Durable long-term survival of adult patients with relapsed B-ALL after CD19 CAR (19-28z) T-cell therapy.

Abstract

7008 Background: CD19-specific chimeric antigen receptor (CAR) T cells have demonstrated high initial responses in patients with relapsed B-ALL. However, clinical characteristics associated with the durability of response remain undefined. Herein, we report the results from analysis of our phase I clinical trial of 19-28z CAR T cells in adult patients with relapsed B-ALL (NCT01044069) with a focus to identify those patients who optimally benefit from 19-28z CAR T cell therapy with durable long-term survival and reduced toxicities. Methods: Adults with relapsed B-ALL were infused with autologous T cells expressing the 19-28z CAR following conditioning chemotherapy. Disease burden was assessed by bone marrow biopsy immediately prior to T cell infusion; patients with < 5% blasts were classified as minimal residual disease (MRD) cohort vs. patients ≥5% blasts as morphologic disease cohort. Response assessment occurred at 4 weeks. Median follow-up duration was 18 months (range, 0.2-57.3). Results: 51 adults received 19-28z CAR T cells; 20 in the MRD and 31 in the morphologic cohort. Complete remission (CR) rates were comparable (95% and 77%, respectively). However, median event-free and overall survivals widely diverged among the 42 patients who achieved MRD-negative CR: not reached (NR) (95% confidence interval [CI]: 4.2-NR) vs. 6.3 months (95% CI, 4.8-9.0) (p = 0.0005), and NR (95% CI, 15.3-NR) vs. 17 months (95% CI, 8.5 – 36.2) (p = 0.0189), in the MRD and morphologic cohorts, respectively. Subsequent allogeneic HSCT in either cohort did not improve survival (p = 0.8). MRD cohort patients developed substantially less severe cytokine release syndrome (CRS) and neurotoxicity, both correlating with peak CAR T cell expansion (p = 0.0326 and p = 0.0001, respectively). Conclusions: Despite comparable initial CR rates regardless of pre-treatment disease burden, durability of 19-28z CAR T cell mediated remissions and survival in adult patients with relapsed B-ALL positively correlated to a low disease burden and do not appear to be enhanced by allogeneic transplant. Our findings strongly support the early incorporation of CD19 CAR therapy before morphologic relapse in B-ALL. Clinical trial information: NCT01044069.