Safety and Efficacy of Tisagenlecleucel (CTL019) in B-Cell Acute Lymphoblastic Leukemia in Children, Adolescents and Young Adults: The French Experience

Objectives: Tisagenlecleucel (CTL019) is a chimeric antigen receptor T cell- therapy that reprograms autologous T cells to target CD19+ leukemia cells, approved in the US (2017) and in the EU (2018). This study reports the feasibility, safety and efficacy of CTL019 in patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) treated in Robert-Debré and Saint-Louis University Hospitals (Assistance Publique-Hôpitaux de Paris/Université de Paris).

Methods: Patients (pts) with an apheresis performed between march 1, 2016 and june 15, 2019, included in sponsored-clinical trials or treated within the French compassionate program or with the commercial product, were analyzed. All infused pts received a fludarabine-cyclophosphamide based lymphodepletion before a single infusion of CAR-T cells (2 to 5 x 10⁶ CTL019/kg if less than 50 kg; a fixed dose of 1 to 2.5 x 10⁸ CTL019/kg if > 50 kg)

Results: 55 pts were referred from 25 French centers. Forty-one pts with a median number of relapses of 2 (range, 1-5) were infused with CTL019 at a median age of 18.2 y (range, 1-29.2). Eight pts were not infused due to progressive disease (n=4), screen failure (n=3) or fatal septic shock (n=1). Six pts were waiting to be infused at time of analysis. Out of the 41 infused pts, 26 had a prior history of allogeneic SCT (63%), 11 had received blinatumomab (27%). Among the 40 pts evaluable at one month post-infusion, 38 were in CR/CRi (95%) (one progression at day 5 after infusion and one toxic death at D6), 35/38 (92.1%) being clone-specific Ig-TCR MRD negative. After 3 months 21 out of 26 evaluable pts (81%) had a negative MRD. The 5 remaining MRD positive pts did relapse. No pt underwent allogeneic HSCT while in CR after CTL019 infusion. Median event free survival (EFS) and overall survival (OS) were not reached with a median follow up of 7.2 months (range, 0.2-36.3). The 18-month OS probability was 80% (95%CI, 58%-92%). The 18-month EFS probability was 58 % (95%CI, 37%-74%). Ten pts relapsed after a median time of 3.4 months (range, 1.9-10): 3 relapses were CD19+ and 5 CD19- (4 out of these 5 pts had a preexposure to blinatumomab), 2 being of undetermined status. Loss of B-cell aplasia (BCA) occurred in 9 pts after a median time of 3 months (range, 2-12), followed by relapse for 2 pts (one concomitant with loss of BCA and one 7 months later). Three pts received a second infusion of CTL019 for loss of BCA with no further expansion of CAR-T cells. Prior treatment with blinatumomab was a significant predictive factor for relapse (HR=6.082, 95%CI, 1.2-30, p=0.0005) in a univariate analysis. There was a trend toward increased risk of relapse with increased disease burden (≥ 5%) before lymphodepletion regimen (HR=2.4, 95%CI, 0.7-8, p=0.14). Twenty-two pts experienced a CRS (≥ grade 3: n=13, all ≥ 10 y). ICU was required for 14 pts (34%). One 29 year-old pt died of an uncontrollable CRS at day 6. Ten pts received tocilizumab, 4 pts siltuximab and 9 pts corticosteroids. Age ≥ 10 y (p=0.04) and a high disease burden just before lymphodepletion (marrow blasts ≥ 5%) (p=0.01) were associated with a higher risk of CRS ≥ grade 3. Nine neurological events have been reported, being reversible except in 2 cases (one death in combination with grade 5 CRS-cf supra-, one HHV6-related encephalitis with neurological sequelae). Among the 9 pts who presented neurological events, 8 experienced CRS grade ≥ 3 (RR=17.2, 95%CI, 3.22-100.3, p=0.0001). By day 28, unresolved neutropenia grade ≥ 3 was reported for 13 pts. G-CSF treatment was required in 21 pts overall. Thrombocytopenia grade ≥3 was reported for 14 pts.

Conclusion: CTL019 confirms its efficacy with a high response rate after infusion and very encouraging early outcomes in a cohort of pts heavily pretreated for refractory or multiply relapsed B-ALL. Persistent remissions with a potential for cure were observed without additional HSCT, relapses occurring within the first year after infusion of CTL019. Accurate assessment of a potentially deleterious effect of Blinatumomab preexposure notable on CD19 negative relapse will need more pts and a longer follow-up. Toxicity profile was tolerable and manageable thanks to collaboration between intensivists, neurologists and hematologists. The identification of severe CRS predictive risk factors (high disease burden just before lymphodepletion and age ≥ 10 y) points towards the reinforcement of toxicity monitoring and treatment anticipation in these cases.