Tu155 - A Model for Acute Myeloid Leukemia Sensitivity and Resistance to T Cell Killing

Ece Canan Sayitoglu – Stanford University; Steven Strubbe – Stanford University; Yusuke Nakauchi – Stanford University; Robert Freeborn – Stanford University; Colin Waichler – Stanford University; Pauline Chen – Stanford University; Bing Wang – Stanford University; Rosa Bacchetta – Stanford University; Alma-Martina Cepika – Standford University; Maria Grazia Roncarolo – Stanford University

Abstract Text: Acute myeloid leukemia (AML) is a malignant disease of the bone marrow characterized by abnormal proliferation and differentiation of myeloid progenitor cells. Although survival rates have increased with improved care and treatment, overall survival remains suboptimal. Lack of markers specific to AML but not normal myeloid cells limit development of targeted immunotherapies, and allo-hematopoietic stem cell transplantation has significant risks of morbidity and mortality. Our lab has developed an engineered polyclonal type 1 regulatory T (Tr1)-like cells, called CD4IL10, which kill most AML cells in vitro via perforin and granzyme B degranulation. However, some AML samples were resistant to CD4IL10 killing. Herein, we developed an in vivo model to study genes involved in AML sensitivity to CD4IL10 killing using gene edited U937 cells, a promyelocytic cell line used as a model for AML. To establish the model, NSG mice were engrafted with U937-WT-Luc+ cells, and on day 5, we injected CD4IL10 cells and monitored tumor progression. On day 8, we observed a reduction in tumor burden in CD4IL10-treated mice vs untreated mice. To investigate an effect of a specific gene on AML sensitivity to killing, we used CRISPR/Cas9 to knockout ICAM1 from U937-WT-Luc+ cells. ICAM1 is a critical component of the immune synapse required for T cell killing of tumor cells. In our in vivo model, tumor burden was significantly reduced in CD4IL-10-treated U937-WT mice in comparison to U937-ICAM1-KO mice. The following studies validate our in vivo model to test mechanisms of AML sensitivity and resistance to T cell killing.