A membrane-associated MHC-I inhibitory axis for cancer immune evasion.

Immune-checkpoint blockade has revolutionized cancer treatment, but some cancers, such as acute myeloid leukemia (AML), do not respond or develop resistance. A potential mode of resistance is immune evasion of T cell immunity involving aberrant major histocompatibility complex class I (MHC-I) antigen presentation (AP). To map such mechanisms of resistance, we identified key MHC-I regulators using specific peptide-MHC-I-guided CRISPR-Cas9 screens in AML. The top-ranked negative regulators were surface protein sushi domain containing 6 (SUSD6), transmembrane protein 127 (TMEM127), and the E3 ubiquitin ligase WWP2. SUSD6 is abundantly expressed in AML and multiple solid cancers, and its ablation enhanced MHC-I AP and reduced tumor growth in a CD8+ T cell-dependent manner. Mechanistically, SUSD6 forms a trimolecular complex with TMEM127 and MHC-I, which recruits WWP2 for MHC-I ubiquitination and lysosomal degradation. Together with the SUSD6/TMEM127/WWP2 gene signature, which negatively correlates with cancer survival, our findings define a membrane-associated MHC-I inhibitory axis as a potential therapeutic target for both leukemia and solid cancers.

The Role of Inflammation in the Initiation and Progression of Myeloid Neoplasms.

Myeloid malignancies are devastating hematologic cancers with limited therapeutic options. Inflammation is emerging as a novel driver of myeloid malignancy, with important implications for tumor composition, immune response, therapeutic options, and patient survival. Here, we discuss the role of inflammation in normal and malignant hematopoiesis, from clonal hematopoiesis to full-blown myeloid leukemia. We discuss how inflammation shapes clonal output from hematopoietic stem cells, how inflammation alters the immune microenvironment in the bone marrow, and novel therapies aimed at targeting inflammation in myeloid disease. SIGNIFICANCE: Inflammation is emerging as an important factor in myeloid malignancies. Understanding the role of inflammation in myeloid transformation, and the interplay between inflammation and other drivers of leukemogenesis, may yield novel avenues for therapy.

Mitophagy Promotes Resistance to BH3 Mimetics in Acute Myeloid Leukemia.

BH3 mimetics are used as an efficient strategy to induce cell death in several blood malignancies, including acute myeloid leukemia (AML). Venetoclax, a potent BCL-2 antagonist, is used clinically in combination with hypomethylating agents for the treatment of AML. Moreover, MCL1 or dual BCL-2/BCL-xL antagonists are under investigation. Yet, resistance to single or combinatorial BH3-mimetic therapies eventually ensues. Integration of multiple genome-wide CRISPR/Cas9 screens revealed that loss of mitophagy modulators sensitizes AML cells to various BH3 mimetics targeting different BCL-2 family members. One such regulator is MFN2, whose protein levels positively correlate with drug resistance in patients with AML. MFN2 overexpression is sufficient to drive resistance to BH3 mimetics in AML. Insensitivity to BH3 mimetics is accompanied by enhanced mitochondria-endoplasmic reticulum interactions and augmented mitophagy flux, which acts as a prosurvival mechanism to eliminate mitochondrial damage. Genetic or pharmacologic MFN2 targeting synergizes with BH3 mimetics by impairing mitochondrial clearance and enhancing apoptosis in AML. SIGNIFICANCE: AML remains one of the most difficult-to-treat blood cancers. BH3 mimetics represent a promising therapeutic approach to eliminate AML blasts by activating the apoptotic pathway. Enhanced mitochondrial clearance drives resistance to BH3 mimetics and predicts poor prognosis. Reverting excessive mitophagy can halt BH3-mimetic resistance in AML. This article is highlighted in the In This Issue feature, p. 1501.

An inflammatory state remodels the immune microenvironment and improves risk stratification in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a hematopoietic malignancy with poor prognosis and limited treatment options. Here we provide a comprehensive census of the bone marrow immune microenvironment in adult and pediatric patients with AML. We characterize unique inflammation signatures in a subset of AML patients, associated with inferior outcomes. We identify atypical B cells, a dysfunctional B-cell subtype enriched in patients with high-inflammation AML, as well as an increase in CD8+GZMK+ and regulatory T cells, accompanied by a reduction in T-cell clonal expansion. We derive an inflammation-associated gene score (iScore) that associates with poor survival outcomes in patients with AML. Addition of the iScore refines current risk stratifications for patients with AML and may enable identification of patients in need of more aggressive treatment. This work provides a framework for classifying patients with AML based on their immune microenvironment and a rationale for consideration of the inflammatory state in clinical settings.

TRAF6 functions as a tumor suppressor in myeloid malignancies by directly targeting MYC oncogenic activity.

Clonal hematopoiesis (CH) is an aging-associated condition characterized by the clonal outgrowth of pre-leukemic cells that acquire specific mutations. Although individuals with CH are healthy, they are at an increased risk of developing myeloid malignancies, suggesting that additional alterations are needed for the transition from a pre-leukemia stage to frank leukemia. To identify signaling states that cooperate with pre-leukemic cells, we used an in vivo RNAi screening approach. One of the most prominent genes identified was the ubiquitin ligase TRAF6. Loss of TRAF6 in pre-leukemic cells results in overt myeloid leukemia and is associated with MYC-dependent stem cell signatures. TRAF6 is repressed in a subset of patients with myeloid malignancies, suggesting that subversion of TRAF6 signaling can lead to acute leukemia. Mechanistically, TRAF6 ubiquitinates MYC, an event that does not affect its protein stability but rather represses its functional activity by antagonizing an acetylation modification.

The gut microbiome switches mutant p53 from tumour-suppressive to oncogenic.

Somatic mutations in p53, which inactivate the tumour-suppressor function of p53 and often confer oncogenic gain-of-function properties, are very common in cancer1,2. Here we studied the effects of hotspot gain-of-function mutations in Trp53 (the gene that encodes p53 in mice) in mouse models of WNT-driven intestinal cancer caused by Csnk1a1 deletion3,4 or ApcMin mutation5. Cancer in these models is known to be facilitated by loss of p533,6. We found that mutant versions of p53 had contrasting effects in different segments of the gut: in the distal gut, mutant p53 had the expected oncogenic effect; however, in the proximal gut and in tumour organoids it had a pronounced tumour-suppressive effect. In the tumour-suppressive mode, mutant p53 eliminated dysplasia and tumorigenesis in Csnk1a1-deficient and ApcMin/+ mice, and promoted normal growth and differentiation of tumour organoids derived from these mice. In these settings, mutant p53 was more effective than wild-type p53 at inhibiting tumour formation. Mechanistically, the tumour-suppressive effects of mutant p53 were driven by disruption of the WNT pathway, through preventing the binding of TCF4 to chromatin. Notably, this tumour-suppressive effect was completely abolished by the gut microbiome. Moreover, a single metabolite derived from the gut microbiota-gallic acid-could reproduce the entire effect of the microbiome. Supplementing gut-sterilized p53-mutant mice and p53-mutant organoids with gallic acid reinstated the TCF4-chromatin interaction and the hyperactivation of WNT, thus conferring a malignant phenotype to the organoids and throughout the gut. Our study demonstrates the substantial plasticity of a cancer mutation and highlights the role of the microenvironment in determining its functional outcome.

Cell-by-Cell Deconstruction of Stem Cell Niches.

Single-cell sequencing approaches offer exploration of tissue architecture at unprecedented resolution. These tools are especially powerful when deconvoluting highly specialized microenvironments, such as stem cell (SC) niches. Here, we review single-cell studies that map the cellular and transcriptional makeup of stem and progenitor niches and discuss how these high-resolution analyses fundamentally advance our understanding of how niche factors shape SC biology and activity. In-depth characterization of the blueprint of SC-niche crosstalk, as well as understanding how it becomes dysregulated, will undoubtedly inform the development of more efficient therapies for malignancies and other pathologies.

Extensive Remodeling of the Immune Microenvironment in B Cell Acute Lymphoblastic Leukemia.

A subset of B cell acute lymphoblastic leukemia (B-ALL) patients will relapse and succumb to therapy-resistant disease. The bone marrow microenvironment may support B-ALL progression and treatment evasion. Utilizing single-cell approaches, we demonstrate B-ALL bone marrow immune microenvironment remodeling upon disease initiation and subsequent re-emergence during conventional chemotherapy. We uncover a role for non-classical monocytes in B-ALL survival, and demonstrate monocyte abundance at B-ALL diagnosis is predictive of pediatric and adult B-ALL patient survival. We show that human B-ALL blasts alter a vascularized microenvironment promoting monocytic differentiation, while depleting leukemia-associated monocytes in B-ALL animal models prolongs disease remission in vivo. Our profiling of the B-ALL immune microenvironment identifies extrinsic regulators of B-ALL survival supporting new immune-based therapeutic approaches for high-risk B-ALL treatment.

Immune-Based Therapies in Acute Leukemia.

Treatment resistance remains a leading cause of acute leukemia-related deaths. Thus, there is an unmet need to develop novel approaches to improve outcome. New immune-based therapies with chimeric antigen receptor (CAR) T cells, bi-specific T cell engagers (BiTEs), and immune checkpoint blockers (ICBs) have emerged as effective treatment options for chemoresistant B cell acute lymphoblastic leukemia (B-ALL) and acute myeloid leukemia (AML). However, many patients show resistance to these immune-based approaches. This review describes crucial lessons learned from immune-based approaches targeting high-risk B-ALL and AML, such as the leukemia-intrinsic (e.g., target antigen loss, tumor heterogeneity) and -extrinsic (e.g., immunosuppressive microenvironment) mechanisms that drive treatment resistance, and discusses alternative approaches to enhance the effectiveness of these immune-based treatment regimens.

Cancer Cell-Autonomous Parainflammation Mimics Immune Cell Infiltration.

Parainflammation is a unique variant of inflammation, characterized by epithelial-autonomous activation of inflammatory response. Parainflammation has been shown to strongly promote mouse gut tumorigenesis upon p53 loss. In a recent study, we explored the prevalence of parainflammation in human cancer and determined its relationship to certain molecular and clinical parameters affecting treatment and prognosis. Parainflammation can be identified from a 40-gene signature and is found in both carcinoma cell lines and a variety of primary tumors, independently of tumor microenvironment. Here, we discuss the implications of our findings in analyses of tumor microenvironment, suggesting that as tumor cell gene expression may often mimic immune and inflammatory infiltration, caution should be applied when interpreting tumor expression data. We also address the connection between parainflammation and prevalence of p53 mutations in specific types of tumors, and cancer prevention by regular usage of NSAIDs. We suggest that parainflammation may serve as a novel biomarker for screening patients who may particularly benefit from NSAID treatment. Cancer Res; 77(14); 3740-4. ©2017 AACR.

Widespread parainflammation in human cancer.

BACKGROUND: Chronic inflammation has been recognized as one of the hallmarks of cancer. We recently showed that parainflammation, a unique variant of inflammation between homeostasis and chronic inflammation, strongly promotes mouse gut tumorigenesis upon p53 loss. Here we explore the prevalence of parainflammation in human cancer and determine its relationship to certain molecular and clinical parameters affecting treatment and prognosis. RESULTS: We generated a transcriptome signature to identify parainflammation in many primary human tumors and carcinoma cell lines as distinct from their normal tissue counterparts and the tumor microenvironment and show that parainflammation-positive tumors are enriched for p53 mutations and associated with poor prognosis. Non-steroidal anti-inflammatory drug (NSAID) treatment suppresses parainflammation in both murine and human cancers, possibly explaining a protective effect of NSAIDs against cancer. CONCLUSIONS: We conclude that parainflammation, a low-grade form of inflammation, is widely prevalent in human cancer, particularly in cancer types commonly harboring p53 mutations. Our data suggest that parainflammation may be a driver for p53 mutagenesis and a guide for cancer prevention by NSAID treatment.

Inflammatory networks underlying colorectal cancer.

Inflammation is emerging as one of the hallmarks of cancer, yet its role in most tumors remains unclear. Whereas a minority of solid tumors are associated with overt inflammation, long-term treatment with non-steroidal anti-inflammatory drugs is remarkably effective in reducing cancer rate and death. This indicates that inflammation might have many as-yet-unrecognized facets, among which an indolent course might be far more prevalent than previously appreciated. In this Review, we explore the various inflammatory processes underlying the development and progression of colorectal cancer and discuss anti-inflammatory means for its prevention and treatment.

Senescence-associated inflammatory responses: aging and cancer perspectives.

Senescent cells, albeit not proliferating, are metabolically and transcriptionally active, thereby capable of affecting their microenvironment, notably via the production of inflammatory mediators. These mediators maintain and propagate the senescence process to neighboring cells, and then recruit immune cells for clearing senescent cells. Among the inflammatory cues are molecules with pronounced tumor-controlling properties, both growth and invasion factors and inhibitory factors, working directly or via recruited immune cells. These senescence-inflammatory effects also prevail within tumors, mediated by the senescent tumor cells and the senescent tumor stroma. Here, we review the course and impact of senescence-associated inflammatory responses in aging and cancer. We propose that controlling senescence-associated inflammation by targeting specific inflammatory mediators may have a beneficial therapeutic effect in treatment of cancer and aging-related diseases.

Adverse immunoregulatory effects of 5FU and CPT11 chemotherapy on myeloid-derived suppressor cells and colorectal cancer outcomes.

Colorectal cancer is associated with chronic inflammation and immunosuppression mediated by myeloid-derived suppressor cells (MDSC). Although chemotherapy reduces tumor burden at early stages, it tends to have limited effect on a progressive disease, possibly due to adverse effects on the immune system in dictating disease outcome. Here, we show that patients with advanced colorectal cancer display enhanced MDSC levels and reduced CD247 expression and that some conventional colorectal cancer chemotherapy supports the immunosuppressive tumor microenvironment. A FOLFOX combined therapy reduced immunosuppression, whereas a FOLFIRI combined therapy enhanced immunosuppression. Mechanistic studies in a colorectal cancer mouse model revealed that FOLFIRI-like therapy including the drugs CPT11 and 5-fluorouracil (5FU) damaged host immunocompetence in a manner that limits treatment outcomes. CPT11 blocked MDSC apoptosis and myeloid cell differentiation, increasing MDSC immunosuppressive features and mouse mortality. In contrast, 5FU promoted immune recovery and tumor regression. Thus, CPT11 exhibited detrimental immunoregulatory effects that offset 5FU benefits when administered in combination. Our results highlight the importance of developing therapeutic regimens that can target both the immune system and tumor towards improved personalized treatments for colorectal cancer.

Critical role for IL-1ß in DNA damage-induced mucositis.

ß-TrCP, the substrate recognition subunit of SCF-type ubiquitin ligases, is ubiquitously expressed from two distinct paralogs, targeting for degradation many regulatory proteins, among which is the NF-κB inhibitor IκB. To appreciate tissue-specific roles of ß-TrCP, we studied the consequences of inducible ablation of three or all four alleles of the E3 in the mouse gut. The ablation resulted in mucositis, a destructive gut mucosal inflammation, which is a common complication of different cancer therapies and represents a major obstacle to successful chemoradiation therapy. We identified epithelial-derived IL-1ß as the culprit of mucositis onset, inducing mucosal barrier breach. Surprisingly, epithelial IL-1ß is induced by DNA damage via an NF-κB-independent mechanism. Tissue damage caused by gut barrier disruption is exacerbated in the absence of NF-κB, with failure to express the endogenous IL-1ß receptor antagonist IL-1Ra upon four-allele loss. Antibody neutralization of IL-1ß prevents epithelial tight junction dysfunction and alleviates mucositis in ß-TrCP-deficient mice. IL-1ß antagonists should thus be considered for prevention and treatment of severe morbidity associated with mucositis.