Suicide gene therapy for recurrent glioblastoma using allogeneic bone marrow–derived mesenchymal stem cell gene delivery (MSC/CD): A first-in-human, dose-escalation phase I clinical trial.

2071 Background: Glioblastoma (GBM) remains an incurable brain tumor characterized by complex heterogeneity and poor prognosis, even with maximal multimodal therapy. Innovative treatments for recurrent GBM are urgently needed to complement existing therapies. This study explores the feasibility, safety, and efficacy of a novel suicide gene therapy using allogeneic mesenchymal stem cells (MSCs) expressing cytosine deaminase (CD) in combination with 5-fluorocytosine (5-FC). Methods: A Phase 1, single-center, non-randomized, dose-escalating study was conducted to evaluate the safety and efficacy of mesenchymal stem cell expressing cytosine deaminase (MSC/CD) therapy in 10 patients with recurrent GBM. Patients received intratumoral injections of MSC/CD followed by oral 5-FC. Pharmacokinetic profiling, pharmacodynamic analysis, targeted panel sequencing, whole transcriptome analysis, integrative omics analysis, and multiplexed immunofluorescence imaging were performed to assess drug conversion and identify predictable candidate biomarkers. Safety and survival outcome were monitored by evaluating adverse events (AEs) and clinical data. Results: MSC/CD therapy was well-tolerated, with most AEs being mild to moderate. There was no drug toxicity related with dose escalation. Severe AEs (≥ Grade 3) were rare and unrelated to the study drug. Effective conversion of 5-FC to 5-fluorouracil (5-FU) was observed in the brain, with detectable levels in the cerebrospinal fluid, confirming the feasibility of intracranial drug delivery. The median progression-free survival was 5.4 months, and the overall survival was 16.3 months. RNA transcriptomic analysis revealed two molecular subclusters with distinct biological characteristics, correlating with different progression-free survival outcomes. The integrative omics analysis revealed that specific cell cycle-related genes were found to be highly expressed in the non-responder group of patients, suggesting that elevated levels of these genes may be associated with resistance to treatment. Conclusions: This study demonstrates that MSC/CD therapy is a feasible, safe, and potentially effective treatment for recurrent GBM. The identification of distinct molecular subtypes and candidate genes offers a potential biomarker for patient selection and therapeutic targeting. Further studies are warranted to validate these findings and optimize therapeutic strategies. Clinical trial information: NCT04657315 .