IMMU-41. NEOADJUVANT PD-1 BLOCKADE INDUCES T CELL AND CDC1 ACTIVATION BUT FAILS TO OVERCOME THE IMMUNOSUPPRESSIVE TUMOR ASSOCIATED MACROPHAGES IN RECURRENT GLIOBLASTOMA

Abstract

Abstract In a small phase I clinical trial, neoadjuvant anti-PD-1 (neo-aPD1) improved survival in glioblastoma patients (GBM) and was associated with increased interferon-γ-related gene expression and an associated decrease in cell cycle-related gene expression in the tumor. Despite this, neo-aPD1 was not curative. To better understand how neo-aPD1 alters the GBM tumor microenvironment and to discover new therapeutic axes, we used CyTOF and single-cell RNAsequencing to analyze the tumor-infiltrating immune populations of 70 GBM patients, 20 of whom had received neo-aPD1. In patients treated with neo-aPD1 the proportion and number of tumor-infiltrating T cells increased and these T cells had increased expression of the cytokines CCL5 and XCL1, which promote dendritic cell migration. Among the infiltrating T cells was a population of progenitor exhausted CD8+ T cells expressing the genes TCF, SLAM6, CCR7, IL7R, and GZMB. Single-cell TCR analysis revealed that these CD8+ T cells arose from a population of early activated, cytotoxic T cells that had expanded in the peripheral blood and trafficked into the tumor. Within the tumor-infiltrating myeloid cells, we found that neo-aPD1 upregulated genes in the interferon-γ response pathways; namely genes related to T cell trafficking and immune suppression, such as CD274 (PD-L1), TREM2, GPNMB, and IL10, indicating a maladaptive response by some myeloid cells to the immune response triggered by neo-aPD1. Finally, we identified a new migratory and interferon-γ activated tumor-infiltrating conventional dendritic cell population that was increased with neo-aPD1 and that notably expressed XCR1, the receptor for XCL1. Additionally, our results provide future basis to study if modalities that enhance the T cell:DC axis or that inhibit the inhibitory myeloid populations may improve survival in patients with GBM when used in conjunction with neo-aPD1. In sum, we characterized the immune landscape in GBM and how it changes with neo-aPD1 at single cell resolution.