Multi-Cistronic Vectors

Simultaneous delivery and expression of two or three genes by a single lentiviral vector is sometimes required.  Most frequently IRES-based elements are used for these particular applications.  However, it has been demonstrated that the genes inserted down-stream of IRES exhibit lower levels of expression.  In addition, the IRES element is a relatively large fragment (> 800bp) and its use is often limited due to the lentiviral packaging capability (<5.0kb). Therefore a promoter system with bi-directional functionality has been developed for simultaneous expression of two or three different genes by a single lentiviral vector. Bi-cistronic vector is superior to IRES-based two-gene expression systems because of its smaller size (500bp) and stronger expression signal for both genes (Amendola et al., 2005).  Up to 3 different genes can be expressed from the same lentiviral vector with the addition of a T2A peptide sequence (Tang et al., 2009).