Glypicans are a family of heparan sulfate proteoglycans that are attached to the cell membrane via a glycosylphosphatidylinositol anchor. Glypicans interact with multiple ligands, including morphogens, growth factors, chemokines, ligands, receptors, and components of the extracellular matrix through their heparan sulfate chains and core protein. Therefore, glypicans can function as coreceptors to regulate cell proliferation, cell motility, and morphogenesis. In addition, some glypicans are abnormally expressed in cancers, possibly involved in tumorigenesis, and have the potential to be cancer-specific biomarkers. Here, we provide a brief review focusing on the expression of glypicans in various cancers and their potential to be targets for cancer therapy.

Targeting solid tumors must overcome several major obstacles, in particular, the identification of elusive tumor-specific antigens. Here, we devise a strategy to help identify tumor-specific epitopes. Glypican 2 (GPC2) is overexpressed in neuroblastoma. Using RNA sequencing (RNA-seq) analysis, we show that exon 3 and exons 7-10 of GPC2 are expressed in cancer but are minimally expressed in normal tissues. Accordingly, we discover a monoclonal antibody (CT3) that binds exons 3 and 10 and visualize the complex structure of CT3 and GPC2 by electron microscopy. The potential of this approach is exemplified by designing CT3derived chimeric antigen receptor (CAR) T cells that regress neuroblastoma in mice. Genomic sequencing of T cells recovered from mice reveals the CAR integration sites that may contribute to CAR T cell proliferation and persistence. These studies demonstrate how RNA-seq data can be exploited to help identify tumorassociated exons that can be targeted by CAR T cell therapies.

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Background and Significance Neuroblastoma is a rare pediatric cancer that forms in immature nerve tissue of infants and accounts for 10 to 15 percent of cancer-related deaths in children. The five-year survival for high-risk neuroblastoma is 50% with current treatment practices being a combination of surgery, chemotherapy, and radiation. A more effective therapy is therefore needed to improve overall patient outcomes. Methods The CT3 mouse antibody that targets GPC2 was previously identified in the lab and has shown activity in the chimeric antigen receptor (CAR) T cell format against neuroblastoma. Humanization of the CT3 antibody was also done through CDR grafting in human germline sequences to prevent potential adverse immunogenic effects when treating patients. In the present study, the CT3 antibody and humanized CT3 (hCT3) antibody were engineered into T cells based on the engineered gamma/delta TCR scaffold (called AbTCR). The activities of the CT3 and hCT3 AbTCRs were tested in luciferase-based cell killing assays and xenograft mouse models. Results Humanized CT3 retains a comparable binding affinity for GPC2. The hCT3 CAR T cell showed its ability to regress tumor expression in mice. Furthermore, the mice treated with the CT3 AbTCR showed tumor regression while the mice treated with the hCT3 AbTCR became tumor free three weeks after treatment. Conclusions Overall, the hCT3 AbTCR T cells are very active when combating neuroblastoma tumors in mice. The efficacy at a low treatment dosage indicates that the GPC2 targeted hCT3 AbTCRs are a promising therapeutic for the treatment of neuroblastoma and other GPC2 positive cancers in patients.