Simian virus 40 (SV40) is a polyomavirus that was first isolated from monkey kidney cell cultures used to produce the poliovirus vaccine. It has a small circular DNA genome wrapped in histone proteins. The genome contains early and late protein coding genes as well as regulatory sequences. The early proteins are non-structural while the late proteins form the viral capsid. The SV40 genome can be modified to replace the early protein coding genes with a gene of interest for gene therapy purposes. A recombinant SV40 viral vector offers advantages such as the ability to transduce both dividing and resting cells with high efficiency and provide long-lasting transgene expression.

1. VIRUS VECTOR

2. Simian virus 40 (SV40)

Belongs to polyoma viruses group.

The virus was first isolated as a contaminant
from a monkey kidney culture
used for the production of poliovirus
vaccine.

Its genome is very small and can be easily
modified for gene therapy purpose.

Its genome has ds circular DNA wrapped up as
nucleosome with the help of
histone proteins

3. 
It is roughly 40-45 nm in diameter.

The chromosome is 5000 bp long. The
genome of SV40 is like a mini
chromosome.

The genome of SV40 consists of early
proteins, late proteins and regulatory
proteins.

Early proteins are non structural while late
proteins are structural proteins.

Regulatory region consist of promoter,

4. 
The capsid proteins are produced later
which then forms viable virus and comes
out of the cell.

The early protein coding genes can be
replaced by the gene of interest. The
mutation in p53 promoter which leads to
cancerous condition was discovered in the
SV40 virus.

Gene therapy using recombinant SV40 is
highly suitable means to transfer the gene
in a number of conditions.

5. Replication of SV40 in the host cell

6. 
The late proteins of SV40 are synthesized
from the opposite strand. Out of four
structural proteins VP1 is the most
abundant one.

The minimum viral specific sequence
required to assemble the virion consists of
origin of replication and encapsidation
sequences they were overlaps with the
early promoter region in the genome.

The transcription of the genome and the
transgene is governed by pol III promoter.

7. 
Recombinant SV40 viral vectors are made
in some plasmid background such as
pGEMT plasmid vector.

The permissible cells are transfected with
the plasmid along with the support
plasmid needed to package the viral
genome.

The recombinant virus containing the
transgene is then recovered by the lysis of
transfected cell.

The recombinant virus is then further

8. Features of a SV40 based
vector
Some of the specific features of an SV40 vector
are as follows
• Capacity of the transgene is limited to 5 Kb.
• Both resting as well as dividing cells are
equally transduced by SV40 based vectors.
• High level of transduction efficiency.
• Long lasting transgene expression. It has
been reported that the transgene expression once
established will remain lifelong.
• Neutralizing antibody against recombinant