ID #221 Reactivation of fetal extracellular matrix programs drives immune exclusion in diffuse midline glioma
Bryce Thomas, Mika Persson, Evangeline Jackson, Florence Bartlett, Zac Germon, Md Masud Rana, Ryan Duchatel, Holly McEwen, Izac Findlay, Alicia Douglas, Birgit Kobbe, Raimund Wagener, Martin Larsen, Pouya Faridi, Jemma Mayall, Jay Horvat, Matthew DunAbstract
Diffuse midline glioma (DMG) is a universally fatal pediatric high-grade glioma characterized by a cold tumor immune microenvironment (TIME). While the extracellular matrix (ECM) is increasingly recognized as a key regulator of tumor–immune interactions and therapeutic responses in glioma, DMG-associated ECM proteins remain poorly defined. Here, we characterize tumor-derived components of the DMG ECM to identify regulators of immunosuppression and therapeutic resistance.
Quantitative membrane-enriched proteomics was performed on three patient-derived DMG cell lines (SU-DIPG-IV, SU-DIPG-VI, and SU-DIPG-XII) and compared with the blood–brain barrier endothelial control cell line hCMEC/D3. Here, we report the identification of the ECM constituent termed Protein-J4 (P-J4) as the most significantly upregulated ECM protein in DMG (log2FC = 3.95, p<0.0001), exceeding the differential expression of established therapeutic membrane and extracellular targets including B7-H3, IL-13Rα2, and PDGFRA. RNA-sequencing data from the Children’s Brain Tumor Network and St Jude PeCan databases detected increased P-J4 expression across multiple pediatric brain and solid malignancies, with high expression in pediatric high-grade gliomas correlating with significantly worse overall survival (Kaplan–Meier, p=0.0379). Consistent with its role in fetal tissue development and ECM-associated growth factor bioavailability, including pro–TGF-β, expression of P-J4 may drive immune exclusion and negatively influence patient outcomes in DMG.
To functionally interrogate these findings, we are establishing a P-J4 knockout DMG in vitro model and will conduct murine in vivo studies alongside spatial transcriptomics and ATAC-sequencing to define immune suppression and treatment resistance pathways. In parallel, we are currently characterizing a cohort of pediatric brain tumors (n = 120) and relevant healthy tissue controls for P-J4 expression and correlating with immune infiltration and immunosuppression signatures using our novel anti-P-J4 humanized antibodies. In conclusion, we have identified P-J4 as a translationally relevant and targetable ECM-constituent in DMG, with a potential role in diffuse growth, infiltration, immunosuppression and therapeutic resistance.