We then screened clonally expanded CD4 TCRs from a patient with diffuse midline glioma (DMG) administered a neoepitope peptide vaccine (22) to understand whether the treatment had elicited a T cell–driven immune response; 20 of 40 tested TCR clonotypes were reactive to the histone 3 K27M vaccinating peptide (Fig. 3B). Here, CD4 is linked to diffuse midline glioma.