In utero hematopoietic stem cell transfer: current status and future strategies

Naturally acquired microchimerism

Bi-directional transplacental trafficking occurs routinely during the course of normal pregnancy, from fetus to mother and from mother to fetus. In addition to a variety of cell-free substances, it is now well recognized that some cells are also exchanged. Microchimerism refers to a small number of cells (or DNA) harbored by one individual that originated in a genetically different individual. While microchimerism can be the result of iatrogenic interventions such as transplantation or transfusion, by far the most common source is naturally acquired microchimerism from maternal-fetal trafficking during pregnancy. Microchimerism is a subject of much current interest for a number of reasons. During pregnancy, fetal microchimerism can be sought from the mothers blood for the purpose of prenatal diagnosis. Moreover, studies of fetal microchimerism during pregnancy may offer insight into complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune diseases such as rheumatoid arthritis which usually ameliorates during pregnancy. Furthermore, it is now known that microchimerism persists decades later, both fetal microchimerism in women who have been pregnant and maternal microchimerism in her progeny. Investigation of the long-term consequences of fetal and maternal microchimerism is another exciting frontier of active study, with initial results pointing both to adverse and beneficial effects. This review will provide an overview of microchimerism during pregnancy and of current knowledge regarding long-term effects of naturally acquired fetal and maternal microchimerism.

Fetal gene therapy: opportunities and risks

Advances in human prenatal medicine and molecular genetics have allowed the diagnosis of many genetic diseases early in gestation. In-utero transplantation of allogeneic hematopoietic stem cells (HSC) has been successfully used as a therapy in different animal models and recently also in human fetuses. Unfortunately, clinical success of this novel treatment is limited by the lack of donor cell engraftment in non-immunocompromised hosts and is thus restricted to diseases where the fetus is affected by severe immunodeficiency. Gene therapy using genetically modified autologous HSC circumvents allogeneic HLA barriers and constitutes one of the most promising new approaches to correct genetic deficits in the fetus. Recent developments of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells include the use of new vector constructs and transduction protocols. These improvements open new perspectives for gene therapy in general and for prenatal gene transfer in particular. The fetus may be especially susceptible for successful gene therapy due to the immunologic naiveté of the immature hematopoietic system during gestation, precluding an immune reaction towards the transgene. Ethical issues, in particular those regarding treatment safety, must be taken into account before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Perinatal stem-cell and gene therapy for hemoglobinopathies

Most genetic diseases of the lymphohematopoietic system, including hemoglobinopathies, can now be diagnosed early in gestation. However, as yet, prenatal treatment is not available. Postnatal therapy by hematopoietic stem cell (HSC) transplantation from bone marrow, mobilized peripheral blood, or umbilical cord blood is possible for several of these diseases, in particular for the hemoglobinopathies, but is often limited by a lack of histocompatible donors, severe treatment-associated morbidity, and preexisting organ damage that developed before birth. In-utero transplantation of allogeneic HSC has been performed successfully in various animal models and recently in humans. However, the clinical success of this novel treatment is limited to diseases in which the fetus is affected by severe immunodeficiency. The lack of donor cell engraftment in nonimmunocompromised hosts is thought to be due to immunologic barriers, as well as to competitive fetal marrow population by host HSCs. Among the possible strategies to circumvent allogeneic HLA barriers, the use of gene therapy by genetically corrected autologous HSCs in the fetus is one of the most promising approaches. The recent development of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells using new vector constructs and transduction protocols opens new perspectives for gene therapy in general, as well as for prenatal gene transfer in particular. The fetus might be especially susceptible for successful gene therapy approaches because of the developing, expanding hematopoietic system during gestation and the immunologic naiveté early in gestation, precluding immune reaction towards the transgene by inducing tolerance. Ethical issues, in particular regarding treatment safety, must be addressed more closely before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Source of cell injected is a critical factors for short and long engraftment in xeno-transplantation

This study aims to investigate engraftment of human cord blood and foetal bone marrow stem cells after in utero transplantation via the intracoelomic route in the sheep. Here, we performed transplantation in 14 single and 1 twin sheep foetuses at 40-47 days of development, using a novel schedule for injection. (i) Single injection of CD34(+) human cord blood stem cells via the coelomic route (from 10 to 50 x 10(4)) in seven single foetuses. (ii) Single injection of CD34(+) foetal bone marrow stem cells via the intracoelomic route with further numbers of cells (20 x 10(5) and 8 x 10(5), respectively) in three single and in one twin foetuses. (iii) Double fractioned injection (20-30 x 10(6)) via the coelomic route and 20 x 10(6) postnatally, intravenously, shortly after birth of CD3-depleted cord blood stem cells in four single foetuses. In the first group, three single foetuses showed human/sheep chimaerism at 1, 8 and 14 months after birth. In the second group, the twin foetuses showed human/sheep chimaerism at 1 month after birth. In the third group, only two out of four single foetuses that underwent transplantation showed chimaerism at 1 month. While foetal bone marrow stem cells showed good short-term engraftment (1 month after birth), cord blood stem cells were able to persist longer in the ovine recipients (at 1, 8 and 14 months after birth).

Determination of engraftment potential of human cord blood stem-progenitor cells as a function of donor cell dosage and gestational age in the NOD/SCID mouse model

OBJECTIVE

The purpose of this study was to determine cell dosage parameters for successful engraftment of human cord blood hematopoietic stem cells (HSC) using an in vivo assay system, and to determine if there are differences with donor gestational age.

STUDY DESIGN

HSCs were transplanted into nonobese diabetic-severe combined immunodeficient (NOD/SCID) mice. Donor cell dosage and gestational age ranges were 1 to 40 x 10(6) CD34+ cells per mouse, and 23 to 40 weeks, respectively. Recipient bone marrow was assessed for engraftment capacity of the HSCs.

RESULTS

There was increasing engraftment levels with increasing dosages of transplanted HSCs. When controlled for donor HSC dosage, engraftment levels using donor cord blood from earlier gestational ages were not different from that seen using later gestational ages.

CONCLUSION

Similar dose responses are seen using HSCs derived from the late second trimester until term in engraftment potential in the NOD/SCID mouse model. Results from this study may be applicable to human postnatal and in utero transplantation studies.

Confronting the Issues of Therapeutic Misconception, Enrollment Decisions, and Personal Motives in Genetic Medicine-Based Clinical Research Studies for Fatal Disorders

Genetic medicine-based therapies have unlocked the potential for ameliorating diseases previously considered inevitably fatal. Inherent in the clinical trials of genetic medicines are ethical issues of therapeutic misconception, enrollment decisions as they relate to the risks and benefits of research, and the complex relationships among funding sources, investigators, and the families of affected individuals. The purpose of this paper is to help define these complex issues relevant to the use of genetic medicines and to describe the strategy we have used to confront these issues in a phase I trial of adeno-associated virus-mediated gene transfer to the central nervous system of children with late infantile neuronal ceroid lipofuscinosis (LINCL), a fatal lysosomal storage disease associated with progressive neurodegeneration and death by mid-childhood. Our approach to these challenges should provide a useful paradigm for investigators initiating other genetic medicine- based studies to treat inevitably fatal diseases.

Cell-based therapies for birth defects: a role for adult stem cell plasticity?

Cell therapy can offer a reasonable approach to the treatment of specific birth defects, particularly those for which hematopoietic stem cells (HSCs) can be used to restore (even partially) the number of cells, protein levels, or enzyme activity. Relatively few clinical experiences have been published on this subject, but when a natural selective advantage exists for the cell graft, a degree of "rescue" is possible. Strategies have been developed to confer a selective advantage through genetic engineering of donor cells, and this approach may prove valuable in the treatment of birth defects, as it is in hematological malignancy. Stem cell (SC) plasticity, or transdifferentiation, may offer another route for delivery of cells to established or developing organs. A wide variety of studies support the concept that adult tissue-specific SCs can, if displaced from their normal niche to another, be reprogrammed to produce cell types appropriate to their new environment. Clinical observations reveal that persistent tissue microchimerism develops not only in blood lineages after transfusion, but also in thyroid follicular epithelium via transplacental exchange. In addition, hepatic and renal parenchyma also become chimeric following allografts or bone marrow transplantation (BMT). Experimental models indicate that a renal glomerulosclerosis phenotype can be transferred by grafting whole BM, and that a severe liver disorder in fah-/- mice can be overcome by grafting HSCs and then exerting a selection pressure. It may be possible in the future to exploit the ability of adult SCs to contribute to diverse tissues; however, our understanding of the processes involved is at a very early stage.

Influence of intrauterine injection of rat fetal hepatocytes on rejection of rat liver transplantation

AIM: To investigate the influence of immune tolerance induced by intrauterine exposure to fetal hepatocytes on liver transplantation in the adult rat.

METHODS: LOU/CN rat fetal hepatocytes were injected into the fetuses of pregnant CHN rats (14-16 days of gestation). At 7-9 weeks of age, the surviving male rats received orthotopic liver transplantation (OLT) from male LOU/CN donors and the survival period was observed and monitered by mixed lymphocyte reaction assay and cytotoxicity test.

RESULTS: (1) A total of 31 pregnant CHN rats with 172 fetuses received fetal hepatocytes from LOU/CN rats via intrauterine injection. Among them, thirteen pregnant rats showed normal parturition, with 74 neonatal rats growing up normally. (2) The mean survival period after OLT in rats with fetal exposure to fetal hepatocytes was 32.1 ± 3.7 days, which was significantly different from the control (11.8 ± 2.3 days, P < 0.01) in rats without fetal induction of immune tolerance. (3) Mixed lymphocyte proliferation assays yielded remarkable discrepancies between the groups of rats with- or without fetal exposure to fetal hepatocytes, with values of 8411 ± 1361 and 22473 ± 1856 (CPM ± SD, P < 0.01) respectively. (4) Cytotoxicity assays showed values of 21.2 ± 6.5% and 64.5 ± 7.2% (P < 0.01) in adult rats with or without fetal induction of immune tolerance.

CONCLUSION: Intrauterine injection of fetal hepatocytes into rat fetuses can prolong the survival period of liver transplant adult male rats recipients, inducting immune tolerance in OLT.

Prospects for prenatal gene therapy in disorders causing mental retardation

Advances in understanding the genetics and pathogenesis of disease and in prenatal diagnosis have lead to an exploration of ways to intervene earlier and earlier in the disease process. The possibility of prenatal gene therapy for severe genetic and developmental disorders has sparked new research and debate as to its feasibility, reliability, and ethics as a therapeutic option. Recent animal studies have demonstrated the feasibility of introducing a vector into the developing fetus. The optimal timing and best mode of delivery, however, have yet to be defined. Whether or not this research should be pursued also has been the subject of recent bioethical debates. There is additional concern with the possibility of in utero gene transfer inducing mutagenesis and subsequent tumor formation. This review will provide a summary of the current state of knowledge in the field of prenatal gene therapy and possible directions for the future research.

Stable transduction with lentiviral vectors and amplification of immature hematopoietic progenitors from cord blood of preterm human fetuses

Umbilical cord blood (CB) from the early gestational human fetus is recognized as a rich source of hematopoietic stem cells. To examine the value of fetal CB for gene therapy of inborn immunohematopoietic disorders, we tested the feasibility of genetic modification of CD34(+) cells from CB at weeks 24 to 34 of pregnancy, using lentiviral vector-mediated transfer of the green fluorescent protein (GFP) gene. The transduction rate of CD34(+) cells was 42 +/- 9%, resulting in GFP expression in 23 +/- 4% of colonies derived from colony-forming units (CFUs) and 11 +/- 1% from primitive long-term culture-initiating cells (LTC-ICs). Cell cycle analysis demonstrated transduction and GFP expression in cells in the G(0) phase, which contains immature hematopoietic progenitors. Transduced fetal CD34(+) cells could be expanded 1000-fold in long-term cultures supplemented with megakaryocyte growth and development factor along with Flt-3 ligand. At week 10, expression of GFP was observed in 40.5 +/- 11.7% of CFU-derived colonies. While prestimulation of CD34(+) cells with cytokines prior to transduction increased the efficiency of GFP transfer 2- to 3-fold, long-term maintenance of GFP-expressing CFUs occurred only in the absence of prestimulation. The GFP gene was found integrated into the genomic DNA of 35% of LTC-IC-derived colonies initiated at week 10, but GFP expression was not detectable, suggesting downregulation of transgene activity during the extended culture period. These results indicate that human fetal CB progenitors are amenable to genetic modification by lentiviral vectors and may serve as a target for gene therapy of hematopoietic disorders by prenatal autologous transplantation.

Gene therapy approaches for modulating bone regeneration

Following injury, bone has the ability to regenerate itself to a form and function nearly indistinguishable from the pre-injury state. However, if the injury is beyond a critical limit, recovery will not occur without therapeutic interventions. Autografts and implants with banked bone continue as the treatments of choice, although each exhibits limitations and liabilities. Alternatives have included the utilization of bone-graft substitutes that may incorporate bone derivatives and soluble signaling molecules such as mitogens and morphogens. In addition, an evolving treatment modality, gene therapy, offers an exciting avenue for bone regeneration. This review presents some of the current concepts for developing a rational gene therapy approach in bone regeneration.

Transabdominal first trimester embryofetoscopy as a potential approach to early in utero stem cell transplantation and gene therapy

OBJECTIVE

To explore the potential of embryofetoscopy for early diagnosis and for access to the fetal circulation in the first trimester of gestation.

DESIGN

Transabdominal embryofetoscopy was performed in 14 patients scheduled for termination of pregnancy using a 1-mm semirigid fibreoptic telescope with a 18 gauge examination sheath and a single-chip digital camera. A 25 gauge needle was inserted through an additional 21 gauge side port to access the fetal circulation.

RESULTS

Fetal head, face, abdomen, complete upper and lower limbs could be visualized in over 80% of cases. On the contrary, the fetal back and external genitalia could be examined in detail only in some cases (35.7% and 64.3%, respectively). Injection of 10-20 ml saline improved visibility in 43% of cases. Funipuncture was successful in two of three attempts.

CONCLUSIONS

Our experience suggests that embryofetoscopy is a useful tool for early diagnosis in the first trimester of pregnancy. Funipuncture is possible thus providing the means for an early intravascular stem cell application.