CD123-Specific Chimeric Antigen Receptor Redirected T Cells Exhibit Potent Cytolytic Activity and Multiple Effector Functions Against Acute Myeloid Leukemia without Altering Normal Hematopoietic Colony Formation in Vitro

• Published in: Blood 2012-11, Vol.120 (21), p.950-950
• Main Authors: Mardiros, Armen, Santos, Cedric Dos, McDonald, Tinisha, Brown, Christine, Wang, Xiuli, Chang, Wen-Chung, Ostberg, Julie R, Bhatia, Ravi, Jensen, Michael C., Forman, Stephen J.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V120.21.950.950

Abstract 950 Current treatment regimes for acute myeloid leukemia (AML) achieve complete remissions in only a subset of individuals and most adult patients will relapse within 5-years, emphasizing the need for novel treatment alternatives. One such therapy may be the administration of T cells engineered to express chimeric antigen receptors (CARs) specific for AML-associated antigens. CARs are typically composed of a single chain variable fragment (scFv) from a monoclonal antibody fused to the CD3ζ signaling domain and may contain one or more costimulatory endodomains. When expressed in T cells, CARs redirect T cell specificity to surface antigens on target cells in an MHC-independent manner. The interleukin 3 receptor alpha chain (IL3Rα, CD123) is a cell surface receptor which is aberrantly over-expressed on multiple hematologic malignancies including AML. Previous work has demonstrated that CD123 is not expressed on all CD34+/CD38− hematopoietic stem cells and is restricted to cells of the myeloid lineage, making CD123 an attractive target for CAR T cell therapy. We have therefore generated two novel CD123-specific (CD123R) CARs using scFvs from previously characterized antibodies, designated 26292 and 32716, which bind two distinct epitopes on CD123. Here we demonstrate that T cells expressing CARs derived from either 26292 or 32716 effectively redirect T cell specificity against CD123+ cells. Healthy donor T cells (n=3) engineered to express the CD123R CARs efficiently lysed CD123+ cell lines LCL and KG1a while sparing the CD123− cell line K562 as demonstrated by a 4 hour chromium-51 (51Cr) release assay. Additionally, both of the CD123R CAR T cells produced similar levels of IFN-γ and TNF-α and displayed comparable levels of antigen-dependent proliferation following co-culture with CD123+ cell lines. The potent cytolytic activity and activation of our CD123-targeting T cells was not limited to tumor cell lines. Indeed, CD123R CAR T cells, but not donor-matched CD19-specific (CD19R) CAR T cells, robustly lysed panel of primary AML samples (n=6, 3 – persistent, 1 – relapsed, 2 - untreated) (* p