PD-L1 expression in medulloblastoma: an evaluation by subgroup.

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PD-L1 expression in medulloblastoma: an evaluation by subgroup.

Oncotarget. 2018 Apr 10;9(27):19177-19191

Authors: Martin AM, Nirschl CJ, Polanczyk MJ, Bell WR, Nirschl TR, Harris-Bookman S, Phallen J, Hicks J, Martinez D, Ogurtsova A, Xu H, Sullivan LM, Meeker AK, Raabe EH, Cohen KJ, Eberhart CG, Burger PC, Santi M, Taube JM, Pardoll DM, Drake CG, Lim M

Abstract
Background: This study evaluated the expression of PD-L1 and markers of immune mediated resistance in human medulloblastoma (MB), the most common malignant pediatric brain tumor.
Results: Overall levels of PD-L1 in human MB were low; however, some cases demonstrated robust focal expression associated with increased immune infiltrates. The case with highest PD-L1 expression was a sonic hedgehog (SHH) MB. In cell lines, SHH MB, which are low-MYC expressing, demonstrated both constitutive and inducible expression of PD-L1 while those in Group 3/4 that expressed high levels of MYC had only inducible expression. In vitro, IFN-γ robustly stimulated the expression of PD-L1 in all cell lines while radiation induced variable expression. Forced high MYC expression did not significantly alter PD-L1.
Methods: Human MB tumor samples were evaluated for expression of PD-L1 and immune cell markers in relation to molecular subgroup assignment. PD-L1 expression was functionally analyzed under conditions of interferon gamma (IFN-γ), radiation, and MYC overexpression.
Conclusions: MB expresses low levels of PD-L1 facilitating immune escape. Importantly, TH1 cytokine stimulation appears to be the most potent inducer of PD-L1 expression in vitro suggesting that an inflamed tumor microenvironment is necessary for PD-1 pathway activation in this tumor.

PMID: 29721192 [PubMed]

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