UCLA

Glioblastoma (GBM) is the most common malignant tumor in the central nervous system and has poor patient survival rates. Unlike other cancers, immune checkpoint therapies, such as PD-1 checkpoint blockade, have been largely ineffective in GBMs for several reasons: an immunosuppressive tumor microenvironment, a lack of suitable neoantigens, and poor intratumoral T cell infiltration and activity. However, there is evidence that using anti-PD-1 therapy in the neoadjuvant setting may generate a more robust anti-tumor immune response, though characterizing how the GBM tumor microenvironment changes with such therapy is incomplete. As such, we performed high dimensional analysis using CyTOF mass cytometry and single-cell RNAsequencing to study the intratumoral immune populations in GBM patients treated with or without neoadjuvant anti-PD-1 therapy. Characterizing PD-1 expressing tumor infiltrating T cell populations showed that PD-1 was associated with markers of T cell activation and dysfunction regardless of treatment and that this association existed less strongly in peripheral PD-1 expressing T cells. We studied the effects of neoadjuvant anti-PD-1 therapy on a large patient cohort of tumor infiltrating immune cells and found that neoadjuvant anti-PD-1 therapy significantly increased the proportion of several intratumoral T cell sub-populations, including a TCF7-expressing progenitor exhausted population. Downstream effects of neoadjuvant anti-PD-1 therapy on T cells, namely increased production of IFN-g, included transcriptionally altering the myeloid and dendritic cell populations to be more immune suppressive but also potentially more vulnerable to other immune checkpoint therapies, specifically anti-TIGIT and anti-CTLA-4 therapies. Due to the impact of neoadjuvant anti-PD-1 therapy on intratumoral T cell populations, we examined whether we could detect tumor-reactive T cells by cloning TCRs from transcriptionally defined populations in a patient treated with neoadjuvant anti-PD-1 and testing reactivity to the patient-derived gliomasphereline. Among TCRs cloned, we discovered that T cells arising from the activated and exhausted population showed tumor reactivity, suggesting that utilizing transcriptional phenotypes can guide selection of potential tumor-reactive TCRs in GBM patients treated with neoadjuvant anti-PD-1 therapy. In conclusion, neoadjuvant anti-PD-1 therapies alters the immune landscape in these tumors and can be potentially used in combination with other immunotherapies to more effectively treat this malignancy.