Introduction: Glioblastoma Multiforme (GBM) ranks among the most lethal of all human cancers, with current therapy offering only palliation. The causes of treatment failure are myriad, but accumulating data support a subset of myeloid derived immune cells, specifically tumor-associate macrophages (TAMs) that contribute to worsening outcomes. Defensins, small molecules with chemotactic properties that play roles in innate immunity, have been proposed as one potential contributor of TAMs in GBM immunomodulation. One particular defensin, human-ß-defensin- 3 (HBD3) is dysregulated in head and neck cancers and is found to be elevated in GBM samples. Based on the immunomodulatory role of HBD3 outside the CNS, we hypothesized that HBD3 affects tumor-associated macrophages and microglia and contributes to immune-evasion in GBM.
Methods: Immunohistochemistry (IHC) of primary tumor sections revealed the presence of HBD-3 in the tumor periphery. Colocalization of HBD-3 with stem cell markers, SOX2 and Nestin, demonstrates that HBD3 expressing cells were glioma stem cells (GSCs). IHC also revealed the presence of CD68+ macrophages alongside HBD-3 expressing SOX2+ GSCs. GSCs were isolated from GBM tumors by FACS. QT-PCR revealed a 7-fold increase in the expression of HBD3 in GSCs compared to control neural stem cells (NSCs). Chemotaxis assays demonstrate that recombinant HBD3 chemoattracts macrophages and microglia associated with GBM.
Results: Our results suggest that HBD3 is expressed by glioma stem cells and plays a role in immunomodulation. In particular, the ability of HBD3 to attract macrophages suggests that it may play a role in the M1 to M2 phenotype switch of macrophages –allowing for immune evasion. Future experiments include blocking the known HBD-3 receptors, including CCR2 and CCR6, to determine their role in HBD-3 mediated chemotaxis.
Conclusions: Understanding the role of immune cells in the tumor microenvironment is essential for development of new therapies for treatment of GBM.
Patient Care: Better understanding of immune suppression will lead to better treatment
Learning Objectives: Understand the physiology of h-BD3;
Understand the physiology of M1 and M2 macrophages
Understand the role of immuntherapy