By Shauna Mazenes
In a Canadian first case, doctors have possibly cured a patient of HIV following a bone marrow transplant to treat a subsequent leukemia diagnosis.
Doctors at
UHN's Toronto General Hospital and
Princess Margaret Cancer Centre, Unity Health Toronto's St. Michael's Hospital, and the
University of Toronto collaborated on the case.
The patient, referred to as the "Toronto patient," is the eleventh in the world in sustained HIV remission. Bone marrow was transplanted from a donor with a genetic mutation, known as CCR5, that renders their cells resistant to the virus.
A bone marrow transplant is a treatment and potential cure for patients with life-threatening blood cancers that works by killing off diseased cells and replacing them with healthy stem cells from a donor. The CCR5 mutation is believed to also prevent HIV from entering immune cells and infecting the body.
"To be able to eliminate HIV from the body is clearly a major advance. This is not something that happens every day," says Dr. Sharon Walmsley, an infectious disease specialist at
UHN's HIV and Immunodeficiency Clinic, who oversees the patient's HIV care.
"We need to find other ways to get rid of the virus. These cases help scientists think about means by which they can do that."
Bone marrow transplants are not a standard treatment for HIV due to the high risk of infections and death. But Dr. Jonas Mattsson says, in this rare case, it was successful in targeting both HIV and cancer in the patient.
"If we can treat two things at once, we should try to do that," says Dr. Mattsson, director of the
Hans Messner Allogenic Stem Cell Transplant Program at the Princess Margaret Cancer Centre, where the transplant took place.
International search for a rare, HIV-resistant bone marrow donor
The patient was referred to Princess Margaret Cancer Centre after Dr. Walmsley suspected they had early leukemia.
"When we found out this patient also had HIV, we initiated an international search to not only find a perfectly matched donor [to treat the cancer], but to see if it was possible to find a donor who also carried the CCR5 mutation," says Dr. Mattsson.
Less than one per cent of people, most of whom are of northern European ancestry, are believed to carry this genetic mutation.
Finding such a donor was a complex process that involved searching some of the largest bone marrow registries in the world, including those in Germany and the U.S.
The Toronto patient underwent the transplant in 2021 and discontinued antiretroviral therapy in July 2025. As of April 2026, HIV remains undetectable in the patient using highly sensitive laboratory testing, including no HIV-specific immune responses — a finding consistent with cases considered cured internationally.
Dr. Walmsley presented the findings at the
Canadian Association of HIV Research Conference and is senior author of the published abstract.
How do bone marrow transplants work in patients with HIV?
A bone marrow transplant is an intensive form of immunotherapy that treats blood cancers and other serious blood disorders by replacing a patient's diseased blood with healthy stem cells from a donor.
Before the transplant, patients undergo "conditioning," which can include chemotherapy and full-body radiation. This process reduces cancer cells and creates space in the bone marrow — considered the most powerful organ of the immune system — for the donor's healthy cells to take hold and replace the cancer cells.
However, a patient's immune system is extremely vulnerable following the transplant, making it a risky treatment for patients with HIV. Much like a newborn baby, it can take several months to rebuild the immune system, putting a patient at a higher risk of infection that can be fatal.
"With the effectiveness of modern antiretroviral therapy for HIV, the risks of a bone marrow transplant far outweigh the benefits if there is no other indication for it," Dr. Walmsley says.
One of the greatest challenges in curing HIV, she explains, is the virus's ability to hide in human cells and remain dormant for decades. When the virus is dormant in these cells, it cannot be killed by HIV medications.
"HIV goes into the immune cells like a lock and a key," she explains. "But when you have the CCR5 mutation, the key doesn't work, so the virus can't get in the cells and can't multiply."
In the Toronto patient's case, the pre-transplant conditioning eliminated the immune system as much as possible, including the cancer cells and the HIV virus hiding in the immune cells. The patient's immune system was then replaced using stem cells with the CCR5 mutation that HIV cannot infect, reducing the likelihood that either the virus or the cancer will return.
Path toward an HIV cure
Dr. Tommy Alfaro Moya, a hematologist who was involved in the Toronto patient's post-transplant care at Princess Margaret Cancer Centre, says this is an important step towards one day finding a cure.
"This case represents years of careful clinical work, close monitoring and collaboration across specialties," says Dr. Moya, also an author on the abstract. "It offers critical insight into how HIV can be eliminated from the body, informing safer approaches in the future."
Dr. Mario Ostrowski, clinician-scientist at St. Michael's Hospital, says while HIV is now medically manageable, the need for a cure remains.
"HIV infection, although well controlled with antiretroviral therapy, still carries enormous stigma and discrimination," says Dr. Ostrowski, also the Ontario HIV Treatment Network Applied Research Chair and professor at the University of Toronto's Temerty Faculty of Medicine.
"A bone marrow transplant from these donors can provide a potential cure. These transplants provide clues to develop similar, less toxic and less expensive therapies by studying these individuals."
Going forward, UHN will continue to explore this approach for patients living with HIV who develop blood disorders that require a transplant.
UHN is also developing a research protocol where patients who undergo this procedure can be followed and studied, in hopes of determining factors associated with success to find better treatments, and potentially a cure, for HIV.
