# CCR5 Chemokine Receptor: HIV-1 Coreceptor Tropism, CCR5-Delta32 Mutation, and Entry Blockers


## Key Takeaways

- CCR5 is a G protein-coupled receptor crucial for leukocyte chemotaxis and serves as the primary coreceptor for R5-tropic HIV-1 strains, mediating viral entry via interaction with the gp120 envelope glycoprotein.
- The CCR5-Δ32 mutation, a 32-base pair deletion, confers near-complete resistance to R5-tropic HIV-1 infection in homozygotes by preventing functional CCR5 expression on the cell surface.
- Maraviroc, an FDA-approved CCR5 antagonist, binds to an allosteric pocket within the receptor's transmembrane bundle, stabilizing an inactive conformation and blocking HIV-1 entry.
- Gene therapy approaches, including ZFNs, TALENs, and CRISPR-Cas9, are being developed to disrupt the *CCR5* gene in hematopoietic stem cells, aiming to confer long-term HIV-1 resistance.
- Beyond HIV-1, CCR5 plays roles in various pathologies including atherosclerosis, rheumatoid arthritis, and cancer progression, with its dysregulation implicated in inflammatory and immune responses.
- Structural biology, particularly X-ray crystallography of CCR5 in complex with ligands like maraviroc and HIV-1 gp120, has enabled rational drug design and elucidated key interaction interfaces for viral entry.

---

## Executive Summary & Key Metadata

The C-C chemokine receptor type 5 (CCR5) is a seven-transmembrane G protein-coupled receptor (GPCR) that serves as the principal chemokine receptor for the inflammatory CC-chemokines CCL3 (MIP-1α), CCL4 (MIP-1β), and CCL5 (RANTES). Beyond its canonical role in leukocyte chemotaxis and immune surveillance, CCR5 is pathologically exploited as a mandatory fusion coreceptor for R5-tropic strains of human immunodeficiency virus type 1 (HIV-1). The discovery of a 32-base pair deletion in the open reading frame (CCR5-Δ32) that confers near-complete resistance to HIV-1 infection in homozygotes has made this locus a paradigm for host genetics in infectious disease and a prime target for gene therapy and small-molecule intervention [6, 79].

The receptor is encoded by the *CCR5* gene, located within a chemokine receptor gene cluster on chromosome 3p21.31. Its expression is tightly regulated at transcriptional, post-transcriptional, and post-translational levels, and its dysregulation is implicated in a spectrum of pathologies ranging from autoimmune diseases and cancer to viral hepatitis and neuroinflammatory disorders [71, 73]. The structural biology of CCR5, particularly its ligand-binding pocket and the extracellular loops involved in gp120 recognition, has been extensively characterized by X-ray crystallography, enabling rational drug design of allosteric antagonists such as maraviroc.

| **Attribute** | **Value** |
|:---|:---|
| **HGNC Symbol** | CCR5 |
| **UniProt Accession** | P51681 |
| **Representative PDB ID** | 4MBS |
| **Chromosomal Locus** | 3p21.31 |
| **Primary Molecular Function** | C-C chemokine receptor; GPCR; HIV-1 coreceptor |
| **Disease & Pathology Associations** | HIV-1/AIDS susceptibility; atherosclerosis; rheumatoid arthritis; cancer progression; COVID-19 severity; tick-borne encephalitis |

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Gene Coordinates and Chromosomal Context

The *CCR5* gene (HGNC:1606) is located on the short arm of chromosome 3 at cytogenetic band 3p21.31. The gene spans approximately 6.2 kilobases (kb) of genomic DNA and is oriented on the minus strand. The precise GRCh38/hg38 coordinates are chr3:46,370,946-46,376,206. The gene is intronless, a feature shared with most chemokine receptor genes, with the entire coding sequence contained within a single exon [15, 48].

The genomic neighborhood of *CCR5* is a dense cluster of chemokine receptor genes, including *CCR2*, *CCR3*, *CCR1*, *CCR5*, and *CXCR6*, arranged in a tandem array. This cluster is evolutionarily conserved across mammals and is thought to have arisen through serial gene duplication events. The proximity of *CCR2* and *CCR5* is particularly notable; they share high sequence homology and are separated by only ~17.5 kb. This close physical arrangement facilitates gene conversion events, which have been documented in both primates and leporids, contributing to allelic diversity and potentially to receptor dimerization interfaces [9, 61].

### 1.2 Promoter Architecture and Transcriptional Regulation

The promoter region of *CCR5* lacks a canonical TATA box but contains multiple GC-rich regions and several putative binding sites for transcription factors, including Sp1, GATA-1, and members of the Ets family [48]. Functional promoter analysis has identified a minimal promoter region spanning approximately 200 base pairs upstream of the transcription start site (TSS) that is sufficient for basal transcriptional activity. However, maximal promoter activity requires upstream enhancer elements located between -1000 and -500 relative to the TSS [15, 48].

A defining feature of the *CCR5* promoter is the presence of a complex polymorphic region containing a variable number of tandem repeats (VNTR) and multiple single nucleotide polymorphisms (SNPs). The most extensively studied promoter SNP is rs1799987 (also known as 59029G>A), which lies within a putative GATA transcription factor binding site. The A allele of rs1799987 has been associated with reduced CCR5 surface expression and altered receptor function, and it has been linked to susceptibility to various diseases, including sarcoidosis and Löfgren's syndrome [29, 63]. Another promoter variant, rs1800023, is part of a haplotype that influences CCR5 expression levels and has been implicated in the progression of diabetic nephropathy [74].

The 5' untranslated region (UTR) of *CCR5* is unusually long and contains multiple upstream open reading frames (uORFs) and a stable stem-loop structure. These elements are thought to regulate translation efficiency, providing a post-transcriptional layer of control. The 3' UTR contains several AU-rich elements (AREs) that mediate mRNA instability, allowing for rapid downregulation of CCR5 expression in response to cellular signals [48].

### 1.3 Epigenetic Regulation and 3D Chromatin Architecture

Recent epigenomic studies have revealed that *CCR5* expression is governed by a complex 3D chromatin architecture. In monocytes and macrophages, the 3p21.31 locus forms a CTCF-dependent regulatory hub that brings distal enhancer elements into physical proximity with the *CCR5* promoter [28]. This chromatin looping is cell-type specific and is disrupted in individuals carrying certain risk haplotypes associated with severe COVID-19. The risk variants alter the binding affinity of CTCF and other architectural proteins, leading to changes in enhancer-promoter interactions and subsequent dysregulation of CCR5 and neighboring genes [28].

### 1.4 Isoforms and Splice Variants

Despite being an intronless gene, *CCR5* produces multiple transcript variants through the use of alternative transcription start sites and alternative polyadenylation signals. The canonical transcript (NM_000579) encodes the full-length 352-amino acid receptor. However, several shorter isoforms have been described, some of which arise from the use of an alternative in-frame start codon downstream of the primary AUG. These N-terminally truncated isoforms lack the first few amino acids of the extracellular N-terminus, which is a critical determinant for chemokine binding and HIV-1 gp120 interaction [2].

Additionally, a naturally occurring truncated form of CCR5, resulting from a premature stop codon, has been identified. This isoform, known as CCR5-Δ32, is produced from the *CCR5-Δ32* allele and encodes a protein of 215 amino acids. The truncated protein is retained in the endoplasmic reticulum and fails to reach the cell surface, acting as a dominant-negative inhibitor of the full-length receptor through heterodimerization [2]. This mechanism of trans-dominant negative effect is a key feature of the CCR5-Δ32 phenotype and contributes to the reduced cell surface expression of CCR5 observed in heterozygotes [2, 90].

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Primary Structure and Topology

The CCR5 protein is a 352-amino acid polypeptide with a molecular weight of approximately 40.6 kDa (unmodified). It belongs to the class A (rhodopsin-like) family of GPCRs and exhibits the canonical seven-transmembrane (7TM) architecture. The protein can be divided into distinct structural and functional domains:

1.  **Extracellular N-terminus (residues 1-33):** This domain is critical for chemokine binding and HIV-1 gp120 recognition. It contains several tyrosine residues (Tyr10, Tyr14, Tyr15) that are post-translationally sulfated. Tyrosine sulfation enhances the electrostatic interaction with the positively charged chemokines and with the V3 loop of HIV-1 gp120. The N-terminus also contains a conserved Cys20 that forms a disulfide bond with Cys269 in extracellular loop 3 (ECL3), stabilizing the receptor conformation.
2.  **Transmembrane Helices (TM1-TM7, residues 34-300):** The seven α-helical transmembrane domains are arranged in a counterclockwise bundle (when viewed from the extracellular side). These helices form the ligand-binding pocket and are the site of action for several small-molecule allosteric antagonists, including maraviroc. The helices contain highly conserved GPCR motifs, such as the DRY (Asp-Arg-Tyr) motif at the cytoplasmic end of TM3, which is essential for G protein coupling and receptor activation.
3.  **Intracellular Loops (ICL1-ICL3) and C-terminus (residues 301-352):** The intracellular loops and the C-terminal tail are involved in G protein coupling, β-arrestin recruitment, and receptor internalization. The C-terminus contains multiple serine and threonine residues that are phosphorylation sites for G protein-coupled receptor kinases (GRKs). Phosphorylation of these residues promotes β-arrestin binding, leading to receptor desensitization and clathrin-mediated endocytosis.
4.  **Extracellular Loops (ECL1-ECL3):** These loops connect the transmembrane helices on the extracellular side. ECL2 is particularly important as it forms a "lid" over the orthosteric binding pocket and contains a conserved cysteine (Cys101) that forms a disulfide bond with Cys20 in the N-terminus. ECL2 also contributes to the binding site for the HIV-1 gp120 V3 loop.

### 2.2 Quaternary Structure and Dimerization

CCR5 exists as a monomer, but it can form homo- and heterodimers (with CCR2, CXCR4, and other GPCRs) on the cell surface. Dimerization is thought to modulate receptor function, ligand affinity, and signaling specificity. The transmembrane helices, particularly TM4 and TM5, are implicated in the dimerization interface. Heterodimerization between CCR5 and CCR2 has been shown to alter the pharmacological properties of both receptors, and it has been proposed that gene conversion events between *CCR2* and *CCCR5* may have co-evolved to facilitate this interaction [9].

The CCR5-Δ32 truncated protein retains the ability to heterodimerize with the full-length receptor. This interaction traps the full-length receptor in the endoplasmic reticulum, preventing its transport to the cell surface. This dominant-negative mechanism explains the reduced CCR5 surface expression observed in CCR5-Δ32 heterozygotes [2].

### 2.3 High-Resolution Crystal Structures

The first high-resolution crystal structure of CCR5 was solved in complex with the HIV-1 entry inhibitor maraviroc (PDB: 4MBS) at a resolution of 2.7 Å. This structure provided unprecedented detail into the binding mode of a negative allosteric modulator (NAM) to a chemokine receptor. Maraviroc binds to a deep hydrophobic pocket formed by TM1, TM2, TM3, and TM7, which is distinct from the orthosteric chemokine binding site. This binding site is located on the intracellular side of the transmembrane bundle, and its occupation stabilizes an inactive conformation of the receptor, preventing G protein coupling.

Subsequent structures of CCR5 bound to the chemokine antagonist [5P7]CCL5 (PDB: 5UIW) and to the HIV-1 gp120-CD4 complex (PDB: 6MET) have further illuminated the conformational changes associated with receptor activation and viral entry. The gp120-bound structure revealed that the V3 loop of gp120 inserts into the extracellular opening of the CCR5 transmembrane bundle, making extensive contacts with the N-terminus and ECL2. This interaction is the primary determinant of R5-tropic HIV-1 entry.

> **[Interactive 3D Protein Visualizer: Load CCR5 (PDB: 4MBS)](/tools/protein-structure-viewer?source=direct&pdbId=4MBS)**
> *Explore the atomic coordinates of CCR5 in complex with maraviroc. The visualizer allows you to rotate the structure, highlight individual domains (N-terminus, TM helices, ECLs), and measure atomic distances between the drug and key residues.*

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Canonical G Protein Signaling

CCR5 is a Gαi-coupled receptor. Upon binding its cognate chemokine ligands (CCL3, CCL4, CCL5), the receptor undergoes a conformational change that promotes the exchange of GDP for GTP on the Gαi subunit. This leads to the dissociation of the Gαi-GTP and Gβγ subunits, which then modulate various downstream effectors:

1.  **Inhibition of Adenylyl Cyclase:** The Gαi subunit directly inhibits adenylyl cyclase, leading to a reduction in intracellular cyclic AMP (cAMP) levels. This decreases the activity of protein kinase A (PKA) and downstream cAMP-responsive element binding protein (CREB) signaling.
2.  **Activation of Phospholipase C (PLC):** The Gβγ subunits activate PLC-β, which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers the release of calcium from the endoplasmic reticulum, while DAG activates protein kinase C (PKC). The increase in intracellular calcium and PKC activity is essential for chemotaxis, degranulation, and integrin activation.
3.  **Activation of PI3K/Akt Pathway:** Gβγ subunits also activate phosphoinositide 3-kinase (PI3K), which generates phosphatidylinositol (3,4,5)-trisphosphate (PIP3). PIP3 recruits and activates Akt (protein kinase B), promoting cell survival, proliferation, and migration.
4.  **Activation of MAPK Pathways:** CCR5 engagement leads to the activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) pathways. These pathways regulate gene expression, cell cycle progression, and cytokine production.

### 3.2 β-Arrestin-Mediated Signaling and Desensitization

Following agonist binding and G protein activation, CCR5 is rapidly phosphorylated by GRKs on serine/threonine residues in the C-terminal tail. This phosphorylation promotes the recruitment of β-arrestin, which sterically hinders further G protein coupling (desensitization) and links the receptor to the clathrin-mediated endocytic machinery. β-arrestin also serves as a scaffold for the activation of additional signaling cascades, including the Src family kinases and the ERK1/2 MAPK pathway, leading to a distinct wave of "G protein-independent" signaling.

### 3.3 Role in Immune Cell Migration and Function

The primary physiological function of CCR5 is to mediate the migration of effector T cells (particularly Th1 cells), monocytes, macrophages, dendritic cells, and natural killer (NK) cells to sites of inflammation. CCR5 ligands are produced by activated immune cells and tissue-resident cells in response to infection or injury. The CCR5/ligand axis is critical for the recruitment of MHC class II-positive Langerhans cells to the corneal epithelium, a process essential for ocular immune surveillance [4]. Similarly, CCR5 is essential for conventional NK cell trafficking to the liver in a murine model of virus-induced fulminant hepatic failure [38].

### 3.4 Non-Canonical Functions and Receptor Trafficking

Beyond its role in chemotaxis, CCR5 has been implicated in several non-canonical functions. It can be transferred between cells via membrane-derived microparticles, a process that confers HIV-1 susceptibility to CCR5-negative cells [70]. This intercellular transfer of functional receptors may contribute to the spread of HIV-1 within tissues.

CCR5 expression is also dynamically regulated by the cellular environment. For example, oxidative stress (e.g., hydrogen peroxide) upregulates CCR5 mRNA and protein levels in human monocytes, potentially enhancing the recruitment of these cells to sites of inflammation and increasing their susceptibility to HIV-1 infection [54]. Furthermore, synthetic opioids like fentanyl have been shown to increase CCR5 expression in lymphocyte cell lines, providing a mechanistic link between opioid use and enhanced HIV replication [40].

### 3.5 Protein-Protein Interaction Networks

The signaling and regulatory functions of CCR5 are mediated by a complex network of protein-protein interactions. Key interaction partners include:

- **G proteins:** Gαi1, Gαi2, Gαi3, Gαo, and Gαz.
- **β-arrestins:** β-arrestin 1 and β-arrestin 2.
- **GRKs:** GRK2, GRK3, GRK5, and GRK6.
- **Chemokine ligands:** CCL3, CCL4, CCL5, CCL8, CCL11, CCL13, CCL14, CCL16.
- **HIV-1 proteins:** gp120 (in complex with CD4).
- **Receptor tyrosine kinases:** EGFR, PDGFR (transactivation).
- **Other GPCRs:** CCR2, CXCR4 (heterodimerization).

These interactions are dynamically regulated and are crucial for the spatiotemporal control of CCR5 signaling.

```mermaid
sequenceDiagram
    participant L as "CCL5 (RANTES)"
    participant R as "CCR5"
    participant G as "Gαi/Gβγ"
    participant E as "PLC-β"
    participant C as "Ca2+ / PKC"
    participant K as "GRK"
    participant B as "β-Arrestin"
    participant V as "Clathrin-Coated Pit"
    L->>R: Ligand Binding
    R->>G: Conformational Change & GDP/GTP Exchange
    G->>E: Gβγ activates PLC-β
    E->>C: IP3/DAG production -> Ca2+ release & PKC activation
    C-->>R: Chemotaxis, Degranulation, Gene Expression
    R->>K: GRK Phosphorylates C-tail
    K->>B: β-Arrestin Recruitment
    B->>R: Desensitization (G protein uncoupling)
    B->>V: Clathrin-Mediated Endocytosis
    V-->>R: Receptor Internalization & Recycling/Degradation
```

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 The CCR5-Δ32 Mutation

The most clinically significant variant of *CCR5* is the CCR5-Δ32 allele, which results from a 32-base pair deletion in the open reading frame. This deletion introduces a frameshift at codon 185, leading to a premature stop codon and the synthesis of a truncated, non-functional protein of 215 amino acids [6, 79]. The truncated protein is retained intracellularly and is not expressed on the cell surface.

**Population Genetics:** The CCR5-Δ32 allele is found almost exclusively in individuals of European descent, with an allele frequency of approximately 10% in Northern European populations. The frequency decreases along a southeast gradient, and the allele is rare or absent in African, East Asian, and Native American populations [84]. This distribution suggests a strong selective pressure, likely from a historical epidemic (possibly Yersinia pestis or Variola major), that favored the Δ32 allele in Europe [79].

**Clinical Consequences:**
- **Homozygotes (Δ32/Δ32):** Individuals homozygous for CCR5-Δ32 lack functional CCR5 on their cell surfaces. They are highly resistant to infection with R5-tropic HIV-1 strains, which are the predominant strains transmitted sexually [6, 98]. These individuals are generally healthy, indicating that CCR5 is dispensable for normal development and immune function, although subtle alterations in immune responses have been observed.
- **Heterozygotes (wt/Δ32):** Heterozygous individuals express reduced levels of CCR5 on their cell surfaces due to the dominant-negative effect of the truncated protein [2]. They are not resistant to HIV-1 infection but exhibit a slower rate of disease progression, with lower viral loads and a delayed decline in CD4+ T cell counts [80, 90]. This effect is more pronounced in certain cohorts and is influenced by other genetic factors [96].

**Non-HIV Disease Associations:** The CCR5-Δ32 variant has been investigated for its association with numerous diseases beyond HIV-1:
- **Atherosclerosis:** A meta-analysis of 13 studies found a significant association between CCR5-Δ32 and a reduced risk of atherosclerosis, suggesting a pro-atherogenic role for CCR5 [30].
- **Rheumatoid Arthritis (RA):** The Δ32 allele is associated with a reduced risk of developing RA and with less severe joint erosion and systemic inflammation [78, 93].
- **COVID-19:** The CCR5-Δ32 variant has been proposed to explain part of the association between the 3p21.31 chemokine receptor gene cluster and severe COVID-19 [20]. However, the exact contribution of CCR5-Δ32 to COVID-19 susceptibility remains debated.
- **Tick-Borne Encephalitis (TBE):** A study found that the CCR5-Δ32 deletion is associated with an increased risk of TBE, suggesting a protective role for CCR5 in the immune response to the TBE virus [18].
- **Other Conditions:** The variant has been studied in relation to hepatitis C virus (HCV) infection, inflammatory bowel disease (IBD), sarcoidosis, and various cancers, with mixed and often conflicting results [49, 86, 95].

### 4.2 Other Pathogenic and Functional Variants

In addition to the Δ32 deletion, numerous other SNPs and mutations have been identified in the *CCR5* gene. These include:

- **Promoter Polymorphisms:** SNPs in the promoter region, such as rs1799987 (59029A/G), rs1800023, and rs1800024, can alter transcription factor binding and affect CCR5 expression levels. These variants have been associated with altered susceptibility to HIV-1 infection, diabetic nephropathy, and sarcoidosis [29, 63, 74].
- **Coding Region SNPs:** Non-synonymous SNPs in the coding region can alter the amino acid sequence of the receptor, potentially affecting ligand binding, receptor trafficking, or signaling. For example, the CCR5-59353C>T (Pro1Leu) variant has been shown to affect receptor expression and function [43]. Computational studies have predicted that several non-synonymous SNPs in CCR5 may be deleterious and could be implicated in cardiovascular disease [66].
- **Rare Mutations:** A variety of rare mutations, including missense, nonsense, and frameshift mutations, have been identified in different populations. Some of these mutations abolish receptor function and confer resistance to HIV-1, while others may have subtle effects on receptor activity [5, 58].

### 4.3 CCR5 in Cancer

CCR5 expression is upregulated in various cancers, and the CCR5/CCL5 axis has been shown to promote tumor growth, angiogenesis, and metastasis [71]. In colorectal cancer, high CCR5/CCL5 expression is associated with specific molecular subtypes and may impact response to immunotherapy [32]. In B-cell non-Hodgkin lymphomas, high CCR5 expression promotes disease progression [36]. The CCR5-Δ32 variant has been investigated as a potential protective factor in breast cancer, but results have been inconsistent [33].

### 4.4 CCR5 in Other Diseases

- **Ocular [Toxoplasmosis](/knowledge/parasites/pet-parasites/toxoplasmosis-feline-transmission-public-health-clinical-management):** Polymorphisms in the CCR5 gene have been associated with the development of ocular toxoplasmosis, a leading cause of infectious uveitis [1].
- **Chagas Disease:** CCR5 gene variants have been studied for their association with chronic Chagas disease, a parasitic infection caused by *Trypanosoma cruzi* [12].
- **End-Stage Renal Disease (ESRD):** CCR5 gene polymorphisms have been linked to the risk of ESRD and to the outcome of renal transplantation [22, 23, 46].
- **Bladder Cancer:** CCR5 gene variants have been associated with the susceptibility and clinicopathological characteristics of bladder cancer [67].
- **Periodontal Disease:** The CCR5-Δ32 mutation has been investigated for its association with periodontal disease, with some studies suggesting a protective effect [57].
- **Behçet's Disease:** The association of CCR5-Δ32 with Behçet's disease appears to be gender-dependent [83].
- **Alzheimer's Disease:** The CCR5-Δ32 mutation is not protective against Alzheimer's disease [47].

## 5. Host-Pathogen & Viral Interactions

### 5.1 HIV-1 Entry Mechanism

The most extensively studied host-pathogen interaction involving CCR5 is its role as a coreceptor for HIV-1. HIV-1 entry into target cells is a multi-step process:

1.  **CD4 Binding:** The viral envelope glycoprotein gp120 binds to the primary receptor CD4 on the surface of target cells. This binding induces a conformational change in gp120 that exposes the V3 loop and the coreceptor binding site.
2.  **Coreceptor Binding:** The exposed V3 loop of gp120 then interacts with the N-terminus and ECL2 of CCR5. This interaction is highly specific and determines the tropism of the virus. R5-tropic viruses use CCR5, X4-tropic viruses use CXCR4, and dual-tropic (R5X4) viruses can use both.
3.  **Membrane Fusion:** The binding of gp120 to CCR5 triggers a second conformational change in gp41, the transmembrane envelope glycoprotein. This change exposes the fusion peptide, which inserts into the target cell membrane, leading to the formation of a six-helix bundle and the fusion of the viral and cellular membranes.

The interaction between gp120 and CCR5 is a critical determinant of viral tropism and pathogenesis. R5-tropic viruses are responsible for the majority of new HIV-1 infections and predominate during the early stages of the disease. The transition to X4-tropic viruses is associated with accelerated CD4+ T cell depletion and disease progression [56].

### 5.2 Other Viral Interactions

CCR5 also plays a role in the pathogenesis of other viruses:

- **Hepatitis C Virus (HCV):** CCR5 is expressed on HCV-specific T cells, and the CCR5-Δ32 mutation has been shown to affect HCV-specific immune responses and liver tissue pathology [49]. However, the mutation does not appear to influence susceptibility to chronic HCV infection or response to therapy [24, 95].
- **Tick-Borne Encephalitis Virus (TBEV):** The CCR5-Δ32 mutation is associated with an increased risk of TBE, suggesting that CCR5 is important for the immune control of TBEV infection [18].
- **[Infectious Bursal Disease Virus](/knowledge/viruses/avian-viruses/infectious-bursal-disease-virus) (IBDV):** CCR5 and CXCR4 might influence virus replication during IBDV infection, although the exact mechanism is unclear [37].
- **Murine Hepatitis Virus (MHV):** CCR5 is essential for conventional NK cell trafficking and liver injury in a murine model of MHV-induced fulminant hepatic failure [38].
- **Caprine Arthritis Encephalitis Virus (CAEV):** A single nucleotide variant in the promoter region of the CCR5 gene increases susceptibility to CAEV in goats, highlighting the evolutionary conservation of CCR5's role in lentiviral infections [45].

### 5.3 Immune Evasion and Modulation

CCR5 is a target for immune evasion by various pathogens. Some viruses, such as HIV-1, exploit CCR5 for entry. Others may modulate CCR5 expression or signaling to subvert the host immune response. For example, the HIV-1 Nef protein has been shown to downregulate CCR5 expression on infected cells, potentially reducing superinfection and immune recognition.

## 6. [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles), Drug Targets & Small-Molecule Inhibitors

### 6.1 FDA-Approved CCR5 Antagonists

**Maraviroc (Selzentry)** is the only FDA-approved CCR5 antagonist for the treatment of HIV-1 infection. It is a negative allosteric modulator (NAM) that binds to a hydrophobic pocket within the transmembrane bundle, stabilizing the receptor in an inactive conformation and preventing gp120 binding [99]. Maraviroc is used in combination with other antiretroviral agents for the treatment of CCR5-tropic HIV-1 infection. It is not effective against X4-tropic or dual-tropic viruses, and its use requires a tropism test to confirm the presence of R5-tropic virus.

**Vicriviroc** and **aplaviroc** are other CCR5 antagonists that were investigated in clinical trials but were not approved due to safety concerns or lack of efficacy.

### 6.2 Investigational Small-Molecule Inhibitors

Numerous other small-molecule CCR5 antagonists have been developed and are in various stages of preclinical and clinical development. These include:

- **TAK-779:** A non-peptide CCR5 antagonist that also blocks CXCR3 [100].
- **TAK-220:** A potent and orally bioavailable CCR5 antagonist.
- **CMPD167:** A CCR5 antagonist with potent antiviral activity.
- **4,4-disubstituted piperidine-based inhibitors:** A class of compounds with high potency against HIV-1 and an improved hERG profile [99].

### 6.3 Monoclonal Antibodies

Monoclonal antibodies targeting CCR5 have also been developed. **PRO 140** (leronlimab) is a humanized monoclonal antibody that binds to CCR5 and blocks HIV-1 entry. It has been evaluated in clinical trials as a therapeutic and as a potential pre-exposure prophylaxis (PrEP) agent. **HGS004** is another anti-CCR5 monoclonal antibody that has been tested in clinical trials.

### 6.4 Gene Therapy and Gene Editing

The CCR5-Δ32 mutation provides a natural proof-of-concept for gene therapy. The "Berlin patient" (Timothy Ray Brown) was cured of HIV-1 after receiving a bone marrow transplant from a donor homozygous for CCR5-Δ32. This has spurred the development of gene editing strategies to disrupt CCR5 in autologous hematopoietic stem and progenitor cells (HSPCs) [35, 39].

- **Zinc Finger Nucleases (ZFNs):** SB-728-T is a ZFN-based therapy that disrupts CCR5 in autologous CD4+ T cells. Clinical trials have shown that this approach is safe and can lead to sustained engraftment of CCR5-modified cells [87].
- **Transcription Activator-Like Effector Nucleases (TALENs):** TALENs targeting CCR5 have been optimized for clinical application, with improved specificity and efficiency [53]. A comparison of TALEN and CRISPR-Cas9 editing patterns for CCR5 has shown that both can effectively disrupt the gene, but with different editing profiles [42].
- **CRISPR-Cas9:** CRISPR-Cas9 has been used to disrupt CCR5 in HSPCs, generating HIV-1 resistant cells [35, 39]. The CD34+CD90+ HSPC population has been identified as an optimal graft source for CCR5 gene editing [35].
- **Ribozymes:** Hairpin and hammerhead ribozymes targeting CCR5 mRNA have been developed as a gene therapy approach to downregulate CCR5 expression [62, 76, 77].

### 6.5 Other Therapeutic Approaches

- **CCR5 Ligands and Peptides:** Modified chemokines, such as [5P7]CCL5, act as potent CCR5 antagonists and have been studied for their therapeutic potential.
- **Peptide Ligands:** Peptide ligands to CCR5 have been identified and matured by gene shuffling, providing a basis for the development of novel peptide-based inhibitors [65].
- **Triplex-Forming Oligonucleotides:** Triplex-forming oligonucleotides have been used to covalently modify the CCR5 gene in permeabilized cells, representing a potential strategy for gene inactivation [55].

### 6.6 [Pharmacogenomics](/knowledge/bioinformatics/pharmacogenomics-tailoring-drugs-to-genetic-profiles)

The response to CCR5 antagonists and the progression of HIV-1 disease are influenced by CCR5 gene polymorphisms. For example, the CCR5-Δ32 allele and certain promoter haplotypes have been associated with altered disease progression and response to therapy [50, 56]. Pharmacogenomic testing for CCR5 variants may help guide treatment decisions in the future.

## 7. Bioinformatic Resources & Database Accessions

The following table provides key database accessions and resources for CCR5.

| **Database** | **Identifier** | **Description** |
|:---|:---|:---|
| **NCBI Gene** | 1234 | Gene ID for CCR5 |
| **Ensembl** | ENSG00000160791 | Ensembl gene ID |
| **UniProt** | P51681 | UniProtKB/Swiss-Prot entry |
| **RCSB PDB** | 4MBS | Crystal structure of CCR5 with maraviroc |
| **HGNC** | 1606 | HUGO Gene Nomenclature Committee symbol |
| **OMIM** | 601373 | Online Mendelian Inheritance in Man entry |
| **GeneCards** | GC03P046370 | GeneCards summary |
| **ClinVar** | Varied | Clinical variants for CCR5 |
| **STRING** | 1234 | Protein-protein interaction network |
| **BioGRID** | 109582 | Biological General Repository for Interaction Datasets |
| **Gene Ontology (GO)** | GO:0016493, GO:0004871, GO:0006935 | Molecular function: C-C chemokine receptor activity; Signal transducer activity; Biological process: Chemotaxis |
| **KEGG** | hsa:1234 | KEGG pathway entry |
| **Reactome** | R-HSA-373076 | Chemokine receptors bind chemokines |
| **PharmGKB** | PA1234 | Pharmacogenomics knowledge base |

## Related Clinical & Scientific Guides

* [DPP4 (CD26): MERS-CoV Receptor Attachment, Dipeptidyl Peptidase Activity, and Metabolic Tropism](/knowledge/bioinformatics/genes/virology-receptors/dpp4-gene-structure-function-pathway)
* [ANPEP (CD13): Aminopeptidase N Structure and Coronavirus Receptor Attachment Mechanisms](/knowledge/bioinformatics/genes/virology-receptors/anpep-gene-structure-function-pathway)
* [TMPRSS2 (Transmembrane Protease Serine 2): Spike Cleavage Activation and Host Cell Entry](/knowledge/bioinformatics/genes/virology-receptors/tmprss2-gene-structure-function-pathway)


## References

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