CCR5 gene editing – Revisiting pros and cons of CCR5 absence

CCR5 promoter region polymorphisms in systemic lupus erythematosus

This study investigated the impacts of CCR5 promoter region polymorphisms on the development of systemic lupus erythematosus (SLE) by comparing CCR5 genotypes and haplotypes from SLE patients with ethnically matched controls. A total of 382 SLE patients (289 European-derived and 93 African-derived) and 375 controls (243 European-derived and 132 African-derived) were genotyped for the CCR2-64I G > A (rs1799864), CCR5-59353 C > T (rs1799988), CCR5-59356 C > T (rs41469351), CCR5-59402 A > G (rs1800023) and CCR5-59653 C > T (rs1800024) polymorphisms through polymerase chain reaction-restriction fragment length polymorphism and direct sequencing. Previous data from CCR5Δ32 analysis was included in the study to infer the CCR5 haplotypes and as a possible confounding factor in the binary logistic regression. European-derived patients showed a higher frequency of CCR5 wild-type genotype (conversely, a reduced frequency of Δ32 allele) and a reduced frequency of the HHG*2 haplotype compared to controls; both factors significantly affecting disease risk [p = .003 (OR 3.5, 95%CI 1.6-7.5) and 2.0% vs. 7.2% (residual p = 2.9E - 5), respectively]. Additionally, the HHA/HHB, HHC and HHG*2 haplotype frequencies differed between African-derived patients and controls [10% vs. 20.5% (residual p = .003), 29.4% vs. 17.4% (residual p = .003) and 3.9% vs. 0.8% (residual p = .023), respectively]. Considering the clinical manifestations of the disease, the CCR5Δ32 presence was confirmed as a susceptibility factor to class IV nephritis in the African-derived group and when all patients were grouped for comparison [pcorrected  = .012 (OR 3.0; 95%CI 3.0-333.3) and pcorrected  = .0006 (OR 6.8; 95%CI 1.9-24.8), respectively]. In conclusion, this study indicates that CCR5 promoter polymorphisms are important disease modifiers in SLE. Present data reinforces the CCR5Δ32 polymorphism as a protective factor for the development of the disease in European-derived patients and as a susceptibility factor for class IV nephritis in African-derived patients. Furthermore, we also described a reduced frequency of HHA/HHB and an increased frequency of HHC and HHG*2 haplotypes in African-derived patients, which could modify the CCR5 protein expression in specific cell subsets.

Derived myeloid lineage induced pluripotent stem as a platform to study human C-C chemokine receptor type 5Δ32 homozygotes

The C-C chemokine receptor type 5 (CCR5) expressed on immune cells supports inflammatory responses by directing cells to the inflammation site. CCR5 is also a major coreceptor for macrophage tropic human immunodeficiency viruses (R5-HIV-1) and its variants can confer protection from HIV infection, making it an ideal candidate to target for therapy. We developed a stepwise protocol that differentiates induced pluripotent stem cells (iPSCs) from individuals homozygous for the CCR5Δ32 variant and healthy volunteers into myeloid lineage induced monocytes (iMono) and macrophages (iMac). By characterizing iMono and iMac against their primary counterparts, we demonstrated that CCR5Δ32 homozygous cells are endowed with similar pluripotent potential for self-renewal and differentiation as iPSC lines generated from non-variant individuals while also showing resistance to HIV infection. In conclusion, these cells are a platform to investigate CCR5 pathophysiology in HIV-positive and negative individuals and to help develop novel therapies.

HLA-G*14 bp indel variant in autism spectrum disorder in a population from southern Brazil

Altered immune response during pregnancy has been associated with ASD susceptibility. HLA-G is expressed by the trophoblast at the maternal/fetal interface and induces allogenic tolerance toward the fetus. A 14-bp insertion in the HLA-G 3'UTR (rs371194629) was associated with reduced levels of HLA-G. We aimed to assess the influence of the HLA-G*14 bp indel variant in ASD susceptibility and symptomatology in a Brazilian admixed sample. The insertion genotype (14 bp+/14 bp+) was firstly associated with hetero aggression, but statistical significance was lost after correction (p = 0.035, pcorrected = 0.35). No association between the HLA-G variant and susceptibility to ASD or differential clinical manifestations were observed.

Prevalence of CCR5 Delta 32 Genetic Variant in the Turkmen Population of Golestan Province, Northeast of Iran

The 32 bp deletion in the chemokine receptor (C-C motif) 5 gene (CCR5Δ32) is a natural loss of function polymorphism that prevents the protein from locating on the cell surface. This genetic variation acts as a double-edge sword in the pathogenesis/defense mechanism of different health conditions, such as viral infections, autoimmune diseases, and cancers. Here, we evaluated the prevalence of the CCR5Δ32 polymorphism in the Turkmen population of Golestan province, northeast of Iran. Blood samples were collected from 400 randomly selected Turkmen populations (199 women and 201 men), and genomic DNA was extracted. Characterization of CCR5Δ32 genotypes was performed by PCR using primers flanking the 32-nucleotide deletion in the CCR5 gene. The amplified DNA fragments were visualized on 2% agarose gel electrophoresis with cybergreen staining under UV light. All individuals were of Turkmen ethnicity and lived in the Golestan province, northeast of Iran. The mean age of all participants was 35.46 years, with a 20-45 year range. All the studied subjects were healthy without any severe conditions such as autoimmune disease and viral infections. All individuals had no history of HIV infection. The PCR product visualization showed that all the samples are at the 330 bp size, which means the CCR5Δ32 allele was utterly absent from the study population. The presence of the CCR5Δ32 allele among Turkmens may be attributed to the admixture with European descent people. We conclude that the CCR5Δ32 polymorphism may be absent in the Iranian Turkmen population, and further studies with a large population are needed.

CCR5 and Biological Complexity: The Need for Data Integration and Educational Materials to Address Genetic/Biological Reductionism at the Interface of Ethical, Legal, and Social Implications

In the age of genomics, public understanding of complex scientific knowledge is critical. To combat reductionistic views, it is necessary to generate and organize educational material and data that keep pace with advances in genomics. The view that CCR5 is solely the receptor for HIV gave rise to demand to remove the gene in patients to create host HIV resistance, underestimating the broader roles and complex genetic inheritance of CCR5. A program aimed at providing research projects to undergraduates, known as CODE, has been expanded to build educational material for genes such as CCR5 in a rapid approach, exposing students and trainees to large bioinformatics databases and previous experiments for broader data to challenge commitment to biological reductionism. Our students organize expression databases, query environmental responses, assess genetic factors, generate protein models/dynamics, and profile evolutionary insights into a protein such as CCR5. The knowledgebase generated in the initiative opens the door for public educational information and tools (molecular videos, 3D printed models, and handouts), classroom materials, and strategy for future genetic ideas that can be distributed in formal, semiformal, and informal educational environments. This work highlights that many factors are missing from the reductionist view of CCR5, including the role of missense variants or expression of CCR5 with neurological phenotypes and the role of CCR5 and the delta32 variant in complex critical care patients with sepsis. When connected to genomic stories in the news, these tools offer critically needed Ethical, Legal, and Social Implication (ELSI) education to combat biological reductionism.

CCR5Δ32 in Brazil: Impacts of a European Genetic Variant on a Highly Admixed Population

The genetic background of Brazilians encompasses Amerindian, African, and European components as a result of the colonization of an already Amerindian inhabited region by Europeans, associated to a massive influx of Africans. Other migratory flows introduced into the Brazilian population genetic components from Asia and the Middle East. Currently, Brazil has a highly admixed population and, therefore, the study of genetic factors in the context of health or disease in Brazil is a challenging and remarkably interesting subject. This phenomenon is exemplified by the genetic variant CCR5Δ32, a 32 base-pair deletion in the CCR5 gene. CCR5Δ32 originated in Europe, but the time of origin as well as the selective pressures that allowed the maintenance of this variant and the establishment of its current frequencies in the different human populations is still a field of debates. Due to its origin, the CCR5Δ32 allele frequency is high in European-derived populations (~10%) and low in Asian and African native human populations. In Brazil, the CCR5Δ32 allele frequency is intermediate (4-6%) and varies on the Brazilian States, depending on the migratory history of each region. CCR5 is a protein that regulates the activity of several immune cells, also acting as the main HIV-1 co-receptor. The CCR5 expression is influenced by CCR5Δ32 genotypes. No CCR5 expression is observed in CCR5Δ32 homozygous individuals. Thus, the CCR5Δ32 has particular effects on different diseases. At the population level, the effect that CCR5Δ32 has on European populations may be different than that observed in highly admixed populations. Besides less evident due to its low frequency in admixed groups, the effect of the CCR5Δ32 variant may be affected by other genetic traits. Understanding the effects of CCR5Δ32 on Brazilians is essential to predict the potential use of pharmacological CCR5 modulators in Brazil. Therefore, this study reviews the impacts of the CCR5Δ32 on the Brazilian population, considering infectious diseases, inflammatory conditions, and cancer. Finally, this article provides a general discussion concerning the impacts of a European-derived variant, the CCR5Δ32, on a highly admixed population.

CCR5 is a potential therapeutic target for cancer

INTRODUCTION

Chemokines and their cognate receptors play a major role in modulating inflammatory responses. Depending on their ligand binding, chemokine receptors can stimulate both immune activating and inhibitory signaling pathways. The CC chemokine receptor 5 (CCR5) promotes immune responses by recruiting immune cells to the sites of inflammation/tumor, and is involved in stimulating tumor cell proliferation, invasion and migration through various mechanisms. Moreover, CCR5 also contributes to an immune-suppressive tumor microenvironment by recruiting regulatory T cells and myeloid-derived suppressor cells facilitating tumor development and progression. In summary, cells expressing CCR5 modulate immune response and tumor progression. Expression of CCR5 is increased in various malignancies and associated with poor outcome. Experimental data show promising efficacy signals with CCR5 antagonists in preclinical tumor models. Therefore, CCR5 has been recognized as a potential therapeutic target for cancer.

AREAS COVERED

In this review, we focus on the role of CCR5 in cancer progression and discuss its impact and potential as a therapeutic target for cancer.

EXPERT OPINION

Beyond immune-checkpoint inhibitors, potentially synergistic immune-modulatory drugs such as CCR5 antagonists are a promising approach to enlarge our treatment armamentarium against cancer.

Beyond HIV infection: Neglected and varied impacts of CCR5 and CCR5Δ32 on viral diseases

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CCR5 regulates multiple cell types (e.g., T regulatory and Natural Killer cells) and immune responses.

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The effects of CCR5, CCR5Δ32 (variant associated with reduced CCR5 expression) and CCR5 antagonists vary between infections.

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CCR5 affects the pathogenesis of flaviviruses, especially in the brain.

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The genetic variant CCR5Δ32 increases the risk of symptomatic West Nile virus infection.

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The triad “CCR5, extracellular vesicles and infections” is an emerging topic.

The interactions between chemokine receptors and their ligands may affect susceptibility to infectious diseases as well as their clinical manifestations. These interactions mediate both the traffic of inflammatory cells and virus-associated immune responses. In the context of viral infections, the human C-C chemokine receptor type 5 (CCR5) receives great attention from the scientific community due to its role as an HIV-1 co-receptor. The genetic variant CCR5Δ32 (32 base-pair deletion in CCR5 gene) impairs CCR5 expression on the cell surface and is associated with protection against HIV infection in homozygous individuals. Also, the genetic variant CCR5Δ32 modifies the CCR5-mediated inflammatory responses in various conditions, such as inflammatory and infectious diseases. CCR5 antagonists mimic, at least in part, the natural effects of the CCR5Δ32 in humans, which explains the growing interest in the potential benefits of using CCR5 modulators for the treatment of different diseases. Nevertheless, beyond HIV infection, understanding the effects of the CCR5Δ32 variant in multiple viral infections is essential to shed light on the potential effects of the CCR5 modulators from a broader perspective. In this context, this review discusses the involvement of CCR5 and the effects of the CCR5Δ32 in human infections caused by the following pathogens: West Nile virus, Influenza virus, Human papillomavirus, Hepatitis B virus, Hepatitis C virus, Poliovirus, Dengue virus, Human cytomegalovirus, Crimean-Congo hemorrhagic fever virus, Enterovirus, Japanese encephalitis virus, and Hantavirus. Subsequently, this review addresses the impacts of CCR5 gene editing and CCR5 modulation on health and viral diseases. Also, this article connects recent findings regarding extracellular vesicles (e.g., exosomes), viruses, and CCR5. Neglected and emerging topics in “CCR5 research” are briefly described, with focus on Rocio virus, Zika virus, Epstein-Barr virus, and Rhinovirus. Finally, the potential influence of CCR5 on the immune responses to coronaviruses is discussed.

CCR5 and CCR5Δ32 in bacterial and parasitic infections: Thinking chemokine receptors outside the HIV box

The CCR5 molecule was reported in 1996 as the main HIV-1 co-receptor. In that same year, the CCR5Δ32 genetic variant was described as a strong protective factor against HIV-1 infection. These findings led to extensive research regarding the CCR5, culminating in critical scientific advances, such as the development of CCR5 inhibitors for the treatment of HIV infection. Recently, the research landscape surrounding CCR5 has begun to change. Different research groups have realized that, since CCR5 has such important effects in the chemokine system, it could also affect other different physiological systems. Therefore, the effect of reduced CCR5 expression due to the presence of the CCR5Δ32 variant began to be further studied. Several studies have investigated the role of CCR5 and the impacts of CCR5Δ32 on autoimmune and inflammatory diseases, various types of cancer, and viral diseases. However, the role of CCR5 in diseases caused by bacteria and parasites is still poorly understood. Therefore, the aim of this article is to review the role of CCR5 and the effects of CCR5Δ32 on bacterial (brucellosis, osteomyelitis, pneumonia, tuberculosis and infection by Chlamydia trachomatis) and parasitic infections (toxoplasmosis, leishmaniasis, Chagas disease and schistosomiasis). Basic information about each of these infections was also addressed. The neglected role of CCR5 in fungal disease and emerging studies regarding the action of CCR5 on regulatory T cells are briefly covered in this review. Considering the "renaissance of CCR5 research," this article is useful for updating researchers who develop studies involving CCR5 and CCR5Δ32 in different infectious diseases.

Role of the genetic variant CCR5Δ32 in HBV infection and HBV/HIV co-infection

CCR5 is a chemokine receptor that mediates the action of inflammatory cells, besides acting as an HIV co-receptor. CCR5Δ32 states for a genetic variant containing a 32 base pair deletion in the coding region of the CCR5 gene. In homozygosis, CCR5Δ32 results in the lack of CCR5 expression on the cell surface, which was associated with protection against HIV infection. Heterozygous individuals for CCR5Δ32 have a reduced CCR5 expression. Recent evidence demonstrates that CCR5 and CCR5Δ32 are involved in the pathogenesis of other viral infections besides HIV infection. Nevertheless, the role of CCR5 and CCR5Δ32 in HBV infection is not clear and conflicting results have been reported. Thus, the objective of this study was to investigate the role of CCR5Δ32 in HBV mono-infection and HBV/HIV co-infection in a population from southern Brazil. A total of 1113 individuals were evaluated, divided in controls (n = 334), HBV+ (n = 335), HBV+/HIV+ (n = 144), and including an HIV+ group to complement the analyses (n = 300, obtained from a previous study of our research team). The CCR5Δ32 allele frequencies found were 7.5 %, 9.0 %, and 3.1 %, respectively for controls, HBV+, and HBV+/HIV+ patients. The individuals were classified in CCR5Δ32 allele carriers and CCR5Δ32 allele non-carriers and the groups were compared using binary logistic regression adjusted for covariates. No significant effect of the CCR5Δ32 variant was observed on the susceptibility or protection against HBV mono-infection in individuals from southern Brazil. A potential protective effect of CCR5Δ32 on HBV/HIV co-infection was observed. However, it can be due to the effect of CCR5Δ32 in the protection against HIV infection or external factors not covered in the study. Finally, this study contributes to the understanding of the role of CCR5 in HBV infection, suggesting no effect of CCR5Δ32 on susceptibility to HBV mono-infection.

A functional interaction between the CCR5 and CD34 molecules expressed in hematopoietic cells can support (or even promote) the development of cancer

Inflammation and angiogenesis are linked to the development of cancer since both can support the establishment of a tumor-prone microenvironment. The CCR5 is a major regulatory molecule involved in inflammation. The CD34 molecule is commonly described as a hematopoietic stem cell marker, and CD34⁺ cells are involved in the regulation of distinct physiological processes, including angiogenesis. CCR5 participates in the development of various types of cancer, and recently, a reduced CCR5 expression was associated with low CD34⁺ cell counts in human cord blood. A naturally occurring genetic variant of the CCR5 gene, the so-called CCR5Δ32 polymorphism, consists of a 32 base-pair deletion in the DNA, interfering in the CCR5 protein levels on the cell surface. When in homozygosis, this variant leads to a total absence of CCR5 expression on the cell surface. In heterozygous individuals, CCR5 surface levels are reduced. Based on these key findings, we hypothesize that a functional interaction can connect CCR5 and CD34 molecules (giving rise to a “CCR5-CD34 axis”). According to this, a CCR5-CD34 interaction can potentially support the development of different types of cancer. Consequently, the lack of CCR5 in association with reduced CD34⁺ cell counts could indicate a protective factor against the development of cancer. It is required to characterize in detail the functional relationship between CCR5 and CD34 proteins, as well as the real influence of both molecules on the susceptibility and development of cancer at population level. If our hypothesis is confirmed, the CCR5-CD34 axis may be a potential target in the development of anti-cancer therapies.

What we say and what we mean when we say redundancy and robustness of the chemokine system - how CCR5 challenges these concepts

Classically, robustness and redundancy are features that define the intricate and connected functioning of the chemokine system. Following these ideas, the lack of a particular chemokine or chemokine receptor could be compensated by the presence of other molecules with similar functions, ensuring robustness to the systems. Although these concepts are generally accepted, they represent an oversimplification of a highly complex system that works in a context-dependent manner. Based on different studies, and taking as an example the chemokine receptor CCR5 (C-C chemokine receptor type 5) and the genetic variant CCR5Δ32, which on several occasions challenge the classical concepts of redundancy and robustness of the chemokine system, we will discuss and question this general and oversimplified point of view.