Traditional and recombinant vaccines

Abstract

Several types of vaccines are currently used or being developed. They can be splited into two categories: live and inactivated vaccines. Traditional live vaccines are attenuated by various methods, including growth in unusual conditions (for bacteria) or in cells or animal species to which they are not initially adapted (for viruses). New generation of live vaccines are obtained trough recombinant DNA technology (recombinant vaccines): they can be generated either by directed mutagenesis of virulence genes or by cloning genes of immunogenic proteins into vectors i.e. other bacteria or viruses with attractive properties of safety and efficiency . Conventional inactivated vaccines are made by the use of physical or chemical treatment of micro-organisms. As the immunogenic components of micro-organisms are more and more well identified, they can be used to make vaccines containing only these major immunogenic components (subunit vaccines), in which the antigenic fraction is derived by purification of antigens, or by in vitro gene expression of proteins (another type of recombinant vaccines) or chemical synthesis of peptides. Finally, recent advances demonstrated that direct inoculation of an immunogenic protein encoding gene into muscle of several animal species (known as genetic immunisation, which defines another type of recombinant vaccines) was able to elicit antibody and cellular immune responses. Systemic and mucosal immunity conferred by live and inactivated vaccines are analysed.