Abstract A041: Hypoxia-responsive CAR T-cells

In recent years, CD19 CAR T-cell therapy has been successfully implemented against therapy-resistant B-cell malignancies. The results are especially striking for acute lymphoblastic leukemia (ALL), while results are somewhat less stunning when it comes to lymphoma. This is in part due to the semi-solid structure of lymphoma with an immune suppressive tumor microenvironment and less oxygenated areas within the tumors. These obstacles become even more pronounced in solid tumors. Furthermore, in the case of solid tumors the lack of tumor-specific antigens represents a major challenge. Instead, overexpressed tumor-associated antigens (TAAs) are often used as targets in CAR T-cell therapy of solid tumors. However, as TAAs are also expressed to some extent in normal tissue, targeting these antigens may result in severe OFF-tumor ON-target toxicity. In the case of CD19 CAR T-cell therapy of B-cell malignancies, OFF-tumor ON-target toxicity causes B-cell aplasia.The aim of this study was to reduce OFF-tumor ON-target toxicity by engineering CAR T-cells that mainly express the CAR molecule in the hypoxic tumor microenvironment. Hypoxia-inducible factor 1 (HIF1) is a transcription factor that is a major mediator of hypoxia-induced gene expression as it binds to hypoxia response elements (HREs) in promoter regions of hypoxia-responsive genes and initiates their expression. In this study, a cassette of HREs was inserted together with a minimal CMV (mCMV) promoter in front of the CD19 CAR cassette to promote expression during hypoxic conditions. Chemically induced hypoxia augmented CD19 CAR expression over time in hypoxia-responsive CD19 CAR T-cells (HRE-mCMV-CD19CAR-GFP), whereas CAR expression was unaffected in CD19 CAR T-cells with constitutively expressed CAR (EF1α-CD19CAR-GFP). Furthermore, hypoxia-responsive CAR T-cells had an increased activation status and killing capacity upon antigen encounter in hypoxic compared to normoxic conditions. This design could be evaluated in the clinic to reduce B-cell aplasia in CD19 CAR T-cell therapy of lymphomas and especially to reduce OFF-target toxicities from CAR T-cells targeting TAAs in solid tumors. Citation Format: Tina Anna Saren, Anne Marie Senz, Mohanraj Ramachandran, Di Yu, Magnus Essand. Hypoxia-responsive CAR T-cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A041.