EphA2 is a receptor tyrosine kinase and is frequently overexpressed in a wide array of advanced cancers. We demonstrate in the current study that the EphA2 protein is restrictedly expressed in primary glioblastoma multiforme and anaplastic astrocytoma tissues in comparison to normal brain tissues. To evaluate the possibility of targeting EphA2 in glioma vaccine strategies, we stimulated human leukocyte antigen (HLA) A2+ peripheral blood mononuclear cells (PBMCs) obtained from healthy donors and glioma patients with autologous dendritic cells (DCs) loaded with synthetic EphA2883-891 peptide (TLADFDPRV), which has previously been reported to induce interferon-gamma in HLA-A2+ PBMCs. Stimulated PBMCs demonstrated antigen-specific cytotoxic T lymphocyte (CTL) responses as detected by specific lysis of T2 cells loaded with the EphA2883 peptide as well as HLA-A2+ glioma cells, SNB19 and U251, that express EphA2. Furthermore, in vivo immunization of HLA-A2 transgenic HHD mice with the EphA2883-891 peptide resulted in the development of an epitope-specific CTL response in splenocytes, despite the fact that EphA2883-891 is an autoantigen in these mice. Taken together, these data suggest that EphA2883-891 may be an attractive antigen epitope for molecularly targeted glioma vaccines.

We have created a novel cellular vehicle for gene therapy of malignant gliomas by transfection of murine bone marrow stroma cells (MSCs) with a cDNA encoding epidermal growth factor receptor (EGFR). These cells (EGFR-MSCs) demonstrate enhanced migratory responses toward glioma-conditioned media in comparison to primary MSCs in vitro. Enhanced migration of EGFR-MSC was at least partially dependent on EGF-EGFR, PI3-, MAP kinase kinase, and MAP kinases, protein kinase C, and actin polymerization. Unlike primary MSCs, EGFR-MSCs were resistant to FasL-mediated cytotoxicity and were capable of stimulating allogeneic mixed lymphocyte reaction, suggesting EGFR-MSCs possess suitable characteristics as vehicles for brain tumor immuno-gene therapy. Following injection at various sites, including the contralateral hemisphere in the brain of syngeneic mice, EGFR-MSCs were able to migrate toward GL261 gliomas or B16 melanoma in vivo. Finally, intratumoral injection with EGFR-MSC adenovirally engineered to secrete interferon-a to intracranial GL261 resulted in significantly prolonged survival in comparison to controls. These data indicate that EGFR-MSCs may serve as attractive vehicles for infiltrating brain malignancies such as malignant gliomas.

We tested whether modulation of the CNS-tumor microenvironment by delivery of IFN-α-transduced dendritic cells (DCs: DC-IFN-α) would enhance the therapeutic efficacy of peripheral vaccinations with cytokine-gene transduced tumor cells. Mice bearing intracranial GL261 glioma or MCA205 sarcoma received peripheral immunizations with corresponding irradiated tumor cells engineered to express IL-4 or GM-CSFs, respectively, as well as intratumoral delivery of DC-IFN-α. This regimen prolonged survival of the animals and induced tumor-specific CTLs that expressed TRAIL, which in concert with perforin and Fas ligand (FasL) was involved in the tumor-specific CTL activity of these cells. The in vivo antitumor activity associated with this approach was abrogated by administration of neutralizing mAbs against TRAIL or FasL and was not observed in perforin−/−, IFN-γ−/−, or FasL−/− mice. Transduction of the tumor cells with antiapoptotic protein cellular FLIP rendered the gene-modified cells resistant to TRAIL- or FasL-mediated apoptosis and to CTL killing activity in vitro. Furthermore, the combination therapeutic regimen was ineffective in an intracranial cellular FLIP-transduced MCA205 brain tumor model. These results suggest that the combination of intratumoral delivery of DC-IFN-α and peripheral immunization with cytokine-gene transduced tumor cells may be an effective therapy for brain tumors that are sensitive to apoptotic signaling pathways.