WHIM syndromes with different genetic anomalies are accounted for by impaired CXCR4 desensitization to CXCL12

Periodontal disease in patients with WHIM syndrome

AIM

WHIM (warts, hypogammaglobulinaemia, infections and myelokathexis) syndrome is a rare combined primary immunodeficiency disease caused by gain-of-function (GOF) mutations in the chemokine receptor CXCR4 and includes severe neutropenia as a common feature. Neutropenia is a known risk factor for periodontitis; however, a detailed periodontal evaluation of a WHIM syndrome cohort is lacking. This study aimed to establish the evidence base for the periodontal status of patients with WHIM syndrome.

MATERIALS AND METHODS

Twenty-two adult WHIM syndrome patients and 22 age- and gender-matched healthy volunteers (HVs) were evaluated through a comprehensive medical and periodontal examination. A mouse model of WHIM syndrome was assessed for susceptibility to naturally progressing or inducible periodontitis.

RESULTS

Fourteen patients with WHIM syndrome (63.6%) and one HV (4.5%) were diagnosed with Stage III/IV periodontitis. No WHIM patient presented with the early onset, dramatic clinical phenotypes typically associated with genetic forms of neutropenia. Age, but not the specific CXCR4 mutation or absolute neutrophil count, was associated with periodontitis severity in the WHIM cohort. Mice with a Cxcr4 GOF mutation did not exhibit increased alveolar bone loss in spontaneous or ligature-induced periodontitis.

CONCLUSIONS

Overall, WHIM syndrome patients presented with an increased severity of periodontitis despite past and ongoing neutrophil mobilization treatments. GOF mutations in CXCR4 may be a risk factor for periodontitis in humans.

CXCR4 WHIM syndrome is a cancer predisposition condition for virus-induced malignancies

Warts, hypogammaglobulinaemia, infections and myelokathexis syndrome (WHIMS) is a rare combined primary immunodeficiency caused by the gain of function of the CXCR4 chemokine receptor. We present the prevalence of cancer in WHIMS patients based on data from the French Severe Chronic Neutropenia Registry and an exhaustive literature review. The median follow-up of the 14 WHIMS 'patients was 28.5 years. A central review and viral evaluation of pathological samples were organized, and we conducted a thorough literature review to identify all reports of WHIMS cases. Six French patients were diagnosed with cancer at a median age of 37.6 years. The 40-year risk of malignancy was 39% (95% confidence interval [CI]: 6%-74%). We observed two human papillomavirus (HPV)-induced vulvar carcinomas, three lymphomas (two Epstein-Barr virus [EBV]-related) and one basal cell carcinoma. Among the 155 WHIMS cases from the literature, 22 cancers were reported in 16 patients, with an overall cancer 40-year risk of 23% (95% CI: 13%-39%). Malignancies included EBV-associated lymphoproliferative disorders and HPV-positive genital and anal cancers as in the French cohort. Worldwide, nine cases of malignancy were associated with HPV and four with EBV. Immunocompromised WHIMS patients appear to be particularly susceptible to developing early malignancy, mainly HPV-induced carcinomas, followed by EBV-related lymphomas.

Tuning of plasma cell lifespan by competition explains the longevity and heterogeneity of antibody persistence

Plasma cells that emerge after infection or vaccination exhibit heterogeneous lifespans; most survive for days to months, whereas others persist for decades, providing antigen-specific long-term protection. We developed a mathematical framework to explore the dynamics of plasma cell removal and its regulation by survival factors. Analyses of antibody persistence following hepatitis A and B and HPV vaccination revealed specific patterns of longevity and heterogeneity within and between responses, implying that this process is fine-tuned near a critical "flat" state between two dynamic regimes. This critical state reflects the tuning of rates of the underlying regulatory network and is highly sensitive to variation in parameters, which amplifies lifespan differences between cells. We propose that fine-tuning is the generic outcome of competition over shared survival signals, with a competition-based mechanism providing a unifying explanation for a wide range of experimental observations, including the dynamics of plasma cell accumulation and the effects of survival factor deletion. Our theory is testable, and we provide specific predictions.

Monogenic etiologies of persistent human papillomavirus infections: A comprehensive systematic review

PURPOSE

Persistent human papillomavirus infection (PHPVI) causes cutaneous, anogenital, and mucosal warts. Cutaneous warts include common warts, Treeman syndrome, and epidermodysplasia verruciformis, among others. Although more reports of monogenic predisposition to PHPVI have been published with the development of genomic technologies, genetic testing is rarely incorporated into clinical assessments. To encourage broader molecular testing, we compiled a list of the various monogenic etiologies of PHPVI.

METHODS

We conducted a systematic literature review to determine the genetic, immunological, and clinical characteristics of patients with PHPVI.

RESULTS

The inclusion criteria were met by 261 of 40,687 articles. In 842 patients, 83 PHPVI-associated genes were identified, including 42, 6, and 35 genes with strong, moderate, and weak evidence for causality, respectively. Autosomal recessive inheritance predominated (69%). PHPVI onset age was 10.8 ± 8.6 years, with an interquartile range of 5 to 14 years. GATA2,IL2RG,DOCK8, CXCR4, TMC6, TMC8, and CIB1 are the most frequently reported PHPVI-associated genes with strong causality. Most genes (74 out of 83) belong to a catalog of 485 inborn errors of immunity-related genes, and 40 genes (54%) are represented in the nonsyndromic and syndromic combined immunodeficiency categories.

CONCLUSION

PHPVI has at least 83 monogenic etiologies and a genetic diagnosis is essential for effective management.

Interplay between androgen and CXCR4 chemokine signaling in myelin repair

In men, reduced levels of testosterone are associated with the prevalence and progression of multiple sclerosis (MS), a chronic and disabling demyelinating disorder. Testosterone has been shown to promote myelin repair. Here, we demonstrate that the cooperation between testosterone and CXCR4 signaling involving astrocytes is required for myelin regeneration after focal demyelination produced in the ventral mouse spinal cord by the infusion of lysolecithin. The testosterone-dependent remyelination of axons by oligodendrocytes was accompanied by an increase in astrocytes expressing CXCR4, its ligand CXCL12 and the androgen receptor (AR) within the demyelinated area. Depriving males of their testosterone or pharmacological inhibition of CXCR4, with the selective antagonist AMD3100, prevented the appearance of astrocytes expressing CXCR4, CXCL12 and AR within the demyelinated area and the concomitant recruitment of myelin forming oligodendrocytes. Conditional genetic ablation of either CXCR4 or AR in astrocytes also completely blocked the formation of new myelin by oligodendrocytes. Interestingly, the gain of function mutation in CXCR4 causing WHIM syndrome allows remyelination to take place, even in the absence of testosterone, but its potentiating effects remained observable. After testosterone deprivation or CXCR4 inhibition, the absence of astrocytes within the demyelinated area led to the incursion of Schwann cells, most likely derived from spinal nerves, and the formation of peripheral nerve type myelin. In patients with progressive MS, astrocytes expressing CXCR4 and AR surrounded myelin lesions, and their presence opposed the incursion of Schwann cells. These results highlight a mechanism of promyelinating testosterone signaling and the importance of normalizing its levels in combined myelin repair therapies.

A phase III randomized crossover trial of plerixafor versus G-CSF for treatment of WHIM syndrome

BACKGROUNDWarts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is a primary immunodeficiency disorder caused by heterozygous gain-of-function CXCR4 mutations. Myelokathexis is a kind of neutropenia caused by neutrophil retention in bone marrow and in WHIM syndrome is associated with lymphopenia and monocytopenia. The CXCR4 antagonist plerixafor mobilizes leukocytes to the blood; however, its safety and efficacy in WHIM syndrome are undefined.METHODSIn this investigator-initiated, single-center, quadruple-masked phase III crossover trial, we compared the total infection severity score (TISS) as the primary endpoint in an intent-to-treat manner in 19 patients with WHIM who each received 12 months treatment with plerixafor and 12 months treatment with granulocyte CSF (G-CSF, the standard of care for severe congenital neutropenia). The treatment order was randomized for each patient.RESULTSPlerixafor was nonsuperior to G-CSF for TISS (P = 0.54). In exploratory endpoints, plerixafor was noninferior to G-CSF for maintaining neutrophil counts of more than 500 cells/μL (P = 0.023) and was superior to G-CSF for maintaining lymphocyte counts above 1,000 cells/μL (P < 0.0001). Complete regression of a subset of large wart areas occurred on plerixafor in 5 of 7 patients with major wart burdens at baseline. Transient rash occurred on plerixafor, and bone pain was more common on G-CSF. There were no significant differences in drug preference or quality of life or the incidence of drug failure or serious adverse events.CONCLUSIONPlerixafor was not superior to G-CSF in patients with WHIM for TISS, the primary endpoint. Together with wart regression and hematologic improvement, the infection severity results support continued study of plerixafor as a potential treatment for WHIM syndrome.TRIAL REGISTRATIONClinicaltrials.gov NCT02231879.FUNDINGThis study was funded by the Division of Intramural Research, National Institute of Allergy and Infectious Diseases.

Severe CD8+ T Lymphopenia in WHIM Syndrome Caused by Selective Sequestration in Primary Immune Organs

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is an ultra-rare combined primary immunodeficiency disease caused by heterozygous gain-of-function mutations in the chemokine receptor CXCR4. WHIM patients typically present with recurrent acute infections associated with myelokathexis (severe neutropenia due to bone marrow retention of mature neutrophils). Severe lymphopenia is also common, but the only associated chronic opportunistic pathogen is human papillomavirus and mechanisms are not clearly defined. In this study, we show that WHIM mutations cause more severe CD8 than CD4 lymphopenia in WHIM patients and WHIM model mice. Mechanistic studies in mice revealed selective and WHIM allele dose-dependent accumulation of mature CD8 single-positive cells in thymus in a cell-intrinsic manner due to prolonged intrathymic residence, associated with increased CD8 single-positive thymocyte chemotactic responses in vitro toward the CXCR4 ligand CXCL12. In addition, mature WHIM CD8+ T cells preferentially home to and are retained in the bone marrow in mice in a cell-intrinsic manner. Administration of the specific CXCR4 antagonist AMD3100 (plerixafor) in mice rapidly and transiently corrected T cell lymphopenia and the CD4/CD8 ratio. After lymphocytic choriomeningitis virus infection, we found no difference in memory CD8+ T cell differentiation or viral load between wild-type and WHIM model mice. Thus, lymphopenia in WHIM syndrome may involve severe CXCR4-dependent CD8+ T cell deficiency resulting in part from sequestration in the primary lymphoid organs, thymus, and bone marrow.

WHIM Syndrome-linked CXCR4 mutations drive osteoporosis

WHIM Syndrome is a rare immunodeficiency caused by gain-of-function CXCR4 mutations. Here we report a decrease in bone mineral density in 25% of WHIM patients and bone defects leading to osteoporosis in a WHIM mouse model. Imbalanced bone tissue is observed in mutant mice combining reduced osteoprogenitor cells and increased osteoclast numbers. Mechanistically, impaired CXCR4 desensitization disrupts cell cycle progression and osteogenic commitment of skeletal stromal/stem cells, while increasing their pro-osteoclastogenic capacities. Impaired osteogenic differentiation is evidenced in primary bone marrow stromal cells from WHIM patients. In mice, chronic treatment with the CXCR4 antagonist AMD3100 normalizes in vitro osteogenic fate of mutant skeletal stromal/stem cells and reverses in vivo the loss of skeletal cells, demonstrating that proper CXCR4 desensitization is required for the osteogenic specification of skeletal stromal/stem cells. Our study provides mechanistic insights into how CXCR4 signaling regulates the osteogenic fate of skeletal cells and the balance between bone formation and resorption.

Reduced G protein signaling despite impaired internalization and β-arrestin recruitment in patients carrying a CXCR4Leu317fsX3 mutation causing WHIM syndrome

WHIM syndrome is an inherited immune disorder caused by an autosomal dominant heterozygous mutation in CXCR4. The disease is characterized by neutropenia/leukopenia (secondary to retention of mature neutrophils in bone marrow), recurrent bacterial infections, treatment-refractory warts, and hypogammaglobulinemia. All mutations reported in WHIM patients lead to the truncations in the C-terminal domain of CXCR4, R334X being the most frequent. This defect prevents receptor internalization and enhances both calcium mobilization and ERK phosphorylation, resulting in increased chemotaxis in response to the unique ligand CXCL12. Here, we describe 3 patients presenting neutropenia and myelokathexis, but normal lymphocyte count and immunoglobulin levels, carrying what we believe to be a novel Leu317fsX3 mutation in CXCR4, leading to a complete truncation of its intracellular tail. The analysis of the L317fsX3 mutation in cells derived from patients and in vitro cellular models reveals unique signaling features in comparison with R334X mutation. The L317fsX3 mutation impairs CXCR4 downregulation and β-arrestin recruitment in response to CXCL12 and reduces other signaling events - including ERK1/2 phosphorylation, calcium mobilization, and chemotaxis - all processes that are typically enhanced in cells carrying the R334X mutation. Our findings suggest that, overall, the L317fsX3 mutation may be causative of a form of WHIM syndrome not associated with an augmented CXCR4 response to CXCL12.

Discovery of Bis-Imidazoline Derivatives as New CXCR4 Ligands

The chemokine receptor CXCR4 and its ligand CXCL12 regulate leukocyte trafficking, homeostasis and functions and are potential therapeutic targets in many diseases such as HIV-1 infection and cancers. Here, we identified new CXCR4 ligands in the CERMN chemical library using a FRET-based high-throughput screening assay. These are bis-imidazoline compounds comprising two imidazole rings linked by an alkyl chain. The molecules displace CXCL12 binding with submicromolar potencies, similarly to AMD3100, the only marketed CXCR4 ligand. They also inhibit anti-CXCR4 mAb 12G5 binding, CXCL12-mediated chemotaxis and HIV-1 infection. Further studies with newly synthesized derivatives pointed out to a role of alkyl chain length on the bis-imidazoline properties, with molecules with an even number of carbons equal to 8, 10 or 12 being the most potent. Interestingly, these differ in the functions of CXCR4 that they influence. Site-directed mutagenesis and molecular docking predict that the alkyl chain folds in such a way that the two imidazole groups become lodged in the transmembrane binding cavity of CXCR4. Results also suggest that the alkyl chain length influences how the imidazole rings positions in the cavity. These results may provide a basis for the design of new CXCR4 antagonists targeting specific functions of the receptor.

Human papillomavirus in the setting of immunodeficiency: Pathogenesis and the emergence of next-generation therapies to reduce the high associated cancer risk

Human papillomavirus (HPV), a common sexually transmitted virus infecting mucosal or cutaneous stratified epithelia, is implicated in the rising of associated cancers worldwide. While HPV infection can be cleared by an adequate immune response, immunocompromised individuals can develop persistent, treatment-refractory, and progressive disease. Primary immunodeficiencies (PIDs) associated with HPV-related disease include inborn errors of GATA, EVER1/2, and CXCR4 mutations, resulting in defective cellular function. People living with secondary immunodeficiency (e.g. solid-organ transplants recipients of immunosuppression) and acquired immunodeficiency (e.g. concurrent human immunodeficiency virus (HIV) infection) are also at significant risk of HPV-related disease. Immunocompromised people are highly susceptible to the development of cutaneous and mucosal warts, and cervical, anogenital and oropharyngeal carcinomas. The specific mechanisms underlying high-risk HPV-driven cancer development in immunocompromised hosts are not well understood. Current treatments for HPV-related cancers include surgery with adjuvant chemotherapy and/or radiotherapy, with clinical trials underway to investigate the use of anti-PD-1 therapy. In the setting of HIV co-infection, persistent high-grade anal intraepithelial neoplasia can occur despite suppressive antiretroviral therapy, resulting in an ongoing risk for transformation to overt malignancy. Although therapeutic vaccines against HPV are under development, the efficacy of these in the setting of PID, secondary- or acquired- immunodeficiencies remains unclear. RNA-based therapeutic targeting of the HPV genome or mRNA transcript has become a promising next-generation therapeutic avenue. In this review, we summarise the current understanding of HPV pathogenesis, immune evasion, and malignant transformation, with a focus on key PIDs, secondary immunodeficiencies, and HIV infection. Current management and vaccine regimes are outlined in relation to HPV-driven cancer, and specifically, the need for more effective therapeutic strategies for immunocompromised hosts. The recent advances in RNA-based gene targeting including CRISPR and short interfering RNA (siRNA), and the potential application to HPV infection are of great interest. An increased understanding of both the dysregulated immune responses in immunocompromised hosts and of viral persistence is essential for the design of next-generation therapies to eliminate HPV persistence and cancer development in the most at-risk populations.

Disease Progression of WHIM Syndrome in an International Cohort of 66 Pediatric and Adult Patients

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome (WS) is a combined immunodeficiency caused by gain-of-function mutations in the C-X-C chemokine receptor type 4 (CXCR4) gene. We characterize a unique international cohort of 66 patients, including 57 (86%) cases previously unreported, with variable clinical phenotypes. Of 17 distinct CXCR4 genetic variants within our cohort, 11 were novel pathogenic variants affecting 15 individuals (23%). All variants affect the same CXCR4 region and impair CXCR4 internalization resulting in hyperactive signaling. The median age of diagnosis in our cohort (5.5 years) indicates WHIM syndrome can commonly present in childhood, although some patients are not diagnosed until adulthood. The prevalence and mean age of recognition and/or onset of clinical manifestations within our cohort were infections 88%/1.6 years, neutropenia 98%/3.8 years, lymphopenia 88%/5.0 years, and warts 40%/12.1 years. However, we report greater prevalence and variety of autoimmune complications of WHIM syndrome (21.2%) than reported previously. Patients with versus without family history of WHIM syndrome were diagnosed earlier (22%, average age 1.3 years versus 78%, average age 5 years, respectively). Patients with a family history of WHIM syndrome also received earlier treatment, experienced less hospitalization, and had less end-organ damage. This observation reinforces previous reports that early treatment for WHIM syndrome improves outcomes. Only one patient died; death was attributed to complications of hematopoietic stem cell transplantation. The variable expressivity of WHIM syndrome in pediatric patients delays their diagnosis and therapy. Early-onset bacterial infections with severe neutropenia and/or lymphopenia should prompt genetic testing for WHIM syndrome, even in the absence of warts.

Dysregulated stem cell niches and altered lymphocyte recirculation cause B and T cell lymphopenia in WHIM syndrome

Gain-of-function (GOF) mutations in CXCR4 cause WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome, characterized by infections, leukocyte retention in bone marrow (BM), and blood leukopenias. B lymphopenia is evident at early progenitor stages, yet why do CXCR4 GOF mutations that cause B (and T) lymphopenia remain obscure? Using a CXCR4 R334X GOF mouse model of WHIM syndrome, we showed that lymphopoiesis is reduced because of a dysregulated mesenchymal stem cell (MSC) transcriptome characterized by a switch from an adipogenic to an osteolineage-prone program with limited lymphopoietic activity. We identify lymphotoxin beta receptor (LTβR) as a critical pathway promoting interleukin-7 (IL-7) down-regulation in MSCs. Blocking LTβR or CXCR4 signaling restored IL-7 production and B cell development in WHIM mice. LTβR blocking also increased production of IL-7 and B cell activating factor (BAFF) in secondary lymphoid organs (SLOs), increasing B and T cell numbers in the periphery. These studies revealed that LTβR signaling in BM MSCs and SLO stromal cells limits the lymphocyte compartment size.

Genotype–phenotype correlations in WHIM syndrome: a systematic characterization of CXCR4WHIM variants

Warts, hypogammaglobulinemia, infections, myelokathexis (WHIM) syndrome is a rare primary immunodeficiency predominantly caused by heterozygous gain-of-function mutations in CXCR4 C-terminus. We assessed genotype–phenotype correlations for known pathogenic CXCR4 variants and in vitro response of each variant to mavorixafor, an investigational CXCR4 antagonist. We used cell-based assays to analyze CXCL12-induced receptor trafficking and downstream signaling of 14 pathogenic CXCR4 variants previously identified in patients with WHIM syndrome. All CXCR4 variants displayed impaired receptor trafficking, hyperactive downstream signaling, and enhanced chemotaxis in response to CXCL12. Mavorixafor inhibited CXCL12-dependent signaling and hyperactivation in cells harboring CXCR4^WHIM mutations. A strong correlation was found between CXCR4 internalization defect and severity of blood leukocytopenias and infection susceptibility, and between AKT activation and immunoglobulin A level and CD4⁺ T-cell counts. This study is the first to show WHIM syndrome clinical phenotype variability as a function of both CXCR4^WHIM genotype diversity and associated functional dysregulation. Our findings suggest that CXCR4 internalization may be used to assess the pathogenicity of CXCR4 variants in vitro and also as a potential WHIM-related disease biomarker. The investigational CXCR4 antagonist mavorixafor inhibited CXCL12-dependent signaling in all tested CXCR4-variant cell lines at clinically relevant concentrations.

CD28 and chemokine receptors: Signalling amplifiers at the immunological synapse

T cells are master regulators of the immune response tuning, among others, B cells, macrophages and NK cells. To exert their functions requiring high sensibility and specificity, T cells need to integrate different stimuli from the surrounding microenvironment. A finely tuned signalling compartmentalization orchestrated in dynamic platforms is an essential requirement for the proper and efficient response of these cells to distinct triggers. During years, several studies have depicted the pivotal role of the cytoskeleton and lipid microdomains in controlling signalling compartmentalization during T cell activation and functions. Here, we discuss mechanisms responsible for signalling amplification and compartmentalization in T cell activation, focusing on the role of CD28, chemokine receptors and the actin cytoskeleton. We also take into account the detrimental effect of mutations carried by distinct signalling proteins giving rise to syndromes characterized by defects in T cell functionality.

Altered CXCR4 dynamics at the cell membrane impairs directed cell migration in WHIM syndrome patients

SignificanceNew imaging-based approaches are incorporating new concepts to our knowledge of biological processes. The analysis of receptor dynamics involved in cell movement using single-particle tracking demonstrates that cells require chemokine-mediated receptor clustering to sense appropriately chemoattractant gradients. Here, we report that this process does not occur in T cells expressing CXCR4^R334X, a mutant form of CXCR4 linked to WHIM syndrome (warts, hypogammaglobulinemia, infections, myelokathexis). The underlaying molecular mechanism involves inappropriate actin cytoskeleton remodeling due to the inadequate β-arrestin1 activation by CXCR4^R334X, which alters its lateral mobility and spatial organization. These defects, associated to CXCR4^R334X expression, contribute to the retention of hematopoietic precursors in bone marrow niches and explain the severe immunological symptoms associated with WHIM syndrome.

Concurrent CDX2 cis-deregulation and UBTF-ATXN7L3 fusion define a novel high-risk subtype of B-cell ALL

CDX2 cis-deregulation and UBTF::ATXN7L3 fusion driven by focal deletions define a novel subtype of B-ALL.

CDX2/UBTF::ATXN7L3 is a high-risk B-ALL subtype in young adults, which warrants improved therapeutic strategies.

Oncogenic alterations underlying B-cell acute lymphoblastic leukemia (B-ALL) in adults remain incompletely elucidated. To uncover novel oncogenic drivers, we performed RNA sequencing and whole-genome analyses in a large cohort of unresolved B-ALL. We identified a novel subtype characterized by a distinct gene expression signature and the unique association of 2 genomic microdeletions. The 17q21.31 microdeletion resulted in a UBTF::ATXN7L3 fusion transcript encoding a chimeric protein. The 13q12.2 deletion resulted in monoallelic ectopic expression of the homeobox transcription factor CDX2, located 138 kb in cis from the deletion. Using 4C-sequencing and CRISPR interference experiments, we elucidated the mechanism of CDX2 cis-deregulation, involving PAN3 enhancer hijacking. CDX2/UBTF ALL (n = 26) harbored a distinct pattern of additional alterations including 1q gain and CXCR4 activating mutations. Within adult patients with Ph⁻ B-ALL enrolled in GRAALL trials, patients with CDX2/UBTF ALL (n = 17/723, 2.4%) were young (median age, 31 years) and dramatically enriched in females (male/female ratio, 0.2, P = .002). They commonly presented with a pro-B phenotype ALL and moderate blast cell infiltration. They had poor response to treatment including a higher risk of failure to first induction course (19% vs 3%, P = .017) and higher post-induction minimal residual disease (MRD) levels (MRD ≥ 10⁻⁴, 93% vs 46%, P < .001). This early resistance to treatment translated into a significantly higher cumulative incidence of relapse (75.0% vs 32.4%, P = .004) in univariate and multivariate analyses. In conclusion, we discovered a novel B-ALL entity defined by the unique combination of CDX2 cis-deregulation and UBTF::ATXN7L3 fusion, representing a high-risk disease in young adults.

Case Report: Altered NK Cell Compartment and Reduced CXCR4 Chemotactic Response of B Lymphocytes in an Immunodeficient Patient With HPV-Related Disease

The study of inborn errors of immunity (IEI) provides unique opportunities to elucidate the microbiome and pathogenic mechanisms related to severe viral infection. Several immunological and genetic anomalies may contribute to the susceptibility to develop Human Papillomavirus (HPV) pathogenesis. They include different acquired immunodeficiencies, EVER1-2 or CIB1 mutations underlying epidermodysplasia verruciformis (EV) syndrome and multiple IEI. Whereas EV syndrome patients are specifically unable to control infections with beta HPV, individuals with IEI show broader infectious and immune phenotypes. The WHIM (warts, hypogammaglobulinemia, infection, and myelokathexis) syndrome caused by gain-of-CXCR4-function mutation manifests by HPV-induced extensive cutaneous warts but also anogenital lesions that eventually progress to dysplasia. Here we report alterations of B and NK cells in a female patient suffering from cutaneous and mucosal HPV-induced lesions due to an as-yet unidentified genetic defect. Despite no detected mutations in CXCR4, B but not NK cells displayed a defective CXCR4-dependent chemotactic response toward CXCL12. In addition, NK cells showed an abnormal distribution with an expanded CD56^bright cell subset and defective cytotoxicity of CD56^dim cells. Our observations extend the clinical and immunological spectrum of IEI associated with selective susceptibility toward HPV pathogenesis, thus providing new insight on the immune control of HPV infection and potential host susceptibility factors.

Consideration of underlying immunodeficiency in refractory or recalcitrant warts: A review of the literature

Although the exact mechanisms have yet to be elucidated, it is clear that cellular immunity plays a role in clearance of human papillomavirus (HPV) infections as it relates to the development of warts. Patients with extensive, recalcitrant, or treatment‐refractory warts may have an underlying immune system impairment at the root of HPV susceptibility. Early recognition of genetic disorders associated with immunologic defects that allow for recalcitrant HPV infection may expedite appropriate treatment for patients. Early recognition is often pivotal in preventing subsequent morbidity and/or mortality that may arise from inborn errors of immunity, such as WHIM (Warts, Hypogammaglobulinemia, Infections, Myelokathexis) syndrome. Among these, cervical cancer is one of the most common malignancies associated with HPV, can be fatal if not treated early, and is seen more frequently in patients with underlying immune deficiencies. A review of diseases with susceptibility to HPV provides clues to understanding the pathophysiology of warts. We also present diagnostic guidance to facilitate the recognition of inborn errors of immunity in patients with extensive and/or recalcitrant HPV infections.

The Chemokine System in Oncogenic Pathways Driven by Viruses: Perspectives for Cancer Immunotherapy

Simple Summary

Oncoviruses are viruses with oncogenic potential, responsible for almost 20% of human cancers worldwide. They are from various families, some of which belong to the microbial communities that inhabit several sites in the body of healthy humans. As a result, they most often establish latent infections controlled by the arsenal of human host responses that include the chemokine system playing key roles at the interface between tissue homeostasis and immune surveillance. Yet, chemokines and their receptors also contribute to oncogenic processes as they are targeted by the virus-induced deregulations of host responses and/or directly encoded by viruses. Thus, the chemokine system offers a strong rationale for therapeutic options, some few already approved or in trials, and future ones that we are discussing in view of the pharmacological approaches targeting the different functions of chemokines operating in both cancer cells and the tumor microenvironment.

Abstract

Chemokines interact with glycosaminoglycans of the extracellular matrix and activate heptahelical cellular receptors that mainly consist of G Protein-Coupled Receptors and a few atypical receptors also with decoy activity. They are well-described targets of oncogenic pathways and key players in cancer development, invasiveness, and metastasis acting both at the level of cancer cells and cells of the tumor microenvironment. Hence, they can regulate cancer cell proliferation and survival and promote immune or endothelial cell migration into the tumor microenvironment. Additionally, oncogenic viruses display the potential of jeopardizing the chemokine system by encoding mimics of chemokines and receptors as well as several products such as oncogenic proteins or microRNAs that deregulate their human host transcriptome. Conversely, the chemokine system participates in the host responses that control the virus life cycle, knowing that most oncoviruses establish asymptomatic latent infections. Therefore, the deregulated expression and function of chemokines and receptors as a consequence of acquired or inherited mutations could bias oncovirus infection toward pro-oncogenic pathways. We here review these different processes and discuss the anticancer therapeutic potential of targeting chemokine availability or receptor activation, from signaling to decoy-associated functions, in combination with immunotherapies.

Characterization of a new WHIM syndrome mutant reveals mechanistic differences in regulation of the chemokine receptor CXCR4

WHIM syndrome is a rare immunodeficiency disorder that is characterized by warts, hypogammaglobulinemia, infections, and myelokathexis. While several gain-of-function mutations that lead to C-terminal truncations, frame shifts and point mutations in the chemokine receptor CXCR4 have been identified in WHIM syndrome patients, the functional effect of these mutations are not fully understood. Here, we report on a new WHIM syndrome mutation that results in a frame shift within the codon for Ser339 (S339fs5) and compare the properties of S339fs5 with wild-type CXCR4 and a previously identified WHIM syndrome mutant, R334X. The S339fs5 and R334X mutants exhibited significantly increased signaling compared to wild-type CXCR4 including agonist-promoted calcium flux and extracellular-signal-regulated kinase activation. This increase is at least partially due to a significant decrease in agonist-promoted phosphorylation, β-arrestin binding, and endocytosis of S339fs5 and R334X compared with wild-type CXCR4. Interestingly, there were also significant differences in receptor degradation, with S339fs5 having a very high basal level of degradation compared with that of R334X and wild-type CXCR4. In contrast to wild-type CXCR4, both R334X and S339fs5 were largely insensitive to CXCL12-promoted degradation. Moreover, while basal and agonist-promoted degradation of wild-type CXCR4 was effectively inhibited by the CXCR4 antagonist TE-14016, this had no effect on the degradation of the WHIM mutants. Taken together, these studies identify a new WHIM syndrome mutant, CXCR4-S339fs5, which promotes enhanced signaling, reduced phosphorylation, β-arrestin binding and endocytosis, and a very high basal rate of degradation that is not protected by antagonist treatment.

Mesenchymal Stem/Stromal Cells Overexpressing CXCR4R334X Revealed Enhanced Migration: A Lesson Learned from the Pathogenesis of WHIM Syndrome

C-X-C chemokine receptor type 4 (CXCR4), initially recognized as a co-receptor for HIV, contributes to several disorders, including the WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome. CXCR4 binds to its ligand SDF-1 to make an axis involved in the homing property of stem cells. This study aimed to employ WHIM syndrome pathogenesis as an inspirational approach to reinforce cell therapies. Wild type and WHIM-type variants of the CXCR4 gene were chemically synthesized and cloned in the pCDH-513B-1 lentiviral vector. Molecular cloning of the synthetic genes was confirmed by DNA sequencing, and expression of both types of CXCR4 at the protein level was confirmed by western blotting in HEK293T cells. Human adipose-derived mesenchymal stem cells (Ad-MSCs) were isolated, characterized, and subjected to lentiviral transduction with Wild type and WHIM-type variants of CXCR4. The presence of copGFP-positive MSCs confirmed the high efficiency of transduction. The migration ability of both groups of transduced cells was then assessed by transwell migration assay in the presence or absence of a CXCR4-blocking agent. Our qRT-PCR results showed overexpression of CXCR4 at mRNA level in both groups of transduced MSCs, and expression of WHIM-type CXCR4 was significantly higher than Wild type CXCR4 (P<0.05). Our results indicated that the migration of genetically modified MSCs expressing WHIM-type CXCR4 had significantly enhanced towards SDF1 in comparison with Wild type CXCR4 (P<0.05), while it was reduced after treatment with CXCR4 antagonist. These data suggest that overexpression of WHIM-type CXCR4 could lead to enhanced and sustained expression of CXCR4 on human MSCs, which would increase their homing capability; hence it might be an appropriate strategy to improve the efficiency of cell-based therapies.

CXCR4 hyperactivation cooperates with TCL1 in CLL development and aggressiveness

Aberrant CXCR4 activity has been implicated in lymphoma pathogenesis, disease progression, and resistance to therapies. Using a mouse model with a gain-of-function CXCR4 mutation (CXCR4C1013G) that hyperactivates CXCR4 signaling, we identified CXCR4 as a crucial activator of multiple key oncogenic pathways. CXCR4 hyperactivation resulted in an expansion of transitional B1 lymphocytes, which represent the precursors of chronic lymphocytic leukemia (CLL). Indeed, CXCR4 hyperactivation led to a significant acceleration of disease onset and a more aggressive phenotype in the murine Eµ-TCL1 CLL model. Hyperactivated CXCR4 signaling cooperated with TCL1 to cause a distinct oncogenic transcriptional program in B cells, characterized by PLK1/FOXM1-associated pathways. In accordance, Eµ-TCL1;CXCR4C1013G B cells enriched a transcriptional signature from patients with Richter's syndrome, an aggressive transformation of CLL. Notably, MYC activation in aggressive lymphoma was associated with increased CXCR4 expression. In line with this finding, additional hyperactive CXCR4 signaling in the Eµ-Myc mouse, a model of aggressive B-cell cancer, did not impact survival. In summary, we here identify CXCR4 hyperactivation as a co-driver of an aggressive lymphoma phenotype.

Hematologic disorder-associated Cxcr4 gain-of-function mutation leads to uncontrolled extrafollicular immune response

The extrafollicular immune response is essential to generate a rapid but transient wave of protective antibodies during infection. Despite its importance, the molecular mechanisms controlling this first response are poorly understood. Here, we demonstrate that enhanced Cxcr4 signaling caused by defective receptor desensitization leads to exacerbated extrafollicular B-cell response. Using a mouse model bearing a gain-of-function mutation of Cxcr4 described in 2 human hematologic disorders, warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome and Waldenström macroglobulinemia, we demonstrated that mutant B cells exhibited enhanced mechanistic target of rapamycin signaling, cycled more, and differentiated more potently into plasma cells than wild-type B cells after Toll-like receptor (TLR) stimulation. Moreover, Cxcr4 gain of function promoted enhanced homing and persistence of immature plasma cells in the bone marrow, a phenomenon recapitulated in WHIM syndrome patient samples. This translated in increased and more sustained production of antibodies after T-independent immunization in Cxcr4 mutant mice. Thus, our results establish that fine-tuning of Cxcr4 signaling is essential to limit the strength and length of the extrafollicular immune response.

GRK6 Depletion Induces HIF Activity in Lung Adenocarcinoma

G protein-coupled receptor kinase 6 (GRK6) is expressed in various tissues and is involved in the development of several diseases including lung cancer. We previously reported that GRK6 is down-regulated in lung adenocarcinoma patients, which induces cell invasion and metastasis. However, further understanding of the role of GRK6 in lung adenocarcinoma is required. Here we explored the functional consequence of GRK6 inhibition in lung epithelial cells. Analysis of TCGA data was coupled with RNA sequencing (RNA-seq) in alveolar epithelial type II (ATII) cells following depletion of GRK6 with RNA interference (RNAi). Findings were validated in ATII cells followed by tissue microarray analysis. Pathway analysis suggested that one of the Hallmark pathways enriched upon GRK6 inhibition is 'Hallmark_Hypoxia' (FDR = 0.014). We demonstrated that GRK6 depletion induces HIF1α (hypoxia-inducible factor 1 alpha) levels and activity in ATII cells. The findings were further confirmed in lung adenocarcinoma samples, in which GRK6 expression levels negatively and positively correlate with HIF1α expression (P = 0.015) and VHL expression (P < 0.0001), respectively. Mechanistically, we showed the impact of GRK6 on HIF activity could be achieved via regulation of VHL levels. Taken together, targeting the HIF pathway may provide new strategies for therapy in GRK6-depleted lung adenocarcinoma patients.

CXCR4 signaling controls dendritic cell location and activation at steady state and in inflammation

Dendritic cells (DCs) encompass several cell subsets that collaborate to initiate and regulate immune responses. Proper DC localization determines their function and requires the tightly controlled action of chemokine receptors. All DC subsets express CXCR4, but the genuine contribution of this receptor to their biology has been overlooked. We addressed this question using natural CXCR4 mutants resistant to CXCL12-induced desensitization and harboring a gain of function that cause the warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome (WS), a rare immunodeficiency associated with high susceptibility to the pathogenesis of human papillomavirus (HPV). We report a reduction in the number of circulating plasmacytoid DCs (pDCs) in WHIM patients, whereas that of conventional DCs is preserved. This pattern was reproduced in an original mouse model of WS, enabling us to show that the circulating pDC defect can be corrected upon CXCR4 blockade and that pDC differentiation and function are preserved, despite CXCR4 dysfunction. We further identified proper CXCR4 signaling as a critical checkpoint for Langerhans cell and DC migration from the skin to lymph nodes, with corollary alterations of their activation state and tissue inflammation in a model of HPV-induced dysplasia. Beyond providing new hypotheses to explain the susceptibility of WHIM patients to HPV pathogenesis, this study shows that proper CXCR4 signaling establishes a migration threshold that controls DC egress from CXCL12-containing environments and highlights the critical and subset-specific contribution of CXCR4 signal termination to DC biology.

Hematopoietic Multipotent Progenitors and Plasma Cells: Neighbors or Roommates in the Mouse Bone Marrow Ecosystem?

The bone marrow is a complex ecosystem in which hematopoietic and non-hematopoietic cells reside. In this review, we discuss the bone marrow niches in mice that facilitate the survival, maintenance, and differentiation of cells of hematopoietic origin based on the recent literature. Our review places a special focus on the hematopoietic multipotent progenitors and on plasma cells, corresponding to the last stage of the B-cell lineage, that play a key role in the humoral memory response. We highlight the similarities between the microenvironments necessary for the establishment and the maintenance of these two immune cell subsets, and how the chemokine CXCL12/CXCR4 signaling axis contributes to these processes. Finally, we bring elements to address the following question: are multipotent progenitors and plasma cells neighbors or roommates within the bone marrow?

Monocytes, macrophages, dendritic cells and neutrophils: an update on lifespan kinetics in health and disease

Phagocytes form a family of immune cells that play a crucial role in tissue maintenance and help orchestrate the immune response. This family of cells can be separated by their nuclear morphology into mononuclear and polymorphonuclear phagocytes. The generation of these cells in the bone marrow, to the blood and finally into tissues is a tightly regulated process. Ensuring the adequate production of these cells and their timely removal is key for both the initiation and resolution of inflammation. Insight into the kinetic profiles of innate myeloid cells during steady state and pathology will permit the rational development of therapies to boost the production of these cells in times of need or reduce them when detrimental.

The G Protein-Coupled Receptor Kinases (GRKs) in Chemokine Receptor-Mediated Immune Cell Migration: From Molecular Cues to Physiopathology

Although G protein-coupled receptor kinases (GRKs) have long been known to regulate G protein-coupled receptor (GPCR) desensitization, their more recently characterized functions as scaffolds and signalling adapters underscore that this small family of proteins governs a larger array of physiological functions than originally suspected. This review explores how GRKs contribute to the complex signalling networks involved in the migration of immune cells along chemokine gradients sensed by cell surface GPCRs. We outline emerging evidence indicating that the coordinated docking of several GRKs on an active chemokine receptor determines a specific receptor phosphorylation barcode that will translate into distinct signalling and migration outcomes. The guidance cues for neutrophil migration are emphasized based on several alterations affecting GRKs or GPCRs reported to be involved in pathological conditions.

Hematopoietic Stem Cell Niches and Signals Controlling Immune Cell Development and Maintenance of Immunological Memory

Studies over the last couple of decades have shown that hematopoietic stem cells (HSCs) are critically dependent on cytokines such as Stem Cell Factor and other signals provided by bone marrow niches comprising of mesenchymal stem and progenitor cells (MSPCs) and endothelial cells (ECs). Because of their critical roles in HSC maintenance the niches formed by MSPCs and ECs are commonly referred to as HSC niches. For the most part, the signals required for HSC maintenance act in a short-range manner, which imposes the necessity for directional and positional cues in order for HSCs to localize and be retained properly in stem cell niches. The chemokine CXCL12 and its Gαi protein coupled receptor CXCR4, besides promoting HSC quiescence directly, also play instrumental roles in enabling HSCs to access bone marrow stem cell niches. Recent studies have revealed, however, that HSC niches also provide a constellation of hematopoietic cytokines that are critical for the production of most, if not all, blood cell types. Some hematopoietic cytokines, namely IL-7 and IL-15 produced by HSC niches, are not only required for lymphopoiesis but are also essential for memory T cell maintenance. Consequently, hematopoietic progenitors and differentiated immune cells, such as memory T cell subsets, also depend on the CXCL12/CXCR4 axis for migration into bone marrow and interactions with MSPCs and ECs. Similarly, subsets of antibody-secreting plasma cells also reside in close association with CXCL12-producing MSPCs in the bone marrow and require the CXCR4/CXCL12 axis for survival and long-term maintenance. Collectively, these studies demonstrate a broad range of key physiological roles, spanning blood cell production and maintenance of immunological memory, that are orchestrated by stem cell niches through a common and simple mechanism: CXCL12/CXCR4-mediated cell recruitment followed by receipt of a maintenance and/or instructive signal. A fundamental flaw of this type of cellular organization is revealed by myeloid and lymphoid leukemias, which target stem cell niches and induce profound transcriptomic changes that result in reduced hematopoietic activity and altered mesenchymal cell differentiation.

The CXCL12/CXCR4/ACKR3 Axis in the Tumor Microenvironment: Signaling, Crosstalk, and Therapeutic Targeting

Elevated expression of the chemokine receptors CXCR4 and ACKR3 and of their cognate ligand CXCL12 is detected in a wide range of tumors and the tumor microenvironment (TME). Yet, the molecular mechanisms by which the CXCL12/CXCR4/ACKR3 axis contributes to the pathogenesis are complex and not fully understood. To dissect the role of this axis in cancer, we discuss its ability to impinge on canonical and less conventional signaling networks in different cancer cell types; its bidirectional crosstalk, notably with receptor tyrosine kinase (RTK) and other factors present in the TME; and the infiltration of immune cells that supporttumor progression. We discuss current and emerging avenues that target the CXCL12/CXCR4/ACKR3 axis. Coordinately targeting both RTKs and CXCR4/ACKR3 and/or CXCL12 is an attractive approach to consider in multitargeted cancer therapies. In addition, inhibiting infiltrating immune cells or reactivating the immune system along with modulating the CXCL12/CXCR4/ACKR3 axis in the TME has therapeutic promise.

Aberrant CXCR4 Signaling at Crossroad of WHIM Syndrome and Waldenstrom's Macroglobulinemia

Given its pleiotropic functions, including its prominent role in inflammation, immune responses and cancer, the C-X-C chemokine receptor type 4 (CXCR4) has gained significant attention in recent years and has become a relevant target in drug development. Although the signaling properties of CXCR4 have been extensively studied, several aspects deserve deeper investigations. Mutations in the C-term tail of the CXCR4 gene cause WHIM syndrome, a rare congenital immunodeficiency associated by chronic leukopenia. Similar mutations have also been recently identified in 30% of patients affected by Waldenstrom’s macroglobulinaemia, a B-cell neoplasia with bone marrow accumulation of malignant cells. An ample body of work has been generated to define the impact of WHIM mutations on CXCR4 signaling properties and evaluate their role on pathogenesis, diagnosis, and response to therapy, although the identity of disease-causing signaling pathways and their relevance for disease development in different genetic variants are still open questions. This review discusses the current knowledge on biochemical properties of CXCR4 mutations to identify their prototypic signaling profile potentially useful to highlighting novel opportunities for therapeutic intervention.

CXCR4 antagonist AMD3100 (plerixafor): From an impurity to a therapeutic agent

AMD3100 (plerixafor), a CXCR4 antagonist, has opened a variety of avenues for potential therapeutic approaches in different refractory diseases. The CXCL12/CXCR4 axis and its signaling pathways are involved in diverse disorders including HIV-1 infection, tumor development, non-Hodgkin lymphoma, multiple myeloma, WHIM Syndrome, and so on. The mechanisms of action of AMD3100 may relate to mobilizing hematopoietic stem cells, blocking infection of X4 HIV-1, increasing circulating neutrophils, lymphocytes and monocytes, reducing myeloid-derived suppressor cells, and enhancing cytotoxic T-cell infiltration in tumors. Here, we first revisit the pharmacological discovery of AMD3100. We then review monotherapy of AMD3100 and combination use of AMD3100 with other agents in various diseases. Among those, we highlight the perspective of AMD3100 as an immunomodulator to regulate immune responses particularly in the tumor microenvironment and synergize with other therapeutics. All the pre-clinical studies support the clinical testing of the monotherapy and combination therapies with AMD3100 and further development for use in humans.

Discovery, structure-activity relationship study and biological evaluation of 2-thioureidothiophene-3-carboxylates as a novel class of C-X-C chemokine receptor 2 (CXCR2) antagonists

The C-X-C motif ligand 8 and C-X-C chemokine receptor 2 (CXCL8-CXCR2) axis is involved in pathogenesis of various diseases including inflammation and cancers. Various CXCR2 antagonists are under development for several diseases. Our previous high-throughput cell-based assay specific for CXCR2 has identified a pyrimidine-based compound CX797 acting on CXCR2 down-stream signaling. A lead optimization campaign through scaffold-hopping strategy led to a series of 2-thioureidothiophene-3-carboxylates (TUTP) as novel CXCR2 antagonists. Structure-activity relationship study of TUTPs led to the identification of compound 52 that significantly inhibited CXCR2-mediated β-arrestin recruitment signaling (IC₅₀ = 1.1±0.01 μM) with negligible effect on CXCL8-mediated cAMP signaling and calcium flux. Similar to the known CXCR2 antagonist SB265610, compound 52 inhibited CXCL8-CXCR2 induced phosphorylation of ERK1/2. TUTP compounds also inhibited CXCL8-mediated cell migration and showed synergy with doxorubicin in ovarian cancer cells, thereby supporting TUTPs as promising compounds for cancer treatment.

The role of neutrophils in host defense and disease

Neutrophils, the most abundant circulating leukocyte, are critical for host defense. Granulopoiesis is under the control of transcriptional factors and culminates in mature neutrophils with a broad armamentarium of antimicrobial pathways. These pathways include nicotinamide adenine dinucleotide phosphate oxidase, which generates microbicidal reactive oxidants, and nonoxidant pathways that target microbes through several mechanisms. Activated neutrophils can cause or worsen tissue injury, underscoring the need for calibration of activation and resolution of inflammation when infection has been cleared. Acquired neutrophil disorders are typically caused by cytotoxic chemotherapy or immunosuppressive agents. Primary neutrophil disorders typically result from disabling mutations of individual genes that result in impaired neutrophil number or function, and provide insight into basic mechanisms of neutrophil biology. Neutrophils can also be activated by noninfectious causes, including trauma and cellular injury, and can have off-target effects in which pathways that typically defend against infection exacerbate injury and disease. These off-target effects include acute organ injury, autoimmunity, and variable effects on the tumor microenvironment that can limit or worsen tumor progression. A greater understanding of neutrophil plasticity in these conditions is likely to pave the way to new therapeutic approaches.

The multilayered complexity of the chemokine receptor system

The chemokines receptor family are membrane-expressed class A-specific seven-transmembrane receptors linked to G proteins. Through interaction with the corresponding ligands, the chemokines, they induce a wide variety of cellular responses including cell polarization, movement, immune and inflammatory responses, as well as the prevention of HIV-1 infection. Like a Russian matryoshka doll, the chemokine receptor system is more complex than initially envisaged. This review focuses on the mechanisms that contribute to this dazzling complexity and how they modulate the signaling events triggered by chemokines. The chemokines and their receptors exist as monomers, dimers and oligomers, their expression pattern is highly regulated, and the ligands can bind distinct receptors with similar affinities. The use of novel imaging-based technologies, particularly real-time imaging modalities, has shed new light on the very dynamic conformations that chemokine receptors adopt depending on the cellular context, and that affect chemokine-mediated responses. This complex scenario presents both challenging and exciting opportunities for drug discovery.

Human inborn errors of immunity to herpes viruses

Infections with any of the nine human herpes viruses (HHV) can be asymptomatic or life-threatening. The study of patients with severe diseases caused by HHVs, in the absence of overt acquired immunodeficiency, has led to the discovery or diagnosis of various inborn errors of immunity. The related inborn errors of adaptive immunity disrupt α/β T-cell rather than B-cell immunity. Affected patients typically develop HHV infections in the context of other infectious diseases. However, this is not always the case, as illustrated by inborn errors of SAP-dependent T-cell immunity to EBV-infected B cells. The related inborn errors of innate immunity disrupt leukocytes other than T and B cells, non-hematopoietic cells, or both. Patients typically develop only a single type of infection due to HHV, although, again, this is not always the case, as illustrated by inborn errors of TLR3 immunity resulting in HSV1 encephalitis in some patients and influenza pneumonitis in others. Most severe HHV infections in otherwise healthy patients remains unexplained. The forward human genetic dissection of isolated and syndromic HHV-driven illnesses will establish the molecular and cellular basis of protective immunity to HHVs, paving the way for novel diagnosis and management strategies.

Cell circuits and niches controlling B cell development

Studies over the last decade uncovered overlapping niches for hematopoietic stem cells (HSCs), multipotent progenitor cells, common lymphoid progenitors, and early B cell progenitors. HSC and lymphoid niches are predominantly composed by mesenchymal progenitor cells (MPCs) and by a small subset of endothelial cells. Niche cells create specialized microenvironments through the concomitant production of short-range acting cell-fate determining cytokines such as interleukin (IL)-7 and stem cell factor and the potent chemoattractant C-X-C motif chemokine ligand 12. This type of cellular organization allows for the cross-talk between hematopoietic stem and progenitor cells with niche cells, such that niche cell activity can be regulated by the quality and quantity of hematopoietic progenitors being produced. For example, preleukemic B cell progenitors and preB acute lymphoblastic leukemias interact directly with MPCs, and downregulate IL-7 expression and the production of non-leukemic lymphoid cells. In this review, we discuss a novel model of B cell development that is centered on cellular circuits formed between B cell progenitors and lymphopoietic niches.

Role of neutrophils in ischemic heart failure

Amplified innate leukocytes (neutrophils and monocytes/macrophages) are associated with advanced ischemic and non-ischemic heart failure (HF). Intensified neutrophilic leukocytosis (neutrophilia) and sustained activation of neutrophils is the predominant factor that determines over activated inflammation in acute HF and the outcome of long-term chronic HF. After heart attack, the first wave of innate responsive and short-lived neutrophils is essential for the initiation of inflammation, resolution of inflammation, and cardiac repair, however uncontrolled and long-term activation of neutrophils leads to collateral damage of myocardium. In the presented review, we highlighted the interactive and integrative role of neutrophil phenotypes in cellular and molecular events of ischemic HF. In addition, we discussed the current, nonimmune, immune, and novel paradigms of neutrophils in HF associated with differential factors with a specific interest in non-resolving inflammation and resolution physiology.

Rat cytomegalovirus-encoded γ-chemokine vXCL1 is a highly adapted, species-specific agonist for rat XCR1-positive dendritic cells

Dendritic cells (DCs) expressing the chemokine receptor XCR1 are specialized in antigen cross-presentation to control infections with intracellular pathogens. XCR1-positive (XCR1⁺) DCs are attracted by XCL1, a γ-chemokine secreted by activated CD8⁺ T cells and natural killer cells. Rat cytomegalovirus (RCMV) is the only virus known to encode a viral XCL1 analog (vXCL1) that competes for XCR1 binding with the endogenous chemokine. Here we show that vXCL1 from two different RCMV strains, as well as endogenous rat XCL1 (rXCL1) bind to and induce chemotaxis exclusively in rat XCR1⁺ DCs. Whereas rXCL1 activates the XCR1 Gi signaling pathway in rats and humans, both of the vXCL1s function as species-specific agonists for rat XCR1. In addition, we demonstrate constitutive internalization of XCR1 in XCR1-transfected HEK293A cells and in splenic XCR1⁺ DCs. This internalization was independent of β-arrestin 1 and 2 and was enhanced after binding of vXCL1 and rXCL1; however, vXCL1 appeared to be a stronger agonist. These findings suggest a decreased surface expression of XCR1 during DC cultivation at 37°C, and subsequent impairment of chemotactic activity and XCR1⁺ DC function.

A chemotaxis model to explain WHIM neutrophil accumulation in the bone marrow of WHIM mouse model

Neutrophils are essential immune cells that defend the host against pathogenic microbial agents. Neutrophils are produced in the bone marrow and are retained there through CXCR4–CXCL12 signaling. However, patients with the Warts, Hypogammaglobulinemia, Infections, and Myelokathexis (WHIM) syndrome are prone to infections due to increased accumulation of neutrophils in the bone marrow leading to low numbers of circulating neutrophils. How neutrophils accumulate in the bone marrow in this condition is poorly understood. To better understand factors involved in neutrophil accumulation in the bone marrow, neutrophils from wildtype and WHIM mouse models were characterized in their response to CXCL12 stimulation. WHIM neutrophils were found to exert stronger traction forces, formed significantly more lamellipodia-type protrusions and migrated with increased speed and displacement upon CXCL12 stimulation as compared to wildtype cells. Migration speed of WHIM neutrophils showed a larger initial increase upon CXCL12 stimulation, which decayed over a longer time period as compared to wildtype cells. We proposed a computational model based on the chemotactic behavior of neutrophils that indicated increased CXCL12 sensitivity and prolonged CXCR4 internalization adaptation time in WHIM neutrophils as being responsible for increased accumulation in the bone marrow. These findings provide a mechanistic understanding of bone marrow neutrophil accumulation in WHIM condition and novel insights into restoring neutrophil regulation in WHIM patients.

WHIM Syndrome: from Pathogenesis Towards Personalized Medicine and Cure

WHIM syndrome is a rare combined primary immunodeficiency disease named by acronym for the diagnostic tetrad of warts, hypogammaglobulinemia, infections, and myelokathexis. Myelokathexis is a unique form of non-cyclic severe congenital neutropenia caused by accumulation of mature and degenerating neutrophils in the bone marrow; monocytopenia and lymphopenia, especially B lymphopenia, also commonly occur. WHIM syndrome is usually caused by autosomal dominant mutations in the G protein-coupled chemokine receptor CXCR4 that impair desensitization, resulting in enhanced and prolonged G protein- and β-arrestin-dependent responses. Accordingly, CXCR4 antagonists have shown promise as mechanism-based treatments in phase 1 clinical trials. This review is based on analysis of all 105 published cases of WHIM syndrome and covers current concepts, recent advances, unresolved enigmas and controversies, and promising future research directions.

Enhanced Bone Marrow Homing of Natural Killer Cells Following mRNA Transfection With Gain-of-Function Variant CXCR4R334X

Adoptive transfer of natural killer (NK) cells can induce remission in patients with relapsed/refractory leukemia and myeloma. However, to date, clinical efficacy of NK cell immunotherapy has been limited to a sub-fraction of patients. Here we show that steps incorporated in the ex vivo manipulation/production of NK cell products used for adoptive infusion, such as over-night IL-2 activation or cryopreservation followed by ex vivo expansion, drastically decreases NK cell surface expression of the bone marrow (BM) homing chemokine receptor CXCR4. Reduced CXCR4 expression was associated with dampened in vitro NK cell migration toward its cognate ligand stromal-derived factor-1α (SDF-1α). NK cells isolated from patients with WHIM syndrome carry gain-of-function (GOF) mutations in CXCR4 (CXCR4^R334X). Compared to healthy donors, we observed that NK cells expanded from WHIM patients have similar surface levels of CXCR4 but have a much stronger propensity to home to BM compartments when adoptively infused into NOD-scid IL2Rgamma^null (NSG) mice. Therefore, in order to augment the capacity of adoptively infused NK cells to home to the BM, we genetically engineered ex vivo expanded NK cells to express the naturally occurring GOF CXCR4^R334X receptor variant. Transfection of CXCR4^R334X-coding mRNA into ex vivo expanded NK cells using a clinically applicable method consistently led to an increase in cell surface CXCR4 without altering NK cell phenotype, cytotoxic function, or compromising NK cell viability. Compared to non-transfected and wild type CXCR4-coding mRNA transfected counterparts, CXCR4^R334X-engineered NK cells had significantly greater chemotaxis toward SDF-1α in vitro. Importantly, expression of CXCR4^R334X on expanded NK cells resulted in significantly greater BM homing following adoptive transfer into NSG mice compared to non-transfected NK cell controls. Collectively, these data suggest up-regulation of cell surface CXCR4^R334X on ex vivo expanded NK cells via mRNA transfection represents a novel approach to improve homing and target NK cell-based immunotherapies to BM where hematological malignancies reside.

Context-Dependent Signaling of CXC Chemokine Receptor 4 and Atypical Chemokine Receptor 3

G protein-coupled receptors (GPCRs) are regulated by complex molecular mechanisms, both in physiologic and pathologic conditions, and their signaling can be intricate. Many factors influence their signaling behavior, including the type of ligand that activates the GPCR, the presence of interacting partners, the kinetics involved, or their location. The two CXC-type chemokine receptors, CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3), both members of the GPCR superfamily, are important and established therapeutic targets in relation to cancer, human immunodeficiency virus infection, and inflammatory diseases. Therefore, it is crucial to understand how the signaling of these receptors works to be able to specifically target them. In this review, we discuss how the signaling pathways activated by CXCR4 and ACKR3 can vary in different situations. G protein signaling of CXCR4 depends on the cellular context, and discrepancies exist depending on the cell lines used. ACKR3, as an atypical chemokine receptor, is generally reported to not activate G proteins but can broaden its signaling spectrum upon heteromerization with other receptors, such as CXCR4, endothelial growth factor receptor, or the α ₁-adrenergic receptor (α ₁-AR). Also, CXCR4 forms heteromers with CC chemokine receptor (CCR) 2, CCR5, the Na⁺/H⁺ exchanger regulatory factor 1, CXCR3, α ₁-AR, and the opioid receptors, which results in differential signaling from that of the monomeric subunits. In addition, CXCR4 is present on membrane rafts but can go into the nucleus during cancer progression, probably acquiring different signaling properties. In this review, we also provide an overview of the currently known critical amino acids involved in CXCR4 and ACKR3 signaling.

Congenital Neutropenia and Rare Functional Phagocyte Disorders in Children

Both profound neutropenia and functional phagocyte disorders render patients susceptible to recurrent, unusual, and/or life-threatening infections. Many disorders also have nonhematologic manifestations and a substantial risk of leukemogenesis. Diagnosis relies on clinical suspicion and interrogation of the complete blood count with differential/bone marrow examination coupled with immunologic and genetic analyses. Treatment of the quantitative neutrophil disorders depends on granulocyte colony-stimulating factor, whereas management of functional phagocyte disease is reliant on antimicrobials and/or targeted therapies. Hematopoietic stem cell transplant remains the only curative option for most disorders but is not used on a routine basis.

Heterologous regulation of CXCR4 lysosomal trafficking

G protein-coupled receptor (GPCR) signaling is regulated by members of the protein kinase C (PKC) and GPCR kinase (GRK) families, although the relative contribution of each to GPCR function varies among specific GPCRs. The CXC motif receptor 4 (CXCR4) is a member of the GPCR superfamily that binds the CXC motif chemokine ligand 12 (CXCL12), initiating signaling that is subsequently terminated in part by internalization and lysosomal degradation of CXCR4. The purpose of this study is to define the relative contribution of PKC and GRK to CXCR4 signaling attenuation by studying their effects on CXCR4 lysosomal trafficking and degradation. Our results demonstrate that direct activation of PKC via the phorbol ester phorbol 12-myristate 13-acetate (PMA) mimics CXCL12-mediated desensitization, internalization, ubiquitination, and lysosomal trafficking of CXCR4. In agreement, heterologous activation of PKC by stimulating the chemokine receptor CXCR5 with its ligand, CXCL13, also mimics CXCL12-mediated desensitization, internalization, ubiquitination, and lysosomal degradation of CXCR4. Similar to CXCL12, PMA promotes PKC-dependent phosphorylation of serine residues within CXCR4 C-tail that are required for binding and ubiquitination by the E3 ubiquitin ligase AIP4 (atrophin-interacting protein 4). However, inhibition of PKC activity does not alter CXCL12-mediated ubiquitination and degradation of CXCR4, suggesting that other kinases are also required. Accordingly, siRNA-mediated depletion of GRK6 results in decreased degradation and ubiquitination of CXCR4. Overall, these results suggest that PKC and GRK6 contribute to unique aspects of CXCR4 phosphorylation and lysosomal degradation to ensure proper signal propagation and termination.

Isotype Specific Assembly of B Cell Antigen Receptors and Synergism With Chemokine Receptor CXCR4

Expression of the membrane-bound form of the immunoglobulin (Ig) as part of the antigen receptor is indispensable for both the development and the effector function of B cells. Among five known isotypes, IgM and IgD are the common B cell antigen receptors (BCRs) that are co-expressed in naïve B cells. Despite having identical antigen specificity and being associated with the same signaling heterodimer Igα/Igβ (CD79a/CD79b), IgM and IgD-BCR isotypes functionally differ from each other in the manner of antigen binding, the formation of isolated nanoclusters and in their interaction with co-receptors such as CD19 and CXCR4 on the plasma membrane. With recent developments in experimental techniques, it is now possible to investigate the nanoscale organization of the BCR and better understand early events of BCR engagement. Interestingly, the cytoskeleton network beneath the membrane controls the BCR isotype-specific organization and its interaction with co-receptors. BCR triggering results in reorganization of the cytoskeleton network, which is further modulated by isotype-specific signals from co-receptors. For instance, IgD-BCR is closely associated with CXCR4 on mature B cells and this close proximity allows CXCR4 to employ the BCR machinery as signaling hub. In this review, we discuss the functional specificity and nanocluster assembly of BCR isotypes and the consequences of cross-talk between CXCR4 and IgD-BCR. Furthermore, given the role of BCR and CXCR4 signaling in the development and survival of leukemic B cells, we discuss the consequences of the cross-talk between CXCR4 and the BCR for controlling the growth of transformed B cells.