Single-Cell Analysis Reveals the Heterogeneity of Monocyte-Derived and Peripheral Type-2 Conventional Dendritic Cells

Avelumab induces greater Fc-Fc receptor-dependent natural killer cell activation and dendritic cell crosstalk compared to durvalumab

Several FDA-approved anti-PD-L1 (programmed cell death ligand-1) monoclonal antibodies (mAbs) are used to treat cancer. While these mAbs primarily target and intercept PD-L1:PD-1 inhibitory signaling in T-cells, the Fc-domains of these mAbs are distinct, and the unique cellular cascades triggered by differing Fc-domains of PD-L1 mAbs have not been directly investigated. In this study, we compared the innate immune effects of two widely used anti-PD-L1 IgG1 mAbs which bear distinct Fc-domains, avelumab (native-Fc) and durvalumab (mutated-Fc), using two-cell and three-cell co-culture systems containing Natural Killer cells (NK-cells), dendritic cells (DCs) and various tumor cell lines of multiple cancer origins. We show a robust enhancement in NK-cell effector function, DC maturation, reciprocal NK:DC crosstalk and DC editing that is unique to avelumab treatment using multiple functional immune assays. By transcriptomic analysis, we show for the first time pivotal differences in gene sets involved in NK-cell effector function, DC maturation, immunoregulatory interactions, and cytokine production between innate immune cells treated with avelumab versus durvalumab. Furthermore, we report several previously unknown Fc-receptor-associated biological pathways uniquely triggered by avelumab. Our findings elucidate novel mechanisms of Fc-dependent actions of PD-L1 mAbs which may inform their use in future clinical trials.

Knockdown of TIM3 Hampers Dendritic Cell Maturation and Induces Immune Suppression by Modulating T-Cell Responses

Various inhibitors targeting T-cell immunoglobulin and mucin-containing molecule 3 (TIM3) aimed at reversing T-cell exhaustion for better immunotherapy outcomes have demonstrated limited clinical efficacy as monotherapy, with the underlying mechanisms remaining ambiguous. TIM3 is markedly expressed in dendritic cells (DCs), and the inconsistent research findings on its role in myeloid cells underscore its vital function within DCs. Through the establishment of an in vitro differentiation model generating mature dendritic cells (mDCs) under TIM3-targeted interventions, combined with an RNA sequencing analysis, this investigation systematically examined TIM3-mediated regulation and ligand interactions in human primary DCs. The findings indicate that TIM3 inhibition hinders DC maturation, which subsequently diminishes the antigen-presenting capacity of DCs, ultimately leading to immune suppression in T cells. These findings collectively establish TIM3 as a regulator of DC differentiation that promotes DC maturation while optimizing the antigen-processing and presentation capacity. This study elucidates the rationale behind the suboptimal efficacy of TIM3 inhibitors and advocates for retaining TIM3 signaling pathways in DCs.

Single-Cell Sequencing: Genomic and Transcriptomic Approaches in Cancer Cell Biology

This article reviews the impact of single-cell sequencing (SCS) on cancer biology research. SCS has revolutionized our understanding of cancer and tumor heterogeneity, clonal evolution, and the complex interplay between cancer cells and tumor microenvironment. SCS provides high-resolution profiling of individual cells in genomic, transcriptomic, and epigenomic landscapes, facilitating the detection of rare mutations, the characterization of cellular diversity, and the integration of molecular data with phenotypic traits. The integration of SCS with multi-omics has provided a multidimensional view of cellular states and regulatory mechanisms in cancer, uncovering novel regulatory mechanisms and therapeutic targets. Advances in computational tools, artificial intelligence (AI), and machine learning have been crucial in interpreting the vast amounts of data generated, leading to the identification of new biomarkers and the development of predictive models for patient stratification. Furthermore, there have been emerging technologies such as spatial transcriptomics and in situ sequencing, which promise to further enhance our understanding of tumor microenvironment organization and cellular interactions. As SCS and its related technologies continue to advance, they are expected to drive significant advances in personalized cancer diagnostics, prognosis, and therapy, ultimately improving patient outcomes in the era of precision oncology.

Characteristics of a CCL21 Gene-Modified Dendritic Cell Vaccine Utilized for a Clinical Trial in Non-Small Cell Lung Cancer

The treatment of non-small cell lung cancer has made major strides with the use of immune checkpoint inhibitors; however, there remains a significant need for therapies that can overcome immunotherapy resistance. Dendritic cell (DC) vaccines have been proposed as a therapy that can potentially enhance the antitumor immune response. We have embarked on a phase I clinical trial of a vaccine consisting of monocyte-derived DCs (moDC) modified to express the chemokine C-C motif chemokine ligand 21 (CCL21-DC) given in combination with pembrolizumab. In this study, we report a comprehensive characterization of this CCL21-DC vaccine and interrogate the effects of multiple factors in the manufacturing process. We show that the cellular makeup of the CCL21-DC vaccine is heterogeneous because of the presence of passenger lymphocytes at a proportion that is highly variable among patients. Single-cell RNA sequencing of vaccines revealed further heterogeneity within the moDC compartment, with cells spanning a spectrum of DC phenotypes. Transduction with a CCL21-containing adenoviral vector augmented CCL21 secretion by moDCs, but otherwise had a minimal effect on vaccine characteristics. A single freeze-thaw cycle for stored vaccines was associated with minor alterations to the DC phenotype, as was the use of healthy donors rather than patient autologous blood. Our results highlight important considerations for the production of DC vaccines and identify underexplored factors that may affect their efficacy and immunologic impact.

IL1R2 Acts as a Negative Regulator of Monocyte Recruitment During Inflammation

IL1-β plays a central role in inflammation but its biological action needs to be tightly controlled. Such negative regulation can be exerted by the decoy receptor IL1R2. However, IL1R2 biology in immune cells remains poorly characterized, in particular in monocytes. Using conditional deficient mice, we show that Il1r2 deficiency in monocytes does not affect their steady-state life cycle but dysregulates their trafficking to inflamed tissues in models of peritonitis and neuro-inflammation. Mechanistically, we found that Il1r2 deficiency in monocytes increases CCL2 secretion in the inflamed peritoneum, thereby amplifying monocyte recruitment from blood. In autoimmune neuro-inflammation, Il1r2 deficiency in monocytes exacerbates disease severity. Our findings suggest that the specific action of IL1R2 in monocytes contributes to a feedback mechanism for fine-tuning the numbers of recruited monocytes during inflammation.

Bifidobacterium breve DSM 32583 and Limosilactobacillus fermentum CECT5716 postbiotics attenuate S. aureus and IL-33-induced Th2 responses

Over the past decades, the prevalence of allergic diseases noticeably increased in industrialized countries. The Th2 immune response plays a central role in these pathologies and its modulation using pro-/postbiotics constitutes a promising approach to prevent or alleviate disease symptoms. The aim of this in vitro study, was to investigate the ability of human milk-derived Bifidobacterium breve DSM 32583 (Bb) and Limosilactobacillus fermentum CECT5716 (Lf), to modulate the Th2 induced responses. To this end, Th2 cells were generated by co-culturing of human naïve Th cells with monocyte-derived dendritic cells (moDCs) either stimulated with Staphylococcus aureus or IL-33. The immunomodulatory effects of pro-/postbiotic preparations of Bb and Lf on moDCs and Th2 cells were evaluated in terms of maturation markers expression and cytokines production. Remarkably, the tested strains induced the anti-inflammatory cytokine IL-10 in moDCs, in a strain-, dose- and viability-dependent manner with no significant upregulation of IL-12p70 nor CD83, CD86 or HLA-DR. Interestingly, Bb and Lf postbiotics were able to dampen the Th2/Th1 response induced upon S. aureus- or IL-33 stimulation. They were also able to synergistically induce IL-10 in moDCs and T cells, upon co-stimulation with LPS. Finally, we observed that live probiotics triggered a mild Th1 response that was attenuated in the presence of galacto-oligosaccharides. Altogether, Bb and Lf pro-/postbiotics exhibited remarkable immune regulatory effects on both moDCs and Th2 cells. Therefore, further in vivo studies should be considered to validate these findings and assess their ability to prevent allergy or alleviate its symptoms in affected patients.

Human cytomegalovirus exploits STING signaling and counteracts IFN/ISG induction to facilitate infection of dendritic cells

Human cytomegalovirus (HCMV) is a widespread pathogen that in immunocompromised hosts can cause life-threatening disease. Studying HCMV-exposed monocyte-derived dendritic cells by single-cell RNA sequencing, we observe that most cells are entered by the virus, whereas less than 30% of them initiate viral gene expression. Increased viral gene expression is associated with activation of the stimulator of interferon genes (STING) that usually induces anti-viral interferon responses, and with the induction of several pro- (RHOB, HSP1A1, DNAJB1) and anti-viral (RNF213, TNFSF10, IFI16) genes. Upon progression of infection, interferon-beta but not interferon-lambda transcription is inhibited. Similarly, interferon-stimulated gene expression is initially induced and then shut off, thus further promoting productive infection. Monocyte-derived dendritic cells are composed of 3 subsets, with one being especially susceptible to HCMV. In conclusion, HCMV permissiveness of monocyte-derived dendritic cells depends on complex interactions between virus sensing, regulation of the interferon response, and viral gene expression.

Classical DC2 subsets and monocyte-derived DC: Delineating the developmental and functional relationship

To specifically tailor immune responses to a given pathogenic threat, dendritic cells (DC) are highly heterogeneous and comprise many specialized subtypes, including conventional DC (cDC) and monocyte-derived DC (MoDC), each with distinct developmental and functional characteristics. However, the functional relationship between cDC and MoDC is not fully understood, as the overlapping phenotypes of certain type 2 cDC (cDC2) subsets and MoDC do not allow satisfactory distinction of these cells in the tissue, particularly during inflammation. However, precise cDC2 and MoDC classification is required for studies addressing how these diverse cell types control immune responses and is therefore currently one of the major interests in the field of cDC research. This review will revise murine cDC2 and MoDC biology in the steady state and under inflammatory conditions and discusses the commonalities and differences between ESAM^lo cDC2, inflammatory cDC2, and MoDC and their relative contribution to the initiation, propagation, and regulation of immune responses.

Single-cell RNA sequencing of peripheral blood reveals that monocytes with high cathepsin S expression aggravate cerebral ischemia-reperfusion injury

BACKGROUND

Stroke is a major cause of morbidity and mortality worldwide. After cerebral ischemia, peripheral immune cells infiltrate the brain and elicit an inflammatory response. However, it is not clear when and how these peripheral immune cells affect the central inflammatory response, and whether interventions that target these processes can alleviate ischemia-reperfusion (I/R) injury.

METHODS

Single-cell transcriptomic sequencing and bioinformatics analysis were performed on peripheral blood of mice at different times after I/R to analyze the key molecule of cell subsets. Then, the expression pattern of this molecule was determined through various biological experiments, including quantitative RT-PCR, western blot, ELISA, and in situ hybridization. Next, the function of this molecule was assessed using knockout mice and the corresponding inhibitor.

RESULTS

Single-cell transcriptomic sequencing revealed that peripheral monocyte subpopulations increased significantly after I/R. Cathepsin S (Ctss)was identified as a key molecule regulating monocyte activation by pseudotime trajectory analysis and gene function analysis. Next, Cathepsin S was confirmed to be expressed in monocytes with the highest expression level 3 days after I/R. Infarct size (p < 0.05), neurological function scores (p < 0.05), and apoptosis and vascular leakage rates were significantly reduced after Ctss knockout. In addition, CTSS destroyed the blood-brain barrier (BBB) by binding to junctional adhesion molecule (JAM) family proteins to cause their degradation.

CONCLUSIONS

Cathepsin S inhibition attenuated cerebral I/R injury; therefore, cathepsin S can be used as a novel target for drug intervention after stroke.

SHP-2 and PD-1-SHP-2 signaling regulate myeloid cell differentiation and antitumor responses

The inhibitory receptor PD-1 suppresses T cell activation by recruiting the phosphatase SHP-2. However, mice with a T-cell-specific deletion of SHP-2 do not have improved antitumor immunity. Here we showed that mice with conditional targeting of SHP-2 in myeloid cells, but not in T cells, had diminished tumor growth. RNA sequencing (RNA-seq) followed by gene set enrichment analysis indicated the presence of polymorphonuclear myeloid-derived suppressor cells and tumor-associated macrophages (TAMs) with enriched gene expression profiles of enhanced differentiation, activation and expression of immunostimulatory molecules. In mice with conditional targeting of PD-1 in myeloid cells, which also displayed diminished tumor growth, TAMs had gene expression profiles enriched for myeloid differentiation, activation and leukocyte-mediated immunity displaying >50% overlap with enriched profiles of SHP-2-deficient TAMs. In bone marrow, GM-CSF induced the phosphorylation of PD-1 and recruitment of PD-1-SHP-2 to the GM-CSF receptor. Deletion of SHP-2 or PD-1 enhanced GM-CSF-mediated phosphorylation of the transcription factors HOXA10 and IRF8, which regulate myeloid differentiation and monocytic-moDC lineage commitment, respectively. Thus, SHP-2 and PD-1-SHP-2 signaling restrained myelocyte differentiation resulting in a myeloid landscape that suppressed antitumor immunity.

Heterogeneity and origins of myeloid cells

PURPOSE OF REVIEW

Myeloid cells - granulocytes, monocytes, macrophages and dendritic cells (DCs) - are innate immune cells that play key roles in pathogen defense and inflammation, as well as in tissue homeostasis and repair. Over the past 5 years, in part due to more widespread use of single cell omics technologies, it has become evident that these cell types are significantly more heterogeneous than was previously appreciated. In this review, we consider recent studies that have demonstrated heterogeneity among neutrophils, monocytes, macrophages and DCs in mice and humans. We also discuss studies that have revealed the sources of their heterogeneity.

RECENT FINDINGS

Recent studies have confirmed that ontogeny is a key determinant of diversity, with specific subsets of myeloid cells arising from distinct progenitors. However, diverse microenvironmental cues also strongly influence myeloid fate and function. Accumulating evidence therefore suggests that a combination of these mechanisms underlies myeloid cell diversity.

SUMMARY

Consideration of the heterogeneity of myeloid cells is critical for understanding their diverse activities, such as the role of macrophages in tissue damage versus repair, or tumor growth versus elimination. Insights into these mechanisms are informing the design of novel therapeutic approaches.

The In Vitro Differentiation of Human CD141+CLEC9A+ Dendritic Cells from Mobilized Peripheral Blood CD34+ Hematopoietic Stem Cells

As shown in various preclinical studies, conventional type-1 dendritic cells, or cDC1s, play a critical role in the immunological rejection of tumors and in the defense against pathogens. This indispensability stems from their potent capacity to activate cytotoxic T cells, especially via the cross-presentation of exogenous antigens. For this reason, cDC1s have become an attractive target for immunotherapy. Here we report a simplified method for generating large numbers of cDC1-like cells in vitro from mobilized human peripheral blood CD34+ hematopoietic stem cells using FMS-like tyrosine kinase 3 ligand (FLT3L) and granulocyte-macrophage colony-stimulating factor (GM-CSF). An important aspect of this Protocol is the growth of cells on a non-tissue culture-treated surface rather than on a tissue culture-treated surface since the latter suppresses cDC1-marker expression. The resulting CD11c+ DCs express high levels of cDC1-specific markers such as CD141, CLEC9A, TLR3, and several DC maturation markers. Compared to alternative differentiation methods, this method generates large numbers of cDC1-like cells without the need for immortalized feeder cells and should prove useful for studying cDC1 immunobiology and clinical applications of this DC subset. © 2022 Wiley Periodicals LLC. Basic Protocol: Generation of human CD141+CLEC9A+ dendritic cells from mobilized peripheral blood CD34+ hematopoietic stem cells Support Protocol: Flow cytometric immunophenotyping of CD141+ dendritic cells.