NCI Pediatric Oncology Branch Conducts Pooled Toxicity Analysis of Three Phase 1 CAR T Clinical Trials

The Pediatric Oncology Branch of the NCI Center for Cancer Research conducted a retrospective pooled analysis of data from three Phase 1 CAR T-cell clinical trials conducted between 2012 and 2020. The study included 134 pediatric and adolescent patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL), divided into three cohorts: CD19-targeted (NCT01593696, 50 patients), CD22-targeted (NCT02315612, 68 patients), and CD19/CD22 dual-targeted (NCT03448393, 16 patients). The median age was 15.2 years, the median number of prior therapies was 5, and 56.7% of patients were in the highly pre-treated group with prior hematopoietic stem cell transplantation (HSCT).

Toxicity Profile: Grade 3+ Adverse Events in 99.3% of Patients

Grade 3 or higher adverse events occurred in 99.3% of all patients, with a median of 10 (IQR 4-19) Grade 3+ events per patient. Among the total of 1,719 events, cytopenias accounted for 57.1%, followed by non-cytopenic adverse events, including metabolic abnormalities (42.3%), hepatotoxicity (15.5%), febrile neutropenia (15.5%), and cardiovascular events (8%). Cytokine release syndrome (CRS) occurred in 77.6% of patients, and the median number of Grade 3+ non-cytopenic adverse events was significantly higher in patients with CRS (4.5) compared to those without CRS (1) (P<0.0001). 93.1% of Grade 3+ non-cytopenic adverse events occurred after the onset of CRS, suggesting that CRS acts as a key trigger for subsequent toxicities.

Paradoxical Intersection of Therapeutic Response and Toxicity

The complete remission (CR) rate was 66.2% (88/133 patients), and 87.5% of those who achieved CR were minimal residual disease (MRD) negative. Among non-responders, the group with CRS had the highest toxicity burden (median of 7 events), while the responder+CRS group had a median of 4 events. A high tumor burden of 25% or more of bone marrow cells was identified as the only consistent predictor of Grade 3+ non-cytopenic adverse events across all three clinical trials. This adds an important nuance to the existing hypothesis that 'CRS occurrence = therapeutic effect' and provides direct evidence for the design of patient selection and prior debulking strategies.

Market Context and Implications for Next-Generation CAR T Development

One Grade 5 adult respiratory distress syndrome (ARDS) death and five dose-limiting toxicities (DLTs) were reported. Currently, the only CAR T product approved by the FDA for pediatric B-ALL is Novartis' (NVS) Kymriah (tisagenlecleucel, CD19-targeted), which has a global revenue of approximately $443 million in 2024 and a price of $475,000 per treatment. The CD22 and dual-target toxicity data from this study provide a safety benchmark for the design of next-generation CARs to overcome antigen escape. With the global CAR T market projected to grow to approximately $10.9 billion in 2026, this data will serve as a baseline for optimizing toxicity, which is essential for expanding indications.