Abstract 1631: T cell dysfunction in pediatric cancer patients at diagnosis and after chemotherapy can limit chimeric antigen receptor potential
Authors: Das Rajat K. , Storm Julie , Barrett David M. 
Published: August 2018

Abstract
Cellular therapy using engineered T cells has demonstrated clinical efficacy in the treatment of hematologic malignancies. Many patients, however, have T cells that result in a poor clinical product that either fails manufacture or does not proliferate in the patient. We have prospectively characterized peripheral blood T cells from 157 pediatric cancer patients and identified key metabolic changes associated with CAR T cell potential. We collected peripheral blood samples from 157 pediatric patients with acute lymphoblastic leukemia (ALL), non-Hodgkin Lymphomas (NHL) , neuroblastoma, osteosarcoma, rhabdomyosarcoma, Wilms, Hodgkins, chronic myelogenous leukemia and Ewings sarcoma at diagnosis and after each cycle of chemotherapy. We depleted the adherent cells from this collection, quantified the CD3+ population using flow cytometry, and expanded these T cells using CD3/CD28 stimulatory beads as in CAR T cell manufacturing. We noted very poor CAR T cell potential in all tumor types (&lt;30% pass) except ALL (80% pass) and Wilms tumor (50% pass) in the pre-chemotherapy samples. We noted a decline in CAR T cell potential with cumulative chemotherapy in all cases, though this was particularly significant in children less than 3yo. Nanostring RNA profiling of metabolic pathways revealed a bias towards glycolysis and away from fatty acids in the poor performing samples. In vitro assays of chemotherapy exposure reveal that certain classes are especially toxic to Naïve T cells versus memory T cells, and that this correlates with poor potential as CAR T cells. In particular, cyclophosphamide and doxorubicin containing regimens severely depleted CAR T cell potential in patients. These chemotherapy agents were associated with mitochondrial dysfunction both in vitro and in patient T cells after in vivo chemotherapy. Oxygen consumption rate (OCR) analysis also reveals a poor spare respiratory capacity (SRC) in the T cell samples that go on to perform poorly as CAR T cells. Enforced use of fatty acids such as palmitate helped restore the SRC in chemotherapy exposed T cells.These data represent the most detailed analysis of T cell number, phenotype and metabolic function from pediatric cancer patients. Low abundance of Naïve T cells (whether pre-chemotherapy or post), reliance on glycolytic pathways and poor SRC define patients with poor potential to have an active CAR T cell product made. This data raises important questions for the development of CAR T cell therapies for cancers other than ALL in pediatrics, as inherent T cell dysfunction and more intensive chemotherapy regimens in solid tumors may represent new barriers to efficacy.
Citation Format: Rajat K. Das, Julie Storm, David M. Barrett. T cell dysfunction in pediatric cancer patients at diagnosis and after chemotherapy can limit chimeric antigen receptor potential [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 1631.