Abstract 2289: Allogenic TCRa/CS1 double knockout T-cells bearing an anti-CS1 chimeric antigen receptor: An improved immunotherapy approach for the treatment of multiple myeloma
Authors: Galetto Roman , Chion-Sotinel Isabelle , Gouble Agnes , Smith Julianne 
Published: July 2016

Abstract
Multiple Myeloma (MM) is a B-cell neoplasia characterized by clonal expansion of malignant plasma cells in the bone marrow. Although currently available therapies can improve patient's overall survival, it still remains incurable in most of them cases. On the other hand, the use of autologous chimeric antigen receptor (CAR)-redirected T-cells have allowed to achieve long-term durable remissions in patients with B cell leukemia, indicating that CAR technology may become a new alternative in cancer treatment. Extensive research is therefore being made in immunotherapy against MM, in order to identify novel antigenic targets to be considered for this approach.
In the present work we have assessed the feasibility of CAR-mediated targeting of the CS1 antigen (SLAMF7), which is highly expressed on tumor cells from most patients with MM. However, expression of CS1 on normal CD8+ T-cells is potentially an obstacle for the development of CAR T-cells against this protein, since antigen-expressing T cells will be targeted, impacting both on the number and the phenotype of the final CAR T cell population.
To address this limitation, Transcription Activator-Like Effector Nuclease (TALEN) gene editing technology was used to inactivate the CS1 gene in T-cells, prior to transduction with a lentiviral vector encoding an anti-CS1 CAR. Our results demonstrate that while non-gene-edited T-cells expressing the anti-CS1 CAR display cytotoxic activity against MM cell lines, CS1-gene-edited CAR cells display significantly increased cytotoxic activity. In addition, a progressive loss of CD8+ T-cells was observed in non-edited CAR+ T-cells, while this population was preserved in CS1 knockout T-cells.
Gene editing technology was also used here to inactivate the TCRa constant (TRAC) gene, minimizing the potential for engineered T-cells to mediate Graft versus Host Disease (GvHD). We have indeed previously shown that editing of the TRAC gene can be achieved at high frequencies, allowing efficient production of TCR-deficient T-cells that no longer mediate alloreactivity in a xeno-GvHD mouse model. Furthermore, we were able to perform multiplex genome editing that led to the production of double KO (TRAC and CS1) T-cells
Finally, we evaluated the in vivo activity of double knockout CAR T-cells (UCARTCS1) by performing experiments in an orthotopic MM mouse model, showing that CS1 disrupted T-cells were able to mediate an in vivo anti-tumoral activity.
Our results show that multiplex genome editing is possible and can lead to the production of double KO TRAC/CS1 T-cells, allowing large scale manufacturing of allogeneic, non alloreactive CS1 specific T-cells with enhanced antitumor activity. Moreover, these allogenic T-cells could be easily available for administration to a large number of MM patients.
Citation Format: Roman Galetto, Isabelle Chion-Sotinel, Agnes Gouble, Julianne Smith. Allogenic TCRa/CS1 double knockout T-cells bearing an anti-CS1 chimeric antigen receptor: An improved immunotherapy approach for the treatment of multiple myeloma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2289.