Protective effect of immunization with virus-infected glioma cells against intracerebrally implanted glioma in mice

The implications of nitric oxide metabolism in the treatment of glial tumors

Glial tumors are the most common intracranial malignancies. Unfortunately, despite such a high prevalence, patients' prognosis is usually poor. It is related to the high invasiveness, tendency to relapse and the resistance of tumors to traditional methods of treatment. An important link in the aspect of these issues may be nitric oxide (NO) metabolism. It is a very complex mechanism with multidirectional effects on the neoplastic process. Depending on the concentration axis, it can both exert pro-tumor action as well as contribute to the inhibition of tumorigenesis. The latest observations show that the control of its metabolism can be very helpful in the development of new methods of treating gliomas, as well as in increasing the effectiveness of the agents currently used. The influence of nitric oxide and nitric oxide synthase (NOS) activity on glioma stem cells seem to be of particular importance. The use of specific inhibitors may allow the reduction of tumor growth and its tendency to relapse. Another important feature of GSCs is their conditioning of glioma resistance to traditional forms of treatment. Recent studies have shown that modulation of NO metabolism can suppress this effect, preventing the induction of radio and chemoresistance. Moreover, nitric oxide is involved in the regulation of a number of immune mechanisms. Adequate modulation of its metabolism may contribute to the induction of an anti-tumor response in the patients' immune system.

TGF-beta2 inhibition augments the effect of tumor vaccine and improves the survival of animals with pre-established brain tumors

TGF-beta2 secretion by high grade gliomas has been implicated as one of the major factors contributing to tumor growth, alterations in the host immune response to tumor, and failure of gliomas to respond to current immunotherapy strategies. We hypothesized that targeted delivery and inhibition of TGF-beta2 by TGF-beta2 antisense oligonucleotides (AS-ODNs) would overcome tumor-induced immunosuppression and enhance the capacity of tumor vaccines to eradicate established brain tumors. Utilizing the mRNA sequences of TGF-beta2, specific AS-ODNs were constructed and tested for their ability to inhibit TGF-beta2 production in 9L glioma cells. The effect of combining local intracranial administration of antisense ODNs with systemic tumor vaccine was examined. Fisher 344 rats were vaccinated subcutaneously with irradiated 9L tumor cells 3 days after intracranial tumor implantation. Four days after vaccination, ODNs were administered into the tumor mass and survival was followed. ODNs delivered locally distributed widely within the brain tumor mass and inhibited TGF-beta2 expression. Survival of tumor-bearing rats treated with the combination of local antisense and systemic tumor vaccine was significantly enhanced (mean survival time (MST): 48.0 days). In contrast, MST for animals treated with nonsense plus vaccine, vaccine alone, antisense alone or PBS showed no survival advantage and no statistical differences between groups (33.5 days, 29.0 days, 37.5 days, and 31.5 days, respectively). Our data supports the hypothesis that local administration of antisense TGF-beta2 ODNs combined with systemic vaccination can increase efficacy of immunotherapy and is a novel, potentially clinically applicable, strategy for high-grade glioma treatment.

Time course analysis and modulating effects of established brain tumor on active-specific immunotherapy

OBJECT

There have been numerous attempts to establish an effective immunotherapy for the treatment of brain tumors. To date, reliable methods to manipulate the immune system for promoting brain tumor regression have been disappointing. Generation of active immune responses in most of these studies was only possible in the absence of viable tumor cells, suggesting that immunotherapy can only be used as preventive therapy. In few studies the investigators have demonstrated success in using immunotherapy to treat a preestablished intracranial tumor. Using the 9L intracranial glioma model, the authors sought to delineate the underlying mechanisms for these observations.

METHODS

In animals vaccinated with irradiated 9L glioma cells and interferon-gamma 14 and 7 days prior to intracranial tumor cell challenge, a significant increase in survival was shown. In contrast, vaccinations applied 3 days prior to, at the time of (Day 0) or 7 days after intracranial tumor cell challenge failed to influence survival. Histological examination of brain tissue specimens obtained in animals vaccinated before or after tumor cell challenge showed no difference in the degree of peritumoral mononuclear cell infiltration. When activated spleen cells obtained obtained from these animals were assayed for cytotoxicity and proliferative capacity, only those spleen cells derived from animals vaccinated prior to intracranial tumor cell challenge showed enhanced activity.

CONCLUSIONS

These data support the presence of a strong modulatory effect of tumor on local and systemic antitumoral immune response. This immunosuppression appears to be secondary to a direct effect on T-cell function. Reversal of this immunosuppression may be a useful adjunct to tumor vaccine therapy.

Immunization with mutagen-treated (tum-) cells causes rejection of nonimmunogenic rat glioma isografts

The ethyl-N-nitrosourea-induced rat glioma N32 was treated with the mutagenic compound N-methyl-N'-nitro-N-nitrosoguanidine and the surviving cells cloned by limited dilution. Out of 20 clones tested 8 did not produce tumors subcutaneously even after challenge doses 3 log units above the minimal tumor dose for N32. All of 5 clones grew in a retarded manner intracerebrally but produced tumors in some animals. Preimmunizations with three of the rejected clones (tum-) gave protection against subcutaneous and intracerebral isografts of the unmutated N32. This effect could be enhanced if the cells used for immunizations were pretreated with interferon gamma (IFN gamma) for 48 h. If immunizations were started subsequent to challenge, only immunization with one of two tested tum- clones pretreated with IFN gamma induced significant rejection against intracerebral N32 isografts. Both N32 and its tum- clones were MHC class I positive and MHC class II negative. IFN gamma treatment enhanced the MHC class I expression with 20%-90% on the tum- clones and with 40% on N32. MHC class II expression could be induced on N32 cells after 7 days of IFN gamma treatment but not on any of the tum- clones tested. We conclude that the enhancing effect of IFN gamma treatment on tumor isograft rejection may depend on up-regulation of MHC class I but not of MHC class II. This investigation demonstrates that it is possible to induce rejection of weakly immunogenic intracerebral brain tumors by immunization with selected highly immunogenic tumor cell mutants. In conjunction with relevant cytokines, the cross-protective effect of these tum- variants might be further enhanced and serve as a model for immunotherapy against malignant human brain tumors.

Immunology of central nervous system tumors

With progress in cellular immunology and the development of hybridoma technology, the idea of manipulating host-tumor immune interactions to improve the prognosis of brain tumors has aroused renewed interest. Although no brain tumor-specific antigens have been found, and in spite of the wide antigenic heterogeneity of brain tumor cells, some monoclonal antibodies possessing restricted specificity have been isolated and their potential clinical applications investigated. One of the most pronounced changes in the cellular immune responses of brain tumor patients is a profound depression of the T4-helper lymphocytes. Clinical and laboratory trials are under way to assess the ability of lymphokines, such as gamma-interferon or interleukin-2, to restore immunologic competence in these patients and potentiate a specific anti-tumor immunologic response. Recent work suggests that the endothelium-astrocyte complex may have a pivotal role in assisting the escape of brain tumors from the host's immunologic responses, since it is responsible for the intracerebral sequestration of antigens and local anti-tumor responses. In this review, the data on the antigenic properties of central nervous system tumors and the host's humoral and cellular immune responses to them are analyzed and potential immunologic therapies are discussed.

Role of the blood-brain barrier in the establishment of the immune response against polyoma virus-induced cerebral tumours in hamsters

The existence of an immunological blood-brain barrier (BBB) is well established but its role in cerebral tumour immunology is less well defined. Attempting to clarify this problem we tested the graft rejection of polyoma virus-induced central nervous (CNS) tumours in hamsters after systemic or intracerebral immunization with polyoma virus. Animals were immunized by intracerebral or subcutaneous inoculations of polyoma virus before tumours were induced by intracerebral or intramuscular graft of polyoma-transformed hamster neuroglial cells. The growth of cerebral and muscular tumours was significantly inhibited in animals immunized subcutaneously. In animals immunized intracerebrally the inhibition of growth was highly significant for cerebral tumours and only very slight for intramuscular tumours. These results suggest that the blood-brain barrier allowed immunocompetent effector cells to penetrate inside the CNS but prevented the locally elicited cell-mediated immune response from diffusing outside the CNS. The ability of the brain to develop a local immune response and the partial lack of circulation of immunocompetent cells to cross the BBB could be mainly responsible for the special immune status of the CNS and may greatly interfere with the establishment of an efficient immune response toward brain tumours.