ABSTRACT
Immunotherapy with chimeric antigen receptor T cells for pediatric solid and brain tumors is constrained by available targetable antigens. Cancer-specific exons present a promising reservoir of targets; however, these have not been explored and validated systematically in a pan-cancer fashion. To identify cancer specific exon targets, here we analyze 1532 RNA-seq datasets from 16 types of pediatric solid and brain tumors for comparison with normal tissues using a newly developed workflow. We find 2933 exons in 157 genes encoding proteins of the surfaceome or matrisome with high cancer specificity either at the gene (n = 148) or the alternatively spliced isoform (n = 9) level. Expression of selected alternatively spliced targets, including the EDB domain of fibronectin 1, and gene targets, such as COL11A1, are validated in pediatric patient derived xenograft tumors. We generate T cells expressing chimeric antigen receptors specific for the EDB domain or COL11A1 and demonstrate that these have antitumor activity. The full target list, explorable via an interactive web portal ( https://cseminer.stjude.org/ ), provides a rich resource for developing immunotherapy of pediatric solid and brain tumors using gene or AS targets with high expression specificity in cancer.
Subject(s)
Brain Neoplasms , Exons , Receptors, Chimeric Antigen , Humans , Brain Neoplasms/immunology , Brain Neoplasms/therapy , Brain Neoplasms/genetics , Animals , Exons/genetics , Child , Receptors, Chimeric Antigen/genetics , Receptors, Chimeric Antigen/immunology , Receptors, Chimeric Antigen/metabolism , Mice , Immunotherapy/methods , Alternative Splicing , Fibronectins/genetics , Fibronectins/metabolism , Fibronectins/immunology , Xenograft Model Antitumor Assays , Gene Expression Regulation, Neoplastic , RNA-Seq , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , Cell Line, Tumor , Immunotherapy, Adoptive/methodsABSTRACT
Immunotherapy with CAR T cells for pediatric solid and brain tumors is constrained by available targetable antigens. Cancer-specific exons (CSE) present a promising reservoir of targets; however, these have not been explored and validated systematically in a pan-cancer fashion. To identify CSE targets, we analyzed 1,532 RNA-seq datasets from 16 types of pediatric solid and brain tumors for comparison with normal tissues using a newly developed workflow. We found 2,933 exons in 157 genes encoding proteins of the surfaceome or matrisome with high cancer specificity either at the gene (n=148) or the alternatively spliced (AS) isoform (n=9) level. Expression of selected AS targets, including the EDB domain of FN1 (EDB), and gene targets, such as COL11A1, were validated in pediatric PDX tumors. We generated CAR T cells specific to EDB or COL11A1 and demonstrated that COL11A1-CAR T-cells have potent antitumor activity. The full target list, explorable via an interactive web portal (https://cseminer.stjude.org/), provides a rich resource for developing immunotherapy of pediatric solid and brain tumors using gene or AS targets with high expression specificity in cancer.
ABSTRACT
Chimeric antigen receptor (CAR) T-cell therapy has had limited success in early-phase clinical studies for solid tumors. Lack of efficacy is most likely multifactorial, including a limited array of targetable antigens. We reasoned that targeting the cancer-specific extra domain B (EDB) splice variant of fibronectin might overcome this limitation because it is abundantly secreted by cancer cells and adheres to their cell surface. In vitro, EDB-CAR T cells recognized and killed EDB-positive tumor cells. In vivo, 1 × 106 EDB-CAR T cells had potent antitumor activity in both subcutaneous and systemic tumor xenograft models, resulting in a significant survival advantage in comparison with control mice. EDB-CAR T cells also targeted the tumor vasculature, as judged by IHC and imaging, and their antivascular activity was dependent on the secretion of EDB by tumor cells. Thus, targeting tumor-specific splice variants such as EDB with CAR T cells is feasible and has the potential to improve the efficacy of CAR T-cell therapy.
Subject(s)
Fibronectins/antagonists & inhibitors , Immunotherapy, Adoptive/methods , Neoplasm Proteins/antagonists & inhibitors , Neoplasms/therapy , T-Lymphocytes/transplantation , Animals , Antigens, Neoplasm , Cell Line, Tumor , Coculture Techniques , Feasibility Studies , Fibronectins/genetics , Fibronectins/immunology , Fibronectins/metabolism , Healthy Volunteers , Human Umbilical Vein Endothelial Cells , Humans , Mice , Neoplasm Proteins/genetics , Neoplasm Proteins/immunology , Neoplasm Proteins/metabolism , Neoplasms/immunology , Neoplasms/pathology , Primary Cell Culture , Protein Isoforms/antagonists & inhibitors , Protein Isoforms/genetics , Protein Isoforms/immunology , Protein Isoforms/metabolism , RNA Splicing , Receptors, Chimeric Antigen/immunology , T-Lymphocytes/immunology , Xenograft Model Antitumor AssaysABSTRACT
Chimeric antigen receptor (CAR) T cell therapy has garnered significant excitement due to its success for hematological malignancies in clinical studies leading to the US Food and Drug Administration (FDA) approval of three CD19-targeted CAR T cell products. In contrast, the clinical experience with CAR T cell therapy for solid tumors and brain tumors has been less encouraging, with only a few patients achieving complete responses. Clinical and preclinical studies have identified multiple "roadblocks," including (1) a limited array of targetable antigens and heterogeneous antigen expression, (2) limited T cell fitness and survival before reaching tumor sites, (3) an inability of T cells to efficiently traffic to tumor sites and penetrate physical barriers, and (4) an immunosuppressive tumor microenvironment. Herein, we review these challenges and discuss strategies that investigators have taken to improve the effector function of CAR T cells for the adoptive immunotherapy of solid tumors.
