Background:

CD19 is a pivotal B-cell lineage marker expressed in newly diagnosed B-cell acute lymphoblastic leukemia (B-ALL). Autologous T cells modified with chimeric antigen receptors targeting CD19 (CD19-CAR-Ts) have demonstrated significant efficacy in patients with multiple relapses in B-ALL, achieving complete remission (CR) rates reaching 90%. Two products have been approved by the FDA include tisagenlecleucel (Tisa-cel) in August 2017 and brexucabtagene autoleucel ( Brexu-cel) in October 2021 for relapsed or refractory B-ALL. Loss of B cell aplasia post infusion is used as an indirect tool to detect functional loss of CD19-CAR-Ts with high risk of disease relapse.

Patients and Methods:

We investigated the impact of CD19 expressing lymphocytes on outcomes in adults (age >14 years) with B-ALL treated with CD19-CAR-Ts at King Faisal Specialist Hospital and Research Center from March 2021 to March 2024. All patients received lymphodepletion (LD) therapy with fludarabine and cyclophosphamide. The study was approved by the hospital's Institutional Review Board, and all patients provided written informed consent. We assessed outcomes including response, relapse, and survival rates. CD19-expressing lymphocyte subsets were monitored before LD and after CD19-CAR-T infusion using flow cytometry.

Results:

Twenty-two patients received CD19-CAR-Ts, with 19 had Tisa-cel and 3 had Brexu-cel. The median age was 20.5 years (range, 14-54), and 77.3% were male. Extra-medullary disease was observed in 8 patients (36.4%), with CNS involvement in 6 patients (27.3%). All patients had received at least two lines of therapy; 86% had received three or more. Prior blinatumumab was administered to 15 patients (68.2%), and 13 patients (59.1%) had undergone stem cell transplantation (SCT). At CAR-T infusion, 14 patients (63.6%) had active disease, and 8 patients (36.4%) were in CR. CD19 expression before LD was positive in 13 patients (59.1%) and negative in 9 patients (40.9%). No significant differences were observed between the two groups in baseline characteristics such as age, CNS involvement, prior blinatumumab use, disease status, or pre-LD LDH levels, though more prior SCTs were noted in the CD19+ group (76.9% vs. 33.3%; p=0.05).

For CD19-CAR-T outcomes, remission rates were 77.3% at day 30 and 72.7% at day 90. The incidence of B-cell aplasia with CD19 recurrence was 27.1%, with a relapse rate of 45.8%. Cytokine release syndrome (CRS) of any grade occurred in 77.3%, with grade >1 in 10 patients (45.5%), and immune effector cell-associated neurotoxicity syndrome (ICANS) occurred in 22.7%. There were five deaths, two of which occurred before day 30 due to hemophagocytic lymphohistiocytosis (HLH) and septic shock. The CD19+ group showed significantly higher remission rates at day 30 (100% vs. 62.5%; p=0.049) and day 90 (100% vs. 57.1%; p=0.036) compared to the CD19- group. No significant differences were found in relapse (33.3% vs. 14.3%; p=0.36), CRS (76.9% vs. 77.8%; p=0.68), or ICANS (23.1% vs. 22.2%; p=0.68).

The mean overall survival (OS) for the whole cohort was 31.4 months (95% CI = 25.4-37.5). The OS for the CD19+ group was 35.1 months (95% CI = 29.3-40.7), compared to 26.4 months (95% CI = 15.8-37.1) for the CD19- group, which was not statistically significant (p=0.32). Progression-free survival (PFS) analysis showed an overall mean survival time for disease progression events of 28.8 months (95% CI = 21.4-36.3), with 26.7 months (95% CI = 17.3-36.1) for the CD19+ group and 32.5 months (95% CI = 22.7-42.4) for the CD19- group, also not statistically significant (p=0.47).

Conclusions:

Pre-CAR-T CD19 lymphocyte status can predict remission outcomes following CAR-T therapy. Monitoring CD19 dynamics throughout CAR-T treatment may have implications for disease management and subsequent therapeutic decisions in B-ALL patients.

Disclosures

Saad:Sanofi: Consultancy; Kite: Consultancy. Alfayez:Astellas: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Abbvie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pfizer: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Biologics: Honoraria, Speakers Bureau; Johnson & Johnson: Consultancy, Honoraria, Research Funding, Speakers Bureau. Alzahrani:Sanofi: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; CSL Behring: Consultancy, Honoraria, Research Funding; Sobi: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Other: All authors received support for third-party writing assistance, furnished by Akshaya Srinivasan, PhD, CMPP, of Nucleus Global, an Inizio company, and funded by F. Hoffmann-La Roche Ltd, Basel, Switzerland., Research Funding; Pfizer: Research Funding.

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2024
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