A Single-Cell Taxonomy Predicts Inflammatory Niche Remodeling to Drive Tissue Failure and Outcome in Human AML.

Cancer initiation is orchestrated by an interplay between tumor-initiating cells and their stromal/immune environment. Here, by adapted single-cell RNA sequencing, we decipher the predicted signaling between tissue-resident hematopoietic stem/progenitor cells (HSPC) and their neoplastic counterparts with their native niches in the human bone marrow. LEPR+ stromal cells are identified as central regulators of hematopoiesis through predicted interactions with all cells in the marrow. Inflammatory niche remodeling and the resulting deprivation of critical HSPC regulatory factors are predicted to repress high-output hematopoietic stem cell subsets in NPM1-mutated acute myeloid leukemia (AML), with relative resistance of clonal cells. Stromal gene signatures reflective of niche remodeling are associated with reduced relapse rates and favorable outcomes after chemotherapy across all genetic risk categories. Elucidation of the intercellular signaling defining human AML, thus, predicts that inflammatory remodeling of stem cell niches drives tissue repression and clonal selection but may pose a vulnerability for relapse-initiating cells in the context of chemotherapeutic treatment. SIGNIFICANCE: Tumor-promoting inflammation is considered an enabling characteristic of tumorigenesis, but mechanisms remain incompletely understood. By deciphering the predicted signaling between tissue-resident stem cells and their neoplastic counterparts with their environment, we identify inflammatory remodeling of stromal niches as a determinant of normal tissue repression and clinical outcomes in human AML. See related commentary by Lisi-Vega and Méndez-Ferrer, p. 349. This article is featured in Selected Articles from This Issue, p. 337.

PD-L1 checkpoint blockade promotes regulatory T cell activity that underlies therapy resistance.

Despite the clinical success of immune checkpoint blockade (ICB), in certain cancer types, most patients with cancer do not respond well. Furthermore, in patients for whom ICB is initially successful, this is often short-lived because of the development of resistance to ICB. The mechanisms underlying primary or secondary ICB resistance are incompletely understood. Here, we identified preferential activation and enhanced suppressive capacity of regulatory T cells (Treg cells) in αPD-L1 therapy-resistant solid tumor-bearing mice. Treg cell depletion reversed resistance to αPD-L1 with concomitant expansion of effector T cells. Moreover, we found that tumor-infiltrating Treg cells in human patients with skin cancer, and in patients with non-small cell lung cancer, up-regulated a suppressive transcriptional gene program after ICB treatment, which correlated with lack of treatment response. αPD-1/PD-L1-induced PD-1+ Treg cell activation was also seen in peripheral blood of patients with lung cancer and mesothelioma, especially in nonresponders. Together, these data reveal that treatment with αPD-1 and αPD-L1 unleashes the immunosuppressive role of Treg cells, resulting in therapy resistance, suggesting that Treg cell targeting is an important adjunct strategy to enhance therapeutic efficacy.

Hematopoietic Cell Autonomous Disruption of Hematopoiesis in a Germline Loss-of-function Mouse Model of RUNX1-FPD.

RUNX1 familial platelet disorder (RUNX1-FPD) is a hematopoietic disorder caused by germline loss-of-function mutations in the RUNX1 gene and characterized by thrombocytopathy, thrombocytopenia, and an increased risk of developing hematologic malignancies, mostly of myeloid origin. Disease pathophysiology has remained incompletely understood, in part because of a shortage of in vivo models recapitulating the germline RUNX1 loss of function found in humans, precluding the study of potential contributions of non-hematopoietic cells to disease pathogenesis. Here, we studied mice harboring a germline hypomorphic mutation of one Runx1 allele with a loss-of-function mutation in the other Runx1 allele (Runx1 L148A/- mice), which display many hematologic characteristics found in human RUNX1-FPD patients. Runx1 L148A/- mice displayed robust and pronounced thrombocytopenia and myeloid-biased hematopoiesis, associated with an HSC intrinsic reconstitution defect in lymphopoiesis and expansion of myeloid progenitor cell pools. We demonstrate that specific deletion of Runx1 from bone marrow stromal cells in Prrx1-cre;Runx1 fl/fl mice did not recapitulate these abnormalities, indicating that the hematopoietic abnormalities are intrinsic to the hematopoietic lineage, and arguing against a driving role of the bone marrow microenvironment. In conclusion, we report a RUNX1-FPD mouse model faithfully recapitulating key characteristics of human disease. Findings do not support a driving role of ancillary, non-hematopoietic cells in the disruption of hematopoiesis under homeostatic conditions.

Expression and Localization of Ferritin-Heavy Chain Predicts Recurrence for Breast Cancer Patients with a BRCA1/2 Mutation.

The ferritin-heavy chain (FTH1) is the catalytic subunit of the ferroxidase ferritin, which prevents oxidative DNA damage via intracellular iron storage. FTH1 was shown to be a prognostic marker for triple-negative breast cancer (BC) patients and associated with an enrichment of CD8+ effector T cells. However, whether the expression and localization of FTH1 are also associated with clinical outcome in other BC subtypes is unknown. Here, we investigated the association of FTH1 with time to survival in BCs from 222 BRCA1/2 mutation carriers by immunohistochemistry on tissue microarrays. In addition, for 51 of these patients, the association between FTH1 and specific subsets of T cells was evaluated on whole slides using automatic scoring algorithms. We revealed that nuclear FTH1 (nFTH1) expression, in multivariable analyses, was associated with a shorter disease-free (HR = 2.71, 95% CI = 1.49-4.92, p = 0.001) and metastasis-free survival (HR = 3.54, 95% CI = 1.45-8.66, p = 0.006) in patients carrying a BRCA1/2 mutation. However, we found no relation between cytoplasmic FTH1 expression and survival of BRCA1/2 mutation carriers. Moreover, we did not detect an association between FTH1 expression and the amount of CD45+ (p = 0.13), CD8+ (p = 0.18), CD4+ (p = 0.20) or FOXP3+ cells (p = 0.17). Consequently, the mechanism underlying the worse recurrence-free survival of nFTH1 expression in BRCA1/2 mutation carriers needs further investigation.

Myeloid cells promote interferon signaling-associated deterioration of the hematopoietic system.

Innate and adaptive immune cells participate in the homeostatic regulation of hematopoietic stem cells (HSCs). Here, we interrogate the contribution of myeloid cells, the most abundant cell type in the mammalian bone marrow, in a clinically relevant mouse model of neutropenia. Long-term genetic depletion of neutrophils and eosinophils results in activation of multipotent progenitors but preservation of HSCs. Depletion of myeloid cells abrogates HSC expansion, loss of serial repopulation and lymphoid reconstitution capacity and remodeling of HSC niches, features previously associated with hematopoietic aging. This is associated with mitigation of interferon signaling in both HSCs and their niches via reduction of NK cell number and activation. These data implicate myeloid cells in the functional decline of hematopoiesis, associated with activation of interferon signaling via a putative neutrophil-NK cell axis. Innate immunity may thus come at the cost of system deterioration through enhanced chronic inflammatory signaling to stem cells and their niches.