Glioblastoma (GBM) is a highly aggressive primary brain tumor with poor outcomes. One contributor to therapeutic failure is the tumor's disorganized and heterogeneous vasculature, commonly referred to as the blood-tumor barrier (BTB). The BTB restricts effective delivery of systemically administered agents and limits beneficial immune cell infiltration into the tumor microenvironment, presenting a major clinical barrier to improving GBM outcomes.
To study tumor–vascular–immune interactions in a setting that more closely models human disease, the authors used a physiologically relevant genetically engineered mouse model (GEMM). The model was generated via in utero electroporation delivering CRISPR-Cas9 targeting of Nf1, Tp53, and Pten (a 3x CRISPR-Cas9 GEMM). According to the authors, this GEMM reproduces key features of human glioma, including infiltrative growth patterns, representative histopathology, relevant molecular alterations, and stage-dependent disruption of the blood–brain barrier.
The intervention tested was focused ultrasound (FUS) in combination with systemically administered microbubbles (MBs). This approach transiently disrupts the BTB, a strategy previously used to enhance delivery of therapeutics to brain tumors. The authors applied FUS+MBs to tumors in the GEMM to evaluate not only vascular permeability changes but also potential effects on the tumor immune landscape, including whether FUS-induced sterile inflammation might remodel immune cell representation within tumors.
Magnetic resonance imaging (MRI) was used to confirm that FUS+MB treatment increased vascular permeability in the treated tumors. The MRI data supported that the BTB was transiently disrupted by the focused ultrasound protocol, consistent with the intended physical effect of the intervention.
Flow cytometric analysis performed three days after FUS+MB treatment revealed robust increases in tumor-infiltrating CD4+ helper and CD8+ effector T cells compared with untreated tumors. Despite the increase in CD8+ T-cell numbers, the ratio of CD8+ T cells to regulatory T cells (Tregs) was not altered by FUS+MBs, indicating that the increase in effector cells did not come with a measurable shift in that particular balance metric.
Immunofluorescence imaging corroborated the flow cytometry results, showing increased lymphocyte presence within tumors after BTB disruption. The authors also detected populations of double-negative and double-positive T cells in the tumors; however, these subsets were not significantly changed by FUS treatment.
To address whether the elevated T-cell counts reflected local proliferation, the authors assessed Ki67 expression. Ki67 analysis indicated that the observed accumulation of T cells in treated tumors was not driven by local T-cell proliferation, supporting the interpretation that increased representation resulted from enhanced infiltration rather than in situ expansion.
The immune effects of a single FUS+MB treatment were transient. By seven days post-treatment, differences in immune cell representation between treated and untreated tumors were no longer detected. This temporal profile suggests that FUS-mediated BTB opening produces a short window of enhanced lymphocyte access to the tumor microenvironment.
Collectively, the results demonstrate that transient BTB disruption using FUS+MBs can selectively and rapidly augment intratumor representation of CD4+ and CD8+ T cells in a clinically relevant glioma GEMM. The increase appears to result from enhanced infiltration rather than local proliferation and is time-limited, resolving within a week. These findings support the concept of using focused ultrasound as a temporally controlled immunomodulatory tool to increase lymphocyte access to GBM, potentially to be combined with immunotherapies or agents that benefit from synchronized delivery.
This work is reported as a preprint and has not been certified by peer review. The authors declared no competing interests. Funding sources listed include National Institutes of Health grants (R01CA279134, R21CA286367, R01NS111102, NS115657, S10OD025024) as reported by the authors. Details beyond what is stated in the preprint, including specific experimental parameters, sample sizes, or statistical values, were not reported in the provided source abstract.