Abstract 5655: preclinical development of a novel anti-tslpr bispecific antibody 1b7/cd3 targeting crlf2-rearranged ph-like b-all

Abstract

Abstract Acute lymphocytic leukemia (ALL) is the most common form of leukemia in childhood and adolescence. Outcomes of relapsed/refractory adult B-ALL remain dismal with long-term survival of less than 10%. Although targeted therapies such as blinatumomab, inotuzumab ozogamicin, and CD19 CAR T cell therapy are a significant treatment advance for patients with B-ALL, there is still an unmet medical need for novel therapies for B-ALL. CRLF2-rearranged B-ALL, a subtype of Philadelphia chromosome-like B-ALL, is a high-risk disease subset with poor long-term outcomes. In an effort to identify new therapeutic targets for B-ALL, we validated by flow cytometry that patients with CRLF2-rearranged Ph-like ALL overexpress thymic stromal lymphopoietin receptor (TSLPR) at levels comparable with CD19. We subsequently generated antibodies against TSLPR from immunized H2L2 Harbor mice through single B cell cloning technology. The lead antibody was further engineered to a CD3-redirecting bispecific antibody (BsAb) using Xencor’s CD3e bispecific antibody technology to create 1B7/CD3 BsAb with an Fc-silent region. 1B7/CD3 BsAb exhibits high affinity binding to both human and cynomolgus monkey CD3e and TSLPR by BLI. Additionally, UHPLC-SEC analysis of 1B7/CD3 shows that this BsAb is stable without any aggregation or degradation present after five weeks incubation at 37 °C. In cell-based analyses,1B7/CD3 BsAb demonstrate potent antigen-specific T cell activation and tumor lysis activity against TSLPR+-REH and MHH-CALL4 cell lines as well as a primary B-ALL patient sample, but none against human peripheral blood mononuclear cells (PBMC) collected from healthy donors. Animal tumor models suggest that 1B7/CD3 triggers a dose-dependent tumor regression or growth inhibition in PBMC humanized TSLPR-REH CDX and BOS-1 PDX models across donors. Correspondingly, T cell activation and expansion were examined by CD69 and CD3+ T cells with the best effect observed at the 1mg/kg dose. 1B7/CD3 exhibits durable PK with T1/2 in NSG mice of up to ten days. Finally, 1B7/CD3 BsAb demonstrated a tolerable safety margin in a two-dose exploratory toxicity study in cynomolgus monkeys with MTD equal to or less than 1mg/kg. Consistent with clinical observation, we observed a transient increase of six major cytokines (IFNγ, IL-6, IL-8, IL-10, MCP-1 and TNFα) 4hr post the initial dosing, but no notable induction of cytokine levels after the second dosing (except for IL-8). Thus, our preclinical data provide the framework for the clinical evaluation of 1B7/CD3 BsAb in patients with CRLF2-rearranged B-ALL. Citation Format: Ze Tian, chunhua shi, Amin AI-Shami, GuoJun Yong, Jason K Allen, Jill Wardell Olson, Melinda G Smith, Qing Chang, Qing Shi, Junping You, Michelle A Gonzalez, Timothy E Lofton, Jasbir Kaur, Qi Zhang, DongXing Zha, Nitin Jain, Marina Y Konopleva, Timothy Heffernan, Jeffrey J Molldrem. preclinical development of a novel anti-tslpr bispecific antibody 1b7/cd3 targeting crlf2-rearranged ph-like b-all. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5655.