Over the past decade, adeno-associated virus (AAV) vectors have emerged as a promising treatment for a number of diseases, particularly for diseases of the eyes and metabolic diseases of the liver. The viruses provide a vector for the delivery of genetic material to target cells, which can take up the DNA and alter protein expression.

1. Thomas Chalberg

2.  Over the past decade, adeno-associated virus (AAV) vectors
have emerged as a promising treatment for a number of
diseases, particularly for diseases of the eyes and metabolic
diseases of the liver. The viruses provide a vector for the
delivery of genetic material to target cells, which can take up
the DNA and alter protein expression.
The genome of an adeno-associated virus consists of single-
stranded DNA, which can be up to 4,700 base pairs in length.
Each end of the strand contains an inverted terminal repeat
(ITR) sequence, which allow the virus to assemble and
express inside the cell.
The protein coat, or capsid, that surrounds the genome in AAV
is made up of three proteins, called VP1, VP2, and VP3.

3.  These are arranged in an icosahedral shape. Different types
of AAV -- often called variants or serotypes -- have different
versions of these three proteins on their surface, which make
them interact with different types of cells. For example, one
serotype (AAV1) infects muscle cells with high efficiency,
whereas another serotype (AAV8) is more efficient at infecting
liver cells.
New variants of AAV are now being engineered by a number
of scientists in academic as well as industry labs. These
"custom" designed variants may be able to go beyond what
naturally occurring viruses can do, including transducing new
types of cells and avoiding detection by the immune system.