Factors Influencing Efficacy of CD19-CAR-T Cells in Children and Adults with Relapsed/Refractory B-Cell Lymphoblastic Leukemia

Abstract Factors Influencing Efficacy of CD19-CAR-T cells in Children and Adults with Relapsed/Refractory B-cell Lymphoblastic Leukemia An Furun1, Liu Zhenyun2, Wu Fan1, Song Xiaotong2, Li Yingwei1, Cheng Fengwei2, Tao Qianshan1, He Weijie2, Wang Huiping1, Wang Wei2, Xu Huadong2, Zhang Jiakui1, Shen Yuanyuan1, Ruan Yanjie1, Qin Hui1, Wang Xiansheng1, Zhai Zhimin1* Author Affiliations: 1 Hematology Department of the Second Hospital and Hematologic Diseases Research Center of Anhui Medical University 2 Sinobioway Cell Therapy Co., Ltd. Fund: National Natural Science Foundation of China (No. 81670179); Sinobioway Cell Therapy Co., Ltd. *Corresponding Author: zzzm889@163.com Purpose: Using CD19-CD137-ζ CAR-T cell (named Sino19 cell) to treat patients with refractory/relapsed B-cell acute lymphoblastic leukemia (r/r B-ALL), assess the efficacy and safety, and the relationship of patients' characteristic to the response rate and long-term outcome. Method: Single-center, phase 1/2 clinical trial (NCT02735291). A total of 1-5×107/kg CD19-CD137-ζ CAR T cells manufactured by lentiviral transfection were infused to treating r/r B-ALL. Before infusion, individualized chemotherapy was given based on the tumor burden and bone marrow hyperplasity, then monitoring temperature, blood pressure etc., so as to determine and handle adverse reactions. CR, EFS, OS and their possible influencing factors were analyzed by SPSS10.01 software. Results: 1) Patients: A total of 40 patients with r/r B-ALL were enrolled, 22 males and 18 females, aged from 2 to 72. Among them, 32 patients were followed at least 2 months post infusion of CAR T-cell; 4 have not reached the minimum time requirement for efficacy assessment; 4 did not have cells infused. In the 32 patients evaluated for efficacy assessment, 2 had primary refractory B-ALL, 30 with relapsed and refractory B-ALL; 7(21.9%) previously received alloHSCT and 2 of them using blinatumomab failed; 23(71.9%) had cytogenetic aberrations relating poor prognosis; 11(34.4%) had extramedullary disease (EMD). 2) Efficacy: Up to the day cutoff, 32 patients who received a Sino19 cell infusion and had at least 2 months of follow up, the total CR rate with or without hematologic recovery was 78.1% (95% CI, 63 to 93), the rates of OS in all who had the infusion of Sino19 cells were 74% (95% CI, 57 to 91) at 6 months and 40% (95% CI, 20 to 60) at 12 months, the median of OS was not reached. Among the 25 patients with CR, 4 patients underwent allogeneic hemtologic stem-cell transplantation (alloHSCT) and alive with no relapse at the cutoff time. The rest of 21 patients had 9.6 months (2.2 to 27.4) of median following-up duration, 5 of them had relapse-free survival for more than 15 months and the longest lasted for 22 months. Except 4 who underwent alloHSCT, the rates of EFS for the other 28 patients were 66% (95% CI, 48 to 84) at 6 months and 32% (95% CI, 14 to 50) at 12 months. 3) Adverse reactions: 91% (29/32) of the patients had fever after CAR T infused. According to the NCI-CTCAE v4.03, 21.9% (7/32) had grade≥3 CRS, 6 reversed with glucocorticoid alone or plus tocilizumab and supportive care, 1 died of disease progression at the same time of CRS. Only 2 patients had transient absent-mindedness or deliration. 4) Factors influencing efficacy: ⅰ) EMD, Patients with EMD showed lower CR (54.5% vs. 90.5%, p=0.032), higher relapse (100% vs. 40%, p=0.019) and shorter OS (P=0.025) and EFS (P<0.001), compare with those without EMD; ⅱ) CAR T-cells in-vivo proliferation, CR rate in patients with no proliferation significantly lower than those with expanding (50% vs. 100%; p=0.021). OS and EFS were also significantly different. ⅲ) Regulatory T cells (Tregs), patients with higher Tregs (more than ULN) had more relapse than that with lower or normal Tregs (91% vs. 11%; p=0.001), the OS and EFS also was obviously poor. ⅳ) Cytogenetic, 4 patients with T315I mutation got CR, but 3 relapsed and all died within 6 months, other 1 undergone alloHSCT. ⅴ) CAR T-cells in vivo detected more than 6 months post-infusion, but its persistence do not show relationship to relapse and OS. C onclusion: The Sino19 cell lead to high CR rates in r/r B-ALL, with good safety profile. Some patients can achieve continuous complete remission. EMD, no in-vivo proliferation, higher Tregs and Ph+ with T315I mutation may hinder the efficacy. This is the first clinical report on the relationship between Tregs and CAR T efficacy. Disclosures No relevant conflicts of interest to declare.