Key Points

  • Expression level, viability and functional capacity of CD70scFv-CAR constructs are strongly influenced by their structural composition

  • CD27z CAR T-cells can effectively eliminate AML cells in vitro and in vivo but spares normal hematopoiesis

The prognosis of patients with acute myeloid leukemia (AML) remains dismal highlighting the need for novel innovative treatment strategies. The application of chimeric antigen receptor (CAR) T-cell therapy to AML patients has been limited in particular by the lack of a tumor-specific target antigen. CD70 is a promising antigen to target AML as it is expressed on the majority of leukemic blasts, whereas little or no expression is detectable in normal bone marrow samples. To target CD70 on AML cells, we generated a panel of CD70-CARs that contained a common single chain variable fragment (scFv) for antigen detection but differed in size and flexibility of the extracellular spacer, and in the transmembrane and the co-stimulatory domains. These CD70scFv CARs were compared with a CAR construct that contained the human CD27, the ligand of CD70 fused to the CD3z chain (CD27z). The structural composition of the CAR strongly influenced expression levels, viability, expansion and cytotoxic capacities of CD70scFv CAR T-cells, but the CD27z-CAR T-cells demonstrated superior proliferation and anti-tumor activity in vitro and in vivo, compared to all CD70scFv-CARs. While CD70-CAR T-cells recognized activated virus-specific T-cells (VSTs) that expressed CD70, they did not prevent colony formation by normal hematopoietic stem cells (HSCs). Thus, CD70-targeted immunotherapy is a promising new treatment strategy for patients with CD70-positive AML that does not affect normal hematopoiesis but will require monitoring of virus-specific T-cell responses.

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