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Biomedical subjects

A W Flake

Publications and source records attributed to A W Flake.

At least 73 records · Page 4Linked to original sources
PubMed1998

Human bone marrow CD34- cells engraft in vivo and undergo multilineage expression that includes giving rise to CD34+ cells.

We used the human/sheep competitive engraft model to investigate the in vivo engraftment potential of human CD34-, Lin- cells. In three separate studies, transplantation of CD34+, Lin- and CD34-, Lin- cells from the same normal human donors into preimmune fetal sheep resulted in long-term engraftment and multilineage hematopoietic cell/progenitor expression. Human cell/progenitor activities of the CD34+ group were CD3, 0.52%; CD13, 0.36%; CD45, 1.02%; glyA, 1.78%; HLA-DR, 0.99%; colony-forming units (CFU)-Mix, 7.1%; and granulocyte-macrophage CFU (CFU-GM), 13.7%; those of the CD34- group were CD3, 0.24%; CD45, 2.49%; glyA, 0.75%; HLA-DR, 0.3%; CFU-Mix, 7.1%; and CFU-GM, 4.3%. Of special interest was the detection of highly significant numbers (1 x 10[9] cells) of human CD34+ cells in animals transplanted with CD34- cells. Secondary transplantation and limiting dilution studies confirmed the presence of cells with long-term engraftment potential in CD34- populations. The results presented here demonstrate that the CD34- fraction of normal human bone marrow contains cells capable of engraftment and differentiation into CD34+ progenitors and multiple lymphohematopoietic lineages in primary and secondary hosts.

Adult↗
PubMed1997

In utero hematopoietic stem cell transplantation. A status report.

In utero hematopoietic stem cell transplantation is currently in its early stage of development, but it holds considerable promise as a therapeutic approach for the treatment of a large number of congenital hematologic diseases. Experimental evidence supports the concept of the early gestational fetus as a favorable recipient for cellular therapy. Unique aspects of normal hematologic and immunologic ontogeny allow engraftment and long-term persistence of transplanted hematopoietic stem cells without the requirement for myeloablation or immunosuppression. To date, 21 in utero transplants have been reported. Success has been limited to 4 fetuses, all with immunodeficiency disorders. Despite this limited evidence of clinical efficacy, interest in stem cell transplantation has been gaining momentum, and clinical application is likely to increase. Parallel advances in prenatal diagnosis, fetal intervention, and hematopoietic stem cell technology have removed many of the practical, technical, and ethical obstacles to clinical application. This progress has been accompanied by an increase in the number of centers with both the stated interest and perceived expertise to develop clinical programs. However, there is currently limited consensus among investigators on many important issues, such as the mode or timing of in utero transplantation, the ideal source or dose of donor cells, estimation of maternal and fetal risks, appropriate candidate diseases for treatment, and important ethical considerations in counseling and therapy.

Aborted Fetus↗
PubMed1997

Transplantation of hematopoietic stem cells in utero.

Hematopoietic stem cell (HSC) transplantation in children and adults with congenital lymphohematopoietic disorders is limited by donor availability, graft failure, graft-versus-host disease (GVHD) and delayed immunological reconstitution. These problems may be circumvented by transplanting the patient before birth. Prenatal cellular therapy for the treatment of congenital diseases has tremendous theoretical appeal. Potential advantages of prenatal transplantation include: A) fetal immunologic immaturity and the potential for induction of donor-specific tolerance; B) available space in the developing bone marrow for engraftment of donor cells; C) the sterile, protective, fetal environment which provides isolation from environmental pathogens, and D) prevention of clinical manifestations of the disease. Normal hematopoietic and immunologic development during ontogeny creates a "window of opportunity" during which events favor the engraftment of transplanted allogeneic (and xenogeneic) HSC and their proliferation. This is a period in which the fetus is immunologically naive and thus incapable of rejecting the foreign HSC, and the expanding bone marrow spaces allow homing and engraftment of HSC without the need for myeloablation. Experiments in sheep have established the optimal age of the recipient, route of donor cell administration, sources of HSC, and other parameters necessary for the successful engraftment and long-term expression of donor HSC. In preclinical studies, transplantation of CD34-enriched or highly purified populations of human adult bone marrow cells in utero resulted in the long-term engraftment and expression of donor HSC without graft failure and GVHD. The strategies developed in allogeneic and xenogeneic fetal sheep models were used to successfully treat human fetuses with X-linked recessive severe combined immunodeficiency.

Animals↗
PubMed1997

Intrapartum airway management for giant fetal neck masses: the EXIT (ex utero intrapartum treatment) procedure.

OBJECTIVE: Our goal was to review our experience with the EXIT (ex utero intrapartum treatment) procedure in the management of five cases with life-threatening fetal neck masses. STUDY DESIGN: We present a retrospective review of prenatal presentation and course, diagnostic accuracy of imaging studies, intraoperative management, complications, and outcomes. RESULTS: Polyhydramnios was the initial presenting symptom in three of five fetuses with a mean gestational age of 25 +/- 6 weeks. Preterm labor occurred in two patients. Fetal magnetic resonance imaging provided accurate diagnosis in all four cases whereas conventional ultrasonography led to the diagnosis in four of five cases. The mean duration of EXIT was 28 +/- 22 minutes. The mean venous cord blood gas values were pH 7.22 +/- 0.05, PCO2 61 +/- 11 mm Hg, and PO2 42 +/- 8 mm Hg. In four of five cases an airway was successfully secured. CONCLUSIONS: The EXIT procedure provides up to 1 hour of good uteroplacental support and is the procedure of choice to secure an airway in the fetus with a giant neck mass.

Airway Obstruction↗
PubMed1997

A new intraluminal antigastroesophageal reflux procedure in baboons.

BACKGROUND: A new endoscopic intraluminal procedure (valvuloplasty) was designed to provide a simple, easy approach to the cardia and to correct and augment any mechanical deficiencies present. The feasibility, durability, and efficacy of this procedure was tested in 13 baboons. METHODS: The valvuloplasty consisted of an intussusception of the gastroesophageal junction into the stomach to create a nipple-type valve. The configuration of the valve was maintained with eight staples and stability was aided by an intramural injection of sodium morrhuate. Gastrointestinal endoscopy and esophageal manometry were performed before and after the procedure. Competency was determined as the intragastric pressure (yield pressure) and volume (yield volume) needed to result in equalization of gastric and esophageal pressure while distending the stomach with water. Comparisons were made with a group of normal baboons (n = 10). RESULTS: All baboons had a normal eating pattern with none showing any evidence of vomiting or regurgitation. Endoscopic circumferential integrity of the valves was 86% at 6 months. The median lower esophageal sphincter length in the valvuloplasty group was significantly (p < 0.01) increased after the procedure from 21 mm to 30 mm. The median yield pressure (22.1 mm Hg) and yield volume (1,525 ml) of the valvuloplasty group was significantly (p < 0.01) greater than the controls (14 mm Hg and 859 ml). CONCLUSIONS: The valvuloplasty is simple, safe, and durable. It augments mechanical function of the cardia and improves competency.

Animals↗
PubMed1997

Cellular therapy.

From a clinical perspective, prenatal transplantation has tremendous potential to broaden the current indications for reconstitution therapy and to offer a safe, efficacious, and cost-effective alternative to conventional postnatal BMT for many congenital hematopoietic diseases. Experimental work and limited clinical experience offer hope for the future. The primary experimental challenges will be to manipulate the biology of in utero HSC transplantation so that the approach will be safe and broadly applicable. This will require strategies to improve engraftment; use alternative sources of cells safely and effectively; and develop techniques for procurement, ex vivo expansion, and tissue banking of safe donor cells. The clinical challenges in the future will be to identify recipients most likely to benefit from the approach, and to define further the clinical and ethical guidelines for its application.

Female↗
PubMed1997

Fetal surgical intervention.

Over the past 25 years obstetricians have developed multiple techniques to diagnose fetal abnormalities whether they be structural or functional. Such diagnoses have allowed couples the option of pregnancy termination when legally permissible. In selective situations it has become possible to correct some abnormalities. In general, structural abnormalities have suggested surgical approaches, whereas metabolic abnormalities have generally been treated pharmacologically or genetically. Over the past few years there have been a number of advances in surgical therapies, some of which will be detailed here.

Journal Article↗
PubMed1996

CD34+ human marrow cells that express low levels of Kit protein are enriched for long-term marrow-engrafting cells.

Using in utero transplantation into fetal sheep, we examined the capability of human bone marrow CD34+ cells fractionated based on Kit protein expression to provide long-term in vivo engraftment. Twelve hundred to 5,000 CD34+ Kit-, CD34+ Kit(low), and CD34+ Kit(high) cells were injected into a total of 14 preimmune fetal sheep recipients using the amniotic bubble technique. Six fetuses were killed in utero 1.5 months after bone marrow cell transplantation. Two fetuses receiving CD34+ Kit(low) cells showed signs of engraftment according to analysis of CD45+ cells in their bone marrow cells and karyotype studies of the colonies grown in methylcellulose culture. In contrast, two fetuses receiving CD34+ Kit(high) cells and two fetuses receiving CD34+ Kit- cells failed to show evidence of significant engraftment. Two fetuses were absorbed. A total of six fetuses receiving different cell populations were allowed to proceed to term, and the newborn sheep were serially examined for the presence of chimerism. Again, only the two sheep receiving CD34+ Kit(low) cells exhibited signs of engraftment upon serial examination. Earlier in studies of murine hematopoiesis, we have shown stage-specific changes in Kit expression by the progenitors. The studies of human cells reported here are in agreement with observations in mice, and indicate that human hematopoietic stem cells are enriched in the Kit(low) population.

Animals↗
PubMed1996

The human/sheep xenograft model: a large animal model of human hematopoiesis.

Although not 'ideal', xenograft models of human hematopoiesis have proved to be extremely useful experimental systems for the study of the in vivo engraftment/proliferation potential of human hematopoietic stem/progenitor cells (HSC). Among these, the human/sheep xenograft model is unique in several respects. This model takes advantage of fetal immunologic immaturity and developing 'homing' spaces in the fetal bone marrow to obtain donor HSC engraftment in normal recipients without marrow conditioning. This avoids both the possible stromal abnormalities associated with irradiation- and/or chemotherapy-induced immunodeficiency which may limit human HSC engraftment or long-term maintenance of human hematopoiesis, and the use of genetically deficient hosts which may result in restricted donor cell expression. In the human/sheep xenograft model, human HSC (1) colonizes the bone marrow, (2) persists for many years, (3) is capable of multilineage differentiation, (4) retains its ability to respond to human cytokines, and (5) retains its ability to engraft/differentiate in secondary recipients. Another unique aspect of the sheep model is its large size; this permits repeated evaluation of human cell activity in the same chimeric sheep over long periods. The model appears to discriminate between the different populations of human HSC and exhibits a degree of sensitivity that suggests this in utero approach may serve as a biologically relevant model for the identification, characterization, and study of the in vivo potential of human HSC from available sources.

Animals↗
PubMed1996

Correction of congenital diaphragmatic hernia in utero VIII: Response of the hypoplastic lung to tracheal occlusion.

Most fetuses with congenital diaphragmatic hernia (CDH) diagnosed before 24 weeks' gestation die despite optimal postnatal care. In fetuses with liver herniation into the chest, prenatal repair has not been successful. In the course of exploring the pathophysiology of CDH and its repair in fetal lambs, the authors found that obstructing the normal egress of fetal lung fluid enlarges developing fetal lungs, reduces the herniated viscera, and accelerates lung growth, resulting in improved pulmonary function after birth. They developed and tested experimentally a variety of methods to temporarily occlude the fetal trachea, allow fetal lung growth, and reverse the obstruction at birth. The authors applied this strategy of temporary tracheal occlusion in eight human fetuses with CDH and liver herniation at 25 to 28 weeks' gestation. With ongoing experimental and clinical experience, the technique of tracheal occlusion evolved from an internal plug (two patients) to an external clip (six patients), and a technique was developed for unplugging the trachea at the time of birth (Ex Utero Intrapartum Tracheoplasty [EXIT]). Two fetuses had a foam plug placed inside the trachea. The first showed dramatic lung growth in utero and survived; the second (who had a smaller plug to avoid tracheomalacia) showed no demonstrable lung growth and died at birth. Two fetuses had external spring-loaded aneurysm clips placed on the trachea; one was aborted due to tocolytic failure, and the other showed no lung growth (presumed leak) and died 3 months after birth. Four fetuses had metal clips placed on the trachea. All showed dramatic lung growth in utero, with reversal of pulmonary hypoplasia documented after birth. However, all died of nonpulmonary causes. Temporary occlusion of the fetal trachea accelerates fetal lung growth and ameliorates the often fatal pulmonary hypoplasia associated with severe CDH. Although the strategy is physiologically sound and technically feasible, complications encountered during the evolution of these techniques have limited the survival rate. Further evolution of this technique is required before it can be recommended as therapy for fetal pulmonary hypoplasia.

Animals↗
PubMed1996

Fetal surgery for congenital diaphragmatic hernia.

Fetal surgery for congenital diaphragmatic hernia (CDH) is controversial. The rationale for fetal intervention remains as compelling today as it was a decade ago. There continue to be newborns delivered with CDH who have severe enough pulmonary hypoplasia to result in significant morbidity or mortality. During the past decade ECMO, high-frequency ventilation, nitric oxide, surfactant therapy, and other advances in neonatal care have been applied to newborns with severe CDH. Although some would disagree, there is little convincing evidence that these therapies have had a major impact on the morbidity rate and mortality rate of patients with severe CDH. On the other hand, fetal surgery has not yet fulfilled its early promise. Although tremendous strides have been made in operative techniques, fetal monitoring, maternal-fetal anesthesia, and tocolysis, fetal repair of CDH has proved to be a formidable challenge and has not improved on the natural history of the disease. Recent application of tracheal ligation as a relatively simple method to accelerate lung growth in utero has been promising but requires further experience. The purpose of this article is to critically assess whether there is a role for fetal surgery in the treatment of CDH, and, if so, under what selected circumstances.

Adult↗
PubMed1995

Retention and multilineage expression of human hematopoietic stem cells in human-sheep chimeras.

We have taken advantage of the permissive environment of the early gestational age fetus to engraft human hematopoietic stem cells (HSC) into preimmune fetal lambs. The resulting chimeras exhibit long-term multilineage engraftment of human cells in the bone marrow (BM) and peripheral blood (PB). Long-term multilineage reconstitution of second generation recipients by human cells isolated from chimeric sheep BM indicates that the engraftment in this model involved long-term repopulating human HSC. The model appears to be sensitive enough to detect relatively small numbers of transplanted HSC from pre- and postnatal human sources. Finally, transplantation of mature T lymphocyte-containing cells from a variety of sources results in lethal graft-versus-host disease (GVHD), analogous to clinical BM transplantation, suggesting that, at least in some respects, the model is biologically relevant. The human-sheep model is promising and may have important advantages over murine models for the in vivo study of normal and abnormal hematopoiesis and as a potential assay system for human HSC.

Animals↗
PubMed1995

Sequential urinalysis improves evaluation of fetal renal function in obstructive uropathy.

OBJECTIVES: The purpose of our study was to determine whether sequential vesicocenteses improve the evaluation of renal damage, compared with single urine sampling in obstructive uropathy. STUDY DESIGN: A total of 29 fetuses with complete obstructive uropathy underwent a minimum of three sequential complete vesicocenteses at 48- to 72-hour intervals. First and last urine values were analyzed for multiple parameters. The ability of first versus last urine values to detect the presence of renal damage was compared according to postnatal or fetal autopsy information. RESULTS: Fetuses with minimal renal damage had patterns of decreasing hypertonicity and last urine values below cutoff thresholds indicative of favorable prognosis. Fetuses with significant renal damage had higher initial values and patterns of increasing hypertonicity. For five of six parameters, last urine samples were more predictive of renal damage than first urine samples. CONCLUSION: Last urine values together with pattern-of-change trend analysis after serial vesicocenteses improve diagnostic precision in fetuses with complete obstructive uropathy.

Electrolytes↗
PubMed1995

The 'PLUG' odyssey: adventures in experimental fetal tracheal occlusion.

In animal experiments, it has been shown that tracheal occlusion counteracts the pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH). Successful clinical implementation requires a reliable, reversible, and atraumatic technique of occluding the fetal trachea. With this clinical goal in mind, the authors evaluated the following three methods of tracheal occlusion in a fetal lamb CDH model: (1) an occluded foam-cuffed endotracheal tube, (2) a foam-cuffed endotracheal tube with a magnetically controlled flow valve, and (3) a tracheal insert constructed of a water-impermeable, expandable, polymeric foam, which is placed by a translaryngeal approach. The foam-cuffed endotracheal tube did not provide consistently reliable fetal tracheal occlusion. Although the magnetically triggered flow valve functioned well, it was not necessary to open the valve in utero (to prevent overdistension of the lungs), and the presence of the valve contributed to several occlusive failures. In contrast, the foam insert was easy to position and to remove from the trachea, while providing reliable tracheal occlusion for several weeks with consequent enlarged fetal lungs, increased lung fluid volumes, complete reduction of abdominal viscera, and improved pulmonary gas exchange after birth. Bronchoscopic evaluation of the foam-occluded neonatal tracheas showed little or no tracheal damage, which was confirmed during necropsy by gross and histological examination. Translaryngeal placement of a compressible, water-impermeable polymeric foam appears to be a simple and safe technique to achieve fetal tracheal occlusion.

Animals↗
PubMed1995

Fetal surgery.

Fetal surgery, as defined for the purpose of this chapter, is the act of opening the gravid uterus, surgically correcting a fetal abnormality, and returning the fetus to the uterus for postoperative recovery and continued gestational development. By this definition, human fetal surgery has now been performed for more than a decade, primarily at a single center (1). Tremendous progress has been made in our understanding of the natural history and pathophysiology of fetal disease, in solving the technical challenges of fetal surgery, and in intra- and postoperative care and monitoring of the maternal-fetal unit. However, success and general application of fetal surgery continue to be limited by a number of unsolved and formidable problems. The most important of these is the control of preterm labor, which is the Achilles heel of fetal surgery. Preterm labor is to the infantile field of fetal surgery what rejection was to the field of transplantation. The discovery of effective tocolysis would be analogous to the development of effective immunosuppression and would allow fetal surgery to achieve its full potential. In addition, less invasive methods of operating on the fetus are emerging that will further reduce the maternal and fetal risk of this currently highly invasive treatment.

Adolescent↗
PubMed1995

Enhancement of human hematopoiesis by mast cell growth factor in human-sheep chimeras created by the in utero transplantation of human fetal hematopoietic cells.

We have previously described a unique model of long-term, multilineage, human hematopoietic chimerism in sheep created by the in utero transplantation of human hematopoietic stem cells (HSC) into pre-immune fetal lambs. In this study, we examined the effect of chronic administration of recombinant human mast cell growth factor (rhMGF) on 1) human cell engraftment in pre-immune sheep and 2) human cell expression in human-sheep chimeras at 2-years posttransplant. rhMGF (25 micrograms/kg) or saline was administered in utero via chronic intraperitoneal (IP) catheters to three separate sets of twin fetuses on alternate days for 10 doses following transplantation of human HSC. Flow-cytometric and karyotype analyses of peripheral blood from two sets of twins at 45-days posttransplant and of peripheral blood from the remaining set of twins at birth revealed a significant increase in percentages of donor (human) progenitors and cells in rhMGF-treated lambs. rhMGF (60 micrograms/kg/day) was also administered by IP injection to two, 2 year-old, human-sheep chimeras for 18 consecutive days. Flow-cytometric analysis of peripheral blood and bone marrow revealed a six- to seven-fold increase in human cell expression. The effect on early human progenitors (i.e., colony-forming unit-mix [CFU-Mix], CFU granulocyte/macrophage [CFU-GM], and burst-forming unit-erythroid [BFU-E]) was determined by karyotype analysis of individual colonies grown under conditions favoring human cell growth. A three- to five-fold increase in human CFU-Mix and BFU-E occurred with a minimal increase in CFU-GM. This in vivo study supports in vitro data suggesting that MGF is a powerful regulator of human hematopoiesis and preferentially stimulates early hematopoietic progenitors. It also supports the potential value of the human-sheep model for the in vivo study of normal and abnormal human hematopoiesis.

Animals↗