Early Response Observed in Pediatric Patients with Refractory/Relapsed B-Cell Non-Hodgkin Lymphoma Treated with Sequential Chimeric Antigen Receptor T Cells

Background:Outcomes for pediatric patients with relapsed/refractory B-cell non-Hodgkin lymphoma (NHL) are poor despite use of high-intensity chemotherapy. CAR-T has shown efficacy in treating refractory/relapsed leukemia in pediatric patients and non-Hodgkin lymphoma in adult patients.

Objectives:To assess the safety and efficacy of sequential CAR-T in the treatment of refractory/ relapsed B-NHL in pediatric patients.

Design/Methods:In our ongoing clinical trial (ChiCTR1800014457), we enrolled and treated 17 pediatric patients with refractory/relapsed B-NHL. Following leukapheresis, T cells were activated with CD3 and CD28 antibodies for 24h, then transduced with lentivirus encoding anti-CD19-CD3zeta-4-1BB CAR and cultured for 5-6 days in serum-free media containing IL2, IL7, IL15, IL21. Meanwhile, all patients briefly received lympho-depleting chemotherapies consisting of fludarabine (30 mg/m2/day) and cyclophosphamide (250 mg/m2/day) on days −5, −4 and −3 according to tumor burden and patient state. On day 0, all patients received a single-dose infusion of CAR-T cells. CAR-T cell dose ranged from 0.5 to 3 million/kg. CAR-T cell numbers and cytokines were measured weekly. Tumor responses were evaluated at day 30 and day 60 post infusion and every two months thereafter. Adverse events were graded according to CTCAEv4 except cytokine release syndrome (CRS) was graded according to Lee et al.

Results:Treated patients had relapsed/refractory Burkitt lymphoma (BL) (13/17), diffuse large B cell lymphoma (DLBCL) (2/17), B-lymphoblastic lymphoma (B-LBL) (2/17), and ranged from 4.5-18.0 years old. By St Jude's staging, 9 cases (46.7%) were in stage III, 8 cases (53.3%) were in stage IV. There were 3 cases with CNS involvement (17.6%) and 7 cases with bone marrow involvement (41.2%). They all failed at prior treatment including an average of 8.9 (6-15) courses of chemotherapy. They were then treated with sequential CAR-T cell therapy. A total of 26 courses of CAR-T cell infusion were administered. The overall complete response rate (CRR) was 41.7% (7/17) when first course of CAR-T therapy was conducted, which were all CD19 targeted. Among the 10 patients who did not achieve CR, 2 patients achieved PR with ongoing response, 1 patient died of severe CRS and progression at day 6 and another patient refused to continue the following therapy when tumor progressed at day 99, and he died 1 week later, the other 6 continued to receive second course of CAR-T therapy targeting CD20 or CD22, and 3 of them achieved CR. Thus the overall CRR increased to 58.8% (10/17). The 3 patients, who still did not achieve CR, continued to receive third course of CAR-T therapy targeting CD20 or CD22. Two of them finally achieved CR and the other failed to get CR and is now retreated with chemotherapy and oral Olaparib and Venclexta. Thus, with a median follow-up of 6.2 months (1-18 months), the overall response rate of sequential CAR-T therapy was 94.1% (16/17) and the overall CRR was 70.6% (12/17). Toxicity information through day 30 revealed the occurrence of mild CRS in 8 subjects (47.1%, grade I n=8, grade II n=0), severe CRS in 9 subjects (52.9%, grade III n=8, grade IV n=1). Neurotoxicity was observed in 7 cases (41.2%, seizure in 3 cases, tremor in 4 cases, headache in 1 cases). One case who died rapidly at day 6 of therapy suffered severe CRS (high fever, Capillary leak syndrome, severe pleural effusion, respiratory failure, shock, cardiopulmonary arrest) and neurotoxicity besides disease progression. Other patients with severe CRS and neurotoxicity recovered fully after glucocorticoid use and symptomatic treatment including anti-epilepsy, fluid, dehydrating agent. No case used tocilizumab. Response assessments were performed at day 15, 30, 45, 60. Updated enrollment, toxicity and response assessments will be presented.

Conclusion: CD19/CD20/CD22-CAR-T therapy showed promising efficacy for pediatric patients with r/r B-NHL and the toxicities are tolerable with proper symptomatic and supportive treatment. Sequential CAR-T therapy can improve the efficacy compared with a single course of CAR-T infusion.