717. UCART19, an Allogeneic “Off-the-Shelf” Adoptive T-Cell Immunotherapy Against CD19+ B-Cell Leukemias

Autologous T-cells engineered to express chimeric antigen receptors (CARs) that target specific tumor antigens are known to be of high potential in treating different kinds of cancer. However, they must be generated on a “per patient” basis, thereby limiting the population of patients that could benefit from this approach. In particular, immune homeostasis may be affected in heavily pre-treated patients, such that autologous T-cells may be low in number, not fully functional, or unable to expand, thereby restricting the amount of cells that could be manufactured. The use of allogeneic T-cells isolated from healthy third party donors could constitute an easy-to-scale-up alternative, producible in advance, with potential for standardized quality controls, better batch consistency, and immediate availability for administration to a larger number of patients. In this context, we have developed a standardized platform for manufacturing T-cells from third-party healthy donors to generate allogeneic “off-the-shelf” engineered CD19-CAR+ T-cell–based frozen products. Our platform involves the use of transcription activator-like effector nucleases (TALEN), which mediate the simultaneous inactivation of two genes through genome editing. The knockout of the TCR alpha gene eliminates TCR expression and is intended to abrogate the donor T-cell's potential for graft-versus-host disease (GvHD), while knocking out the CD52 gene makes donor T-cells resistant to the lymphodepleting agent alemtuzumab. In addition, 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.We have obtained proof-of-concept for the application of this approach by manufacturing TCR/CD52-deficient RQR8+ and cD19-CAR+ T-cells (UCART19) using a good manufacturing practice-compatible process and have demonstrated that the resulting UCART19 cells were functional using in vitro assays. Furthermore we have demonstrated the ability of UCART19 cells to engraft into an orthotopic human CD19+ lymphoma xenograft immunodeficient mouse model. UCART19 cells exhibited antitumor activity equivalent to that of standard CD19 CAR T-cells. We also demonstrated that UCART19 cells did not mediate alloreactivity in a xeno-GvHD mouse model. Finally, the effectiveness of the rituximab-induced depletion mechanism of RQR8+ cells was shown in an immunocompetent mouse model. This valuable dataset supports the development of allogeneic CAR T-cells, and UCART19 will be investigated in an exploratory, first-in-human, clinical trial where refractory/relapsed CD19+ B-cell leukemia patients are to be enrolled.