Oxygen Sensing by T Cells Establishes an Immunologically Tolerant Metastatic Niche.

Cancer cells must evade immune responses at distant sites to establish metastases. The lung is a frequent site for metastasis. We hypothesized that lung-specific immunoregulatory mechanisms create an immunologically permissive environment for tumor colonization. We found that T-cell-intrinsic expression of the oxygen-sensing prolyl-hydroxylase (PHD) proteins is required to maintain local tolerance against innocuous antigens in the lung but powerfully licenses colonization by circulating tumor cells. PHD proteins limit pulmonary type helper (Th)-1 responses, promote CD4(+)-regulatory T (Treg) cell induction, and restrain CD8(+) T cell effector function. Tumor colonization is accompanied by PHD-protein-dependent induction of pulmonary Treg cells and suppression of IFN-γ-dependent tumor clearance. T-cell-intrinsic deletion or pharmacological inhibition of PHD proteins limits tumor colonization of the lung and improves the efficacy of adoptive cell transfer immunotherapy. Collectively, PHD proteins function in T cells to coordinate distinct immunoregulatory programs within the lung that are permissive to cancer metastasis. PAPERCLIP.

BACH2 regulates CD8(+) T cell differentiation by controlling access of AP-1 factors to enhancers.

T cell antigen receptor (TCR) signaling drives distinct responses depending on the differentiation state and context of CD8(+) T cells. We hypothesized that access of signal-dependent transcription factors (TFs) to enhancers is dynamically regulated to shape transcriptional responses to TCR signaling. We found that the TF BACH2 restrains terminal differentiation to enable generation of long-lived memory cells and protective immunity after viral infection. BACH2 was recruited to enhancers, where it limited expression of TCR-driven genes by attenuating the availability of activator protein-1 (AP-1) sites to Jun family signal-dependent TFs. In naive cells, this prevented TCR-driven induction of genes associated with terminal differentiation. Upon effector differentiation, reduced expression of BACH2 and its phosphorylation enabled unrestrained induction of TCR-driven effector programs.

A Modified Floxuridine Reduced-Dose Protocol for Patients with Unresectable Colorectal Liver Metastases Treated with Hepatic Arterial Infusion.

BACKGROUND: Most patients treated with the standard dosing protocol (SDP) of hepatic arterial infusion (HAI) floxuridine require dose holds and reductions, thereby limiting their HAI therapy. We hypothesized that a modified dosing protocol (MDP) with a reduced floxuridine starting dose would decrease dose holds, dose reductions, and have similar potential to convert patients with unresectable colorectal liver metastases (uCRLM) to resection. PATIENTS AND METHODS: We reviewed our institutional database of patients with uCRLM treated with HAI between 2016 and 2022. In 2019, we modified the floxuridine starting dose to 50% (0.06 mg/kg) of the SDP (0.12 mg/kg). We compared treatment related outcomes between the SDP and MDP cohorts. RESULTS: Of n = 33 patients, 15 (45%) were treated on the SDP and 18 (55%) with our new institutional MDP. The MDP cohort completed more cycles before a dose reduction (mean 4.2 vs. 2), received more overall cycles (median 7.5 vs. 5), and averaged 39 more days of treatment (all P < 0.05). The SDP experienced more dose reductions (1.4 vs. 0.61) and dose holds (1.2 vs. 0.2; both P < 0.01). Of the patients in each group potentially convertible to hepatic resection, three patients (23%) in the SDP and six patients (35%) in the MDP group converted to resection (P = 0.691). Overall, four patients (27%) in the SDP developed treatment ending biliary toxicity compared with one patient (6%) in the MDP. CONCLUSIONS: A 50% starting dose of HAI floxuridine provides fewer treatment disruptions, more consecutive floxuridine cycles, and a similar potential to convert patients with initially uCRLM for disease clearance.

Identification of essential genes for cancer immunotherapy.

Somatic gene mutations can alter the vulnerability of cancer cells to T-cell-based immunotherapies. Here we perturbed genes in human melanoma cells to mimic loss-of-function mutations involved in resistance to these therapies, by using a genome-scale CRISPR-Cas9 library that consisted of around 123,000 single-guide RNAs, and profiled genes whose loss in tumour cells impaired the effector function of CD8+ T cells. The genes that were most enriched in the screen have key roles in antigen presentation and interferon-γ signalling, and correlate with cytolytic activity in patient tumours from The Cancer Genome Atlas. Among the genes validated using different cancer cell lines and antigens, we identified multiple loss-of-function mutations in APLNR, encoding the apelin receptor, in patient tumours that were refractory to immunotherapy. We show that APLNR interacts with JAK1, modulating interferon-γ responses in tumours, and that its functional loss reduces the efficacy of adoptive cell transfer and checkpoint blockade immunotherapies in mouse models. Our results link the loss of essential genes for the effector function of CD8+ T cells with the resistance or non-responsiveness of cancer to immunotherapies.

Surgical timing after preoperative chemotherapy is associated with oncologic outcomes in resectable colorectal liver metastases.

INTRODUCTION: Preoperative chemotherapy (POC) is often employed for patients with resectable colorectal liver metastasis (CRLM). The time to resection (TTR) following the end of chemotherapy may impact oncologic outcomes; this phenomenon has not been studied in CRLM. METHODS: We queried our institutional cancer database for patients with resected CRLM after POC from 2003 to 2019. TTR was calculated from date of last cytotoxic chemotherapy. Kaplan-Meier analysis and multivariable Cox proportional hazards modeling were used to analyze recurrence-free survival (RFS) and overall survival (OS). RESULTS: We identified n = 187 patients. One hundred twenty-four (66%) patients had a TTR of <2 months, while 63 (33%) had a TTR of ≥2 months. Median follow-up was 36 months. On Kaplan-Meier analysis, patients with TTR ≥ 2 months had shorter RFS (median 11 vs. 17 months, p = 0.002) and OS (median 44 vs. 62 months, p < 0.001). On multivariable analysis, TTR ≥ 2 months was independently associated with worse RFS (hazard ratio [HR] = 1.54, 95% confidence interval [CI] = 1.06-2.22, p = 0.02) and OS (HR = 1.75, 95% CI = 1.11-2.77, p = 0.01). CONCLUSION: TTR ≥ 2 months following POC is independently associated with worse oncologic outcomes in patients with resectable CRLM. We therefore recommend consideration for hepatic resection of CRLM within this window whenever feasible.

Ionic immune suppression within the tumour microenvironment limits T cell effector function.

Tumours progress despite being infiltrated by tumour-specific effector T cells. Tumours contain areas of cellular necrosis, which are associated with poor survival in a variety of cancers. Here, we show that necrosis releases intracellular potassium ions into the extracellular fluid of mouse and human tumours, causing profound suppression of T cell effector function. Elevation of the extracellular potassium concentration ([K+]e) impairs T cell receptor (TCR)-driven Akt-mTOR phosphorylation and effector programmes. Potassium-mediated suppression of Akt-mTOR signalling and T cell function is dependent upon the activity of the serine/threonine phosphatase PP2A. Although the suppressive effect mediated by elevated [K+]e is independent of changes in plasma membrane potential (Vm), it requires an increase in intracellular potassium ([K+]i). Accordingly, augmenting potassium efflux in tumour-specific T cells by overexpressing the potassium channel Kv1.3 lowers [K+]i and improves effector functions in vitro and in vivo and enhances tumour clearance and survival in melanoma-bearing mice. These results uncover an ionic checkpoint that blocks T cell function in tumours and identify potential new strategies for cancer immunotherapy.

CCR8 marks highly suppressive Treg cells within tumours but is dispensable for their accumulation and suppressive function.

CD4+ regulatory T (Treg) cells, dependent upon the transcription factor Foxp3, contribute to tumour immunosuppression but are also required for immune homeostasis. There is interest in developing therapies that selectively target the immunosuppressive function of Treg cells within tumours without disrupting their systemic anti-inflammatory function. High levels of expression of chemokine (C-C motif) receptor 8 (CCR8) discriminate Treg cells within tumours from those found in systemic lymphoid tissues. It has recently been proposed that disruption of CCR8 function using blocking anti-CCR8 antibodies results in reduced accumulation of Treg cells within tumours and disruption of their immunosuppressive function. Here, using Ccr8-/- mice, we show that CCR8 function is not required for Treg cell accumulation or immunosuppression in the context of syngeneic MC38 colorectal adenocarcinoma and B16 melanoma tumours. We observed high levels of CCR8 expression on tumour-infiltrating Treg cells which were abolished in Ccr8-/- mice. High levels of CCR8 marked cells with high levels of suppressive function. However, whereas systemic ablation of Treg cells resulted in strikingly diminished tumour burden, growth of subcutaneously implanted tumours was unaffected by systemic CCR8 loss. Consistently, we observed minimal impact of systemic CCR8 ablation on the frequency, phenotype and function of tumour-infiltrating Treg cells and conventional T (Tconv) function. These findings suggest that CCR8 is not required for Treg cell accumulation and immunosuppressive function within tumours and that depletion of CCR8+ Treg cells rather than blockade of CCR8 function is a more promising avenue for selective immunotherapy.

Nomogram for predicting the benefit of neoadjuvant chemoradiotherapy for patients with esophageal cancer: a SEER-Medicare analysis.

BACKGROUND: The survival impact of neoadjuvant chemoradiotherapy (CRT) on esophageal cancer remains difficult to establish for specific patients. The aim of the current study was to create a Web-based prediction tool providing individualized survival projections based on tumor and treatment data. METHODS: Patients diagnosed with esophageal cancer between 1997 and 2005 were selected from the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. The covariates analyzed were sex, T and N classification, histology, total number of lymph nodes examined, and treatment with esophagectomy or CRT followed by esophagectomy. After propensity score weighting, a log-logistic regression model for overall survival was selected based on the Akaike information criterion. RESULTS: A total of 824 patients with esophageal cancer who were treated with esophagectomy or trimodal therapy met the selection criteria. On multivariate analysis, age, sex, T and N classification, number of lymph nodes examined, treatment, and histology were found to be significantly associated with overall survival and were included in the regression analysis. Preoperative staging data and final surgical margin status were not available within the SEER-Medicare data set and therefore were not included. The model predicted that patients with T4 or lymph node disease benefitted from CRT. The internally validated concordance index was 0.72. CONCLUSIONS: The SEER-Medicare database of patients with esophageal cancer can be used to produce a survival prediction tool that: 1) serves as a counseling and decision aid to patients and 2) assists in risk modeling. Patients with T4 or lymph node disease appeared to benefit from CRT. This nomogram may underestimate the benefit of CRT due to its variable downstaging effect on pathologic stage. It is available at skynet.ohsu.edu/nomograms.

Intracellular K+ Limits T-cell Exhaustion and Preserves Antitumor Function.

T cells are often compromised within cancers, allowing disease progression. We previously found that intratumoral elevations in extracellular K+, related to ongoing cell death, constrained CD8+ T-cell Akt-mTOR signaling and effector function. To alleviate K+-mediated T-cell dysfunction, we pursued genetic means to lower intracellular K+. CD8+ T cells robustly and dynamically express the Na+/K+ ATPase, among other K+ transporters. CRISPR-Cas9-mediated disruption of the Atp1a1 locus lowered intracellular K+ and elevated the resting membrane potential (i.e., Vm, Ψ). Despite compromised Ca2+ influx, Atp1a1-deficient T cells harbored tonic hyperactivity in multiple signal transduction cascades, along with a phenotype of exhaustion in mouse and human CD8+ T cells. Provision of exogenous K+ restored intracellular levels in Atp1a1-deficient T cells and prevented damaging levels of reactive oxygen species (ROS), and both antioxidant treatment and exogenous K+ prevented Atp1a1-deficient T-cell exhaustion in vitro. T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will require balancing the beneficial aspects of intracellular K+ with the ROS-dependent nature of T-cell effector function. See related Spotlight by Banuelos and Borges da Silva, p. 6.

Hepatic signal transducer and activator of transcription-3 signalling drives early-stage pancreatic cancer cachexia via suppressed ketogenesis.

BACKGROUND: Patients with pancreatic ductal adenocarcinoma (PDAC) often suffer from cachexia, a wasting syndrome that significantly reduces both quality of life and survival. Although advanced cachexia is associated with inflammatory signalling and elevated muscle catabolism, the early events driving wasting are poorly defined. During periods of nutritional scarcity, the body relies on hepatic ketogenesis to generate ketone bodies, and lipid metabolism via ketogenesis is thought to protect muscle from catabolizing during nutritional scarcity. METHODS: We developed an orthotopic mouse model of early PDAC cachexia in 12-week-old C57BL/6J mice. Murine pancreatic cancer cells (KPC) were orthotopically implanted into the pancreas of wild-type, IL-6-/-, and hepatocyte STAT3-/- male and female mice. Mice were subject to fasting, 50% food restriction, ad libitum feeding or ketogenic diet interventions. We measured longitudinal body composition by EchoMRI, body mass and food intake. At the endpoint, we measured tissue mass, tissue gene expression by quantitative real-time polymerase chain reaction, whole-body calorimetry, circulating hormone levels, faecal protein and lipid content, hepatic lipid content and ketogenic response to medium-chain fatty acid bolus. We assessed muscle atrophy in vivo and C2C12 myotube atrophy in vitro. RESULTS: Pre-cachectic PDAC mice did not preserve gastrocnemius muscle mass during 3-day food restriction (-13.1 ± 7.7% relative to food-restricted sham, P = 0.0117) and displayed impaired fatty acid oxidation during fasting, resulting in a hypoketotic state (ketogenic response to octanoate bolus, -83.0 ± 17.3%, P = 0.0328; Hmgcs2 expression, -28.3 ± 7.6%, P = 0.0004). PDAC human patients display impaired fasting ketones (-46.9 ± 7.1%, P < 0.0001) and elevated circulating interleukin-6 (IL-6) (12.4 ± 16.5-fold increase, P = 0.0001). IL-6-/- PDAC mice had improved muscle mass (+35.0 ± 3.9%, P = 0.0031) and ketogenic response (+129.4 ± 44.4%, P = 0.0033) relative to wild-type PDAC mice. Hepatocyte-specific signal transducer and activator of transcription 3 (STAT3) deletion prevented muscle loss (+9.3 ± 4.0%, P = 0.009) and improved fasting ketone levels (+52.0 ± 43.3%, P = 0.018) in PDAC mice. Without affecting tumour growth, a carbohydrate-free diet improved tibialis anterior myofibre diameter (+16.5 ± 3.5%, P = 0.0089), circulating ketone bodies (+333.0 ± 117.6%, P < 0.0001) and Hmgcs2 expression (+106.5 ± 36.1%, P < 0.0001) in PDAC mice. Ketone supplementation protected muscle against PDAC-induced atrophy in vitro (+111.0 ± 17.6%, P < 0.0001 myofibre diameter). CONCLUSIONS: In early PDAC cachexia, muscle vulnerability to wasting is dependent on inflammation-driven metabolic reprogramming in the liver. PDAC suppresses lipid ß-oxidation and impairs ketogenesis in the liver, which is reversed in genetically modified mouse models deficient in IL-6/STAT3 signalling or through ketogenic diet supplementation. This work establishes a direct link between skeletal muscle homeostasis and hepatic metabolism. Dietary and anti-inflammatory interventions that restore ketogenesis may be a viable preventative approach for pre-cachectic patients with pancreatic cancer.

Intracellular K + limits T cell exhaustion and preserves antitumor function.

The cancer-killing activity of T cells is often compromised within tumors, allowing disease progression. We previously found that intratumoral elevations in extracellular K + related to ongoing cell death constrained CD8 + T cell Akt-mTOR signaling and effector function (1,2). To alleviate K + mediated T cell suppression, we pursued genetic means to lower intracellular K + . Transcriptomic analysis of CD8 + T cells demonstrated the Na + /K + ATPase to be robustly and dynamically expressed. CRISPR-Cas9 mediated deletion of the catalytic alpha subunit of the Na + /K + ATPase lowered intracellular K + but produced tonic hyperactivity in multiple signal transduction cascades along with the acquisition of co-inhibitory receptors and terminal differentiation in mouse and human CD8 + T cells. Mechanistically, Na + /K + ATPase disruption led to ROS accumulation due to depletion of intracellular K + in T cells. Antioxidant treatment or high K + media prevented Atp1a1 deficient T cells from exhausted T (T Ex ) cell formation. Consistent with transcriptional and proteomic data suggesting a T Ex cell phenotype, T cells lacking Atp1a1 had compromised persistence and antitumor activity in a syngeneic model of orthotopic murine melanoma. Translational application of these findings will include efforts to lower intracellular K + while limiting ROS accumulation within tumor specific T cells. Synopsis: High extracellular K + (↑[K + ] e ) is found within tumors and suppresses T cell effector function. Collier et al. find that deletion of the Na + /K + ATPase in T cells lowers intracellular K + and promotes ROS accumulation, tonic signal transduction and T cell exhaustion owing to ROS accumulation. Engineering T cell ion transport is an important consideration for cancer immunotherapy.

Hepatectomy is associated with improved oncologic outcomes in recurrent colorectal liver metastases: A propensity-matched analysis.

BACKGROUND: Following resection of colorectal liver metastasis, most patients have disease recurrence, most commonly intrahepatic. Although the role of resection in colorectal liver metastasis is well-established, there have been limited investigations assessing the benefit of repeat hepatic resection compared with systemic treatment alone for intrahepatic recurrence. METHODS: A retrospective single-institution cohort study of patients with recurrent colorectal liver metastasis following curative-intent hepatectomy was performed from 2003 to 2019. The oncologic outcomes, including post-recurrence overall survival, were evaluated using Kaplan-Meier and Cox proportional hazards modeling. Patients undergoing repeat hepatic resection were propensity-matched with patients receiving systemic treatment alone based on relevant clinicopathologic variables. RESULTS: There were 338 patients treated with hepatic resection for colorectal liver metastasis over the study period. Liver recurrence was observed in 147 (43%) patients at a median time of 10 months from prior resection, with a median post-recurrence overall survival of 29 months. There were 37 patients managed with repeat hepatic resection; 33 (89%) received perioperative chemotherapy. On propensity matching, there were no significant clinicopathologic differences between 37 patients having repeat hepatic resection and 37 patients treated with systemic treatment alone. Repeat hepatic resection was independently associated with improved 5-year post-recurrence overall survival compared with systemic treatment alone (median overall survival 41 vs 35 months, 5-year overall survival 19% vs 3%, P = .048). CONCLUSION: Disease characteristics of patients with intrahepatic recurrence of colorectal liver metastasis, specifically the number of liver lesions and size of the largest lesion, are most predictive of survival and response to systemic therapy. Patients who recur with oligometastatic liver disease experience improved outcomes and derive benefit from curative-intent repeat hepatic resection with integrated perioperative systemic therapy.

Updated Management of Colorectal Cancer Liver Metastases: Scientific Advances Driving Modern Therapeutic Innovations.

Colorectal cancer is the second leading cause of cancer-related deaths in the United States and accounts for an estimated 1 million deaths annually worldwide. The liver is the most common site of metastatic spread from colorectal cancer, significantly driving both morbidity and mortality. Although remarkable advances have been made in recent years in the management for patients with colorectal cancer liver metastases, significant challenges remain in early detection, prevention of progression and recurrence, and in the development of more effective therapeutics. In 2017, our group held a multidisciplinary state-of-the-science symposium to discuss the rapidly evolving clinical and scientific advances in the field of colorectal liver metastases, including novel early detection and prognostic liquid biomarkers, identification of high-risk cohorts, advances in tumor-immune therapy, and different regional and systemic therapeutic strategies. Since that time, there have been scientific discoveries translating into therapeutic innovations addressing the current management challenges. These innovations are currently reshaping the treatment paradigms and spurring further scientific discovery. Herein, we present an updated discussion of both the scientific and clinical advances and future directions in the management of colorectal liver metastases, including adoptive T-cell therapies, novel blood-based biomarkers, and the role of the tumor microbiome. In addition, we provide a comprehensive overview detailing the role of modern multidisciplinary clinical approaches used in the management of patients with colorectal liver metastases, including considerations toward specific molecular tumor profiles identified on next generation sequencing, as well as quality of life implications for these innovative treatments.

Conventional hepatic arterial anatomy? Novel findings and insights of a multi-disciplinary hepatic arterial infusion pump program.

INTRODUCTION: Variant hepatic arterial anatomy (vHAA) is thought to occur in 20-30% of patients. Hepatic arterial infusion (HAI) pump placement for liver cancers requires thorough hepatic artery dissection; we sought to compare vHAA identified during pump placement with established dogma. METHODS: Between 2016 and 2020, n = 30 patients received a HAI pump. Intra-operatively identified vHAA was characterized and compared with published data. RESULTS: vHAA was identified in 60% (n = 18) of patients, significantly higher than 19% (3671 of 19013) in the largest published series (P < 0.001). The most common variations were accessory left (n = 12; 40%) and replaced right (n = 6; 20%) hepatic arteries; six (20%) had ≥2 variants. Pre-operative imaging correctly identified 67% of variant hepatic arteries. DISCUSSION: Meticulous operative dissection of the hepatic arterial tree reveals vHAA not captured by imaging or cadaveric dissection. vHAA likely has a higher prevalence than previously reported and should be addressed to optimize therapeutic efficacy of HAI pump therapy.

Surgical and oncologic outcomes following repeat hepatic resection of colorectal liver metastasis: Who benefits?

BACKGROUND: Resected colorectal liver metastases (CRLM) frequently recur intrahepatically. Selection criteria for repeat hepatectomy of recurrent CRLM are ill-defined. METHODS: We performed an institutional review of patients with recurrent CRLM undergoing repeat hepatectomy from 2003 to 19. Post-recurrence overall (rOS) and recurrence-free survival (RFS) were analyzed with Cox proportional hazards modeling. RESULTS: n = 147 experienced recurrent CRLM; 11% (n = 38) received repeat hepatectomy of which there was one Clavien-Dindo IIIa complication. Median rOS was 41 months; median RFS was 9 months. Improved rOS and RFS were independently associated with additional post-operative chemotherapy after repeat hepatectomy (HR 0.35 and 0.34, respectively); poor rOS with recurrent CRLM >3 cm (HR 4.4) and <12 months from first hepatectomy to recurrence (HR 4.8); poor RFS with ≥3 recurrence liver metastases (HR 2.8) (All P < 0.05). DISCUSSION: Repeat hepatectomy for recurrent CRLM can be performed safely. Worse survival following repeat hepatectomy is independently associated with >3 cm and ≥3 liver lesions at recurrence, and <12 months to recurrence. Additional post-operative chemotherapy after repeat hepatectomy is associated with improved outcomes.

BACH2 drives quiescence and maintenance of resting Treg cells to promote homeostasis and cancer immunosuppression.

Regulatory T (Treg) cell populations are composed of functionally quiescent resting Treg (rTreg) cells which differentiate into activated Treg (aTreg) cells upon antigen stimulation. How rTreg cells remain quiescent despite chronic exposure to cognate self- and foreign antigens is unclear. The transcription factor BACH2 is critical for early Treg lineage specification, but its function following lineage commitment is unresolved. Here, we show that BACH2 is repurposed following Treg lineage commitment and promotes the quiescence and long-term maintenance of rTreg cells. Bach2 is highly expressed in rTreg cells but is down-regulated in aTreg cells and during inflammation. In rTreg cells, BACH2 binds to enhancers of genes involved in aTreg differentiation and represses their TCR-driven induction by competing with AP-1 factors for DNA binding. This function promotes rTreg cell quiescence and long-term maintenance and is required for immune homeostasis and durable immunosuppression in cancer. Thus, BACH2 supports a "division of labor" between quiescent rTreg cells and their activated progeny in Treg maintenance and function, respectively.

Multi-phenotype CRISPR-Cas9 Screen Identifies p38 Kinase as a Target for Adoptive Immunotherapies.

T cells are central to all currently effective cancer immunotherapies, but the characteristics defining therapeutically effective anti-tumor T cells have not been comprehensively elucidated. Here, we delineate four phenotypic qualities of effective anti-tumor T cells: cell expansion, differentiation, oxidative stress, and genomic stress. Using a CRISPR-Cas9-based genetic screen of primary T cells we measured the multi-phenotypic impact of disrupting 25 T cell receptor-driven kinases. We identified p38 kinase as a central regulator of all four phenotypes and uncovered transcriptional and antioxidant pathways regulated by p38 in T cells. Pharmacological inhibition of p38 improved the efficacy of mouse anti-tumor T cells and enhanced the functionalities of human tumor-reactive and gene-engineered T cells, paving the way for clinically relevant interventions.

T cell stemness and dysfunction in tumors are triggered by a common mechanism.

A paradox of tumor immunology is that tumor-infiltrating lymphocytes are dysfunctional in situ, yet are capable of stem cell-like behavior including self-renewal, expansion, and multipotency, resulting in the eradication of large metastatic tumors. We find that the overabundance of potassium in the tumor microenvironment underlies this dichotomy, triggering suppression of T cell effector function while preserving stemness. High levels of extracellular potassium constrain T cell effector programs by limiting nutrient uptake, thereby inducing autophagy and reduction of histone acetylation at effector and exhaustion loci, which in turn produces CD8+ T cells with improved in vivo persistence, multipotency, and tumor clearance. This mechanistic knowledge advances our understanding of T cell dysfunction and may lead to novel approaches that enable the development of enhanced T cell strategies for cancer immunotherapy.

T cells genetically engineered to overcome death signaling enhance adoptive cancer immunotherapy.

Across clinical trials, T cell expansion and persistence following adoptive cell transfer (ACT) have correlated with superior patient outcomes. Herein, we undertook a pan-cancer analysis to identify actionable ligand-receptor pairs capable of compromising T cell durability following ACT. We discovered that FASLG, the gene encoding the apoptosis-inducing ligand FasL, is overexpressed within the majority of human tumor microenvironments (TMEs). Further, we uncovered that Fas, the receptor for FasL, is highly expressed on patient-derived T cells used for clinical ACT. We hypothesized that a cognate Fas-FasL interaction within the TME might limit both T cell persistence and antitumor efficacy. We discovered that genetic engineering of Fas variants impaired in the ability to bind FADD functioned as dominant negative receptors (DNRs), preventing FasL-induced apoptosis in Fas-competent T cells. T cells coengineered with a Fas DNR and either a T cell receptor or chimeric antigen receptor exhibited enhanced persistence following ACT, resulting in superior antitumor efficacy against established solid and hematologic cancers. Despite increased longevity, Fas DNR-engineered T cells did not undergo aberrant expansion or mediate autoimmunity. Thus, T cell-intrinsic disruption of Fas signaling through genetic engineering represents a potentially universal strategy to enhance ACT efficacy across a broad range of human malignancies.

Novel "Elements" of Immune Suppression within the Tumor Microenvironment.

Adaptive evolution has prompted immune cells to use a wide variety of inhibitory signals, many of which are usurped by tumor cells to evade immune surveillance. Although tumor immunologists often focus on genes and proteins as mediators of immune function, here we highlight two elements from the periodic table-oxygen and potassium-that suppress the immune system in previously unappreciated ways. While both are key to the maintenance of T-cell function and tissue homeostasis, they are exploited by tumors to suppress immuno-surveillance and promote metastatic spread. We discuss the temporal and spatial roles of these elements within the tumor microenvironment and explore possible therapeutic interventions for effective and promising anticancer therapies. Cancer Immunol Res; 5(6); 426-33. ©2017 AACR.