Engagement of the PD-1 immunoinhibitory receptor by a novel B7 family member leads to negative regulation of lymphocyte activation

PD-1 is an immunoinhibitory receptor expressed by activated T cells, B cells, and myeloid cells. Mice deficient in PD-1 exhibit a breakdown of peripheral tolerance and demonstrate multiple autoimmune features. We report here that the ligand of PD-1 (PD-L1) is a member of the B7 gene family. Engagement of PD-1 by PD-L1 leads to the inhibition of T cell receptor-mediated lymphocyte proliferation and cytokine secretion. In addition, PD-1 signaling can inhibit at least suboptimal levels of CD28-mediated costimulation. PD-L1 is expressed by antigen-presenting cells, including human peripheral blood monocytes stimulated with interferon gamma, and activated human and murine dendritic cells. In addition, PD-L1 is expressed in nonlymphoid tissues such as heart and lung. The relative levels of inhibitory PD-L1 and costimulatory B7-1/B7-2 signals on antigen-presenting cells may determine the extent of T cell activation and consequently the threshold between tolerance and autoimmunity. PD-L1 expression on nonlymphoid tissues and its potential interaction with PD-1 may subsequently determine the extent of immune responses at sites of inflammation.

PD-L2 is a second ligand for PD-1 and inhibits T cell activation

Programmed death I (PD-I)-deficient mice develop a variety of autoimmune-like diseases, which suggests that this immunoinhibitory receptor plays an important role in tolerance. We identify here PD-1 ligand 2 (PD-L2) as a second ligand for PD-1 and compare the function and expression of PD-L1 and PD-L2. Engagement of PD-1 by PD-L2 dramatically inhibits T cell receptor (TCR)-mediated proliferation and cytokine production by CD4+ T cells. At low antigen concentrations, PD-L2-PD-1 interactions inhibit strong B7-CD28 signals. In contrast, at high antigen concentrations, PD-L2-PD-1 interactions reduce cytokine production but do not inhibit T cell proliferation. PD-L-PD-1 interactions lead to cell cycle arrest in G0/G1 but do not increase cell death. In addition, ligation of PD-1 + TCR leads to rapid phosphorylation of SHP-2, as compared to TCR ligation alone. PD-L expression was up-regulated on antigen-presenting cells by interferon gamma treatment and was also present on some normal tissues and tumor cell lines. Taken together, these studies show overlapping functions of PD-L1 and PD-L2 and indicate a key role for the PD-L-PD-1 pathway in regulatingT cell responses.

Design features, developmental status, and experimental results with the Heartmate III centrifugal left ventricular assist system with a magnetically levitated rotor

A long-term left ventricular assist system for permanent use in advanced heart failure is being developed on the basis of a compact centrifugal pump with a magnetically levitated rotor and single-fault-tolerant electronics. Key features include its "bearingless" (magnetic levitation) design, textured surfaces similar to the HeartMate XVE left ventricular assist device (LVAD) to reduce anticoagulation requirements and thromboembolism, a sensorless flow estimator, and an induced pulse mode for achieving an increased level of pulsatility with continuous flow assistance. In vitro design verification testing is underway. Preclinical testing has been performed in calves demonstrating good in vivo performance at an average flow rate of 6 L/min (maximum: >11 L/min) and normal end-organ function and host response. Induced pulse mode demonstrated the ability to produce a physiological pulse pressure in vivo. Thirteen LVADs have achieved between 16 to 40 months of long-term in vitro reliability testing and will be continued until failure. Both percutaneous and fully implanted systems are in development, with a modular connection for upgrading without replacing the LVAD.

HeartMate III: pump design for a centrifugal LVAD with a magnetically levitated rotor

A long-term, compact left ventricular assist device (LVAD), the HeartMate III, has been designed and fabricated, featuring a centrifugal pump with a magnetically levitated rotor. The pump has been optimized by in vitro testing to achieve a design point of 7 L/min against 135 mm Hg at high hydrodynamic efficiency (30%) and to be capable of up to 10 L/min under such a load. Furthermore, the pump has demonstrated no mechanical failures, low hemolysis (4-10 mg/dl plasma free Hb), and low thrombogenicity during six (40, 27, 59, 42, 27, and 49-day) in vivo bovine studies.

The Heartmate III: design and in vivo studies of a maglev centrifugal left ventricular assist device

A compact implantable centrifugal left ventricular assist device (LVAD) (HeartMate III) featuring a magnetically levitated impeller is under development. The goal of our ongoing work is to demonstrate feasibility, low hemolysis, and low thrombogenicity of the titanium pump in chronic bovine in vivo studies. The LVAD is based on so-called bearingless motor technology and combines pump rotor, drive, and magnetic bearing functions in a single unit. The impeller is rotated (theta z) and levitated with both active (X, Y) and passive (Z, theta x, theta y) suspension. Six prototype systems have been built featuring an implantable titanium pump (69 mm diameter, 30 mm height) with textured blood contacting surfaces and extracorporeal electronics. The pumps were implanted in 9 calves (< or = 100 kg at implant) that were anticoagulated with Coumadin (2.5 < or = INR < or = 4.0) throughout the studies. Six studies were electively terminated (at 27-61 days), 1 study was terminated after the development of severe pneumonia and lung atelectasis (at 27 days) another study was terminated after cardiac arrest (at 2 days) while a final study is ongoing (at approximately 100 days). Mean pump flows ranged from 2 to 7 L/min, except for brief periods of exercise at 6 to 9 L/min. Plasma free hemoglobin ranged from 4 to 10 mg/dl. All measured biochemical indicators of end organ function remained within normal range. The pumps have met performance requirements in all 9 implants with acceptable hemolysis and no mechanical failures.

In Vivo Assessment of a Rotary Left Ventricular Assist Device-induced Artificial Pulse in the Proximal and Distal Aorta

The increasing clinical use of rotary left ventricular assist devices (LVADs) suggests that chronic attenuation of arterial pulse pressure has no clinically significant detrimental effects. However, it remains possible that modulating LVAD rotor speed to produce an artificial pulse may be of temporary or occasional benefit. We sought to evaluate a pulse produced by a continuous-flow, centrifugal pump in an ovine thoracic and abdominal aorta. Both ventricles of an adult sheep were resected to eliminate all native cardiac contributions to pulsatility, each replaced by a continuous-flow Thoratec HeartMate III blood pump (Burlington, MA, USA). An LVAD-induced pulsatile flow was achieved by sharply alternating the speed of the magnetically levitated rotor of the left pump between 1,500 rpm (artificial diastole) and 5,500 rpm (artificial systole) at a rate of 60 bpm at a "systolic" interval of 30%. A catheter was advanced from the ascending aorta to the iliac bifurcation via the ventricular assist device outflow graft for pressure measurement and data acquisition. The mean LVAD-induced pulse pressures were 34, 29, 27, and 26 mm Hg in the ascending, thoracic, and abdominal aorta, and the iliac bifurcation, respectively. The maximum rate of pressure rise (deltap/deltat) was between 189 and 238 mm Hg/s, approaching that of the native pulse, although the energy equivalent pressure did not exceed the mean arterial pressure. The HeartMate III's relatively stiff speed control, low rotor mass, and robust magnetic rotor suspension result in a responsive system, enabling very rapid speed changes that can be used to simulate physiologic pulse pressure and deltap/deltat.

Computational fluid dynamics analysis of a maglev centrifugal left ventricular assist device

The fluid dynamics of the Thoratec HeartMate III (Thoratec Corp., Pleasanton, CA, U.S.A.) left ventricular assist device are analyzed over a range of physiological operating conditions. The HeartMate III is a centrifugal flow pump with a magnetically suspended rotor. The complete pump was analyzed using computational fluid dynamics (CFD) analysis and experimental particle imaging flow visualization (PIFV). A comparison of CFD predictions to experimental imaging shows good agreement. Both CFD and experimental PIFV confirmed well-behaved flow fields in the main components of the HeartMate III pump: inlet, volute, and outlet. The HeartMate III is shown to exhibit clean flow features and good surface washing across its entire operating range.

Investigation of the 'switch-epitope' concept with random peptide libraries displayed as thioredoxin loop fusions

The 'FLITRX' random peptide library, consisting of dodecamer loop peptides displayed on a thioredoxin-flagellin scaffold on Escherichia coli, was used to select peptide sequences with affinity for a monoclonal antibody. These peptides were further screened for pH- and metal-sensitive antibody binding. Several zinc-sensitive peptides were identified, termed 'switch epitopes'. A soluble, monomeric thioredoxin loop ('Trxloop') insertion analog of a FLITRX switch epitope was constructed and its antibody binding properties were characterized by Western blots. Zinc-dependent antibody recognition was maintained in the Trxloop protein although the apparent antibody affinity was lower. This Trxloop protein bound to an immobilized metal affinity chromatography matrix, similar to a 'histidine-patch' thioredoxin variant, and was reversibly precipitated by 1 mM Zn(2+) or Cu(2+) ions. Residues important for zinc and antibody binding were determined by site-directed mutagenesis. The Trxloop antibody affinity was increased by saturation mutagenesis. Biotinylated Trxloop ('Biotrxloop') variants of the original and improved affinity Trxloop proteins were constructed and characterized by surface plasmon resonance measurements. Increased antibody affinity was partially due to a slower antibody desorption rate, although the relative adsorption rates were dependent on the amount of immobilized Biotrxloop protein, indicating an influence of avidity on the apparent affinity.

Novel stereochemical equilibria in crown ethers. Detection of additional conformations of cis-syn-cis- and cis-anti-cis-dicyclohexano-18-crown-6 by 100.6-MHz 13C nuclear magnetic resonance at 173 K

High field, 13C nmr has been utilized for the analysis of new conformational equilibria in each of the title crown ethers at low temperature. Evidence indicates that these equilibria arise from restricted rotation in the macrocyclic portions of these molecules. The conformational free energy differences between the isomers are small (0.1–0.3 kcal/mol) while barriers to their interconversion are of the order of 8.5–9.0 kcal/mol. Comparisons are made with the degenerate equilibria involving inversion of the cyclohexane rings.

Adverse Hemodynamic Consequences of Continuous Left Ventricular Mechanical Support: JACC Review Topic of the Week

Left ventricular assist devices (LVADs) provide lifesaving therapy for patients with advanced heart failure. The recognition of pump thrombosis, stroke, and nonsurgical bleeding as hemocompatibility-related adverse events (HRAEs) led to pump design improvements and reduced adverse event rates. However, continuous flow can predispose patients to right-sided heart failure (RHF) and aortic insufficiency (AI), especially as patients live longer with their device. Given the hemodynamic contributions to AI and RHF, these comorbidities can be classified as hemodynamic-related events (HDREs). Hemodynamic-driven events are time dependent and often manifest later than HRAEs. This review examines the emerging strategies to mitigate HDREs, with a focus on defining best practices for AI and RHF. As we head into the next generation of LVAD technology, it is important to differentiate HDREs from HRAEs so that we can continue to advance the field and improve the true durability of the pump-patient continuum.

cis-Cyclohexano-9-crown-3 ether. Solid state and low-temperature solution stereochemistry as determined by X-ray crystallography and nuclear magnetic resonance spectroscopy

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature 1H1H COSY, 13C1H HETCOR, and DEPT 13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase 13C spectrum has many common features with the solid phase 13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on 13C shieldings are discussed in detail.

Physiologic and hematologic concerns of rotary blood pumps: what needs to be improved?

Over the past few decades, advances in ventricular assist device (VAD) technology have provided a promising therapeutic strategy to treat heart failure patients. Despite the improved performance and encouraging clinical outcomes of the new generation of VADs based on rotary blood pumps (RBPs), their physiologic and hematologic effects are controversial. Currently, clinically available RBPs run at constant speed, which results in limited control over cardiac workload and introduces blood flow with reduced pulsatility into the circulation. In this review, we first provide an update on the new challenges of mechanical circulatory support using rotary pumps including blood trauma, increased non-surgical bleeding rate, limited cardiac unloading, vascular malformations, end-organ function, and aortic valve insufficiency. Since the non-physiologic flow characteristic of these devices is one of the main subjects of scientific debate in the literature, we next emphasize the latest research regarding the development of a pulsatile RBP. Finally, we offer an outlook for future research in the field.

Incorporation of electronics within a compact, fully implanted left ventricular assist device

The promise of expanded indications for left ventricular assist devices in the future for very long-term applications (10+ years) prompts sealed (i.e. fully implanted) systems and less-obtrusive and more reliable implanted components than their external counterparts in percutaneous configurations. Furthermore, sealed systems increase the fraction of total power losses dissipated intracorporeally, a disadvantage that must be carefully managed. We set out to incorporate the motor drive and levitation control electronics within the HeartMate III blood pump without substantially increasing the pump's size. Electronics based on a rigid-flex satellite printed circuit board (PCB) arrangement that could be folded into a very compact, dense package were designed, fabricated, and tested. The pump's lower housing was redesigned to accommodate these PCBs without increasing any dimension of the pump except the height, and that by only 5 mm. The interconnect cable was reduced from 22 wires to 10 (two fully redundant sets of 5). An ongoing test of the assembled pump in vitro has demonstrated no problems in 5 months. In addition, a 20-day in vivo test showed only 1 degrees C temperature rises, equivalent to pumps without incorporated electronics at similar operating conditions.

Solid state and solution stereochemistry of crown ethers and models. ortho-Dimethoxydiphenyl ether and related dibenzo-15-crown-5 and tetrabenzo-30-crown-10 ethers as studied by X-ray crystallography and 1H and 13C NMR spectroscopy

Solid phase 45.3 MHz 13C NMR spectra of ortho-dimethoxydiphenyl ether, 1, dibenzo[b,e]-15-crown-5- ether, 2, and tetrabenzo[b,e,q,t]-30-crown-10 ether, 3, have been obtained. Chemical shift trends are discussed in terms of the asymmetric units and structural features available from X-ray crystallographic data. Comparison with solution 13C spectra are made. The crystal structures of 1 and 3 were determined by X-ray diffraction at room temperature. 1 crystallizes in space group P21/a with a = 13.366(1), b = 8.230(1), c = 12.303(1) Å, β = 116.63(1)°, Z = 4. 3 crystallizes in space group P21/c with a = 7.903(1), b = 26.337(2), c = 7.852(1) Å, β = 97.28(1)°, Z = 2. The structures were solved by direct methods and refined by full-matrix least squares to residuals of 0.055 using 1727 reflections for 1 and of 0.042 using 2590 reflections for 3.

Lithum ion complexation effects on stereochemical dynamics of 14-crown-4 ethers in solution as studied by 13C nuclear magnetic resonance

The barrier to ring inversion for the cis–syn–cis isomer of dicyclohexano-14-crown-4 has been determined via 13C nuclear magnetic resonance coalescence temperature measurements to be 42.3 ± 0.8 kJ/mol. For the LiNCS complex of this isomer, the inversion barrier increases by ca. 5 kJ/mol. For the Li+ complex of the cis–anti–cis isomer, evidence for two dynamic conformational processes in solution is presented, with Li complexation inducing an increase in the barrier to degenerate cyclohexane ring inversion similar to that found in the cis–syn–cis isomer. 13C T1 measurements indicate a substantial decrease in the mobilities of both isomers in the presence of Li+ ions in solution.

Dicyclohexylethyleneglycol, -diethyleneglycol, -triethyleneglycol, and related monosubstituted cyclohexanes. Conformational analysis using low-temperature 13C and 1H NMR spectroscopy

Two conformations of each of the title molecules have been detected by 100 MHz 13C NMR at 210 K. For the dicyclohexyl systems, the conformations are related via a single ring inversion. In each case the equatorial–axial conformer is 4.7 ± 0.4 kJ/mol less stable than the diequatorially substituted form in CD2Cl2 solution. For monosubstituted models, the conformational free energy (−ΔG0) values of the -O-CH2-CH2-OCH3, -OCH2-CH2-O-CH2-CH3, and -O-CH2-CH2-O-CH-(CH3)2 groups have been determined to be 5.4,6.1, and 6.1 ± 0.2 kJ/mol, respectively. In methanol, the latter equilibria are slightly more biased towards the axially substituted conformers. Keywords: substituted ethylene glycols, conformational equilibria.

Graft Resistance Difference after HVAD to HeartMate 3 Left Ventricular Assist Device Exchange

BACKGROUND

A likely consequence of discontinued distribution and sale of the Medtronic HVAD™ System (HVAD) will be an increase in replacement with the Abbott HeartMate 3™ Left Ventricular Assist Device (HeartMate 3) when device exchange is necessary. If part or all if the HVAD 10 mm-diameter outflow graft is retained during replacement, the HeartMate 3 will have to run at a higher speed than it would with its 14 mm-diameter graft.

METHODS

A steady-state, in vitro study was run with 250 mm-long samples of HVAD, HeartMate 3, and half-HVAD/half-HeartMate 3 grafts and, additionally, 125 and 375 mm-long samples of HVAD graft. Flows of 3.0, 3.9, 4.3, 4.7, and 6.0 L/min were applied to encompass expected clinical conditions.

RESULTS

At typical and high flow rates of 4.3 and 6.0 L/min, HeartMate 3 rotor speeds with the full HVAD graft had to be increased relative to those with the HeartMate 3 graft from 5350 to 5700 and 6350 to 6900 rpm, respectively, with power consumption increases from 3.7 to 4.3 (16%) and 5.5 to 6.8 W (24%), respectively.

CONCLUSIONS

The study did not elucidate a severe consequence of utilizing remnant HVAD graft during pump exchange, but the incremental risks of a higher rotor speed, disadvantage to the patient in battery runtime, and the general benefit of complete conversion to the HeartMate 3 graft should be balanced against other procedural considerations. Complete graft replacement during HVAD-to-HeartMate 3 conversion remains the preferred approach from an engineering point of view.

ACTION-ARC Pediatric and Adult Congenital Heart Disease Ventricular Assist Device Adverse Event Definitions-2023

Adverse events (AEs) experienced by children and adults with congenital heart disease (CHD) on ventricular assist devices (VADs) are sometimes unique to these populations. The Advanced Cardiac Therapies Improving Outcomes Network (ACTION) and the Academic Research Consortium (ARC) aimed to harmonize definitions of pediatric and CHD AEs for use in clinical trials, registries, and regulatory evaluation. Data from the ACTION registry and adjudication committee were used to adapt general mechanical circulatory support ARC definitions. This ACTION-ARC international expert panel of trialists, clinicians, patients, families, statisticians, biomedical engineers, device developers, and regulatory agencies drafted and iterated definitions harmonized to ACTION data and existing literature during sessions conducted between December 2022 and May 2023, followed by dissemination across clinical/research audiences and professional organizations and further revision. Both email-linked, internet-based surveys and in-person discussions were used as a modified Delphi process. Nineteen AE types were identified and defined, including seven new event types and six event types that were deleted and will no longer be collected, achieving consensus. ACTION-ARC paired rigorous development with methodical stakeholder involvement and dissemination to define pediatric VAD AEs to facilitate assimilation of data across future clinical trials and evaluation of devices for VAD-supported children and adults with CHD.

The effect of bend relief perforations upon extrinsic graft obstruction risk - a histological analysis

Extrinsic Outflow Graft Obstruction (EOGO) is a potential complication of durable left ventricular assist device (LVAD) therapy characterized by obstructive biodebris accumulation between the outflow graft (OG) and, in the case of HM3, the bend relief (BR). Recent reports have suggested that perforating the HM3 BR may help prevent EOGO. The study objective was to histologically compare the nature and constituency of explanted biologic material from beneath intact HM3 BRs (n = 7; with n = 3 EOGO) beneath perforated HM3 BRs (n = 5), and outside the BR (n = 2). Results indicate that material beneath intact BRs (EOGO and non-EOGO samples) is consistently acellular protein (fibrin) or biodebris while material beneath perforated BRs demonstrated collagen and cell infiltration through the perforations, resembling the material found outside the graft beyond the BR where EOGO is not observed. Despite the small sample size, this study provides a hypothetical mechanism(s) underlying potential benefits of BR perforations in preventing EOGO by attenuating biodebris accumulation through collagen and cell infiltration.