Thymic Stromal Lymphopoietin Receptor Research Articles

Precision Co-Targeting of the Thymic Stromal Lymphopoietin Receptor in Childhood CRLF2-Rearranged Acute Lymphoblastic Leukemia

Introduction : Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is associated with high rates of chemoresistance and relapse. CRLF2 (cytokine receptor-like factor 2) rearrangements occur in 50% of Ph-like and 60% of Down Syndrome (DS)-associated ALL and induce constitutive JAK/STAT and other kinase signaling. Current clinical trials are studying chemotherapy with the JAK inhibitor ruxolitinib in patients with CRLF2-rearranged Ph-like ALL, but results are not yet known. While chimeric antigen receptor T-cell (CART) immunotherapies have induced remarkable remissions in children with relapsed/refractory B-ALL, approximately 50% of CD19CART-treated patients will relapse again, many with CD19 antigen loss. New therapies are needed to prevent relapse and overcome immunotherapeutic resistance.Methods : We previously developed CAR T cells targeting the thymic stromal lymphopoietin receptor (TSLPR; encoded by CRLF2) and demonstrated potent preclinical activity in Ph-like ALL models (Qin Blood 2015), which has led to a soon-to-open phase 1 clinical trial for patients with relapsed/refractory CRLF2-overexpressing ALL. In the current preclinical studies, we hypothesized that combinatorial targeting with bispecific TSLPRxCD19CART or TSLPRxCD22CART (Ross Cancer Res 2020) or with TSLPRCART + ruxolitinib will have superior activity against CRLF2-rearranged Ph-like and DS-ALL.Results : TSLPRCART treatment of CRLF2-rearranged ALL cell line (n=1) and patient-derived xenograft (PDX) models potently inhibited leukemia proliferation in vitro and in vivo and induced long-term ‘cure’ of xenograft mice. However, co-administration of TSLPRCART + ruxolitinib markedly diminished in vivo T cell numbers, blunted cytokine production, and facilitated leukemia relapse, which could be abrogated by delaying ruxolitinib. Importantly, ruxolitinib co-treatment prevented severe TSLPRCART-induced cytokine release syndrome (CRS) and animal death. Interestingly, ruxolitinib withdrawal led to return of T-cell functionality with re-detection of TSLPRCART in peripheral blood, induction of IFN-γ production, and leukemia clearance upon CRLF2+ ALL rechallenge (Figure 1).Conclusions: In these preclinical studies, we report potent activity of TSLPRCART in cell line (n=1) and PDX models of childhood CRLF2-rearranged Ph-like ALL (n=2) and DS-ALL (n=2) and, interestingly, deleterious effects of concomitant JAK inhibition upon CAR T cell functionality. We demonstrated that ruxolitinib co-administration impaired in vivo TSLPRCART-induced ALL cell killing but was also beneficial in protection against life-threatening cytokine release syndrome in co-treated animals. Importantly, TSLPRCART was not eliminated, only suppressed, by JAKi co-treatment with restoration of T cell functionality upon ruxolitinib removal and/or leukemia relapse/rechallenge studies. Ongoing studies are defining optimal TSLPRCART + ruxolitinib sequence(s) to maximize both anti-leukemia efficacy and potential CRS mitigation, as well as assessing in vivo efficacy of bispecific TSLPRCARTs in CRLF2-R Ph-like ALL and DS-ALL PDX models for future translation and clinical evaluation in next-generation trials. [Display omitted] DisclosuresFry: ElevateBio: Research Funding; Sana Biotechnology: Current Employment, Current equity holder in publicly-traded company. Tasian: Aleta Biotherapeutics: Consultancy; Kura Oncology: Consultancy; Gilead Sciences: Research Funding; Incyte Corporation: Research Funding.

ASP7266, a Novel Antibody against Human Thymic Stromal Lymphopoietin Receptor for the Treatment of Allergic Diseases.

Thymic stromal lymphopoietin (TSLP), positioned at the top of the inflammatory cascade, is a key regulator that enhances allergic inflammatory responses by activating T helper type 2 cells, Group 2 innate lymphoid cells (ILC2), and myeloid dendritic cells (mDCs) via the TSLP receptor (TSLPR). We evaluated the inhibitory effects of ASP7266, a novel recombinant fully human IgG1 monoclonal antibody against TSLPR, on TSLP signaling and inflammation. The inhibitory effects of ASP7266 and the control antibody tezepelumab on TSLP and TSLPR interactions were investigated using a proliferation assay with TSLP stimulation and a chemokine production assay. The pharmacological effects of ASP7266 were investigated by examining differentiation of naive CD4+ T cells, ILC2 cytokine production, and ascaris extract-induced skin allergic reaction in cynomolgus monkeys. ASP7266 potently inhibited TSLP-induced cell proliferation and C-C motif chemokine ligand 17 production. Furthermore, ASP7266 inhibited TSLP-stimulated mDC-mediated naive CD4+ T-cell differentiation and interleukin 5 production by lineage-negative peripheral blood mononuclear cells, which can be considered ILC2 in vitro. In sensitized monkeys, ASP7266 completely suppressed ascaris extract-induced allergic skin reactions. Based on these results, ASP7266, a novel human therapeutic antibody against TSLPR, is a potential therapy for patients with allergic diseases. SIGNIFICANCE STATEMENT: TSLP, positioned at the top of the inflammatory cascade, plays a key role in various allergic diseases, including asthma, chronic rhinosinusitis with nasal polyposis, and atopic dermatitis. Here we show that the anti-TSLPR antibody ASP7266 exhibited excellent pharmacological activity in preclinical studies. Therefore, ASP7266 has the potential to be a promising treatment option for patients with allergic disorders.

Functional characterisation of two receptor interaction determinants in human thymic stromal lymphopoietin.

Thymic stromal lymphopoietin (TSLP) is a pro-inflammatory cytokine with important pathological roles in Asthma bronchiale, malignant tumours and other diseases. The heterodimeric human TSLP receptor (hTSLPR) consists of the TSLP-binding subunit (TSLPRα) and the IL-7Rα-subunit. We studied the properties of hTSLP variants with mutations in their bipartite interaction interface towards IL-7Rα. One mutant (T46D/K101D) showed only mild impairment in receptor affinity but a massive reduction in biological activity. To facilitate the future development of hTSLP mutants with drug properties, we have devised a eukaryontic cytokine display assay with activity read-out and intrinsic genotype-phenotype coupling.

Interferon-λ Improves the Efficacy of Intranasally or Rectally Administered Influenza Subunit Vaccines by a Thymic Stromal Lymphopoietin-Dependent Mechanism.

Previous work showed that interferon-λ (IFN-λ) can trigger the synthesis of thymic stromal lymphopoietin (TSLP) by specialized epithelial cells in the upper airways of mice, thereby improving the performance of intranasally administered influenza vaccines. Here we demonstrate that protein-only influenza vaccines containing either IFN-λ or TSLP boosted antigen-specific IgG1 and IgA responses and enhanced the resistance of mice to influenza virus challenge, irrespective of whether the vaccines were applied via the intranasal or the rectal route. TSLP receptor deficiency negatively influenced vaccine-induced antiviral immunity by impairing the migration of dendritic cells from the airways to the draining lymph nodes of immunized mice, thereby restraining follicular helper T cell and germinal center B cell responses. As previously observed during intranasal vaccination, the adjuvant effect of IFN-λ on a rectally administered influenza vaccine was no longer observed when TSLP receptor-deficient mice were used for immunization, highlighting the central role of the IFN-λ/TSLP axis for vaccine-induced antiviral immunity in the mucosa.

Synthesis and Biochemical Evaluation of Baicalein Prodrugs.

Baicalein (5,6,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one), a flavonoid analog from Scutellaria baicalensis, possesses several pharmacological activities including antioxidant, antiproliferative, and anti-inflammatory activities. We previously reported that baicalein inhibits the thymic stromal lymphopoietin (TSLP)/TSLP receptor (TSLPR) signaling pathways and can be used as an active ingredient in the treatment of asthma and atopic dermatitis. However, baicalein is rapidly metabolized to baicalin and baicalein-6-O-glucuronide in vivo, which limits its preclinical and clinical use. In this study, we designed, synthesized, and evaluated baicalein prodrugs that protect the OH group at the 7-position of the A ring in baicalein with the amino acid carbamate functional group. Comprehensive in vitro and in vivo studies identified compound 2 as a baicalein prodrug candidate that improved the plasma exposure of baicalein in mouse animal studies. Our results demonstrated that this prodrug approach could be further adopted to discover oral baicalein prodrugs.

Expression and Polymorphism of TSLP/TSLP Receptors as Potential Diagnostic Markers of Colorectal Cancer Progression.

Colorectal cancer (CRC) is the third most common malignancy and the fourth leading cause of cancer-related mortality worldwide. Inflammation is considered as a critical driver for CRC development and growth. We investigated the association between polymorphisms/expression levels of thymic stromal lymphopoietin (TSLP) /TSLP receptors and CRC risk in Saudi population. DNA samples were isolated from blood samples from 220 participants. Case subjects were 112 patients diagnosed with CRC, while control subjects were 108 healthy individuals, who were not diagnosed with any type of malignancy. We selected two single nucleotide polymorphisms (SNPs) located in the thymic stromal lymphopoietin gene (rs10043985 and rs2289276), three SNPs in TSLP receptor gene (TSLPR; rs36139698, rs36177645, and rs36133495), and two other SNPs in interleukin-7 receptor gene (IL-7R; rs12516866 and rs1053496), and designated these SNPs for a case-control genotyping study. The gene expression was analyzed using quantitative RT-PCR and immunohistochemistry assays array on 20 matching colorectal cancer/normal tissues. mRNA expressions and protein levels of TSLP, TSLPR-α subunit, and IL-7R-α subunit showed a 4-fold increase in colon cancer tissues when compared to normal colon tissues. Furthermore, two SNPs (rs10043985 of TSLP and rs1053496 of IL-7R) showed statistically significant correlations with CRC susceptibility. Interestingly, only rs10043985 showed a statistically significant association (p < 0.0001) in the genotypic and phenotypic levels with CRC for all clinical parameters (age, gender, and tumor location) tested. However, IL-7R rs1053496 genotyping results presented a significant correlation (p < 0.05) in male CRC patients and in individuals under 57 years of age. TSLP rs2289276, IL-7R rs12516866, and all TSLPR variants did not display any significant genotypic or phenotypic correlations in all tested clinical parameters. This study identified that TSLP rs10043985 and IL-7R rs1053496 SNPs, and the expression levels of TSLP and TSLPR-α subunit, can be used as markers for CRC development and treatment. However, additional investigations are required on larger group of patients from diverse ethnicities to confirm the genetic association of these variants to CRC.

A recombinant antibody fragment directed to the thymic stromal lymphopoietin receptor (CRLF2) efficiently targets pediatric Philadelphia chromosome-like acute lymphoblastic leukemia

Antibody fragments are promising building blocks for developing targeted therapeutics, thus improving treatment efficacy while minimising off-target toxicity. Despite recent advances in targeted therapeutics, patients with Philadelphia-like acute lymphoblastic leukemia (Ph-like ALL), a high-risk malignancy, lack specific and effective targeted treatments. Cytokine receptor-like factor 2 (CRLF2) is overexpressed in 50% of Ph-like ALL cases, conferring the survival of leukemia blasts through activation of the JAK/STAT signalling pathway. Targeting such a vital cell-surface protein could result in potent anti-leukaemic efficacy and reduce the likelihood of relapse associated with antigen loss. Herein, we developed a novel single-chain variable fragment (scFv) against CRLF2 based on a monoclonal antibody raised against the recombinant extracellular domain of human TSLPRα chain. The scFv fragment demonstrated excellent binding affinity with CRLF2 protein in the nanomolar range. Cellular association studies in vitro using an inducible CRLF2 knockdown cell line and ex vivo using patient-derived xenografts revealed the selective association of the scFv with CRLF2. The fragment exhibited significant receptor antagonistic effects on STAT5 signalling, suggesting possible therapeutic implications in vivo. This study is the first to describe the potential use of a novel scFv for targeting Ph-like ALL.

Human Lung-Resident Macrophages Express and Are Targets of Thymic Stromal Lymphopoietin in the Tumor Microenvironment.

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine highly expressed by epithelial cells and several innate and adaptive immune cells. TSLP exerts its biological effects by binding to a heterodimeric complex composed of TSLP receptor (TSLPR) and IL-7Rα. In humans, there are two TSLP isoforms: the short form (sfTSLP), constitutively expressed, and the long form (lfTSLP), which is upregulated in inflammation. TSLP has been implicated in the induction and progression of several experimental and human cancers. Primary human lung macrophages (HLMs), monocyte-derived macrophages (MDMs), and peripheral blood monocytes consitutively expressed sfTSLP mRNA. Incubation of HLMs, MDMs, and monocytes with lipopolysaccharide (LPS) or IL-4, but not with IL-13, induced TSLP release from HLMs. LPS, but not IL-4 or IL-13, induced CXCL8 release from HLMs. LPS, IL-4 alone or in combination with IL-13, induced the expression of lfTSLP, but not of sfTSLP from HLMs. Preincubation of HLMs with IL-4, alone or in combination with IL-13, but not IL-13 alone, synergistically enhanced TSLP release from LPS-activated macrophages. By contrast, IL-4, alone or in combination with IL-13, inhibited LPS-induced CXCL8 release from HLMs. Immunoreactive TSLP was detected in lysates of HLMs, MDMs, and monocytes. Incubation of HLMs with TSLP induced the release of proinflammatory (TNF-α), angiogenic (VEGF-A, angiopoietin 2), and lymphangiogenic (VEGF-C) factors. TSLP, TSLPR, and IL-7Rα were expressed in intratumoral and peritumoral areas of human lung cancer. sfTSLP and lfTSLP mRNAs were differentially expressed in peritumoral and intratumoral lung cancer tissues. The TSLP system, expressed in HLMs, MDMs, and monocytes, could play a role in chronic inflammatory disorders including lung cancer.

The correlation between single nucleotide polymorphisms of the thymic stromal lymphopoietin receptor and breast cancer in a cohort of female patients in Saudi Arabia.

The current study aimed to examine thymic stromal lymphopoietin receptor (TSLPR) genetic variation and breast cancer (BC) susceptibility in women in Saudi Arabia. Therefore, 127 blood samples from female patients diagnosed with BC and 116 blood samples from healthy female controls were studied using a genotyping assay to determine the association between three TSLPR single nucleotide polymorphisms (SNPs)-P196L, X201W, and A238V-and the risk of BC progression. In addition, gene expression was evaluated in 20 matching BC and normal tissues using immunohistochemistry. TSLPR protein levels were higher among BC patients than those with matching normal breast tissue. In addition, TSLPR SNP P196L was found to have a significant protective effect on BC progression (OR = 0.4427), although only the T allele for TSLPR P196L had this protective effect against BC progression in participants who were younger than 48 years old. In contrast, no association was found between the T allele and risk of BC in participants who were older than 48 years old, and the CT and TT genotypes were significantly associated with BC risk protection in the older group. The effects of the TT genotype and the T allele were closely associated with a decreased risk of BC in participants with estrogen receptors (ER+) and without them (ER-). Overall, the findings revealed a significant correlation between SNPs in the TSLPR genes and BC progression among women in Saudi Arabia.

IL-37 Targets TSLP-Primed Basophils to Alleviate Atopic Dermatitis

Atopic dermatitis (AD) represents a severe global burden on physical, physiological and mental health. Innate immune cell basophils are essential for provoking allergic inflammation in AD. However, the roles of novel immunoregulatory cytokine IL-37 in basophils remain elusive. We employed in vitro co-culture of human basophils and human keratinocyte HaCaT cells and an in vivo MC903-induced AD murine model to investigate the anti-inflammatory mechanism of IL-37. In the in vitro model, IL-37b significantly decreased Der p1-induced thymic stromal lymphopoietin (TSLP) overexpression in HaCaT cells and decreased the expression of TSLP receptor as well as basophil activation marker CD203c on basophils. IL-37 could also reduce Th2 cytokine IL-4 release from TSLP-primed basophils ex vivo. In the in vivo model, alternative depletion of basophils ameliorated AD symptoms and significantly lowered the Th2 cell and eosinophil populations in the ear and spleen of the mice. Blocking TSLP alleviated the AD-like symptoms and reduced the infiltration of basophils in the spleen. In CRISPR/Cas9 human IL-37b knock-in mice or mice with direct treatment by human IL-37b antibody, AD symptoms including ear swelling and itching were significantly alleviated upon MC903 challenge. Notably, IL-37b presence significantly reduced the basophil infiltration in ear lesions. In summary, IL-37b could regulate the TSLP-mediated activation of basophils and reduce the release of IL-4. The results, therefore, suggest that IL-37 may target TSLP-primed basophils to alleviate AD.

Hematological characteristics, cytogenetic features, and post-induction measurable residual disease in thymic stromal lymphopoietin receptor (TSLPR) overexpressed B-cell acute lymphoblastic leukemia in an Indian cohort.

The overexpression of cytokine receptor-like factor-2 (CRLF2) identified by anti-thymic stromal lymphopoietin receptor/TSLPR flow cytometry (FCM) has been reported as a screening tool for the identification of BCR-ABL1-like B-cell acute lymphoblastic leukemia/B-ALL with CRLF2 re-arrangement. TSLPR expression was studied prospectively in consecutive 478 B-ALLs (≤ 12years(n = 244); 13-25years (n = 129); > 25years (n = 105)) and correlated with various hematological parameters and end-of-induction measurable residual disease (day 29; MRD ≥ 0.01% by 10-colorFCM). TSLPR positivity in ≥ 10% leukemic cells was detected in 14.6% (n = 70) of B-ALLs. CRLF2 re-arrangement was detected in eight cases (11.4%) including P2RY8-CRLF2 (n = 6), and IgH-CRLF2 (n = 2) with a median TSLPR positivity of 48.8% and 99% leukemic cells, respectively. Recurrent gene fusions/RGF (BCR-ABL1 (17.1%); ETV6-RUNX1 (4.2%), TCF3-PBX1 (1.4%)), other BCR-ABL1-like chimeric gene fusions/CGFs (PDGFRB-rearrangement (2.9%), IgH-EPOR (1.4%)), CRLF2 extra-copies/hyperdiploidy (17.1%), and IgH translocation without a known partner (10%) were also detected in TSLPR-positive patients. CD20 positivity (52.9% vs 38.5%; p = 0.02) as well as iAMP21 (4.3% vs 0.5%; p = 0.004) was significantly more frequent in TSLPR-positive cases. TSLPR-positive patients did not show a significantly higher MRD, compared to TSLPR-negative cases (37% vs 33%). Increasing the threshold cut-off (from ≥ 10 to > 50% or > 74%) increased the specificity to 88% and 100% respectively in identifying CRLF2 translocation. TSLPR expression is not exclusive for CRLF2 translocations and can be seen with various other RGFs, necessitating their testing before its application in diagnostic algorithms. In patients with high TSLPR positivity (> 50%), the testing may be restricted to CRLF2 aberrancies, while patients with 10-50% TSLPR positivity need to be tested for both CRLF2- and non-CRLF2 BCR-ABL1-like CGFs.

Involvement of Activation of Mast Cells via IgE Signaling and Epithelial Cell-Derived Cytokines in the Pathogenesis of Pollen Food Allergy Syndrome in a Murine Model.

Murine models to elucidate the pathogenesis of pollen food allergy syndrome (PFAS), characterized by oral hypersensitivity symptoms induced by specific foods in patients previously sensitized with a pollen, are lacking. The study aimed to examine PFAS pathogenesis in a novel murine model. Birch pollen-immunized mice were orally administered apple extract, and oral symptoms were evaluated based on oral rubbing frequency following the challenge. The birch pollen-immunized mice orally challenged with apple extract exhibited PFAS-like symptoms, including oral rubbing and positive reaction of swelling by the prick test. The apple extract administered with a protease inhibitor reduced the oral rubbing frequency, which was also significantly reduced in the immunized Fcer1a -/- and mast cell-deficient mice compared with the immunized control mice. The oral rubbing frequency, serum IgE levels, and Th2-cytokine production by the cervical lymph node cells were significantly reduced in the immunized Il-33 -/- and thymic stromal lymphopoietin receptor-deficient (Crlf2 -/-) mice as compared with the immunized wild-type mice. IL-33 and thymic stromal lymphopoietin involve the pathogenesis of PFAS. The apple-extract stimulation did not lead to increased Th2-cytokine production in the oral mucosa or number of group 2 innate lymphoid cells or eosinophils. PFAS involves an early-phase response by mast cell degranulation via IgE signaling after the cross-reactivity of Bet v 1-specific IgE and the food allergen, and exacerbation of allergic symptom via proteases in food; PFAS does not involve a late phase with local Th2/eosinophilic inflammation in the oral mucosa. This novel murine model might be used for elucidating the pathogenesis and assessing new therapeutic strategies for PFAS.

Baicalein Protects Against Aspergillus fumigatus Keratitis by Reducing Fungal Load and Inhibiting TSLP-Induced Inflammatory Response.

PurposeTo investigate the antifungal and anti-inflammatory effects of baicalein on Aspergillus fumigatus (A. fumigatus) keratitis and the underlying mechanisms.MethodsThe noncytotoxic antifungal concentration of baicalein was determined using CCK8, cell scratch assay, minimum inhibitory concentration, biofilm formation, scanning electron microscopy, propidium iodide uptake test and adherence assay in vitro and Draize test in vivo. In fungal keratitis (FK) mouse models, clinical score and plate count were used to evaluate FK severity, and myeloperoxidase assay and immunofluorescence staining were performed to examine neutrophil infiltration and activity. Real-time PCR, ELISA, and Western blot were performed to explore the anti-inflammatory activity of baicalein and the underlying mechanisms in vivo and in vitro.ResultsBaicalein at 0.25 mM (noncytotoxic) significantly inhibited A. fumigatus growth, biofilm formation, and adhesion in vitro. In A. fumigatus keratitis mice, baicalein mitigated FK severity, reduced fungal load, and inhibited neutrophil infiltration and activity. Baicalein not only suppressed mRNA and protein levels of proinflammatory factors IL-1β, IL-6, and TNF-α, but also inhibited the expression of thymic stromal lymphopoietin (TSLP) and TSLP receptor (TSLPR) in vivo and in vitro. In HCECs, mRNA and protein levels of IL-1β, IL-6, and TNF-α were significantly lower in the TSLP siRNA–treated group, while higher in the rTSLP-treated group than in the corresponding control. Baicalein treatment significantly inhibited rTSLP induced the expression of IL-1β, IL-6, and TNF-α.ConclusionsBaicalein plays a protective role in mouse A. fumigatus keratitis by inhibiting fungal growth, biofilm formation, and adhesion, and suppressing inflammatory response via downregulation of the TSLP/TSLPR pathway.

TSLP rather than IL-33 signaling drives intestinal mucosal mast accumulation and allergen-induced diarrhea in mice following epicutaneous sensitization to food allergen.

Abstract Background: A major route of sensitization to food allergen is through an impaired skin barrier. IL33 and TSLP have both been implicated in epicutaneous sensitization and development of food allergy. Method: We assessed the respective contributions of TSLP and IL33 to the development of food allergy in TSLP and IL33 receptor deficient mice following epicutaneous food allergen sensitization, where mice were exposed to thrice weekly skin patches of either saline, OVA or a combination of OVA and Aspergillus fumigatus extract (ASP). Results: ASP+OVA-patched but not OVA-patched mice developed an atopic dermatitis (AD)-like skin phenotype, while sensitization to OVA occurred in both OVA and OVA+ASP patched mice. OVA-specific IgE levels were significantly lower in OVA(±ASP)-patched TSLPR−/− mice compared to wild type mice and ST2−/− mice. Repeated intragastric challenges with 50mg of OVA, induced intestinal accumulation of mast cells but not ILC2s in OVA(±ASP)-patched WT and ST2−/− mice, and to a much lesser degree in TSLPR−/− mice. While OVA-induced mast cell degranulation assessed by measuring MCPT1 blood levels and the development of food allergy (diarrhea occurrences) was observed in almost all WT mice and two thirds of OVA+ASP patched ST2−/− mice, all TSLPR−/− mice were protected from developing food allergy and had significantly lower MCPT1 levels. Conclusion: Epicutaneous sensitization to food allergen and subsequent development of food allergy does not require atopic dermatitis skin lesions and is dependent on TSLP, suggesting that prophylactic targeting of TSLP may be useful in mitigating the development of food allergy early in life.

Tezepelumab: A Potential New Biological Therapy for Severe Refractory Asthma.

Thymic stromal lymphopoietin (TSLP) is an innate cytokine, belonging to the group of alarmins, which plays a key pathogenic role in asthma by acting as an upstream activator of cellular and molecular pathways leading to type 2 (T2-high) airway inflammation. Released from airway epithelial cells upon tissue damage induced by several noxious agents including allergens, viruses, bacteria, and airborne pollutants, TSLP activates dendritic cells and group 2 innate lymphoid cells involved in the pathobiology of T2-high asthma. Tezepelumab is a fully human monoclonal antibody that binds to TSLP, thereby preventing its interaction with the TSLP receptor complex. Preliminary results of randomized clinical trials suggest that tezepelumab is characterized by a good safety and efficacy profile in patients with severe, uncontrolled asthma.

Abstract PR014: A novel immunotherapy for relapsed/refractory pediatric T-cell acute lymphoblastic leukemia

Abstract With the recent addition of nelarabine to first-line therapy, the overall 5-year survival for pediatric T-cell acute lymphoblastic leukemia (T-ALL) patients approaches 90%. Patient prognosis for those who relapse is heavily dependent on their specific subtype of ALL: those with B-cell ALL (B-ALL) have several antibody therapies available, including blinatumomab and inotuzumab, which specifically target B-cells for degradation. However, no effective standard therapy is available for patients with relapsed T-cell ALL (T-ALL) and few new therapies are in development; as a result, these patients have a much poorer 5-year survival rate, on the order of 20-30%. Therefore, the development of a targeted immunotherapy for T-cell ALL is critical towards improving patient outcome. The IL-7Ralpha protein is part of the IL-7 receptor complex expressed on the surface of T-cells, and the thymic stromal lymphopoietin (TSLP) receptor complex on the surface of B-cells. The IL-7Ralpha protein is critical for the proliferation and maintenance of T-cells and T-ALL cells, and is overexpressed or constitutively activated in up to 70% of pediatric T-ALL patients. Furthermore, the IL-7Ralpha appears to be overexpressed in chemotherapy-resistant T-ALL cells, highlighting the potential for targeting this protein in relapsed T-ALL patients. Here we describe a novel monoclonal antibody (4A10) raised against the IL-7Ralpha protein which effectively labels T-ALL cells for degradation via antibody-dependent cell-mediated cytotoxicity (ADCC) and independent mechanisms and results in significant control of T-ALL xenografts in animal models, diminished infiltration of T-ALL cells into other organs, and prolonged survival time. The 4A10 antibody is effective against relapsing disease in animal models, and may therefore be effective for relapsed T-ALL patients, or in combination with first-line therapy to further improve initial 5-year survival rates. The 4A10 antibody has undergone extensive optimization and formulation for clinical-grade manufacture and is completing IND-enabling toxicology studies with plans to enter Phase I clinical trials in mid-2021. We are developing a novel clinical trial schema, in collaboration with the Therapeutics Advances in Childhood Leukemia and Lymphoma consortium, to assess tolerability and efficacy via a primarily pediatric Phase I trial, to advance relapsed leukemia patients to curative therapies, including bone marrow transplantation or cell therapies. This abstract is also being presented as PO004. Citation Format: Christopher Foley, Julie Hixon, Wengqing Li, Eric Schafer, Susan Rheingold, Atul Varadhachary, Scott Durum. A novel immunotherapy for relapsed/refractory pediatric T-cell acute lymphoblastic leukemia [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PR014.

Vitamin D3-elicited CD14+ human skin dendritic cells promote thymic stromal lymphopoietin-independent type 2 T-helper responses.

Immune modulation by vitamin D3 through dendritic cells (DCs) remains controversial. Human DCs exposed in vitro counteract type-1 T-helper (Th1) differentiation and induce regulatory T cells. However, cutaneous application on mice promotes Th2-driven inflammation resembling atopic dermatitis and relying on thymic stromal lymphopoietin (TSLP) from keratinocytes and T-cell orientation by TSLP-stimulated skin DCs. We studied the effects of vitamin D3 in human skin, focusing on TSLP production and the role of skin DCs in T-cell differentiation. Human healthy skin explants were exposed in vitro to vitamin D3 analogs. Migrating DCs were analyzed and TSLP quantified in the supernatant. Allogeneic naïve CD4+ T cells were cocultured with DCs to assess their proliferation and cytokine production. Vitamin D3 induced skin DCs to differentiate Th2 cells producing IL-4 and IL-13. Vitamin D3 triggered TSLP release in ~30% of skin explants, correlating with IL-13 detection in Th2 cells. In these donors, blocking TSLP receptor during skin explant cultures abrogated IL-13 production, yet IL-4+ Th2 cells were unaffected. Among skin DCs emerged CD14+ cells that had responded directly to vitamin D3 and differed from classical CD14+ dermal emigrants. Vitamin D3-elicited CD14+ DCs sufficed to promote IL-4+ Th2 cells in a TSLP-independent manner. Vitamin D3, despite inducing TSLP in some donors, had a direct influence on skin DCs, affecting their phenotype and ability to drive Th2 responses independently of TSLP. Our findings pave the way toward in vitro systems that accurately model human cutaneous Th2 responses, notably involved in atopic dermatitis.

TSLP Induces Platelet Mitophagy and Promotes Thrombosis in Kawasaki Disease

Background: Kawasaki disease (KD) is an acute systemic vasculitis primarily affecting infants and children with an unclear etiology. Coronary artery aneurysm (CAA) is a common manifestation in severe KD patents, which may lead to thrombotic cardiovascular events such as heart attack and stroke even years after onset. Although platelet activation is common in KD patients, but the underlying cause of platelet activation and thrombosis remains unclear. The present study is to investigate the role of thymic stromal lymphopoietin (TSLP) in KD-associated thrombosis. Methods: We included 129 healthy controls and 310 KD patients. And conducted a protein chip assay and discovered a significant upregulation in thymus stromal lymphopoietin (TSLP), especially those with thrombosis KD patients, and TSLP induces platelet activation, mitophagy, and thrombosis in vitro. Clinical samples (plasma and platelets) from KD patients and healthy control were analyzed via ELISA, immunofluorescent confocal microscopy, flow cytometry, western blot, immunoprecipitation and thrombosis assays. Findings: To discover potential proteins underlying platelet activation in KD, we conducted a protein chip assay using clinical samples and discovered a significant upregulation in thymus stromal lymphopoietin (TSLP), a novel interleukin-7 (IL-7)-like cytokine that promotes pathological inflammation and most notably, platelet activation. The upregulation of TSLP in KD patients was corroborated by ELISA, which showed a further increase of TSLP in convalescent patients complicated with thrombosis. The expression of TSLP receptors (TSLPRs) on platelets were also significantly upregulated in KD patients complicated with thrombosis. Platelet activation, apoptosis, and mitochondrial autophagy (mitophagy) were increased in KD patients, which were exacerbated in patients complicated with thrombosis. In vitro, TSLP induced platelet activation and platelet mitophagy as we observed in KD patients, as well as thrombosis, which was attenuated by the mitophagy inhibitor Mvidi and comparable to mitophagy agonist CCCP. Co-immunoprecipitation in TSLP-treated platelets revealed TSLPR bound to mitophagy regulators, Parkin and VDAC1, suggesting a potential novel TSLP-mediated platelet mitophagy pathway. Interpretation: Our results demonstrate that TSLP induces platelet mitophagy via a novel TSLPR/Parkin/VDAC1 mitophagy pathway that promotes thrombosis in KD. To the best of our knowledge, this is the first report that shows TSLP plays an important role in KD patients complicated with thrombosis. These results suggest TSLP as a novel anti-thrombotic therapeutic target for KD-associated thrombosis. Funding: Canadian Institutes of Health Research Foundation grant, the Guangdong Natural Science Foundation grant, the Guangzhou Science and Technology Program Project grant, the Guangzhou Institute of Pediatrics/Guangzhou Women and Children's Medical Center Foundation grant. Declaration of Interest: The authors report no conflicts of interest. Ethical Approval: This study was approved by the Ethics Committee of Guangzhou Women and Children's Medical Center (Number: 2014073009 and 2018052105).

A Novel Engineered Single-Chain Antibody Fragment for Targeting Pediatric Philadelphia Chromosome-like Acute Lymphoblastic Leukemia

Introduction: Philadelphia-like acute lymphoblastic leukaemia (Ph-like ALL) is a high-risk ALL subtype characterized by an inferior survival rate and chemotherapeutic drug resistance (Tasian et al, Blood 130: 2064-2072, 2017). Around 50% of Ph-like ALL cases harbour gene rearrangements leading to the overexpression of cytokine receptor-like factor 2 (CRLF2) (Loh et al, Blood 121: 485-488, 2013). CRLF2 (also known as thymic stromal lymphopoietin receptor, TSLPR) heterodimerizes with the interleukin-7 receptor alpha (IL-7Rα) subunit to form the functional TSLPR. Upon TSLP binding, CRLF2 activates the JAK/STAT signalling pathway, leading to enhanced proliferation and survival of leukemia cells resulting in poor outcomes in patients (Harvey et al, Blood 115: 5312-5321, 2010). The extracellular overexpression of CRLF2 and association with poor prognosis suggest the translational value of designing precision-based therapeutics targeting CRLF2 in Ph-like ALL. Although conventional immunotherapy using full-sized antibodies is a promising treatment strategy that can improve treatment efficiency and minimize off-target toxicity, their clinical translation is challenging due to the high production cost and large size affecting targeting efficiency (Holliger et al, Nat Biotech 23: 1126-1136, 2005). Herein, we validated a novel single-chain variable fragment against CRLF2 (CRLF2-ScFv) for targeting Ph-like ALL cells. Methods: A CRLF2-rearranged Ph-like ALL cell line (MHH-CALL-4) was lentivirally transduced with a CRLF2-targeting shRNA driven by an inducible promoter, enabling the inducible knockdown of CRLF2. CRLF2 expression in MHH-CALL-4 cells after shRNA induction (KD-CALL-4) was evaluated using fluorescence-activated cell sorting (FACS). The cellular association of the CRLF2-ScFv was determined in MHH-CALL-4 and KD-CALL-4 at 4° and 37°C using an indirect immunofluorescence assay. Confocal laser scanning microscopy was used to visualize and compare the cellular association of CRLF2-ScFv in MHH-CALL-4 and KD-CALL-4. The cellular association of CRLF2-ScFv was also investigated ex vivo using a small panel of Ph-like and non-Ph-like ALL patient-derived xenografts (PDXs), representing similar immunophenotype and genetic characteristics to their original disease subtypes (Liem et al, Blood 103: 3905-3914, 2004), and peripheral blood mononuclear cells (PBMCs) to investigate the non-selective association. CRLF2 expression in MHH-CALL-4 and Ph-like ALL PDX cells was quantified using indirect immunofluorescence assay. The downstream impact of CRLF2-ScFv on STAT5 phosphorylation (pSTAT5) was determined by FACS either with or without TSLP stimulation. The statistical significance was tested using Unpaired unequal variances t-test or one-way ANOVA followed by multiple comparisons test. Statistical significance was considered when P ≤ 0.05. All experiments were performed in triplicate. Results: KD-CALL-4 showed a 75% reduction in CRLF2 expression compared with MHH-CALL-4 cells (P = 0.0009). CRLF2-ScFv exhibited a 94% higher association with MHH-CALL-4 compared with KD-CALL-4 cells at 37°C (P = 0.0013). The association of CRLF2-ScFv with MHH-CALL-4 cells was reduced by 75% at the non-proliferating state of cells at 4°C compared to 37°C (P = 0.006). Orthogonally viewed confocal microscopy images showed 82% higher intracellular uptake of CRLF2-ScFv in MHH-CALL-4 compared to KD-CALL-4 cells (P = 0.0003). CRLF2-ScFv showed &amp;gt;80% higher association with a Ph-like PDX sample compared with a control CRLF2low PDX and PBMCs (P &amp;lt; 0.001). Of note, a Ph-like ALL PDX exhibited only one-third of the association with CRLF2-ScFv compared with MHH-CALL-4 cells (P = 0.04), corresponding to the significant difference in CRLF2 surface expression (P = 0.01). CRLF2-ScFv significantly reduced pSTAT5 expression in MHH-CALL-4 cells (P = 0.05) and prevented TSLP-induced STAT5 phosphorylation (P = 0.01), suggesting competition with the TSLP binding site. Conclusion: CRLF2-ScFv is a selective targeting moiety for CRLF2 with a significant internalization potential and receptor antagonistic effect, highlighting the therapeutic implications for targeting Ph-like ALL. Keywords: CRLF2, ScFv, STAT5 phosphorylation, Patient-Derived Xenografts. Disclosures No relevant conflicts of interest to declare.

T-bet and STAT6 Coordinately Suppress the Development of IL-9–Mediated Atopic Dermatitis–Like Skin Inflammation in Mice

T-bet and signal transducer and activator of transcription (STAT) 6 are critical factors for helper T-cell differentiation in humans and mice. Additionally, polymorphisms in TBX21 (T-bet) and STAT6 are associated with the susceptibility of allergic diseases. However, precise mechanisms of the reciprocal regulation between T-bet and STAT6 in allergy remain unclear. To determine the reciprocal regulation invivo, we investigated the phenotype of T-bet/STAT6 double-deficient (T-bet-/- STAT6-/-) mice. Unexpectedly, T-bet-/- STAT6-/- mice but not T-bet-/- mice or STAT6-/- mice spontaneously developed severe dermatitis. Not only eosinophils and mast cells but also CD4+ T cells infiltrated into the skin of T-bet-/- STAT6-/- mice. Adoptive transfer of CD4+ T cells of T-bet-/- STAT6-/- mice into severe combined immunodeficient mice induced the accumulation of eosinophils and mast cells in the skin, whereas depletion of CD4+ T cells ameliorated the dermatitis in T-bet-/- STAT6-/- mice. Comprehensive transcriptome analyses revealed that IL-9 expression was enhanced in T-bet-/- STAT6-/- CD4+ T cells. Indeed, IL-9 neutralization ameliorated the dermatitis in T-bet-/- STAT6-/- mice. T-bet-/- STAT6-/- CD4+ T cells expressed functional thymic stromal lymphopoietin receptors and produced large amounts of IL-9 on thymic stromal lymphopoietin stimulation. These results indicate that T-bet and STAT6 coordinately suppress atopic dermatitis-like skin inflammation, possibly by inhibiting thymic stromal lymphopoietin-dependent IL-9 production in CD4+ T cells.