Circulating tumor DNA assessment in patients with diffuse large B-cell lymphoma following CAR-T therapy.

7552 Background: Circulating tumor DNA(CTD) have been used for disease monitoring in Diffuse Large B Cell Lymphoma(DLBCL) (Kurtz ASCO 2016). Role of CTD assessment in DLBCL patients treated with CAR-T therapy has not been studied. We prospectively analyzed CTD of dynamics measured by next generation sequencing(NGS) of BCR using ClonoSeq MRD(Adaptive Biotechnologies), before and after CAR-T therapy to determine feasibility and clinical utility. Methods: At Stanford, 7 patients were enrolled on ZUMA-1 clinical trial NCT02348216, treating chemo-refractory DLBCL patients with anti-CD19, CAR-T. Complete radiologic data and CTD analysis was collected for six subjects. Tumor-DNA was extracted from archival paraffin-embeded tissue & analyzed using the NGS-based assay. PCR amplification of IGH-VDJ, IGH-DJ & IGK regions using universal consensus primers was performed followed by NGS to determine the tumor clonotype(s). Blood collected at day 0,7,14,28,60 & 90 days in relation to CAR-T infusion was used to detect CTD by ClonoSeq quantification of clonotypes. Results: Clonotypes were successfully determined for all 6 subjects, and 30 blood samples for 6 patients were prospectively analyzed. All patients had measurable disease burden pre-CAR-T infusion. CTD dynamics correlated with PET-CT outcomes in 100% of the patients. Increasing CTD temporally preceded progressive disease(PD) before PETCT recognition in 4 of 5 patients and was always increasing when PETCT showed PD. Preceding CTD quantification correlated with disease volume increase. One patient achieved durable KTE-19 complete response(CR) and detectable CTD became undetectable on day 14(and on subsequent samples) following CAR-T infusion, corresponding to 1 & 3 month PETCT CR. Additionally, the burden of disease measured by lymphoma molecules per ml allowed volumetric response assessment in all the patients who experienced massive reduction in tumor volume, but by traditional response definition had partial response. Conclusions: ClonoSeq CTD provides precise total tumor quantification of DLBCL in the CAR-T cell setting. This technology may overcome fundamental limitations of DLBCL imaging(cost, radiation exposure & limited repetition).