In-utero transplantation of parental CD34 haematopoietic progenitor cells in a patient with X-linked severe combined immunodeficiency (SCIDXI)

Review: Stem cells and gene therapy

Both stem cell and gene therapy research are currently the focus of intense research in institutions and companies around the world. Both approaches hold great promise by offering radical new and successful ways of treating debilitating and incurable diseases effectively. Gene therapy is an approach to treat, cure, or ultimately prevent disease by changing the pattern of gene expression. It is mostly experimental, but a number of clinical human trials have already been conducted. Gene therapy can be targeted to somatic or germ cells; the most common vectors are viruses. Scientists manipulate the viral genome and thus introduce therapeutic genes to the target organ. Viruses, in this context, can cause adverse events such as toxicity, immune and inflammatory responses, as well as gene control and targeting issues. Alternative modalities being considered are complexes of DNA with lipids and proteins. Stem cells are primitive cells that have the capacity to self renew as well as to differentiate into 1 or more mature cell types. Pluripotent embryonic stem cells derived from the inner cell mass can develop into more than 200 different cells and differentiate into cells of the 3 germ cell layers. Because of their capacity of unlimited expansion and pluripotency, they are useful in regenerative medicine. Tissue or adult stem cells produce cells specific to the tissue in which they are found. They are relatively unspecialized and predetermined to give rise to specific cell types when they differentiate. The current review provides a summary of our current knowledge of stem cells and gene therapy as well as their clinical implications and related therapeutic options.

A mouse model of in utero transplantation

The transplantation of stem cells and viruses in utero has tremendous potential for treating congenital disorders in the human fetus. For example, in utero transplantation (IUT) of hematopoietic stem cells has been used to successfully treat patients with severe combined immunodeficiency. In several other conditions, however, IUT has been attempted without success. Given these mixed results, the availability of an efficient non-human model to study the biological sequelae of stem cell transplantation and gene therapy is critical to advance this field. We and others have used the mouse model of IUT to study factors affecting successful engraftment of in utero transplanted hematopoietic stem cells in both wild-type mice and those with genetic diseases. The fetal environment also offers considerable advantages for the success of in utero gene therapy. For example, the delivery of adenoviral, adeno-associated viral, retroviral, and lentiviral vectors into the fetus has resulted in the transduction of multiple organs distant from the site of injection with long-term gene expression. in utero gene therapy may therefore be considered as a possible treatment strategy for single gene disorders such as muscular dystrophy or cystic fibrosis. Another potential advantage of IUT is the ability to induce immune tolerance to a specific antigen. As seen in mice with hemophilia, the introduction of Factor IX early in development results in tolerance to this protein. In addition to its use in investigating potential human therapies, the mouse model of IUT can be a powerful tool to study basic questions in developmental and stem cell biology. For example, one can deliver various small molecules to induce or inhibit specific gene expression at defined gestational stages and manipulate developmental pathways. The impact of these alterations can be assessed at various timepoints after the initial transplantation. Furthermore, one can transplant pluripotent or lineage specific progenitor cells into the fetal environment to study stem cell differentiation in a non-irradiated and unperturbed host environment. The mouse model of IUT has already provided numerous insights within the fields of immunology, and developmental and stem cell biology. In this video-based protocol, we describe a step-by-step approach to performing IUT in mouse fetuses and outline the critical steps and potential pitfalls of this technique.

Maternal T cells limit engraftment after in utero hematopoietic cell transplantation in mice

Transplantation of allogeneic stem cells into the early gestational fetus, a treatment termed in utero hematopoietic cell transplantation (IUHCTx), could potentially overcome the limitations of bone marrow transplants, including graft rejection and the chronic immunosuppression required to prevent rejection. However, clinical use of IUHCTx has been hampered by poor engraftment, possibly due to a host immune response against the graft. Since the fetal immune system is relatively immature, we hypothesized that maternal cells trafficking into the fetus may pose the true barrier to effective IUHCTx. Here, we have demonstrated that there is macrochimerism of maternal leukocytes in the blood of unmanipulated mouse fetuses, with substantial increases in T cell trafficking after IUHCTx. To determine the contribution of these maternal lymphocytes to rejection after IUHCTx, we bred T and/or B cell-deficient mothers to wild-type fathers and performed allogeneic IUHCTx into the immunocompetent fetuses. There was a marked improvement in engraftment if the mother lacked T cells but not B cells, indicating that maternal T cells are the main barrier to engraftment. Furthermore, when the graft was matched to the mother, there was no difference in engraftment between syngeneic and allogeneic fetal recipients. Our study suggests that the clinical success of IUHCTx may be improved by transplanting cells matched to the mother.

Transplantation immunology: solid organ and bone marrow

Development of the field of organ and tissue transplantation has accelerated remarkably since the human MHC was discovered in 1967. Matching of donor and recipient for MHC antigens has been shown to have a significant positive effect on graft acceptance. The roles of the different components of the immune system involved in the tolerance or rejection of grafts and in graft-versus-host disease have been clarified. These components include antibodies, antigen-presenting cells, helper and cytotoxic T-cell subsets, immune cell-surface molecules, signaling mechanisms, and cytokines. The development of pharmacologic and biological agents that interfere with the alloimmune response has had a crucial role in the success of organ transplantation. Combinations of these agents work synergistically, leading to lower doses of immunosuppressive drugs and reduced toxicity. Reports of significant numbers of successful solid-organ transplantations include those of the kidneys, liver, heart, and lung. The use of bone marrow transplantation for hematologic diseases, particularly hematologic malignancies and primary immunodeficiencies, has become the treatment of choice in many of these conditions. Other sources of hematopoietic stem cells are also being used, and diverse immunosuppressive drug regimens of reduced intensity are being proposed to circumvent the mortality associated with the toxicity of these drugs. Gene therapy to correct inherited diseases by means of infusion of gene-modified autologous hematopoietic stem cells has shown efficacy in 2 forms of severe combined immunodeficiency, providing an alternative to allogeneic tissue transplantation.

In Utero Haematopoietic Stem Cell Transplantation (IUHSCT)

In utero haematopoietic stem cell transplantation (IUHSCT) is a non-myeloablative approach for the prenatal treatment of genetic disorders. However, in target disorders, where there is not a selective advantage for donor cells, a useful donor-cell chimerism has not been achieved. There are three possible barriers to engraftment following IUHSCT: limited space in the fetus due to host-cell competition; the large number of donor cells needed, and the immunological asset of recipient.

Stem cells and the frontiers of neonatology

The aim of the most recent studies on regenerative medicine was to focus on capability of stem cells deriving not only from haematopoietic system, but also from other organ and tissues, to regenerate damaged tissues. Stem cells derived from foetal annexes such as cord blood, placenta and amniotic fluid can be currently used in the effort to treat prenatally diagnosed genetic diseases. Cells derived from cord blood have been used since 1988 as an alternative source to realize stem cell transplantation. Compared with bone marrow, cord blood has shown the advantages of quick availability, less risk of GHVD, together with higher compatibility rates, and less risk of infections. Mesenchymal stem cells (MSCs) are multi-potent stem cells able to differentiate into different lineages, including osteocytes, chondrocytes, and adipocytes. Because of their trafficking capacity to injured tissues, clinical trials have been started evaluating the use of MSCs in the treatment of metabolic diseases like Hurler syndrome and metachromatic leukodystrophy, or Osteogenesis Imperfecta. MSCs were initially identified in adult bone marrow (BM-MSC), but cells resembling BM-MSCs have also been found in other tissues, both adult (peripheral blood, synovial membrane) and foetal (peripheral blood, liver, spleen, placenta, umbilical cord, and amniotic membrane). BM-MSCs have been widely used in clinical applications, as for cell-based therapy of Osteogenesis Imperfecta and metabolic diseases. In addition, human multi-potent MSCs present in second-trimester amniotic fluids may be a good target for prenatal gene therapy because of their expandability, their ability to differentiate into multiple lineages and their high transduction efficiency.

Haploidentical in utero hematopoietic cell transplantation improves phenotype and can induce tolerance for postnatal same-donor transplants in the canine leukocyte adhesion deficiency model

In the murine model, in utero hematopoietic cell transplantation (IUHCT) has been shown to achieve low levels of allogeneic chimerism and associated donor-specific tolerance permitting minimal conditioning postnatal hematopoietic stem cell transplantation (HSCT). In this pilot study, we investigated IUHCT in the canine leukocyte adhesion deficiency (CLAD) model. Haploidentical IUHCT resulted in stable low-level donor cell chimerism in all dogs that could be analyzed by sensitive detection methodology (4 of 10) through 18 months of follow-up. In the 2 CLAD recipients, low-level chimerism resulted in amelioration and complete reversal of the CLAD phenotype, respectively. Six recipients of IUHCT (5 carriers and 1 CLAD) subsequently received postnatal HSCT from the same haploidentical prenatal donor after minimal conditioning with busulfan 10 mg/kg. Chimerism in 2 of 5 CLAD carriers that underwent HSCT increased from < 1% pre-HSCT to sustained levels of 35% to 45%. Control animals undergoing postnatal haploidentical HSCT without IUHCT had no detectable donor chimerism. These results demonstrate that haploidentical IUHCT in the CLAD model can result in low-level donor chimerism that can prevent the lethal phenotype in CLAD dogs, and can result in donor-specific tolerance that can facilitate postnatal minimal conditioning HSCT.

A murine model of graft-vs-host disease after in utero hematopoietic cell transplantation

PURPOSE

Graft-vs-host disease (GvHD) is a known complication of in utero bone marrow transplantation. However, GvHD has been difficult to study owing to frequent fetal demise. We describe the first consistent murine model of GvHD with postnatal survival after in utero hematopoietic cell transplantation.

METHODS

A 50/50 mixture of bone marrow and splenocytes (10(6)) from 6-week-old C57/BL6 (H2-b) mice was injected intraperitoneally into Balb/c (H2-d) fetuses at e14 to 16. Live born pups were followed for clinical GvHD. Peripheral blood and hematopoietic organ chimerism was confirmed by flow cytometry and polymerase chain reaction. Organ samples were isolated for histology.

RESULTS

Twenty-seven (75%) of 36 surviving pups displayed clinical GvHD by 2 weeks compared with 9 developmentally normal pups. Mean difference in weight between the 2 groups was 2.9 g at 7 days and 5.2 g at 14 days of life (P < .0001). All 27 pups with clinical GvHD and 1 normal-appearing pup had blood chimerism ranging from 1.5% to 65%. Eight of the 9 normal-appearing pups had 0% chimerism. Histologic analysis revealed findings of GvHD in liver, spleen, small intestine, and skin specimens of only chimeric pups.

CONCLUSIONS

A consistent murine model of GvHD can be achieved after in utero transplantation of major histocompatibility complex-mismatched bone marrow and splenocytes. Future studies will use this model to examine approaches to prevent GvHD after in utero stem cell transplantation.

Prenatal stem cell transplantation and gene therapy

At the present time, the most likely and eminent application of stem cell therapy to the fetus is in utero hematopoietic stem cell transplantation (IUHCT), and this stem cell type will be discussed as a paradigm for all prenatal stem cell therapy. The authors feel that the most likely initial application of IUHCT will use adult HSC derived from bone marrow (BM) or peripheral blood (PB), and will focus this article on this specific approach. The article also reviews the experimental data that support the capacity of IUHCT to induce donor-specific tolerance.

Polyclonal T-cell reconstitution of X-SCID recipients after in utero transplantation of lymphoid-primed multipotent progenitors

Although successful in utero hematopoietic cell transplantation (IUHCT) of X-linked severe combined immune deficiency (X-SCID) with enriched stem and progenitor cells was achieved more than a decade ago, it remains applied only in rare cases. Although this in part reflects that postnatal transplantations have overall given good results, there are no direct comparisons between IUHCT and postnatal transplantations of X-SCID. The proposed tolerance of the fetal immune system to foreign human leukocyte antigen early in gestation, a main rationale behind IUHCT, has recently been challenged by evidence for a considerable immune barrier against in utero transplanted allogeneic bone marrow cells. Consequently, there is need for further exploring the application of purified stem and progenitor cells to overcome this barrier also in IUHCT. Herein, we demonstrate in a congenic setting that recently identified lymphoid-primed multipotent progenitors are superior to hematopoietic stem cells in providing rapid lymphoid reconstitution after IUHCT of X-SCID recipients, and sustain in the long-term B cells, polyclonal T cells, as well as short-lived B-cell progenitors and thymic T-cell precursors. We further provide evidence for IUHCT of hematopoietic stem cells giving superior B- and T-cell reconstitution in fetal X-SCID recipients compared with neonatal and adolescent recipients.

Fetal liver cells transplanted in utero rescue the osteopetrotic phenotype in the oc/oc mouse

Autosomal recessive osteopetrosis (ARO) is a group of genetic disorders that involve defects that preclude the normal function of osteoclasts, which differentiate from hematopoietic precursors. In half of human cases, ARO is the result of mutations in the TCIRG1 gene, which codes for a subunit of the vacuolar proton pump that plays a fundamental role in the acidification of the cell-bone interface. Functional mutations of this pump severely impair the resorption of bone mineral. Although postnatal hematopoietic stem cell transplantation can partially rescue the hematological phenotype of ARO, other stigmata of the disease, such as secondary neurological and growth defects, are not reversed. For this reason, ARO is a paradigm for genetic diseases that would benefit from effective prenatal treatment. Using the oc/oc mutant mouse, a murine model whose osteopetrotic phenotype closely recapitulates human TCIRG1-dependent ARO, we report that in utero transplantation of adult bone marrow hematopoietic stem cells can correct the ARO phenotype in a limited number of mice. Here we report that in utero injection of allogeneic fetal liver cells, which include hematopoietic stem cells, into oc/oc mouse fetuses at 13.5 days post coitum produces a high level of engraftment, and the oc/oc phenotype is completely rescued in a high percentage of these mice. Therefore, oc/oc pathology appears to be particularly sensitive to this form of early treatment of the ARO genetic disorder.

Infantile malignant, autosomal recessive osteopetrosis: the rich and the poor

Human recessive osteopetrosis (ARO) represents a group of diseases in which, due to a defect in osteoclasts, bone resorption is prevented. The deficit could arise either from failure in osteoclast differentiation or from inability to perform resorption by mature, multinucleated, but nonfunctional cells. Historically, osteopetrosis due to both these mechanisms was found in spontaneous and artificially created mouse mutants, but the first five genes identified in human ARO (CA-II, TCIRG1, ClCN7, OSTM1, and PLEKHM1) were all involved in the effector function of mature osteoclasts, being linked to acidification of the cell/bone interface or to intracellular processing of the resorbed material. Differentiation defects in human ARO have only recently been described, following the identification of mutations in both RANKL and RANK, which define a new form of osteoclast-poor ARO, as expected from biochemical, cellular, and animal studies. The molecular dissection of ARO has prognostic and therapeutic implications. RANKL-dependent patients, in particular, represent an interesting subset which could benefit from mesenchymal cell transplant and/or administration of soluble RANKL cytokine.

Donor major histocompatibility complex class I expression determines the outcome of prenatal transplantation

PURPOSE

The failure of in utero transplantation in immune-competent recipients suggests the existence of a fetal immune barrier. The importance of donor major histocompatibility complex (MHC) class I expression in the induction of prenatal tolerance remains undefined. We hypothesized that donor cell MHC class I expression facilitates engraftment in prenatal allogeneic recipients rather than promoting immune rejection.

METHODS

B6.Ly5.2 (class I(+)) or B6.TAP(-/-) (class I(-)) murine fetal liver cells were transplanted into age-matched allogeneic fetal recipients. Survival to weaning and subsequent growth was assessed. Engraftment rates and peripheral blood chimerism levels were measured serially.

RESULTS

The presence or absence of class I expression did not affect survival or growth of recipients and no graft-vs-host disease developed. Allogeneic recipients of B6.Ly5.2 cells exhibited significantly higher levels of donor hematopoietic chimerism when compared to recipients of B6.TAP(-/-) cells (27% + 10% vs 11% + 8%; P = .004) that deteriorated further over time.

CONCLUSIONS

Donor class I MHC antigen expression is essential for stable long-term engraftment and maintenance of donor-specific tolerance. Further studies are needed to better characterize the role of the fetal innate immune system in prenatal allotransplantation.

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Fetal stem-cell transplantation

Fetal stem-cell transplantation is an attractive approach to the treatment of a variety of hematological, metabolic and immunological diseases before birth. The possibility of delivering a large number of cells in an early stage of life, and of taking advantage of normal fetal stem-cell migration and development, is promising. During fetal life, the capacity to mount an immune response to allogeneic cells is impaired compared with adult life. This provides an opportunity to induce tolerance to alloantigens without the need for myeloablation, although there are possible immune barriers to foreign cells in the fetus.

Application of Carnegie stages of development to unify human and baboon ultrasound findings early in pregnancy

The objective of this study was to determine if very early ultrasonographic measurements obtained from human and baboon are comparable. For this purpose, the gestational, amniotic and yolk sacs, embryonic crown rump length (CRL) and heart rate were measured ultrasonographically between 35 and 47 days from the mean day of a three-day mating period in baboons (n=18) and between 42 to 58 days from fertilization as calculated from the CRL measurements in human pregnancies (n=82). Ultrasonographic measurements from both species were then plotted in the same graph using Carnegie stages of embryonic development as the independent variable to allow for visual comparisons. Mean gestational age at ultrasonographic studies was significantly different for humans and baboons (50.4 vs. 41 days, respectively; p>0.01). Significant correlations (p>0.01) were noted between ultrasonographic measurements and Carnegie stages of development in both humans and baboons. Only the gestational and the yolk sacs were significantly smaller in baboons than in humans (p>0.05). The findings that embryonic CRL, extra-embryonic space and heart rate are very similar between the 17th and 23rd Carnegie developmental stages make the baboon a promising surrogate of human pregnancy for investigations using celocentesis.

Use of T-cell antibodies for donor dosaging in a canine model of in utero hematopoietic stem cell transplantation

AIM

Microchimerism following canine in utero hematopoietic stem cell transplantation (IUHSCT) development of T-cell dosing regimens.

OBJECTIVE

To investigate the use of anti-T-cell antibodies for cell dosing of the donor graft in a canine model of IUHSCT.

STUDY DESIGN

Canine IUHSCT was performed by ultrasound-guided intraperitoneal injection in days 35-38 of fetal canines with CD34(+) cells at doses of 4.5 x 10(8) to 1.3 x 10(9) cells/kg and T cells (CD3(+) CD5(+)) at doses of 8 x 10(6) to 8.8 x 10(8) cells/kg. Postnatal studies included tissue histology and polymerase chain reaction-based chimerism analysis.

RESULTS

Term survival was 86-100%. Microchimerism (0-2%) was detected in five of eight recipients in multiple tissues. Histopathology revealed no evidence of graft-versus-host disease (GVHD).

CONCLUSION

Canine IUHSCT is a useful model to investigate the role of donor T cells in engraftment and GVHD. IUHSCT at early gestational ages with high doses of donor T cells in the graft yields microchimerism in multiple tissues without GVHD.

Widespread distribution and muscle differentiation of human fetal mesenchymal stem cells after intrauterine transplantation in dystrophic mdx mouse

Duchenne muscular dystrophy (DMD) is a common X-linked disease resulting from the absence of dystrophin in muscle. Affected boys suffer from incurable progressive muscle weakness, leading to premature death. Stem cell transplantation may be curative, but is hampered by the need for systemic delivery and immune rejection. To address these barriers to stem cell therapy in DMD, we investigated a fetal-to-fetal transplantation strategy. We investigated intramuscular, intravascular, and intraperitoneal delivery of human fetal mesenchymal stem cells (hfMSCs) into embryonic day (E) 14-16 MF1 mice to determine the most appropriate route for systemic delivery. Intramuscular injections resulted in local engraftment, whereas both intraperitoneal and intravascular delivery led to systemic spread. However, intravascular delivery led to unexpected demise of transplanted mice. Transplantation of hfMSCs into E14-16 mdx mice resulted in widespread long-term engraftment (19 weeks) in multiple organs, with a predilection for muscle compared with nonmuscle tissues (0.71% vs. 0.15%, p < .01), and evidence of myogenic differentiation of hfMSCs in skeletal and myocardial muscle. This is the first report of intrauterine transplantation of ontologically relevant hfMSCs into fully immunocompetent dystrophic fetal mice, with systemic spread across endothelial barriers leading to widespread long-term engraftment in multiple organ compartments. Although the low-level of chimerism achieved is not curative for DMD, this approach may be useful in other severe mesenchymal or enzyme deficiency syndromes, where low-level protein expression may ameliorate disease pathology.

A Study to Determine if Human Umbilical Cord Hematopoietic Stem Cells Can Survive in Baboon Extra-Embryonic Celomic Fluid: A Prerequisite for Determining the Feasibility of in-utero Stem Cell Xeno-Transplantation via Celocentesis

OBJECTIVES

To determine if: (1) human umbilical cord stem cells could survive for 20 h in extra-embryonic celomic fluid obtained at 40 days of development from baboon pregnancies by ultrasound-guided celocentesis and, (2) human hematopoietic stem cell survival could be enhanced by adding increasing concentrations of hematopoietic stem cell culture medium to the celomic fluid.

METHODS

CD34+ cells were isolated from umbilical cord blood using a magnetic activated cell sorter and flow cytometry. Cells were then cultured in five platforms containing different combinations of baboon extra-embryonic celomic fluid and hematopoietic stem cell culture medium to determine cell survival kinetics over a 20-hour period in each of the conditions.

RESULTS

Human umbilical cord stem cells can survive for at least 20 h in baboon's celomic fluid. Chi-square for linear trends demonstrated that the number of viable cells was significantly enhanced by adding the increasing concentrations of culture medium to the celomic fluid (29% cell survival in pure celomic fluid, 48% at 1:8, 50% at 1:2, 54.5% at 1:1, 61% in pure culture medium; p < 0.001).

CONCLUSIONS

Human umbilical cord stem cells survive in baboon celomic fluid and cell survival improves when the celomic fluid is mixed with greater concentrations of hematopoietic stem cell culture medium. Based on these findings, future in-vivo experiments in the pregnant baboon animal model can be directed at determining whether in-utero injection of human hematopoietic stem cells prior to 10 weeks of pregnancy can lead to permanent chimeras.

Prenatal transplantation of cytokine-stimulated marrow improves early chimerism in a resistant strain combination but results in poor long-term engraftment

OBJECTIVE

In the absence of immunodeficiency, only microchimerism (<0.1%) has been achieved in human fetal recipients or nonhuman primates following in utero hematopoietic cell transplantation (IUHCT). We hypothesized that enhanced long-term engraftment might be more reliably achieved in microchimeric systems if higher levels of chimerism existed during development of adaptive immunity. To evaluate this hypothesis, we stimulated the donor cells with vascular endothelial growth factor (VEGF) and stem cell factor (SCF) prior to IUHCT in a chimerism-resistant murine strain combination.

METHODS

Donor Balb/c marrow was cultured in media with or without VEGF and SCF supplementation for 12 hours prior to IUHCT into B6 fetuses at 14 days postcoitum (dpc). Donor cell phenotype, homing, and chimerism were assessed at short and long-term time points and transplanted animals received skin allografts at 8 weeks.

RESULTS

In pretreated allogeneic recipients, early chimerism rates were more than double that of controls (71% vs 33%, p = 0.01). These differences were associated with higher numbers of pretransplant donor cell colony-forming cells without change in donor cell homing. Despite prolonged skin allograft survival for pretreated recipients compared with controls (mean survival = 20.8 vs 8.2 days, p < 0.001), long-term engraftment was unchanged.

CONCLUSIONS

These findings demonstrate that higher levels of early chimerism in recipients of cytokine-stimulated marrow result in improved short-term chimerism and tolerance. Future studies are needed to confirm the existence of a "threshold" level of chimerism necessary to sustain long-term engraftment.

Evidence for an immune barrier after in utero hematopoietic-cell transplantation

The competence of the immune system of the developing fetus to act as a barrier to in utero hematopoietic-cell transplantation (IUHCT) has been a source of debate. Until now, comparisons of allogeneic and congenic engraftment have been inconclusive due to methodologic limitations resulting in minimal and inefficient engraftment. In this study, E14 fetal mice received transplants of either allogeneic or congenic bone marrow using a new intravascular technique that allows definitive administration of much higher doses of donor cells. Our results demonstrate that 100% of surviving recipients demonstrate engraftment at 1 week of age, but that 70% of allogeneic recipients lose engraftment by 1 month of age, and 80% ultimately fail to sustain long-term chimerism. In contrast, all congenic recipients maintain stable, long-term, multilineage chimerism. These results strongly support an immune barrier to allogeneic engraftment after IUHCT.

CD26 inhibition enhances allogeneic donor-cell homing and engraftment after in utero hematopoietic-cell transplantation

In utero hematopoietic-cell transplantation (IUHCT) can induce donor-specific tolerance to facilitate postnatal transplantation. Induction of tolerance requires a threshold level of mixed hematopoietic chimerism. CD26 is a peptidase whose inhibition increases homing and engraftment of hematopoietic cells in postnatal transplantation. We hypothesized that CD26 inhibition would increase donor-cell homing to the fetal liver (FL) and improve allogeneic engraftment following IUHCT. To evaluate this hypothesis, B6GFP bone marrow (BM) or enriched hematopoietic stem cells (HSCs) were transplanted into allogeneic fetal mice with or without CD26 inhibition. Recipients were analyzed for FL homing and peripheral-blood chimerism from 4 to 28 weeks of life. We found that CD26 inhibition of donor cells results in (1) increased homing of allogeneic BM and HSCs to the FL, (2) an increased number of injected animals with evidence of postnatal engraftment, (3) increased donor chimerism levels following IUHCT, and (4) a competitive engraftment advantage over noninhibited congenic donor cells. This study supports CD26 inhibition as a potential method to increase the level of FL homing and engraftment following IUHCT. The resulting increased donor chimerism suggests that CD26 inhibition may in the future be used as a method of increasing donor-specific tolerance following IUHCT.

Busulfan-conditioned bone marrow transplantation results in high-level allogeneic chimerism in mice made tolerant by in utero hematopoietic cell transplantation

OBJECTIVE

In utero hematopoietic cell transplantation (IUHCT) is a non-ablative approach that achieves mixed allogeneic chimerism and donor-specific tolerance. However, clinical application of IUHCT has been limited by minimal engraftment. We have previously demonstrated in the murine model that low-level allogeneic chimerism achieved by IUHCT can be enhanced to near-complete donor chimerism by postnatal minimally myeloablative total body irradiation (TBI) followed by same-donor bone marrow transplantation. Because of concerns of toxicity related to even low-dose TBI in early life, we wondered if a potentially less toxic strategy utilizing a single myelosuppressive agent, Busulfan (BU), would provide similar enhancement of engraftment.

METHODS

In this study, mixed chimerism was created by IUHCT in a fully allogeneic strain combination. After birth, chimeric mice were conditioned with BU followed by transplantation of bone marrow cells congenic to the prenatal donor.

RESULTS

We demonstrate that: 1) low-level chimerism after IUHCT can be converted to high-level chimerism by this protocol; 2) enhancement of chimerism is BU dose-dependent; and 3) BU reduces the proliferative potential of hematopoietic progenitor cells thus conferring a competitive advantage to the non-BU-treated postnatal donor cells.

CONCLUSION

This study confirms the potential of IUHCT for facilitation of minimally toxic postnatal regimens to achieve therapeutic levels of allogeneic engraftment.

Cytokine-mediated signalling and early defects in lymphoid development

PURPOSE OF REVIEW

The aim of the review is to report on recent advances in cytokine-mediated signalling, as illustrated by the study of natural human mutants. In particular, the role of cytokines and cytokine-mediated signalling in human T-cell development is analysed in detail, and currently available forms of treatment including experimental trials are described.

RECENT FINDINGS

Defects of the cytokine/JAK/STAT axis have been recently described as responsible for human Severe Combined Immune Deficiency. In particular, defects in gammac, JAK3 and IL7RA have been analysed in terms of development of novel diagnostic tools as well as of new therapeutic agents for the treatment of autoimmune diseases and graft-versus-host disease.

SUMMARY

Dissection of the genetic defects underlying the various forms of Severe Combined Immune Deficiency has helped develop new and more accurate diagnostic assays and novel forms of treatment.

Rescue of ATPa3-deficient murine malignant osteopetrosis by hematopoietic stem cell transplantation in utero

Autosomal recessive osteopetrosis (ARO) is a paradigm for genetic diseases that cause severe, often irreversible, defects before birth. In ARO, osteoclasts cannot remove mineralized cartilage, bone marrow is severely reduced, and bone cannot be remodeled for growth. More than 50% of the patients show defects in the osteoclastic vacuolar-proton-pump subunit, ATP6a3. We treated ATP6a3-deficient mice by in utero heterologous hematopoietic stem cell (HSC) transplant from outbred GFP transgenic mice. Dramatic phenotype rescue by GFP osteoclasts was obtained with engraftment, which was observed in most cases. Engraftment survived for variable periods. Recipients were not immunosuppressed, and graft-versus-host disease was not observed in all pups born after in utero treatment. Thus, differentiation of unmatched HSC transplanted in utero is sufficient to prevent fatal defects in ARO and may prevent complications of ARO unresponsive to conventional bone marrow transplantation. The presence of defective cells is not a barrier to the rescue of the phenotype by donor HSC.

The use of CD 34(+) mobilized peripheral blood as a donor cell source does not improve chimerism after in utero hematopoietic stem cell transplantation in non-human primates

In utero hematopoietic stem cell transplantation is a therapeutic procedure that could potentially cure many developmental diseases affecting the immune and hematopoietic systems. In most clinical and experimental settings of fetal hematopoietic transplantation the level of donor cell engraftment has been low, suggesting that even in the fetus there are significant barriers to donor cell engraftment. In postnatal hematopoietic transplantation donor cells obtained from mobilized peripheral blood engraft more rapidly than cells derived from marrow. We tested the hypothesis that use of donor hematopoietic/stem cells obtained from mobilized peripheral blood would improve engraftment and the level of chimerism after in utero transplantation in non-human primates. Despite the potential competitive advantage from the use of CD 34(+) from mobilized peripheral blood, the level of chimerism was not appreciably different from a group of animals receiving marrow-derived CD 34(+) donor cells. Based on these results, it is unlikely that this single change in cell source will influence the clinical outcome of fetal hematopoietic transplantation.

In utero transplantation: baby steps towards an effective therapy

In utero transplantation (IUT) offers the potential to treat a large number of diseases by transplantation of healthy cells into a fetus with a birth defect. Prenatal diagnosis is feasible for many diseases prior to the full development of the fetal immune system offering the opportunity to introduce foreign cells and antigens into the developing fetus. At least 45 cases of IUT have been performed for a variety of diseases. IUT has successfully treated severe combined immunodeficiency and there are indications that it may be effective in treating some nonhematopoietic diseases. However, many diseases remain resistant to fetal therapy owing to the low levels of chimerism that can be achieved. Promising efforts to improve the levels of engraftment are focusing on optimizing the graft and developing donor-specific tolerance in the fetal recipient. Mounting evidence suggests that donor T cells can aid in achieving clinically significant levels of chimerism. The use of fetal donor cells may also offer some benefit. Animal experiments suggest that even low-level chimerism can lead to tolerance, which can be exploited by booster transplants in the neonate. Continued research appears likely to succeed in developing IUT into an effective form of therapy for a variety of diseases.

The prospects for in utero stem cell transplantation

In utero transplantation of haematopoietic stem cells into the foetus, early in gestation, offers a new approach to genetic disorders. Immunological naivete and the sterile uterine environment are perfect conditions for transplantation, so that even mismatched cells will engraft. There have been notable successes world-wide, although numbers are small, which gives encouragement to further work directed at means to enhance and sustain engraftment in a foetal recipient. For example, stem cells for transplant can be obtained from various sources but these have different properties that can be exploited for therapy in specific disorders. However, some disorders may not be amenable to in utero transplantation and there is need to achieve consensus in order to ensure that the procedure is used appropriately, for the benefit of all.

Conditioning of Neonatal Pigs Using Low-Dose Chemotherapy and Murine Fetal Tissue before Murine Hybridoma Transplantation

Immunosuppression, myeloablation, and the use of immunologically immature tissue can overcome major histocompatibility complex barriers by inducing tolerance. With the goal of inducing tolerance to BALB/c-derived murine hybridoma cells producing the 4C6 monoclonal antibody (mAb), we transplanted BALB/c fetal tissue into neonatal pigs during a regimen of low-dose conditioning with busulfan and cyclophosphamide. After the tolerance induction phase, animals received intraperitoneal injections of 4C6 mAb hybridoma cells. Evidence of persistence of injected cells over time was sought by molecular analysis of peripheral blood for the presence of mouse genomic sequences and circulating 4C6 mAb. Persistence of donor polymerase chain reaction signal during the entire duration of the study, detectable mAb titer for 6 weeks, and a twofold increase of mAb concentration after a boost hybridoma infusion was observed in one animal receiving six consecutive administrations of the conditioning regimen. Our model has the distinctive advantage of allowing functional monitoring of engrafted cells for studying tolerance induction strategies. In addition, this model could be the basis for approaches aimed at producing mAbs in tolerized large animals.

T-cell-depleted CD34+ cell transplantation from an HLA-mismatched donor in a low-birthweight infant with X-linked severe combined immunodeficiency

The best strategy of hematopoietic stem cell (HSC) transplantation for low-birthweight (LBW) infants with severe combined immunodeficiency (SCID) remains to be determined. To avoid the toxicity of drugs used for the transplantation and the risk of graft-versus-host disease (GVHD), the authors performed allogeneic bone marrow HSC transplantation with a combination of CD34 selection and T-cell depletion in a LBW infant with X-linked SCID. The authors analyzed the process of T-cell reconstitution after the transplantation in this patient. The patient was born at 30 weeks and 2 days' gestational age via cesarean section. He was diagnosed as having SCID at birth. The patient received a transplant of 1 million CD34+ cells/kg body weight. Immunologic reconstitution was investigated by means of phenotypic analysis of T cells and genetic analysis of coding joint T-cell receptor rearrangement excision circle expression. Increases in donor-derived NK cells and T cells were observed 2 and 3 months after the transplantation, respectively. The patient had no infectious complications or GVHD despite the presence of SCID and prematurity-associated immunodeficiency. Analysis of T-cell regeneration pathways revealed that T cells reconstituted mainly via the thymus-dependent pathway. T-cell-depleted CD34+ cell transplantation would be a safe and useful therapy for LBW infants with SCID.

In utero stem cell transplantation

In utero haematopoietic cell transplantation (IUHCT) is a promising approach for the treatment of a variety of genetic disorders. The rationale is to take advantage of normal events during haematopoietic and immunological ontogeny to facilitate allogeneic haematopoietic engraftment. Strategies that will be discussed include the direct achievement of therapeutic levels of donor cell engraftment by IUHCT, the achievement of adequate levels of engraftment to donor-specific tolerance by IUHCT, followed by postnatal non-myeloablative regimens to enhance levels of donor cell engraftment into the therapeutic range. Although in utero haematopoietic cell transplantation has been clinically successful in severe combined immunodeficiency disease (SCID), it has been unsuccessful in target disorders where there is not a selective advantage for donor cells. This chapter presents the recognized barriers to engraftment in the fetus and discusses promising experimental strategies to overcome these barriers.

Chimerism and Tolerance Post-In Utero Transplantation with Embryonic Stem Cells

BACKGROUND

Clinical application of in utero transplantation (IUT) in human fetuses with intact immune systems resulted in a very low level of donor chimerism. In this study, we examined whether the fetal immune system early in the second trimester of pregnancy (13.5 dpc) can initiate immune tolerance for major histocompatibility complex (MHC)-mismatched embryonic stem (ES) cells. We also examined whether immune tolerance mechanisms respond differently to ontogenetically different stem cells.

METHODS

MHC-mismatched ES, fetal liver (FL), and bone-marrow (BM) cells (H-2kd) at 1 x 10(9) cells/kg fetal body weight were injected intraperitoneally into 13.5 dpc BALB/c fetuses (H-2Kd). Peripheral chimerism was determined in blood by flow cytometry (sensitivity< or =0.1%) at monthly intervals. Donor-specific immune responses were determined by cytotoxic lymphocyte (CTL) assay, mixed lymphocyte reaction, and T helper (Th)1 and Th2 cytokine assays. Chimeric mice at the age of 9 months received postnatal boosts (PB) with minimal conditioning of 200 cGy by intravenous injection of 1 x 10(9) of the corresponding cells/kg body weight.

RESULTS

After IUT with ES, FL, or BM cells, the level of peripheral chimerism within the first 9 months of life was 0% to 0.4%. PB with 1 x 10(9)/kg of corresponding cells resulted in a decrease in the peripheral chimerism to 0% within 2 weeks of PB. CTL and cytokine assays before and after PB demonstrated a shift toward immunity.

CONCLUSIONS

Immunologic tolerance was not achieved after IUT of murine fetuses at 13.5 dpc with MHC-mismatched ES cells, and only a low level chimerism was achieved.

In utero stem cell transplantation: a European overview

In utero stem cell transplantation (IUTx) is a therapeutic option for some lymphohaematopoietic disorders which can be diagnosed early in pregnancy. However, the promise of effective treatment before potentially life-threatening pathology becomes manifested has not been realised in all cases. This has prompted investigators to reassess their understanding of fetal haematopoiesis and of developmental pathways in the fetal immune system, to unravel the problem of failure to engraft after IUTx. The European Network for Fetal Transplantation (ENFET) was established to address these issues and to develop a concerted approach to IUTx. In this way, ENFET aims to study the basic biology of stem cell development and to put the findings into the context of engraftment potential following IUTx. One issue which has gained currency since ENFET was established, is the concept of stem cell 'plasticity', which has changed our view of the utility of IUTx so that there is now a real prospect for using this therapy in a larger range of disorders than was initially envisaged. Paradoxically, our current knowledge of stem cell plasticity must also change our views on the utility of IUTx for haematopoietic disorders, since it might offer some insights into the reasons for lack of engraftment observed in some of these conditions. The issue of in utero gene therapy is also being addressed by members of the ENFET consortium. Recent setbacks in postnatal gene therapy trials have put this therapeutic modality under intense scrutiny and there is much work still to be done before such therapy can realistically be offered in utero.

Fetal Immune Suppression as Adjunctive Therapy for In Utero Hematopoietic Stem Cell Transplantation in Nonhuman Primates

In utero hematopoietic stem cell transplantation could potentially be used to treat many genetic diseases but rarely has been successful except in severe immunodeficiency syndromes. We explored two ways to potentially increase chimerism in a nonhuman primate model: (a) fetal immune suppression at the time of transplantation and (b) postnatal donor stem cell infusion. Fetal Macaca nemestrina treated with a combination of the corticosteroid betamethasone (0.9 mg/kg) and rabbit thymoglobulin (ATG; 50 mg/kg) were given haploidentical, marrow-derived, CD34+ -enriched donor cells. Animals treated postnatally received either donor-derived T cell-depleted or CD34+ -enriched marrow cells. Chimerism was determined by traditional and real-time polymerase chain reaction from marrow, marrow progenitors, peripheral blood, and mature peripheral blood progeny. After birth, the level of chimerism in the progenitor population was higher in the immune-suppressed animals relative to controls (11.3% +/- 2.7% and 5.1% +/- 1.5%, respectively; p = .057). Chimerism remained significantly elevated in both marrow (p = .02) and fluorescence-activated cell sorted and purified CD34+ cells (p = .01) relative to control animals at > or = 14 months of age. Peripheral blood chimerism, both at birth and long term, was similar in immune-suppressed and control animals. In the animals receiving postnatal donor cell infusions, there was an initial increase in progenitor chimerism; however, at 6-month follow-up, the level of chimerism was unchanged from the preinfusion values. Although fetal immune suppression was associated with an increase in the level of progenitor and marrow chimerism, the total contribution to marrow and the levels of mature donor progeny in the peripheral blood remained low. The level of long-term chimerism also was not improved with postnatal donor cell infusion.

Mutations of the T-cell receptor constant region after in utero stem cell transplantation

Like the immunoglobulin genes, the T-cell receptor genes are generated by rearrangements of non-contiguous genomic V, D and J regions, but unlike the immunoglobulin genes, somatic hypermutation is an infrequent event in T-cell receptor genes. Here, we describe the occurrence of spontaneous mutations in the constant regions of the T-cell receptor beta chains of T lymphocytes obtained from two babies who underwent in utero transplantation because of severe combined immunodeficiency. In view of the fact that in babies receiving transplants before birth, hematopoietic chimerism is consistently present, the lymphocytes are likely to be under chronic activation, which may represent a relevant biologic stimulus for generating the observed T-cell receptor hypermutation. This possibility is supported by the finding that the highest number of mutations was identified in clonally expanded T cells. These results provide further support indicating that hypermutation of the T-cell receptor genes may indeed occur, given the necessary conditions.

Complete allogeneic hematopoietic chimerism achieved by in utero hematopoietic cell transplantation and cotransplantation of LLME-treated, MHC-sensitized donor lymphocytes

OBJECTIVE

In utero hematopoietic cell transplantation (IUHCT) typically achieves low-level mixed hematopoietic chimerism. However, the goal of IUHCT is to achieve therapeutic levels of chimerism. We hypothesized that prenatal adoptive immunotherapy might achieve high-level donor chimerism after IUHCT.

MATERIALS AND METHODS

BALB/CE15 fetal mice were transplanted with a mixture of C57BL/6 (B6) T-cell-depleted bone marrow (TCD BM) cells and splenocytes from B6 mice presensitized to BALB/C alloantigen. The splenocytes were preincubated in L-leucyl-L-leucine methyl ester (LLME), to minimize graft vs host disease (GVHD). Recipients were followed after birth for donor cell chimerism and GVHD.

RESULTS

Full donor hematopoietic chimerism following a single prenatal transplant was achieved in seven transplanted animals. Fully chimeric animals were healthy, without evidence of GVHD, and maintained their engraftment for the duration of the study (48 weeks). However, the addition of presensitized LLME-treated cells decreased survival until weaning relative to TCD BM alone, suggesting that some animals were lost to acute GVHD. Surviving chimeric animals demonstrated increased frequencies of T-regulatory cell populations in their spleen and BM, suggesting that they had successfully suppressed GVHD, allowing survival.

CONCLUSIONS

This study represents "proof in principle" that prenatal immunotherapeutic strategies may achieve complete hematopoietic engraftment across full MHC barriers when combined with IUHCT. However, strategies with greater hematopoietic specificity must be developed prior to consideration of clinical application.

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.

MolecularDefects inHumanSevereCombinedImmunodeficiency andApproaches toImmuneReconstitution

Mutations in nine different genes have been found to cause the human severe combined immunodeficiency syndrome. The products of three of the genes--IL-2RG, Jak3, and IL-7R alpha--are components of cytokine receptors, and the products of three more-RAG1, RAG2, and Artemis-are essential for effecting antigen receptor gene rearrangement. Additionally, a deficiency of CD3 delta, a component of the T-cell antigen receptor, results in a near absence of circulating mature CD3+ T cells and a complete lack of gamma/delta T cells. Adenosine deaminase deficiency results in toxic accumulations of metabolites that cause T cell apoptosis. Finally, a deficiency of CD45, a critical regulator of signaling thresholds in immune cells, also causes SCID. Approaches to immune reconstitution have included bone marrow transplantation and gene therapy. Bone marrow transplantation, both HLA identical unfractionated and T cell-depleted HLA haploidentical, has been very successful in effecting immune reconstitution if done in the first 3.5 months of life and without pretransplant chemotherapy. Gene therapy was highly successful in nine infants with X-linked SCID, but the trials have been placed on hold due to the development of a leukemic process in two of the children because of insertional oncogenesis.

In utero hematopoietic stem cell transplantation in nonhuman primates: the role of T cells

In utero transplantation of hematopoietic stem cells is a promising treatment for immune and hematologic diseases of fetuses and newborns. Unfortunately, there are limited data from nonhuman primates and humans describing optimal transplantation conditions. The purpose of this investigation was to determine the effect of T-cell number on engraftment and the level of chimerism after in utero transplantation in nonhuman primates. CD34(+) allogeneic adult bone marrow cells, obtained from the sire after G-CSF and stem cell factor administration, were transplanted into female fetal recipients. The average CD34(+) cell dose was 3.0 x 10(9)/kg (range, 9.9 x 10(8) to 4.4 x 10(9)) and the T-cell dose ranged from 2.6 x 10(5) to 1.1 x 10(8)/kg. Chimerism was determined in peripheral blood subsets (CD2, CD13, and CD20) and in progenitor cell populations by using polymerase chain reaction. Chimerism was noted in seven of eight live-born animals. The level of chimerism in the progenitor population was related to the fetal T-cell dose (r = 0.64, p < 0.02). At the lowest T-cell dose (2.6 x 10(5)/kg), no chimerism was detected. As the T-cell dose increased to 10(6-7)/kg, the level of chimerism increased. Adjusting the T-cell dose to 1.1 x 10(8)/kg resulted in fatal graft-versus-host disease (GVHD). The results of this study emphasize the importance of T cells in facilitating donor cell engraftment and in producing GVHD in fetal nonhuman primates. Some animals achieved levels of chimerism in the marrow hematopoietic progenitor cell population that would likely have clinical relevance. However, the levels of chimerism in peripheral blood were too low for therapeutic benefit. Further studies are needed to test methods that are likely to enhance donor cell engraftment and peripheral blood levels of donor cells.