A miniaturized wash-free microfluidic assay for electrical impedance-based assessment of red blood cell-mediated microvascular occlusion.

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.

Concurrent Assessment of Deformability and Adhesiveness of Sickle Red Blood Cells by Measuring Perfusion of an Adhesive Artificial Microvascular Network.

Biomarker development is a key clinical research need in sickle cell disease (SCD). Hemorheological parameters are excellent candidates as abnormal red blood cell (RBC) rheology plays a critical role in SCD pathophysiology. Here we describe a microfluidic device capable of evaluating RBC deformability and adhesiveness concurrently, by measuring their effect on perfusion of an artificial microvascular network (AMVN) that combines microchannels small enough to require RBC deformation, and laminin (LN) coating on channel walls to model intravascular adhesion. Each AMVN device consists of three identical capillary networks, which can be coated with LN (adhesive) or left uncoated (non-adhesive) independently. The perfusion rate for sickle RBCs in the LN-coated networks (0.18 ± 0.02 nL/s) was significantly slower than in non-adhesive networks (0.20 ± 0.02 nL/s), and both were significantly slower than the perfusion rate for normal RBCs in the LN-coated networks (0.22 ± 0.01 nL/s). Importantly, there was no overlap between the ranges of perfusion rates obtained for sickle and normal RBC samples in the LN-coated networks. Interestingly, treatment with poloxamer 188 decreased the perfusion rate for sickle RBCs in LN-coated networks in a dose-dependent manner, contrary to previous studies with conventional assays, but in agreement with the latest clinical trial which showed no clinical benefit. Overall, these findings suggest the potential utility of the adhesive AMVN device for evaluating the effect of novel curative and palliative therapies on the hemorheological status of SCD patients during clinical trials and in post-market clinical practice.

Pediatric to Adult Transition in Sickle Cell Disease: Survey Results from Young Adult Patients.

BACKGROUND/AIMS: We surveyed sickle cell disease (SCD) patients who transitioned from pediatric care at Texas Children's Hematology Center (TCHC) to adult care to determine the characteristics of patients with an adult SCD provider, continuation rates of pre-transition therapies, and patient perceptions of the transition process. METHODS: A cross-sectional study was conducted by telephone survey of 44 young adults with SCD, aged 19-29 years, who transitioned from TCHC to adult care within the last 15 years. RESULTS: Findings of the 23-item questionnaire revealed that transitioned patients with current adult providers (68.2%) were more likely to have seen a provider within 6 months of transition (p = 0.023) and to have been on hydroxyurea and/or monthly blood transfusions pre-transition (p = 0.021) than transitioned patients without a provider; 83% of patients on pre-transition hydroxyurea reported continuing hydroxyurea after transition. Transition challenges included inadequate preparation, difficulty finding knowledgeable adult providers, and lack of healthcare insurance/coverage. CONCLUSION: Transition to adult providers is predicted by establishing care with an adult SCD provider within 6 months of transition and being on pre-transition disease-modifying therapy. Transition may be improved if pediatric hematology centers assist and verify adult provider contact within 6 months of transition and engage patients of all disease severity during transition.