TT52CAR19: Phase 1 Trial of CRISPR/Cas9 Edited Allogeneic CAR19 T Cells for Paediatric Relapsed/Refractory B-ALL

Background

'Off-the-shelf' CAR T cell therapies are being investigated as alternatives to autologous CAR therapy, and can be generated using genome editing from allogeneic donors. Strategies to address HLA barriers include disruption of T cell receptor expression to prevent GVHD and removal of cell surface HLA expression to obviate host mediated rejection, as well as removal of CD52 to create a survival advantage in the presence of Alemtuzumab. In this study, lentiviral mediated CAR19 expression is linked to CRISPR editing through the incorporation of CRISPR guide RNA sequences within the vector 3'Long terminal repeat (LTR). The trial is in progress using pre-manufactured batches of TT52CAR19 T cells.

Investigational medicinal product (IMP)

Three allogeneic non-HLA matched donor derived CAR19 T cell banks were manufactured from steady state apheresis harvests from registry volunteer donors, using a semi-automated process under compliant conditions. Cells were activated with anti-CD3/CD28 (Transact) reagent and transduced with a lentiviral vector, TT52CAR19, and dual guide sgRNA cassettes targeting the T cell receptor alpha chain (TRAC) and CD52 loci. Next electroporation of Cas9 mRNA elicited transient genome editing, and automated magnetic bead depletion removed remaining TCRαβ+ T cells (mean 0.7%) and enriched CAR19+ T cells (mean 92.8%). Cells were cryopreserved in aliquots suitable for dose-banding and subjected to release testing, including flow cytometry, quantification of copy number (mean 3.83) and exclusion of replication competent lentivirus. Potency of each bank was confirmed in human:murine chimera experiments.

Trial sponsorship & approvals

The study is open at a single site and is sponsored by Great Ormond Street Hospital NHS trust and is supported by the Medical Research Council and National Institute for Health Research. Clinical trial authorisation was awarded by the MHRA after expert review, and ethical approval including gene therapy advisory committee (GTAC) review, and health research authority (HRA) approval. The study is open label, single arm and non-randomised.

Study aims and Objectives

The study aims to establish the safety and feasibility of TT52CAR19 for the induction of molecular remission in children with relapsed /refractory CD19-positive B-cell acute lymphoblastic leukaemia (B-ALL) within 28 days, ahead of planned allogeneic haematopoietic stem cell transplantation (allo-SCT). Assessments include time to remission, duration of remission, disease-free survival and overall survival. Expansion, persistence and elimination of TT52CAR19 cells and tracking of immune recovery after allo-SCT is monitored. Recording of complications and toxicities, including possible genotoxic side effects from CRISPR/Cas9 modification provides safety profile information.

Eligibility, infusion and outcomes

The study plans to treat 10 children aged between 6 months and < 18 years with CD19+ B-ALL quantified at >10 ^-4 in marrow (by flow or PCR) who are ineligible for autologous therapy. To date 2/4 children screened were found eligible and proceeded to lymphodepletion comprising Fludarabine, Cyclophosphamide and Alemtuzumab followed by a single infusion of 0.8-2.0x10 ⁶ CAR19 T cells and a maximum of 5x10 ⁴/kg TCRαβ T cells. In both cases, there was no GVHD or CRS >grade 1 and recovery of neutrophil counts by d28. Molecular remission was achieved in one child, where TT52CAR19 cells persistence was tracked by chimerism and copy number until further conditioning and allo-SCT. This child remains in remission >6 months later.

Conclusions

Feasibility of pre-manufacturing off-the-shelf CRISPR/Cas9 edited CAR19 T cells is demonstrated and the trial has provided first in human safety data and preliminary indications of potent anti-leukaemic activity in one of two subjects dosed.