The Hindu : FIGHTING HIV & AIDS

Online edition of India's National Newspaper
Thursday, Nov 27, 2003

Opinion

Opinion - Editorials

FIGHTING HIV & AIDS

THE GLOBAL AIDS epidemic shows no sign of abating, according to the latest update issued by the Joint United Nations Programme on HIV/AIDS (UNAIDS) and the World Health Organisation (WHO). Globally, 40 million people are currently carrying the human immunodeficiency virus (HIV), five million of whom were newly infected in 2003. Three million died of AIDS this year. In India, between four million and five million people are probably infected with HIV at this point. The UNAIDS-WHO report speaks of "serious epidemics" under way in several States, including Maharashtra and Tamil Nadu. Especially since there is no cure available, an effective vaccine against HIV will be a powerful weapon in the global fightback against AIDS. However, developing such a vaccine is proving exceedingly difficult.

Ever since Edward Jenner discovered in England that deliberately infecting people with cowpox protected them from smallpox, vaccines have saved millions of human lives and been a great boon to public health. The vast majority of vaccines in use today work by generating antibodies. These chemicals latch on to the germs when they enter the body and stop them in their tracks. But the challenges in the path of developing such a vaccine against HIV are formidable. The vaccine must prepare the immune system to produce antibodies that target the germ where it is vulnerable. But HIV has evolved so that crucial sites on the outside of the virus that it uses to gain entry into cells, including those of the immune system itself, are cleverly hidden away and protected from antibodies. In addition, the virus changes so rapidly that it is able easily to evade many antibodies and so the vaccine must target sites on the virus that do not change much. Yet another difficult requirement for a preventive vaccine against HIV is that it must get the immune system ready to produce high levels of antibodies as soon as the virus is detected. A recently published review of HIV vaccines suggests that finding a vaccine that can induce antibodies reliably and at sufficiently high levels may require advances in basic immunology.

It is perhaps not surprising that the first HIV preventive vaccine to reach the final stages of clinical testing has turned out to be ineffective. The AIDSVAX vaccine was found to be safe but not efficacious in large-scale trials in North America and Europe, and recently in Thailand as well. The good news, however, is that vaccine development has accelerated in recent times and many candidate vaccines are in the pipeline. Clinical trials of one such vaccine are expected to begin in India next year. The International AIDS Vaccine Initiative, a nongovernmental body with widespread public and private support, has signed agreements with India's Ministry of Health, the Indian Council of Medical Research, and a U.S.-based firm, Therion Biologics, for the development and testing of a vaccine appropriate to this country. Unlike AIDSVAX and in common with most current vaccine approaches, the proposed Indian vaccine will seek to stimulate what are called cytotoxic T-lymphocytes (CTLs). The CTLs can recognise other cells that become infected and destroy them. An advantage of using this approach is that a wider range of viral proteins can be targeted, not just those on the outer surface (as is the case with antibodies). The CTLs will not prevent the first wave of HIV from infecting cells. But the hope is that a vaccine can prepare CTLs to limit the level of infection and keep it from spreading. Achieving even this limited goal is a real challenge, given HIV's ability to modify itself rapidly and evade the clutches of the body's immune system.

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