Abstract
Pediatric high-grade gliomas (pHGG) drastically differ from their adult counterparts in terms of genetic and epigenetic alterations, suggesting they may also differ in the constituency of their tumor microenvironment. It is known tumor associated macrophages (TAMs) can constitute up to 30–40% of the total tumor cell mass in adult high-grade gliomas, yet little is known for pHGGs. This raises the question of whether pHGGs possess a distinct constituency of TAMs due to their unique genetic and epigenetic landscapes. To uncover the composition and behavior of TAMs in pHGG we utilize RCAS/tva, a somatic cell-type specific gene transfer system in which we administer RCAS-PDGFA or RCAS-PDGFB to Nestin-positive cells in the brain of immunocompetent Cdkn2a knockout mice. We observe PDGFB-driven tumors have a significantly lower median survival compared to PDGFA-driven tumors. PDGFB tumors also have increased infiltration of TAMs, made evident by immunohistochemical staining for IBA1. Flow cytometry indicates the increased number of TAMs is due to bone-marrow derived inflammatory monocytes, not the microglial population. Unsupervised clustering and principle component analysis indicates these tumors possess distinct expression profiles. Several chemokines and receptors are highly expressed in PDGFB tumors such as Ccl2, Ccl3, and Ccl7, suggesting chemokine mediated infiltration of TAMs may be occurring. To study PDGF signaling and TAM infiltration in human pHGGs, we stained over 40 tumors for IBA1, PDGF-receptors, and PDGF-ligands. There is a positive correlation between PDGFRβ, PDGFB, and CD31 staining with IBA1, suggesting a stromal role exists for the infiltration of TAMs. Current in vivo studies are being conducted to determine if TAM infiltration can be inhibited by genetically or pharmacologically targeting chemokine signaling pathways. In vivo and in vitro studies are also being performed to determine which cell types are the main sources of chemokines and inflammatory molecules are in the microenvironment.