Lentivirus and adenovirus expression system
Virus, as a vector for exogenous gene espression, has been widely applied in many fields, including fucntional verification of gene, small RNA, transcription factor, recombinant protein production and transgenic animal research, et al. With the characteristic of virus infection and recombinant plasmid which contains viral genome, exogenous gene and others, protein overexpression or interference could be performed in mammalian cells.
The technical system is mainly composed of two parts: virus packaging and virus infection (Fig1 and Fig 2). The virus packaging is the process of preparation recombinant plasmids by genetic engineering method. It can be divided into lentiviral packaging system and adenovirus packaging system depending on the type of packaging virus. The packaged lentivirus and adenovirus can infect mammalian cells and introduce exogenous genes autonomously.
The lentivirus packaging system is derived from the modified HIV virus system. It is make up of a expression plasmid and multiple helper plasmids. Usually, 293T cells can be used as host for propagation of the packaged lentivirus. The packaged lentivirus can infect mammalian cells directly. At the same time the target gene will be inserted into the genome of the host randomly and stably, which will lead to stable and long term expression of target protein. The adenovirus packaging system is derived from modified human Ad5 virus system. It is make up of one expression plasmid and one or several helper plasmids. 293 cells are regularly used as host to propagate the packaged adenovirus, and the packaged adenovirus can infect mammalian cells directly, as well. The target gene exsists outside of the host’s genome, it expresses target protein independently, rapidly, and with high abundance. Although the lentiviral expression system and adenovirus expression system are both widely used espression system, there are lots of differences (shown in Table 1).
Table 1. Characteristics and differences of lentiviral and adenovirus expression system
| Name | Lentiviral expression system | Adenovirus expression system |
| Viral genome | RNA | DNA |
| Original virus | HIV1 | AD5 |
| Vector system | one expression plasmid and multiple helper plasmids | one expression plasmid and one or several helper plasmids |
| Packaging cell | 293T cells | 293 cells |
| Virus packing method | Expression vector and auxiliary vectors co-transform packaging cells to obtain recombinant virus particles. This process does not lysis the cell, and the virus will accumulate in the supernatant of cell culture medium. | Expression vector and auxiliary vectors co-transform packaging cells to obtain recombinant virus particles.The recombinant virus particles will be purified in cell lysis. |
| Whether insert host genome? | Yes | No |
| Expression abundance | High | High |
| Expression time | Slow（2-4 days） | Fast（1-2 days） |
| Viral titer | 1*108~1*1010TU/ml | 1*1011~1*1013TU/ml |
| Clone capacity | ≤6kd | ≤8kd |
| Immunogenicity | Weak | Strong |
| Infection efficiency | Weak | Strong |
| Protein overexpression | Fit | Fit |
| MicroRNA overexpression | Fit | Unsuited |
| RNAi | Fit | Fit |
| Stably transformed cells or animals | Fit | Unsuited |
| Animal infection experiment | Unsuited | Fit |
| Cell infection experiment | Suitable for infection of dividing or non dividing mammalian cells, there is a poor infection efficiency for nerve cells. | Suitable for infection of dividing or non dividing mammalian cells. |
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