Using the iCasp9 suicide strategy to control the growth and function of genome-edited B cells with redirected antigen specificity.

B cells could be effective immunotherapeutic "drug cells," but reports of genomic editing to redirect their specificity have not included safety strategies. To address the potential complications of cell therapy, there is a growing demand for integrated safety switches. This is particularly pertinent in the case of B cells, which are prone to malignant transformation. We evaluated in B cells the efficacy of inserting the inducible caspase-9 (iCasp9) suicide gene, together with either a reporter gene or a single-chain immunoglobulin cassette specific for a tumor antigen. We demonstrate that a single edit of the IgH locus enables the expression of both iCasp9 and the cassette hijacking antigen specificity, while preserving B cell functionality. In both primary and malignant lymphoma B cells, activation of iCasp9 using the drug AP1903 readily induced apoptosis of edited cells, both in vitro and in established tumors grafted to immunodeficient animals. Although AP1903 treatment strongly curbed edited cell survival, this was constantly followed by the selection of resistant cells with lowered expression of both iCasp9 and the therapeutic antibody cassette. Therefore, in adoptive immunotherapy protocols, the iCasp9/AP1903 safety switch could stand as an efficient neoadjuvant therapy, as well as a rheostat to modulate the infusion of a therapeutic molecule.