CTIM-34. EFFECTS OF NEOADJUVANT IMMUNE CHECKPOINT INHIBITION ON PEDIATRIC AND ADULT HIGH-GRADE GLIOMAS

Abstract High-grade gliomas (HGG) are lethal tumors with few long-term survivors affecting adult and pediatric patients. Studies investigating immune checkpoint inhibition (ICI) suggest administration of neoadjuvant anti-PD1 blockade (neo-aPD1) enhances local and systemic anti-tumor responses. This data is supported by increased T cell density in the tumor and proportion of cytotoxic T cells in peripheral blood. In a previous randomized clinical trial, neo-aPD1 improved survival in adult with recurrent glioblastoma. In this study, we utilized multiplex immunofluorescence (mIF), and single-cell RNA sequencing (scRNA-seq) to investigate the effects of neoadjuvant ICI on the TME and compare between pediatric and adult populations. Tissue samples from adult patients with recurrent GBM treated with neo-aPD1 (n=22) or adjuvant only therapy (n=5) were obtained from our UCLA off-label neo-PD1 study. Tissue samples were also obtained from pediatric patients with recurrent/progressive HGG treated with neoadjuvant ICI from the ongoing Pediatric Neuro-Oncology Consortium study PNOC19. Samples included diagnostic tissue from two patients and on study surgery tissue from four patients. All tissue samples were subjected to mIF and underwent imaging analysis to assess immune cell infiltration by quantifying lymphoid and myeloid cell densities across the two treatment groups. Our preliminary findings elucidated a trend of higher T cell infiltration in adult neoadjuvant compared to adjuvant-only treated patients (median density 58.11 vs 15.15 T-cells/mm2). Compared to their adult counterparts, neoadjuvant ICI treated pediatric patients had even more robust total T cell infiltration (median density 268.10 vs 58.11 T-cell/mm2, pediatric vs adult respectively). scRNA-seq analysis revealed a greater enrichment of monocytic macrophages in the pediatric population compared to tissue resident microglia in the adults. This early data requires analysis of additional samples to better understand differences in the anti-tumor immune response between adult and pediatric recurrent/progressive HGG patients.