Abstract 6703: Innovative mRNA strategies to encode CD19/CD3 T cell engagers in the treatment of B cell hematological malignancies

Abstract The advent of T Cell Engager (TCE) immunotherapies marks a transformative shift in cancer treatment paradigms, introducing a novel action mechanism. Blinatumomab, a bispecific CD19/CD3 TCE, has shown remarkable efficacy in treating refractory or relapsed B-cell Acute Lymphoblastic Leukaemia (B-ALL), including cases resistant to conventional chemotherapy, leading to its global approval for B-ALL management. Despite its pronounced clinical success, Blinatumomab faces challenges with patient adherence, primarily due to the protein’s short half-life. This necessitates continuous administration requested 24 hours injection throughout the treatment course. Additionally, the drug’s association with the induction of cytokine release syndrome (CRS), presumably linked to the hyperactivation of the cytokine network, presents a significant concern. To address these limitations, we leverage mRNA modality to develop innovative therapeutic mRNAs encoding CD19/CD3 TCE. These mRNA drugs hold the potential to improve protein exposure in vivo with a steady production of encoded protein in-situ. On the other hand, with the gradual expression of protein, mRNA shifted the transient, “pulse”-like pharmacokinetic (PK) feature of the protein drugs to a more “plateau”PK curve, which allows a natural priming of T cells to reduce the risk of CRS induction. In this work, we developed a series of mRNAs encoding CD19/CD3 TCE through our mRNA technology platform and LNP delivery platform. Comparative analyses demonstrated that the TCEs produced in vivo by these mRNAs match the structure and function of recombinantly expressed proteins. PK studies in both mice and non-human primates confirmed a favorable PK profile with over 10-fold increase in TCE exposure compared to their protein counterparts. This increased exposure correlated with superior antitumor efficacy in both ALL and lymphoma models, evidenced by the potent effects of single mRNA doses compared to multiple doses of protein-based treatments. Meanwhile IL6 cytokines induced in mRNA treated mice were significantly alleviated than those in protein treated animals, indicating a reduced risk of induction of CRS. One candidate mRNA demonstrated an optimal "plateau" pharmacokinetic profile, achieving extensive target cell eradication over 20 days with a single low dose of 0. 001 mpk in non-human primates. An investigator-initiated clinical study with mRNA encoding CD19/CD3 TCE is underway in relapsed and/or refractory acute lymphoblastic leukemia patients. The preliminary data from the on-going study showed ABO2015 with an acceptable safety profile, and activation of peripheral T cells was observed in one patient with low dose. These findings underscore the significant clinical potential of mRNA-encoded CD19/CD3 TCE in treating B-cell malignancies, heralding a paradigm shift in the clinical application of protein-based T cell engagers. Citation Format: Xia Zhong, Liang Du, Zhenxing Yang, Xiaoli Xu, Jijun Yuan, Bo Ying. Innovative mRNA strategies to encode CD19/CD3 T cell engagers in the treatment of B cell hematological malignancies abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6703.