WHIM Syndrome-linked CXCR4 mutations drive osteoporosis

Clinicopathologic features and the spectrum of myelokathexis in WHIM syndrome

WHIM syndrome is a rare primary immunodeficiency disorder predominantly caused by germline CXCR4 variants. Bone marrow (BM) evaluation showing myelokathexis helps to establish the diagnosis of WHIM syndrome, but unfamiliarity with pertinent diagnostic features and variability in morphologic and clinical findings may result in disease under-recognition. We characterize the clinical, BM and peripheral blood (PB) features of 30 patients with germline CXCR4 variants, including genotype-phenotype analysis and correlation between morphologic features and functional CXCR4 receptor internalization defect. We also examine PB features of a mouse model of WHIM syndrome (Cxcr4+/1013), and examine WHIM syndrome and WHIM mouse PB morphologic changes after CXCR4 antagonist therapy. Carboxy-terminal nonsense/frameshift CXCR4 variants were associated with myelokathectic neutrophil morphology in 32-80% (median: 66%) and 4-14% (median: 9%) of total neutrophils in the BM and PB, respectively. In contrast, myelokathectic neutrophils were infrequent in five missense CXCR4 variants (three CXCR4D84H; two CXCR4S341Y). Compared to neutropenic controls, carboxy-terminal CXCR4 nonsense/frameshift variants were associated with >10% BM or >5% PB myelokathectic neutrophils (100% specific; 100% (BM) or 93% (PB) sensitive), as well as more frequent neutrophil apoptosis (BM p=0.0093; PB p<0.0001), dysmorphic/vacuolated eosinophils (BM p=0.012; PB p<0.0001), neutrophil vacuolization (BM p<0.0001), and non-paratrabecular neutrophil clusters in the BM (p=0.0059). BM myeloid hyperplasia occurred in 54% of carboxy-terminal CXCR4 nonsense/frameshift variants and no controls. BM myelokathectic neutrophil percentage correlated with the functional CXCR4 internalization defect (p≤0.0042). Like humans, WHIM mice (Cxcr4+/1013) demonstrated circulating myelokathectic-like neutrophils with nuclear hypersegmentation. CXCR4 antagonist therapy in patients with WHIM syndrome (n=5) and mice increased both morphologically normal and myelokathectic neutrophils in PB. We demonstrate notable genotype-phenotype heterogeneity between CXCR4 variants and myelokathexis, which correlates with functional CXCR4 internalization defect. The morphologic features of WHIM syndrome may be subtle, resulting in misdiagnosis. We describe key morphologic features that are useful to facilitate diagnosis.

CXCR4 antagonism ameliorates leukocyte abnormalities in a preclinical model of WHIM syndrome

Background

WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome is an ultra-rare, combined primary immunodeficiency and chronic neutropenic disorder characterized by a range of clinical presentations, including peripheral neutropenia, lymphopenia, and recurrent infections. WHIM syndrome is most often caused by gain-of-function mutations in the gene encoding C-X-C chemokine receptor 4 (CXCR4). As such, inhibition of CXCR4 with XOLREMDI® (mavorixafor), an orally bioavailable CXCR4 antagonist, demonstrated clinically meaningful increases in absolute neutrophil and lymphocyte counts and concomitant reduction in infections in patients with WHIM syndrome, resulting in its recent U.S. Food and Drug Administration approval. The impact of CXCR4 antagonism on other aspects of the pathobiology in WHIM syndrome, such as lymphopoiesis and leukocyte trafficking between primary and secondary lymphoid organs, is less understood.

Methods

In the current study, the effects of CXCR4 antagonism on leukocyte trafficking and distribution in primary and secondary lymphoid organs were investigated in a mouse model of WHIM syndrome carrying the heterozygous Cxcr41013 mutation. Cxcr4+/1013 and Cxcr4 wild-type mice received the orally bioavailable CXCR4 antagonist X4-185. Blood, spleen and bone marrow samples were collected for numeration, flow cytometry, and functional studies.

Results

Cxcr4+/1013 mice exhibited profound peripheral blood leukopenia as seen in patients with WHIM syndrome. CXCR4 antagonism corrected circulating leukopenia and mobilized functional neutrophils without disrupting granulopoiesis in the bone marrow of Cxcr4+/1013 mice. Furthermore, Cxcr4+/1013 displayed aberrant splenic T and B-cell counts and frequency. Treatment with X4-185 normalized splenic T-cell abnormalities, correcting the reduced CD8+ T-cell numbers, restoring the CD4/CD8 T-cell ratio, and ameliorating peripheral blood T-cell lymphopenia. In addition, CXCR4 antagonism was able to correct the abnormal frequencies and numbers of splenic marginal zone and follicular B cells in Cxcr4+/1013 mice, and ultimately normalize B-cell lymphopenia in the peripheral circulation.

Conclusions

Our study provides comprehensive evidence that oral dosing with a CXCR4 antagonist can effectively correct WHIM-associated neutrophil and lymphocyte abnormalities in a mouse model of WHIM syndrome. These findings extend our understanding of how targeting the dysregulated CXCR4 signaling pathway can ameliorate the pathogenesis of WHIM syndrome.

CXCR4 signaling determines the fate of hematopoietic multipotent progenitors by stimulating mTOR activity and mitochondrial metabolism

Both cell-intrinsic and niche-derived, cell-extrinsic cues drive the specification of hematopoietic multipotent progenitors (MPPs) in the bone marrow, which comprise multipotent MPP1 cells and lineage-restricted MPP2, MPP3, and MPP4 subsets. Patients with WHIM syndrome, a rare congenital immunodeficiency caused by mutations that prevent desensitization of the chemokine receptor CXCR4, have an excess of myeloid cells in the bone marrow. Here, we investigated the effects of increased CXCR4 signaling on the localization and fate of MPPs. Knock-in mice bearing a WHIM syndrome-associated CXCR4 mutation (CXCR41013) phenocopied the myeloid skewing of bone marrow in patients. Whereas MPP4 cells in wild-type mice differentiated into lymphoid cells, MPP4s in CXCR41013 knock-in mice differentiated into myeloid cells. This myeloid rewiring of MPP4s in CXCR41013 knock-in mice was associated with enhanced signaling mediated by the kinase mTOR and increased oxidative phosphorylation (OXPHOS). MPP4s also localized further from arterioles in the bone marrow of knock-in mice compared with wild-type mice, suggesting that the loss of extrinsic cues from the perivascular niche may also contribute to their myeloid skewing. Chronic treatment with the CXCR4 antagonist AMD3100 or the mTOR inhibitor rapamycin restored the lymphoid potential of MPP4s in knock-in mice. Thus, CXCR4 desensitization drives the lymphoid potential of MPP4 cells by dampening the mTOR-dependent metabolic changes that promote myeloid differentiation.

The complex nature of CXCR4 mutations in WHIM syndrome

Heterozygous autosomal dominant mutations in the CXCR4 gene cause WHIM syndrome, a severe combined immunodeficiency disorder. The mutations primarily affect the C-terminal region of the CXCR4 chemokine receptor, specifically several potential phosphorylation sites critical for agonist (CXCL12)-mediated receptor internalization and desensitization. Mutant receptors have a prolonged residence time on the cell surface, leading to hyperactive signaling that is responsible for some of the symptoms of WHIM syndrome. Recent studies have shown that the situation is more complex than originally thought, as mutant WHIM receptors and CXCR4 exhibit different dynamics at the cell membrane, which also influences their respective cellular functions. This review examines the functional mechanisms of CXCR4 and the impact of WHIM mutations in both physiological and pathological conditions.

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.