Peptide Vaccines for Pediatric High-Grade Glioma and Diffuse Midline Glioma: Current Progress and Future Perspectives.

High-grade gliomas (HGGs) and diffuse midline gliomas (DMGs) in pediatric patients carry a poor prognosis, necessitating the rapid development of novel therapies. Peptide vaccines represent a safe, repeatable, and rational immunotherapeutic modality aimed at inducing potent, tumor-specific T-cell responses. In this review, we define the scope of current progress by arguing that immunogenicity in children with HGG/DMG hinges on three factors: appropriate antigen class (neoantigen vs. TAA), the use of potent immunoadjuvants, and successful navigation of immune suppression. To address the gap between biological promise and clinical reality, we analyze clinical trials targeting shared tumor-associated antigens (e.g., CMV pp65, Survivin) and specific shared neoantigens (H3.3K27M). Crucially, we highlight pivotal data from the PNOC007 trial, where the magnitude of H3.3K27M-specific T-cell expansion correlated directly with significantly longer overall survival (OS), establishing a causal link between pharmacodynamics and clinical benefit. However, the unique challenges of the immunosuppressive tumor microenvironment and the detrimental effect of necessary corticosteroids remain paramount barriers. Future success relies on multi-modal combination strategies, the development of next-generation personalized neoantigen vaccines, and the application of advanced neuroimaging to accurately assess treatment response.