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IMAGE: IBA-1 staining reveals heavy microglial infiltration in SHH MB with many microglia co-expressing PD-L1. Immunohistochemistry of one representative SHH MB, 18872, stained for IBA-1 (A) and PD-L1 (B). Many of… view more 

Credit: Allison M. Martin at amarti65@jhmi.edu

This study evaluated the expression of PD-L1 and markers of immune mediated resistance in human medulloblastoma, the most common malignant pediatric brain tumor.

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.

MB expresses low levels of PD-L1 facilitating immune escape.

“Tumors in the SHH subgroup are characterized by genetic alterations activating this key developmental pathway. WNT subgroup tumors have alterations in the wingless/ -catenin developmental pathway.”

Most patients are assessed for PD-L1 expression prior to starting therapy, but the expression of PD-L1 during the entire course of treatment remains unclear, as does the relationship between changing PD-L1 expression and therapeutic responses.

In support of PD-L1 pathway activity in human MB, the researchers demonstrated that MB cell lines robustly up-regulated PD-L1 when they simulated an anti-tumor immune response in vitro by exposing the cell lines to recombinant

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