Abstract 4418: Heterogeneity of IFN-γ responsiveness in myeloid malignancies- implication for the possible impact on IFN-γ immunotherapy
Authors: Ventura Kedwin , Kovalenko Iuliia , Lee Jui-En Ray , Neupane Biswas , Stapor Daniel , Ito Sawa 
Published: June 2023

Abstract
Introduction: Allogeneic stem cell transplantation (alloSCT) can potentially cure hematologic malignancies through graft-versus-leukemia effect (GVL). Several studies have suggested that IFN-γ pathway is critical for GVL sensitivity or resistance in leukemia cells. In mouse model, acute myeloid leukemia (AML) generated in IFN-γ receptor-deficient mice acquired resistance to GVL (Matte-Martone, Shlomchik WD, J Clin Invest. 2017). Other groups have reported that IFN-γ restores HLA expression on myeloid blasts from patients who relapsed AMLs after alloSCT. These data support the clinical application of IFN-γ to augment GVL in subjects with post-transplant relapse. However, AML is molecularly heterogeneous, and the IFN-γ responsiveness may vary by AML subtypes. We analyzed IFN-γ responsiveness of primary AML cells and investigated the role of IFN-γ on cell death and T-cell recognition of AML cell lines.
Methods: Primary AML cells collected at diagnosis (n=60), at relapse after chemotherapy (n=4), and at post-transplant relapse (n=8) were stimulated with IFN-γ at 1 ng/ml or 50 ng/mL in vitro, and IFN-γ responsiveness was analyzed by measuring phosphorylation of STAT1 (pSTAT) after 15 minutes and upregulation of HLA-DR after 48 hours by flow cytometry. U937 and THP-1 cell lines were used to investigate IFN-γ induced cell death and the impact of IFN-γ priming of leukemia cells on the activation of alloreactive T cells. For this, Jurkat cells transduced with anti-HA1 T cell receptor (αHA1-TCR-T) were used, and the activation was analyzed through CD69 upregulation by flow cytometry.
Results: IFN-γ responsiveness was heterogeneous in both pSTAT1 and HLA-DR upregulation of primary AML blasts. IFN-γ responsiveness also varied within the subpopulation of leukemic blasts within the sample at diagnosis and relapse, implying clonal evolution. Compared to THP-1, U937 cells fail to upregulate HLA-DR with IFN-γ despite appropriate pSTAT1 response to IFN-γ, suggesting silencing of downstream IFN-γ activation site (GAS) and transcription of IFN-stimulated genes (ISGs). IFN-γ directly induced cell death in THP-1 in vitro, while U937 was resistant to IFN-γ induced cell death. Priming of THP-1 with IFN-γ significantly improved the affinity of αHA1-TCR-T to peptide-stimulated THP-1.
Conclusion: IFN-γ responsiveness of AML blasts was heterogeneous, and cell line data suggest an impact of IFN-γ sensitivity on IFN-γ mediated cell death and alloreactive T cell recognition. Future studies aim to understand the mechanisms underlying IFN-γ sensitivity or resistance in AML, which would help to design clinical trials by selecting the patients who would obtain maximal benefit from IFN-γ therapy in post-transplant relapse (NCT04628338).
Citation Format: Kedwin Ventura, Iuliia Kovalenko, Jui-En Ray Lee, Biswas Neupane, Daniel Stapor, Sawa Ito. Heterogeneity of IFN-γ responsiveness in myeloid malignancies- implication for the possible impact on IFN-γ immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4418.