Immune escape of gliomas

Systemic injection of TLR1/2 agonist improves adoptive antigen-specific T cell therapy in glioma-bearing mice

Adoptive immunotherapy is an attractive strategy for glioma treatment. However, some obstacles still need be overcome. In this study, GL261-bearing mice treated with adoptively transferred antigen-specific T cells and systemic injection of bacterial lipoprotein (BLP), a TLR1/2 agonist, got a long-term survival and even immune protection. By analyzing adoptive T cells, it was found that BLP maintained T cell survival, proliferation and anti-tumor efficacy in the brains of tumor-bearing hosts. Moreover, tumor microenvironment was modified by up-regulating IFN-γ-secreting CD8+ T cells and down-regulating MDSC, which might be related with high CXCL10 and low CCL2 expression. In addition, TLR2 deficiency abrogated therapeutic effect with increased MDSC accumulation and decreased IFN-γ-secreting CD8+ T cells in the brains. Thus, the systemic injection of BLP could improve the adoptive T cell therapy by maintaining T cell persistence, modifying the tumor microenvironment and even inducing systemic anti-tumor immunity, which might offer a clinically promising immunotherapeutic strategy for glioma.

Proteomic comparison of 3D and 2D glioma models reveals increased HLA-E expression in 3D models is associated with resistance to NK cell-mediated cytotoxicity

Three-dimensional cell culture techniques can better reflect the in vivo characteristics of tumor cells compared with traditional monolayer cultures. Compared with their 2D counterparts, 3D-cultured tumor cells showed enhanced resistance to the cytotoxic T cell-mediated immune response. However, it remains unclear whether 3D-cultured tumor cells have an enhanced resistance to NK cell cytotoxicity. In this study, a total of 363 differentially expressed proteins were identified between the 2D- and 3D-cultured U251 cells by comparative proteomics, and an immune-associated protein-protein interaction (PPI) network based on these differential proteins was constructed by bioinformatics. Within the network, HLA-E, as a molecule for inhibiting NK cell activation, was significantly up-regulated in the 3D-cultured tumor cells. Then, we found that the 3D-cultured U251 cells exhibited potent resistance to NK cell cytotoxicity in vitro and were prone to tumor formation in vivo. The resistance of the 3D-cultured tumor cells to NK cell lysis was mediated by the HLA-E/NKG2A interaction because the administration of antibodies that block either HLA-E or NKG2A completely eliminated this resistance and significantly decreased tumor formation. Taken together, our findings indicate that HLA-E up-regulation in 3D-cultured cells may result in enhanced tumor resistance to NK cell-mediated immune response.

Immunotherapy of pediatric brain tumor patients should include an immunoprevention strategy: a medical hypothesis paper

Adults diagnosed with Glioblastoma multiforme (GBM) are frequently faced with a 7% chance of surviving 2 years compared with pediatric patients with GBM who have a 26% survival rate. Our recent screen of possible glioma-associated antigen precursor protein (TAPP) profiles displayed from different types of pediatric brain tumors showed that pediatric patients contained a subset of the tumor antigens displayed by adult GBM patients. Adult GBM possess at least 27 tumor antigens that can potentially stimulate T cell immune responses, suggesting that these tumors are quite antigenic. In contrast, pediatric brain tumors only expressed nine tumor antigens with mRNA levels that were equivalent to those displayed by adult GBM. These tumor-associated antigens could be used as possible targets of therapeutic immunization for pediatric brain cancer patients. Children have developing immune systems that peak at puberty. An immune response mounted by these pediatric patients might account for their extended life spans, even though the pediatric brain tumors express far fewer total tumor-associated antigens. Here we present a hypothesis that pediatric brain tumor patients might be the best patients to show that immunotherapy can be used to successfully treat established cancers. We speculate that immunotherapy should include a panel of tumor antigens that might prevent the out-growth of more malignant tumor cells and thereby prevent the brain tumor relapse. Thus, pediatric brain tumor patients might provide an opportunity to prove the concept of immunoprevention.

TLR ligands in the local treatment of established intracerebral murine gliomas

Local TLR stimulation is an attractive approach to induce antitumor immunity. In this study, we compared various TLR ligands for their ability to affect murine GL261 cells in vitro and to eradicate established intracerebral murine gliomas in vivo. Our data show that GL261 cells express TLR2, TLR3, and TLR4 and respond to the corresponding TLR ligands with increasing MHC class I expression and inducing IL-6 secretion in vitro, while TLR5, TLR7, and TLR9 are essentially absent. Remarkably, CpG-oligonucleotides (CpG-ODN, TLR9) appeared to inhibit GL261 cell proliferation in a cell-type specific, but CpG-motif and TLR9-independent manner. A single intratumoral injection of CpG-ODN most effectively inhibited glioma growth in vivo and cured 80% of glioma-bearing C57BL/6 mice. Intratumoral injection of Pam3Cys-SK4 (TLR1/2) or R848 (TLR7) also produced a significant survival benefit, whereas poly(I:C) (TLR3) or purified LPS (TLR4) stimulation alone was not effective. Additional studies using TLR9(+/+) wild-type and TLR9(-/-) knockout mice revealed that the efficacy of local CpG-ODN treatment in vivo required TLR9 expression on nontumor cells. Additional experiments demonstrated increased frequencies of tumor-infiltrating IFN-gamma producing CD4(+) and CD8(+) effector T cells and a marked increase in the ratio of CD4(+) effector T cells to CD4(+)FoxP3(+) regulatory T cells upon CpG-ODN treatment. Surviving CpG-ODN treated mice were also protected from a subsequent tumor challenge without further addition of CpG-ODN. In summary, this study underlines the potency of local TLR treatment in antiglioma therapy and demonstrates that local CpG-ODN treatment most effectively restores antitumor immunity in a therapeutic murine glioma model.

Cancer-associated immune-mediated syndromes: Pathogenic values and clinical implementation

The ability of tumors to provoke formation of cancer-associated secondary immunodeficiency (CASID) with predominant suppression of CMI and cancer-associated secondary immunodeficiency with clinical autoimmunity syndrome (CASICAS) with triggering of a set of the autoimmune deviations is appearing to be a key event in the restriction of hosts' anti-tumor immunity. Earlier the existence of the above-mentioned syndromes was demonstrated in BCC and GBM patients. In order to reach a point where immunological phenotypes in GBM and BCC can be clarified clinically and, partly, pathogenically, we have conducted a series of studies of typical and atypical types of immune responsiveness in patients with GBM and BCC. For GBM and BCC three scenarios of the involvement of the immune responsiveness have been established in a series of our studies, i.e., (i) malignancy with no immunopathology, (ii) malignancy as CASID, and (iii) malignancy as CASICAS. All of those scenarios demonstrated significant differences in their immune-mediated manifestations which, in turn, were proven to reveal close associative relationships with a specific clinicopathologic type and clinical manifestations of the tumor. CASID and CASICAS share two common features, i.e., (i) signs of immunodeficiency and (ii) a tandem of the deviations within the adaptive and innate links of the host immune responsiveness. At the same time, CASID and CASICAS are distinct pathogenically and clinically, and in terms of depth of the immune deviations observed, CASID patients manifest a breakage in both links, whereas in CASICAS patients, a breakage in the adaptive link would dominate. To get these differences clarified, we summarized major types of the immune imbalances and sets of clinical and clinicopathologic manifestations to illustrate the above-mentioned features in CASID and CASICAS patients. There are distinct close correlations between clinicopathologic features of the disease course and sets of the immune-mediated imbalances in patients harboring the tumors. The latter implicates a panel of the new immunodiagnostic and immunoprognostic criteria for patients with solid tumors, i.e., BCC, MCC and GB, which is of great value for clinical practice. In particular, the blood levels of some of the immunocompetent cells, state of their functional activity, serum titers of the antigenic markers and autoantibodies, apoptotic parameters, and others may be accepted as additional and clinically informative criteria to be implemented for immunological monitoring and immunotherapy of patients with solid tumors.

CD4+FoxP3+ regulatory T cells gradually accumulate in gliomas during tumor growth and efficiently suppress antiglioma immune responses in vivo

The suppressive activity of regulatory T cells (Treg) has been implicated as an important factor limiting immune mediated destruction of tumor cells. However, not much is known about the presence and function of Treg within tumors. Here we show in a syngeneic murine glioma model a time-dependent accumulation of CD4+FoxP3+ Treg in brain tumors. Further analysis revealed a time-dependent upregulation of CD25, CTLA-4, GITR and CXCR4 on intratumoral CD4+FoxP3+ Treg during tumor growth. Moreover, freshly isolated intratumoral Treg were highly suppressive when tested directly ex vivo. Treatment with anti-CD25 monoclonal antibodies (mAbs) significantly reduced the number of these highly suppressive CD4+FoxP3+ cells within the growing tumor and provoked a CD4 and CD8 T cell dependent destruction of the glioma cells. Combining Treg depletion with administration of blocking CTLA-4 mAbs further boosted glioma-specific CD4+ and CD8+ effector T cells as well as antiglioma IgG2a antibody titers resulting in complete tumor eradication without any signs of autoimmunity. These data illustrate that intratumoral accumulation and activation of CD4+FoxP3+ Treg act as a dominant immune escape mechanism for gliomas and underline the importance of controlling tumor-infiltrating Treg in glioma immunotherapy.

Regeneration and Tolerance Factor: A Novel Mediator of Glioblastoma-Associated Immunosuppression

Regeneration and tolerance factor (RTF) was originally identified in placenta where it is thought to be essential for fetal allograft survival. Here we report that RTF mRNA and protein are also expressed in human glioma cells in vitro and in vivo. Suppression of RTF expression by RNA interference promotes the lysis of glioma cells by natural killer (NK) and T cells in vitro. Moreover, RTF-depleted glioma cells are less tumorigenic than control cells in nude mice in vivo. Depletion of NK cells in these animals abolished this effect. RTF is thus a novel aberrantly expressed molecule which confers immune privilege to human malignant gliomas.

Double suicide gene therapy using a replication defective herpes simplex virus vector reveals reciprocal interference in a malignant glioma model

Herpes simplex virus thymidine kinase (HSV-TK) and Escherichia coli cytosine deaminase (CD) are non-mammalian enzymes capable of converting innocuous prodrugs into cytotoxic metabolites. Both enzymes have been utilized independently, as well as together in 'suicide' gene therapy protocols to eliminate tumor cells in vitro and in vivo. We have used a set of replication defective HSV vectors expressing either or both enzymes to compare the efficacies of single and double suicide gene therapies in the 9L gliosarcoma model in vitro and in vivo. In cell culture experiments at high and low multiplicities of infection, combined expression of the two genes by vector TOCD/TK along with exposure to the matching prodrugs (ganciclovir and 5-fluorocytosine) showed increased cytotoxicity compared with exposure to either prodrug alone. However, the two gene combination was inferior to single gene treatments, suggesting that HSVtk and CD are mutually counteractive in the prodrug-dependent killing of glioma cells. In animal experiments, survival was not significantly prolonged by administration of both prodrugs to TOCD/TK-treated animals, while each single gene/prodrug pair resulted in increased survival. These results indicate that single suicide gene systems employing HSVtk or CD may be preferable over combinations of the two.