By Ben Hirschler

LONDON (Reuters) - There's no cure but, for the rich at least, HIV is no longer a death sentence.

An arsenal of 16 antiviral drugs and simplified dosing regimes have transformed treatment in the developed world, turning the virus that causes AIDS into a manageable chronic condition for many.

Scientists will tell next week's AIDS conference in Durban, South Africa, of the latest moves to outwit HIV, including progress on a new class of drug that prevents the virus from entering cells, rather than blocking its action once it arrives.

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　　While not yet proven, the T-20 ``fusion inhibitor'', made by US biotech firm Trimeris in partnership with Roche, offers hope to a growing number of people with resistance to existing drugs.

``The data so far is promising and so far all the expectations have been confirmed. More information will be provided at Durban,'' Roche spokesman Horst Kramer told Reuters.

T-20 - now in Phase II/III trials - and follow-up product T-1249 have been given fast-track designation by the US Food and Drug Administration, speeding up their review.

Both work by stopping the virus from fusing with cell membranes, although a drawback is that they need to be injected. Currently available drugs block HIV inside cells by inhibiting reverse transcriptase or protease, enzymes used by the virus.

Early-stage work is also underway on other ``entry inhibitors'', including a group of compounds known as bicyclams being studied by Canada's AnorMED, which interfere with a receptor used by variants of HIV to get into cells.

At the same time, new drug classes are in the pipeline for fighting HIV inside the cell, including nucleotide analogues, like Gilead Sciences tenofovir, and integrase inhibitors, which block another enzyme used by HIV.

Coupled with other recently launched new drugs, including DuPont's Sustiva and Abbott Laboratories' Norvir, the firepower available to clinicians is improving all the time.

This is as it should be. With up to 40 percent of HIV patients in the US carrying virus strains resistant to established drugs, new defenses are in constant demand. ``There is a large population who have already failed all the existing drugs and who may develop AIDS within the next year or so unless they get their viral loads back under control,'' said Keith Alcorn of National AIDS Manual, a London-based charity.

``The only way of doing that is with new drugs which to which they are not resistant.'' AFRICA'S POVERTY GAP

For millions of Africans, however, the advances in drug technology earnestly debated at the 13th International AIDS Conference will have a hollow ring.

At $10,000 a year, the triple-drug combination therapies which have slashed mortality rates in North America and Europe since their introduction in 1996, are simply too costly.

Drug makers agreed with the United Nations in May to axe the cost of AIDS drugs in developing countries, with Glaxo Wellcome promising an 85 percent price cut for its Combivir combination therapy. Further pledges are expected in Durban.

But even if the cost is brought down dramatically, antiretrovirals are likely to remain out of reach for much of sub-Saharan Africa, home to 70 percent of the world's 34.3 million people living with HIV/AIDS.

For South Africa alone, the cost of providing triple therapy for a just one quarter of those infected with HIV would be $19 billion over five years, even allowing for UN-brokered price reductions, according to researchers from the British Columbia Centre of Excellence in HIV/AIDS.

Such mass drug use could prevent some 430,000 AIDS cases but the cost to South Africa would be crippling. To put the bill into context, worldwide annual sales of all HIV/AIDS drugs of current total only around $5 billion.

There may be more realistic ways to use cheaper AIDS drugs in developing countries, however. The same researchers calculated in a paper published last month that 110,000 HIV births could be prevented if all pregnant women were given a short preventative antiretroviral course at a cost of just $54 million.

The scale of the problem is daunting. New UN statistics show South Africa now has largest number of people living with HIV/AIDS in the world with a total of 4.2 million people infected, or 19.9 percent of the population. VACCINES PROVE A LONG HAUL

Long term, the ``holy grail'' of AIDS research is a vaccine, which could bring affordable treatment to Africa and other poor regions.

There is little doubt that vaccines are among the most cost-effective health interventions - but the road to a version for AIDS has proved extremely bumpy.

The first small-scale clinical trials of HIV vaccines got underway back in 1987 but a series of setbacks confounded hopes of any early breakthrough.

Now vaccines are back on the agenda with the recent launch of the first large-scale final-stage Phase III study, conducted by California-based VaxGen, in the US and Thailand.The company is testing two formulations of its AIDSVAX vaccine on nearly 8,000 volunteers - but initial results from the trial will be available only in two years' time.

(From Yahoo)