The news of a second person being cured of HIV represents a significant milestone in medical history, offering renewed hope for a widespread cure. This achievement builds upon insights from a previous, similarly successful case. While not a universally applicable treatment, this outcome provides crucial scientific understanding of how HIV can be cleared from the body. It underscores the potential for future therapeutic strategies that could one day offer a cure to more individuals living with HIV.
The Second Patient’s Story
The second individual to be cured of HIV, Adam Castillejo, became known as the “London Patient.” He was diagnosed with HIV in 2003 and later with Hodgkin lymphoma, a cancer affecting the lymphatic system, in 2012. His HIV infection had been managed with antiretroviral therapy (ART) for years.
His aggressive cancer required a specialized medical procedure in 2016 at Hammersmith Hospital in London. Following this treatment, his antiretroviral medications were gradually discontinued. After approximately 30 months without antiretrovirals, tests confirmed no viable HIV in his blood, brain fluid, intestinal, or lymph tissue, leading to the declaration of his remission.
The Stem Cell Transplant Method
Adam Castillejo’s HIV remission resulted from an allogeneic hematopoietic stem cell transplant. This involves replacing a patient’s diseased bone marrow with healthy stem cells from a donor. In this case, the donor possessed a rare genetic mutation known as CCR5-delta 32.
The CCR5 gene codes for a protein on the surface of immune cells, particularly CD4+ T-cells, which HIV uses as a co-receptor to enter and infect these cells. The CCR5-delta 32 mutation causes a truncation of this protein, effectively preventing the HIV virus from binding to and entering the cells. By transplanting stem cells from a donor with this mutation, Castillejo’s immune system was essentially replaced with cells inherently resistant to HIV infection, leading to the sustained remission observed.
Significance for HIV Research
This successful outcome provides significant validation for the CCR5-mediated cure pathway, demonstrating that HIV can be eliminated from the body. However, the stem cell transplant method is not a practical or scalable solution for the millions of people living with HIV worldwide. The procedure carries substantial risks, including severe complications like graft-versus-host disease and a high mortality rate, making it suitable only for individuals with life-threatening hematological malignancies who are also HIV-positive.
The rarity of suitable donors with the CCR5-delta 32 mutation further limits its widespread applicability; only about 1% of people of European or Western Asian ancestry carry this mutation. Despite these limitations, the “London Patient” offers invaluable insights into the mechanisms of HIV persistence and remission. It reinforces the scientific understanding that blocking the CCR5 co-receptor can lead to a functional cure, guiding ongoing research toward less invasive and more broadly accessible cure strategies, such as gene therapies or novel immunotherapies targeting CCR5.
Connecting to the First Cured Patient
Adam Castillejo’s case closely mirrors Timothy Ray Brown, known as the “Berlin Patient,” who was the first person cured of HIV in 2007. Both individuals were HIV-positive and also suffered from blood cancers—Brown with acute myeloid leukemia and Castillejo with Hodgkin lymphoma. The curative treatment in both instances involved an allogeneic hematopoietic stem cell transplant from a donor carrying the CCR5-delta 32 genetic mutation.
Both patients achieved sustained HIV remission after discontinuing antiretroviral therapy, with no detectable active virus in their bodies. While Timothy Ray Brown’s case involved two transplants and a more intense conditioning regimen including radiation, the fundamental mechanism of cure—replacement of susceptible immune cells with HIV-resistant ones—remained consistent. These two cases, separated by over a decade, provide robust evidence that targeting the CCR5 co-receptor through stem cell transplantation can effectively eliminate HIV from the body.