The phagocyte in human gliomas

Microglia phagocytose alloreactive CTL-damaged 9L gliosarcoma cells

Intracranial adoptive transfers of alloreactive cytotoxic T lymphocytes (aCTL) for brain tumor treatment were safe and showed promise in preclinical and early clinical trials. To better understand the endogenous immune responses that may ensue following cellular therapy with aCTL, we examined the ability of microglia to phagocytose aCTL-damaged and undamaged rat 9L gliosarcoma cells in vitro and in vivo. In vitro, 5.5+/-0.9% of microglial cells isolated from adult tumor-bearing rat brains phagocytosed aCTL-damaged 9L cells, whereas microglia did not bind to or ingest undamaged 9L cells. Addition of supernates from either 9L cell cultures or from aCTL+9L co-incubate cell cultures to microglia did not significantly alter their ability to bind to or phagocytose damaged glioma cells even though the latter contained T helper 1 and 2 cytokines. At 3 days following intracranial 9L cell infusion, 17.5+/-0.1% of the microglia phagocytosed CFSE-labeled aCTL-damaged 9L tumor cells within the adult rat brain, confirming the in vitro data. The results suggest that microglia within the tumor microenvironment of the adult rat glioma model selectively remove damaged, but not undamaged, glioma cells.

Robust ability of IFN-gamma to upregulate class II MHC antigen expression in tumor bearing rat brains

T cells are attractive for delivering therapy to brain tumor, especially disseminated micro-tumor. However, to trigger effector function, tumor antigen must be re-presented to T cells, via major histocompatibility complex (MHC) proteins, at the tumor site. In normal brain, MHC+ antigen-presenting cells (APC) are rare, but abundant after gamma interferon (IFN-gamma) injection. Here we studied tumor-bearing brains. IFN-gamma (or buffer) was injected stereotactically into brains with established tumors from a panel of immunologically varied glioma cell lines, some expressing b-galactosidase as a micro-tumor marker. Four days later, cryostat sections were stained for tumor and MHC proteins. In phosphate-buffered saline-injected controls, class II MHC+ potential APC (microglia, macrophages) were seen only at (some) tumor sites. In rats that received IFN-gamma, class II+ potential APC were widespread, including all actual and potential micro-tumor sites and all tumor-free areas. In the same slides, neither class I nor class II MHC antigen was detected in neural cells or most tumor cells. This MHC pattern favors indirect re-presentation of tumor antigen, by tumor-adjacent APC. The robust response to IFN-gamma might also be exploited in other ways: activated microglia and macrophages can attack tumor directly, and class II+ APC may help mark micro-tumor sites.

Macrophage/microglial cell subpopulations in glioblastoma multiforme relapses are differentially altered by radiochemotherapy

Following surgical removal of glioblastoma multiforme (GBM), radiochemotherapy impedes neoplastic outgrowth and relapse formation. Macrophages/microglial cells are believed to be potent mediators of the host defense system in GBM. However, little is known about their alteration by postsurgical therapies. We have now analyzed expression of LCA (leucocyte common antigen), CD68 (phagocytic cells), HLA-DR, -DP, -DQ (MHC class II), MRP-8 (myeloid-related protein, S100A8), MRP-14 (S100A9), LCF (lymphocyte chemoattractant factor, IL-16) and NOS II (inducible nitric oxide synthase) in macrophages/microglial cells in 39 GBM relapses and their matched primary tumors. Following surgery of the primary tumors, 15 patients received irradiation and chemotherapy, 17 irradiation and 7 no treatment. In irradiated relapses, we observed significantly more macrophages/microglial cells expressing MRP-14 compared to untreated GBM relapses. Furthermore, we observed a significant increase of CD68 expressing macrophages/microglial cells in patients without postsurgical treatment, but not in those with radiochemotherapy. In conclusion, our findings suggest that radiochemotherapy alters the number of MRP-14 expressing cells. The lacking increase of CD68 expressing cells in patients with radiochemotherapy suggests depletion of this cell type by postsurgical therapy.