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Tumor Rejection by Immunomodulation:
A Novel Approach for the Treatment of Cancer
Apostolos Stathopoulos, MD
It is estimated that over 18,000 primary brain tumors occur in the United States each year. Of the those 18,000, over 60% are gliomas. Glioblastoma multiforme (GBM) is the most common and most malignant of all gliomas with 75% of patients dying within 18 months of diagnosis and cannot be cured by surgery, radiation therapy, chemotherapy, or any other available treatment modality. Using basic principles of immunology, our research focuses on the immunological escape of brain tumors as they progress towards GBM. We recently have had astounding success in stimulating the immune system of rats to recognize and reject various tumors. The immunologic properties are an important area of investigation because immune–gene therapy by many approaches have shown promising results in animals models and constitute theoretically attractive new approach for any treatment against malignancy.
The Major Histocompatibility Complex (MHC) is a genetic region (piece of DNA) that codes for proteins, MHC class I and class II, that play an essential role in regulating and modulating immune response. MHC class I are surface glycoproteins located on most cells that bind to proteins derived from tumors and viruses and, as a unit, interact with natural killer cells (NK) and cytotoxic T-lymphocytes (CTL). These cells then induce the death of these tumor and virus infected cells
These viral and tumor proteins are derived from degraded intracellular proteins from virus and tumor infected cells by a process known as antigen processing. Antigen processing is a complex mechanism that involves numerous steps from degrading the protein into tiny pieces, to transporting it to the surface of the cell. A defect in any of these steps may lead to non-expression of the MHC class I : antigen complex, and escape from recognition by the immune system, resulting in unchecked growth.
The MHC class I molecule is not only highly specific in differentiating self from non-self, but is also much conserved since they are inherited with very little if any genetic recombination. This quality has been exploited in transplantation medicine. Identical twins and genetically close family members are less likely to reject transplanted tissue since they have similar MHC I genes. Therefore, homozygous (genetically identical) individuals such as identical twins and syngeneic rats could theoretically accept a brain tumor from his/her homozygous donor (twin). Yet more critically, they would reject a brain tumor from a heterozygous (non-identical) donor based on a specific and targeted immune response.
For example, MHC I is reported to be involved in immune surveillance and elimination of cells with mitochondrial mutations. In human glioma cells multiple mutations in mitochondria have been found. From this it is possible to theorize that all gliomas of a certain type/grade will have similar mitochondrial mutations not found in normal human brain cells. Therefore we hypothesized that GBM transplantation between two non-genetically identical individuals will not only induce rejection of the transplanted tissue, but also train the immune system to recognize proteins specific to GBMs and hopefully lead to rejection of the tumor.
Our initial experiments used two different strains of rat, the Sprague Dawley and Fisher and various cell lines that are capable of producing tumors, syngeneic, in these rats. Therefore syngeneic cell lines injected into rats will continue to grow into a progressively larger tumor (see data); and allogeneic (not capable of producing tumors) cell lines will either not grow at all (as in the Sprague Dawley), or grow minimal tumors that are later rejected without intervention (as in the Fisher).
We induced tumors in each of 9 Sprague Dawley by injecting syngeneic(compatible) tumor cell lines into their left hind flank and observed substantial tumor growth. Three of these rats were used as control, not treated, and were subsequently sacrificed. Five rats were injected with cell lysates (components from bust cells) from the original tumor and other allogenic cell lines at regular intervals. These tumors became progressively smaller and the rats were eventually able to completely reject the tumor (see graph). The remaining rat started began as a control rat, and then began receiving lysate injections when the other control rats were sacrificed. Like the rats in the treatment group, this rat also rejected the tumor. This experiment is currently being repeated with the fisher rats, and we are observing similar results.
Most recently we began to examine immune memory in cancer rejection. It is already documented that once the body mounts an immune response, it carries with it a “memory” of that event so that it may react more quickly if greeted with a similar insult. Knowing this, we wondered what would happen if we re-injected our “cured” Sprague Dawley rats with the same cell line that produced the original tumor. Each of the three rats we used has remained tumor free for twenty days. Before treatment, we were able to induce tumors in these rats using 1/5 the number of cells (100,000 vs 500,000) which produced substantial tumors within ten days.
The implications of this experiment are far reaching. The induction of the immune system to treat cancer runs contrary to some currently accepted therapies such as chemotherapy, which kills not only rapidly dividing cells such as cancer cells but also hair cells, gastrointestinal lining cells and cells of the blood/immune system. This leads to the much undesired side effects of chemotherapy: baldness, diarrhea, infection and anemia. Our research suggests that regular injections with allogenic and syngeneic strains of tumor induce a cell-killing response that is specific for the tumor. Also, these injections provide immunization from further exposure to the same tumor. In the future this may not only be used as part of the regimen to treat cancers in general, but possibly also as vaccination for them.
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