Gene defects in humans can lead to deficiencies in proteins such as insulin, human growth hormone, and Factor VIII that may result in problems (diabetes, dwarfism, and impaired blood clotting, respectively). Proteins for these chemicals can now be replaced by proteins manufactured through biotechnology. For insulin production, two protein chains are encoded by separate genes in plasmids inserted into bacteria. The protein chains are then chemically joined to form the final insulin product. Human growth hormone is also produced within bacteria, but special techniques are used because the bacteria do not usually produce human proteins.
Therapeutic proteins, such as the following, can also be produced by biotechnology:
■ Tissue plasminogen activator (TPA), a clot-dissolving protein, can now be produced in recombined mammalian cells.
■ Interferon, an antiviral protein produced in E. coli cells, is currently used to fight certain types of cancers and for certain skin diseases.
■ An antisense molecule is a molecule of RNA that reacts with and neutralizes the mRNA molecule used in protein synthesis. In doing so, the antisense molecule prevents the synthesis of a protein involved in a specific disease. For example, an antisense molecule can prohibit human host cells from producing key portions of the human immunodeficiency virus (HIV) when infection has occurred.
Vaccines represent another application of recombinant DNA technology. The hepatitis B vaccine now in use is composed of viral proteins manufactured by yeast cells and recombined with viral genes. The vaccine is safe because it contains no viral particles. Experimental vaccines against AIDS are being produced in the same way. One vaccine uses vaccinia (cowpox) virus as a vector. The virus has been combined with genes from several viruses, and it is hoped that injections of the vaccine will stimulate resistance to multiple diseases. Vaccines can also be produced by eliminating certain disease-inducing genes from a pathogen, leading to a harmless organism that will stimulate an immune response.