Abstract
INTRODUCTION
Glioblastoma (GBM) typically recurs after standard of care therapies. A major obstacle is that GBMs employ various mechanisms to suppress the host immune system, preventing destruction and removal of cancer cells. A better understanding of the crosstalk mechanisms between tumor and immune cell types is needed to advance immunotherapeutic approaches against GBM. GBMs contain primary cilia, organelles likened to both cellular 'antennae' and transmitters, and their presence is associated with more aggressive and treatment resistant tumors.
OBJECTIVE
To explore whether ciliated GBM cells associate with infiltrating immune cells and to determine if these interactions are specific for certain immune cell populations.
METHODS
We immunostained GBM patient specimens and sections from syngeneic mouse models of GBM for markers of cilia (ARL13B and gTub) together with various immune cell markers (CD45, CD11b, Ly-6 B.1, CD3). Cilia were also examined in brain tumors generated in CCR2
+/rfp/CX3CR1
+/gfp mice, to evaluate the proximity of glioma cell cilia to CCR2- and CX3CR1-expressing myeloid cell subpopulations (brain resident microglia as well as peripheral-derived macrophages and monocyctic- MDSCs (M-MDSCs). Proximity of tumor cell cilia to different markers or cell types was quantified using nearest neighbor analyses.
RESULTS
In patient samples, CD45+ cells extended processes that contacted the tumor cilia and cilia tip. Similar observations were made in intracranial GBM-bearing mice where we detected juxtaposition of cilia with recruited immune cells (i.e. CD45, CD11b and Ly-6B.1). Notably, cilia predominately associated with immune-suppressive M-MDSCs. Further, CD3+ T cells rarely juxtaposed tumor cilia and maintained greater distances away from ciliated tumor cells compared to M-MDSCs.
CONCLUSION
Our data suggest specific interactions between ciliat ed tumor cells and select immune-suppressive cell types, raising the possibility immunologically cold tumors may contain more ciliated cells. Ongoing studies are examining how the tumor immune cell landscape develops depending on the presence of tumor cilia.
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