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3424 Co-Targeting of the Thymic Stromal Lymphopoietin Receptor to Decrease Immunotherapeutic Resistance in CRLF2-Rearranged Ph-like and Down Syndrome ALL

Program: Oral and Poster Abstracts
Session: 702. CAR-T Cell Therapies: Basic and Translational: Poster II
Hematology Disease Topics & Pathways:
Research, Lymphoid Leukemias, ALL, Translational Research, Diseases, Lymphoid Malignancies, Study Population, Animal model
Sunday, December 8, 2024, 6:00 PM-8:00 PM

Tommaso Balestra, PhD1, Lisa M Niswander, MD, PhD1,2, Asen Bagashev, PhD1*, Joseph P Loftus1*, Savannah L Ross3*, Robert K Chen1*, Samantha M McClellan1*, Jacob J Junco4,5*, Diego Alberto Barcenas-Lopez, PhD1, Karen R Rabin, MD, PhD5,6, Terry J Fry, MD3,7 and Sarah K Tasian, MD2,8,9

1Division of Oncology and Center for Childhood Cancer Research, Children's Hospital of Philadelphia, Philadelphia, PA
2Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA
3Division of Hematology/Oncology/Bone Marrow Transplant and Center for Cancer and Blood Disorders, Children’s Hospital of Colorado, Aurora, CO
4Department of Pediatrics, Baylor College of Medicine, Houston, TX
5Cancer Center and Division of Pediatric Hematology/Oncology, Texas Children’s Hospital, Houston, TX
6Department of Pediatrics, Division of Pediatric Hematology/Oncology, Baylor College of Medicine, Houston, TX
7Immunology Department and HI3 Initiative, University of Colorado Anschutz Medical Campus, Aurora, CO
8University of Pennsylvania School of Medicine, Philadelphia, PA
9Division of Oncology & Center for Childhood Cancer Research, Children's Hospital of Philadelphia, Philadelphia, PA

Background: CRLF2 (cytokine receptor-like factor 2) rearrangements occur in 50% of Philadelphia chromosome-like (Ph-like) and Down syndrome (DS)-associated B-acute lymphoblastic leukemia (ALL), resulting in aberrant cell surface overexpression of the thymic stromal lymphopoietin receptor (TSLPR) protein and constitutive intracellular JAK/STAT and other kinase pathway signaling. Children and adolescents/young adults (AYAs) with Ph-like ALL have high rates of chemoresistance and poor event-free survival and have been enriched in early-phase relapsed leukemia clinical trials testing novel therapeutics. Patients with DS-ALL also have inferior clinical outcomes and experience high rates of toxicity with conventional chemotherapy. The potential improved efficacy of addition of the JAK1/2 inhibitor ruxolitinib to chemotherapy in children and AYAs with Ph-like ALL is under active clinical trial investigation, but has not been studied to date in patients with DS-ALL, and trial results are not yet known. Chimeric antigen receptor (CAR) T cell immunotherapies targeting CD19 or CD22 have achieved impressive initial remission induction in >80% of children and AYAs with relapsed/refractory B-ALL, but approximately 50% of CD19CART-treated patients subsequently relapse, including a high proportion with CD19 antigen loss. As an alternative approach, we previously developed and demonstrated robust activity of TSLPRCART immunotherapy in CRLF2/TSLPR-overexpressing ALL preclinical models (Qin Blood 2015).

Methods: In the current studies, we tested the hypothesis that co-targeting extracellular TSLPR with CART immunotherapy and intracellular JAK/STAT signaling with ruxolitinib would induce synergistic anti-leukemia activity in CRLF2-rearranged (CRLF2-R) Ph-like and DS-ALL using cell lines and patient-derived xenograft (PDX) models.

Results: TSLPRCART monotherapy showed effective and durable inhibition of leukemia proliferation in vitro in CRLF2-R Ph-like ALL cell lines and in vivo in both CRLF2-R Ph-like ALL (n=4) and DS-ALL (n=3) PDX models. However, we unexpectedly observed fatal TSLPRCART-induced toxicity in ALL PDX mice treated at higher CART doses that correlated with high levels of in vivo inflammatory cytokine production. Interestingly, simultaneous TSLPRCART and ruxolitinib co-administration prevented early animal death, but also significantly reduced T cell proliferation, blunted cytokine production, and/or facilitated leukemia relapse. Importantly, delaying ruxolitinib co-exposure by two weeks completely preserved desired anti-leukemia TSLPRCART activity and prevented cytokine release syndrome (CRS)-type mortality, resulting in long-term ‘cure’ and survival of Ph-like ALL PDX mice. We further observed in additional Ph-like ALL PDX model experiments that ruxolitinib withdrawal following TSLPRCART-induced leukemia remission resulted in recovery of CAR T cell functionality with in vivo re-expansion of TSLPRCART, IFN-γ production, and leukemia clearance after subsequent CRLF2/TSLPR+ ALL ‘relapse’ rechallenge. These results were fully recapitulated in DS-ALL PDX models, validating JAK/STAT pathway hyperactivation and the TSLPR antigen as a critical immunotherapeutic target, and with CD19CART in orthogonal in vitro ALL cell line and in vivo PDX model studies.

Conclusion: Ruxolitinib-induced inhibition of TSLPRCART and CD19CART fitness and anti-ALL activity is robust, but reversible. Biologically-appropriate time sequencing of CART immunotherapy and ruxolitinib achieved both effective acute CRS mitigation and robust long-term anti-ALL activity in preclinical models, which has high translational potential as a relapse prevention ‘maintenance’ strategy for patients with CRLF2-R Ph-like ALL or DS-ALL.

Disclosures: Bagashev: Carisma Therapeutics: Current Employment. Ross: Parexel International: Current Employment. Fry: Sana Biotechnology: Consultancy, Current equity holder in publicly-traded company, Ended employment in the past 24 months; United States Patent and Trademark Office: Patents & Royalties: WO2019178382A1; United States Patent and Trademark Office: Patents & Royalties: WO2017205747A1; United States Patent and Trademark Office: Patents & Royalties: WO2015084513A1. Tasian: Amgen: Other: Travel support; Aleta Biotherapeutics: Membership on an entity's Board of Directors or advisory committees; Kura Oncology: Research Funding; Incyte Corporation: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Wugen, Inc: Membership on an entity's Board of Directors or advisory committees.

*signifies non-member of ASH