Phase I Trial of Inducible Caspase 9 T Cells in Adult Stem Cell Transplant Demonstrates Massive Clonotypic Proliferative Potential and Long-term Persistence of Transgenic T Cells.

Abstract

Inducible caspase 9 (<i>iCasp9</i>) is a cellular safety switch that can make T-cell therapy safer. The purpose of this phase I trial was to investigate the use of <i>iCasp9</i>-transduced T-cell addback in adult patients undergoing haploidentical stem cell transplantation for high-risk hematologic malignancies. Patients undergoing myeloablative, CD34-selected haploidentical stem cell transplantation were treated with 0.5-1.0 × 10⁶/kg donor-derived <i>iCasp9</i>-transduced T cells on day +25 or 26 post-transplant, with additional doses allowed for disease relapse, infection, or mixed chimerism. Three patients were enrolled. <i>iCasp9</i>-transduced T cells were readily detectable by 4 weeks post-infusion in all patients and remained at high level (114 cells/μL, 11% of T cells) in 1 patient alive at 3.6 years. One patient developed donor-derived Epstein-Barr virus-associated post-transplant lymphoproliferative disease (EBV-PTLD), which was followed by a marked expansion of <i>iCasp9</i> T cells and cytokine release syndrome (CRS). These <i>iCasp9</i>-transduced T cells infiltrated the affected lymph nodes and secreted IFNγ and IL-10. They peaked at 1,848 cells/μL and were found to be monoclonal by T-cell receptor (TCR) clonotype and oligoclonal by viral integrant analysis, representing a 6-log <i>in vivo</i> expansion of the dominant T-cell clone. These T cells were not autonomous and contracted with the resolution of EBV-PTLD, which did not recur. <i>iCasp9</i>-transduced T cells could persist long-term. They retained very high <i>in vivo</i> clonotypic proliferative capacity and function, and could cause CRS in response to <i>de novo</i> lymphoma development.