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Immunotherapy of brain tumors
1Department of Neurosurgery, University Hospital, Lausanne, Switzerland.
Abstract:
In the process of malignant transformation, astrocytoma cells display a number of surface antigens not expressed by their normal adult counterparts and which have been identified by monoclonal antibodies and characterized biochemically. These include tumor associated antigens (TAA) such as oncofetal antigens of neuroectodermal origin or oncogene products such as epitopes in the extracellular domain of the epidermal growth factor receptor, as well as major histocompatibility antigens (MHC) of class I and class II. Glioma cells also secrete lymphokines like IL-1 and IL-6. The concomitant expression of TAA and MHC together with the disruption of the blood brain barrier may elicit a humoral or cell mediated immune response from the tumor bearing host as demonstrated by the functional analysis of tumor infiltrating lymphocytes. However this response is extremely weak and obviously inefficient because the tumor cells secrete factors which can inhibit or completely abrogate the immune attack by cytotoxic T cells. Among these factors, TGF-beta 2 and PGE2 are of particular interest since they may explain the generally depressed cellular immune response observed in patients with malignant gliomas. To be efficient any form of immunotherapy will require abatement of these suppressive activities in addition to stimulation of the effector functions.
Insights
Malignant astrocytoma cells express tumor antigens and immune suppressors like TGF-beta 2. Immunotherapy requires overcoming these suppressive factors for effective treatment of gliomas.
Area of Science:
- Neuro-oncology
- Immunology
Background:
- Astrocytoma cells exhibit unique surface antigens, including tumor-associated antigens (TAA) and major histocompatibility complex (MHC) molecules, during malignant transformation.
- These cells also secrete immunosuppressive factors such as interleukin-1 (IL-1), IL-6, transforming growth factor-beta 2 (TGF-beta 2), and prostaglandin E2 (PGE2).
Purpose of the Study:
- To investigate the immune response evasion mechanisms employed by malignant astrocytoma cells.
- To identify key immunosuppressive factors contributing to the inefficiency of anti-tumor immunity in glioma patients.
Main Methods:
- Biochemical characterization of surface antigens on astrocytoma cells.
- Identification of secreted lymphokines and immunosuppressive factors.
- Functional analysis of tumor-infiltrating lymphocytes (TILs).
Main Results:
- Astrocytoma cells express TAA and MHC class I and II antigens.
- Tumor cells secrete immunosuppressive factors, notably TGF-beta 2 and PGE2, which inhibit cytotoxic T cell activity.
- The immune response mounted by the host is often weak and inefficient due to these suppressive factors.
Conclusions:
- Malignant astrocytoma cells employ multiple strategies to evade immune surveillance, including the expression of specific antigens and the secretion of potent immunosuppressors.
- The identified suppressive factors, TGF-beta 2 and PGE2, are critical in abrogating anti-tumor immune responses in glioma patients.
- Effective immunotherapy for malignant gliomas necessitates strategies to counteract these suppressive mechanisms alongside stimulating effector immune functions.