Because the therapeutic effect of αGITR in ICB-responsive GL26121 was shown to be independent of Treg cells’ presence in GBM and largely relied on CD8 T cell gain of function, we first tested whether αGITR treatment alters the phenotype of Treg cells isolated from GL261-MGH, CT2A, or 005GSC bearing mice ex vivo. Here, CD8A is linked to glioblastoma.