IL18-armored CAR T cells in relapsed/refractory B cell acute lymphoblastic leukemia

Abstract Introduction Despite high complete remission (CR) rates after CD19-directed chimeric antigen receptor (CAR) T cells for relapsed/refractory (R/R) B cell malignancies, relapse remains a significant challenge. To improve efficacy, we designed a novel “armored” humanized CAR T cell targeting CD19 that secretes the proinflammatory cytokine interleukin-18 (huCART19-IL18). huCART19-IL18 has shown promising efficacy in R/R non-Hodgkin lymphoma (Svoboda et al. NEJM 2025), and here we share our initial experience treating patients with R/R B cell acute lymphoblastic leukemia (ALL). Methods In a single center, first in human clinical trial utilizing huCART19-IL18 (NCT04684563), adult patients with R/R CD19+ ALL were eligible, including those with CNS disease and those with relapses after prior CART19, blinatumomab, and allogeneic transplant (alloHCT). The primary objective was to determine safety. Secondary objectives included product manufacturing feasibility, pharmacokinetic activity, and preliminary efficacy. Subjects with ALL underwent autologous leukapheresis followed by 3-day manufacturing of huCART19-IL18 at a target dose of 7x106CAR+ cells. Subjects then received lymphodepleting (LD) fludarabine and cyclophosphamide followed by huCART19-IL18 infusion. Results As of Aug. 1, 2025, 5 ALL patients underwent apheresis with no manufacturing failures. All patients were infused at the target dose after LD chemotherapy. All patients were male with a median (min-max) age of 41 (35-64), and 3 (60%) were Ph (Philadelphia chromosome)+. Subjects had a median of 5 (3-11) prior lines of therapy including alloHCT in 4 patients, blinatumomab in 4 (3 as salvage for post-alloHCT relapse), and brexucabtagene autoleucel in 2. All patients had CNS involvement at time of enrollment. All patients received bridging therapy, and prior to infusion 2 (40%) had residual morphologic disease, 1 (20%) measurable residual disease (MRD) only, and 2 (40%) were MRD negative. Four patients had adequate follow-up for safety and preliminary efficacy. Median vein-to-vein time was 41 (27-50) days accounting for manufacturing, quality control, and protocol-defined staggers. All patients experienced cytokine release syndrome (CRS) with a maximum grade of 2 and median onset of 4.5 (3-6) days after infusion lasting a median duration of 6.5 (5-7) days. Immune effector cell-associated neurotoxicity syndrome (ICANS) occurred in 1 patient with a maximum grade of 2, onset at 13 days, and duration of 8 days. Three patients received tocilizumab for CRS, and 1 received corticosteroids and anakinra for ICANS. There were no occurrences of immune effector cell-associated HLH-like syndrome. All patients achieved MRD-negative remissions by day 28, and all remain in MRD-negative CR with a median follow-up of 15.1 (2.6-18.7) months. Peak in vivo huCART19-IL18 expansion in the peripheral blood (PB) occurred at a median of 11 days (9-14), and all patients had detectable huCART19-IL18 in the cerebrospinal fluid (CSF) at day 28. One patient had ongoing B cell aplasia at 18 months with persistently detectable huCART19-IL18 in the PB and CSF. Three patients had loss of B cell aplasia at a median of 3 months with undetectable-to-low levels of PB huCART19-IL18, though one retained detectable levels in the CSF at 18 months. One patient with extensively pre-treated ALL (7 prior lines of therapy) received a second treatment with huCART19-IL18 while in MRD-negative CR and regained B cell aplasia. Three Ph+ patients who lost B cell aplasia remained in molecular CR and restarted tyrosine kinase inhibitor maintenance therapy prophylactically. No patients had subsequent consolidative alloHCT. Conclusion huCART19-IL18 was well-tolerated in this cohort of patients with R/R ALL. No CRS or ICANS > grade 2 was seen, nor were any severe unanticipated toxicities or treatment-related deaths. All treated patients with adequate follow-up achieved early MRD-negative CR (including in the CNS), and there have been no relapses or deaths with a median follow-up of 15.1 months. Correlative studies demonstrate avid CAR T cell expansion in the blood and CSF with a subset demonstrating persistence in both compartments. Armored CD19-directed CAR T cells secreting interleukin-18 are a promising option for patients with heavily pretreated B cell ALL, including those who relapse following prior CD19-targeted salvage therapies and those with CNS involvement.