The production of HbS — an abnormal hemoglobin (Hb) — in sickle cell disease (SCD) results in poorly deformable red blood cells (RBCs) that are prone to microcapillary occlusion, causing tissue ischemia and organ damage. Novel treatments, including gene therapy, may reduce SCD morbidity, but methods to functionally evaluate RBCs remain limited. Previously, we presented the microfluidic impedance red cell assay (MIRCA) for rapid assessment of RBC deformability, employing electrical impedance-based readout to measure RBC occlusion of progressively narrowing micropillar openings. We describe herein the design, development, validation, and clinical utility of the next-generation MIRCA assay, featuring enhanced portability, rapidity, and usability. It incorporates a miniaturized impedance analyzer and features a simplified wash-free operation that yields an occlusion index (OI) within 15 min as a new metric for RBC occlusion. We show a correlation between OI and percent fetal hemoglobin (%HbF), other laboratory biomarkers of RBC hemolysis, and SCD severity. To demonstrate the assay’s versatility, we tested RBC samples from treatment-naïve SCD patients in Uganda that yielded OI levels similar to those from hydroxyurea (HU)-treated patients in the U.S., highlighting the role of %HbF in protecting against microcapillary occlusion independent of other pharmacological effects. The MIRCA assay could also identify a subset of HU-treated patients with high occlusion risks, suggesting that they may require treatment adjustments including a second-line therapy to improve their outcomes. This work demonstrates the potential of the MIRCA assay for accelerated evaluation of RBC health, function, and therapeutic effect in an ex vivo model of the microcapillary networks.

We present a rapid hemoglobin-oxygen dissociation measurement approach to screen for and detect hemoglobin-oxygen affinity abnormalities and to evaluate the function and efficacy of hemoglobin modifying therapies within minutes.

Could the phenomenon of catch bonding-force-strengthened cellular adhesion-play a role in sickle cell disease, where abnormal red blood cell (RBC) adhesion obstructs blood flow? Here, we investigate the dynamics of sickle RBCs adhering to a surface functionalized with the protein laminin (a component of the extracellular matrix around blood vessels) under physiologically relevant microscale flow. First, using total internal reflectance microscopy we characterize the spatial fluctuations of the RBC membrane above the laminin surface before detachment. The complex dynamics we observe suggest the possibility of catch bonding, where the mean detachment time of the cell from the surface initially increases to a maximum and then decreases as a function of shear force. We next conduct a series of shear-induced detachment experiments on blood samples from 25 sickle cell disease patients, quantifying the number and duration of adhered cells under both sudden force jumps and linear force ramps. The experiments reveal that a subset of patients does indeed exhibit catch bonding. By fitting the data to a theoretical model of the bond dynamics, we can extract the mean bond lifetime versus force for each patient. The results show a striking heterogeneity among patients, both in terms of the qualitative behavior (whether or not there is catch bonding) and in the magnitudes of the lifetimes. Patients with large bond lifetimes at physiological forces are more likely to have certain adverse clinical features, like a diagnosis of pulmonary arterial hypertension and intracardiac shunts. By introducing an in vitro platform for fully characterizing RBC-laminin adhesion dynamics, our approach could contribute to the development of patient-specific antiadhesive therapies for sickle cell disease. The experimental setup is also easily generalizable to studying adhesion dynamics in other cell types, for example, leukocytes or cancer cells, and can incorporate disease-relevant environmental conditions like oxygen deprivation.

Endothelial activation and sickle red blood cell (RBC) adhesion are central to the pathogenesis of sickle cell disease (SCD). Quantitatively, RBC-derived extracellular vesicles (REVs) are more abundant from SS RBCs compared with healthy RBCs (AA RBCs). Sickle RBC-derived REVs (SS REVs) are known to promote endothelial cell (EC) activation through cell signalling and transcriptional regulation at longer terms. However, the SS REV-mediated short-term non-transcriptional response of EC is unclear. Here, we examined the impact of SS REVs on acute microvascular EC activation and RBC adhesion at 2 h. Compared with AA REVs, SS REVs promoted human pulmonary microvascular ECs (HPMEC) activation indicated by increased von Willebrand factor (VWF) expression. Under microfluidic conditions, we found abnormal SS RBC adhesion to HPMECs exposed to SS REVs. This enhanced SS RBC adhesion was reduced by haeme binding protein haemopexin or VWF cleaving protease ADAMTS13 to a level similar to HPMECs treated with AA REVs. Consistent with these observations, haemin- or SS REV-induced microvascular stasis in SS mice with implanted dorsal skin-fold chambers that was inhibited by ADAMTS13. The adhesion induced by SS REVs was variable and was higher with SS RBCs from patients with increased markers of haemolysis (lactate dehydrogenase and reticulocyte count) or a concomitant clinical diagnosis of deep vein thrombosis. Our results emphasise the critical contribution made by REVs to the pathophysiology of SCD by triggering acute microvascular EC activation and abnormal RBC adhesion. These findings may help to better understand acute pathophysiological mechanism of SCD and thereby the development of new treatment strategies using VWF as a potential target.

A microfluidic assay integrated with capillary network-inspired microcapillary arrays and endothelial-associated protein functionalization enables concurrent assessment of red blood cell adhesion and microcapillary occlusion.

Abnormal erythrocyte adhesion owing to polymerization of sickle hemoglobin is central to the pathophysiology of sickle cell disease (SCD). Mature erythrocytes constitute >80% of all erythrocytes in SCD; however, the relative contributions of erythrocytes to acute and chronic vasculopathy in SCD are not well understood. Here, we showed that bending stress exerted on the erythrocyte plasma membrane by polymerization of sickle hemoglobin under hypoxia, enhances sulfatide-mediated abnormal mature erythrocyte adhesion. We hypothesized that sphingomyelinase (SMase) activity, which is upregulated by accumulated bending energy, leads to elevated membrane sulfatide availability, and thus, hypoxic mature erythrocyte adhesion. We found that mature erythrocyte adhesion to laminin in controlled microfluidic experiments is significantly greater under hypoxia than under normoxia (1856 ± 481 vs 78 ± 23, mean ± SEM), whereas sickle reticulocyte (early erythrocyte) adhesion, high to begin with, does not change (1281 ± 299 vs 1258 ± 328, mean ± SEM). We showed that greater mean accumulated bending energy of adhered mature erythrocytes was associated with higher acid SMase activity and increased mature erythrocyte adhesion (P = .022, for acid SMase activity and P = .002 for the increase in mature erythrocyte adhesion with hypoxia, N = 5). In addition, hypoxia results in sulfatide exposure of the erythrocyte membrane, and an increase in SMase, whereas anti-sulfatide inhibits enhanced adhesion of erythrocytes. These results suggest that the lipid components of the plasma membrane contribute to SCD complications. Therefore, sulfatide and the components of its upregulation pathway, particularly SMase, should be further explored as potential therapeutic targets for inhibiting sickle erythrocyte adhesion.

Background: In 2019 FDA approved the use of an antibody anti P-selectin (Crizanlizumab) for the treatment of sickle cell disease (SCD) to reduce the vaso occlusive crisis (VOCs). New anti-adhesive treatments are being developed recently. Global Blood Therapeutics, Inc., acquired by Pfizer Inc. in October 2022, acquired Inclacumab from Roche and started two clinical trials now in phase 3 to evaluate the capacity of this humanized IgG4 monoclonal antibody anti P-selectin to reduce the VOCs in patients with SCD. In our recent work presented at EHA 23 in Frankfurt Germany, we showed that Inclacumab prevents the adhesion of RBCs to chronically and acutely heme activated human umbilical vein endothelial cells (HUVECs) with a statistically significant higher effect in comparison to Crizanlizumab. In this work we used a similar approach to test the capacity of Inclacumab in the reduction of preexisting adhesion events on acutely heme activated HUVECs. Methods:Whole blood EDTA samples from six SCD subjects all with HbSS genotypes were collected at University Hospital Cleveland Medical Center, Cleveland, OH, USA. To standardize the samples, we isolated RBCs by centrifugation and subsequential washes in Phospahte buffer s of the whole blood and resuspended in basal cell culture medium (EBM; Lonza, Morristown, NJ, USA) at a hematocrit of 20% with 10 mM of HEPES. HUVECs (Lonza, Morristown, NJ, USA) were introduced and maintained within the endothelialized microfluidic channels at physiological flow for at least 48-72 hours prior to experiments. We performed an acute short-term activation, where the blood samples were supplemented with 40 µM heme +/- 100 µg/ml injected through the microfluidic channels for 15 minutes, after the adhesion took place we washed the non-adherent cells with Inclacumab and Crizanlizumab and we compared with untreated washing buffer (both compounds were provided by Global Blood Therapeutics, Inc., a wholly owned subsidiary of Pfizer Inc. South San Francisco, CA, USA) A phase-contrast images of the remaining RBCs were acquired with an inverted microscope (DMi8 Leica Microsystems Inc. Deerfield, IL, USA) and quantified based on previous published methods (Figure 1A). Paired t-test was used to calculate statistical significance. Results: Acute short-term heme activation induces high level of RBCs adhesion. Both compounds Inclacumab and Crizanlizumab showed a reduction of the number of adherent RBCs to the activated heme, but only Inclacumab results statistically a significant higher reduction compared to untreated RBCs (Figure 1B). Conclusions: Inclacumab is able not only to prevent the adhesion of RBCs to acutely and chronically activated HUVECs but is able to remove the preexisting adhesion and results in significant higher reduction compared to untreated. RBCs adhesion assay on Endothelium-on-a-chip is a novel and efficient way to study the efficacy of the new antiadhesive drug and could be used to monitor patient response to new therapies in SCD. Figure1 : Effect of Inclacumab vs Crizanlizumab on removal of SCD RBC adhesion to heme activated HUVECs. A) Schematic of adhesion experiment and inverted microscope contrast of phase images 10X of adherent RBCs at acutely heme activated HUVECs. B) Inclacumab has statistically significant effect on remove adherent RBCs to acutely heme activated HUVECs (p=0.009, N=7) For all experiments, the heme concentrations were 40 µM and Inclacumab and Crizanlizumab were 100 µg/ml. Scale bare 20 µm. P-values were based on paired t-test. Error bars represent the standard error of the mean (SEM)

Single cells have unique biophysical signatures that can rapidly change during various disease states. For instance, cellular density is an inherent property differing between cell types. Characterizing changes in fundamental density properties down to the single-cell level can reveal sub-populations in pathological states. Here, we have developed a microfluidic, magnetic levitation-based assay (MagDense) that detects minute density differences of individual red blood cells (RBCs) down to 0.0001 g mL-1 resolution. This assay fractionates RBCs based on their density profiles in a non-ionic paramagnetic medium flowing in a capillary microchannel placed between magnets with same poles facing each other. Based on precisely measured levitation height and density of individual RBCs at their specific equilibrium state, we demonstrated that MagDense can accurately analyze the density of sickle hemoglobin (HbS)-containing RBCs and normal hemoglobin (HbA)-containing RBCs. In addition, the precise density and cell size measurements at the single cell level showed three different sub-populations of RBCs in blood samples from individuals with homozygous sickle cell disease receiving blood transfusions; where less dense, HbA-containing RBCs levitated higher, while the denser, HbS-containing RBCs levitated lower. We compared the mean RBC densities of sickle cell disease subjects with healthy controls and found distinctly separated bands of RBC density for each group denoting the likely range of cell densities seen in the blood samples. The high resolution of our method enabled measurement of deviation from the mean RBC density. Moreover, we introduced a new term as a measure of density dispersion, "RBC levitational density width, RLDW". Mean RBC density in sickle cell disease associated with hemoglobin from complete blood count (p = 0.032, linear regression) and RLDW associated with absolute reticulocyte count (ARC) and RBC distribution width (RDW) from complete blood count (p = 0.002 for ARC and p = 003 for RDW, linear regression). Our magnetic levitation-based assay enables rapid, accurate, density-based imaging, profiling and label-free monitoring of single RBCs. Our approach can be broadly applicable to investigate blood cell disorders and the effects of emerging pharmacological and curative therapies in patient outcomes.

Neutrophil recruitment to the inflamed endothelium is a multistep process and is of utmost importance in the development of the hallmark vaso-occlusive crisis in sickle cell disease (SCD). However, there lacks a standardized, clinically feasible approach for assessing neutrophil recruitment to the inflamed endothelium for individualized risk stratification and therapeutic response prediction in SCD. Here, we describe a microfluidic device functionalized with E-selectin, a critical endothelial receptor for the neutrophil recruitment process, as a strategy to assess neutrophil binding under physiologic flow in normoxia and clinically relevant hypoxia in SCD. We show that hypoxia significantly enhances neutrophil binding to E-selectin and promotes the formation of neutrophil-platelet aggregates. Moreover, we identified two distinct patient populations: a more severe clinical phenotype with elevated lactate dehydrogenase levels and absolute reticulocyte counts but lowered fetal hemoglobin levels associated with constitutively less neutrophil binding to E-selectin. Mechanistically, we demonstrate that the extent of neutrophil activation correlates with membrane L-selectin shedding, resulting in the loss of ligand interaction sites with E-selectin. We also show that inhibition of E-selectin significantly reduces leukocyte recruitment to activated endothelial cells. Our findings add mechanistic insight into neutrophil-endothelial interactions under hypoxia and provide a clinically feasible means for assessing neutrophil binding to E-selectin using clinical whole blood samples, which can help guide therapeutic decisions for SCD patients.

Introduction: Sickle cell disease (SCD) is characterized by the polymerization of hemoglobin S (HbS) that results in sickle red blood cell (sRBC) formation under deoxygenation. Subsequent alterations in the rheological properties of sRBC lead to abnormal deformability, adhesion, and ultimately vasculopathy. Vascular occlusion leads to repeated cycles of organ ischemia and pain. Voxelotor (Oxbryta, Global Blood Therapeutics, South San Francisco, CA, USA) is an FDA-approved medication that reversibly binds to sickle hemoglobin in a dose-dependent fashion to increase its oxygen affinity and reduce sickling and polymerization. Previous studies using voxelotor under hypoxic conditions have shown an improvement in blood flow (Azul & Wood, 2020) and sRBC deformability (Dufu et al., 2018). As previously published, endothelialized microfluidic devices have been used to quantify sRBC adhesion (Kucukal et al., 2021). This experimental study is the first in-vitro assessment of the effect of voxelotor on adhesion under normoxic conditions using an endothelialized microfluidic system. Methods: Human umbilical vein endothelial cells (HUVECs, Lonza, Morristown, USA) were cultured within a microfluidic system for at least 72 hours prior to experiments. HUVECs underwent four-hour activation with tumor necrosis factor alpha (TNFα) at a concentration of 20ng/mL. Under an IRB-approved study, whole blood samples from 12 patients with HbSS SCD were collected in EDTA tubes and red blood cells were isolated via centrifugation. RBCs were then resuspended in basal media (Lonza) with HEPES for pH-adjustment and treated with and without voxelotor (Selleckchem, Radnor, PA, USA) to a final hematocrit of 20% and concentration of 600μM. After one-hour in the incu-shaker, the samples were injected through the activated channels under normoxia at a rate of 2μL/min. Non-adherent cells were then removed by flushing the channels with additional media with HEPES. Adhered cells were counted via Adobe Photoshop Software. Statistical significance was calculated via paired t-test. Results: RBC adhesion ranged between 580 and 15,492 cells in untreated, activated samples and between 516 and 14,216 cells in voxelotor-treated, activated samples (Figure 1). Voxelotor treatment resulted in decreased sRBC adhesion in all but two of twelve samples and the percentage of adhesion reduction ranged between 7 and 70 percent (Figure 2, p=0.2). No conclusions were made when comparing patient's laboratory values (white blood cell, hemoglobin, platelets, absolute neutrophil count, absolute reticulocyte count, lactate dehydrogenase) to percent of adhesion reduction. Conclusion: Our results show that voxelotor does result in adhesion reduction under normoxia although, overall, the drug did not significantly decrease RBC adhesion. We theorize that by improving oxygen affinity and decreasing polymerization, voxelotor may limit the downstream effects of polymerization, specifically adhesion and vaso-occlusion. One major limitation is that RBCs were not deoxygenated and as mentioned above, voxelotor has improved RBC rheology under hypoxia. Therefore, future experiments will assess the effect of voxelotor on adhesion under hypoxic conditions. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Introduction: The sickle mutation of hemoglobin (HbS) afflicts millions of people worldwide and is characterized by hemolytic anemia, inflammation, painful vaso-occlusive crises, significant morbidity, and early mortality. In sickle cell disease (SCD), HbS polymerization under deoxygenation increases red blood cell (RBC) rigidity, adhesivity and susceptibility to lysis. Products of intravascular hemolysis including heme and RBC-released extracellular vesicles (REVs) promote acute and chronic inflammation triggering endothelial activation and abnormal RBC adhesion. Extracellular vesicles (EVs) are nano- or micro-particles composed of a lipid bilayer, comprised of transmembrane proteins, and enclosing intracellular remnants, including cytosolic proteins and miRNAs. EVs are known to exchange biomaterial between cells, and may serve as surrogate markers for the activated state of the parent cell thus are of high clinical significance. Quantitatively, REVs are more abundant from sickle RBCs (SS RBCs) compared with normal HbA-containing RBCs (AA RBCs). SS REVs are known to promote endothelial cell (EC) activation through cell signaling and transcriptional regulation at longer terms. However, the SS REV-mediated short term non transcriptional response of EC is unclear. Methods: Here, we have developed the SCD-EV-BioChip using microfluidic technology. SCD-EV-BioChip assesses RBC adhesion as a biomarker for REV-mediated human pulmonary microvascular endothelial cells (HPMECs) dysfunction using functional biomarker of RBC adhesion. Utilizing SCD-EV-BioChip, Here, we examined the impact of SS REVs on acute microvascular EC activation and RBC adhesion at 2 hours. For in vitro studies, SS REVs and AA REVs were collected from pooled human SS RBCs and AA RBCs activated using calcium ionophore. The generated REVs were characterized using scanning electron microscopy (SEM) and nanoparticle tracking analyzer (NTA). HPMECs were cultured in microfluidic channels under controlled shear stress for more than 72 hours then treated with REVs at 37 ºC for 2 hours. Von Willebrand factor (vWF) expression on REVs-treated HPMECs were quantified. RBC adhesion tests were conducted with and without vWF protease ADAMTS13 and heme-binding protein hemopexin under shear stress at 1 dyne/cm2 followed by a rinse step and quantification of adhered RBCs. For in vivo study, HbSS-Townes mice and a dorsal skin-fold chamber model was used to determine if ADAMTS13 would reduce microvascular stasis in response to hemin. Results: Within 2 hours, SS REVs, but not AA REVs, promoted increased levels of vWF expression on HPMECs, indicating HPMEC activation (Fig. 1A-C). VWF is known to trigger SRBC adhesion and vaso-occlusion. Using SCD-EV-BioChip, we found significantly increased SS RBC adhesion to HPMECs exposed to SREVs, compared to SRBC adhesion to HPMECs exposed to AA REVs, and AA RBC adhesion to HPMECs exposed to SS REVs (Fig. 1D-G). SS RBC adhesion was significantly reduced on HPMECs treated with SS REVs pre-incubated with hemopexin. ADAMTS13 is a regulator which is responsible for cleaving ultra large vWF. In this study, SS RBC adhesion was significantly reduced by vWF cleaving protease ADAMTS13 to a level similar to HPMECs treated with AA REVs (Fig. 1G). Consistent with these observations, studies in SS mice with implanted dorsal skin-fold chambers found hemin-induced stasis was inhibited by ADAMTS13 (Fig. 1F). SRBC adhesion was variable within a total of 15 test subjects with SCD, and was higher with SRBCs from patients with increased markers of hemolysis (LDH and reticulocyte count) or a concomitant clinical diagnosis of deep vein thrombosis. Conclusions: This work demonstrated the acute, non-transcriptional contribution made by REVs to the microvascular EC activation and vWF-mediated SRBC adhesion. Results from SCD-EV-BioChip indicated the effect of hemopexin in mitigating SREV-mediated HPMEC activation. Additionally, results from in vitro SCD-EV BioChip tests agreed with in vivo stasis tests using SS mice, both of which indicated the effect of ADAMTS13 in mitigating SS RBC adhesion and vaso-occlusion. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Introduction: Abnormal red blood cell (RBC) adhesion due to polymerization of sickle hemoglobin (HbS) is central to the pathophysiology of SCD. Early erythrocytes (reticulocytes), expanded in number due to sustained stress erythropoiesis stimulated by anemia and hypoxia, are more adhesive to vascular endothelial proteins and surfaces than are mature erythrocytes. However, mature erythrocytes typically constitute >80% of all RBCs in SCD, and the relative contribution made by erythrocytes vs. reticulocytes to acute and chronic vasculopathy is not well understood. We hypothesized that sphingomyelinase (SMase) activity that is upregulated by accumulated bending energy leads to elevated membrane sulfatide availability and thus hypoxic mature erythrocyte adhesion under hypoxia. Methods: We probed the adhesion of RBCs obtained from SCD patients (#NCT02824471) stained with acridine orange under various physiological conditions in microchannels that were coated with laminin. Then we analyzed the morphology of single sickle reticulocytes and mature erythrocytes to estimate the membrane bending energy. Results and Discussion: We found that mature erythrocyte adhesion to laminin in controlled microfluidic experiments is significantly greater under hypoxia than under normoxia (1856±481 vs. 78±23, mean±SEM), while sickle reticulocyte adhesion, high to begin with, does not change (1281 ±299 vs. 1258±328, mean±SEM). Furthermore, we show that among the adherent RBCs, mature erythrocytes have greater elongation and accumulated membrane bending energy compared to reticulocytes under hypoxia (Figure 1A). Accumulated membrane bending is known to elicit SMase, and laminin establishes highly specific bonds with sulfatides which are downstream of the SMase. These results suggest that SMase is likely elicited particularly in sickle mature erythrocytes, which become highly adhesive with deoxygenation. This is likely due to loss of membrane surface area with RBC maturation, which may be excessive in SCD due to membrane vesiculation and microparticle release. To elucidate the roles of SMase and sulfatide in the adhesion of mature erythrocytes, we repeated the adhesion experiments with SMase and anti-sulfatide incubation. We found that SMase increases the hypoxia-enhanced adhesion of mature erythrocytes and the anti-sulfatide antibody inhibits the enhanced adhesion of mature erythrocytes seen under hypoxia (Figure 1B). Collectively, these data demonstrate the effect of accumulated membrane damage on the abnormal adhesion of sickle mature erythrocytes. Conclusions: Patient-to-patient variability in hypoxia enhanced mature erythrocyte adhesion suggests a role in modulating clinical comorbidities and or genetic polymorphisms relevant to red cell health and hypoxic regulation. These results also implicate the lipid components of the plasma membrane in the pathophysiology of RBC dysfunction in SCD. Therefore, sulfatide and the components of its pathway, such as SMase, could be explored as potential therapeutic targets to inhibit sickle erythrocyte adhesion in SCD. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Red blood cell (RBC) deformability is a valuable hemorheological biomarker that can be used to assess the clinical status and response to therapy of individuals with sickle cell disease (SCD). RBC deformability has been measured by ektacytometry for decades, which uses shear or osmolar stress. However, ektacytometry is a population based measurement that does not detect small-fractions of abnormal RBCs. A single cell-based, functional RBC deformability assay would complement ektacytometry and provide additional information. Here, we tested the relative merits of the OcclusionChip, which measures RBC deformability by microcapillary occlusion, and ektacytometry. We tested samples containing glutaraldehyde-stiffened RBCs for up to 1% volume fraction; ektacytometry detected no significant change in Elongation Index (EI), while the OcclusionChip showed significant differences in Occlusion Index (OI). OcclusionChip detected a significant increase in OI in RBCs from an individual with sickle cell trait (SCT) and from a subject with SCD who received allogeneic hematopoietic stem cell transplant (HSCT), as the sample was taken from normoxic (pO2:159 mmHg) to physiologic hypoxic (pO2:45 mmHg) conditions. Oxygen gradient ektacytometry detected no difference in EI for SCT or HSCT. These results suggest that the single cell-based OcclusionChip enables detection of sickle hemoglobin (HbS)-related RBC abnormalities in SCT and SCD, particularly when the HbS level is low. We conclude that the OcclusionChip is complementary to the population based ektacytometry assays, and providing additional sensitivity and capacity to detect modest abnormalities in red cell function or small populations of abnormal red cells.

Individuals with sickle cell disease (SCD) have persistently elevated thrombin generation that results in a state of systemic hypercoagulability. Antithrombin-III (ATIII), an endogenous serine protease inhibitor, inhibits several enzymes in the coagulation cascade, including thrombin. Here, we utilize a biomimetic microfluidic device to model the morphology and adhesive properties of endothelial cells (ECs) activated by thrombin and examine the efficacy of ATIII in mitigating the adhesion of SCD patient-derived red blood cells (RBCs) and EC retraction. Microfluidic devices were fabricated, seeded with ECs, and incubated under physiological shear stress. Cells were then activated with thrombin with or without an ATIII pretreatment. Blood samples from subjects with normal haemoglobin (HbAA) and subjects with homozygous SCD (HbSS) were used to examine RBC adhesion to ECs. Endothelial cell surface adhesion molecule expression and confluency in response to thrombin and ATIII treatments were also evaluated. We found that ATIII pretreatment of ECs reduced HbSS RBC adhesion to thrombin-activated endothelium. Furthermore, ATIII mitigated cellular contraction and reduced surface expression of von Willebrand factor and vascular cell adhesion molecule-1 (VCAM-1) mediated by thrombin. Our findings suggest that, by attenuating thrombin-mediated EC damage and RBC adhesion to endothelium, ATIII may alleviate the thromboinflammatory manifestations of SCD.

Introduction: Sickle cell disease (SCD) is one of the most common inherited blood disorders and affects over 100,000 individuals in US only. SCD is caused by a single mutation in the β-globin gene that leads to the production of sickle hemoglobin (HbS). Red blood cells (RBCs) from patients with SCD are sticky, rigid, and prone to hemolysis, resulting in a wide range of acute and chronic complications, such as vaso-occlusive crises, acute chest syndrome, cerebrovascular disease, and multi-organ damage. Hematopoietic stem cell transplant (HSCT) is a curative therapy for SCD, that results in stabilization of organ function and gradual amelioration of cerebrovascular and pulmonary complications, as well vaso-occlusive crises. We report a clinically applicable microfluidic device (SCD Biochip) that enables quantitative evaluation of RBC adhesion to endothelium-associated protein-immobilized microchannels before and after HSCT.

Anemia affects over 25% of the world's population with the heaviest burden borne by women and children. Genetic hemoglobin (Hb) variants, such as sickle cell disease, are among the major causes of anemia. Anemia and Hb variant are pathologically interrelated and have an overlapping geographical distribution. We present the first point-of-care (POC) platform to perform both anemia detection and Hb variant identification, using a single paper-based electrophoresis test. Feasibility of this new integrated diagnostic approach is demonstrated via testing individuals with anemia and/or sickle cell disease. Hemoglobin level determination is performed by an artificial neural network (ANN) based machine learning algorithm, which achieves a mean absolute error of 0.55 g dL-1 and a bias of -0.10 g dL-1 against the gold standard (95% limits of agreement: 1.5 g dL-1) from Bland-Altman analysis on the test set. Resultant anemia detection is achieved with 100% sensitivity and 92.3% specificity. With the same tests, subjects with sickle cell disease were identified with 100% sensitivity and specificity. Overall, the presented platform enabled, for the first time, integrated anemia detection and hemoglobin variant identification using a single point-of-care test.

OBJECTIVES:We present a standardized in vitro microfluidic assay and Occlusion Index (OI) for the assessment of red blood cell (RBC)-mediated microcapillary occlusion and its clinical associations in sickle cell disease (SCD). METHODS:Red blood cell mediated microcapillary occlusion represented by OI and its clinical associations were assessed for seven subjects with hemoglobin-SC disease (HbSC), 18 subjects with homozygous SCD (HbSS), and five control individuals (HbAA). RESULTS:We identified two sub-populations with HbSS based on the OI distribution. HbSS subjects with relatively higher OIs had significantly lower hemoglobin levels, lower fetal hemoglobin (HbF) levels, and lower mean corpuscular volume (MCV), but significantly higher serum lactate dehydrogenase levels and absolute reticulocyte counts, compared to subjects with HbSS and lower OIs. HbSS subjects who had relatively higher OIs were more likely to have had a concomitant diagnosis of intrapulmonary shunting (IPS). Further, lower OI associated with hydroxyurea (HU) responsiveness in subjects with HbSS, as evidenced by significantly elevated HbF levels and MCV. CONCLUSIONS:We demonstrated that RBC-mediated microcapillary occlusion and OI associated with subject clinical phenotype and HU responsiveness in SCD. The presented standardized microfluidic assay may be useful for evaluating clinical phenotype and assessing therapeutic outcomes in SCD, including emerging targeted and curative treatments that aim to improve RBC deformability and microcirculatory health.

Introduction: Anemia affects a third of the world's population with the heaviest burden borne by women and children. Anemia leads to preventable impaired development in children, as well as high morbidity and early mortality among sufferers. Inherited hemoglobin (Hb) disorders, such as sickle cell disease (SCD), are associated with chronic hemolytic anemia causing high morbidity and mortality. Anemia and SCD are inherently associated and are both prevalent in the same regions of the world including sub-Saharan Africa, India, and south-east Asia. Anemia and SCD-related complications can be mitigated by screening, early diagnosis followed by timely intervention. Anemia treatment depends on the accurate characterization of the cause, such as inherited Hb disorders. Meanwhile, Hb disorders or SCD treatments, such as hydroxyurea therapy, requires close monitoring of blood Hb level and the patient's anemia status over time. As a result, it is crucially important to perform integrated detection and monitoring of blood Hb level, anemia status, and Hb variants, especially in areas where anemia and inherited Hb disorders are the most prevalent. Blood Hb level (in g/dL) is used as the main indicator of anemia, while the presence of Hb variants (e.g., sickle Hb or HbS) in blood is the primary indicator of an inherited disorder. The current clinical standards for anemia testing and Hb variant identification are complete blood count (CBC) and High-Performance Liquid Chromatography (HPLC), respectively. State-of-the-art laboratory infrastructure and trained personnel are required for these laboratory tests. However, these resources are typically scarce in low- and middle-income countries, where anemia and Hb disorders are the most prevalent. As a result, there is a dire need for high accuracy portable point-of-care (POC) devices to perform integrated anemia and Hb variant tests with affordable cost and high throughput. Methods: In 2019, the World Health Organization (WHO) listed Hb electrophoresis as an essential in vitro diagnostic (IVD) technology for diagnosing SCD and sickle cell trait. We have leveraged the common Hb electrophoresis method and developed a POC microchip electrophoresis test, Hemoglobin Variant/Anemia (HbVA). This technology is being commercialized under the product name "Gazelle" by Hemex Health Inc. for Hb variant identification with integrated anemia detection (Fig. 1A&B). We hypothesized that computer vision and deep learning will enhance the accuracy and reproducibility of blood Hb level prediction and anemia detection in cellulose acetate based Hb electrophoresis, which is a clinical standard test for Hb variant screening and diagnosis worldwide (Fig. 1C). To test this hypothesis, we integrated, for the first time, a new, computer vision and artificial neural network (ANN) based deep learning imaging and data analysis algorithm, to Hb electrophoresis. Here, we show the feasibility of this new, computer vision and deep learning enabled diagnostic approach via testing of 46 subjects, including individuals with anemia and homozygous (HbSS) or heterozygous (HbSC or Sβ-thalassemia) SCD. Results and Discussion: HbVA computer vision tracked the electrophoresis process real-time and the deep learning neural network algorithm determined Hb levels which demonstrated significant correlation with a Pearson Correlation Coefficient of 0.95 compared to the results of reference standard CBC (Fig.1D). Furthermore, HbVA demonstrated high reproducibly with a mean absolute error of 0.55 g/dL and a bias of -0.10 g/dL (95% limits of agreement: 1.5 g/dL) according to Bland-Altman analysis (Fig. 1E). Anemia determination was achieved with 100% sensitivity and 92.3% specificity with a receiver operating characteristic area under the curve (AUC) of 0.99 (Fig. 1F). Within the same test, subjects with SCD were identified with 100% sensitivity and specificity (Fig. 1G). Overall, the results suggested that computer vision and deep learning methods can be used to extract new information from Hb electrophoresis, enabling, for the first time, reproducible, accurate, and integrated blood Hb level prediction, anemia detection, and Hb variant identification in a single affordable test at the POC. Disclosures An: Hemex Health, Inc.: Patents & Royalties. Hasan:Hemex Health, Inc.: Patents & Royalties. Ahuja:Genentech: Consultancy; Sanofi-Genzyme: Consultancy; XaTec Inc.: Consultancy; XaTec Inc.: Research Funding; XaTec Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Genentech: Honoraria; Sanofi-Genzyme: Honoraria. Little:GBT: Research Funding; Bluebird Bio: Research Funding; BioChip Labs: Patents & Royalties: SCD Biochip (patent, no royalties); Hemex Health, Inc.: Patents & Royalties: Microfluidic electropheresis (patent, no royalties); NHLBI: Research Funding; GBT: Membership on an entity's Board of Directors or advisory committees. Gurkan:Hemex Health, Inc.: Consultancy, Current Employment, Patents & Royalties, Research Funding; BioChip Labs: Patents & Royalties; Xatek Inc.: Patents & Royalties; Dx Now Inc.: Patents & Royalties.

Sickle cell disease (SCD) is a recessive genetic blood disorder exhibiting abnormal blood rheology. Polymerization of sickle hemoglobin, due to a point mutation in the β-globin gene of hemoglobin, results in aberrantly adhesive and stiff red blood cells (RBCs). Hemolysis, abnormal RBC adhesion, and abnormal blood rheology together impair endothelial health in people with SCD, which leads to cumulative systemic complications. Here, we describe a microfluidic assay combined with a micro particle image velocimetry technique for the integrated in vitro assessment of whole blood viscosity (WBV) and RBC adhesion. We examined WBV and RBC adhesion to laminin (LN) in microscale flow in whole blood samples from 53 individuals with no hemoglobinopathies (HbAA, N = 10), hemoglobin SC disease (HbSC, N = 14), or homozygous SCD (HbSS, N = 29) with mean WBV of 4.50 cP, 4.08 cP, and 3.73 cP, respectively. We found that WBV correlated with RBC count and hematocrit in subjects with HbSC or HbSS. There was a significant inverse association between WBV and RBC adhesion under both normoxic and physiologically hypoxic (SpO2 of 83%) tests, in which lower WBV associated with higher RBC adhesion to LN in subjects with HbSS. Low WBV has been found by others to associate with endothelial activation. Altered WBV and abnormal RBC adhesion may synergistically contribute to the endothelial damage and cumulative pathophysiology of SCD. These findings suggest that WBV and RBC adhesion may serve as clinically relevant biomarkers and endpoints in assessing emerging targeted and curative therapies in SCD.

Upregulated expression of P-selectin on activated endothelium and platelets significantly contributes to the initiation and progression of vaso-occlusive crises (VOC), a major cause of morbidity in sickle cell disease (SCD). Crizanlizumab (ADAKVEO®), a humanized monoclonal antibody against P-selectin, primarily inhibits the interaction between leukocytes and P-selectin, and has been shown to decrease the frequency of VOCs in clinical trials. However, the lack of reliable in vitro assays that objectively measure leukocyte adhesion to P-selectin remains a critical barrier to evaluating and improving the therapeutic treatment in SCD. Here, we present a standardized microfluidic BioChip whole blood adhesion assay to assess leukocyte adhesion to P-selectin under physiologic flow conditions. Our results demonstrated heterogeneous adhesion by leukocytes to immobilized P-selectin, and dose-dependent inhibition of this adhesion following pre-exposure to Crizanlizumab. Importantly, treatment with Crizanlizumab following adhesion to P-selectin promoted detachment of rolling, but not of firmly adherent leukocytes. Taken together, our results suggest that the microfluidic BioChip system is a promising in vitro assay with which to screen patients, monitor treatment response, and guide current and emerging anti-adhesive therapies in SCD.