A universal CD4 epitope enhances cytotoxic T-cell priming and memory in glioblastoma peptide vaccination 2257077

Abstract Introduction Immunotherapy has yet to show efficacy in glioblastoma (GBM). To enhance immune priming, the ETAPA phase 1 trial (NCT05283109) evaluated P30-EPS, a multicomponent peptide vaccine linking class I tumor-associated antigens (CMV pp65, Survivin, EphA2) to the universal class II tetanus toxoid epitope P30 (TVSFWLRVPKVSASHLE), designed to promote coordinated CD4+ and CD8+ activation. Methods Adults with newly diagnosed, MGMT-unmethylated GBM (n = 18) received 7 intramuscular vaccinations with the TLR3 agonist Hiltonol (20 µg/kg) at doses of 300 µg or 400 µg P30-EPS. Peripheral blood mononuclear cells were assessed longitudinally by IFN-γ ELISPOT, spectral flow cytometry, and TCR sequencing to evaluate cytokine secretion, T-cell phenotype, and repertoire diversity. In parallel, baseline and selected on-treatment tumor samples are being analyzed by Xenium spatial transcriptomics and CODEX multiplex proteomics to map local immune remodeling and spatial coordination of CD4+ and CD8+ responses. Results The vaccine was well tolerated (all adverse events ≤ grade 2). P30-EPS induced robust antigen-specific IFN-γ responses in 11 of 12 evaluable patients, with stronger recall responses at 400 µg. Patients with longer progression-free survival exhibited higher baseline frequencies of naïve CD4+ T cells and reduced terminally differentiated effector-memory (CD45RA+CCR7⁻) subsets, indicating a less exhausted, more adaptable helper T-cell pool conducive to effective priming. Single cell 5’ TCR sequencing revealed expansion of unique clonotypes following booster vaccination, consistent with durable memory formation. Conclusion ETAPA achieved its objectives and the universal CD4 epitope enhanced magnitude and quality of CD8+ cytotoxic and memory responses. Ongoing spatial profiling will define intratumoral correlates of systemic immune activation. These results are informing an epitope-linked and retroviral antigen—targeted vaccine that we are developing next to broaden anti-tumor immunity in CNS malignancies. Funding Source NCI P50 CA190991-08 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)