185P Interim analysis of the EOGBM1-18 study: Strong immune response to therapeutic vaccination with EO2401 microbiome derived therapeutic vaccine + nivolumab

EO2401 is a therapeutic vaccine designed to activate memory commensal-specific T cells cross-reacting with tumor-associated antigens (TAAs). includes synthetically produced HLA-A2 peptides molecular mimicry TAAs (IL13Rα2, BIRC5 and FOXM1) upregulated in glioblastoma, the CD4 helper peptide UCP2. Patients glioblastoma at first progression after radiotherapy/temozolomide received (300μg/peptide, q2w x4 then q4w) nivolumab (3 mg/kg q2w; EN), or EN bevacizumab (10 ENB) (NCT04116658). Blood collection was performed baseline every 2-4 weeks. Immune responses were investigated on PBMCs ex vivo vitro stimulation (IVS) using tetramer staining, IFN-γ ELISpot intracellular cytokine staining. Vaccination induces strong durable CD8+ cell response against bacterial human TAAs. monitoring demonstrated 3 microbiome-derived for 97% of patients IVS. Cross-reactivity theTAA target 96% by ELISpot. Frequency IVS extremely high, max value above 40% EO2317 EO2318. Ex vivo, least one are detected almost all evaluable some exhibiting up 5% circulating specific cells. Polyfunctionality induce upon vaccination demontrated most (CD107a,IFN-γ TNF-α production stimulation). Memory-specific found as early 2 weeks 1st maintenance immune could be more than 10 months. demonstrates ability generate fast treated E02401/nivolumab +/- bevacizumab. Activation commensal thereby validated an efficient approach difficult treat tumor. Updated immuno-monitoring data will presented.