commentary

PHAGOCYTES, GRANULOCYTES, AND MYELOPOIESIS needed for spreading, polarization, and mechanotactic migration under flow Comment on Salvermoser et al, page 1887 conditions as well as chemotactic mi- gration in two-dimensional (2D) environ- ments. The latter results are in agreement Myo1f is critical for with in vivo findings showing that leukocyte rolling flux fraction, rolling velocity, and the neutrophil migration in vivo number of adherent leukocytes in TNF- Downloaded from http://ashpublications.org/blood/article-pdf/131/17/1879/1406302/blood837872.pdf by guest on 30 July 2021 stimulated cremaster muscle venules was Mauro M. Teixeira | Universidade Federal de Minas Gerais 2 2 similar in wild-type and Myo1f / mice. In this issue of Blood, Salvermoser et al demonstrate that the unconventional Therefore, the observed effects on ex- class I 1f (Myo1f) is crucial for neutrophil trafficking during acute travasation were likely not because of al- tered interactions with endothelial cells in inflammation in vascular beds in vivo. Importantly, they demonstrate that vitro under conditions of flow or in vivo. Myo1f is crucial for the dynamics of the deformation of the neutrophil nucleus This is in contrast with enhanced adhe- and consequent capacity of these cells to extravasate in vivo and to negotiate siveness to adhesion molecules under through three-dimensional (3D) environments.1 static conditions. Two major messages derive from these findings: (1) increased Neutrophils are polymorphonuclear leuko- chemoattractant molecules, adhesion adhesiveness observed under static con- cytes known to play a crucial role in acute molecules, and intracellular pathways ditions was not responsible for the ex- infection. Indeed, in neutropenic individuals necessary for neutrophil recruitment. travasation defect; and (2) static assays, or in conditions in which neutrophil migra- although useful to study certain charac- tion to tissue is deficient, there is significant Salvermoser and colleagues show that teristics of neutrophil behavior, may fail risk of death because of bacterial and fungal in mice deficient for the Myo1f to mimic the rich interactions that occur 2 2 infections. To deal with invading microor- (Myo1f / mice), neutrophil migration in vivo. ganisms, neutrophils circulating in blood after induction of acute inflammation is need to interact with endothelial cells, trans- decreased in multiple vascular beds, in- Subsequent experiments showed that, in migrate into the relevant tissue, and cluding the cremaster muscle, the peri- contrast to the lack of observed effects negotiate their way into the site of infection. toneal cavity, and the lungs. This study in the 2D environment, Myo1f was crucial Much is known about the processes and confirms findings of Kim and colleagues,3 for neutrophil transmigration through molecular interactions needed for neutro- who showed decreased neutrophil re- physical barriers and in a 3D environ- phil recruitment and accumulation in tis- cruitment and defects in host defense ment. Significantly, the authors show un- sues, which have been reviewed elsewhere.2 in Myo1f2/2 mice. However, the study by equivocally that Myo1f was required for Significant knowledge in the field has been Salvermoser et al advances the field migration in 3D environments to enable gained by using in vitro models that try to significantly by providing detailed infor- the squeezing of the nucleus through mimic the complex process of neutrophil mation on the phenotype and suggesting narrow spaces (see figure). Migration of extravasation in vivo. In this regard, static a potential mechanism for the defect. The human neutrophils in a restrictive barrier of and usual chemotaxis assays have been authors show in the paper and accom- a meshwork of collagen fibers is initiated instrumental in the characterization of panying illustrations that Myo1f was not by the formation of a small nuclear lobe

Myo1f +/+ Myo1f -/- Flow chamber Filter with pores

Collagen gel

Under physiological flow conditions (1 dyne/cm2), murine neutrophils attach to membranes coated with recombinant murine ICAM-1 (rmICAM-1) and rmP-selectin and successfully transmigrate through pores into collagen gel containing a chemoattractant molecule. In contrast, Myo1f-deficient neutrophils are mostly unable to transmigrate, and the majority of neutrophils are found within the flow chamber or stuck within the pores. This figure provides a robust demonstration of the need for Myo1f for neutrophils to migrate through 3D environments in vitro and an explanation for the failure of Myo1f-deficient neutrophils to accumulate into sites of inflammation in vivo. See the complete Figure 3 in the article by Salvermoser et al that begins on page 1887.

blood® 26 APRIL 2018 | VOLUME 131, NUMBER 17 1879 preparing the deformation of the nucleus. are thought to contribute to their mi- 3. Kim SV, Mehal WZ, Dong X, et al. Modulation of This step is followed by further deformation gration into the lung parenchyma and cell adhesion and motility in the immune system by Myo1f. Science. 2006;314(5796):136-139. and elongation of the nucleus and, once airway spaces.9 It will be very interesting migration is completed, the nucleus is to evaluate the relevance of Myo1f in this 4. Barzilai S, Yadav SK, Morrell S, et al. Leukocytes refolded into a roundish, multilobular context, as activation and retention of breach endothelial barriers by insertion of nu- clear lobes and disassembly of endothelial 4 shape. Nuclear deformation has been neutrophils within capillaries may con- filaments. Cell Reports. 2017;18(3):685-699. shown to be required for neutrophil mi- tribute to lung injury and the systemic gration within tissues with pore cross inflammatory response syndrome second- 5. Wolf K, Te Lindert M, Krause M, et al. Physical limits of cell migration: control by ECM space 5 sections of 2 to 20 mm. This process was ary to sepsis. Clearly, Myo1f may contribute and nuclear deformation and tuning by pro- significantly impaired in Myo1f-deficient not only to the beneficial role of neu- teolysis and traction force. J Cell Biol. 2013; murine neutrophils or HL-60 cells stably trophils to fight infection, but also to the 201(7):1069-1084. expressing EGFP-Myo1f. Altogether, role these cells play in acute and chronic 6. Sokac AM, Bement WM. Regulation and ex- these studies suggest that defective inflammatory diseases not caused by pression of metazoan unconventional . nucleus deformation was the reason for infection. Int Rev Cytol. 2000;200:197-304. impaired 3D migration and accumula- 7. Fruleux A, Hawkins RJ. Physical role for the tion in vivo in the genetic absence of Conflict-of-interest disclosure: The author nucleus in cell migration. J Phys Condens

Matter. 2016;28(36):363002. Downloaded from http://ashpublications.org/blood/article-pdf/131/17/1879/1406302/blood837872.pdf by guest on 30 July 2021 Myo1f. declares no competing financial interests. n 8. Worthen GS, Schwab B III, Elson EL, Downey Class I myosins are widely expressed GP. Mechanics of stimulated neutrophils: REFERENCES cell stiffening induces retention in capillaries. members of the myosin superfamily that 1. Salvermoser M, Pick R, Weckbach LT, et al. Science. 1989;245(4914):183-186. bind to actin filaments and hydrolyze Myosin 1f is specifically required for neutrophil migration in 3D environments during acute 9. Doerschuk CM. Mechanisms of leukocyte se- adenosine triphosphate to produce me- fl 6 inflammation. Blood. 2018;131(17):1887-1898. questration in in amed lungs. Microcirculation. chanical force. These bind to 2001;8(2):71-88. membranes by their basic tail homology 2. Kolaczkowska E, Kubes P. Neutrophil 1 (TH-1) domains and may be important recruitment and function in health and inflammation. Nat Rev Immunol. 2013; DOI 10.1182/blood-2018-03-837872 for membrane-associated functions, such 13(3):159-175. © 2018 by The American Society of Hematology as endocytosis, cell signaling, and cell motility. Myo1f was found to be mainly 3 expressed in neutrophils. Although the CLINICAL TRIALS AND OBSERVATIONS neutrophil nucleus may be quite mal- leable, the nucleus- con- Comment on O’Brien et al, page 1910 nection is essential for 3D migration by transmitting force from the cytoskeleton to the inside of the nucleus.7 An in- Ibrutinib: coming of age? teresting possibility raised from the Jennifer R. Brown | Dana-Farber Cancer Institute; Harvard Medical School studies of Salvermoser and colleagues is that Myo1f may link the cytoskeleton In this issue of Blood,O’Brien et al report long-term efficacy and safety of to the nuclear envelope via its TH1 ibrutinib in the first cohort of patients with chronic lymphocytic leukemia (CLL) domain to provide a high malleability of treated, now with 5-year follow-up, the longest of any CLL cohort to date.1 the neutrophil nucleus. This possibility clearly deserves further investigation. Ibrutinib has come into widespread use have a distribution similar to that of the since its initial US Food and Drug Ad- classic survival curves of Dohner¨ et al4 Lipopolysaccharide-induced neutrophil ministration approval for relapsed CLL (see figure panel A), with del(17p) remaining extravasation into the lung interstitium 4 years ago, based on the early results of highest risk, with a median PFS of 26 months. and in the bronchoalveolar space was 2 2 2 this same study. Although many other Complex karyotype has emerged as a pre- significantly impaired in Myo1f / mice studies have confirmed the high efficacy 5 as compared with Myo1f1/1 mice. In dictor of shortened PFS in ibrutinib studies, of ibrutinib in CLL, follow-up has remained contrast, there was increased neutrophil and in this study, it was associated with a quite short. Thus, many questions about fi accumulation within capillaries of the 31-month PFS, driven signi cantly by co- 2 2 fi lungs of Myo1f / mice. Interestingly, it durability and predictors of response, as well occurrencewithdel(17p)(see gure panel B). has been shown that various mediators as long-term tolerability, have remained The extent to which the adverse prognosis of of inflammation can cause neutrophil se- unanswered. In this study of high-risk pa- complex karyotype is driven by its associa- questration in the lungs and other capil- tients with relapsed/refractory disease, the tion with del(17p) remains unknown, but laries during acute inflammation by median progression-free survival (PFS) was clearly, this needs to be investigated pro- increasing the stiffness of the neutrophils. reached at a strikingly good 51 months, spectively in future ibrutinib studies. Stimulated neutrophils (diameter, 8 mm) which compares favorably to that achieved are retained in pulmonary capillaries with older regimens in a comparable patient Overall, these findings seem aligned with (5.5 mm) as a result of a decreased ability population.3 The median treatment dura- the recently reported 59% 3-year PFS of the cell to deform within the capillary tion for the relapsed/refractory cohort was achieved with ibrutinib in the confirmatory in response to the hydrodynamic forces 39 months, with 33% discontinuing for RESONATE trial,6 which randomly assigned of the bloodstream.8 Increased neutro- disease progression. Interestingly, the patients with relapsed CLL to ibrutinib or phil stiffness and retention in the lungs PFS curves by cytogenetic abnormality ofatumumab. In the study by O’Brien et al,

1880 blood® 26 APRIL 2018 | VOLUME 131, NUMBER 17