Key Takeaways
- A 62‑year‑old man living with HIV for 27 years achieved sustained remission after a bone‑marrow transplant for acute myelogenous leukemia.
- The donor stem cells carried the rare CCR5 Δ32 mutation, which blocks HIV entry into cells.
- Antiretroviral therapy (ART) was stopped in July 2025; as of April 2026 HIV remains undetectable in blood and tissue assays.
- If the undetectable status continues for another 2.5 years post‑ART, he would become the 11th person worldwide considered cured of HIV.
- The case adds to the growing evidence that CCR5‑deficient transplants can lead to HIV remission, informing future gene‑therapy and immunotherapy strategies.
Patient Overview and HIV History
The individual was first diagnosed with HIV in 1999 and has lived with the virus for 27 years, maintaining viral suppression through continuous antiretroviral therapy (ART). Throughout this period he adhered to a standard ART regimen, which kept plasma HIV RNA levels below the limit of detection and preserved his immune function. Long‑term ART also prevented progression to AIDS, allowing him to remain relatively healthy until an unrelated malignancy emerged. His extensive treatment history provides a robust baseline for assessing any changes in HIV reservoirs after the transplant procedure.
Development of Cancer and Need for Transplant
In 2021 the patient was diagnosed with acute myelogenous leukemia (AML), an aggressive blood cancer that necessitated intensive chemotherapy followed by hematopoietic stem‑cell transplantation. AML treatment often destroys the patient’s bone marrow, making a transplant essential for reconstituting blood cell production. The urgency of the leukemia treatment created a clinical opportunity to simultaneously address his HIV infection by selecting a donor with genetic resistance to the virus.
Selection of CCR5 Delta-32 Donor Stem Cells
The transplant team searched for a donor whose hematopoietic stem cells possessed the homozygous CCR5‑Δ32 mutation—a 32‑base‑pair deletion that renders the CCR5 co‑receptor non‑functional and prevents most strains of HIV from entering CD4⁺ T cells. Identifying such a donor is uncommon; the mutation occurs in roughly 1 % of individuals of Northern European descent and is far rarer in other populations. After extensive screening, a compatible donor with the CCR5‑Δ32 genotype was found, providing the theoretical basis for an HIV‑resistant immune system post‑transplant.
Procedure and Immediate Post‑Transplant Phase
At the Princess Margaret Cancer Centre, part of the University Health Network, the patient received myeloablative chemotherapy followed by infusion of the selected donor stem cells. The transplant engrafted successfully, with donor-derived neutrophils and platelets appearing within the expected timeframe. Early post‑transplant monitoring showed no signs of graft‑versus‑host disease or graft rejection, and the patient’s hematologic parameters normalized. Importantly, early PCR testing of peripheral blood mononuclear cells revealed a rapid decline in HIV DNA, suggesting that the donor cells were replacing the host’s HIV‑susceptible immune compartment.
Discontinuation of Antiretroviral Therapy and Monitoring
After confirming stable hematopoietic chimerism and undetectable HIV plasma viral load on ART, the clinical team decided to interrupt antiretroviral therapy in July 2025, under close supervision. Subsequent monitoring included frequent plasma HIV RNA ultrasensitive assays (limit of detection < 1 copy/mL), HIV DNA quantification in sorted CD4⁺ T cells, and viral outgrowth assays to assess replication‑competent reservoirs. All assays remained negative for detectable virus through MRI‑guided tissue sampling of gut‑associated lymphoid tissue and lymph nodes, performed at three‑month intervals.
Outcome: Sustained HIV Remission and Implications
As of April 2026—nine months after ART cessation—the patient continues to exhibit undetectable HIV levels in all tested compartments, with no evidence of viral rebound. His CD4⁺ T‑cell count remains within the normal range, and he reports no HIV‑related symptoms. The sustained remission meets the operational definition used in HIV cure research: prolonged off‑ART viral suppression without detectable reservoirs. Should this status persist for an additional 2.5 years post‑ART, he would join the small cohort of individuals considered cured of HIV, currently numbering ten worldwide.
Comparison to Global Cases and Definition of Cure
The Toronto case mirrors the few previously reported instances of HIV remission following CCR5‑Δ32–matched transplants, most notably the “Berlin” and “London” patients. However, it distinguishes itself by occurring in a Canadian healthcare setting, involving an older recipient, and employing a contemporary transplant protocol with reduced-intensity conditioning in some steps. The case reinforces the consensus that durable HIV remission is achievable when the recipient’s immune system is replaced by CCR5‑deficient cells, although the approach remains limited by donor rarity and transplant risks.
Research Significance and Future Directions
This successful outcome provides valuable proof‑of‑concept data for strategies aiming to replicate the CCR5‑Δ32 effect without the hazards of allogeneic transplantation. Approaches such as CRISPR‑based gene editing of autologous hematopoietic stem cells, CCR5‑targeted chimeric antigen receptor (CAR) T‑cell therapies, and therapeutic vaccines are actively being explored. Insights from the patient’s immune reconstitution, cytokine profile, and residual immune activation will help refine these methods and define safety benchmarks for future clinical trials.
Conclusion and Acknowledgements
The sustained HIV remission observed in this 62‑year‑old patient underscores the potential of genetically resistant stem‑cell transplantation as a pathway toward an HIV cure. While the procedure is not presently scalable for the broader HIV‑positive population, each case deepens scientific understanding and informs the development of less invasive, gene‑based curative strategies. The research team expresses gratitude to the patient and his family for their trust and participation, to the stem‑cell donor, and to the multidisciplinary clinicians at UHN, Unity Health Toronto, and the University of Toronto whose collaborative effort made this milestone possible.