Progress in the search for a cure for HIV, the viability of placing girls and young women on preventative treatment and new drugs and vaccines are among the key issues on the agenda of the 21st International Aids Conference, starting in Durban today. As 5,000 activists planned to march through the city to demand access to treatment for the 20 million people globally who remain untreated, billionaire philanthropist Bill Gates pledged $5-billion to medical research.Speaking in Pretoria last night, Gates said the biggest slice of his investment would go towards research into diseases such as HIV, tuberculosis, diarrhoea, pneumonia and malnutrition.Among those calling for a cure were former British bus driver and activist Gus Cairns and the woman who helped discover the virus - Francoise Barre-Sinnoussi."I'm HIV-positive, but I would like to die HIV-negative," said Cairns at a pre-conference event.Finding a cure for HIV has evaded scientists for more than 30 years. They are now using various strategies to try to eliminate a disease described as always "one step ahead of the immune system".It will take "many years", warned Cairns. He and Nobel laureate Barre-Sinnoussi said HIV-positive people were calling for a cure instead of daily medication.Barre-Sinnoussi has called for a cure for years - either eliminating the virus from the body completely or sending it into remission.She argues that scientists have to meet the needs of patients, who want to be disease-free and stop taking medication.But talk of a cure is controversial. Anti-retroviral medication keeps a person alive for almost as long as people without the virus and is relatively inexpensive, usually with mild side effects.So, "a cure would have to be better than ARVs, safe, less toxic than what the person is on, and scalable," arguesAmerican immunologist Prof Anthony Fauci.Prof Francois Venter, deputy director at the Wits Reproductive Health and HIV Institute, says: "Currently, the cure scientists are using oncology and immune system interventions that are likely to be toxic."One reason HIV is so hard to cure is that the virus integrates its way into our genetic material, becoming part of a person's DNA and hiding in what is known as 'reservoir cells' - undetectable but ever present."Scientists have focused on finding out where the virus is hiding and flushing it out, hoping that once it is no longer invisible to the immune system it will be killed. But this has not worked.Sharon Lewin, director of the Peter Doherty Institute for Infection and Immunity at the University of Melbourne, said at the weekend: "We've discovered that waking up the virus is not enough. We need something to also eliminate it."Researchers are now "borrowing techniques" from cancer research to teach the body to recognise HIV and kill it.Oncologists educate the immune system to recognise cancer as a threat and kill it.There were ongoing trials using immunotherapy cancer drugs on HIV patients, explained Lewin.Gene editing is also under consideration.About 3.4 million South Africans are on anti-retroviral medication, leaving an estimated 3 million still not on treatment.Of major concern is the rate of infection among young women.Leaders and scientists are expected to discuss whether young female South Africans from the age of 15 should be given daily prevention such as ARV drug Truvada as therapy until they are about 25. This is because they are at extreme risk of contracting HIV and preventing a disease is better and cheaper than giving treatment for life.The government has high hopes for the conference."When the curtain comes down on Aids 2016 at the end of these five days ... the world must be a better place as a result of our deliberations in Durban. Given some unsettling developments globally, Aids 2016 is indeed a beacon of hope for the world - a gathering that proves that we can work together across geography, nationality, class and race to confront challenges that affect all people on our planet," said Minister in the Presidency Jeff Radebe.- Additional reporting Matthew Savides, Leonie Wagner..