Safety and Efficacy of Iltamiocel Cellular Therapy for the Treatment of Fecal Incontinence. Results of a Phase 1/2 Study

OBJECTIVE

To examine the safety and efficacy of iltamiocel, an investigational cellular therapy of autologous muscle-derived cells, as a treatment for fecal incontinence (FI) in adults.

BACKGROUND

Limited therapeutic options are available for patients with FI refractory to conservative treatments. Cell therapy using autologous muscle-derived cells represents a promising, minimally invasive approach for restoring anal sphincter function.

METHODS

In this multicenter, prospective, non-randomized study, 48 participants were treated with a single iltamiocel dose of 250×10 6 cells. The primary outcome was the incidence of product or procedure-related adverse events (AEs) and serious AEs. Secondary outcomes were changes in the number of FI episodes, Cleveland Clinic Incontinence Score, Fecal Incontinence Quality of Life, and anorectal manometry at 3, 6, and 12 months compared to baseline.

RESULTS

No serious AEs and only one product-related AE of inflammation at the injection site were reported. At 12 months, there was a reduction in median FI episodes (-6.0; 95% confidence interval (CI): -10.0, -1.0) and days with episodes (-4.0; 95% CI: -8.0, -1.0). A ≥50% reduction in FI episodes was observed in 53.7% of participants, and 24.4% had complete restoration of continence. Symptom severity and quality of life improved with mean Cleveland Clinic Incontinence Score reduction (-2.9; 95% CI: -3.7, -2.1), and Fecal Incontinence Quality of Life increased (2.2; 95% CI:1.4, 2.9). No significant changes were detected in anorectal manometry measurements. A history of episiotomy was significantly associated with treatment response in multivariate analysis.

CONCLUSION

The administration of iltamiocel cellular therapy is safe. Iltamiocel shows promise for significantly improving fecal incontinence symptoms and quality of life.

Autologous Muscle-Derived Cell Therapy for Swallowing Impairment in Patients Following Treatment for Head and Neck Cancer

OBJECTIVES/HYPOTHESIS

To evaluate the safety and potential efficacy of autologous muscle-derived cells (AMDCs) for the treatment of swallowing impairment following treatment for oropharynx cancer.

STUDY DESIGN

Prospective, phase I, open label, clinical trial.

METHODS

Oropharynx cancer survivors disease free ≥2 years post chemoradiation were recruited. All patients had swallowing impairment but were not feeding tube dependent (Functional Oral Intake Scale [FOIS] ≥ 5). Muscle tissue (50-250 mg) was harvested from the vastus lateralis and 150 × 10⁶ AMDCs were prepared (Cook MyoSite Inc., Pittsburgh, PA). The cells were injected into four sites throughout the intrinsic tongue musculature. Participants were followed for 24 months. The primary outcome measure was safety. Secondary endpoints included objective measures on swallowing fluoroscopy, oral and pharyngeal pressure, and changes in patient-reported outcomes.

RESULTS

Ten individuals were enrolled. 100% (10/10) were male. The mean age of the cohort was 65 (±8.87) years. No serious adverse event occurred. Mean tongue pressure increased significantly from 26.3 (±11.1) to 31.8 (±9.5) kPa (P = .017). The mean penetration-aspiration scale did not significantly change from 5.6 (±2.1) to 6.8 (±1.8), and the mean FOIS did not significantly change from 5.4 (±0.5) to 4.6 (±0.7). The incidence of pneumonia was 30% (3/10) and only 10% (1/10) experienced deterioration in swallowing function throughout 2 years of follow-up. The mean eating assessment tool (EAT-10) did not significantly change from 24.1 (±5.57) to 21.3 (±6.3) (P = .12).

CONCLUSION

Results of this phase I clinical trial demonstrate that injection of 150 × 10⁶ AMDCs into the tongue is safe and may improve tongue strength, which is durable at 2 years. A blinded placebo-controlled trial is warranted.

LEVEL OF EVIDENCE

3 Laryngoscope, 132:523-527, 2022.

Human skeletal muscle cells with a slow adhesion rate after isolation and an enhanced stress resistance improve function of ischemic hearts

Identification of cells that are endowed with maximum potency could be critical for the clinical success of cell-based therapies. We investigated whether cells with an enhanced efficacy for cardiac cell therapy could be enriched from adult human skeletal muscle on the basis of their adhesion properties to tissue culture flasks following tissue dissociation. Cells that adhered slowly displayed greater myogenic purity and more readily differentiated into myotubes in vitro than rapidly adhering cells (RACs). The slowly adhering cell (SAC) population also survived better than the RAC population in kinetic in vitro assays that simulate conditions of oxidative and inflammatory stress. When evaluated for the treatment of a myocardial infarction (MI), intramyocardial injection of the SACs more effectively improved echocardiographic indexes of left ventricular (LV) remodeling and contractility than the transplantation of the RACs. Immunohistological analysis revealed that hearts injected with SACs displayed a reduction in myocardial fibrosis and an increase in infarct vascularization, donor cell proliferation, and endogenous cardiomyocyte survival and proliferation in comparison with the RAC-treated hearts. In conclusion, these results suggest that adult human skeletal muscle-derived cells are inherently heterogeneous with regard to their efficacy for enhancing cardiac function after cardiac implantation, with SACs outperforming RACs.

Physiological effects of human muscle-derived stem cell implantation on urethral smooth muscle function

The physiological effects of human muscle-derived stem cell (MDSC) implantation on urethral smooth muscle function were investigated in pudendal nerve-transected nude rats with human MDSC (TM) or saline (TS) injection into the proximal urethra compared with sham-operated, saline-injected nude rats (SS). Leak point pressure (LPP) before and after hexamethonium application, which can block autonomic efferent nerves, and proximal urethral contractile responses to carbachol and phenylephrine in muscle strip study were examined 6 weeks after the implantation. There was no significant difference between the LPPs in SS and TM. Following hexamethonium application, the LPP in TM was, however, significantly decreased compared with SS. The contractile responses to phenylephrine, but not to carbachol, in TM were significantly increased compared with SS and TS. These results suggest that the restorative effects of MDSCs are mediated by autonomic nerves and that increased sensitivity of alpha(1)-adrenoceptors may be related to restore the deficient urethral function.

State of the art of where we are at using stem cells for stress urinary incontinence

AIMS

This review aims to discuss: 1) the neurophysiology, highlighting the importance of the middle urethra, and treatment of stress urinary incontinence (SUI); 2) current injectable cell sources for minimally-invasive treatment; and 3) the potential of muscle-derived stem cells (MDSCs) for the delivery of neurotrophic factors.

METHODS

A PUB-MED search was conducted using combinations of heading terms: urinary incontinence, urethral sphincter, stem cells, muscle, adipose, neurotrophins. In addition, we will update the recent work from our laboratory.

RESULTS

In anatomical and functional studies of human and animal urethra, the middle urethra containing rhabdosphincter, is critical for maintaining continence. Cell-based therapies are most often associated with the use of autologous multipotent stem cells, such as the bone marrow stromal cells. However, harvesting bone marrow stromal stem cells is difficult, painful, and may yield low numbers of stem cells upon processing. In contrast, alternative autologous adult stem cells such as MDSCs and adipose-derived stem cells can be easily obtained in large quantities and with minimal discomfort. Not all cellular therapies are the same, as demonstrated by the differences in safety and efficacy from muscle-sourced MDSCs versus myoblasts versus fibroblasts.

CONCLUSIONS

Transplanted stem cells may have the ability to undergo self-renewal and multipotent differentiation, leading to sphincter regeneration. In addition, such cells may release, or be engineered to release, neurotrophins with subsequent paracrine recruitment of endogenous host cells to concomitantly promote a regenerative response of nerve-integrated muscle. The dawn of a new paradigm in the treatment of SUI may be near.

The potential of muscle-derived stem cells for stress urinary incontinence

The suburethral sling procedures, such as transvaginal tape (TVT), have recently gained popularity for the treatment of stress urinary incontinence (SUI). This TVT procedure can reinforce the weakness of pelvic floor muscles but urethral sphincter deficiency remains. Adult stem cell injection therapy for SUI has recently been at the forefront of the repair of deficient urethral function. Muscle-derived stem cells and adipose-derived stem cells are regarded as candidates for the treatment of SUI because these stem cells can be easily obtained in large quantities under local anesthesia, they have the potential to undergo long-term proliferation, self-renewal and multipotent differentiation, and can serve as a vehicle of releasing neurotrophins, such as nerve growth factor, to repair the deficient urethra.

Human muscle-derived cell injection in a rat model of stress urinary incontinence

We investigated the use of human muscle-derived cells (hMDCs) for the treatment of stress urinary incontinence (SUI) in a nude rat model. hMDCs were isolated from adult skeletal muscle. Three groups of six animals consisting of controls, animals undergoing sciatic nerve transection (SNT) with periurethral sham-injection, and SNT with hMDCs (1 x 10(6) cells/20 microl saline) were utilized. Leak point pressure (LPP) was measured 4 weeks following injection. Bilateral SNT resulted in a significantly lower LPP that was significantly higher following hMDCs than sham injection. The results demonstrate the efficacy of human muscle cell therapy alone in improving physiologic outcomes in an animal model of SUI.

The promise of stem cell therapy to restore urethral sphincter function

The promise of stem cell therapy for the treatment of stress urinary incontinence is that transplanted stem cells may undergo self-renewal and potential multipotent differentiation, leading to urethral sphincter regeneration. Cell-based therapies are most often associated with the use of autologous multipotent stem cells, such as bone marrow cells. However, harvesting bone marrow stromal stem cells is difficult, painful, and may yield low numbers of stem cells. Alternatively, autologous adult stem cells, such as muscle-derived stem cells, can be obtained in large quantities and with minimal discomfort. Not all cells and cellular therapies are the same, however, and proper placement of cells into target structures may be critical to eventual treatment success. In particular, restoration and repair of the damaged urethral sphincter is crucial to maintain urinary continence because active urethral closure is largely mediated by pudendal nerves that innervate the striated muscles and rhabdosphincter of the middle urethra.

Ex vivo biomechanical properties of the female urethra in a rat model of birth trauma

Stress urinary incontinence (SUI) is the involuntary release of urine during sudden increases in abdominal pressures. SUI is common in women after vaginal delivery or pelvic trauma and may alter the biomechanical properties of the urethra. Thus we hypothesize that injury due to vaginal distension (VD) decreases urethral basal tone and passive stiffness. This study aimed to assess the biomechanical properties of the urethra after VD in the baseline state, where basal muscle tone and extracellular matrix (ECM) are present, and in the passive state, where inactive muscle and ECM are present. Female rat urethras were isolated in a rat model of acute SUI induced by simulated birth trauma. Our established ex vivo system was utilized, wherein we applied intraluminal static pressures ranging from 0 to 20 mmHg. Outer diameter was measured via a laser micrometer. Measurements were recorded via computer. Urethral thickness was assessed histologically. Stress-strain responses of the urethra were altered by VD. Quantification of biomechanical parameters indicated that VD decreased baseline stiffness. The passive peak incremental elastic modulus of the distal segment in VD urethras was less than for controls (1.84 ± 0.67 vs. 1.19 ± 0.70 × 106 dyne/cm2, respectively; P = 0.016). An increase was noted in passive low-pressure compliance values in proximal VD urethras compared with controls (9.44 ± 2.43 vs. 4.62 ± 0.60 mmHg−1, respectively; P = 0.04). Biomechanical analyses suggest that VD alters urethral basal tone, proximal urethral compliance, and distal stiffness. Lack of basal smooth muscle tone, in combination with these changes in the proximal and distal urethra, may contribute to SUI induced by VD.

Biomechanical characterization of the urethral musculature

Rigorous study of the associations between urethral structural anatomy and biomechanical function is necessary to advance the understanding of the development, progression, and treatment of urethral pathologies. An ex vivo model was utilized to define the relative biomechanical contributions of the active (muscle) elements of the female urethra relative to its passive (noncontractile) elements. Whole urethras from female, adult rats were tested under a range of applied intraluminal pressures (0 to 20 mmHg) as a laser micrometer simultaneously measured midurethral outer diameter. Active tissue characterization was performed during induced contraction of either smooth muscle alone ( Nω-nitro-l-arginine, phenylephrine), striated muscle alone (sodium nitroprusside, atropine, hexamethonium, acetylcholine), or during collective activation of both muscles ( Nω-nitro-l-arginine, phenylephrine, acetylcholine). The subsequent collection of paired passive biomechanical responses permitted the determination of parameters related to intrinsic muscle contractile function. Activation of each muscle layer significantly influenced the biomechanical responses of the tissue. Measures of muscle responsiveness over a wide range of sustained opposing pressures indicated that an activated striated muscle component was approximately one-third as effective as activated smooth muscle in resisting tissue deformation. The maximum circumferential stress generated by the striated muscle component under these conditions was also determined to be approximately one-third of that generated by the smooth muscle (748 ± 379 vs. 2,229 ± 409 N/m2). The experiments quantitatively reveal the relative influence of the intrinsic urethral smooth and striated muscle layers with regard to their effect on the mechanical properties and maximum functional responses of the urethra to applied intralumenal stresses in the complete absence of extrinsic influences.

Modeling stem cell population growth: incorporating terms for proliferative heterogeneity

Expansion of the undifferentiated stem cell phenotype is one of the most challenging aspects in stem cell research. Clinical protocols for stem cell therapeutics will require standardization of defined culture conditions. A first step in the development of predictable and reproducible, scalable bioreactor processes is the development of mathematical growth models. This paper provides practical models for describing cell growth in general, which are particularly well suited for examining stem cell populations. The nonexponential kinetics of stem cells derive from proliferative heterogeneity, which is biologically recognized as mitosis, quiescence, senescence, differentiation, or death. Here, we examined the assumptions of the Sherley model, which describes heterogeneous expansion in the absence of cell loss. We next incorporated terms into the model to account for A) cell loss or apoptosis and B) cell differentiation. We conclude that the basic assumptions of the model are valid and a high correlation between the modified equations and experimental data obtained using muscle-derived stem cells was observed. Finally, we demonstrate an improved estimation of the kinetic parameters. This study contributes to both the biological and mathematical understanding of stem cell dynamics. Further, it is expected that the models will prove useful in establishing standardization of cell culture conditions and scalable systems and will be required to develop clinical protocols for stem cell therapeutics.

Myogenic cellular transplantation and regeneration: sorting through progenitor heterogeneity

Growth and regeneration of skeletal muscle fibers in response to injury are made possible by the presence of resident myogenic progenitor cells. Researchers have attempted to isolate and transplant these cells to regenerate new muscle in cases involving injury, disease, or genetic deficiencies. Reports from such experiments underscore the functional diversity of progenitors obtained from skeletal muscle; however, currently there is no reliable means by which to positively identify and isolate the most desirable muscle progenitor populations. Taking a cue from the hematopoietic community, researchers in this area have begun to investigate cell surface protein expression in progenitor populations. Previous findings in cultured myogenic cells and our results in cells obtained directly from dissociated muscle suspensions indicate that cells sorted based on their expression of the commonly-studied myogenic cell surface proteins Sca-1 and CD34 exhibit differing regenerative abilities. However, results obtained to date are insufficient to clearly delineate whether the expression of either of these proteins is an exclusive characteristic of efficient myogenic progenitors. Nonetheless, observations from these studies clearly suggest that progenitor heterogeneity should be an important consideration during the development and implementation of muscle regeneration strategies. Additional research is necessary to establish reliable selection criteria for the isolation of efficient progenitors, which will facilitate therapeutic discoveries and enhance our understanding of factors affecting regeneration outcomes.

Development of an experimental system for the study of urethral biomechanical function

Despite its principal mechanical function in the storage and release of urine, the biomechanical properties of the urethra have remained largely unexplored. The purpose of this study was to develop and validate an experimental model that can be used for evaluating whole urethral tissue in such a manner. Bladder-urethral specimens were excised from halothane-anesthetized female rats and mounted at in vivo length within the experimental apparatus consisting of a tissue perfusion chamber, an adjustable fluid column, and a laser micrometer. Outer diameter measurements were made at proximal, mid, and distal axial locations in response to increases in intraluminal pressure and after addition of various muscle-responsive agents. Basal smooth muscle tone and regional variations in compliance were detected through pressure-diameter responses. Chemically evoked contractile responses were measured and correspond to regional compositions of intrinsic smooth and striated muscle components. The results presented illustrate the utility of this system, which should permit a more thorough characterization of structure-function relationships and urethral biomechanical function in relation to normal and dysfunctional tissue states.

Establishing reliable criteria for isolating myogenic cell fractions with stem cell properties and enhanced regenerative capacity

Despite a focused effort within the myogenic cell transplantation community, little progress has been made toward the reliable identification and isolation of progenitors that are capable of tolerating the initial posttransplantation environment and effectively regenerating clinically relevant quantities of muscle. The future success of myogenic-based treatment modalities requires an enhanced understanding of the highly heterogeneous nature of the myogenic progenitor cell pool, which has been previously documented by numerous researchers. Further, for translation of experimental animal results to clinical application, reliable in vitro selection criteria must be established and must be translatable across species. While research into the utility of surface markers is ongoing, as an alternative we have investigated in vitro cell behavioral characteristics under imposed conditions which challenge the propensity of myogenic progenitors to choose between various cell fates (i.e., proliferation, quiescence, or differentiation). Previous observations in the mouse suggest an enhanced in vivo regenerative capacity of myogenic populations with respect to their in vitro ability to maintain a proliferative and undifferentiated state [J. Cell Sci. 115 (2002) 4361]. From these observations it is thus proposed that such behavior may represent an a priori indicator of regenerative capacity following transplantation. To challenge this proposition, a rat cell isolation and transplantation model was evaluated in an identical manner. In agreement with the results obtained from the mouse, a significant correlation between regenerative capacity and induction of differentiation was observed. These results contribute to the growing body of scientific evidence documenting the underlying behavioral differences that exist between various myogenic progenitors while also, importantly, providing evidence that such differences may significantly impact the functional capabilities of these cells posttransplantation. This information further implies that from a therapeutic standpoint isolation strategies aimed toward obtaining efficient myogenic progenitors should, in the absence of a reliable surface marker(s), focus on identifying populations displaying desirable in vitro behavior (i.e., high proliferative capacity and low induced differentiation). Incorporating such criteria into cell isolation and/or purification schemes may yield significant returns in the clinical myogenic transplantation setting.

Muscle stem cells differentiate into haematopoietic lineages but retain myogenic potential

Muscle-derived stem cells (MDSCs) can differentiate into multiple lineages, including haematopoietic lineages. However, it is unknown whether MDSCs preserve their myogenic potential after differentiation into other lineages. To address this issue, we isolated from dystrophic muscle a population of MDSCs that express stem-cell markers and can differentiate into various lineages. After systemic delivery of three MDSC clones into lethally irradiated mice, we found that differentiation of the donor cells into various lineages of the haematopoietic system resulted in repopulation of the recipients' bone marrow. Donor-derived bone-marrow cells, isolated from these recipients by fluorescence-activated cell sorting (FACS), also repopulated the bone marrow of secondary, lethally irradiated, recipients and differentiated into myogenic cells both in vitro and in vivo in normal mdx mice. These findings demonstrate that MDSC clones retain their myogenic potential after haematopoietic differentiation.

The role of CD34 expression and cellular fusion in the regeneration capacity of myogenic progenitor cells

Characterization of myogenic subpopulations has traditionally been performed independently of their functional performance following transplantation. Using the preplate technique, which separates cells based on their variable adhesion characteristics, we investigated the use of cell surface proteins to potentially identify progenitors with enhanced regeneration capabilities. Based on previous studies, we used cell sorting to investigate stem cell antigen-1 (Sca-1) and CD34 expression on myogenic populations with late adhesion characteristics. We compared the regeneration efficiency of these sorted progenitors, as well as those displaying early adhesion characteristics, by quantifying their ability to regenerate skeletal muscle and restore dystrophin following transplantation into allogenic dystrophic host muscle. Identification and utilization of late adhering populations based on CD34 expression led to differential regeneration, with CD34-positive populations exhibiting significant improvements in dystrophin restoration compared with both their CD34-negative counterparts and early adhering cell populations. Regenerative capacity was found to correspond to the level of myogenic commitment, defined by myogenic regulatory factor expression, and the rate and degree of induced cell differentiation and fusion. These results demonstrate the ability to separate definable subpopulations of myogenic progenitors based on CD34 expression and reveal the potential implications of defining myogenic cell behavioral and phenotypic characteristics in relation to their regenerative capacity in vivo.

Muscle-derived stem cells

The existence of cells with stem cell-like abilities derived from various tissues can now be extended to include the skeletal muscle compartment. Although researchers have focused on the utilization of these cells with regard to their myogenic capacity, initially exploring more efficient cellular therapy treatments for muscular dystrophy, it is becoming increasingly apparent that such cells may one day be used in the treatment of non-myogenic disorders. Evidence regarding the existence and differentiation capacity of muscle-derived stem cells is discussed, along with current theories regarding their proposed position within the myogenic hierarchy.

Muscle-derived stem cells

The existence of cells with stem cell-like abilities derived from various tissues can now be extended to include the skeletal muscle compartment. Although researchers have focused on the utilization of these cells with regard to their myogenic capacity, initially exploring more efficient cellular therapy treatments for muscular dystrophy, it is becoming increasingly apparent that such cells may one day be used in the treatment of non-myogenic disorders. Evidence regarding the existence and differentiation capacity of muscle-derived stem cells is discussed, along with current theories regarding their proposed position within the myogenic hierarchy.

Muscle-derived stem cells: characterization and potential for cell-mediated therapy

Skeletal muscle may represent a convenient source of stem cells for cell-mediated gene therapy and tissue-engineering applications. A population of cells isolated from skeletal muscle exhibits both multipotentiality and self-renewal capabilities. Satellite cells, referred to by many as muscle stem cells, are myogenic precursors that are capable of regenerating muscle and demonstrating self-renewal properties; however, they are considered to be committed to the myogenic lineage. Muscle-derived stem cells, which may represent a predecessor of the satellite cell, are considered to be distinct. This article considers the evidence for the existence of muscle-derived stem cells as well as their potential embryonic origin. Comparison of muscle-derived stem cells to bone marrow and hematopoietic-derived stem cells illustrates similarities and distinctions among these various stem cells. Hematopoietic stem cell research provides lessons for the isolation of a defined phenotype as well as for the expansion of the stem cells in vitro. Recent investigations highlighting the potential of stem cell transplantation for the treatment of muscular dystrophies are discussed.

Flow cytometric characterization of myogenic cell populations obtained via the preplate technique: potential for rapid isolation of muscle-derived stem cells

Myoblast transplantation has been investigated as a therapy for muscle-related diseases and as a gene delivery vehicle for therapeutic recombinant proteins. Clinical successes involving muscle cell transplantation have been limited, in part because of poor donor cell survival, and the heterogeneous nature of myogenic donor cells has largely been ignored. We have previously reported an isolation technique, preplating, that results in purified myogenic cells that are capable of significantly higher rates of donor cell survival leading to enhanced gene transfer to skeletal muscle. Characterization of these purified cells revealed that they display markers common to stem cells and are capable of multilineage differentiation. This study was performed to phenotypically characterize, by flow cytometry, muscle-derived cell populations obtained by the preplate technique for the purpose of eventually developing a method to quickly identify and isolate viable muscle cells best suited for transplantation. Muscle cell cultures were analyzed for expression of the surface proteins Sca-1, c-Kit, and CD34. We found that the preplate technique purifies distinct myogenic cell subpopulations expressing CD34 alone (Sca-1 negative) and Sca-1 alone (CD34 negative), but that this expression is subject to change with time in culture. Isolation and transplantation of phenotypically pure Sca-1-positive myogenic cells, obtained by magnetic cell sorting, demonstrates the ability to quickly select viable myogenic cells capable of regenerating skeletal muscle and restoring dystrophin expression within dystrophic host skeletal muscle. Flow cytometric described phenotypes will aid in the rapid isolation of specific donor cell populations for muscle cell transplants and muscle cell-mediated gene therapies, thereby enhancing their future success.

Directions in cardiovascular tissue engineering

The generation of tissue replacements or supplements for diseased tissue within the cardiovascular system has been the target of recent tissue engineering efforts. While clinically applicable methodologies remain to be achieved, important foundational experimentation has been performed in recent years to begin the move toward engineered tissue replacement therapy. Inadequacies of current valve, vessel, and other heart prostheses are reviewed briefly, followed by the discussion of selected progress in the supplementation or replacement of each cardiovascular component with tissue constructs. Topics addressed include the endothelialization of bio-prosthetic valves and synthetic vascular grafts, the generation of tissue valve leaflets and vascular conduits, the genetic manipulation of endothelial cells with implications for graft endothelialization, and cardiomyoplasty achieved through cellular and genetic means.

Targeting and ultrasound imaging of microbubble-based contrast agents

Preparation and characterization of targeted microbubbles (ultrasound contrast agents) is described. Specific ligands were attached to the microbubble shell, and ligand-coated microbubbles were selectively attached to various targets, using either an avidin biotin model system or an antigen-antibody system for targeting to live activated endothelial cells. Firm attachment of microbubbles to the target was achieved. Forces necessary to detach microbubbles from the target were estimated to exceed dozens of pN. Microbubbles were bound to the target even in the rapidly moving stream of the aqueous medium. Down to 20 ng of the ultrasound contrast material on the target surface could be detected by the ultrasound imaging with a commercial medical imaging system. At high bubble density on the target surface, strong ultrasound image attenuation was observed.

Microbubbles targeted to intercellular adhesion molecule-1 bind to activated coronary artery endothelial cells

BACKGROUND

Preclinical atherosclerosis is associated with increased endothelial cell (EC) expression of leukocyte adhesion molecules (LAMs), which mediate monocyte adhesion during atherogenesis. Identification of cell-surface LAMs may uniquely allow assessment of endothelial function, but there are no in vivo methods for detecting LAMs. We tested a new microbubble designed to bind to and allow specific ultrasound detection of intercellular adhesion molecule-1 (ICAM-1).

METHODS AND RESULTS

A perfluorobutane gas-filled lipid-derived microsphere with monoclonal antibody to ICAM-1 covalently bound to the bubble shell was synthesized. Bubbles with either nonspecific IgG or no protein on the shell were synthesized as controls. Coverslips of cultured human coronary artery ECs were placed in a parallel-plate perfusion chamber and exposed to 1 of the 3 microbubble species, followed by perfusion with culture medium. Experiments were performed with either normal or interleukin-1beta-activated ECs overexpressing ICAM-1, and bubble adherence was quantified with epifluorescent videomicroscopy. There was limited adherence of control bubbles to normal or activated ECs, whereas a 40-fold increase in adhesion occurred when anti-ICAM-1-conjugated bubbles were exposed to activated ECs compared with normal ECs (8.1+/-3.5 versus 0.21+/-0.09 bubbles per cell, respectively, P<0.001). Although diminished, this difference persisted even after perfusion at higher wall shear rates.

CONCLUSIONS

A gas-filled microbubble with anti-ICAM-1 antibody on its shell specifically binds to activated ECs overexpressing ICAM-1. Diagnostic ultrasound in conjunction with targeted contrast agents has the unique potential to characterize cell phenotype in vivo.

Effect of retroviral transduction on human endothelial cell phenotype and adhesion to Dacron vascular grafts

PURPOSE

Retroviral transduction for genetic enhancement of endothelial cell (EC) anti-thrombotic phenotype offers potential for improving the clinical success of vascular graft seeding; however, application of this technique may bring concomitant alteration in cell functionality.

METHODS

Human microvascular ECs were transduced with a retroviral vector encoding for the marker gene beta-galactosidase. Transduced endothelial cells (rtECs) and nontransduced endothelial cells (ntECs) were evaluated by flow cytometry for expression of intercellular adhesion molecule (ICAM)-1 and tissue factor (TF) on both smooth (coverslips) and graft (Dacron, 6 mm inside diameter) surfaces under static and shear exposed conditions. Graft EC retention was measured after 6-hour pulsatile perfusions. Platelet and neutrophil adherence was measured on perfused coverslips.

RESULTS

Lower levels of ICAM-1 were expressed by rtECs on coverslips under both static (p < 0.01 vs static ntECs) and shear exposed conditions (p < 0.01 vs static and shear ntECs). Accordingly, fewer polymorphonuclear leukocytes adhered to rtEC monolayers (p < 0.01 vs ntECs). No difference in ICAM-1 and TF expression by static graft seeded rtECs and ntECs was observed. However, graft-seeded rtECs that were exposed to wall shear stress displayed less TF than sheared ntECs (p < 0.05). Transduction did not affect EC retention to the sheared graft surface.

CONCLUSIONS

These data suggest that retroviral transduction does not elicit a prothrombotic/proinflammatory phenotype, rather indices of these states appear in some conditions to be reduced. Further, transduction does not adversely affect EC adherence to Dacron graft surfaces under arterial hemodynamics.

Albumin microbubble adherence to human coronary endothelium: implications for assessment of endothelial function using myocardial contrast echocardiography

OBJECTIVES

We hypothesized that sonicated 5% human albumin microbubbles (Albunex) adhere to disrupted vascular endothelium and that this interaction is a marker of endothelial integrity. This study sought to identify sites and determinants of Albunex-endothelial cell (EC) attachment.

BACKGROUND

Under normal conditions, Albunex microbubbles used in myocardial contrast echocardiography (MCE) pass unimpeded through the coronary microcirculation. During pathophysiologic states associated with endothelial dysfunction, however, microbubbles linger in the myocardium despite normal flow. The sites and conditions regulating microbubble adhesion are unknown.

METHODS

Coverslips with cultured human coronary artery ECs were mounted in a parallel plate perfusion system and perfused with a suspension of fluorescein-labeled Albunex in culture medium, followed by a bubble-free wash at a wall shear rate of 100 s-1. To create inflammatory ECs, phorbol myristate acetate was added 4.5 h before perfusion, and flow cytometry was used to confirm an inflammatory response. Perfusions were performed under normal and inflammatory conditions using surfaces of confluent and subconfluent ECs and isolated extracellular matrix. Bubble adherence was quantified in 20 random fields per cover-slip using epifluorescent video microscopy.

RESULTS

No microbubbles adhered to normal confluent ECs, although small numbers adhered to inflamed ECs (0.03 +/- 0.01 bubbles/cell, p < 0.01 vs. normal cells). Fever microbubbles attached to normal versus inflamed matrix of both partially exposed (1,800 +/- 520 vs. 4,100 +/- 1,000 bubbles/mm2, p = 0.05) and completely denuded (2,700 +/- 1,300 vs. 7,200 +/- 1,100 bubbles/ mm2, p < 0.03) endothelium.

CONCLUSIONS

Albunex microbubbles preferentially adhere to inflammatory endothelial extracellular matrix. These data suggest that MCE can be used to noninvasively study endothelial integrity and may have implications for the assessment of preclinical atherosclerotic heart disease.