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Letters to the Editor
functions.9 In contrast, efficacy of the CXCL8-induced chemotaxis for P1-derived neutrophils was drastically reduced (up to 86%) for all tested CXCL8 concentrations. For P3-derived neutrophils, this response was more weakly lowered (up to 59%) indicating that the Arg212Trp CXCR2 mutation only partially abrogates CXCR2 function. This was further confirmed by the SB265610-mediated inhibition of the remaining Arg212Trp CXCR2-driven chemotaxis (Figure 1C). P3- derived neutrophils expressed similar levels of CXCR2 than control neutrophils (Figure 1B) and their remaining chemotactic responses toward CXCL8 were out of the range of the ones provided by control neutrophils (Online Supplementary Figure S3A), further supporting the CXCR2 loss-of-function phenotype. We extrapolated that this loss-of-function phenotype would be similarly conferred by P2’s and P4’s CXCR2 missense mutations, affecting the protein’s critical DRY domain7 or N-terminal domain,8 respectively. CXCR1 could account for the remaining migration of P1’s neutrophils, which were not affected by the inhibitor SB265610.10 Indeed, although CXCR1 and CXCR2 have closely linked actions, they dif- fer notably in their signaling properties and chemokine- ligand spectra, with CXCR1 being engaged by CXCL5 and CXCL6 and having high affinity for CXCL8, while CXCR2 promiscuously binds to all seven CXCL8-family chemokines.11 CXCR1 expression levels on P1 and con- trol neutrophils were within the same range (Online Supplementary Figure S3B), thereby substantiating that hypothesis.
The patients described herein did not experience severe recurrent bacterial infections, suggesting that although CXCR2 actively participated in neutrophil recruitment into inflammatory tissues, this function was largely counterbalanced. Indeed, patients’ neutrophils remained responsive to N-formylmethionine-leucyl- phenylalanine (fMLP) (Online Supplementary Figure S3C), indicating that they might be efficiently guided to inflam- matory sites by chemoattractant signals, such as fMLP and possibly others including the C5a complement fac- tor, both abundantly generated in foci of bacterial infec- tion.12 Likewise, CXCL12-driven migration was equiva- lent for CD3+CD4+ cells (Online Supplementary Figure S3D) and the other lymphocyte subpopulations (data not shown) from P1 and P3, their parents and controls. These findings support the postulate of normal CXCR4 function in patients harboring CXCR2 mutations acting as drivers of congenital neutropenias although it remains to be experimentally demonstrated.
Different clinical manifestations distinguish these four patients with CXCR2 mutations from the clinical spec- trum of the 14 WHIM syndrome cases enrolled in the French Severe Chronic Neutropenia Registry, as summa- rized in Table 2. Myelokathexis, a pathognomonic fea- ture of WHIM syndrome,6 was solely detected in P1, har- boring the CXCR2 gene deletion, thereby extending the description of the two previously reported cases with CXCR2 loss-of-function mutations.5 Its absence in the clinical pictures of P2, P3 and P4, together with the par- tial CXCR2-chemotaxis response retained by Arg212Trp, further suggests that their chronic neutropenia is not the only consequence of a CXCR2-dependent mobilization defect; neutrophil homeostasis also seems to be affected. That hypothesis is supported by the reported association of rare heterozygous CXCR2 missense variants, including the one carried by P4, with low white blood-cell counts.4
Elucidating the mechanisms underlying the relation- ship between the biallelic CXCR2 mutations identified herein and neutropenia will require the development of
relevant experimental models. Alternative models to mice should be considered, in light of the lack of a murine CXCL8 homologue and the neutrophilia of mice lacking Cxcr2.13,14 However, targeted Cxcr2 invalidation in mouse neutrophils led to their retention in bone marrow, repro- ducing a myelokathexis phenotype,4 thereby suggesting a role for Cxcr2 in the regulation of neutrophil biology and, intrinsically, in neutrophil trafficking. In contrast to patients with WHIM syndrome, who suffer from chronic lymphopenia, often associated with hypogammaglobu- linemia,6,15 patients with CXCR2 mutations experienced only transient episodes of lymphopenia and had elevated levels of immunoglobulins, mostly IgG and IgA (Table 2). B-lymphocyte counts were normal, unlike those in mice with invalidated Cxcr2, which exhibited B-cell expansion,13 highlighting the limitation of mice to model CXCR2 deficiency. No papilloma virus-induced warts, neoplasia or syndromic features, such as tetralogy of Fallot, observed in WHIM syndrome15 were noted during the follow-up of the patients. However, we could not exclude incomplete penetrance of these phenotypes, as reported in WHIM syndrome.6,15
In conclusion, CXCR2 deficiency seems to be a distinct molecular entity associated with congenital neutropenia with clinical severity and pathogenic mechanisms dis- tinct from those of WHIM syndrome, thereby highlight- ing the importance of determining CXCR2 mutational status in patients with chronic neutropenia.
Viviana Marin-Esteban,1 Jenny Youn,2 Blandine Beaupain,3,4 Agnieszka Jaracz-Ros,1 Vincent Barlogis,5 Odile Fenneteau,6 Thierry Leblanc,7 Florence Bellanger,8 Philippe Pellet,8 Julien Buratti,8 Hélène Lapillonne,9 Françoise Bachelerie,1 Jean Donadieu2,3,4 and Christine Bellanné-Chantelot4,8,10
1Université Paris-Saclay, Inserm UMR996, Inflammation,
Microbiome and Immunosurveillance, Clamart; 2Sorbonne Université,
Service d’Hémato-oncologie Pédiatrique, Assistance Publique–Hopitaux
de Paris (AP-HP), Hôpital Trousseau, Paris; 3Registre Français des
Neutropénies Congénitales, Hôpital Trousseau, Paris; 4Centre de
Référence des Neutropénies Chroniques, AP-HP, Hôpital Trousseau,
5
Paris; CHU Marseille, Hôpital La Timone, Service d’Hémato-oncolo-
gie Pédiatrique, Assistance Publique–Hôpitaux de Marseille, Marseille; 6AP-HP, Laboratoire d’Hématologie, Hôpital Robert-Debré, Paris; 7AP- HP, Hôpital Robert-Debré, Service d’Hématologie Pédiatrique, Paris; 8Sorbonne Université, Département de Génétique Médicale, AP-HP, Hôpital Pitié–Salpêtrière, Paris; 9Sorbonne Université, CRSA–Unité INSERM, AP-HP, Hôpital Trousseau, Paris and 10Inserm U1287, Villejuif, France
Correspondence:
CHRISTINE BELLANNÉ-CHANTELOT christine.bellanne-chantelot@aphp.fr
VIVIANA MARIN-ESTEBAN viviana.marin-esteban@universite-paris-saclay.fr
doi:10.3324/haematol.2021.279254 Received: May 20, 2021.
Accepted: November 25, 2021. Pre-published: December 2, 2021. Disclosures: no conflicts of interest to disclose.
Contributions: VM-E, FB, JD and CB-C designed the study. VM- E collected and interpreted functional data. JY analyzed clinical data. BB collected biological and clinical data. AJ-R performed chemotaxis assays. VB and TL provided samples and clinical data. OF performed and reviewed bone marrow examinations. FB and PP performed molecular experiments and exome sequencing. JB performed exome annotation. HL performed cytological analysis. JD analyzed clinical data and performed the statistical analysis. CB-C analyzed exome
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haematologica | 2022; 107(3)