Abstract 2622: T cell content of lymphatic fluid in pediatric patients is biased towards naïve and early memory cells: Implications for immunotherapy

Abstract

Abstract Lymphatic fluid originating from tissue and organs drains back into the venous system usually near the innominate vein on the left side. T lymphocytes make up a large majority of the cells in lymphatic fluid, but little is known about their functional status. Cellular therapies such as chimeric antigen receptor T cell (CAR T) therapy appear to depend on collecting large numbers of naïve or early memory T cells, which may not be available in peripheral blood. We have prospectively characterized peripheral blood and lymphatic fluid T cells from 25 pediatric patients receiving therapeutic thoracic duct access procedures and identified the phenotype and CAR T cell potential. Patients were treated at the Children's Hospital of Philadelphia for congenital or acquired lymphatic flow disorders, such as chylothorax, during which the thoracic duct was cannulated for therapeutic purposes. Excess fluid as well as a concomitant peripheral blood sample was collected and de-identified under an IRB-approved protocol. We quantified the CD3+ population using flow cytometry, and expanded these T cells using CD3/CD28 stimulatory beads as in CAR T cell manufacturing. We found an average cell concentration of 1.48e6 cells/mL of lymphatic fluid, with an average of 44% CD3+T cells versus 18% in blood (p<0.05). The lymphatic fluid to blood percent of naïve T cells was 36% v. 17% (p<0.01), Stem Central Memory 13% v. 7%(p<0.01), Central Memory 14% v. 27%(p<0.01), Effector Memory 7% v. 5% (ns) and Terminal Effector 30% vs 43% (ns). This bias towards naïve and SCM T cells was correlated with fewer negative checkpoint regulators (PD-1, LAG3 and Tim3) in lymphatic fluid T cells (7%) versus blood (30%). The T cells from lymphatic fluid expanded more robustly to CD3/28 stimulation as in CAR T manufacture, with an average of 32-fold expansion versus 9-fold for blood (p<0.01). In a xenograft model of pediatric leukemia, the CAR T cells derived from lymphatic fluid produced a deeper and more sustained remission than matched CAR T cells made from peripheral blood. This is the most detailed description of T cells from the lymphatic fluid of children to date. The shift in naïve and SCM T cells in lymphatic fluid versus peripheral blood of the same patient is a confirmation of expectations. The fact that lymphatic fluid is rich in cells that are potentially better suited to CAR manufacture raises the possibility of collecting cells from this source if peripheral blood is not suitable. Further studies on the functional potential of lymphatic fluid T cells are planned. Citation Format: David M. Barrett, Julie Storm, Jessica Perazzelli, Yoav Dori. T cell content of lymphatic fluid in pediatric patients is biased towards naïve and early memory cells: Implications for immunotherapy [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 2622.