Dozens of leading AIDS researchers and scientists are understood to be amongst those on board flight flight MH17 shot down in Ukraine.

They were on their way to an international conference in Melbourne.

Anthony Hayes, managing director of public affairs and policy at Gay Men’s Health Crisis said the amount of knowledge lost would be irreplaceable.

“You’re going to have a loss of institutional memory about an epidemic that’s 30 years old. And so these people were going to this conference in the spirit of bringing people’s lives and making them better. So I think that the loss is a lot of that institutional memory about where the epidemic’s been and where it is today, and where we’ll be in the future.”

Joep Lange, the former president of the International Aids Society and a leading HIV researcher, was one those killed. He had fought to improve access to life-saving drugs for HIV positive patients living in poor countries. His partner, Jacqueline van Tongeren, also died.

Conference organisers say they are still trying to confirm exactly how many delegates were on the plane.

Around 12,000 people are expected at the 20th anniversary AIDS 2014 conference in Melbourne which is due to start on Saturday.