Abstract 5681: Prediction of immunotherapy outcome by multimodal assessment of minimal residual disease and persistence of allogeneic anti-CD123 CAR T-cells (UCART123) in pre-clinical models of acute myeloid leukemia

Acute myeloid leukemia (AML) is a fatal disease. The promise of autologous T-cells expressing chimeric antigen receptors (CARs) in targeting B-cell malignancies has encouraged extension of this approach to AML. However, clinical guidance regarding infusion and re-infusion regimens for CAR-T technology is unclear for any cancer including AML. Given that studies demonstrate clear benefit for minimal residual disease (MRD) assessment in predicting relapse for AML, we thus sought to ascertain whether simultaneous molecular assessment of MRD markers and CAR-T-specific markers could inform decisions around CAR-T dosing and re-infusion. We tested this approach using patient-derived xenograft (PDX) models with allogeneic anti-CD123 CAR-T cells (UCART123). UCART123 are genetically modified allogeneic T-cells expressing an anti-CD123 CAR. These cells lack expression of the T-cell receptor (TCRabKO), in order to minimize graft vs. host disease (GvHD). PDX were established using prognostically adverse AML (FLT3-ITD+NPM1+) and treated with 1x10 6 or 2.5x10 6 UCART123. The median overall survival (OS) of control mice injected with saline or CAR-T negative (TCRabKO) T-cells succumbed to disease was 124.5 and 126 days, respectively. In contrast, UCART123 groups survived >180 days (hazard ratio 0.08, P=0.003). Clonal dynamics between disease and CAR-T were simultaneously monitored post-infusion by quantifying mutated NPM1 and CAR-T genetic markers, respectively, using digital droplet PCR (ddPCR). We found that ddPCR monitoring was more sensitive than multiparameter flow cytometry (MFC) at detecting MRD and persistence of UCART123. Using ddPCR, leukemia and UCART123 cells were detected when human cells were not evaluable using MFC in peripheral blood (PB). Mice with persistent UCART123 remained disease-free. Importantly, when mutated NPM1 levels became elevated with simultaneous loss of UCART123, relapse was evident by MFC in PB in subsequent time-points (2 out 20 mice, all at 1x10 6 dose, ~180 days) re-infusion of UCART123 cells resulted in effective elimination of AML. Taken together, we have demonstrated that simultaneous monitoring of disease and UCART123 cells provides valuable insight into the kinetics and effectiveness of UCART123 cells. Currently, we have implemented the ddPCR assay in the phase I clinical trial of UCART123 in AML allowing to simultaneously detect UCART123 cells and blasts in peripheral blood of NPM1 mutant AML patients. Citation Format: Mayumi Sugita, Nuria Mencia-Trinchant, Nathan Ewing-Crystal, Gabrielle Suppa, Roman Galetto, Agnes Gouble, Julianne Smith, Gail J. Roboz, Duane C. Hassane, Monica L. Guzman. Prediction of immunotherapy outcome by multimodal assessment of minimal residual disease and persistence of allogeneic anti-CD123 CAR T-cells (UCART123) in pre-clinical models of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5681.