Abstract 3001: Investigating the quantity and quality of dendritic cells in human glioblastoma tissues and in orthotopic murine xenograft and syngraft models of glioblastoma
Authors: Brown Michael P. , Gargett Tessa , Gardam Bryan J. 
Published: April 2023

Abstract
WHO grade 4 glioblastoma multiforme (GBM) has a very poor prognosis even after standard treatment with surgery, radiotherapy, and chemotherapy. Tumor recurrence is virtually inevitable when it is fatal. Chimeric Antigen Receptor (CAR)-T cell therapy is a promising new modality of therapy for GBM patients. Even though second-generation CAR-T cells may be considered to operate autonomously because co-stimulation is inherent to CAR design, the tumor microenvironment of GBM is particularly hostile to immune cells and their normal functions. In our recently published work (Gargett et al. J Immunother Cancer 2022; 10(9): e005187), CAR-T cells specific for the glioblastoma antigen, GD2, had improved antitumor activity if the CAR-T cells co-expressed IL-15. Although IL-15 co-expression prolonged control of intracranial tumor xenografts, tumors escaped immune control in most cases. Our early data suggest that a relative lack of intratumoral dendritic cells (DCs) may be a contributory factor. DCs are central to the initiation and maintenance of adaptive immune responses. Hence, we were interested to survey and characterize the DC content of glioblastoma tissues obtained either from human surgical samples or mice bearing orthotopic xenografts and syngrafts. We have used multi-colour flow cytometry to enumerate and evaluate the maturation status of subsets of DCs together with other types of immune cells among single cell suspensions of isolated glioblastoma tissues. Our preliminary findings are: Total DCs (mean +/- SD), which were defined as lineage-negative and HLA-DR (+), were significantly reduced among total viable cells of glioblastoma tissues (0.845% +/- 0.569) and peripheral blood mononuclear cells (PBMCs) (0.755% +/- 0.601) from GBM patients (n=12) compared to PBMCs (1.77% +/- 0.611) from healthy donors (n=12).No significant differences were detected in the percentages of total DCs among splenocytes of nontumor-bearing C57BL/6 (B6) mice (n=6) compared to B6 bearing othotopic syngrafts of the GL261 (n=3) or C2TA (n=3) glioblastoma cell lines. We will present more detailed analyses from human glioblastoma samples. In addition, we will present a more extensive characterization of DCs from the orthotopic murine models of glioblastoma: we will compare DCs and other types of immune cells in tumor and in the primary and secondary lymphoid tissues of both tumor-bearing and nontumor-bearing mice. We expect that the final data will fill a current gap in knowledge and indicate possible therapeutic strategies that might correct for the quantitative and qualitative defects in dendritic cells in glioblastoma. We hypothesize that adequate correction of these defects in vivo may augment the anti-glioblastoma activity of CAR-T cell therapies.
Citation Format: Michael P. Brown, Tessa Gargett, Bryan J. Gardam. Investigating the quantity and quality of dendritic cells in human glioblastoma tissues and in orthotopic murine xenograft and syngraft models of glioblastoma [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 3001.