ER-mitochondria contacts control surface glycan expression and sensitivity to killer lymphocytes in glioma stem-like cells

Glioblastoma is a highly heterogeneous aggressive primary brain tumor, with the glioma stem-like cells (GSC) being more sensitive to cytotoxic lymphocyte-mediated killing than glioma differentiated cells (GDC). However, the mechanism behind this higher sensitivity is unclear. Here, we found that the mitochondrial morphology of GSCs modulates the ER-mitochondria contacts that regulate the surface expression of sialylated glycans and their recognition by cytotoxic T lymphocytes and natural killer cells. GSCs displayed diminished ER-mitochondria contacts compared to GDCs. Forced ER-mitochondria contacts in GSCs increased their cell surface expression of sialylated glycans and reduced their susceptibility to cytotoxic lymphocytes. Therefore, mitochondrial morphology and dynamism dictate the ER-mitochondria contacts in order to regulate the surface expression of certain glycans and thus play a role in GSC recognition and elimination by immune effector cells. Targeting the mitochondrial morphology, dynamism, and contacts with the ER could be an innovative strategy to deplete the cancer stem cell compartment to successfully treat glioblastoma.

Synergy between CD8 T cells and Th1 or Th2 polarised CD4 T cells for adoptive immunotherapy of brain tumours

The feasibility of cancer immunotherapy mediated by T lymphocytes is now a clinical reality. Indeed, many tumour associated antigens have been identified for cytotoxic CD8 T cells, which are believed to be key mediators of tumour rejection. However, for aggressive malignancies in specialised anatomic sites such as the brain, a limiting factor is suboptimal tumour infiltration by CD8 T cells. Here we take advantage of recent advances in T cell biology to differentially polarise CD4 T cells in order to explore their capacity to enhance immunotherapy. We used an adoptive cell therapy approach to work with clonal T cell populations of defined specificity. Th1 CD4 T cells preferentially homed to and accumulated within intracranial tumours compared with Th2 CD4 T cells. Moreover, tumour-antigen specific Th1 CD4 T cells enhanced CD8 T cell recruitment and function within the brain tumour bed. Survival of mice bearing intracranial tumours was significantly prolonged when CD4 and CD8 T cells were co-transferred. These results should encourage further definition of tumour antigens recognised by CD4 T cells, and exploitation of both CD4 and CD8 T cell subsets to optimise T cell therapy of cancer.

Immune infiltration of spontaneous mouse astrocytomas is dominated by immunosuppressive cells from early stages of tumor development

Immune infiltration of advanced human gliomas has been shown, but it is doubtful whether these immune cells affect tumor progression. It could be hypothesized that this infiltrate reflects recently recruited immune cells that are immediately overwhelmed by a high tumor burden. Alternatively, if there is earlier immune detection and infiltration of the tumor, the question arises as to when antitumor competency is lost. To address these issues, we analyzed a transgenic mouse model of spontaneous astrocytoma (GFAP-V(12)HA-ras mice), which allows the study of immune interactions with developing glioma, even at early asymptomatic stages. T cells, including a significant proportion of Tregs, are already present in the brain before symptoms develop, followed later by macrophages, natural killer cells, and dendritic cells. The effector potential of CD8 T-cells is defective, with the absence of granzyme B expression and low expression of IFN-gamma, tumor necrosis factor, and interleukin 2. Overall, our results show an early defective endogenous immune response to gliomas, and local accumulation of immunosuppressive cells at the tumor site. Thus, the antiglioma response is not simply overwhelmed at advanced stages of tumor growth, but is counterbalanced by an inhibitory microenvironment from the outset. Nevertheless, we determined that effector molecule expression (granzyme B, IFN-gamma) by brain-infiltrating CD8 T-cells could be enhanced, despite this unfavorable milieu, by strong immune stimuli. This potential to modulate the strong imbalance in local antiglioma immunity is encouraging for the development and optimization of future glioma immunotherapies.