Abstract 3139: CD33 directed chimeric antigen receptor T cell therapy as a novel regimen prior to allogeneic stem cell transplantation in acute myeloid leukemia

Allogeneic stem cell transplantation is the only option in relapsed acute myeloid leukemia (AML). However, patients are often excluded due to refractory disease. The successful translation of Chimeric Antigen Receptor (CAR) T cell therapy to AML would constitute a vertical advance in the field. We developed a 2nd generation CAR using the anti CD33 scFv of Gemtuzumab ozogamicin, 41BB costimulation, CD3ζ signaling domain, and a lentiviral (LV) vector. In vitro, CART33 resulted in robust functions when incubated with the CD33+ cell line MOLM14. In NSGS mice (NOD SCID γc-/-(NSG), transgenic for stem cell factor, IL3 and GM-CSF) engrafted with primary AML, CART33 eradicated AML and led to a long term disease free survival (Table 1). Since CD33 is also expressed on normal myeloid progenitors, we assessed the potential myelotoxicity of CART33 in humanized immune system (HIS) mice (NSG mice engrafted with human fetal liver CD34+ cells). CART33 resulted in human lineage cytopenias and in a significant reduction of CD34+CD38- hematopoietic stem cells and CD34+CD38+ myeloid progenitors. Both the anti-leukemic activity and myeloablative potential of CART33 could be used as a novel conditioning regimen in refractory AML. However, the effect of the CAR T cells needs to be terminated to avoid engraftment failure. We therefore designed a “biodegradable” mRNA modified CAR33. T cells were electroporated with this construct and expressed CAR for up to six days. When compared with LV-CART33, RNA-CART33 resulted in comparable in vitro functions that declined over time post electroporation. In NSG mice engrafted with MOLM14, treatment with cyclophosphamide (for lymphodepletion) plus RNA-CART33 resulted in deeper and longer leukemic response compared to cyclophosphamide plus control T cells. In conclusion, our preclinical studies show potent activity of CART33 in AML. Biodegradable CART33 could be used as a novel anti-leukemic cellular conditioning in patients with relapsed AML Note: This abstract was not presented at the meeting. Citation Format: Saad S. Kenderian, Marco Ruella, Olga Shestova, Michael Klichinsky, John Scholler, Decheng Song, David L. Porter, Martin Carroll, Carl H. June, Saar Gill. CD33 directed chimeric antigen receptor T cell therapy as a novel regimen prior to allogeneic stem cell transplantation in acute myeloid leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3139. doi:10.1158/1538-7445.AM2015-3139