Aspirin and Hemocompatibility Events With a Left Ventricular Assist Device in Advanced Heart Failure: The ARIES-HM3 Randomized Clinical Trial.

IMPORTANCE: Left ventricular assist devices (LVADs) enhance quality and duration of life in advanced heart failure. The burden of nonsurgical bleeding events is a leading morbidity. Aspirin as an antiplatelet agent is mandated along with vitamin K antagonists (VKAs) with continuous-flow LVADs without conclusive evidence of efficacy and safety. OBJECTIVE: To determine whether excluding aspirin as part of the antithrombotic regimen with a fully magnetically levitated LVAD is safe and decreases bleeding. DESIGN, SETTING, and PARTICIPANTS: This international, randomized, double-blind, placebo-controlled study of aspirin (100 mg/d) vs placebo with VKA therapy in patients with advanced heart failure with an LVAD was conducted across 51 centers with expertise in treating patients with advanced heart failure across 9 countries. The randomized population included 628 patients with advanced heart failure implanted with a fully magnetically levitated LVAD (314 in the placebo group and 314 in the aspirin group), of whom 296 patients in the placebo group and 293 in the aspirin group were in the primary analysis population, which informed the primary end point analysis. The study enrolled patients from July 2020 to September 2022; median follow-up was 14 months. Intervention: Patients were randomized in a 1:1 ratio to receive aspirin (100 mg/d) or placebo in addition to an antithrombotic regimen. MAIN OUTCOMES AND MEASURES: The composite primary end point, assessed for noninferiority (-10% margin) of placebo, was survival free of a major nonsurgical (>14 days after implant) hemocompatibility-related adverse events (including stroke, pump thrombosis, major bleeding, or arterial peripheral thromboembolism) at 12 months. The principal secondary end point was nonsurgical bleeding events. RESULTS: Of the 589 analyzed patients, 77% were men; one-third were Black and 61% were White. More patients were alive and free of hemocompatibility events at 12 months in the placebo group (74%) vs those taking aspirin (68%). Noninferiority of placebo was demonstrated (absolute between-group difference, 6.0% improvement in event-free survival with placebo [lower 1-sided 97.5% CI, -1.6%]; P < .001). Aspirin avoidance was associated with reduced nonsurgical bleeding events (relative risk, 0.66 [95% confidence limit, 0.51-0.85]; P = .002) with no increase in stroke or other thromboembolic events, a finding consistent among diverse subgroups of patient characteristics. CONCLUSIONS AND RELEVANCE: In patients with advanced heart failure treated with a fully magnetically levitated LVAD, avoidance of aspirin as part of an antithrombotic regimen, which includes VKA, is not inferior to a regimen containing aspirin, does not increase thromboembolism risk, and is associated with a reduction in bleeding events. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04069156.

A Fully Magnetically Levitated Left Ventricular Assist Device - Final Report.

BACKGROUND: In two interim analyses of this trial, patients with advanced heart failure who were treated with a fully magnetically levitated centrifugal-flow left ventricular assist device were less likely to have pump thrombosis or nondisabling stroke than were patients treated with a mechanical-bearing axial-flow left ventricular assist device. METHODS: We randomly assigned patients with advanced heart failure to receive either the centrifugal-flow pump or the axial-flow pump irrespective of the intended goal of use (bridge to transplantation or destination therapy). The composite primary end point was survival at 2 years free of disabling stroke or reoperation to replace or remove a malfunctioning device. The principal secondary end point was pump replacement at 2 years. RESULTS: This final analysis included 1028 enrolled patients: 516 in the centrifugal-flow pump group and 512 in the axial-flow pump group. In the analysis of the primary end point, 397 patients (76.9%) in the centrifugal-flow pump group, as compared with 332 (64.8%) in the axial-flow pump group, remained alive and free of disabling stroke or reoperation to replace or remove a malfunctioning device at 2 years (relative risk, 0.84; 95% confidence interval [CI], 0.78 to 0.91; P<0.001 for superiority). Pump replacement was less common in the centrifugal-flow pump group than in the axial-flow pump group (12 patients [2.3%] vs. 57 patients [11.3%]; relative risk, 0.21; 95% CI, 0.11 to 0.38; P<0.001). The numbers of events per patient-year for stroke of any severity, major bleeding, and gastrointestinal hemorrhage were lower in the centrifugal-flow pump group than in the axial-flow pump group. CONCLUSIONS: Among patients with advanced heart failure, a fully magnetically levitated centrifugal-flow left ventricular assist device was associated with less frequent need for pump replacement than an axial-flow device and was superior with respect to survival free of disabling stroke or reoperation to replace or remove a malfunctioning device. (Funded by Abbott; MOMENTUM 3 ClinicalTrials.gov number, NCT02224755.).

Factors Related to Pump Thrombosis With the Heartmate II Left Ventricular Assist Device.

BACKGROUND: Recent reports suggested that HeartMate II (HMII) thrombosis rates may be higher in implants after 2011. We characterize events at HMII centers (>100 HMII implants) whose device thrombosis rates are equivalent or lower than reported by INTERMACS. METHODS: Seven centers pooled implants from 2011 through June 2013 to examine pump thrombus and identify characteristics and clinical strategies that potentially mitigate the risk. A total of 666 patients (age 59 ± 13 years; 81% male) were studied (support duration: 13.7 ± 8.3 months, cumulative: 759 patient years). Median target INR was 2.25 (range 2.0 to 2.5), and median pump speed was 9200 rpm (range 8600 to 9600). Pump thrombus was suspected with clinical evidence (e.g., hemolysis, positive ramp test) requiring intervention (e.g., anticoagulation therapy, pump exchange) or patient death. RESULTS: Suspected pump thrombus occurred in 24/666 (3.6%) patients within three months of implant. At six months, 38/666 (5.7%) had suspected pump thrombus including 24 (3.6%) resulting in pump exchange or death. Stroke (hemorrhagic: 0.049, and ischemic: 0.048 events/patient year) and survival (six months: 88 ± 1%; 1 year: 81 ± 2%) were consistent with national averages. Suspected pump thrombus patients were younger (55 ± 13 vs. 59 ± 13, p = 0.046) and had more females (31.6% vs. 18.3%, p = 0.054). There was no difference in indication, etiology of heart failure, or body size. CONCLUSIONS: This analysis demonstrates low HMII thrombus events. Minimization of risk factors by uniform implant techniques and consistent post-op management may reduce device thrombosis. A larger scale multicenter evaluation may better elucidate the difference in thrombus events between centers.

Safety of bone marrow derived mesenchymal stem cell extracellular vesicle injection for lumbar facet joint pain.

Aim: A 3-month pilot study to evaluate the safety of injecting a bone marrow-derived mesenchymal stem cell extracellular vesicle advanced investigational product (IP) into the lumbar facet joint space as a treatment for chronic low back pain. Methods: 20 healthy adults were treated with IP injections (0.5 ml/joint) and evaluated by three functional assessments 1, 3, 7, 14, 30, 60 and 90 days later. Results: No adverse effects or complications occurred across the 3-month follow-up. There were no reports of worsening pain. After 3 months group average scores improved significantly (p < 0.0001) in the Severity Index (65.04%), Interference Index (72.09%) and Oswestry Disability Index (58.43%) assessments. Conclusion: IP injections were safe and associated with significant functional improvements.

What is this article about? Bone marrow mesenchymal stem cell derived extracellular vesicles (BM-MSC EV), a novel biologic therapeutic candidate, are a safe and promising therapeutic intervention for patients with lumbar facet joint pain, a malady that manifests as persistent low back pain (LBP). 20 adult subjects with lumbar facet joint pain received a single injection of BM-MSC EV investigational product in the lumbar facet joint space. What were the results? Follow-up was conducted through in-office and virtual visits that included outcome measures to determine the safety and efficacy of this therapy. By the 3-month end point, follow-up was successful, and no complications or adverse events were noted. Significant improvements in all three assessments of pain and disability occurred throughout the study. What do the results of the study mean? The results are promising and suggest that BM-MSC EV may represent a revolutionary treatment option with durable efficacy and minimal safety risks. Randomized, controlled clinical studies into the application of BM-MSC EV in lumbar facet joint pain should be pursued to confirm the potential benefits of this novel intervention.

Safety and Efficacy of Intravenous ExoFlo in the Treatment of Complex Regional Pain Syndrome.

BACKGROUND: Complex regional pain syndrome (CRPS) is an extremely painful disorder driven primarily by inflammation. OBJECTIVES: We hypothesized that the immunomodulatory biologic, ExoFloTM, composed of bone marrow mesenchymal stem cell-derived extracellular vesicles, could be safely administered to CRPS patients and alleviate symptoms. STUDY DESIGN: Ten patients received 2 intravenous (IV) infusions, each containing 15 mL ExoFlo, on day one and day 4. A series of tests were performed at baseline (day 0, prior to infusion), week one, and months one, 3, and 6 after the second infusion. SETTING: All patients were treated in one of 2 outpatient pain management clinics in Orange County, CA. METHODS: Testing for clinical improvement included: visual analog scale of pain, brief pain inventory, 36-item short-form questionnaire, range of motion analysis, and jamar dynamometer testing. RESULTS: No serious adverse events related to ExoFlo treatment occurred. Statistically significant improvements in pain and motion assessments occurred across the patient pool. LIMITATIONS: This study was limited by its patient number enrolled (10), it lacked a control arm, and one patient who dropped out of the study. CONCLUSIONS: IV delivery of ExoFlo appears safe in patients with CRPS. In addition, ExoFlo exhibited efficacy in addressing CRPS symptoms. Given the lack of effective and safe treatments available to CRPS patients, these results suggest that further studies are warranted to explore and validate this potential treatment for CRPS.

Enhanced Thrombin Formation in Patients With Ventricular Assist Devices Experiencing Bleeding: Insights From the Multicenter PREVENT Study.

The aim of this investigation was to characterize the hemostatic status of heart failure patients with implanted left ventricular assist devices (LVADs) to propose a mechanism associated with bleeding. Patients (n = 300) from 23 US hospitals were enrolled in the PREVENtion of HeartMate II Pump Thrombosis through Clinical Management (PREVENT) study. A biobank was established with serum and plasma samples prospectively collected from a cohort of 175 patients preimplant baseline (BL) and 3 months (3M) postimplant. Outcomes were collected for 6 months. Thrombin (prothrombin fragment 1.2 [F1.2], functional thrombin generation [TG]) and fibrinolytic activity (D-dimer, plasminogen activator inhibitor-1 [PAI-1]), but not contact activation (complement C5a), were elevated in heart failure patients at BL. F1.2, TG, and PAI-1 levels decreased 3M after LVAD implantation ( p < 0.01) but did not revert to normal in all patients; conversely, D-dimer increased BL to 3M ( p < 0.01). Compared with patients without events, thrombin activity (F1.2) was increased in patients with late bleeding (3-4 months postimplant) ( p = 0.06) and in those with late gastrointestinal (GI) bleeding ( p = 0.01). Patients with 3M F1.2 levels above the cohort mean had a higher incidence of bleeding ( p < 0.001) and GI bleeding ( p < 0.001) compared with those with below mean F1.2. Patients experiencing multiple bleeding events were more likely to have 3M F1.2 greater than the cohort mean. Despite anticoagulation with aspirin and warfarin, LVAD implanted patients exhibit hemostatic activation. Excess thrombin formation, particularly shown by increased F1.2, was demonstrated in association with bleeding in LVAD implanted patients.

Association of Angiopoetin-2 and TNF-α With Bleeding During Left Ventricular Assist Device Support: Analysis From the PREVENT Biorepository.

The purpose of this study was to describe the changes in plasma levels of angiogenic and inflammatory biomarkers, specifically Ang-2 and TNF-α, in patients receiving HeartMate II (HMII) left ventricular assist device (LVAD) and correlate them with nonsurgical bleeding. It has been shown that angiopoietin-2 (Ang-2) and tissue necrosis factor-α (TNF-α) may be linked to bleeding in LVAD patients. This study utilized biobanked samples prospectively collected from the PREVENT study, a prospective, multicenter, single-arm, nonrandomized study of patients implanted with HMII. Paired serum samples were obtained in 140 patients before implantation and at 90 days postimplantation. Baseline demographics were as follows: age 57 ± 13 years, 41% had ischemic etiology, 82% male, and 75% destination therapy indication. In the 17 patients with baseline elevation of both TNF-α and Ang-2, 10 (60%) experienced a significant bleeding event within 180 days postimplant compared with 37 of 98 (38%) patients with Ang-2 and TNF-α below the mean ( p = 0.02). The hazard ratio for a bleeding event was 2.3 (95% CI: 1.2-4.6) in patients with elevated levels of both TNF-α and Ang-2. In the PREVENT multicenter study, patients with elevations in serum Angiopoietin-2 and TNF-α at baseline before LVAD implantation demonstrated increased bleeding events after LVAD implantation.

Bone Marrow Mesenchymal Stem Cell-Derived Extracellular Vesicle Infusion for the Treatment of Respiratory Failure From COVID-19: A Randomized, Placebo-Controlled Dosing Clinical Trial.

BACKGROUND: Bone marrow mesenchymal stem cell (BM-MSC)-derived extracellular vesicles (ExoFlo) convey the immunomodulatory and regenerative properties of intact BM-MSCs. This study aimed to determine the safety and efficacy of ExoFlo as treatment for moderate to severe ARDS in patients with severe COVID-19. RESEARCH QUESTION: Do two doses of ExoFlo safely reduce mortality in COVID-19-associated moderate to severe ARDS compared with placebo? STUDY DESIGN AND METHODS: A prospective phase 2 multicenter double-anonymized randomized placebo-controlled dosing trial was conducted at five sites across the United States with infusions of placebo, 10 mL of ExoFlo, or 15 mL of ExoFlo on days 1 and 4. Patients (N = 102) with COVID-19-associated moderate to severe ARDS were enrolled and randomized to treatment. Adverse events were documented throughout the study. The primary outcome measure was all-cause 60-day mortality rate. Secondary outcomes included time to death (overall mortality); the incidence of treatment-emergent serious adverse events; proportion of discharged patients at 7, 30, and 60 days; time to hospital discharge; and ventilation-free days. RESULTS: No treatment-related adverse events were reported. Mortality (60-day) in the intention-to-treat population was reduced with 15 mL ExoFlo mixed with 85 mL normal saline (ExoFlo-15) compared with placebo (not significant, χ2, P = .1343). For the post hoc subgroup analyses, 60-day mortality was decreased with ExoFlo-15 compared with placebo (relative risk, 0.385; 95% CI, 0.159-0.931; P = .0340; n = 50). With ExoFlo-15, a relative risk of 0.423 (95% CI, 0.173-1.032; P = .0588; n = 24) was determined for participants aged 18 to 65 years with moderate to severe ARDS. Ventilation-free days improved with ExoFlo-15 (P = .0455; n = 50) for all participants aged 18 to 65 years. INTERPRETATION: The 15 mL dose of ExoFlo was found to be safe in patients with severe or critical COVID-19-associated respiratory failure. In participants aged 18 to 65 years, the risk reduction in 60-day mortality was further improved from subjects of all ages in the intention-to-treat population after two doses of 15 mL of ExoFlo compared with placebo. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov; No.: NCT04493242; URL: www. CLINICALTRIALS: gov.

Impact of Race on Clinical Outcomes After Implantation With a Fully Magnetically Levitated Left Ventricular Assist Device: An Analysis From the MOMENTUM 3 Trial.

BACKGROUND: Heart failure disproportionately affects Black patients. Whether differences among race influence outcomes in advanced heart failure with use of a fully magnetically levitated continuous-flow left ventricular assist device remains uncertain. METHODS: We included 515 IDE (Investigational Device Exemption) clinical trial patients and 500 Continued Access Protocol patients implanted with the HeartMate 3 left ventricular assist device in the MOMENTUM 3 study (Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3). Outcomes were compared between Black and White left ventricular assist device recipients for the primary end point of survival free of disabling stroke or reoperation to replace or remove a malfunctioning device at 2 years, overall survival, adverse events, 6-minute walk distance, and quality of life scores. RESULTS: Of 1015 HeartMate 3 patients, 675 were self-identified as White and 285 as Black individuals. The Black patient cohort was younger, more obese and with a history of hypertension, and more nonischemic cause of heart failure, relative to the White patient group. Black and White patients did not experience a difference in the primary end point (81.1% versus 77.9%; hazard ratio, 1.08 [95% CI, 0.76-1.54], P=0.6568). Black patients were at higher risk of adverse events (calculated as events per 100 patient-years), including bleeding (75.4 versus 63.5; P<0.0001), stroke (9.5 versus 7.2; P=0.0183), and hypertension (10.1 versus 3.2; P<0.0001). The 6-minute walk distance was not different at baseline and 6 months between the groups, however, the absolute change from baseline was greater for White patients (median: +183.0 [interquartile range, 42.0-335.3] versus +163.8 [interquartile range, 42.3-315.0] meters, P=0.01). The absolute quality of life measurement (EuroQoL group, 5-dimension, 5-level instrument visual analog scale) at baseline and 6 months was better in the Black patient group, but relative improvement from baseline to 6 months was greater in White patients (median: +20.0 [interquartile range, 5.0-40.0] versus +25.0 [interquartile range, 10.0-45.0]; P=0.0298). CONCLUSIONS: Although the survival free of disabling stroke or reoperation to replace/remove a malfunctioning device at 2 years with the HM 3 left ventricular assist device did not differ by race, Black HeartMate 3 patients experienced a higher morbidity burden and smaller gains in functional capacity and quality of life when compared with White patients. These findings require efforts designed to better understand and overcome these gaps through systematic identification and tackling of putative factors. Registration: URL: https://www.clinicaltrials.gov; Unique identifiers: NCT02224755 and NCT02892955.

Supplementation of fat grafts with adipose-derived regenerative cells improves long-term graft retention.

Current practice of autologous fat transfer for soft tissue augmentation is limited by poor long-term graft retention. Adipose-derived regenerative cells (ADRCs) contain several types of stem and regenerative cells, which may help improve graft retention through multiple mechanisms. Using a murine fat transplantation model, ADRCs were added to transplanted fat to test whether ADRCs could improve the long-term retention of the grafts. This study showed, at both 6 and 9 months after transplantation, ADRCs not only increased graft retention by 2-fold but also improved the quality of the grafts. ADRC-supplemented grafts had a higher capillary density, indicating ADRCs could promote neovascularization. Further cell tracking and gene expression studies suggest ADRCs may promote angiogenesis and adipocyte differentiation and prevent apoptosis through the expression of various growth factors, including VEGFA and IGF-1. Taken together, these results suggest a potential clinical utility of ADRCs in facilitating autologous fat transfer for soft tissue augmentation.

Association of Clinical Outcomes With Left Ventricular Assist Device Use by Bridge to Transplant or Destination Therapy Intent: The Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3 (MOMENTUM 3) Randomized Clinical Trial.

Importance: Left ventricular assist devices (LVADs) are well established in the treatment of advanced heart failure, but it is unclear whether outcomes are different based on the intended goal of therapy in patients who are eligible vs ineligible for heart transplant. Objective: To determine whether clinical outcomes in the Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3 (MOMENTUM 3) trial differed by preoperative categories of bridge to transplant (BTT) or bridge to transplant candidacy (BTC) vs destination therapy (DT). Design, Setting, and Participants: This study was a prespecified secondary analysis of the MOMENTUM 3 trial, a multicenter randomized clinical trial comparing the magnetically levitated centrifugal-flow HeartMate 3 (HM3) LVAD to the axial-flow HeartMate II (HMII) pump. It was conducted in 69 centers with expertise in managing patients with advanced heart failure in the United States. Patients with advanced heart failure were randomized to an LVAD, irrespective of the intended goal of therapy (BTT/BTC or DT). Main Outcomes and Measures: The primary end point was survival free of disabling stroke or reoperation to remove or replace a malfunctioning device at 2 years. Secondary end points included adverse events, functional status, and quality of life. Results: Of the 1020 patients with implants (515 with HM3 devices [50.5%] and 505 with HMII devices [49.5%]), 396 (38.8%) were in the BTT/BTC group (mean [SD] age, 55 [12] years; 310 men [78.3%]) and 624 (61.2%) in the DT group (mean [SD] age, 63 [12] years; 513 men [82.2%]). Of the patients initially deemed as transplant ineligible, 84 of 624 patients (13.5%) underwent heart transplant within 2 years of LVAD implant. In the primary end point analysis, HM3 use was superior to HMII use in patients in the BTT/BTC group (76.8% vs 67.3% for survival free of disabling stroke and reoperation; hazard ratio, 0.62 [95% CI, 0.40-0.94]; log-rank P = .02) and patients in the DT group (73.2% vs 58.7%; hazard ratio, 0.61 [95% CI, 0.46-0.81]; log-rank P < .001). For patients in both BTT/BTC and DT groups, there were not significantly different reductions in rates of pump thrombosis, stroke, and gastrointestinal bleeding with HM3 use relative to HMII use. Improvements in quality of life and functional capacity for either pump were not significantly different regardless of preimplant strategy. Conclusions and Relevance: In this trial, the superior treatment effect of HM3 over HMII was similar for patients in the BTT/BTC or DT groups. It is possible that use of arbitrary categorizations based on current or future transplant eligibility should be clinically abandoned in favor of a single preimplant strategy: to extend the survival and improve the quality of life of patients with medically refractory heart failure. Trial Registration: ClinicalTrials.gov identifier: NCT02224755.

Pump Position Impacts HeartMate II Left Ventricular Assist Device Thrombosis.

The PREVENtion of HeartMate II pump Thrombosis through clinical management (PREVENT) study was a multicenter, prospective investigation to evaluate the rate of pump thrombosis (PT) with adoption of a uniform set of surgical and medical practices for left ventricular assist device implantation. We sought to quantify pump position at baseline and retrospectively define a pump position associated with poor clinical outcomes. Chest x-rays at baseline were prospectively obtained per protocol. Pump pocket depth, inflow cannula (IC) angle relative to the pump, and IC angle relative to the vertical were measured. Pumps falling in the tail-ends of the IC angle and pump pocket depth distributions were categorized as having an extreme pump position within the PREVENT study. Patients with extreme pump position had a significantly higher risk of confirmed and suspected PT, hemolysis, and elevated lactate dehydrogenase. In a multivariable analysis of survival free of confirmed PT, extreme pump position was an independent risk factor (hazard ratio = 3.6; 95% confidence interval = 1.5-8.9; p = 0.006) when adjusting for differences in pump speed and anticoagulation level. Our analysis shows that HeartMate II pump position at implant can significantly impact event-free survival and the incidence of adverse events at 6 months.

PREVENtion of HeartMate II Pump Thrombosis Through Clinical Management: The PREVENT multi-center study.

BACKGROUND: Recommended structured clinical practices including implant technique, anti-coagulation strategy, and pump speed management (PREVENT [PREVENtion of HeartMate II Pump Thrombosis Through Clinical Management] recommendations) were developed to address risk of early (<3 months) pump thrombosis (PT) risk with HeartMate II (HMII; St. Jude Medical, Inc. [Thoratec Corporation], Pleasanton, CA). We prospectively assessed the HMII PT rate in the current era when participating centers adhered to the PREVENT recommendations. METHODS: PREVENT was a prospective, multi-center, single-arm, non-randomized study of 300 patients implanted with HMII at 24 participating sites. Confirmed PT (any suspected PT confirmed visually and/or adjudicated by an independent assessor) was evaluated at 3 months (primary end-point) and at 6 months after implantation. RESULTS: The population included 83% men (age 57 years ± 13), 78% destination therapy, and 83% Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) Profile 1-3. Primary end-point analysis showed a confirmed PT of 2.9% at 3 months and 4.8% at 6 months. Adherence to key recommendations included 78% to surgical recommendations, 95% to heparin bridging, and 79% to pump speeds ≥9,000 RPMs (92% >8,600 RPMs). Full adherence to implant techniques, heparin bridging, and pump speeds ≥9,000 RPMs resulted in a significantly lower risk of PT (1.9% vs 8.9%; p < 0.01) and lower composite risk of suspected thrombosis, hemolysis, and ischemic stroke (5.7% vs 17.7%; p < 0.01) at 6 months. CONCLUSIONS: Adoption of all components of a structured surgical implant technique and clinical management strategy (PREVENT recommendations) is associated with low rates of confirmed PT.

High-throughput microfluidic mixing and multiparametric cell sorting for bioactive compound screening.

HyperCyt, an automated sample handling system for flow cytometry that uses air bubbles to separate samples sequentially introduced from multiwell plates by an autosampler. In a previously documented HyperCyt configuration, air bubble separated compounds in one sample line and a continuous stream of cells in another are mixed in-line for serial flow cytometric cell response analysis. To expand capabilities for high-throughput bioactive compound screening, the authors investigated using this system configuration in combination with automated cell sorting. Peptide ligands were sampled from a 96-well plate, mixed in-line with fluo-4-loaded, formyl peptide receptor-transfected U937 cells, and screened at a rate of 3 peptide reactions per minute with approximately 10,000 cells analyzed per reaction. Cell Ca(2+) responses were detected to as little as 10(-11) M peptide with no detectable carryover between samples at up to 10(-7) M peptide. After expansion in culture, cells sort-purified from the 10% highest responders exhibited enhanced sensitivity and more sustained responses to peptide. Thus, a highly responsive cell subset was isolated under high-throughput mixing and sorting conditions in which response detection capability spanned a 1000-fold range of peptide concentration. With single-cell readout systems for protein expression libraries, this technology offers the promise of screening millions of discrete compound interactions per day.