Two HIV-positive men have been cleared of the virus after a bone marrow transplant, Australian researchers report.

The patients, who want to remain anonymous, were treated at Sydney's St Vincent's Hospital and have undetectable levels of HIV.

The results are being presented as part of the 20th International AIDS conference in Melbourne, which is going ahead despite a number of delegates being killed in the Malaysia Airlines tragedy.

University of NSW Kirby Institute's Professor David Cooper says the results herald a new direction in HIV research.

"We are so pleased that both patients are doing reasonably well years after the treatment for the cancers and remain free of the cancer and virus," Professor Cooper said.

While both men were cleared of the virus, they remain on antiretroviral therapy as a protective measure.

In one case, the patient had a successful bone marrow transplant for non-Hodgkin's lymphoma. His donor had one of two possible copies of a gene that gives protection against HIV.

But in the second case, the man had a bone marrow transplant for acute myeloid leukaemia with a donation that did not have the gene protecting against HIV.

Bone marrow transplants not the cure for HIV/AIDS

Until this research, the only person considered to have cleared HIV is an American man, Timothy Ray Brown, who had bone marrow transplants in 2007 and 2008.

His donor had both copies of the gene that protects against HIV.

Mr Brown was able to stop antiretroviral therapy and remains clear of virus. But when two patients in Boston had transplants without the gene mutation, the virus returned after antiretroviral treatment ceased.

Experts stress that while the Sydney results are significant, bone marrow transplants are not a cure for HIV, as it remains a costly and potentially dangerous procedure.

The two Sydney patients are being closely monitored to see if there is any residual virus and how it can be controlled.

Professor Cooper says working out where the remains of the virus are hiding has become the big scientific question in HIV/AIDS research.

"It will be essential to understand in order to achieve a cure," he said.

Researchers say the results offer new hope for HIV-positive people with leukaemia and lymphoma.

"For the time being, the Sydney results mean more people who are suitable for bone marrow transplants could participate in clinical trials," UNSW Kirby Institute's Dr Kersten Koelsch said.

AIDS conference to honour plane crash victims

Thousands of HIV researchers, advocates and journalists from 200 countries will be in Melbourne from July 20 to 25 for AIDS 2014, the largest health conference ever hosted in Australia.

This year's conference has been marred by the deaths of scores of delegates on board the Malaysia Airlines jet that was shot down over eastern Ukraine.

About 100 of the 298 people killed on the downed jet were heading to the AIDS conference, including researchers, health workers, activists and people living with HIV.

Conference chairwoman Professor Sharon Lewin says the event will go ahead in honour of their colleagues.

"Everyone in the audience, and I know everyone on the organising committee, is feeling so torn, feeling such sadness."

Victorian Premier Denis Napthine agrees.

"They would want us to use this loss to increase our efforts here and across the world to pursue their goal to end the loss and harm caused by AIDs and HIV across the world," he said.

It has been confirmed that the victims include renowned HIV researcher Professor Joep Lange and his wife, along with Glen Thomas from the World Health Organisation.