Interferons are proteins, produced by white blood cells, that are part of the body's defence against virus diseases and were thought to have potential in the treatment of cancer (Burnett, 1985). Nowadays, it is known that there exists different kinds of interferons and that they are effective in the treatment of certain cancers and virus diseases.
Vaccines
Prior to the development of recombinant DNA technology, two types of vaccines were used. Inactivated vaccines are chemically killed derivatives of the actual infectious agents. Attenuated vaccines are live bacteria or viruses altered so that they no longer multiply in the inoculated organism. However, these types of vaccines are potentially dangerous as they can be contaminated by infectious organisms (Watson et al, 1992). Genetic vaccines are quite different in structure from traditional ones. The most studied consist of plasmids. The plasmids used for immunisation have been altered to carry genes specifying one or more antigenic proteins normally made by a selected pathogen; at the same time, they exclude genes that would enable the pathogen to reconstitute itself and cause disease. Once inside cells, some of the recombinant plasmids make their way to the nucleus and instruct the cell to synthesise the encoded antigenic proteins. Those proteins can elicit humoral (antibody-type) immunity when they escape from cells, and they can elicit cellular (killer-cell) immunity when they are broken down and properly displayed on the cell surface (Sci.Am., 1999/0799). Genetic vaccines are easy to design and to generate in large quantities using recombinant DNA technology, and they are as stable as other vaccines when stored. They should therefore be relatively inexpensive to manufacture and to distribute widely. Further, because they can be engineered to carry genes from different strains of a pathogen, they can potentially provide immunity against several strains at once, something that should be very helpful when the micro-organism is highly variable, as in the case of influenza viruses and HIV. So far human tests are examining vaccines designed to prevent various infections (by HIV, herpes, influenza, hepatitis B and Plasmodium), to promote the impaired immunity of patients already infected with HIV and to treat a number of cancers (among them lymphomas and malignancies of the prostate and colon). Although cancer is not an infectious disease, much evidence indicates that harnessing the body's immune defences may help combat it. Genetic vaccines preserve all the positive aspects of existing vaccines while avoiding their risks.
'Magic Bullets'
This is a treatment that could effectively seek and destroy tumour cells and infectious agents wherever they resided. The concept is derived from the use of antibodies as targeting devices since these are highly specific and can bind to a single target among millions of irrelevant ones (Watson et al, 1992).
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