CCR5 is a protein on the surface of immune cells that acts as a docking station for chemical signals guiding those cells toward infections and injuries. It became famous because HIV exploits it as a doorway into cells, but CCR5’s actual job is helping your immune system function normally. Its full name, C-C chemokine receptor type 5, reflects its role as a receiver for small signaling molecules called chemokines.
What CCR5 Does in the Immune System
CCR5 sits on the surface of several types of white blood cells, including T cells, macrophages, and monocytes. When tissue is damaged or infected, nearby cells release chemical distress signals (specifically CCL3, CCL4, and CCL5). These signals bind to CCR5 like a key fitting a lock, telling immune cells where to go. The result is targeted migration: immune cells travel through the bloodstream and arrive precisely where they’re needed.
This guidance system is essential for fighting infections. During a brain infection with West Nile virus, for example, the brain releases CCR5-binding signals that draw protective immune cells across the blood-brain barrier. Without functional CCR5, those cells can’t find their way. In mice completely lacking CCR5, West Nile virus infection is uniformly fatal. In humans, people missing both copies of the CCR5 gene face roughly 13 times the odds of a fatal outcome from West Nile compared to people with normal CCR5.
Beyond infection control, CCR5 helps regulate inflammation. It influences the movement and behavior of regulatory T cells, a subset of immune cells that dial inflammation up or down. It also affects macrophage activity in the lungs, where it plays a role in tissue remodeling and inflammatory responses.
How HIV Hijacks CCR5
HIV cannot enter a cell by grabbing just one receptor. It needs two. The virus first attaches to a protein called CD4 on the surface of immune cells. This initial contact triggers a shape change in the virus’s outer envelope, exposing a hidden region that then grabs CCR5. Only after binding both CD4 and CCR5 can the virus fuse its membrane with the cell and inject its genetic material inside.
The process happens in a tight sequence. The bond between the virus and CD4 alone is unstable and quickly reversible. CCR5 binding must follow almost immediately to lock the virus in place. Once CCR5 is engaged, it pulls the virus close enough to the cell surface for a specialized viral protein to punch into the cell membrane, creating a bridge between the two membranes. That bridge collapses inward, merging the viral and cell membranes and opening a pore through which HIV enters.
Not all HIV strains use CCR5. Some use a different coreceptor called CXCR4, and some can use either. Strains that rely on CCR5 are called R5-tropic, while those using CXCR4 are called X4-tropic. This distinction matters for treatment decisions, because drugs targeting CCR5 only work against R5-tropic virus. Before prescribing a CCR5-blocking medication, doctors use a laboratory test called a tropism assay to determine which coreceptor a patient’s HIV strain depends on.
The CCR5-Delta 32 Mutation
A naturally occurring genetic mutation, called CCR5-delta 32, deletes 32 base pairs from the CCR5 gene. This deletion produces a shortened, nonfunctional version of the protein that never reaches the cell surface. People who inherit one copy of this mutation (from one parent) produce less CCR5 and tend to have slower HIV progression if infected. People who inherit two copies (one from each parent) produce no functional CCR5 at all and are highly resistant to R5-tropic HIV.
The mutation is concentrated in populations of European descent, where 10% to 20% of people carry at least one copy. Ashkenazi Jewish populations show a similar frequency, around 21%. The mutation is rare outside Europe. In Middle Eastern countries like Syria, the frequency drops below 1%, and in Lebanon it has not been detected at all. In Gulf states like Bahrain, Iraq, Kuwait, and Saudi Arabia, prevalence hovers between 2% and 3%. Jordan and Egypt sit at the low end, around 0.6%.
This geographic pattern has led researchers to speculate that the mutation spread through European populations because it provided a survival advantage against some historic pathogen, though the exact selective pressure remains debated.
The Berlin Patient and HIV Cure Research
The most dramatic demonstration of CCR5’s role in HIV came from Timothy Ray Brown, known as the Berlin Patient. In 2007, Brown was living with HIV and developed acute myeloid leukemia, a blood cancer requiring a bone marrow transplant. His doctor, Gero Hütter, deliberately selected a donor who carried two copies of the CCR5-delta 32 mutation. On the day of the transplant, Brown stopped taking his HIV medications.
Brown’s leukemia returned later that year, requiring a second transplant from the same donor in 2008. After recovering, his HIV remained undetectable without medication for over a decade. He was the first person considered functionally cured of HIV. His case proved that replacing a patient’s immune system with CCR5-negative cells could eliminate the virus, and it opened an entirely new direction in cure research. A small number of additional patients have since achieved similar results through the same approach, though bone marrow transplants carry serious risks and are not a viable strategy for most people living with HIV.
CCR5-Blocking Medications
Maraviroc is the only approved drug that works by blocking CCR5. Rather than binding to the virus itself, it wedges into a pocket within the CCR5 protein, changing its shape just enough that HIV’s envelope can no longer grab hold. This is called allosteric inhibition: the drug doesn’t block the binding site directly but distorts it from the inside.
In clinical trials, patients taking maraviroc at 300 mg twice daily alongside other HIV medications saw their viral loads drop significantly. In a 10-day study of maraviroc alone, viral levels fell by roughly 98% on average. The drug is typically used in combination with other antiretroviral medications and only in patients confirmed to have R5-tropic virus.
Because CCR5 has roles beyond HIV, blocking it raises safety questions. The West Nile virus data is one concern: clinical guidelines have noted that patients on CCR5 blockers living in areas where West Nile virus is common should take extra precautions against mosquito bites. Other investigational CCR5-targeting drugs, including the antibody leronlimab, have been studied in phase 2 trials for conditions like long COVID, reflecting growing interest in the receptor’s broader role in inflammation.
CCR5 in Cancer
CCR5 has drawn increasing attention in oncology. In healthy tissue, only immune cells typically display CCR5 on their surface. But when normal epithelial cells become cancerous, they can begin producing CCR5 where it doesn’t belong. This misplaced CCR5 effectively gives cancer cells the same migratory ability that immune cells use, enabling them to travel through the body and establish new tumors at distant sites.
The receptor contributes to cancer progression through several mechanisms. CCR5 expression in cancer cells enhances their ability to resist DNA-damaging treatments like chemotherapy and radiation. It also promotes a “stemness” quality, helping cancer cells behave more like stem cells with greater survival capacity. Tumors actively release CCR5-binding signals that recruit immune-suppressing cells into the tumor environment, including regulatory T cells and a type of immune cell called myeloid-derived suppressor cells. These recruited cells then shield the tumor from the body’s own anti-cancer immune response.
In animal studies, blocking CCR5 with maraviroc reduced the number of regulatory T cells reaching tumors and decreased metastatic tumor burden in the lungs. Blocking CCR5 with antibodies inhibited melanoma growth and reduced the accumulation of immune-suppressing cells within tumors. Single-cell genetic analysis of breast cancer tissue has identified CCR5 as one of the top genes linked to immune cell diversity within the tumor environment, suggesting it plays a central coordinating role in how tumors manipulate local immunity.