Molecular disease monitoring in patients with relapsed/refractory B-cell non-Hodgkin lymphoma receiving anti-CD19 CAR T-cell therapy.

7531 Background: Chimeric antigen receptor (CAR) T-cell therapy has improved the historically poor outcomes for relapsed and refractory (R/R) B-cell non-Hodgkin’s lymphoma (NHL). However, nearly 60% of patients will either fail to respond or relapse after CAR T-cell therapy. Currently, PET/CT scans are used to assess response. Cell-free circulating tumor DNA (ctDNA) is released by tumor cells into the peripheral blood and can be measured for minimal residual disease (MRD) assessment. Methods: In this retrospective, IRB approved pilot study, archived lymphoma tissues and ctDNA from peripheral blood samples on day 0, 14, 28, 56, 80, 180, and 365 after CAR T-cell infusion from 10 patients with R/R NHL were collected for next-generation sequencing (NGS) of clonal variable-diversity-joining (VDJ) rearrangements [Adaptive biotechnologies (Seattle, WA)]. Response was assessed by PET/CT on days 30, 60, 90, 180 and 365 and graded according to the Lugano 2014 criteria. The primary endpoint was to determine the feasibility of detecting ctDNA to monitor disease response after anti-CD19 CAR T-cells. The secondary endpoint was to compare the sensitivity/specificity of MRD assessment from ctDNA to PET/CT imaging. Results: Nine out of 10 patients with a trackable sequence [median age 69 (range: 56-76); 55.6% male; median LDH 224], were included in this study. Each received tisagenlecleucel CAR T-cell therapy after median two prior treatments (range: 2-4). 7/9 patients had R/R diffuse large B-cell lymphoma (DLBCL), and 2/9 had transformed follicular lymphoma. At a median follow up of 12.7 months (range: 1.5-30 months), four patients were alive. By day 90, three patients (33.3%) achieved a radiographic complete response (CR) whilst six patients (66.6%) had progressive disease (PD). MRD and radiographic response are outlined in the Table. Detectable MRD on day 14 or day 28 had 83% sensitivity and 100% specificity for radiographic progression at any time before one year. For patients with PD, the median (interquartile range) MRD at day 0, 14, and 28 were 17.31 (1.01, 96.84), 9.12 (0.30, 18.8), and 23.77 (8.01, 137.53) copies per milliliter (mL), respectively. For patients with detectable MRD at day 28, mOS and mPFS were 205 and 38 days, respectively. Conclusions: Our pilot study demonstrated that monitoring MRD was a sensitive and specific method to detect disease response and relapse. In addition, MRD can be monitored more frequently, thus allowing for earlier detection of relapse. MRD and PET/CT identified progressive disease (PD) or complete response (CR) by day 90 in nine patients (A-I) with R/R NHL post CAR T-cell infusion.[Table: see text]