Mammalian artificial chromosomes and clinical applications for genetic modification of stem cells: an overview

Minicircle DNA vectors for gene therapy: advances and applications

INTRODUCTION

Nucleic-acid-based biopharmaceuticals enclose a remarkable potential for treating debilitating or life-threatening diseases that currently remain incurable. This promising area of research envisages the creation of state-of-the-art DNA vaccines, pluripotent cells or gene-based therapies, which can be used to overcome current issues. To achieve this goal, DNA minicircles are emerging as ideal nonviral vectors due to their safety and persistent transgene expression in either quiescent or actively dividing cells.

AREAS COVERED

This review focuses on the characteristics of minicircle DNA (mcDNA) technology and the current advances in their production. The possible modifications to further improve minicircle efficacy are also emphasized and discussed in light of recent advances. As a final point, the main therapeutic applications of mcDNA are summarized, with a special focus on pluripotent stem cells production and cancer therapy.

EXPERT OPINION

Achieving in-target and persistent transgene expression is a challenging issue that is of critical importance for a successful therapeutic outcome. The use of miniaturized mcDNA cassettes with additional modifications that increase and prolong expression may contribute to an improved generation of biopharmaceuticals. The unique features of mcDNA render it an attractive alternative to overcome current technical issues and to bridge the significant gap that exists between basic research and clinical applications.

Novel method to load multiple genes onto a mammalian artificial chromosome

Mammalian artificial chromosomes are natural chromosome-based vectors that may carry a vast amount of genetic material in terms of both size and number. They are reasonably stable and segregate well in both mitosis and meiosis. A platform artificial chromosome expression system (ACEs) was earlier described with multiple loading sites for a modified lambda-integrase enzyme. It has been shown that this ACEs is suitable for high-level industrial protein production and the treatment of a mouse model for a devastating human disorder, Krabbe's disease. ACEs-treated mutant mice carrying a therapeutic gene lived more than four times longer than untreated counterparts. This novel gene therapy method is called combined mammalian artificial chromosome-stem cell therapy. At present, this method suffers from the limitation that a new selection marker gene should be present for each therapeutic gene loaded onto the ACEs. Complex diseases require the cooperative action of several genes for treatment, but only a limited number of selection marker genes are available and there is also a risk of serious side-effects caused by the unwanted expression of these marker genes in mammalian cells, organs and organisms. We describe here a novel method to load multiple genes onto the ACEs by using only two selectable marker genes. These markers may be removed from the ACEs before therapeutic application. This novel technology could revolutionize gene therapeutic applications targeting the treatment of complex disorders and cancers. It could also speed up cell therapy by allowing researchers to engineer a chromosome with a predetermined set of genetic factors to differentiate adult stem cells, embryonic stem cells and induced pluripotent stem (iPS) cells into cell types of therapeutic value. It is also a suitable tool for the investigation of complex biochemical pathways in basic science by producing an ACEs with several genes from a signal transduction pathway of interest.