SAN DIEGO – A chimeric antigen receptor (CAR) targeting both CD19 and CD22 shows promising safety and efficacy for the treatment of relapsed or refractory B-cell malignancies in adults, according to early findings from a phase 1 trial of the novel bispecific CAR.
Of six patients with diffuse large B-cell lymphoma (DLBCL) and two patients with B-cell acute lymphoblastic leukemia (B-ALL) enrolled in the single-institution dose escalation study and available for safety analysis after the bispecific CAR T-cell infusion, five developed reversible grade 1 cytokine release syndrome (CRS) and one developed grade 2 CRS requiring treatment with tocilizumab, Nasheed Hossain, MD, reported at the annual meeting of the American Society of Hematology.
Additionally, two patients developed grade 1 neurotoxicity, and one developed grade 2 neurotoxicity requiring treatment with dexamethasone.
“But no dose-limiting toxicities have been encountered thus far,” saidof Loyola University Medical Center, Chicago. “With regard to efficacy, the DLBCL overall response rate is 60%, with 1 [complete response] and 2 [partial responses] at day 28 and day 90, and the ALL overall response rate is 100%, with 1 CR and 1 PR at day 28.
“With longer follow-up, five patients have relapsed and biopsies at the time of progression all showed ongoing CD19 expression,” he said, adding that all enrolled patients are alive, except for one patient who died from disease progression.
Study participants were adults aged 35-75 years with DLBCL or B-ALL that was refractory to standard therapies.
“Our primary objectives are twofold: One is to determine the feasibility of making our CAR ... and [the other] is to assess the safety using an escalating CAR dose following standard cyclophosphamide/fludarabine conditioning,” Dr. Hossain said.
The dose assessed in the current analysis was 1 x 106 CAR T cells/kg; other planned doses include 3 x 106 CAR T cells/kg and 1 x 107 CAR T cells/kg, he said.
All patients underwent lymphodepletion with cyclophosphamide (500 mg/m2 daily x 3 doses) and fludarabine (30 mg/m2 daily x 3 doses) followed by CAR T-cell infusion 2 days later.
The findings of this ongoing study – the first in-human study of a bispecific loop CAR in the United States – suggest that the novel CAR has low toxicity and promising efficacy, Dr. Hossain said.
Currently approved therapies target CD19 alone, he said, noting that they all use the same anti-CD19 domain, but different costimulatory domains, and have good clinical efficacy of greater than 70% CRs in ALL and up to 52% CRs in DLBCL.
“But questions remain about determining the durability of response and the causes of therapy failure,” he said.
One common cause of treatment failure is CD19 antigen loss, and efforts to reduce such antigen loss using bispecific loop CARs targeting both CD19 and CD22 have shown promise. The CAR construct evaluated in this study was developed to target CD19 and CD22 with intracellular signaling domains incorporating 4-1BB and CD3-zeta to overcome CD19 immune escape.
“We have now escalated the dose to 3 x 106 CAR T cells/kg ... and an expansion study of 60 patients will follow,” Dr. Hossain said.
A companion phase 1 pediatric trial using the same CAR construct is also underway, with preliminarypresented at the ASH meeting demonstrating safety and tolerability in children with relapsed or refractory B-cell ALL.
Dr. Hossain reported having no financial disclosures.
SOURCE: Hossain N et al. ASH 2018, .