Biomedical subjects
Publications and source records attributed to A W Flake.
Repair of fetal diaphragmatic hernia has proven technically difficult especially when the left lobe of the fetal liver is incarcerated in the chest. A step-wise approach from both above and below the diaphragm solves several frustrating technical problems.
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Extensive experimental work suggests that repair of congenital diaphragmatic hernia (CDH) in utero may salvage severely affected fetuses who otherwise have a high expected mortality despite optimal postnatal care including extracorporeal membrane oxygenation (ECMO). We have reported that repair of CDH in utero is physiologically sound and safe for the mother, but technically difficult especially when the liver is herniated into the fetal chest. In the 3 years since our last report (1989 to 1991), 61 additional patients were referred for consideration of in utero repair. Fetal repair was attempted in 14 with severe isolated left CDH diagnosed before 24 weeks gestation. Five fetuses died intraoperatively, from technical problems related to reduction of incarcerated liver and uterine contractions--problems which have subsequently been surmounted. Nine patients were successfully repaired. Four babies survived, two delivered prematurely and died, and three died in utero within 48 hours of repair. Intraoperative technical problems have been overcome; the factors limiting successful outcome are postoperative physiologic management of the maternal-fetal unit and effective tocolysis to control preterm labor.
Despite significant improvements in postnatal care of infants with congenital diaphragmatic hernia (CDH), mortality remains high. Delayed surgery, improved respiratory support, and extracorporeal membrane oxygenation (ECMO) have undoubtedly improved outcome for babies diagnosed after birth, but a prospective study of 52 fetuses with isolated, potentially correctable CDH diagnosed prior to 25 weeks gestation showed that 60% died despite optimal care presently available after birth. Repair of CDH before birth, although physiologically compelling, has proven exceedingly difficult especially when the fetal liver is incarcerated in the chest. Our recent experience suggests that intraoperative technical problems are surmountable, but a trial will be necessary to determine if prenatal repair can improve outcome for babies with diaphragmatic hernia.
The fetus with sacrococcygeal teratoma (SCT) is at high risk for prenatal and perinatal complications. The natural history and pathophysiology of fetal SCT is different than that of postnatally diagnosed SCT, and has only recently been defined. Survival of fetuses with SCT is dependent on anticipation and recognition of pathophysiologic events, and optimal obstetric and surgical management. In a subset of fetuses with SCT, fetal resection of tumor may offer the only hope for survival.
Complications of gastroesophageal reflux are common in adults and children. A variety of surgical procedures have been successfully used to treat this condition. All current techniques require open surgery and are associated with significant morbidity and mortality, particularly in the high risk, neurologically damaged child. The authors have developed a novel method of creating a gastric fundoplication using an endoscopic transgastric approach in pigs. The procedure involves the creation of an esophageal intussusception into the stomach under direct vision with an endoscope. The gastric fundus is then plicated around the esophagus using a custom stapling device. The transgastric approach allows creation of a fundoplication, is easily performed, is potentially effective at preventing gastroesophageal reflux, and has the obvious advantages of minimally invasive surgery over open techniques of fundoplication.
Hemopoietic stem cells from human fetal liver were transplanted in utero into preimmune fetal sheep (48-54 days of gestation). The fate of donor cells was followed using karyotype analysis, by immunofluorescence labeling with anti-CD antibodies, and by fluorescent in situ hybridization using human-specific DNA probes. Engraftment occurred in 13 of 33 recipients. Of five live born sheep that exhibited chimerism, all expressed human cells in the marrow, whereas three expressed them in blood as well. Engraftment was multilineage (erythroid, myeloid, and lymphoid) and human hemopoietic progenitors (multipotent colony-forming units, colony-forming units-granulocyte, macrophage, and erythroid burst-forming units) capable of forming colonies in vitro were detected in all five lambs for greater than 2 yr. These progenitors responded to human-specific growth factors both in vitro and in vivo. Thus the administration of recombinant human IL-3 and granulocyte macrophage-colony-stimulating factor to chimeric sheep resulted in a 2.1-3.4-fold increase in the relative expression of donor (human) cells. These results demonstrate that the permissive environment of the preimmune fetal sheep provides suitable conditions for the engraftment and long-term multilineage expression of human hemopoietic stem cells in a large animal model. In this model, donor human cells appear to retain certain phenotypic and functional characteristics that can be used to manipulate the size of donor cell pool.
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The preimmune status of the early gestational age fetus provides a permissive environment that bypasses the immunological barrier and permits the engraftment and expression of hemopoietic stem cells (HSC). We used in utero approach to establish long term (greater than 2 years) engraftment and expression of human fetal liver HSC in sheep. Engraftment occurred in 40% (13 of 33) of the recipients. Of 5 live born sheep, all were chimeric. Engraftment was multilineage, involving lymphoid, myeloid and erythroid donor (human) cells. Interestingly, these progenitors have continued to exhibit responsiveness to human specific growth factors both in vitro and in vivo. Therefore, the integration of human HSC into the hemopoietic framework of the host appeared to be incomplete, with donor progenitors retaining certain phenotypic characteristics that may be exploited to preferentially manipulate the donor (human) cell population in these animals. Donor HSC primarily seeded the host bone marrow. Since the donor cells were of liver origin and the host liver at the time of transplantation was the major hemopoietic organ, this near exclusive seeding to the marrow indicates the greater affinity of marrow for the homing HSC. Nonetheless, no cells of donor origin appeared in the host circulation until the perinatal period, suggesting that donor HSC expand with the developing marrow spaces, but do not undergo terminal differentiation. The absence of a significant immunological barrier and the availability of expanding marrow homing sites render the fetus an excellent host (and donor) for HSC transplantation.
In the present work we used allogeneic in utero transplantation of fetal stem cells in sheep and monkeys. Thus, both the donor and recipient cells had preimmune status. We showed engraftment of allogeneic stem cells in the tolerant environment of the host. The engrafted cells showed trilineage (lymphoid, erythroid and myeloid) expression of differentiation. Long term maintenance of these engrafted cells was observed. We also demonstrated that ex vivo incubation of donor cells with growth factor can enhance the engraftment. Moreover, we have shown that the engrafted cells respond to phlebotomy in the same manner as endogenous cells. We, therefore, conclude that (a) Preimmune fetuses are highly suitable for stem cell transplantation both as donors and recipients. (b) Engraftment can be modulated by brief maneuvers such as ex vivo manipulation. (c) Functionally, the engrafted cells can respond to hemopoietic stimuli in a similar manner as the endogenous cells. Implications of this transplantation system in clinical medicine is discussed. Everyone who is involved in organ transplantation must, sooner or later, come to grips with immunological barriers which establishes the individuality of each organism by recognizing "self" from "non-self". Transplanters must overcome this barrier, if allogeneic organ transplantation is to be successful. In the case of hemopoietic stem cells (HSC), where immunocompetent cells are transplanted, graft-vs-host disease (GVHD) may also be expected. Tolerance can be expected when the recipient is genetically immunodeficient, thus being unable to mount an immunological barrier.(ABSTRACT TRUNCATED AT 250 WORDS)
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Pediatric liver transplantation continues to be limited by the availability of suitable liver donors, a factor that restricts programmatic development and ultimately contributes to death on the recipient waiting list. We report the application of segmental liver transplantation as a technique to address both these problems as well as improving the outcome of the child undergoing the transplant procedure. Since 1986, 37 children have undergone orthotopic liver transplantation. Twenty-three children have received whole-organ grafts; 81% survived. Of those receiving whole-organ grafts, 15% had arterial thrombotic complications and 23% required retransplantation. More importantly, 29% of those children listed for transplantation died while waiting for a donor organ to become available, with a mean interval of 1.7 months (range, 2 days to 4.5 months). Since July 1988, segmental liver transplantation has been a component of our therapeutic armamentarium, and of the past 20 liver recipients, 16 have received a left lobe segmental graft. The results of the segmental transplant series have shown striking improvements. First, no child has died while awaiting donor organ availability. Second, segmental liver recipient survival is equivalent to that of whole-organ graft recipients (81%). Third, hepatic arterial thrombosis, especially a problem in high-risk infant transplants, was reduced by this technique (5%). Retransplantation due to graft complications has not increased (21%). These data suggest a vital role for segmental liver transplantation not only as a remedial salvage procedure for the critically ill child, but also as a primary transplant option.
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Fetal sacrococcygeal teratoma (SCT) is being recognized with increasing frequency. Placentomegaly and hydrops fetalis are preterminal events, and it has been suggested that fetal death may be due to high-output cardiac failure from arteriovenous shunting through the tumor. We had a chance to examine this hypothesis when a 21-week fetus presented with a huge sacrococcygeal teratoma. There were marked placentomegaly, cardiomegaly, hyperdynamic ventricles, and a pericardial effusion. Doppler studies showed tremendous flow through the SCT with extreme enlargement of the inferior vena cava, consistent with congestive heart failure from increased flow through the tumor. Hydrops developed, and the fetus was delivered because of placental abruption. This case provides supportive evidence that the teratoma acts as a large arteriovenous shunt, causing high-output cardiac failure. We have now collected 18 more cases of sacrococcygeal teratoma diagnosed in utero. Of the total 45 cases of fetal SCT, 9 had placentomegaly and/or fetal hydrops and all 9 fetuses died in utero or shortly after birth. We conclude that the only hope for survival in these severely affected fetuses is to reduce blood flow to the tumor before birth.
The development of fetal surgical techniques has made the antenatal correction of congenital defects possible. These techniques have evolved from trials with animal models, permitting increasingly sophisticated operations with low morbidity and mortality. Experimental models range from large animals offering longer gestations but with single pregnancies and high cost, to smaller animals offering multiple pregnancies at reduced cost but with shorter gestations. This paper describes operative techniques in the fetal rabbit and its advantages as a fetal surgical model. Experience with the pregnant rabbit has shown it to be a suitable surgical model for several reasons. Pregnancies are multiple, increasing cost effectiveness and permitting operation on up to eight fetuses per litter without fetal loss. Techniques that promote fetal survival include local housing of does several days prior to operation and preoperative sedation. Spontaneous mask ventilation provides ease of anesthetic administration and titration. Overall surgery is well tolerated with a low incidence of intraoperative complications. Rabbit models have been used in the study of transamniotic fetal feeding, abdominal wall defects, and wound healing. These techniques have resulted in postoperative fetal viability approaching 90%, with negligible maternal mortality in over 4000 fetal operations, thereby making the rabbit a manageable cost-effective model of fetal surgery.
To investigate the long-term success of heart transplantation in newborn infants who have complex congenital heart disease, we have developed a model of heterotopic heart transplantation in immature pigs. We chose the heterotopic technique because it is simple, does not require cardiopulmonary bypass or heparin, allows for significant size disparity between the recipient and donor hearts, and allows for experimental comparisons between the two hearts. Small newborn piglet hearts are harvested, prepared, and then transplanted into the left chest of larger weanling pigs to augment or substitute for the native left ventricle. Preliminary data from transplants into 49 pigs suggest that the technique is technically possible, the pigs can be immunosuppressed over the long term, and the donor heart can contribute hemodynamically. Experimentally, the model is well designed for the investigation of issues critical for the long-term success of heart transplantation in infants and children, including growth and development, optimal long-term immunosuppression, differences in immunotolerance, and the study of coronary obliterative disease. Clinically, the model has potential applicability in congenital heart anomalies if one native functioning atrium and ventricle are present.
The absorbable stapling device was used in 22 hysterotomies in gravid rhesus monkeys. The efficacy of the device, subsequent fertility and delivery route, fetal effects, and pathohistology were all studied. No statistically significant difference between experimental and control animals was noted.
Retroviral-mediated gene transfer was used to insert a Neo R gene into fetal sheep hematopoietic cells obtained by exchange transfusion from lambs in utero. After gene transfer the cells were returned to the donor fetus. The lambs were examined after birth for the presence of a functioning Neo R gene. Of ten analyzable animals, six were positive for G418 resistant progenitor cells (CFU-Mix, CFU-C, BFU-E, CFU-E). Two animals were studied for extended periods of time: 8 and 24 months. Each has demonstrated a pattern wherein positive periods are interspersed with times when there were no detectable G418-resistant cells. We conclude that retroviral-mediated gene transfer can be used to insert genes into early progenitor cells of fetal sheep in utero and that the animals can continue to demonstrate blood cells expressing the gene for more than 2 years after birth. This is a US government work. There are no restrictions on its use.