419. Allogenic CAR T-Cells Targeting CD123 for Adoptive Immunotherapy of Acute Myeloid Leukemia (AML)

Abstract

Chimeric antigen receptor (CAR)-redirected T-cells have given rise to long-term durable remissions and remarkable objective response rates in patients with refractory leukemia, raising hopes that a wider application of CAR technology may lead to a new paradigm in cancer treatment. A limitation of the current autologous approach is that CAR T-cells must be manufactured on a “per patient basis”. We have developed a standardized platform for manufacturing T-cells from third-party healthy donors to generate allogeneic “off-the-shelf” engineered CAR+ T-cell–based frozen products. This platform utilizes Transcription Activator-Like Effector Nuclease (TALEN) gene editing technology to inactivate the TCRα constant (TRAC) gene, eliminating the potential for T-cells bearing alloreactive TCR's to mediate Graft versus Host Disease (GvHD). We have previously demonstrated that editing of the TRAC gene can be achieved at high frequencies, obtaining up to 80% of TCRα negative cells. This allows us to efficiently produce TCR-deficient T-cells that have been shown to no longer mediate alloreactivity in a xeno-GvHD mouse model. In addition to CAR expression, our T-cells are engineered to co-express the RQR8 gene as a safety feature, with the aim of rendering them sensitive to the monoclonal antibody rituximab.In this work we present the adaptation of this allogeneic platform to the production of T cells targeting CD123, the transmembrane alpha chain of the interleukin-3 receptor, which is expressed in tumor cells from the majority of patients with Acute Myeloid Leukemia (AML). To identify an effective CAR targeting CD123, we have screened multiple antigen recognition domains in the context of several different CAR architectures to identify candidates displaying activity against cell lines expressing variable levels of the CD123 antigen. Furthermore, experiments in an AML mouse model using anti-CD123 CAR T cells demonstrate important anti-tumor activity in vivo. The ability to carry out large scale manufacturing of allogeneic, non alloreactive CD123 specific T cells from a single healthy donor will thus offer the possibility of an off-the-shelf treatment that would be immediately available for administration to a large number of AML patients.