In utero hematopoietic cell transplantation--recent progress and the potential for clinical application

In Utero Cell Treatment of Hemophilia A Mice via Human Amniotic Fluid Mesenchymal Stromal Cell Engraftment

Hemophilia is a genetic disorder linked to the sex chromosomes, resulting in impaired blood clotting due to insufficient intrinsic coagulation factors. There are approximately one million individuals worldwide with hemophilia, with hemophilia A being the most prevalent form. The current treatment for hemophilia A involves the administration of clotting factor VIII (FVIII) through regular and costly injections, which only provide temporary relief and pose inconveniences to patients. In utero transplantation (IUT) is an innovative method for addressing genetic disorders, taking advantage of the underdeveloped immune system of the fetus. This allows mesenchymal stromal cells to play a role in fetal development and potentially correct genetic abnormalities. The objective of this study was to assess the potential recovery of coagulation disorders in FVIII knockout hemophilia A mice through the administration of human amniotic fluid mesenchymal stromal cells (hAFMSCs) via IUT at the D14.5 fetal stage. The findings revealed that the transplanted human cells exhibited fusion with the recipient liver, with a ratio of approximately one human cell per 10,000 mouse cells and produced human FVIII protein in the livers of IUT-treated mice. Hemophilia A pups born to IUT recipients demonstrated substantial improvement in their coagulation issues from birth throughout the growth period of up to 12 weeks of age. Moreover, FVIII activity reached its peak at 6 weeks of age, while the levels of FVIII inhibitors remained relatively low during the 12-week testing period in mice with hemophilia. In conclusion, the results indicated that prenatal intrahepatic therapy using hAFMSCs has the potential to improve clotting issues in FVIII knockout mice, suggesting it as a potential clinical treatment for individuals with hemophilia A.

Experimental and clinical progress of in utero hematopoietic cell transplantation therapy for congenital disorders

In utero hematopoietic cell transplantation (IUHCT) is considered a potentially efficient therapeutic approach with relatively few side effects, compared to adult hematopoietic cell transplantation, for various hematological genetic disorders. The principle of IUHCT has been extensively studied in rodent models and in some large animals with close evolutionary similarities to human beings. However, IUHCT has only been used to rebuild human T cell immunity in certain patients with inherent immunodeficiencies. This review will first summarize the animal models utilized for IUHCT investigations and describe the associated outcomes. Recent advances and potential barriers for successful IUHCT are discussed, followed by possible strategies to overcome these barriers experimentally. Lastly, we will outline the progress made towards utilizing IUHCT to treat inherent disorders for patients, list out associated limitations and propose feasible means to promote the efficacy of IUHCT clinically.

Routing pathway of syngeneic donor hematopoietic stem cells after simple intra-amniotic delivery

BACKGROUND

We sought to determine the pathway through which syngeneic hematopoietic stem cells (HSCs) delivered into the amniotic fluid can reach the fetal circulation.

METHODS

Lewis rat fetuses were divided in two groups based on the content of intra-amniotic injections performed on gestational day 17 (E17; term=E21-22): either a suspension of luciferase-labeled syngeneic HSCs (n = 137), or acellular luciferase (n = 44). Samples from placenta, chorion, amnion, amniotic fluid, umbilical cord, and 8 fetal sites were procured at 5 daily time points thereafter until term for analysis.

RESULTS

When controlled by acellular luciferase, donor HSCs were identified in the amnion, chorion, placenta, and amniotic fluid of fetuses receiving cells at all time points (p = 0.033 to <0.001), peaking first at the amnion and subsequently at the chorion and placenta. Cells could be detected in the fetal liver as early as day 1, progressively expanding to all the other fetal sites over time, in parallel to their increased presence in the chorion and placenta.

CONCLUSIONS

The chronology of syngeneic donor hematopoietic stem cell trafficking after intra-amniotic injection is suggestive of controlled routing through the gestational membranes and placenta. Hematogenous donor cell routing is a constituent of transamniotic hematopoietic stem cell therapy, significantly expanding its potential applications.

A new ethical framework to determine acceptable risks in fetal therapy trials

OBJECTIVE

Fetal therapy trials pose complex ethical challenges because risks and benefits to both fetuses and pregnant persons must be considered. Existing regulatory guidance is limited and many proposed ethical frameworks have unnecessarily restrictive criteria that would block the development and implementation of important new fetal therapies. We aimed to develop a new ethical framework for assessing the risks and benefits of fetal therapy trials.

METHODS

We reviewed existing regulatory and ethical guidance on fetal therapy trials. We used conceptual analysis to design a new ethical framework, which is grounded in general ethical principles for clinical research.

RESULTS

We propose a new framework for assessing the risks and benefits of fetal therapy trials. We suggest that the potential benefits of a fetal therapy trial - for the fetus, the pregnant person, and society - should outweigh the risks for the fetus and the pregnant person. Furthermore, the risk-benefit profile for just the fetus and the risk-benefit profile for just the pregnant person should be appropriate.

CONCLUSIONS

We hope that this new framework will permit important studies while protecting pregnant persons and fetuses from disproportionate harms.

A New Ethical Framework for Assessing the Unique Challenges of Fetal Therapy Trials

New fetal therapies offer important prospects for improving health. However, having to consider both the fetus and the pregnant woman makes the risk-benefit analysis of fetal therapy trials challenging. Regulatory guidance is limited, and proposed ethical frameworks are overly restrictive or permissive. We propose a new ethical framework for fetal therapy research. First, we argue that considering only biomedical benefits fails to capture all relevant interests. Thus, we endorse expanding the considered benefits to include evidence-based psychosocial effects of fetal therapies. Second, we reject the commonly proposed categorical risk and/or benefit thresholds for assessing fetal therapy research (e.g., only for life-threatening conditions). Instead, we propose that the individual risks for the pregnant woman and the fetus should be justified by the benefits for them and the study's social value. Studies that meet this overall proportionality criterion but have mildly unfavorable risk-benefit ratios for pregnant women and/or fetuses may be acceptable.

Targeted drug delivery for maternal and perinatal health: Challenges and opportunities

Pre-existing conditions at reproductive age, and complications arising during pregnancy can be detrimental to maternal and fetal health. Current therapies to combat obstetric disorders are limited due to the inherent complexity of pregnancy, and can have harmful effects on developing fetus. Emerging research shows intricate signaling between the cells from mother and fetus at maternal-fetal interface, providing unique opportunities for interventions specifically targeted to the mother, fetus, or placenta. Advancements in nanotechnology, stem-cell biology and gene therapy have resulted in target-specific treatments with promising results in pre-clinical maternal and fetal disorder models. Comprehensive understanding of the effect of physicochemical properties of delivery systems on their uptake, retention and accumulation across placenta will help in the better diagnosis and treatment of perinatal disorders. This review describes the factors leading to obstetric complications along with their effect on pregnancy outcomes, and discusses key targeted therapeutic strategies for addressing conditions related to maternal and fetal health.

Fetal hematogenous routing of a donor hematopoietic stem cell line in a healthy syngeneic model of transamniotic stem cell therapy

BACKGROUND/PURPOSE

In utero administration of hematopoietic stem cells (HSCs) has a variety of actual or potential clinical applications but is hindered by invasive, morbid administration techniques. We sought to determine whether donor HSCs could reach the fetal circulation after simple intra-amniotic delivery in a syngeneic rat model of transamniotic stem cell therapy (TRASCET).

METHODS

Pregnant Lewis rat dams underwent volume-matched intra-amniotic injections in all fetuses (n = 90) on gestational day 17 (E17; term=E21-22) of a suspension of commercially available syngeneic Lewis rat HSCs labeled with luciferase (n = 37 fetuses) or an acellular suspension of recombinant luciferase (n = 53). HSC phenotype was confirmed by flow cytometry. Fetuses were euthanized at term for screening of luciferase activity at select anatomical sites. Statistical comparisons were by Fisher's exact test.

RESULTS

Among survivors (47/90; 52.2%), donor HSCs were identified selectively in the placenta (p = 0.003), umbilical cord (p < 0.001), bone marrow (p < 0.001), thymus (p = 0.009), bowel (p = 0.003), kidney (p = 0.022), and skin (p < 0.001) when compared with acellular luciferase controls.

CONCLUSIONS

Donor hematopoietic stem cells undergo hematogenous routing and can reach the fetal bone marrow after simple intra-amniotic delivery in a syngeneic rat model. Transamniotic stem cell therapy may become a practicable, minimally invasive strategy for the prenatal administration of these cells.

Fetal interventions for congenital renal anomalies

Congenital abnormalities of the kidney and urinary tract (CAKUT) represent 20% of prenatally diagnosed congenital abnormalities. Although the majority of these abnormalities do not require intervention either pre or postnatally, there is a subset of patients whose disease is so severe that it may warrant intervention prior to delivery to prevent morbidity and mortality. These cases consist of patients with moderate lower urinary tract obstruction (LUTO) in which vesicocentesis, shunting or cystoscopy are options and patients with early pregnancy renal anhydramnios (EPRA) in whom amnioinfusion therapy may be an option. The main causes of EPRA are congenital bilateral renal agenesis (CoBRA), cystic kidney disease (CKD) and severe LUTO. Untreated, EPRA is universally fatal secondary to anhydramnios induced pulmonary hypoplasia. The evidence regarding therapy for LUTO is limited and the stopped early PLUTO (Percutaneous Shunting in Lower Urinary Tract Obstruction) trial was unable to provide definitive answers about patient selection. Evidence for EPRA therapy is also scant. Serial amnioinfusions have shown promise in cases of EPRA due to CoBRA or renal failure and this treatment modality forms the basis of the ongoing NIH funded RAFT (Renal Anhydramnios Fetal Therapy) trial. At present, there is consensus that treatment for EPRA should only occur in the setting of a clinical trial.

The Theoretical Basis of In Utero Hematopoietic Stem Cell Transplantation and Its Use in the Treatment of Blood Disorders

Since its conception, prenatal therapy has been successful in correction of mainly anatomical defects, although the range of application has been limited. Research into minimally invasive fetal surgery techniques and prenatal molecular diagnostics has facilitated the development of in utero stem cell transplantation (IUT)-a method of delivering healthy stem cells to the early gestation fetus with the hope of engraftment, proliferation, and migration to the appropriate hematopoietic compartment. An area of application that shows promise is the treatment of hematopoietic disorders like hemoglobinopathies. The therapeutic rationale of IUT with hematopoietic stem cells (HSCs) is based on the proposed advantages the fetal environment offers based on its unique physiology. These advantages include the immature immune system facilitating the development of donor-specific tolerance, the natural migration of endogenous hematopoietic cells providing space for homing and engraftment of donor cells, and the fetal environment providing HSCs with the same opportunity to survive and proliferate regardless of their origin (donor or host). Maternal immune tolerance to the fetus and placenta also implies that the maternal environment could be accepting of donor cells. In theory, the fetus is a perfect recipient for stem cell transplant. Clinically, however, IUT is yet to see widespread success calling into question these assumptions of fetal physiology. This review aims to discuss and evaluate research surrounding these key assumptions and the clinical success of IUT in the treatment of thalassemia.

In Utero Hematopoietic Cell Transplantation Does Not Alter the Germ Line

BACKGROUND

In utero hematopoietic cell transplantation (IUHCT) has been demonstrated to reliably generate chimeric offspring. This technique introduces transplanted cells into a fetus while the immune system is still developing, allowing for engraftment without the need for myeloablation. However, little is known about the effect of engraftment on the gonadal tissue or within the germ line of the resultant chimeras.

MATERIALS AND METHODS

BALB/cJ mice pups were injected with B6-green fluorescent protein mononuclear bone marrow (BM) cells at gestational ages E13 or E14. Two female and two male chimeras were then crossbred with untreated mice. The gonadal tissue of the chimeras was evaluated with fluorescent stereomicroscopy and green fluorescent protein histologic staining. The progeny of the cross-bred mice was analyzed using flow cytometric evaluation of both the peripheral blood and BM.

RESULTS

Although transplanted cells engrafted within the gonads, no evidence of chimerism was found in oocytes or spermatogonia of female and male mice treated with IUHCT, respectively. Crossbreeding chimeric mice with untreated mice generated progeny without evidence of chimerism in peripheral blood and BM.

CONCLUSIONS

IUHCT yields chimeric mice that have engrafted cells within the gonads but not within the germ line itself. Correspondingly, progeny from the unaltered germ line has no detectable chimerism. This has clinical implications as the offspring of future patients treated with IUHCT would carry the disease for which their parents were treated with IUHCT.

Successful in utero stem cell transplantation in X-linked severe combined immunodeficiency

IUT enables rapid immune reconstitution and avoids many clinical and economic problems; however, the indication is still limited. IUT may be a treatment option in select cases, eg, fetuses exposed to a significant infectious risk, where a matched sibling donor exists.

Prenatal stem cell therapy for inherited diseases: Past, present, and future treatment strategies

Imagine the profits in quality of life that can be made by treating inherited diseases early in life, maybe even before birth! Immense cost savings can also be made by treating diseases promptly. Hence, prenatal stem cell therapy holds great promise for developing new and early‐stage treatment strategies for several diseases. Successful prenatal stem cell therapy would represent a major step forward in the management of patients with hematological, metabolic, or immunological disorders. However, treatment before birth has several limitations, including ethical issues. In this review, we summarize the past, the present, and the future of prenatal stem cell therapy, which includes an overview of different stem cell types, preclinical studies, and clinical attempts treating various diseases. We also discuss the current challenges and future strategies for prenatal stem cell therapy and also new approaches, which may lead to advancement in the management of patients with severe incurable diseases.

Transamniotic Stem Cell Therapy

Transamniotic stem cell therapy (TRASCET) is a novel prenatal therapeutic alternative for the treatment of congenital anomalies. It is based upon the principle of augmenting the pre-existing biological role of select populations of fetal stem cells for targeted therapeutic benefit. For example, amniotic fluid-derived mesenchymal stem cells (afMSCs) play an integral role in fetal tissue repair, validating the use of afMSCs in regenerative strategies. The simple intra-amniotic delivery of these cells in expanded numbers via TRASCET has been shown to promote the repair of and/or significantly ameliorate the effects associated with major congenital anomalies such as neural tube and abdominal wall defects. For example, TRASCET can induce partial or complete coverage of experimental spina bifida through the formation of a host-derived rudimentary neoskin, thus protecting the spinal cord from further damage secondary to amniotic fluid exposure. Furthermore, TRASCET can significantly reduce the bowel inflammation associated with gastroschisis, a common major abdominal wall defect. After intra-amniotic injection, donor stem cells home to the placenta and the fetal bone marrow in the spina bifida model, suggesting a role for hematogenous cell routing rather than direct defect seeding. Therefore, the expansion of TRASCET to congenital diseases without amniotic fluid exposure, such as congenital diaphragmatic hernia, as well as to maternal diseases, is currently under investigation in this emerging and evolving field of fetal stem cell therapy.

Intravenous and Intra-amniotic In Utero Transplantation in the Murine Model

In utero transplantation (IUT) is a unique and versatile mode of therapy that can be used to introduce stem cells, viral vectors, or any other substances early in the gestation. The rationale behind IUT for therapeutic purposes is based on the small size of the fetus, the fetal immunologic immaturity, the accessibility and proliferative nature of the fetal stem or progenitor cells, and the potential to treat a disease or the onset of symptoms prior to birth. Taking advantage of these normal developmental properties of the fetus, the delivery of hematopoietic stem cells (HSC) via an IUT has the potential to treat congenital hematologic disorders such as sickle cell disease, without the required myeloablative or immunosuppressive conditioning required for postnatal HSC transplants. Similarly, the accessibility of progenitor cells in multiple organs during development potentially allows for a more efficient targeting of stem/progenitor cells following an IUT of viral vectors for gene therapy or genome editing. Additionally, IUT can be used to study normal developmental processes including, but not limited to, the development of immunologic tolerance. The murine model provides a valuable and affordable means to understanding the potential and limitations of IUT prior to pre-clinical large animal studies and an eventual clinical application. Here, we describe a protocol for performing an IUT in the murine fetus through intravenous and intra-amniotic routes. This protocol has been used successfully to elucidate the necessary conditions and mechanisms behind in utero hematopoietic stem cell transplantation, tolerance induction, and in utero gene therapy.

Preclinical Canine Model of Graft-versus-Host Disease after In Utero Hematopoietic Cell Transplantation

In utero hematopoietic cell transplantation (IUHCT) offers the potential to achieve allogeneic engraftment and associated donor-specific tolerance without the need for toxic conditioning, as we have previously demonstrated in the murine and canine models. This strategy holds great promise in the treatment of many hematopoietic disorders, including the hemoglobinopathies. Graft-versus-host disease (GVHD) represents the greatest theoretical risk of IUHCT and has never been characterized in the context of IUHCT. We recently described a preclinical canine model of IUHCT, allowing further study of the technique and its complications. We aimed to establish a threshold T cell dose for IUHCT-induced GVHD in the haploidentical canine model and to define the GVHD phenotype. Using a range of T cell concentrations within the donor inoculum, we were able to characterize the phenotype of IUHCT-induced GVHD and establish a clear threshold for its induction between 3% and 5% graft CD3⁺ cell content. Given the complete absence of GVHD at CD3 doses of 1% to 3% and the excellent engraftment with the lowest dose, there is a safe therapeutic index for a clinical trial of IUHCT.

Systemic multilineage engraftment in mice after in utero transplantation with human hematopoietic stem cells

IUHCT of human cord blood-derived CD34⁺ cells into fetal NSG mice results in systemic multilineage engraftment with human cells.Preconditioning with in utero injection of an anti-c-Kit receptor antibody (ACK2) results in an improved rate of engraftment.

Transamniotic stem cell therapy: a novel strategy for the prenatal management of congenital anomalies

Transamniotic stem cell therapy, or TRASCET, is an emerging therapeutic concept for the management of congenital anomalies based on the augmentation of the biological role of select populations of stem cells that already occur in the amniotic fluid, for targeted therapeutic benefit. Amniotic fluid-derived mesenchymal stem cells (afMSCs) have a central role in the enhanced ability of the fetus to repair tissue damage. This germane recent finding constitutes the biological foundation for the use of afMSCs in TRASCET. It has been shown experimentally that simple intra-amniotic delivery of afMSCs in large numbers can either elicit the repair, or significantly mitigate the effects associated with major congenital anomalies by boosting the activity that these cells normally have. For example, TRASCET can induce partial or complete coverage of experimental spina bifida by promoting the local formation of host-derived skin, thus protecting the spinal cord from further damage. In another example, it can significantly alleviate the bowel damage associated with gastroschisis, one of the most common major abdominal wall defects. Other applications involving different congenital anomalies and/or other stem cells present in the amniotic fluid in diseased pregnancies are currently under investigation in this freshly evolving facet of fetal stem cell therapy.

Fetal bone marrow homing of donor mesenchymal stem cells after transamniotic stem cell therapy (TRASCET)

PURPOSE

Donor cell engraftment patterns following transamniotic stem cell therapy (TRASCET) with amniotic fluid mesenchymal stem cells (afMSCs) are incompatible with solely direct amniotic seeding. We sought to determine whether fetal bone marrow is a component of such engraftment and to examine the chronology of afMSC placental trafficking.

METHODS

Two groups of Sprague-Dawley rat fetuses received volume-matched intraamniotic injections on gestational day 17 (E17; term E22): either afMSCs labeled with a luciferase reporter gene or luciferase protein alone. Placental samples were procured at daily time points thereafter until term. Fetal bone marrow was obtained at term only owing to size constraints. Specimens were screened for luminescence via microplate luminometry.

RESULTS

Donor afMSCs were identified in the bone marrow and placenta of fetuses receiving labeled afMSCs, but not in those receiving luciferase alone (P<0.001). Luminescence was significantly higher in placentas at E18 compared to E19 (P<0.001), E20 (P=0.007), and E21 (P=0.004), with no difference with E22/term (P=0.97).

CONCLUSIONS

Donor mesenchymal stem cells home to the fetal bone marrow after intraamniotic injection. The chronology of placental trafficking is suggestive of controlled cell routing rather than plain cell clearance. Fetal bone marrow engraftment of donor cells significantly expands potential applications of transamniotic stem cell therapy.

An international registry of survivors with Hb Bart's hydrops fetalis syndrome

Hemoglobin (Hb) Bart's hydrops fetalis syndrome (BHFS) resulting from α0-thalassemia is considered a universally fatal disorder. However, over the last 3 decades, improvements in intrauterine interventions and perinatal intensive care have resulted in increasing numbers of BHFS survivors. We have initiated an international registry containing information on 69 patients, of which 31 are previously unpublished. In this perspective, we analyze the available clinical information to document the natural history of BHFS. In the future, once we have accrued sufficient cases, we aim to build on this study and provide information to allow counseling of at-risk couples. To date, 39 patients have survived beyond the age of 5 years, 18 of whom are now older than 10 years. Based on the available cases, we find evidence to suggest that intrauterine therapy provides benefits during the perinatal and neonatal period; however, it may not provide additional benefits to long-term growth and neurodevelopmental outcomes. Growth retardation is a major adverse long-term outcome among BHFS patients with ∼40% being severely affected in terms of weight and ∼50% in terms of height. There is also an increased risk of neurodevelopmental delay as we find 20% (11/55) of BHFS survivors suffer from a serious delay of ≥6 months. Most patients in the registry require lifelong transfusion and often have associated congenital abnormalities and comorbidities. This perspective is a first step in gathering information to allow provision of informed counseling on the predicted outcomes of affected babies.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

The Intravenous Route of Injection Optimizes Engraftment and Survival in the Murine Model of In Utero Hematopoietic Cell Transplantation

In utero hematopoietic cell transplantation (IUHCT) has the potential to treat a number of congenital hematologic disorders. Clinical application is limited by low levels of donor engraftment. Techniques that optimize donor cell delivery to the fetal liver (FL), the hematopoietic organ at the time of IUHCT, have the potential to enhance engraftment and the clinical success of IUHCT. We compared the 3 clinically applicable routes of injection (intravenous [i.v.], intraperitoneal [i.p.], and intrahepatic [i.h.]) and assessed short- and long-term donor cell engraftment and fetal survival in the murine model of IUHCT. We hypothesized that the i.v. route would promote direct donor cell homing to the FL, resulting in increased engraftment and allowing for larger injectate volumes without increased fetal mortality. We demonstrate that the i.v. route results in (1) rapid diffuse donor cell population of the FL compared with delayed diffuse engraftment after the i.p. and i.h. routes; (2) higher FL and spleen engraftment at early prenatal time points; (3) enhanced stable long-term peripheral blood donor cell engraftment; and (4) improved survival at higher injectate volumes, allowing for higher donor cell doses and increased long-term engraftment. These findings support the use of an i.v. route for clinical protocols of IUHCT.

Banking on iPSC--is it doable and is it worthwhile

The discovery of induced pluripotent stem cells (iPSCs) and concurrent development of protocols for their cell-type specific differentiation have revolutionized studies of diseases and raised the possibility that personalized medicine may be achievable. Realizing the full potential of iPSC will require addressing the challenges inherent in obtaining appropriate cells for millions of individuals while meeting the regulatory requirements of delivering therapy and keeping costs affordable. Critical to making PSC based cell therapy widely accessible is determining which mode of cell collection, storage and distribution, will work. In this manuscript we suggest that moderate sized bank where a diverse set of lines carrying different combinations of commonly present HLA alleles are banked and differentiated cells are made available to matched recipients as need dictates may be a solution. We discuss the issues related to developing such a bank and how it could be constructed and propose a bank of selected HLA phenotypes from carefully screened healthy individuals as a solution to delivering personalized medicine.

Stem cells from amniotic fluid--Potential for regenerative medicine

Regenerative medicine has recently been established as an emerging field focussing on repair, replacement or regeneration of cells, tissues and whole organs. The significant recent advances in the field have intensified the search for novel sources of stem cells with potential for therapy. Recently, researchers have identified the amniotic fluid as an untapped source of stem cells that are multipotent, possess immunomodulatory properties and do not have the ethical and legal limitations of embryonic stem cells. Stem cells from the amniotic fluid have been shown to differentiate into cell lineages representing all three embryonic germ layers without generating tumours, which make them an ideal candidate for tissue engineering applications. In addition, their ability to engraft in injured organs and modulate immune and repair responses of host tissues suggest that transplantation of such cells may be useful for the treatment of various degenerative and inflammatory diseases affecting major tissues/organs. This review summarises the evidence on amniotic fluid cells over the past 15 years and explores the potential therapeutic applications of amniotic fluid stem cells and amniotic fluid mesenchymal stem cells.

Placental drug delivery for treatment of congenital hematopoietic disorders

OBJECTIVE

The success of in utero hematopoietic cell transplantation (IUHCTx) hinges on successful conditioning strategies of the host to overcome barriers to engraftment. The "space" barrier is a reflection of a finite number of hematopoietic stem cell (HSC) niches within the host. Independent of the number of donor HSCs transplanted, engraftment is frequently low. By conditioning fetal mice using a monoclonal antibody against the c-kit receptor (ACK2) found on HSCs, we can effectively increase space for donor HSC engraftment. We questioned whether simple placental injection of ACK2 early in gestation could effectively deplete host HSCs within the fetal liver and neonatal bone marrow.

METHODS

In this set of experiments, we injected mice with ACK2 (5 μg/fetus) or PBS at E11.5-12.5 and harvested the fetal liver at 2 and 4 days and the neonatal bone marrow at 7 days following injection. Survival and total number of HSCs within the fetal liver or bone marrow were quantified and compared.

RESULTS

Survival between the treated and control group was similar (73% and 71%, respectively). The total number of HSCs within the fetal liver was not significantly lower following ACK2 treatment compared to PBS injected fetuses at 2 days but was by 4 days. Additionally, ACK2 resulted in a significant reduction in the number of HSCs within neonatal mice 7 days after treatment.

CONCLUSION

Survival following placental ACK2 injection is comparable to control animals and provides a simple non-invasive strategy to deliver ACK2 into the fetal circulation which successfully depletes the host HSCs.

Fetal surgery: an overview

In utero fetal surgery interventions are currently considered in selected cases of congenital diaphragmatic hernia, cystic pulmonary abnormalities, amniotic band sequence, selected congenital heart abnormalities, myelomeningocele, sacrococcygeal teratoma, obstructive uropathy, and complications of twin pregnancy. Randomized controlled trials have demonstrated an advantage for open fetal surgery of myelomeningocele and for fetoscopic selective laser coagulation of placental vessels in twin-to-twin transfusion syndrome. The evidence for other fetal surgery interventions, such as tracheal occlusion in congenital diaphragmatic hernia, excision of lung lesions, fetal balloon cardiac valvuloplasty, and vesicoamniotic shunting for obstructive uropathy, is more limited. Conditions amenable to intrauterine surgical treatment are rare; the mother may consider termination of pregnancy as an option for many of them; treatment can be lifesaving but in itself carries risks to both the infant (preterm premature rupture of the membranes, preterm delivery) and the mother. This makes conducting prospective or randomized trials difficult and explains the relative lack of good-quality evidence in this field. Moreover, there is scanty information on long-term outcomes. It is recommended that fetal surgery procedures be performed in centers with extensive facilities and expertise. The aims of this review were to describe the main fetal surgery procedures and their evidence-based results and to provide generalist obstetricians with an overview of current indications for fetal surgery.

In utero hematopoietic cell transplantation for hemoglobinopathies

In utero hematopoietic cell transplantation (IUHCTx) is a promising strategy to circumvent the challenges of postnatal hematopoietic stem cell (HSC) transplantation. The goal of IUHCTx is to introduce donor cells into a naïve host prior to immune maturation, thereby inducing donor–specific tolerance. Thus, this technique has the potential of avoiding host myeloablative conditioning with cytotoxic agents. Over the past two decades, several attempts at IUHCTx have been made to cure numerous underlying congenital anomalies with limited success. In this review, we will briefly review the history of IUHCTx and give a perspective on alpha thalassemia major, one target disease for its clinical application.

In utero hematopoietic cell transplantation: induction of donor specific immune tolerance and postnatal transplants

In utero hematopoietic cell transplantation (IUHCT) is a non-myeloablative non-immunosuppressive transplant approach that allows for donor cell engraftment across immunologic barriers. Successful engraftment is associated with donor-specific tolerance. IUHCT has the potential to treat a large number of congenital hematologic, immunologic, and genetic diseases either by achieving high enough engraftment levels following a single IUHCT or by inducing donor specific tolerance to allow for non-toxic same-donor postnatal transplants. This review evaluates donor specific tolerance induction achieved by IUHCT. Specifically it addresses the need to achieve threshold levels of donor cell engraftment following IUHCT to consistently obtain immunologic tolerance. The mechanisms of tolerance induction including partial deletion of donor reactive host T cells by direct and indirect antigen presentation and the role of regulatory T cells in maintaining tolerance are reviewed. Finally, this review highlights the promising clinical potential of in utero tolerance induction to provide a platform on which postnatal cellular and organ transplants can be performed without myeloablative or immunosuppressive conditioning.

Stable long-term mixed chimerism achieved in a canine model of allogeneic in utero hematopoietic cell transplantation

Optimization of IUHCT in a preclinical canine model yields stable long-term donor engraftment. Clinically significant levels of chimerism can be achieved without conditioning, immunosuppression, or graft-versus-host disease.

Influence of a dual-injection regimen, plerixafor and CXCR4 on in utero hematopoietic stem cell transplantation and engraftment with use of the sheep model

BACKGROUND AIMS

Inadequate engraftment of hematopoietic stem cells (HSCs) after in utero HSC transplantation (IUHSCT) remains a major obstacle for the prenatal correction of numerous hereditary disorders. HSCs express CXCR4 receptors that allow homing and engraftment in response to stromal-derived factor 1 (SDF-1) ligand present in the bone marrow stromal niche. Plerixafor, a mobilization drug, works through the interruption of the CXCR4-SDF-1 axis.

METHODS

We used the fetal sheep large-animal model to test our hypotheses that (i) by administering plerixafor in utero before performing IUHSCT to release fetal HSCs and thus vacating recipient HSC niches, (ii) by using human mesenchymal stromal/stem cells (MSCs) to immunomodulate and humanize the fetal BM niches and (iii) by increasing the CXCR4(+) fraction of CD34(+) HSCs, we could improve engraftment. Human cord blood-derived CD34(+) cells and human bone marrow-derived MSCs were used for these studies.

RESULTS

When MSCs were transplanted 1 week before CD34(+) cells with plerixafor treatment, we observed 2.80% donor hematopoietic engraftment. Combination of this regimen with additional CD34(+) cells at the time of MSC infusion increased engraftment levels to 8.77%. Next, increasing the fraction of CXCR4(+) cells in the CD34(+) population albeit transplanting at a late gestation age was not beneficial. Our results show engraftment of both lymphoid and myeloid lineages.

CONCLUSIONS

Prior MSC and HSC cotransplantation followed by manipulation of the CXCR4-SDF-1 axis in IUHSCT provides an innovative conceptual approach for conferring competitive advantage to donor HSCs. Our novel approach could provide a clinically relevant approach for enhancing engraftment early in the fetus.