CD25high Effector Regulatory T Cells Hamper Responses to PD-1 Blockade in Triple-Negative Breast Cancer.

Regulatory T cells (Treg) impede effective antitumor immunity. However, the role of Tregs in the clinical outcomes of patients with triple-negative breast cancer (TNBC) remains controversial. Here, we found that an immunosuppressive TNBC microenvironment is marked by an imbalance between effector αßCD8+ T cells and Tregs harboring hallmarks of highly suppressive effector Tregs (eTreg). Intratumoral eTregs strongly expressed PD-1 and persisted in patients with TNBC resistant to PD-1 blockade. Importantly, CD25 was the most selective surface marker of eTregs in primary TNBC and metastases compared with other candidate targets for eTreg depletion currently being evaluated in trials for patients with advanced TNBC. In a syngeneic TNBC model, the use of Fc-optimized, IL2 sparing, anti-CD25 antibodies synergized with PD-1 blockade to promote systemic antitumor immunity and durable tumor growth control by increasing effector αßCD8+ T-cell/Treg ratios in tumors and in the periphery. Together, this study provides the rationale for the clinical translation of anti-CD25 therapy to improve PD-1 blockade responses in patients with TNBC. SIGNIFICANCE: An imbalance between effector CD8+ T cells and CD25high effector Tregs marks immunosuppressive microenvironments in αPD-1-resistant TNBC and can be reversed through effector Treg depletion to increase αPD-1 efficacy.

High-throughput mass cytometry staining for deep phenotyping of human natural killer cells.

This protocol details the step-by-step procedure for in-depth immune phenotyping of peripheral blood natural killer (NK) cells from clinical samples by mass cytometry. The protocol consists of three main steps: PBMC incubation with a mix of metal-conjugated antibodies for extracellular phenotyping followed by fixation, permeabilization and incubation with a mix of metal-conjugated antibodies for staining of intracellular proteins, and sample acquisition on a mass cytometer. High-dimensional analysis enables the visualization of NK cell subsets and their phenotypical characteristics. For complete details on the use and execution of this protocol, please refer to Chretien et al. (2021).

Mass Cytometry Reveals Classical Monocytes, NK Cells, and ICOS+ CD4+ T Cells Associated with Pembrolizumab Efficacy in Patients with Lung Cancer.

PURPOSE: Immune checkpoint inhibitors (ICI) have revolutionized the treatment of non-small cell lung cancer (NSCLC), but predictive biomarkers of their efficacy are imperfect. The primary objective is to evaluate circulating immune predictors of pembrolizumab efficacy in patients with advanced NSCLC. EXPERIMENTAL DESIGN: We used high-dimensional mass cytometry (CyTOF) in baseline blood samples of patients with advanced NSCLC treated with pembrolizumab. CyTOF data were analyzed by machine-learning algorithms (Citrus, tSNE) and confirmed by manual gating followed by principal component analysis (between-group analysis). RESULTS: We analyzed 27 patients from the seminal KEYNOTE-001 study (median follow-up of 60.6 months). We demonstrate that blood baseline frequencies of classical monocytes, natural killer (NK) cells, and ICOS+ CD4+ T cells are significantly associated with improved objective response rates, progression-free survival, and overall survival (OS). In addition, we report that a baseline immune peripheral score combining these three populations strongly predicts pembrolizumab efficacy (OS: HR = 0.25; 95% confidence interval = 0.12-0.51; P < 0.0001). CONCLUSIONS: As this immune monitoring is easy in routine practice, we anticipate our findings may improve prediction of ICI benefit in patients with advanced NSCLC.

Therapeutic Targeting of Tumor-Infiltrating Regulatory T Cells in Breast Cancer.

Regulatory T cells (Treg) are an immunosuppressive subtype of CD4+ T cells essential for maintaining self-tolerance in physiological settings. Tregs also abundantly infiltrate inflamed tumor tissues, impeding the host's antitumor immune response and contributing to tumor growth and metastasis. In breast cancers, subsets of Tregs express highly immunosuppressive effector phenotypes that favor tumorigenesis, progression, and resistance to immune-checkpoint inhibitor therapies. Tregs share phenotypic features with cytotoxic lymphocytes, rendering them difficult to inhibit without compromising productive antitumor immunity. In addition, systemic targeting of Tregs causes serious autoimmune adverse events in patients with cancer. Hence, the identification of candidate targets or methodologies allowing the specific elimination of tumor antigen-specific Tregs, including tumor-infiltrating Tregs, is a prerequisite for developing efficient and safe combinatorial immunotherapeutic strategies in breast cancers. To date, numerous preclinical studies have demonstrated that specific targeting of breast tumor-infiltrating Tregs restores a competent antitumor immune response and improves responses to immune-checkpoint inhibitors such as PD-1/PD-L1 blockade. Herein, we discuss major candidate molecules for Treg-targeted therapeutic strategies in breast cancers, detailing the pros and cons of various approaches, including mAb-mediated depletion, homeostasis destabilization, and functional blockade.

Endometrial Carcinoma: Immune Microenvironment and Emerging Treatments in Immuno-Oncology.

Endometrial cancer (EC) can easily be cured when diagnosed at an early stage. However, advanced and metastatic EC is a common disease, affecting more than 15,000 patients per year in the United Sates. Only limited treatment options were available until recently, with a taxane-platinum combination as the gold standard in first-line setting and no efficient second-line chemotherapy or hormone therapy. EC can be split into four molecular subtypes, including hypermutated cases with POLE mutations and 25-30% harboring a microsatellite instability (MSI) phenotype with mismatch repair deficiency (dMMR). These tumors display a high load of frameshift mutations, leading to increased expression of neoantigens that can be targeted by the immune system, including (but not limited) to T-cell response. Recent data have demonstrated this impact of programmed death 1 and programmed death ligand 1 (PD-1/PD-L1) inhibitors on chemo-resistant metastatic EC. The uncontrolled KEYNOTE-158 and GARNET trials have shown high response rates with pembrolizumab and dostarlimab in chemoresistant MSI-high tumors. Most responders experiment long responses that last more than one year. Similar, encouraging results were obtained for MMR proficient (MMRp) cases treated with a combination of pembrolizumab and the angiogenesis inhibitor lenvatinib. Approvals have, thus, been obtained or are underway for EC with immune checkpoint inhibitors (ICI) used as monotherapy, and in combination with antiangiogenic agents. Combinations with other targeted therapies are under evaluation and randomized studies are ongoing to explore the impact of ICI-chemotherapy triplets in first-line setting. We summarize in this review the current knowledge of the immune environment of EC, both for MMRd and MMRp tumors. We also detail the main clinical data regarding PD-1/PD-L1 inhibitors and discuss the next steps of development for immunotherapy, including various ICI-based combinations planned to limit resistance to immunotherapy.

High-dimensional mass cytometry analysis of NK cell alterations in AML identifies a subgroup with adverse clinical outcome.

Natural killer (NK) cells are major antileukemic immune effectors. Leukemic blasts have a negative impact on NK cell function and promote the emergence of phenotypically and functionally impaired NK cells. In the current work, we highlight an accumulation of CD56-CD16+ unconventional NK cells in acute myeloid leukemia (AML), an aberrant subset initially described as being elevated in patients chronically infected with HIV-1. Deep phenotyping of NK cells was performed using peripheral blood from patients with newly diagnosed AML (n = 48, HEMATOBIO cohort, NCT02320656) and healthy subjects (n = 18) by mass cytometry. We showed evidence of a moderate to drastic accumulation of CD56-CD16+ unconventional NK cells in 27% of patients. These NK cells displayed decreased expression of NKG2A as well as the triggering receptors NKp30 and NKp46, in line with previous observations in HIV-infected patients. High-dimensional characterization of these NK cells highlighted a decreased expression of three additional major triggering receptors required for NK cell activation, NKG2D, DNAM-1, and CD96. A high proportion of CD56-CD16+ NK cells at diagnosis was associated with an adverse clinical outcome and decreased overall survival (HR = 0.13; P = 0.0002) and event-free survival (HR = 0.33; P = 0.018) and retained statistical significance in multivariate analysis. Pseudotime analysis of the NK cell compartment highlighted a disruption of the maturation process, with a bifurcation from conventional NK cells toward CD56-CD16+ NK cells. Overall, our data suggest that the accumulation of CD56-CD16+ NK cells may be the consequence of immune escape from innate immunity during AML progression.

Quantification of Immune Variables from Liquid Biopsy in Breast Cancer Patients Links Vδ2+ γδ T Cell Alterations with Lymph Node Invasion.

The rationale for therapeutic targeting of Vδ2+ γδ T cells in breast cancer is strongly supported by in vitro and murine preclinical investigations, characterizing them as potent breast tumor cell killers and source of Th1-related cytokines, backing cytotoxic αß T cells. Nonetheless, insights regarding Vδ2+ γδ T cell phenotypic alterations in human breast cancers are still lacking. This paucity of information is partly due to the challenging scarcity of these cells in surgical specimens. αß T cell phenotypic alterations occurring in the tumor bed are detectable in the periphery and correlate with adverse clinical outcomes. Thus, we sought to determine through an exploratory study whether Vδ2+ γδ T cells phenotypic changes can be detected within breast cancer patients' peripheral blood, along with association with tumor progression. By using mass cytometry, we quantified 130 immune variables from untreated breast cancer patients' peripheral blood. Supervised analyses and dimensionality reduction algorithms evidenced circulating Vδ2+ γδ T cell phenotypic alterations already established at diagnosis. Foremost, terminally differentiated Vδ2+ γδ T cells displaying phenotypes of exhausted senescent T cells associated with lymph node involvement. Thereby, our results support Vδ2+ γδ T cells implication in breast cancer pathogenesis and progression, besides shedding light on liquid biopsies to monitor surrogate markers of tumor-infiltrating Vδ2+ γδ T cell antitumor activity.