22.1 Introduction

For non-viral gene delivery to mammalian and human cells DNA based transposon vectors offer a varied mechanism. These DNA based transposon vectors work either by “cut-and-paste” or by “copy-and-paste” mechanism. Transposase enzyme helps in integrating a transgene(s) which is present in transposon DNA into chromosomal DNA. Sleeping beauty and piggyBac are the two most commonly used transposon system used for genetic modification of mammalian and human cells. Ease and relatively low cost of producing sufficient amounts which is required to meet the entire patient population, less storage problems, less innate immunogenicity, and easy co-delivery of multiple genes unlike viral vectors are some of the main advantages of transposon vectors. Transposons have shown good results in genetic modification of cell types of various clinical grades such as induced pluripotent stem cells, human T lymphocytes and stem cells. Integration of transposon DNA cargo by user-selected and site-directed genomic integration is the on-going research which is focused on manipulating transposon systems thereby improving safety and efficacy of transgene delivery.

22.2 Transposons as gene delivery systems:

Transposons or mobile genetic elements as “jumping genes” which are responsible for mosaicism in maize (corn) were first described by Barbara McClintock. Transposons are found in all eukaryotes. In humans around 47% of the genome is derived from transposons. Class I (copy and paste) and Class II (cut and paste) mechanisms are the two means by which transposons work in eukaryotes.

In Class I mechanism a copy of transposon itself is made via an RNA intermediate and hence they are also known as “retrotransposons”. In Class II DNA transposons, the enzyme transposase excises the transposon which gets relocated to a new locus by creating double stranded breaks in situ . In this mechanism, inverted terminal repeat sequences (IRs) are recognized by the enzyme transposase.