Abnormal Changes of IL3/IL3R and Its Downstream Signaling Pathways in the Prion-Infected Cell Line and in the Brains of Scrapie-Infected Rodents.

Interleukin 3 (IL-3) plays an important role in hematopoiesis and immune regulation, brain IL-3/IL-3R signaling has been shown to involve in the physiological and pathological processes of a variety of neurodegenerative diseases, but its role in prion diseases is rarely described. Here, the changes of IL-3/IL-3R and its downstream signaling pathways in a scrapie-infected cell line and in the brains of several scrapie-infected rodent models were evaluated by various methods. Markedly decreased IL-3Rα were observed in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cell model, which showed increased in the brain samples collected at early and middle stage of infection. The IL-3 levels were almost unchanged in the brains of scrapie-infected mice and in the prion-infected cell line. Morphological assays identified close co-localization of the increased IL-3Rα signals with NeuN- and Iba1-positive cells, whereas co-localization of IL-3 signals with NeuN- and GFAP-positive cells in the scrapie-infected brain tissues. Some downstream components of IL-3/IL-3R pathways, including JAK2-STAT5 and PI3K/AKT/mTOR pathways, were downregulated in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cells. Stimulation of recombinant IL-3 on the cultured cells showed prion that the prion-infected cells displayed markedly more reluctant responses of JAK2-STAT5 and PI3K/AKT/mTOR pathways than the normal partner cells. These data suggest that although prion infection or PrPSc accumulation in brain tissues does not affect IL-3 expression, it significantly downregulates IL-3R levels, thereby inhibiting the downstream pathways of IL-3/IL-3R and blocking the neuroregulatory and neuroprotective activities of IL-3.

Targeting CD123 in BPDCN: an emerging field.

INTRODUCTION: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic malignancy with historically poor outcomes for patients, often refractory to traditional chemotherapy. Recent research has focused on targeted therapy to improve responses and limit potential toxicity. AREAS COVERED: CD123 (also known as IL-3 Rα) is a cell surface marker and attractive therapeutic target for many myeloid malignancies, particularly BPDCN, whose cells ubiquitously overexpress CD123. We review the history of CD123 research regarding BPDCN, recent advances including FDA approval of tagraxofusp (formerly SL-401) for BPDCN, and ongoing clinical studies utilizing novel therapeutic strategies to target CD123. EXPERT OPINION: The approval of tagraxofusp for the treatment of BPDCN in December 2018 drastically changed the treatment landscape for patients with this rare neoplasm. While tagraxofusp is better tolerated than traditional multi-agent chemotherapy regimens, it requires close monitoring and sound clinical judgment by providers to prevent and mitigate severe treatment-related complications with special attention to the recognition and management of capillary leak syndrome (CLS). Several other promising strategies for targeting CD123 in BPDCN are currently under investigation, including antibody-drug conjugates, T-cell engagers, and CAR-T cellular therapeutics. These CD123 targeted approaches may soon become standard of care for patients with this difficult to treat malignancy.

Structural and evolutionary exploration of the IL-3 family and its alpha subunit receptors.

Interleukin-3 (IL-3) is a cytokine belonging to the family of common ß (ßc) and is involved in various biological systems. Its activity is mediated by the interaction with its receptor (IL-3R), a heterodimer composed of two distinct subunits: IL-3Rα and ßc. IL-3 and its receptor, especially IL-3Rα, play a crucial role in pathologies like inflammatory diseases and therefore are interesting therapeutic targets. Here, we have performed an analysis of these proteins and their interaction based on structural and evolutionary information. We highlighted that IL-3 and IL-3Rα structural architectures are conserved across evolution and shared with other proteins belonging to the same ßc family interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The IL-3Rα/IL-3 interaction is mediated by a large interface in which most residues are surprisingly not conserved during evolution and across family members. In spite of this high variability, we suggested small regions constituted by few residues conserved during the evolution in both proteins that could be important for the binding affinity.

Targeting CD123 in hematologic malignancies: identifying suitable patients for targeted therapy.

Following the observation of interleukin 3 receptor α chain (IL-3Rα; CD123) upregulation on leukemia stem cells (LSCs) almost two decades ago, targeted treatment via CD123-diptheria toxin conjugates has now been tested in patients with diverse myeloid malignancies. Targeted eradication of LSCs could result in effective treatments for many challenging diseases initiated by these cells. Consequently, considerable effort has been directed toward targeting CD123 as a potential strategy for treating patients with hematologic malignancies in which CD123 is overexpressed. However, these therapies have had limited success so far, highlighting the need for suitable criteria to identify patients who could benefit from them. Given the diversity in CD123 expression across different hematologic malignancies, understanding CD123 expression patterns and the functional pathogenetic significance is crucial. Here, we review the methodologies available for CD123 assessment and discuss the biological and clinical characteristics of patients for whom CD123-targeting therapies may have a clinical impact.

Phenotypic characterization of malignant progenitor cells in patients with idiopathic myelofibrosis.

OBJECTIVE/BACKGROUND: Idiopathic myelofibrosis (IM) is a clonal hematological malignancy originating from pluripotent hematopoietic stem cells (HSC). HSC are very rare potent cells that reside in the bone marrow (BM) and at a lower level in peripheral blood (PB). Previous studies showed that IM PB CD34+ cells contain not only BM repopulating cells belonging to the malignant clone but also residual normal HSC. METHODS: In the current study, we separated the subpopulations of IM PB CD34+ cells using IL-3Rα/CD123 labeling and further characterized them by genetic and functional analyses. RESULTS: We differentiated IM PB CD34+ cells into three subpopulations (IL-3Rαhigh, IL-3Rαlow, and IL-3Rαnegative). IL-3Rαhigh CD34+ cell subgroup represents a small population in IM PB CD34+ cells which was not seen in normal G-CSF mobilized CD34+ cells. IM IL-3Rαhigh CD34+ cells contained significant higher percentage of cells bearing marker chromosome detected by fluorescence in situ hybridization (FISH) analysis. In the absence of growth factors, IM IL-3Rαhigh CD34+ cells exhibited abnormal colony forming ability and carried greater percentage of JAK2V617F mutant allele compared with IL-3Rαlow and IL-3Rαnegative CD34+ cells. CONCLUSION: These data indicate that IL-3Rαhigh CD34+ cells from IM enriched for the malignant progenitor cells and IL-3Rα/CD123 may be a potential biomarker and therapeutic target for IM. Our findings will be further validated in future studies with a larger sample size and serial transplant in murine models.

A Human Lin- CD123+ CD127low Population Endowed with ILC Features and Migratory Capabilities Contributes to Immunopathological Hallmarks of Psoriasis.

Innate lymphoid cells (ILC) are members of a heterogeneous family with a lymphoid origin that mimics the T helper (Th) cytokine profile. ILC are involved in early effector cytokine-mediated responses during infections in peripheral tissues. ILC also play an important role in chronic skin inflammatory diseases, including psoriasis. Although classical ILC express CD127, it has been recently reported that the presence of non-classical CD127- ILC populations and an early ILC precursor (EILP) CD127low. ILC development has predominately been investigated in mouse models. However, in humans, different transcription factors have been described for ILC identification. NFIL3 (nuclear factor, IL-3 regulated) is crucial for ILC development in response to IL-7. CD123 (IL-3Rα) is usually used to exclude basophils during ILC identification, however, it is unknown if in response to IL-3, NFIL3 could be relevant to induce ILC features in Lin- CD123+ populations in addition, is also unknown whether peripheral blood (PB) population with ILC features may have skin-homing potential to participate in skin inflammatory chronic diseases. Here, we report a Lin- CD123+ CD127low CD7+ CLA+ population that share some phenotypic properties with basophils, but expresses several transcription factors for ILC commitment such as inhibitor of DNA binding 2 (Id2), NFIL3, promyelocytic leukemia zinc finger (PLZF), thymocyte selection-associated high-mobility group box protein (TOX), and T cell factor-1 (TCF-1). In addition, this population expresses different ILC markers: CD132, CD90, CD161, α4 integrin, c-Kit, CRTH2, AhR, and IL-23R. IL-3 prevents apoptosis and increases their NFIL3, TOX, and PLZF expression. In PB, the CD123+ CD127low population is predominantly a conspicuous population that expresses T-bet and RORγt. The Lin- CD123+ CD127low population in PB has a limited Th type cytokine expression and highly expresses IL-8. The Lin- CD123+ CD127low population expresses skin-homing receptors (cutaneous lymphocyte antigen and CXCR4) and transmigrates through endothelial cells in response to SDF-1. An equivalent Lin- CD123low population was identified in control skin, which shows a broader phenotypic diversity and cytokine production, including IL-22 and IL-17. Remarkably, the CD123low population in the lesion and non-lesion skin of psoriasis patients expresses IL-17 and IL-22. Our findings suggest the identification of an alternative Lin- CD123+ CD127low population with ILC features endowed with migratory capabilities that might contribute to immunopathological hallmarks of psoriasis.

Omalizumab increases the intrinsic sensitivity of human basophils to IgE-mediated stimulation.

BACKGROUND: Treatment of allergic patients with omalizumab results in a paradoxical increase in their basophil histamine release (HR) response ex vivo to cross-linking anti-IgE antibody. It is not known whether this change in response is associated with an increase in intrinsic cellular sensitivity, which would be a paradoxical response. OBJECTIVE: We sought to determine whether the increase in response to anti-IgE antibody is a reflection of an increased cellular sensitivity expressed as molecules of antigen-specific IgE per basophil required to produce 50% of the maximal response. METHODS: Patients were treated with omalizumab or placebo for 12 weeks (NCT01003301 at ClinicalTrials.gov), and the metric of basophil sensitivity was assessed at 4 time points: baseline, 6 to 8 weeks, 12 weeks (after which treatment stopped), and 24 weeks (12 weeks after the end of treatment). RESULTS: As observed previously, treatment with omalizumab resulted in a marked increase in the maximal HR induced by cross-linking anti-IgE antibody. This change was accompanied by a marked shift in intrinsic basophil sensitivity, ranging from 2.5- to 125-fold, with an average of 6-fold at the midpoint of the treatment to 12-fold after 12 weeks. The magnitude of the increase in cellular sensitivity was inversely related to the starting sensitivity or the starting maximum HR. The increased cellular sensitivity also occurred when using leukotriene C4 secretion as a metric of the basophil response. Twelve weeks after the end of treatment, cellular sensitivity was found to shift toward the baseline value, although the return to baseline was not yet complete at this time point. CONCLUSIONS: Treatment with omalizumab results in a markedly increased sensitivity of basophils to IgE-mediated stimulation in terms of the number of IgE molecules required to produce a given response. These results provide a better quantitative sense of the phenotypic change that occurs in basophils during omalizumab treatment, which has both mechanistic and clinical implications.