Abstract 1548: Potent activity of CAR T cells targeting the oncofetal protein GPC2 engineered to recognize low antigen density in neuroblastoma

• Published in: Cancer research (Chicago, Ill.) Ill.), 2021-07, Vol.81 (13_Supplement), p.1548-1548
• Main Authors: Heitzeneder, Sabine, Bosse, Kristopher R., Zhu, Zhongyu, Jelev, Dontcho, Dhingra, Shaurya, Majzner, Robbie, Sotillo-Pineiro, Elena, Buongervino, Samantha, Xu, Peng, Huang, Jing, Delaidelli, Alberto, Hasselblatt, Martin, Parker, Kevin, Anbunathan, Hima, Alag, Anya, Hwang, Jennifer, Huang, Min, Klysz, Dorota D., Theruvath, Johanna L., Vilches-Moure, Jose G., Satpathy, Ansuman T., Sorensen, Poul H., Dimitrov, Dimiter S., Maris, John M., Mackall, Crystal L.
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2021-1548

Background: CAR T-cells targeting solid tumor antigens have not yet demonstrated similar success as seen for CD19, BCMA and CD22 in B-cell malignancies. Truly tumor-specific antigens are rare, yet pediatric solid tumors manifest stalled fetal developmental programs and often overexpress oncofetal antigens, normally restricted to prenatal tissues. Antigen density is a major factor determining CAR potency and whether such nonmutant antigens can be effectively and safely targeted remains unknown. Here, we engineered CAR T-cells targeting GPC2 to recognize clinically relevant antigen thresholds and assess safety. Methods: Expression of GPC2 was assessed during organ development (Cardoso-Moreira et al. 2019), by IHC in prenatal, infant and pediatric brain and in ssRNAseq datasets of fetal (La Manno et. al 2016) and adult brain (Allen Brain Atlas). To measure the molecules/cell of GPC2 and other immunotherapy-relevant targets on bone-marrow infiltrating neuroblastoma (NB) cells of high-risk patients, we developed a Flow Cytometric quantification assay and engineered GPC2-CAR T-cells to recognize relevant antigen thresholds. To assess binding specificity towards GPC2, a membrane proteome array encompassing >5,300 human proteins was utilized. Taking advantage of the murine cross-reactivity of our lead GPC2-CAR, toxicity was assessed in a relevant xenograft model. Results: During organ development, we found GPC2 expression restricted to the developing brain and a gradual decrease until silenced after birth. IHC of prenatal brain revealed an inverse correlation between GPC2 and gestational age (r = -0.775, p = 0.008) and very low staining in infant and pediatric brain (H-scores