Mapping CD4 ⁺ T Cell Landscapes in Glioblastoma Reveals Effectors and Bystanders

The tumor immune microenvironment (TME) has been demonstrated to significantly shape glioblastoma (GBM) progression and therapeutic response, yet the role of CD4 ⁺ T cells remains incompletely defined. Here, by integrating single-cell RNA, surface-protein, and TCR profiling of 39,788 T cells from 16 high-grade gliomas with five matched blood samples, we mapped 23,550 CD4 ⁺ T cells across 11 states and revealed predominance of CD4 ⁺ T cells in primary, but not recurrent, tumors, alongside pronounced tumor–blood discordance. Clonal analyses revealed expansion of cytotoxic effector CD4 ⁺ T cells within tumors and T _EMRA CD4 ⁺ T cells in blood. A small set of dominant clonotypes (0.2% of unique TCRβ sequences) accounted for >6% of all CD4 ⁺ T cells across both compartments and were shared across different transcriptional subsets, suggesting diverse transcriptional development stemming from a shared progenitor. In contrast, virally annotated clonotypes were broadly dispersed and largely unexpanded, consistent with bystander populations. Collectively, we investigated the cellular and clonal architecture of human CD4 ⁺ T cells in GBM and highlight the contrast between PBMC and TIL compartments.