Abstract P050: Oncogenic kinase therapy restricts CD8 T cell differentiation and clonal expansion
Authors: Tieniber Andrew , Hanna Andrew , Medina Benjamin , Do Kevin , Levin Lillian , Rossi Ferdiando , DeMatteo Ronald 
Published: January 2022

Abstract
Introduction: Targeted therapy with tyrosine kinase inhibitors (TKI) including imatinib is effective in treating gastrointestinal stromal tumor (GIST), but resistance often develops within 18 months. Despite a robust immune T cell infiltrate, combining TKIs with immune checkpoint inhibitors has largely been unsuccessful in treating advanced GIST. The superagonist IL15/1L15Rα has shown promise in a number of cancer types. The objective of this study was to determine the effects of TKI therapy on intratumoral T cells in GIST and evaluate IL15/1L15Rα as an adjunctive therapy. Methods: KitV558Δ/+ mice were treated with imatinib (600mg/L in water) and/or IL15/IL15Rα (2ug/12ug/dose, 3x/week), for 1-4 weeks and evaluated by TCRB sequencing (Immunoseq), RNA-seq, and flow cytometry (n=4-5/group). Intratumoral immune cells from KitV558Δ/+ mice were evaluated by single cell RNA sequencing (scRNAseq) (n=3). Results: RNA-seq of sorted CD8 T cells following 1 week of imatinib treatment suggested intratumoral CD8 T cells gain antigen experience but lose their effector profile, as cd44, sell, and tcf7 increased while gzmb and tnfrsf9 decreased (p&lt;0.05). At 1 and 4 weeks of imatinib therapy, flow cytometry of intratumoral CD8 T cells demonstrated increased CCR7 and CD127 and decreased CD69, Tbet, Granzyme B, and Ki67 (p&lt;0.05), confirming an intratumoral phenotypic transition from an activated/effector subtype. Imatinib therapy reduced p-AKT and p-mTOR MFI in intratumoral CD8 T cells by flow cytometry (p&lt;0.05), signifying a deficiency in TCR signaling and/or co-stimulation. TCRB sequencing after 1 week of imatinib treatment showed no difference in T cell clonality, indicating T cells failed to undergo clonal expansion. scRNAseq in tumors from KitV558Δ/+ mice established that IL-15R and IL-15 were primarily expressed on Batf3 dendritic cells and macrophages, while both IL-2R beta and gamma were expressed on NK and T cells. Although IL15/1L15Rα alone had no anti-tumor efficacy, combining IL15/IL15Rα with imatinib improved the anti-tumor response as measured by tumor weight (p&lt;0.05). After combination treatment, CD8 T cells evaluated by flow cytometry exhibited a significant increase in granzyme B, Tbet, CD69, and Ki67, and PI3K signaling was restored (p&lt;0.05). Conclusions: Imatinib therapy in GIST fails to induce T cell clonal expansion and results in a reduced CD8 activation/effector profile. IL15/IL15Rα therapy improves upon the effects of imatinib by rescuing CD8 T cell PI3K signaling and effector response.
Citation Format: Andrew Tieniber, Andrew Hanna, Benjamin Medina, Kevin Do, Lillian Levin, Ferdiando Rossi, Ronald DeMatteo. Oncogenic kinase therapy restricts CD8 T cell differentiation and clonal expansion [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P050.