Costimulatory Molecules and Immune Checkpoints Are Differentially Expressed on Different Subsets of Dendritic Cells

Abstract

Dendritic cells (DCs) play a crucial role in initiating and shaping immune responses. The effects of DCs on adaptive immune responses depend partly on functional specialization of distinct DC subsets, and partly on the activation state of DCs, which is largely dictated by environmental signals. Fully activated immunostimulatory DCs express high levels of costimulatory molecules, produce pro-inflammatory cytokines, and stimulate T cell proliferation, whereas tolerogenic DCs express low levels of costimulatory molecules, produce immunomodulatory cytokines and impair T cell proliferation. Relevant to the increasing use of immune checkpoint blockade in cancer treatment, signals generated from inhibitory checkpoint molecules on DC surface may also contribute to the inhibitory properties of tolerogenic DCs. Yet, our knowledge on the expression of inhibitory molecules on human DC subsets is fragmentary. Therefore, in this study, we investigated the expression of three immune checkpoints on peripheral blood DC subsets, in basal conditions and upon exposure to pro-inflammatory and anti-inflammatory stimuli, by using a flow cytometric panel that allows a direct comparison of the activatory/inhibitory phenotype of DC-lineage and inflammatory DC subsets. We demonstrated that functionally distinct DC subsets are characterized by differential expression of activatory and inhibitory molecules, and that cDC1s in particular are endowed with a unique immune checkpoint repertoire characterized by high TIM-3 expression, scarce PD-L1 expression and lack of ILT2. Notably, this unique cDC1 repertoire was subverted in a group of patients with myelodysplastic syndromes included in the study. Applied to the characterization of DCs in the tumor microenvironment, this panel has the potential to provide valuable information to be used for investigating the role of DC subsets in cancer, guiding DC-targeting treatments, and possibly identifying predictive biomarkers for clinical response to cancer immunotherapy.

High PD-L1/CD274 Expression of Monocytes and Blood Dendritic Cells Is a Risk Factor in Lung Cancer Patients Undergoing Treatment with PD1 Inhibitor Therapy

“…Furthermore, PD-L1/CD274 silencing on DC could enhance T-cell responses leading to tumor clearance [ 2 ], which is in accordance with several studies demonstrating the advantages of knocking down PD-L1/CD274 regarding the efficacy of DC vaccine therapy [ 27 , 28 ]. Whereas a negligible PD-L1/CD274 expression of blood pDC and mDC of healthy donors has been described [ 29 ], blood DC of lung cancer patients show a clear PD-L1/CD274 expression in this study, thereby confirming the data of blood DC in patients with ovarian cancer [ 2 ] and melanoma [ 30 ]. Similarly, monocytes in healthy controls express only a small amount of PD-L1/CD274, whereas monocytes in cervical cancer patients show an increased expression [ 31 ].…”

Daratumumab prevents programmed death ligand‐1 expression on antigen‐presenting cells in de novo multiple myeloma

“…In our study, we found that while PD‐L1 expression is increased on peripheral DC and monocytes during VTD treatment, combination with the anti‐CD38 monoclonal antibody Dara seems to prevent this phenomenon. In fact, it has been reported that inflammation can lead to an increased expression of PD‐L1 on DC, suggesting that inflammation induced by chemotherapy could be responsible for the increase PD‐L1 expression observed in the control group upon treatment . In contrast, in the Dara group, as DC subsets are continuously depleted by Dara, we hypothesized that the low PD‐L1 expression was the reflect of the expression level on de novo produced DC.…”

“…In fact, it has been reported that inflammation can lead to an increased expression of PD-L1 on DC, suggesting that inflammation induced by chemotherapy could be responsible for the increase PD-L1 expression observed in the control group upon treatment. 22 In contrast, in the Dara group, as DC subsets are continuously depleted by Dara, we hypothesized that the low PD-L1 expression was the reflect of the expression level on de novo produced DC. Given the important expression of Fc receptors (FcR) on DC, 23 we cannot exclude that the anti-CD38 monoclonal antibody may react simultaneously on the same cell via their binding site and also via FcR by implementing the so-called scorpion effect.…”

Comprehensive Phenotyping of Dendritic Cells in Cancer Patients by Flow Cytometry

“…More recently, we developed an 18-color flow cytometric panel dedicated to the analysis of DCs (a representative analysis showing the gating strategy is reported in Fig. 1) and demonstrated that cDC1s, cDC2s, and pDCs have also a differential expression of inhibitory molecules, with cDC1s having a unique immune checkpoint repertoire characterized by high expression of T-cell immunoglobulin and mucin-domain containing-3 (TIM-3, CD366), low PD-L1 expression, and lack of ILT2 (48). Notably, this unique repertoire was subverted in patients affected by myelodysplastic syndromes, suggesting that the analysis of PBDC phenotype may be helpful to provide new insights in the comprehension of the role played by distinct DC subsets in the pathogenesis and progression of different types of cancer (48).…”