Members of the international HIV research community are reeling from the news that many of their own, including world-renowned AIDS researcher Joep Lange, perished when Malaysia Airlines Flight 17 was shot down Thursday over eastern Ukraine.

The victims were on their way to the International AIDS Conference that begins this weekend in Melbourne, Australia, a trip halfway around the world that necessitated a change of planes in Kuala Lumpur.

The identities of the victims have not been officially confirmed by the airlines. But Lange’s office in Amsterdam confirmed in a statement that he died in the crash.

Lange, a Dutch citizen, had been a pioneer in the field since the early days of the AIDS epidemic and had worked tirelessly, his friends and colleagues said, to improve access to life-saving drugs in impoverished corners of the globe.

“His loss casts a pall over the International AIDS Conference just getting underway in Melbourne,” wrote Daniel R. Kuritzkes, a professor of medicine at Harvard Medical School. He called Lange “an extraordinary leader, scientist and humanitarian” who, as a past president of the International AIDS Society and as a leading Dutch academic researcher, “fought ceaselessly for the dignity of all HIV-infected persons throughout the world.”

Shawn Jain, spokesman for the Whitman-Walker Clinic in Washington, said late Thursday by e-mail: “The conference already brings out a lot of emotion in attendees because so many have been lost to HIV/AIDS (and the global epidemic, of course, continues), so to have this happen will only compound the sense of loss that many cope with at this event. To hear that Joep Lange, a former president of the organization that puts on the conference (the International AIDS Society) perished in the crash is especially devastating.”

Also killed were Pim de Kuijer and Martine de Schutter, who worked for organizations associated with the AIDS Fonds foundation, according to a colleague, Stop AIDS Now Executive Director Louise van Deth.

“It is incomprehensible that they’re no longer here,” van Deth said. “It is a heavy blow that people who have been so active for so long in the fight against AIDS have been wiped out.”

She said Lange’s death was a particular loss, noting that he was the driving force behind the Amsterdam Institute for Global Health and Development.

The International AIDS Society confirmed that “a number of colleagues and friends” en route to the conference were on the plane. About 14,000 delegates are expected at the conference.

“At this incredibly sad and sensitive time, the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy,” the society said in an official statement.

Paul Volberding, professor of medicine and director of the AIDS Research Institute at the University of California at San Francisco, was already in Australia, and said by e-mail of Lange: “He was coming to share with us his deep insights in attacking the HIV epidemic from his long-standing and leading role in work across the world but particularly in Asia and Africa. Joep was a a calm voice but an absolutely fierce and committed advocate for access to HIV care for all. He was unafraid of speaking the truth and especially willing to take public officials to task when they deserved it. Many of us knew him as a wonderful friend as well as an outstanding scientific colleague. He was broad in his expertise and a voracious reader. This is an unspeakable loss, yet again to a senseless act of violence.”

AIDS research has been marked by previous aviation disasters. Irving Sigal, a molecular biologist who helped develop the drugs used to treat HIV, died in the explosion of Pan Am Flight 103 over Lockerbie, Scotland, in 1988. Ten years later, prominent researchers Jonathan Mann and Mary Lou Clements-Mann died in the crash of Swissair Flight 111 off the coast of Nova Scotia.