CCR5Δ32 Hematopoietic Stem Cell Transplantation: The Berlin, London, and Düsseldorf HIV Cures

1. Introduction: The Exceptional Cases That Redefined HIV Cure Research

Combination antiretroviral therapy (ART) suppresses HIV-1 replication, restores CD4+ T-cell counts, and converts a once-fatal infection into a manageable chronic disease. Yet ART is not curative. It must be taken lifelong, it does not eliminate the latent viral reservoir integrated into the genome of long-lived memory CD4+ T cells, and interruption almost invariably leads to viral rebound within weeks. Against this background, a small number of individuals have achieved sustained HIV remission after receiving an allogeneic hematopoietic stem cell transplantation (HSCT) from a donor who carries the CCR5Δ32 mutation. These cases are among the most influential in the entire field, because they provide the clearest proof of concept that HIV infection can, in principle, be durably controlled without ART.

At the same time, these cases are frequently misunderstood. They are medical exceptions produced as a side effect of cancer treatment, not a therapy that can be offered to the roughly 39 million people living with HIV worldwide. The procedure carries substantial mortality, requires a rare and closely matched donor, and depends on the patient already having a hematologic malignancy that justifies transplantation. This article reviews the biology of CCR5 and the Δ32 mutation, the mechanism by which CCR5Δ32 HSCT could clear or control HIV, the documented cases reported to date, and the limitations that keep this approach firmly outside of routine care.

2. The Biology of CCR5 and the Δ32 Mutation

2.1. CCR5 as a Co-receptor for HIV Entry

HIV-1 enters target cells through a sequential interaction between the viral envelope glycoprotein (Env) and two host surface molecules. The CD4 receptor binds the gp120 subunit of Env and induces a conformational change that exposes a co-receptor binding site. The virus then engages a chemokine receptor — most commonly CCR5 — to trigger fusion of the viral and cellular membranes. Viruses that use CCR5 are termed R5-tropic (or macrophage-tropic); those that use the related receptor CXCR4 are termed X4-tropic. R5-tropic variants are the predominant transmitted viruses and dominate during the early and chronic phases of most infections, which is precisely why removing CCR5 from the target-cell population is such an attractive strategy.

CCR5 is a seven-transmembrane G-protein-coupled receptor normally involved in chemotaxis of immune cells toward inflammatory chemokines such as RANTES (CCL5), MIP-1α (CCL3), and MIP-1β (CCL4). Individuals who lack functional CCR5 are, for the most part, immunologically healthy, which indicates that the receptor is dispensable under ordinary circumstances — a critical safety consideration for any therapy that seeks to disable it.

2.2. The 32-Base-Pair Deletion

The CCR5Δ32 allele contains a 32-base-pair deletion within the coding region of the CCR5 gene. The deletion causes a frameshift and introduces a premature stop codon, so the truncated protein is not expressed on the cell surface. Homozygotes (inheriting the Δ32 allele from both parents) therefore lack functional surface CCR5 on their cells and are highly resistant to infection by R5-tropic HIV, although resistance is not absolute. A well-documented case of an individual homozygous for CCR5Δ32 who nonetheless became infected with an X4-tropic or otherwise CCR5-independent virus has been reported in the literature and is often cited to emphasize that the mutation is protective rather than sterilizing. [Marked for verification.]

Heterozygotes (a single Δ32 allele) express reduced levels of CCR5 and show slower disease progression on average, but they remain susceptible to infection. The protective effect is therefore graded and depends on the genetic background of the virus the person encounters.

2.3. Population Genetics

The CCR5Δ32 allele is most common in populations of Northern European descent, where the homozygous genotype occurs in approximately 1% of people and the heterozygous genotype in roughly 10-15%. The allele is rarer or absent in many African, East Asian, and Indigenous American populations. This geographic distribution has direct practical consequences: even if the procedure were otherwise scalable, suitable homozygous donors would be far less available to patients of non-European ancestry — a disparity that has been highlighted in the discussion of the «New York Patient» case described below.

3. Allogeneic HSCT as an Accidental Cure Strategy

3.1. How the Procedure Works

Allogeneic HSCT is an established treatment for high-risk hematologic malignancies such as acute myeloid leukemia (AML) and lymphoma. The patient first receives conditioning — chemotherapy with or without total body irradiation — to destroy the diseased bone marrow and make room for donor cells. Donor hematopoietic stem cells (HSCs) are then infused and engraft, rebuilding the entire blood and immune system from the donor’s genetic template. Graft-versus-leukemia immunity contributes to cancer control, but the same donor immune cells can attack the recipient’s tissues, producing graft-versus-host disease (GvHD).

The HIV-specific twist is that if the donor HSCs are homozygous for CCR5Δ32, the reconstituted immune system lacks functional CCR5 and is therefore resistant to R5-tropic HIV. In effect, the procedure replaces the viral target population with one the virus cannot easily enter.

3.2. Proposed Mechanisms of HIV Clearance

Several mechanisms plausibly contribute, and their relative importance remains a subject of study:

• Replacement with resistant target cells. New thymic output and peripheral expansion populate the body with donor-derived, CCR5-negative CD4+ T cells that R5-tropic HIV cannot readily infect, cutting off the virus from its principal replication niche.
• Conditioning-induced reservoir depletion. Myeloablative or reduced-intensity conditioning, together with any anti-HIV effect of immunosuppressive drugs, kills many of the latently infected cells present at the time of transplant, shrinking the reservoir that would otherwise seed rebound.
• Graft-versus-reservoir (GvR) effect. Allogeneic donor lymphocytes may recognize and eliminate residual recipient immune cells harboring latent provirus, an effect conceptually analogous to graft-versus-leukemia.
• Ongoing immune surveillance. A new, genetically distinct immune system may mount effective HIV-specific responses against any residual virus.

The distinction between these mechanisms matters because it determines how essential the CCR5Δ32 genotype really is. If conditioning and GvR alone were sufficient, then ordinary matched transplantation might cure HIV — an idea tested by the «Boston Patients,» whose outcomes argue strongly that the CCR5-negative donor genotype is central (see Section 5).

4. The Documented Cases

The cases below are widely reported in the scientific and lay press. Where a detail is widely accepted but rests on conference abstracts or ongoing follow-up, it is flagged. This article deliberately separates confirmed, peer-reviewed remissions from early or partial reports.

4.1. The Berlin Patient (Timothy Ray Brown)

The first and best-known case. Timothy Ray Brown was diagnosed with HIV in 1995 and later developed acute myeloid leukemia. In 2007 he received an allogeneic HSCT in Berlin from a donor homozygous for CCR5Δ32, followed by a second transplant. After the procedure he remained off ART with no detectable viral rebound, and his case was presented as the first credible cure in 2008. He became a global advocate and publicly disclosed his identity in 2010. He died in September 2020 from a relapse of his leukemia, not from HIV; at the time of death his HIV remained in remission. His case established the core proof of concept and remains foundational.

4.2. The London Patient (Adam Castillejo)

The second well-documented case. Adam Castillejo, who had HIV and Hodgkin lymphoma, underwent allogeneic HSCT in 2016 in London from a CCR5Δ32 homozygous donor using reduced-intensity conditioning. He continued ART for roughly 16 months after transplantation and then stopped. Sustained HIV remission was reported in 2019, and he publicly identified himself in 2020. His case demonstrated that the Berlin result was reproducible and, importantly, that a less intensive conditioning regimen could suffice. He has remained in remission in subsequent follow-up. [Continued follow-up is ongoing; details of the most recent virologic monitoring to be verified.]

4.3. The Düsseldorf Patient

A third case was reported in 2023. The patient, diagnosed with HIV in 2008 and AML in 2011, received an allogeneic HSCT in Düsseldorf in 2013 from a CCR5Δ32 homozygous donor. ART was discontinued in 2018, and the patient has since remained free of viral rebound. This case strengthened the reproducibility of the approach and added to the small, growing series of confirmed remissions. [Exact duration of ART-free follow-up and current status to be verified against the primary publication.]

4.4. The City of Hope and New York Patients

Two further cases were reported around 2022-2023, extending the strategy in important ways:

• City of Hope patient. An older man with long-standing HIV and leukemia who received a transplant from a CCR5Δ32 homozygous donor and remained in HIV remission after stopping ART. The case was notable for the patient’s age and prolonged prior HIV history, suggesting that even long-established infection may not preclude remission. Detailed characterization is drawn largely from conference presentations and follow-up publications. [Marked for verification.]
• New York Patient. A middle-aged woman of mixed ancestry with HIV and leukemia who received a haploidentical (haplo-cord) transplant combining partially matched adult donor stem cells with umbilical cord blood carrying the CCR5Δ32 mutation. She was the first woman and first person of mixed racial ancestry reported to achieve this outcome, and the case illustrated how cord-blood grafts might broaden donor availability. [Marked for verification; long-term follow-up ongoing.]

These cases also intersect with gene-editing approaches, in which a patient’s own cells are modified to disrupt CCR5 before reinfusion — a conceptually related but biologically distinct strategy discussed in Section 6.

4.5. The Boston Patients: The Critical Negative Control

Between 2011 and 2013, two patients in Boston («the Boston Patients») with HIV and lymphoma received allogeneic HSCT from donors who were not CCR5Δ32 homozygous. Both initially appeared to have no detectable virus after stopping ART for a period. However, HIV rebounded in both, confirming that replacement with CCR5-positive donor cells is insufficient for durable remission on its own. This contrast is a cornerstone of the current interpretation: the CCR5Δ32 genotype, rather than transplantation per se, is the decisive factor.

More recently, individual transplant recipients with HIV who received donors lacking CCR5Δ32 have been described as achieving apparently long-term remission. If validated, such cases would complicate the assumption that the mutation is absolutely required — but they remain exceptional and are best regarded as early reports rather than established science. [Marked for verification.]

4.6. Confirmed Versus Early Reports

5. Why It Is Not a General HIV Treatment

5.1. Procedure-Related Mortality

Allogeneic HSCT is one of the most toxic interventions in medicine. Transplant-related mortality varies with age, conditioning intensity, underlying disease, and donor match, but in general it is measured in the range of roughly 10% or more, and significantly higher in older or less fit patients. Offering such a procedure to the approximately 39 million people living with HIV who are not otherwise facing a life-threatening malignancy would be indefensible. For a person with well-controlled HIV on ART, the risk of the transplant vastly exceeds the risk of the infection.

5.2. Graft-Versus-Host Disease

GvHD occurs when donor immune cells attack the recipient’s tissues, and it can affect the skin, gut, and liver; it is a leading cause of morbidity and late mortality after transplantation. The Berlin Patient himself experienced significant GvHD. Chronic GvHD can require prolonged immunosuppression, which in turn carries infectious risks. A cure that trades lifelong ART for lifelong immunosuppression is not an acceptable trade for most patients.

5.3. Donor Rarity and HLA Matching

Finding a donor who is both CCR5Δ32 homozygous and HLA-compatible is a severe bottleneck. Only about 1% of people of Northern European descent are homozygous, the allele is much rarer in other populations, and HLA matching imposes its own constraints. This double requirement means that even among patients who might medically benefit, most would never find a suitable donor. Registries such as the international stem cell donor networks have been screened for CCR5Δ32 donors, but the pool remains minute relative to demand.

5.4. The Malignancy Requirement

Every confirmed cure has occurred in a patient who needed HSCT anyway to treat cancer. This is not incidental: the malignancy is the ethical justification for accepting the risks of transplantation, and it also means that «cure» here is a byproduct of a cancer therapy, not an HIV therapy. Without an independent indication, the risk-benefit calculus does not permit the procedure.

5.5. Non-Scalability and Cost

Even setting aside donor scarcity and toxicity, the procedure is expensive, resource-intensive, and dependent on specialized transplant centers. It cannot be deployed at population scale, particularly in the low- and middle-income settings where most HIV infections occur. The honest conclusion is that CCR5Δ32 HSCT is a proof of concept and a source of mechanistic insight, not a route to an HIV-free world.

6. Gene Editing: Trying to Capture the Same Idea with Autologous Cells

The logical response to the donor problem is to edit the patient’s own cells instead of relying on a rare donor. Two broad approaches have been explored:

• Zinc-finger nucleases (ZFNs) targeting CCR5 were used in early trials to knock out the receptor in autologous CD4+ T cells. These studies demonstrated that modified cells could persist and expand in vivo, but they did not cure HIV, and the populations of edited cells were insufficient to block infection of the unedited majority.
• CRISPR-Cas9 and related nucleases have been applied to disrupt CCR5 in CD4+ T cells and hematopoietic stem/progenitor cells. Delivering an edited, HIV-resistant immune system without allogeneic transplantation would avoid GvHD and donor matching entirely. However, editing efficiency, off-target effects, the need for myeloablative conditioning to make edited stem cells engraft, and the fact that X4-tropic virus or other co-receptor usage can escape a CCR5-only strategy all remain obstacles.

None of these gene-editing approaches has yet produced a confirmed cure in humans, and they should be described as experimental. They are nevertheless the most direct attempt to translate the Berlin/London/Düsseldorf lesson into something potentially scalable. [Marked for verification regarding the current clinical status of specific CCR5-editing trials.]

7. Ethical and Interpretive Considerations

These cases raise questions that go beyond biology. First, patients who undergo such procedures are not enrolled in a randomized cure trial; they are receiving a cancer therapy in which HIV remission is an incidental outcome, which complicates consent and interpretation. Second, the media narrative of «cured» patients can create unrealistic expectations for people living with HIV, for whom ART remains an effective, safe, and remarkably successful treatment. Third, the reliance on a donor genotype concentrated in Northern European populations raises equity issues that the more genetically diverse New York Patient case only partially addresses.

Finally, there is a subtle scientific caution: «cure» in this context usually refers to sustained ART-free remission, not necessarily the complete eradication of every latently infected cell. Sensitive reservoir assays can still detect viral DNA, and the possibility of later rebound cannot be excluded with certainty. Precision in language — remission versus sterilizing cure — is essential when communicating these results.

8. Conclusion

The Berlin, London, and Düsseldorf patients — together with the City of Hope and New York cases — have established that allogeneic HSCT from a CCR5Δ32 homozygous donor can produce durable HIV remission in the context of cancer treatment. The CCR5Δ32 genotype appears to be the decisive ingredient: transplantation from wild-type donors (the Boston Patients) did not prevent rebound. Mechanistically, the strategy combines replacement of the viral target population, conditioning-induced reservoir depletion, and likely graft-versus-reservoir effects.

Yet the very features that make the approach work also make it non-scalable: high transplant-related mortality, graft-versus-host disease, extreme donor scarcity, and the need for an independent malignancy to justify the procedure. It is a cure achieved by accident, for a few, at great risk. Its true value lies less in providing a treatment than in proving that durable HIV remission is biologically achievable — thereby driving the search for safer, autologous, gene-edited, or immune-based strategies that can one day be offered broadly. For the foreseeable future, ART remains the standard of care for the overwhelming majority of people living with HIV.

Sources and Key Research Centers

1. National Institute of Allergy and Infectious Diseases (NIAID), NIH — The principal US funder of HIV pathogenesis, reservoir, and cure research, including studies of CCR5 biology and transplantation-based remission.
2. National Institutes of Health (NIH) — Umbrella agency supporting the clinical and translational infrastructure behind HIV cure studies.
3. Charité — Universitätsmedizin Berlin — Institution associated with the Berlin Patient case, the first reported durable HIV remission after CCR5Δ32 HSCT. [Primary clinical report details to be verified.]
4. University College London (UCL) — Research home of the team reporting the London Patient. [Citation details to be verified.]
5. Heinrich Heine University Düsseldorf — Associated with the Düsseldorf Patient report (2023). [Citation details to be verified.]
6. City of Hope — Cancer and research center associated with a CCR5Δ32 transplant HIV remission case. [Details to be verified.]
7. Weill Cornell Medicine / New York-Presbyterian — Associated with the haplo-cord New York Patient case. [Details to be verified.]
8. IciStem Consortium (International Collaboration to Guide and Investigate the Potential for HIV Cure by Stem Cell Transplantation) — A European research collaboration dedicated to systematically studying HIV remission after stem cell transplantation and to identifying the mechanisms involved.
9. Nature Medicine — Peer-reviewed journal that has published primary reports and follow-ups on transplantation-associated HIV remission. [Specific article citations to be verified.]
10. The New England Journal of Medicine — Publishes major HIV treatment and cure-related clinical research, including transplantation and gene-therapy studies.
11. The Lancet HIV — Dedicated journal covering HIV clinical research, including cure case reports and editorials.
12. Blood (American Society of Hematology) — Leading hematology journal covering allogeneic transplantation, GvHD, and donor selection.
13. World Health Organization (WHO) — Provides global epidemiological context and treatment guidelines that define why scalable options, not transplant, are needed.
14. UNAIDS — Source of global HIV prevalence and treatment-access data referenced in the discussion of scalability.
15. Centers for Disease Control and Prevention (CDC), Division of HIV Prevention — Public-health data and guidance on HIV treatment and prevention.
16. International AIDS Society (IAS) — Towards an HIV Cure — Global scientific initiative coordinating and prioritizing HIV cure research, including transplantation and gene-editing approaches.
17. amfAR, The Foundation for AIDS Research — A major philanthropic funder of HIV cure research, including studies of CCR5 and reservoir biology.
18. ClinicalTrials.gov (US National Library of Medicine) — Registry of ongoing and completed clinical trials of stem cell transplantation and CCR5 gene editing for HIV. [Specific NCT numbers to be verified.]
19. US Food and Drug Administration (FDA) — Regulates cell and gene therapies and provides the regulatory framework under which any future curative approaches would be evaluated.