, abolishing 3HB production) or with a pharmacological antagonist of the 3HB receptor GPR109A abolished the antitumor effects. Mechanistically, 3HB prevented the immune checkpoint blockade-linked upregulation of PD-L1 on myeloid cells, while favoring the expansion of CXCR3+ T cells. KD induced compositional changes of the gut microbiota, with distinct species such as Eisenbergiella massiliensis commonly emerging in mice and humans subjected to carbohydrate-low diet interventions and highly correlating with serum concentrations of 3HB. Altogether, these results demonstrate that KD induces a 3HB-mediated antineoplastic effect that relies on T cell-mediated cancer immunosurveillance.

Ileal immune tonus is a prognosis marker of proximal colon cancer in mice and patients.

Ileal epithelial cell apoptosis and the local microbiota modulate the effects of oxaliplatin against proximal colon cancer by modulating tumor immunosurveillance. Here, we identified an ileal immune profile associated with the prognosis of colon cancer and responses to chemotherapy. The whole immune ileal transcriptome was upregulated in poor-prognosis patients with proximal colon cancer, while the colonic immunity of healthy and neoplastic areas was downregulated (except for the Th17 fingerprint) in such patients. Similar observations were made across experimental models of implanted and spontaneous murine colon cancer, showing a relationship between carcinogenesis and ileal inflammation. Conversely, oxaliplatin-based chemotherapy could restore a favorable, attenuated ileal immune fingerprint in responders. These results suggest that chemotherapy inversely shapes the immune profile of the ileum-tumor axis, influencing clinical outcome.

Biliary calprotectin, lactoferrin and dimeric pyruvate kinase after liver transplantation are associated with biliary damage and graft survival in a case-control study.

BACKGROUND: After liver transplantation (LT), biliary complications are associated with reduced graft survival. We tested inflammation markers for their association with biliary damage and graft loss in bile. MATERIAL AND METHODS: The study design was a retrospective case-control study. Calprotectin, lactoferrin and pyruvate kinase were measured in endoscopically retrieved bile with ELISA. RESULTS: Calprotectin and lactoferrin were significantly higher in bile of ischemic-type biliary lesions and donor duct non-anastomotic strictures than in control, bile leakage, Cytomegalovirus infection, anastomotic stricture or acute cellular rejection patients (p<0.001) independent of serum liver values at endoscopy. Calprotectin (p=0.02) was independently associated with retransplantation free survival in multivariate analysis, as was γGT (p=0.03) but not ERC radiographic classification of the bile duct or cold ischemia time. CONCLUSION: Calprotectin and lactoferrin are bile markers for biliary damage and are associated with re-transplantation free survival. They can differentiate progressive biliary damage from non-biliary liver value alterations after LT.

Intrahepatic biliary strictures after liver transplantation are morphologically similar to primary sclerosing cholangitis but immunologically distinct.

OBJECTIVE: Biliary strictures are an important cause of morbidity and mortality in primary hepatic disease and after liver transplantation (LT). We aimed to characterize inflammatory cytokines in biliary fluids in biliary strictures to investigate their immunological origin. METHODS: We conducted a retrospective study on 72 patients with strictures after LT, eight patients with primary sclerosing cholangitis (PSC) and 15 patients with secondary sclerosing cholangitis (SSC). We measured cytokines interleukin (IL)-2, -4, -6, -10, -17, monocyte chemoattractant protein (MCP)-1, fibroblast growth factor (FGF)-2 and interferon (IFN)-γ as well as biochemical components such as protein and phospholipids in biliary fluid obtained from endoscopic retrograde cholangiography (ERC). Cell viability assays were performed on human cholangiocytes (H69) after being treated with IL-6, IL-4 and IFN-γ. RESULTS: Bile of patients with diffuse strictures after LT or due to SSC showed low values of all measured cytokines except for IL-6 levels, which were largely elevated in patients with diffuse strictures after LT. Patients high in biliary IL-6 showed an increase in profibrotic markers FGF-2 and MCP-1. In contrast, PSC bile was dominated by a Th1/Th17 profile with elevated IL-2, IL-17 and IFN-γ. In LT patients with biliary strictures, biliary IL-6 negatively predicted retransplantation-free survival after ERC. CONCLUSION: PSC patients showed a biliary Th1/Th17 cytokine profile, while SSC and diffuse strictures showed low values of cytokines except IL-6. In diffuse intrahepatic strictures after LT, biliary IL-6 is strongly associated with retransplantation-free survival after ERC.

Gut Bacteria Composition Drives Primary Resistance to Cancer Immunotherapy in Renal Cell Carcinoma Patients.

BACKGROUND: The development of immune checkpoint blockade (ICB) has revolutionized the clinical outcome of renal cell carcinoma (RCC). Nevertheless, improvement of durability and prediction of responses remain unmet medical needs. While it has been recognized that antibiotics (ATBs) decrease the clinical activity of ICB across various malignancies, little is known about the direct impact of distinct intestinal nonpathogenic bacteria (commensals) on therapeutic outcomes of ICB in RCC. OBJECTIVE: To evaluate the predictive value of stool bacteria composition for ICB efficacy in a cohort of advanced RCC patients. DESIGN, SETTING, AND PARTICIPANTS: We prospectively collected fecal samples from 69 advanced RCC patients treated with nivolumab and enrolled in the GETUG-AFU 26 NIVOREN microbiota translational substudy phase 2 trial (NCT03013335) at Gustave Roussy. We recorded patient characteristics including ATB use, prior systemic therapies, and response criteria. We analyzed 2994 samples of feces from healthy volunteers (HVs). In parallel, preclinical studies performed in RCC-bearing mice that received fecal transplant (FMT) from RCC patients resistant to ICB (NR-FMT) allowed us to draw a cause-effect relationship between gut bacteria composition and clinical outcomes for ICB. The influence of tyrosine kinase inhibitors (TKIs) taken before starting nivolumab on the microbiota composition has also been assessed. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Metagenomic data (MG) from whole genome sequencing (WGS) were analyzed by multivariate and pairwise comparisons/fold ratio to identify bacterial fingerprints related to ATB or prior TKI exposure and patients' therapeutic response (overall response and progression-free survival), and compared with the data from cancer-free donors. RESULTS AND LIMITATIONS: Recent ATB use (n = 11; 16%) reduced objective response rates (from 28% to 9%, p < 0.03) and markedly affected the composition of the microbiota, facilitating the dominance of distinct species such as Clostridium hathewayi, which were also preferentially over-represented in stools from RCC patients compared with HVs. Importantly, TKIs taken prior to nivolumab had implications in shifting the microbiota composition. To establish a cause-effect relationship between gut bacteria composition and ICB efficacy, NR-FMT mice were successfully compensated with either FMT from responding RCC patients or beneficial commensals identified by WGS-MG (Akkermansia muciniphila and Bacteroides salyersiae). CONCLUSIONS: The composition of the microbiota is influenced by TKIs and ATBs, and impacts the success of immunotherapy. Future studies will help sharpen the role of these specific bacteria and their potential as new biomarkers. PATIENT SUMMARY: We used quantitative shotgun DNA sequencing of fecal microbes as well as preclinical models of fecal or bacterial transfer to study the association between stool composition and (pre)clinical outcome to immune checkpoint blockade. Novel insights into the pathophysiological relevance of intestinal dysbiosis in the prognosis of kidney cancer may lead to innovative therapeutic solutions, such as supplementation with probiotics to prevent primary resistance to therapy.

Chemotherapy-induced ileal crypt apoptosis and the ileal microbiome shape immunosurveillance and prognosis of proximal colon cancer.

The prognosis of colon cancer (CC) is dictated by tumor-infiltrating lymphocytes, including follicular helper T (TFH) cells and the efficacy of chemotherapy-induced immune responses. It remains unclear whether gut microbes contribute to the elicitation of TFH cell-driven responses. Here, we show that the ileal microbiota dictates tolerogenic versus immunogenic cell death of ileal intestinal epithelial cells (IECs) and the accumulation of TFH cells in patients with CC and mice. Suppression of IEC apoptosis led to compromised chemotherapy-induced immunosurveillance against CC in mice. Protective immune responses against CC were associated with residence of Bacteroides fragilis and Erysipelotrichaceae in the ileum. In the presence of these commensals, apoptotic ileal IECs elicited PD-1+ TFH cells in an interleukin-1R1- and interleukin-12-dependent manner. The ileal microbiome governed the efficacy of chemotherapy and PD-1 blockade in CC independently of microsatellite instability. These findings demonstrate that immunogenic ileal apoptosis contributes to the prognosis of chemotherapy-treated CC.

Impact of age at diagnosis on disease progression in patients with primary sclerosing cholangitis.

BACKGROUND: The median age of diagnosis of primary sclerosing cholangitis (PSC) is ∼30-40 years. OBJECTIVE: We aimed to analyse disease progression and liver-dependent survival in patients diagnosed with PSC after 50 years of age. METHODS: Patients with PSC were analysed with regard to their age at diagnosis. Patients with a first diagnosis of PSC after the age of 50 years were considered as the late-onset group. RESULTS: A total of 32/215 (14.9%) patients were diagnosed with PSC after 50 years of age. The proportion of females was significantly higher among patients with late-onset PSC (48.4 vs. 27.3%; p = 0.02). Patients with later diagnosis required dilatation therapy more often due to dominant stenosis (84.2 vs. 53.1%; p = 0.01) and suffered from recurrent cholangitis more often (48.3 vs. 21.0%; p = 0.003). Patients with late-onset PSC had reduced transplantation-free survival (10.5 ± 0.6 years vs. 20.8 ± 1.7 years, p < 0.0001), with progredient liver failure and cholangiocarcinoma as the leading causes of death. CONCLUSIONS: Patients with later age at diagnosis of PSC displayed a different clinical phenotype with a different sex ratio, immune status and an increased risk for progressive liver failure and biliary malignancies.

Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors.

Immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis induce sustained clinical responses in a sizable minority of cancer patients. We found that primary resistance to ICIs can be attributed to abnormal gut microbiome composition. Antibiotics inhibited the clinical benefit of ICIs in patients with advanced cancer. Fecal microbiota transplantation (FMT) from cancer patients who responded to ICIs into germ-free or antibiotic-treated mice ameliorated the antitumor effects of PD-1 blockade, whereas FMT from nonresponding patients failed to do so. Metagenomics of patient stool samples at diagnosis revealed correlations between clinical responses to ICIs and the relative abundance of Akkermansia muciniphila Oral supplementation with A. muciniphila after FMT with nonresponder feces restored the efficacy of PD-1 blockade in an interleukin-12-dependent manner by increasing the recruitment of CCR9+CXCR3+CD4+ T lymphocytes into mouse tumor beds.

Von Willebrand factor and alkaline phosphatase predict re-transplantation-free survival after the first liver transplantation.

BACKGROUND: After liver transplantation (LT), there are liver-related, infectious and cardiovascular complications that contribute to reduced graft survival. These conditions are associated with an increase in the Von Willebrand factor antigen (VWF-Ag), which was previously correlated with survival in cirrhotic patients. OBJECTIVE: Evaluate VWF-Ag as a predictive marker of re-transplantation-free survival in patients after LT. METHODS: We measured VWF-Ag in patients after first LT and then followed them prospectively with regard to the primary endpoint, namely re-transplantation-free survival. RESULTS: There were 6 out of 80 patients who died or received re-LT during follow-up. In these patients, the median VWF-Ag was 510.6%, which was significantly higher (p = 0.001) than in the patients who were alive at the end of follow-up (with a median VWF-Ag = 186.8%). At a cut-off of 286.8%, VWF-Ag was significantly correlated with re-transplantation-free survival (p < 0.001). VWF-Ag was independently associated with re-transplantation-free survival in a multivariate analysis; as was alkaline phosphatase (ALP), but not the model of end-stage liver disease (MELD) score, donor age, nor cold ischemia time. A score combining VWF-Ag and ALP showed an impressive capability in the receiver operating characteristic (ROC) analysis (with area under the curve (AUC) = 0.958) to distinguish between patients with regard to the primary endpoint. CONCLUSIONS: VWF-Ag is a non-invasive marker that can predict outcome in patients after LT. Its diagnostic performance increased when combined with ALP in a newly developed scoring system.

TLR activation and ionizing radiation induce strong immune responses against multiple tumor entities.

Toll-like receptor (TLR) 7/8 ligands act together with radiotherapy and induce profound systemic antitumor immune reactions coordinated by dendritic cells and executed by natural killer (NK) and cytotoxic T cells. Combining TLR ligands and radiation improves both local and distant tumor control and has been shown to be effective against multiple tumor entities.

Radiotherapy combined with TLR7/8 activation induces strong immune responses against gastrointestinal tumors.

In addition to local cytotoxic activity, radiotherapy may also elicit local and systemic antitumor immunity, which may be augmented by immunotherapeutic agents including Toll-like receptor (TLR) 7/8 agonists. Here, we investigated the ability of 3M-011 (854A), a TLR7/8 agonist, to boost the antigen-presenting activity of dendritic cells (DC) as an adjuvant to radiotherapy. The combined treatment induced marked local and systemic responses in subcutaneous and orthotopic mouse models of colorectal and pancreatic cancer. In vitro cytotoxicity assays as well as in vivo depletion experiments with monoclonal antibodies identified NK and CD8 T cells as the cell populations mediating the cytotoxic effects of the treatment, while in vivo depletion of CD11c+ dendritic cells (DC) in CD11c-DTR transgenic mice revealed DC as the pivotal immune hub in this setting. The specificity of the immune reaction was confirmed by ELISPOT assays. TLR7/8 agonists therefore seem to be potent adjuvants to radiotherapy, inducing strong local and profound systemic immune responses to tumor antigens released by conventional therapy.