Dendritic cells modulate c-kit expression on the edge between activation and death

Mouse dendritic cells in the steady state: Hypoxia, autophagy, and stem cell factor

Dendritic cells (DCs) are innate immune cells with a central role in immunity and tolerance. Under steady-state, DCs are scattered in tissues as resting cells. Upon infection or injury, DCs get activated and acquire the full capacity to prime antigen-specific CD4⁺ and CD8⁺ T cells, thus bridging innate and adaptive immunity. By secreting different sets of cytokines and chemokines, DCs orchestrate diverse types of immune responses, from a classical proinflammatory to an alternative pro-repair one. DCs are highly heterogeneous, and physiological differences in tissue microenvironments greatly contribute to variations in DC phenotype. Oxygen tension is normally low in some lymphoid areas, including bone marrow (BM) hematopoietic niches; nevertheless, the possible impact of tissue hypoxia on DC physiology has been poorly investigated. We assessed whether DCs are hypoxic in BM and spleen, by staining for hypoxia-inducible-factor-1α subunit (HIF-1α), the master regulator of hypoxia-induced response, and pimonidazole (PIM), a hypoxic marker, and by flow cytometric analysis. Indeed, we observed that mouse DCs have a hypoxic phenotype in spleen and BM, and showed some remarkable differences between DC subsets. Notably, DCs expressing membrane c-kit, the receptor for stem cell factor (SCF), had a higher PIM median fluorescence intensity (MFI) than c-kit^- DCs, both in the spleen and in the BM. To determine whether SCF (a.k.a. kit ligand) has a role in DC hypoxia, we evaluated molecular pathways activated by SCF in c-kit⁺ BM-derived DCs cultured in hypoxic conditions. Gene expression microarrays and gene set enrichment analysis supported the hypothesis that SCF had an impact on hypoxia response and inhibited autophagy-related gene sets. Our results suggest that hypoxic response and autophagy, and their modulation by SCF, can play a role in DC homeostasis at the steady state, in agreement with our previous findings on SCF's role in DC survival.

Application of dendritic cells in tumor immunotherapy and progress in the mechanism of anti-tumor effect of Astragalus polysaccharide (APS) modulating dendritic cells: a review

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that are essential in mediating the body's natural and adaptive immune responses. The body can regulate the function of DCs in various ways to enhance their antitumor effects. In the tumour microenvironment (TME), antigen-specific T cell responses are initiated through DC processing and delivery of tumour-associated antigens (TAAs); conversely, tumour cells inhibit DC recruitment by releasing metabolites, cytokines and other regulatory TME and function. Different subpopulations of DCs exist in tumour tissues, and their functions vary. Insight into DC subgroups in TME allows assessment of the effectiveness of tumour immunotherapy. Astragalus polysaccharide (APS) is the main component of the Chinese herb Astragalus membranaceus. The study found that the antitumor effects of APS are closely related to DCs. APS can promote the expression of surface molecules CD80 and CD86, promote the maturation of DCs, and activate CTL to exert antitumor effects. We reviewed the application of DCs in tumor immunotherapy and the mechanism of modulation of DCs by Astragalus polysaccharide to provide new directions and strategies for tumor therapy and new drug development.

Major alterations in the mononuclear phagocyte landscape associated with COVID-19 severity

Dendritic cells (DCs) and monocytes are crucial mediators of innate and adaptive immune responses during viral infection, but misdirected responses by these cells may contribute to immunopathology. Here, we performed high-dimensional flow cytometry-analysis focusing on mononuclear phagocyte (MNP) lineages in SARS-CoV-2-infected patients with moderate and severe COVID-19. We provide a deep and comprehensive map of the MNP landscape in COVID-19. A redistribution of monocyte subsets toward intermediate monocytes and a general decrease in circulating DCs was observed in response to infection. Severe disease coincided with the appearance of monocytic myeloid-derived suppressor cell-like cells and a higher frequency of pre-DC2. Furthermore, phenotypic alterations in MNPs, and their late precursors, were cell-lineage-specific and associated either with the general response against SARS-CoV-2 or COVID-19 severity. This included an interferon-imprint in DC1s observed in all patients and a decreased expression of the coinhibitory molecule CD200R in pre-DCs, DC2s, and DC3 subsets of severely sick patients. Finally, unsupervised analysis revealed that the MNP profile, alone, pointed to a cluster of COVID-19 nonsurvivors. This study provides a reference for the MNP response to SARS-CoV-2 infection and unravels mononuclear phagocyte dysregulations associated with severe COVID-19.

Biological and Clinical Changes in a Pediatric Series Treated with Off-Label JAK Inhibitors

Off-label use of medications is still a common practice in pediatric rheumatology. JAK inhibitors are authorized in adults in the treatment of rheumatoid arthritis, psoriatic arthritis and ulcerative colitis. Although their use is not authorized yet in children, JAK inhibitors, based on their mechanism of action and on clinical experiences in small series, have been suggested to be useful in the treatment of pediatric interferon-mediated inflammation. Accordingly, an increased interferon score may help to identify those patients who might benefit of JAK inhibitors. We describe the clinical experience with JAK inhibitors in seven children affected with severe inflammatory conditions and we discuss the correlation between clinical features and transcriptomic data. Clinical improvements were recorded in all cases. A reduction of interferon signaling was recorded in three out of seven subjects at last follow-up, irrespectively from clinical improvements. Other signal pathways with significant differences between patients and controls included upregulation of DNA repair pathway and downregulation of extracellular collagen homeostasis. Two patients developed drug-related adverse events, which were considered serious in one case. In conclusion, JAK inhibitors may offer a valuable option for children with severe interferon-mediated inflammatory disorders reducing the interferon score as well as influencing other signal pathways that deserve future studies.

Tyrosine kinase inhibitors modulate dendritic cell activity via confining c-Kit signaling and tryptophan metabolism

Dendritic cell (DC)-based vaccine has been established in tumor immunotherapy. Importantly, the efficiency of anti-tumor T-cells in draining lymph nodes is dependent on the status of DCs surrounding in tumors. It has been shown that Indoleamine 2,3-dioxygenase (IDO) plays a key role to induce tolerogenic DCs in tumor microenvironment, and tyrosine kinase inhibitors (TKIs) can suppress the function of IDO in DCs. However, the stimulatory effect of TKI-modified DCs on T cells remains unclear. In this report, we found that one type of TKI-dasatinib can modify DCs to increasing the activation of allogenic T cells. These TKI-modified DCs delayed the onset of B16 melanoma progression in mice. In mechanistic studies, TKIs did not increase the maturation but reduce the expression and phosphorylation levels of IDO and IDO mediated tryptophan metabolism in DCs. In addition, the suppressive effect of TKIs on tryptophan metabolism may be caused by blocking c-Kit pathway in DCs. Furthermore, the increased phosphorylation of general control nonderepressible (GCN2) and decreased expression of aryl hydrocarbon receptor (AhR)/aryl hydrocarbon receptor nuclear translocator (ARNT) were observed in the T cells activated by TKI-modified DCs, suggesting the enhancement of effector function of T cells. These results indicate that TKI could be used to modulate DC immunogenic activity and may potentially be applied in DC-based cancer immunotherapy.