A Review of Emerging Immunotherapeutic Strategies for IDH-Mutant Glioma

IDH-mutant gliomas (IMGs) are a unique subset of diffuse gliomas that follow a relatively indolent course compared to IDH-wildtype glioblastoma (GBM) but inevitably progress, often to a higher histologic grade. Current standard therapies, including surgery, chemoradiation, and the recently approved mutant IDH inhibitor (mIDHi) vorasidenib, provide limited disease control and are not curative. Given the immunosuppressive tumor microenvironment (TME) driven by the mutant IDH enzyme and its associated oncometabolite 2-hydroxyglutarate (2-HG), novel immunotherapies offer a promising avenue for treatment. The goal of this paper is to review the main immunologic characteristics that distinguish IMG from GBM, including reduced T cell infiltration and function, fewer myeloid cells, and increased immune-dampening signaling. We also evaluate the preclinical and clinical evidence for immunotherapeutic approaches with the most potential to induce meaningful clinical activity, such as immune checkpoint inhibitors, CAR T cells, tumor vaccines, myeloid redirection, and oncolytic viruses. Despite significant advances in immunotherapy for IMG, fundamental questions persist, including optimal timing and combination strategies, mechanisms underpinning treatment resistance, and strategies to overcome the suppressive microenvironment. Future exploration of these treatment modalities, with a focus on mitigating soluble immunosuppressive factors in the TME, enhancing in situ T cell persistence, and leveraging novel antigen targets, is critical for advancing the state of therapy for this presently incurable group of tumors.