Novel humanized CD19-CAR-T (Now talicabtagene autoleucel, Tali-cel™) cells in relapsed/ refractory pediatric B-acute lymphoblastic leukemia- an open-label single-arm phase-I/Ib study

Abstract

Chimeric Antigen Receptor-T (CAR-T) cell therapy is effective for relapsed/refractory B-acute lymphoblastic leukemia (r/r B-ALL) but is not universally available. We developed a novel humanized CD19-directed CAR-T (HCAR19) approved for Phase 1/1b/2 trials. Patients aged 3-25 years were enrolled with r/r B-ALL and ineligible for allogeneic stem cell transplant. Lymphodepletion utilized standard-dose fludarabine and cyclophosphamide. A 3 + 3 design testing 3 dose-ranges was used to determine Phase-2 Dose (P2D): Dose-A, 1 × 10⁶ HCAR19 cells/kg, Dose-B, 3-5 × 10⁶/kg, and Dose-C, 10-15 × 10⁶/kg. Primary endpoint was overall response rate (ORR) at day-30 on bone-marrow flow-cytometry. From May-2021 to September-2023 12 patients [median age-14 (range: 5-24) years] were enrolled with median bone marrow blasts 19.5% at screening. Cytokine release syndrome occurred in 10 (83%) patients, predominantly Grades 1-2, and Grade-2 immune-cell associated neurotoxicity (ICANS) in 1. All patients had Grade-3 cytopenia. ORR was 91.7% (11/12), complete response (CR) in 8 (66.7%) and partial response in 3 (25%). Seven of 8 CRs were at Dose-levels B and C, all of which were sustained till 12 months follow-up. Patients who received dose levels below 3 × 10⁶/kg, or did not achieve CR, had early loss of response or rapid progression. HCAR19 demonstrated safety, manageable toxicity, and durable remissions. and P2D was determined as 5-10 × 10⁶ HCAR19-cells/kg. CLINICAL TRIAL REGISTRATION: The study is registered in the Clinical Trials Registry- India (CTRI/2021/05/033348 and CTRI/2023/03/050689).

Fig. 1. Study course for participants from the time of enrollment to treatment.

Dose levels- Dose-A: 1 × 10⁶/kg, Dose-B: 3–5 × 10⁶/kg, Dose-C:10–15 × 10⁶/ kg body weight.

Fig. 2. Log-reduction of disease in the bone marrow by flow cytometry on day 30 after HCAR-19 infusion for each patient.

BMA bone marrow aspirate, pre inf MRD pre-infusion minimal residual disease.

Fig. 3. Swimmer’s Plot predicting responses and follow-up across varied dose levels of HCAR-19 therapy.

CR complete remission (minimal residual disease-negative), PR partial remission (morphological remission, minimal residual disease-positive), CT chemotherapy, Allo SCT allogenic stem cell transplant. An MRD cutoff of <0.01% is defined as negative, while ≥0.01% is considered positive.

Fig. 4. Expansion and persistence of HCAR-19 in each patient at different time-points.

WBC white blood cells.

Fig. 5

IL-6 levels monitored at different time points for each patient.