The Human Immune System Plays a Critical Role in Warding off Various Types of Human Cancer
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This document discusses the role of the human immune system in warding off cancer. It notes that individuals with compromised immune systems, such as organ transplant recipients and HIV/AIDS patients, have a much higher risk of developing certain cancers, especially virus-induced cancers. While the immune system effectively controls most viral infections and eliminates virus-transformed cancer cells, immunocompromised individuals lack these defenses. The document also examines evidence that the immune system may recognize and eliminate some non-viral tumors through tumor-infiltrating lymphocytes and anti-tumor antibodies, though more research is still needed to fully understand immune surveillance against cancer.
The Human Immune System Plays a Critical Role in Warding off Various Types of Human Cancer
- 1. THE HUMAN IMMUNE SYSTEM PLAYS A CRITICAL ROLE IN WARDING OFF VARIOUS TYPES OF HUMAN CANCER
- 2. • Human immune system plays an important role in defending against cancer • Past few decades, individuals with compromised immune systems has extended life span • For three reasons First • Organ Transplantation become common . Unwanted reaction controlled by immunosuppressive drugs Second • Almost 60 million people suffering from HIV virus Third • For long-term survival, Both types are treated with diverse range of antibiotics
- 3. • Thousands patients bearing transplanted organs --- developed solid tumors & hematopoietic malignancies • Small number of tumors -- derived from occasional metastatic cancer cells that were hiding in the bodies of organ donors • Tumors triggered by transplanted cells provides no insights about whether tumors of endogenous origin arise with greater-than- normal frequency in immunocompromised patients. • Nonviral cancers occur with almost equal incidence among immunocompetent and immunodeficient individuals • Viral tumors occur at greatly increased incidence in immunocompromised patients • Kaposi’s sarcoma (caused by human herpesvirus-8, HHV-8), incidence rate is 3000 times higher in AIDS patients
- 4. Virus-induced cancers are normally controlled by the immune system by two models • (1) The immune system is normally responsible for protecting us against all types of viral infections, independent of whether certain viruses are bent on inducing cancer. • (2) Alternatively, the normal immune system is responsible for recognizing and eliminating virus-transformed cancer cells. In immunocompromised individuals, however, such cells may be able to survive indefinitely.
- 5. • Either or both mechanisms may explain the greatly increased rates of virus-induced cancers in immunocompromised people. • In AIDS patients, for example, high levels of circulating Epstein–Barr virus are not commonly observed, while the levels of actively proliferating EBV-infected lymphoid cells often increase dramatically, yielding, in turn, virus-induced lymphomas. • Whether a competent immune system also erects defenses against the great majority of human tumors (~80%) that are of nonviral origin. • Two- to fourfold increased risk of melanoma has been found among adult organ transplant recipients • Non-Kaposi’s sarcomas were found at rates three times above those of the general population.
- 7. how are nonviral tumors recognized and eliminated? • Authochthonous tumors of nonviral origin may not attract the attentions of an immune system • Some arms of the immune system can indeed recognize tumors that have no associations with viral infections. • Human tumors often have substantial numbers of lymphocytes that have infiltrated into the tumor mass. • These tumor-infiltrating lymphocytes (TILs) might represent yet another type of stromal cell that has been recruited into the tumor mass by neoplastic cells in order to support the expansion of the tumor as a whole • These TILs may have been dispatched by the immune system in order to eliminate cancer cells.
- 8. In one group of patients, who had been treated initially by surgical removal of the bulk of their tumors followed by chemotherapy, 74% were alive five years later if their initial tumors carried large numbers of these TILs. In contrast, among those patients whose ovarian tumors lacked significant populations of TILs, only 12% were still alive
- 9. • Research reports have demonstrated the presence of anti-tumor antibodies in the blood of patients suffering from various types of cancer • Presence of these antibodies clearly suggests some type of immunosurveillance. • Remains unclear whether these antibodies actively contribute to eliminating tumor cells from the body • Antigens that are displayed by cancer cells and provoke immune responses; their identities are often elusive. • Even more complex are the identities of the immunocytes that are responsible for responding to these antigenic signals.
- 10. • Multiple distinct types of leukocytes are recruited to tumors. • Each type of leukocyte may be represented by multiple subtypes that may play distinct, even conflicting roles in fostering or suppressing tumor growth