Gain of function represents the set of laboratory techniques thanks to which it is possible to genetically modify a pathogen (for example a virus) in order to provide it with new capabilities.The field of application of the gain-of-function, in fact, is virology, in order to improve the understanding of viral genomics and proteomics as well as the variables that affect the virus-host interaction (for example, receptors, vaccines, therapies, etc.)2.