hit viruses

To find new target for antiviral drugs, scientists look for genes that human cells don't need but viruses do. One search method is shown here

1. Find unneeded genes
a harmless retrovirus (red) is used to knock out a different gene (green) in each human cell of a colony. If a cell survives, that means the targeted, gene wasn't producing an essential protein.

2. Bring on the enemy
Remaining cells, lacking a gene they don't need, are infected with a virus, such as flu (orange), that would ordinarily kill them all. Yet it fails to kill some.

3. Identify survivors
If a cell survives the virus, that suggests the virus, couldn't reproduce without the protein encoded by the missing gene. A new antiviral drug might target that protein without harming human cells.

4. Break the cycle
A virus's life cycle could be disrupted at different stages by drug that targets a human protein.The only such drug approved so far blocks a receptor that HIV needs to enter human, immune cells.

# Conventional antiviral drugs target the virus itself. For example, Tamiflu blocks a surface protein on the influenza virus that enables it to escape from one cell to infect another.