The immune system-a strategic weapon in the battle against cancer

Abstract

Tumor cells have an altered regulation of their cell cycle and commence to proliferate uncontrollably owing to mutations in their genetic material. Furthermore in addition to the altered proliferation there are genetic modifications which alter the expression of proteins in the malignant cell. This is manifested in the overexpression of some genes or activation which in normal tissue are not normally expressed. These genes encode for proteins which can be recognized as aberrant by the immune system thus generating an anti-tumor response. Recently in studies of animal models and in patients it has been shown that the principal anti-tumor effect is caused by the cellular immune response. In this situation it is the T lymphocyte which play a principal role, by way of their antigen receptors which have been processed and presented in association with the molecules of the major histocompatability complex (MHC). The majority of tumor associated antigens and recognized by CD8+ cytotoxic T lymphocytes are peptides derived from proteins expressed by the tumor cells and furthermore are encountered in the normal tissue of origin. For example in human melanoma exist antigens derived from proteins involved in the synthesis of melanin and expressed both in the tumor and normal melanocytes. There are other MHC restricted antigens which are common to various tumor types. These are embryologically derived proteins and normally are not expressed in the somatic tissues. The identification of various TAA has permitted the production of modern anti-tumor vaccines which are in the experimental stage. These vaccines based on descrete antigens which could be of peptide or DNA origen and would come to replace immunological therapies of less specificity, such as cytokines or adaptive therapy. Pre-clinical and clinical studies in the last two years indicate that the form of immunization essential in order to produce an effective immune response and avoid anergia or tolerance. Here play an important role the dendrite cells in their function as presenting cells of antigens and some preinflammatory citokines. The parody exists between the presence of anti-tumor cells in the patients with cancer and the systemic progression of the disease, this suggests the existence of mechanisms mediated by the tumor to evade the immune response. This strategies range from the secretion of factors immuno-inhibitory to mutations in the molecules related to the presenting antigen. An understanding of the immunological mechanisms involved in the anti-tumor response permits the development of immunotherapy as an alternative or complementary therapy to those already established in the fight against cancer.