Which viral vector should I use?
Common viral vectors used in biomedical research include lentivirus, Moloney murine leukemia virus (MMLV), adenovirus, and adeno-associated virus (AAV), each with its advantages and disadvantages. Many factors affect the decision on what type of viral vector to use in your experiment. The key considerations include: Does the virus have the tropism for the target cells (namely, can it efficiently infect target cells)? Are the cells dividing or non-dividing? Do you want transient transduction or stable integration into the host genome? What transduction efficiency is needed? Do you need to use a customized promoter to drive the gene of interest? Will your vector be used in cell culture or in vivo? Will an immune response to the virus affect your experiment? The table below lists these considerations when choosing commonly used viruses:
|Tropism||Broad||Broad||Ineffective for some cells||Depending on viral serotype|
|Can infect non-dividing cells?||Yes||No||Yes||Yes|
|Stable integration or transient||Stable integration||Stable integration||Transient, episomal||Transient, episomal|
|Maximum titer||High||Moderate||Very High||High|
|Primary use||Cell culture and in vivo||Cell culture and in vivo||In vivo||In vivo|
|Immune response in vivo||Low||Low||High||Very low|
Lentivirus is a type of retrovirus. Upon infecting cells, the RNA genome of the virus is reversely transcribed and then permanently integrated into the host genome, thus allowing long-term stable expression of genes carried on the viral vector. Lentivirus is the most commonly used viral system for gene delivery, as it is a highly efficient vehicle for introducing genes permanently into mammalian cells. This system has broad tropism (i.e. it can infect a wide range of cell types) for both dividing and non-dividing cells, with relatively low cellular toxicity or immune response. Live lentivirus can be produced at high titer (>108 TU/ml), and transduction efficiency for cultured cells can approach 100% under optimal conditions. While lentivirus is primarily used for in vitro transduction of cultured cells, it can also be used to transduce cells in live animals.
MMLV is a type of retrovirus just like lentivirus. It also has broad tropism and stably integrates into the host genome, allowing stable gene expression. However, MMLV does not efficiently infect non-dividing cells, and can produce more significant cellular immune response than lentivirus. Additionally, the viral titer of MMLV and similar retroviruses is usually only about one tenth that of lentivirus. Another major shortcoming of the MMLV vector is that it does not allow customization of the promoter used to drive the gene of interest (GOI). Rather, the expression of GOI is driven by viral 5’ LTR. In contrast, lentivirus, adenovirus and AAV all allow customized promoters to be used to drive GOI expression. For these reasons, the use of MMLV has declined and generally been replaced by lentivirus. However, because of historical precedent and for certain technical reason, MMLV is still used in some applications such as the derivation of iPS cells.
When adenovirus infects cells, its genome does not integrate into the host genome, but rather remains in an episomal state within infected cells. Expression of genes carried by the adenoviral vector is usually transient, particularly in rapidly dividing cells, which will lose the viral episome over time. Many cell types (both diving and non-dividing) can be transduced with adenovirus, but certain cell types lack the appropriate cell surface receptor and therefore cannot be efficiently transduced. Cellular and in vivo immune response due to adenoviral infection can be significant, and may interfere with certain experiments. Adenovirus can be produced at very high titer (>1010 TU/ml), which allows for very efficient transduction of susceptible target cells. This system is primarily used for in vivo gene delivery, such as gene therapy and vaccination.
Adeno-associated virus (AAV)
AAV is another non-integrating, episomal virus commonly used to produce transient gene expression. Unlike adenovirus, AAV has very low immunogenicity and is almost entirely nonpathogenic in vivo. A practical advantage is that AAV can in most cases be handled in biosafety level 1 (BSL1) facilities. AAV can infect both dividing and non-dividing cells. When VectorBuilder’s AAV vectors are packaged into virus, different serotypes can be conferred to the virus by using different capsid proteins for the packaging. Viruses of different serotypes have different tissue tropisms, so care should be taken to select the proper serotype when attempting to infect a particular tissue type. The relatively high titer of most AAV preparations makes it an efficient gene delivery system. AAV is the ideal viral vector system for many animal studies.
We recommend that you use VectorBuilder offered virus packaging services, which utilize a wide range of proprietary technologies to provide you with high-quality, high-titer viruses at lower cost and faster turnaround than what you can do on your own.
|J Virol. 72:8463 (1998)||The 3rd generation lentivirus vectors|
|Curr Gene Ther. 5:387 (2005)||Tropism of lentiviral vectors|
|Exp Hematol. 31:1007 (2003)||Review of retrovirus-mediated gene delivery|
|J Virol. 61:1639 (1987)||Extended packaging signal increases the titer of MMLV vectors|
|Gene Ther. 7:1063 (2000)||Tropism of MMLV vectors depends on packaging cell lines|
|Proc Natl Acad Sci U S A. 91:8802 (1994)||The 2nd generation adenovirus vectors|
|Methods in Enzy. 507:229-54 (2012)||Review of AAV virology and uses|
|Curr Opin Pharmacol. 24:59-67 (2015)||AAV use in gene therapy, and serotype differences|