快猫短视频

DESIGNER viruses can now be bred especially for gene therapy. A Californian
biotech company has developed a way of 鈥渆volving鈥� viruses to target specific
types of cells.

Tailor-made viruses could make gene therapy safer and more effective, but
they are hard to engineer using conventional methods. For example, retroviruses
are ideal for gene therapy as they integrate their genes into the DNA of their
hosts. But the intricate lock-and-key mechanism these viruses use to break into
cells is difficult to alter without disabling it.

Now a team at Maxygen, a biotechnology company based in Redwood City,
California, has found a way around this. Instead of trying to engineer specific
changes to a virus, they generate lots of random varieties and then let natural
selection do the rest.

In the wild, when two retroviruses infect the same cell they often swap bits
of DNA鈥攁 process called recombination. It鈥檚 the viral equivalent of sex.
The Maxygen researchers, led by Nay Wei Soong, have gone a step further. They
have organised an orgy of gene-swapping among six retroviruses to create new
strains that might never have evolved naturally. 鈥淲e make a Yellow
Pages of viral variants, and let the virus do its own walking,鈥� says
Soong.

The team first isolated the gene that encodes the outer coat of each of six
strains of mouse leukaemia virus (MLV) and chopped these genes up with an enzyme
called DNase. They then glued the pieces back together randomly, using a
technique called 鈥淒NA shuffling鈥�
(快猫短视频, 21 November 1998, p 4).
The resulting genes were stitched back into one of the parent virus
strains.

The researchers then picked out viruses whose altered coats enabled them to
infect hamster cells, which are normally resistant to infection by MLV. They
think this molecular breeding technique could be an effective way of optimising
gene therapy viruses, especially if the way the viruses work is not completely
understood.

It鈥檚 a nice piece of work, says Robin Weiss, a retrovirus expert at
University College London, but he adds that other 鈥渟huffling鈥� methods can also
achieve enhanced targeting.

If the idea of breeding viruses sounds sinister, rest easy. 鈥淭o subvert this
technology for offensive use would be extremely difficult and specialist,鈥� a
spokesperson for Britain鈥檚 Defence Evaluation and Research Agency at Porton Down
in Wiltshire told 快猫短视频.