BTK inhibition enhances immunovirotherapy in glioblastoma via tertiary lymphoid structure modulation.

Glioblastoma (GBM) is a highly aggressive type of glioma that is resistant to immunotherapy and is associated with poor prognosis, largely due to its immunosuppressive tumor microenvironment. Bruton's tyrosine kinase (BTK) is a non-receptor kinase that not only plays an important role in oncogenic signaling, particularly in tumor growth, but also regulates the activity of tumor-infiltrating myeloid cells, including dendritic cells, macrophages, and microglia in brain tumors. High BTK expression is associated with poor survival in patients with glioma. Oncolytic herpes simplex virus type 1 (oHSV)-derived virotherapy, a novel treatment strategy, has demonstrated effectiveness against GBM; however, its efficacy is limited by the tumor microenvironment. In this study, we found that BTK is predominantly expressed in GBM-infiltrating myeloid cells. Intratumoral injection of oHSV not only promotes infiltration of myeloid cells and T cells but also activates BTK in these myeloid cells, thereby limiting oHSV infection and replication in tumor cells. Combination treatment with BTK inhibitor ibrutinib improves anti-tumor efficacy of oHSV in both human GBM12 xenograft and syngeneic murine GSC005 models. Mechanistically, BTK inhibition increases oHSV-mediated tumor cell death (cleaved caspase-3) and cytotoxic CD8+ T cell infiltration, while decreasing tumor cell proliferation (Ki-67). BTK inhibition not only suppresses oHSV clearance by tumor-infiltrating microglia and macrophages but also reduces their pro-invasive effects on tumor cells. Addition of IDO inhibitor, an immune modulator, further prolongs survival in tumor-bearing mice in a syngeneic GBM model. Single-cell mRNA sequencing (scRNA-seq) analysis indicates that combination treatment modifies key signaling pathways in both tumor-infiltrating myeloid cells (macrophages and microglia) and CD8+ T cells. Further analysis shows that BTK inhibition, with or without IDO inhibition, promotes the formation of tumor-infiltrating tertiary lymphoid structures (TLS) during intratumoral oHSV treatment, subsequently remodeling T cell, NKT cell, and monocyte-macrophage populations. These results indicate that BTK inhibition exerts multifaceted effects in enhancing the anti-tumor efficacy of oHSV therapy.