Abstract B86: Treatment of glioma cells with IGF-1R antisense and irradiation induces the production of antigens that stimulate IFNγ production by tumor-specific CD4 T cells
Authors: Garcia Samantha , Kean Rhonda , Lebrun Aurore , Bongiorno Emily , Andrews David W. , Hooper D. Craig 
Published: June 2021

Abstract
We describe here a novel process for the production by glioma cells of cell-free, tumor-specific antigens that supplant the need for intact tumor cells in the induction of immunity against autologous tumor antigen. Radiation is thought to trigger the release of potentially immunostimulatory tumor antigens. However, a variety of tumor cells, including human glioblastoma multiforme (GBM) and mouse GL261 glioma cells, express high levels of insulin-like growth factor-1 receptor (IGF-1R), which has been associated with radioresistance. To determine if the combination of targeting IGF-1R with an antisense oligodeoxynucleotide (AS) and radiation causes the release of glioma antigens, we encapsulated GL261 cells in biodiffusion chambers with different doses of IGF-1R AS, subjected the chambers to 5Gy radiation, and cultured the chambers for approximately 18 hours. Bone marrow-derived dendritic cells (BMDCs) from naive mice were pulsed with the cell-free chamber contents and cultured with CD4 T cells from mice protected against the growth of GL261 cells implanted in the cerebral cortex by immunization with a GL261 cell-based vaccine. The numbers of T cells producing IFNγ in an ELISPOT assay were used as an index of antigen recognition. The contents of chambers that were incubated with viable GL261 or were irradiated but cultured without IGF-1R AS stimulated only weak T-cell responses. Substantial T-cell reactivity was only seen with BMDCs pulsed with the cell-free contents of irradiated chambers containing GL261 cells and IGF-1R AS. Overnight treatment of GL261 cells with IGF-1R AS prior to encapsulation and irradiation also promoted antigen release but was most effective only when a small amount of IGF-1R AS was also added to the chambers. Fully formulated chambers contained tumor tissues that had been cultured overnight with the IGF1-R antisense, encapsulated with additional antisense and irradiated. Chambers were incubated in PBS or implanted in the flanks of naive C57BL/6 mice overnight, then contents were retrieved and used to pulse naive BMDCs. CD4 T cells recovered from GL261-immune C57BL/6 mice were used to detect tumor antigenic determinants presented by the BMDCs with the readout being the number of cells producing IFNγ. We conclude that the treatment of IGF-1R-positive glioma cells with IGF-1R AS and sublethal irradiation stimulates the cells to release antigens capable of stimulating the IFNγ-producing CD4 Th1 cells that have been associated with therapeutic immunity against glioma cells in the GL261 model. When performed in a biodiffusion chamber, this process leads to the accumulation of immunostimulatory antigens in the absence of tumor cell products known to have inhibitory properties for Th1 cells. Immunization via the implantation of irradiated biodiffusion chambers containing autologous tumor cells recovered at surgery and IGF-1R AS is currently under investigation in a clinical trial for patients with GBM (IND 14379; ClinicalTrials.gov, NCT01550523).
Citation Format: Samantha Garcia, Rhonda Kean, Aurore Lebrun, Emily Bongiorno, David W. Andrews, D. Craig Hooper. Treatment of glioma cells with IGF-1R antisense and irradiation induces the production of antigens that stimulate IFNγ production by tumor-specific CD4 T cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B86.