Citations

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain tumor. Median survival is 15 months despite surgery, radiation, and chemotherapy. Immunotherapy is promising but GBM-mediated immunosuppression remains a barrier. Recently, extracellular vesicles (EVs) have been implicated in GBM-mediated immunosuppression through expression of the immune checkpoint molecule PD-L1. Data from our group has suggested this is predominantly through induction of immunosuppressive monocytes including myeloid-derived suppressor cells (MDSCs) and non-classical monocytes (NCMs). PD-L1 expression is increased in most nucleated cells following IFN-γ exposure. We, therefore, sought to determine if IFN-γ exposure would result in super-induction of immunosuppressive GBM EVs. EVs were harvested in vitro from matched differentiated and stem-like human GBM cell lines +/- IFN-γ. IFN-γ exposure did not alter EV production or expression of common EV markers but increased PD-L1 expression in EVs from differentiated but not stem-like GBM cells. In keeping with our earlier findings, no direct inhibition of T cell proliferation by stem-like or differentiated GBM EVs was observed regardless of IFN-γ exposure or PD-L1 expression. In contrast, differentiated but not stem-like GBM cell EVs induced MDSC and NCM differentiation from normal monocytes. This was increased following IFN-γ exposure and was dependent upon PD-L1 expression. Monocytes exposed to differentiated but not stem-like GBM cell EVs inhibited T cell proliferation in a similar manner (increased with IFN-γ exposure, decreased with PD-L1 knockdown). Thus, IFN-γ exposure results in super-induction of immunosuppressive EVs from differentiated but not stem-like GBM cells that increase MDSC and NCM differentiation in normal monocytes and increase their ability to inhibit T cell proliferation. These effects are dependent upon PD-L1 up-regulation induced by IFN-γ. This may be an important mechanism GBMs utilize to suppress anti-tumor T cell responses that are typically accompanied by increased IFN-γ expression.

Abstract Glioblastoma (GBM) is the most common and lethal primary brain tumor, and novel therapeutic strategies that make a substantial impact on outcomes are sorely needed. Immunotherapies have shown great promise in the treatment of a number of cancers in recent year, and a concerted effort is being made to apply these treatment paradigms to GBM. However, many GBM patients exhibit profound immunosuppression, likely limiting the efficacy of such approaches. The mechanisms of this immunosuppression are poorly understood, but tumor-derived extracellular vesicles (EVs), may play a role. We demonstrate that GBM-derived EVs induce the development of myeloid-derived suppressor cells (MDSCs) and non-classical monocytes (NCMs). We further demonstrate that these EV-induced monocytic cells are immunosuppressive, resulting in impaired T cell proliferation upon co-culture. We found that the immunosuppressive effects of tumor-derived EVs appear to be driven by the induction of these immunosuppressive monocytes, as EV treatment of T cells did not significantly impact T cell proliferation. Further, we sought to characterize the important of programmed death ligand 1 (PD-L1) in the induction of these immunosuppressive monocyte populations. We found PD-L1 to be expressed in the EVs from GBM cell lines, and that modulation in PD-L1 expression via either constitutive overexpression or shRNA-mediated knockdown resulted in concordant changes in expression in tumor-derived EVs. We demonstrate that PD-L1 is important for the induction of NCM but not for MDSCs. Taken together, these findings point to a significant role for tumor-derived EVs in the induction of immunosuppressive monocytes in GBM, and that these cells may be a driving force of systemic immunosuppression. PD-L1 is one factor expressed in EVs that has immunomodulatory properties, but additional EV cargo likely plays a major role in the induction of immunosuppressive cells.

Abstract Systemic immunosuppression following neurological insults including stroke, traumatic brain injury, and glioblastoma (GBM) causes mortality and leads to failure of immune-modulating therapies. Exact immunological nature and the underlying mechanisms of this immunosuppression are unknown. Our goal was to define effects of neurological insults given exclusively to the brain on the thymus. The thymus is the primary immune organ responsible for T-cell development and maintenance both in children and in adults. We evaluated the brain-thymus communication using the following neurological insults: physical injury, CNS viral infection, sterile injury, tumor implantation, and seizures. All insults resulted in significant thymic involution that was reversible upon clearance of the insult. Thymic involution did not occur following similar peripheral insults. We next demonstrated that the GL261 model of GBM recapitulates hallmark features of peripheral immunosuppression observed in GBM patients including low CD4 T-cell counts. Thus, we aimed to further study the immunosuppression affecting the thymus in this clinically relevant model. Principle component analysis following RNA-sequencing of thymi from naïve and glioma-bearing mice revealed unbiased separation of the groups suggesting that the thymus is directly affected by a brain tumor. To determine the extent to which thymic involution was caused by a soluble factor we employed parabiosis. We demonstrated that thymic involution was transferable from glioma-bearing to non-tumor-bearing parabionts. Similarly, serum taken from GL261 glioma-bearing mice potently inhibited proliferation of T-cells in vitro. Together our data demonstrate that CNS-specific insults, regardless of nature, cause immunosuppression by prompting thymic involution through circulating factors. This accounts at least partially for immune deficiencies observed following neurological injuries. Identification of this suppressive factor is crucial in designing future therapeutics for GBM patients, and patients with other acute and chronic neurological trauma.

The authors present the case of a man with a papillary craniopharyngioma, first diagnosed at 47 years of age, who experienced multiple recurrences. Review of the pathologic specimen from his first resection demonstrated the BRAF V600E mutation. With his most recent recurrence following previous surgery and radiotherapy, at 52 years of age, the decision was made to initiate treatment with the BRAF V600E inhibitor dabrafenib. Imaging following initiation of dabrafenib demonstrated reduction in tumor size. He remained on dabrafenib therapy for approximately 1 year and continued to demonstrate a good clinical result. At that time the decision was made to discontinue dabrafenib therapy and follow up with serial imaging. After more than 1 year of follow-up since stopping dabrafenib, the patient has continued to do well with no radiographic evidence of tumor progression and continues to be monitored with frequent interval imaging.

The authors present a case of delayed peroneal neuropathy following a lateral gastrocnemius rotational flap reconstruction. The patient presented 1.5 years after surgery with a new partial foot drop, which progressed over 3 years. At operation, a fascial band on the deep side of the gastrocnemius flap was compressing the common peroneal nerve proximal to the fibular head, correlating with preoperative imaging. Release of this fascial band and selective muscle resection led to immediate improvement in symptoms postoperatively.