The immune landscape of common CNS malignancies: implications for immunotherapy

Immunotherapy has enabled remarkable therapeutic responses across cancers of various lineages, albeit with some notable exceptions such as glioblastoma. Several previous misconceptions, which have impaired progress in the past, including the presence and role of the blood-brain barrier and a lack of lymphatic drainage, have been refuted. Nonetheless, a subset of patients with brain metastases but, paradoxically, not the vast majority of those with gliomas are able to respond to immune-checkpoint inhibitors. Immune profiling of samples obtained from patients with central nervous system malignancies using techniques such as mass cytometry and single-cell sequencing along with experimental data from genetically engineered mouse models have revealed fundamental differences in immune composition and immunobiology that not only explain the differences in responsiveness to these agents but also lay the foundations for immunotherapeutic strategies that are applicable to gliomas. Herein, we review the emerging data on the differences in immune cell composition, function and interactions within central nervous system tumours and provide guidance on the development of novel immunotherapies for these historically difficult-to-treat cancers. Patients with primary central nervous system (CNS) malignancies largely do not derive benefit from immune-checkpoint inhibitors. Paradoxically, a subset of those with CNS metastases from tumours located outside of the CNS will respond to the same approach. In this Perspective, the authors explore the key differences in the immune cell composition of primary CNS malignancies and brain metastases and provide guidance on potential alternative immunotherapies that might be effective in patients with these historically difficult-to-treat malignancies.

Automated summary

Immunotherapy has shown remarkable therapeutic responses in treating various cancers, with exceptions like glioblastoma. Immune profiling of samples from central nervous system tumors and brain metastases has revealed fundamental differences in immune composition, providing guidance for novel immunotherapeutic strategies.