The Role of Tregs in Human Glioma Patients and their Inhibition with a Novel STAT-3 Inhibitor

Abstract

INTRODUCTION: The incidence of the immune inhibitor regulatory T cells (Tregs), activated by STAT-3, within intrinsic central nervous system malignancies is unknown. Our hypothesis was that the most malignant gliomas have a prominent glioma infiltrating Treg population that contributes to the immunosuppressive biology and prognosis of patients and that the generation of Tregs can be blocked by a STAT-3 inhibitor (WP1066), allowing for the immunological clearance of intracerebral tumors. METHODS: We measured the incidence of Tregs in 135 glial tumors on a glioma microarray using immunohistochemical analysis and correlated the presence of Tregs with prognosis using uni- and multivariate analyses. The anti-tumor activities and mechanisms of efficacy of WP1066 were investigated in vitro and in an established intracerebral syngeneic murine tumor model. RESULTS: We observed significant differences in the prevalence of Tregs between astrocytic and oligodendroglial tumors and between different grades. Tregs were most frequently identified in glioblastoma multiforme, but their presence was not a prognostic indicator. In mice with established intracerebral syngeneic tumors, long-term survival (>78 d) was observed in 80% of WP1066-treated mice compared with a median survival of 15 days in control mice. The in vivo efficacy of WP1066 was completely ablated in nude animals indicating the crucial role of the immune system in mediating tumor clearance with STAT-3 inhibitor agents. Although blockade of STAT-3 did not induce immunological memory or enhance humeral responses, treatment inhibited Treg chemokines and the generation of Tregs, which secondarily increased the cytotoxic tumor immune clearance by T cells. CONCLUSION: Treg infiltration differed significantly in the tumors according to lineage, pathology, and grade. Tregs appeared to have the highest predilection for tumors of astrocytic lineages and specifically for high-grade gliomas, such as GBMs. Tregs can be markedly inhibited with anti-STAT-3 agents and this results in marked in vivo activity against established intracerebral tumors. The use of STAT-3 inhibitors for patients with malignant glioma warrants consideration in clinical trials.