Gene cloning involves the production in vitro of new DNA molecules which contain novel combinations of genes or oligonucleotides and the propagation of such recombinant DNA molecules by the exploitation in vivo of the replicative mechanisms of bacteria and other organisms. The developments of genetic engineering techniques have permitted the alteration of the genome of microorganisms so that it produces substances of little intrinsic value but of great medical or economic value to mankind. Foreign genes have been implanted into the DNA of E. coli to enable the production of useful proteins. Members of the antiviral family of proteins called interferons have been produced by these methods, and clinical trials to ascertain their efficacy in the treatment of certain cancers have been conducted. Gene cloning could potentially provide contaminant-free blood products of high purity. A coagulation factor, Factor VIII, is required by certain haemophiliacs. The risk of hepatitis and acquired immune deficiency syndrome (AIDS) due to the unintentional collection of blood from virus carriers identified this factor as a candidate for production by DNA recombinant techniques. In agriculture, techniques have been developed which permit the transfer of the characteristics of one plant to another through bacterial infection. Such techniques may create new varieties of plants with desirable characteristics, e.g. resistance to infection, the ability to withstand adverse weather conditions or the capability of nitrogen fixation.