Cancer Healthcare Providers Vaccines Therapy

Information on Cancer Vaccines and Presentation.

Tumor antigens nd antigen presentation------

Tumor cells accumulate DNA mutations during transformation into a cancer. These mutations leads to the production of altered antigens not found in normal tissues. These represent targets for selective recognition by the host immune system. These antigens are expressed with a molecule called major histocompatibility complex (MHC) for potential recognition by CD8 T-cells, which induce the immune response. In addition, antigen-presenting cells, such as dendritic cells, present antigens to CD4 helper cells, inducing a response including antibodies generated by the immune system.
T cell activation is also greatly enhanced by co-stimulatory molecules, which leads to the release of several cytokines. These, in turn, lead to further T- cell activation and the positive feedback system required for an aggressive immune response. Tumor-specific responses are muted, however, because cancer cells present antigen without the co-stimulatory molecules required for this immunity. Hence, potentially reactive T-cells are not induced, causing tolerance to antigens. In addition, tumor cells have been shown to express factors that inhibit antigen-presenting cell function and migration, also suppressing immunity. Several strategies are being pursued to enhance efficacy of cancer vaccines.

Peptide vaccines------

The premise of this strategy is that the introduction of a tumor antigen will be taken up by an antigen presenting cell and presented to T-cells. The resultant recognition of the foreign antigen by the T-cells causes an expansion of the population of these specific T-cells with the resultant immune response. Peptide vaccination has most commonly been studied in melanoma. Clinical trials have shown evidence of T-cell induction and response, though minimal. Hence, ongoing work in peptide vaccines is in improving the capacity to stimulate the immune response more and to understand the mechanism of immune suppression by the tumor. The concurrent administration of cytokines has been used as has altering one or more amino acids in the antigen to improve the immunogenicity of the antigen. These methods have both shown to enhance the response to peptide antigens.

Other problems also exist with peptide antigens. They depend on intact antigen presenting and the development of a population of T cells in order to be effective. If the antigens, which remember are just small proteins, are rapidly cleared, a response obviously will not be generated. Also, tumor cells can avoid immune recognition by simply downregulating the antigen that the immune system is responding toward. Especially if the antigen is not essential, this can be very easy for the tumor cells to accomplish.

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