A research team announced yesterday that it has identified 273 human proteins that the HIV virus apparently needs to infect a person.  The findings may offer hundreds of potential new targets for drug therapies that could halt the virus, said the researchers from the Harvard Medical School and the Howard Hughes Medical Institute.

The vast majority of these human proteins -- more than 200 -- were not previously known to play a role in the complicated choreography by which the virus attaches to a cell, enters it, gets copied and establishes permanent residence.

The study was published online Thursday and will appear in the Feb. 8 edition of the journal Science.

The discovery was made with a technique called a "genome-wide scan," which is only a few years old.  The genome-wide scan is not the last word on what HIV needs to infect and destroy human cells, but it is a much more comprehensive inventory than has existed before.

Stephen Elledge, professor of genetics and the study's principal investigator and his co-workers scanned all 21,000 human genes that encode proteins, blocking them one at a time and seeing what effect that had on the virus's ability to infect a cell. They found 273 proteins that the virus seemed to need.

Of that number, 36 had been previously identified. But the researchers also found 237 proteins that had not been known to be necessary for HIV to attack, grow and destroy cells.

While not every protein will turn out to be absolutely essential to the virus, most appear to be. By finding drugs that would deny the virus even one of these proteins, scientists may be able to prevent the attack, said Elledge.

"It's clearly a new direction for this field," says Bhagirath Singh, head of infection and immunity with the Canadian Institutes of Health Research. "It will (define) the new way of thinking about how to prevent the infection of the virus and its transmission."

Elledge says the new strategy would circumvent one problem with existing drugs: HIV is notorious for its ability to mutate rapidly, rendering many drugs ineffective.

This problem is why people with HIV are given a cocktail of antiretroviral medications, in the hope the virus will not be able to change sufficiently to escape an onslaught of many drugs at once.

The study is another example of the potential payoff of the Human Genome Project, the international effort to identify and record the entire human genetic message. This job was largely finished in 2003 and has been refined since then.