Neoepitope-specific vaccination of a patient with diffuse midline glioma targeting H3K27M induces polyclonal B and T cell responses across diverse HLA alleles

Abstract

H3K27M, a driver mutation with T- and B-cell neoepitope characteristics, defines an aggressive subtype of diffuse glioma with poor survival. We functionally dissect the immune response of one patient who was treated with an H3K27M peptide vaccine and subsequently entered complete remission. The vaccine robustly expanded class II HLA-restricted peripheral H3K27M-specific T cells. Using functional assays, we characterized 34 clonally unique H3K27M-reactive T cell receptors and identified critical, conserved motifs in their CDR3 regions. Using detailed HLA mapping, we further demonstrate that diverse HLA-DQ, and -DR alleles present immunogenic H3K27M epitopes. Furthermore, we identified and profiled H3K27M-reactive B cell receptors from activated B cells in the cerebrospinal fluid. Our results uncover the breadth of the adaptive immune response against a shared clonal neoantigen across multiple HLA allelotypes and support the use of class II-restricted peptide vaccines to stimulate tumor-specific T and B cells harboring receptors with therapeutic potential.