Abstract
BACKGROUND: T cells immunotherapy holds the promise to improve outcomes for pediatric brain tumor patients. We have an interest in cell therapy with T cells expressing chimeric antigen receptors (CARs). CAR T cells recognize cell surface antigens. One goal of our study is to evaluate the cell surface expression of five potential CAR targets: IL13Ra2, HER2, EphA2, B7-H3, and GD2 in pediatric brain tumors. In addition, we wanted to determine HLA class I expression, to evaluate the possibility of targeting pediatric brain tumors with conventional T cells that require HLA class I expression for tumor cell recognition. METHODS: We established a flow cytometry-based method to profile CAR targets, and HLA class I expression from frozen pediatric patient derived xenograft (PDX) samples, which had never been cultured in vitro. We validated our method, antibodies and gating rules on established brain tumor cell lines before analyzing PDX samples. RESULTS: We have profiled 39 pediatric brain tumor PDX samples: 17 medulloblastomas, 5 ependymomas, 5 ATRT, 2 embryonal tumors, 6 HGG and 4 DIPG samples. We found that antigen expression has high intra- and inter-PDX sample variability with B7-H3 and IL13Ra2 being most consistently expressed. HLA class I was present on the cell surface of HGG and DIPG samples, however significantly down-regulated in 20 out of 29 other brain tumor types. CONCLUSION: To our knowledge this is the largest collection of pediatric brain tumor PDX samples that have been systematically analyzed for the expression of targetable cell surface antigens. Our results indicate that more than one antigen needs to be targeted to prevent the emergence of antigen loss variants. In addition, variable expression of HLA class I in the majority of pediatric brain tumors suggest that pediatric brain tumors have developed immune evasion strategies to prevent recognition by conventional T cells.