Tumor perfusion enhancement by focus ultrasound-induced blood-brain barrier opening to potentiate anti-PD-1 immunotherapy of glioma

• FUS combined with microbubbles can promote the opening of BBB and increase the infiltration of T lymphocytes. • The combination of FUS and PD-1 inhibitors significantly enhances tumor T-cell infiltration, delays tumor progression, and prolongs survival. • Focused ultrasound therapy can promote the blood perfusion of the tumor, change the hypoxic environment of the tumor, and inhibit the growth of the tumor. To demonstrate the feasibility of using focused ultrasound to enhance delivery of PD-1 inhibitors in glioma rats and determine if such an approach increases treatment efficacy. C6 glioma in situ rat model was used in this study. Transcranial irradiation with FUS combined with microbubbles was administered to open the blood-brain barrier (BBB). The efficacy of BBB opening was evaluated in normal rats. The rats with glioma were grouped to evaluate the role of PD-1 inhibitors combined with FUS-induced immune responses in suppressing glioma when the BBB opens. Flow cytometry was used to examine the changes of immune cell populations of lymphocytes in peripheral blood, tumor tissue and spleen tissue of the rats. A section of rat brain tissue was also used for histological and immunohistochemical analysis. The survival of the rats was then monitored; the tumor progression and changes in blood perfusion of tumor were dynamically observed in vivo using multimodal MRI. FUS combined with microbubbles could enhance the blood perfusion of tumors by increasing the permeability of BBB ( p < 0.0001), thus promoting the infiltration of CD4 + T lymphocytes ( p < 0.01). Compared with the control group, the combination treatment group had increased in the infiltration number of CD4 + ( p < 0.05) and CD8 + T ( p < 0.05); the tumor volume of the combined treatment group was smaller than that of the control group ( p < 0.01) and the survival rate of the rats was prolonged ( p < 0.05). In this study, we demonstrated that the transient opening of the BBB induced by FUS enhanced tumor vascular perfusion and facilitated the delivery of PD-1 inhibitors, ultimately improving the therapeutic efficacy for glioblastoma.