Enhanced anti-tumor activity of CD5 CAR T cells manufactured with tyrosine kinase inhibitors in patients with relapsed/refractory T-ALL.
Authors: Hill LaQuisa C , Rouce Rayne H , Smith Tyler S , Boriskie Blakely , Srinivasan Madhuwanti , Thakkar Sachin G , Zhang Huimin , Mehta Birju , Sritabal-Ramirez Juntima , Grilley Bambi J , Heslop Helen E , Brenner Malcolm K , Mamonkin Maksim 
Published: June 2023

7002 Background: An effective CAR T cell platform for the therapy of T-ALL requires minimizing CAR-driven fratricide of normal T cells. CD5 is a pan-T-cell surface protein present in ~85% of T-ALL. We developed a 2nd generation CD5 CAR that produces minimal T cell fratricide without additional engineering. Tonic CAR signaling accelerated terminal differentiation of CD5 CAR T cells potentially reducing their potency. In this study, we evaluated whether blocking tonic signaling with tyrosine kinase inhibitors (TKI) ibrutinib and dasatinib improves anti-leukemic activity of CD5 CAR T cells in patients with r/r T-ALL (NCT03081910). Methods: In the initial cohort of patients (CH1, n = 8), we generated CD5 CAR T cells from autologous PBMCs followed by expansion in the presence of IL-7 and IL-15 without TKI. In the subsequent cohort (CH2, n = 7) we manufactured cells from autologous (Arm A; n = 4) or HSC donor-derived (Arm B; n = 3) PBMCs in the presence of TKI. A total of 14 pts were treated (9 adult and 5 pediatric; age 11-70 years [median 36 yrs]); one pediatric pt was treated on both cohorts. Results: In CH1, all pts received autologous CAR T cells: 1 pt on DL1 (1x107 CAR T cells/m2), 5 on DL2 (5x107 CAR T cells/m2), and 2 on DL3 (1x108 CAR T cells/m2). In CH2, we treated 4 pts on Arm A (one on DL2; 3 on DL3) and 3 pts on Arm B (all on DL1). The overall expansion of CAR T cells was comparable between cohorts, but we observed more sustained persistence of CD5 CAR T cells in pts on CH2. In CH1, one pt experienced a morphologic CR. Of 7 pts treated on CH2, we observed 4 MRD-negative CRs (2 on Arm A and 2 on Arm B). The CAR T cells produced minimal early toxicity with most grade ≥3 AEs related to cytopenias, febrile neutropenia and transient abnormal laboratory values. CRS occurred in 3 pts on CH1 and 4 on CH2 (Arm A: n = 1; Arm B: n = 3); all ≤ grade 2. No pts developed ICANS. Two pts in CH2 (one on Arm A and Arm B) developed EBV viremia and post-transplant/immunodeficient lymphoproliferative disease (LPD) at wks 5 and 7 post-infusion, respectively. Both were treated with intensive multiagent chemotherapy, and one pt also received EBV specific T cells (EBVSTs) with significant reduction in viral load. Unfortunately, both passed away from complications of treatment for PTLD (unrelated to EBVSTs) with no evidence of residual T-ALL. No other significant infections occurred. Conclusions: These results demonstrate CD5 CAR T cells can induce clinical responses in heavily treated patients with r/r T-ALL. Manufacturing CD5 CAR T cells with TKI improved their potency and anti-tumor activity but also possibly suppressed CD5+ virus-specific T-cells thus leading to 2 cases of EBV associated LPD. We have subsequently modified our clinical protocol to administer prophylactic rituximab to EBV seropositive pts and identify a partially matched EBVST line prior to CAR T cell infusion as a strategy to prevent additional cases of LPD in future subjects. Clinical trial information: NCT03081910 .