Fetal liver cell transplantation for the creation of lymphohematopoietic chimerism in fetal baboons

Pre-Existing Maternal Antibodies Cause Rapid Prenatal Rejection of Allotransplants in the Mouse Model of In Utero Hematopoietic Cell Transplantation

In utero hematopoietic cell transplantation (IUHCT) is a nonmyeloablative nonimmunosuppressive alternative to postnatal hematopoietic stem cell transplantation for the treatment of congenital hemoglobinopathies. Anti-HLA donor-specific Abs (DSA) are associated with a high incidence of graft rejection following postnatal hematopoietic stem cell transplantation. We determine if DSA present in the mother can similarly cause graft rejection in the fetus following IUHCT. Ten million C57BL/6 (B6, H2k^b) bone marrow cells were transplanted in utero into gestational day 14 BALB/c (H2k^d) fetuses. The pregnant BALB/c dams carrying these fetuses either had been previously sensitized to B6 Ag or were injected on gestational days 13-15 with serum from B6-sensitized BALB/c females. Maternal-fetal Ab transmission, Ab opsonization of donor cells, chimerism, and frequency of macrochimeric engraftment (chimerism >1%) were assessed by flow cytometry. Maternal IgG was transmitted to the fetus and rapidly opsonized donor cells following IUHCT. Donor cell rejection was observed as early as 4 h after IUHCT in B6-sensitized dams and 24 h after IUHCT in dams injected with B6-sensitized serum. Efficient opsonization was strongly correlated with decreased chimerism. No IUHCT recipients born to B6-sensitized dams or dams injected with B6-sensitized serum demonstrated macrochimeric engraftment at birth compared with 100% of IUHCT recipients born to naive dams or dams injected with naive serum (p < 0.001). In summary, maternal donor-specific IgG causes rapid, complete graft rejection in the fetus following IUHCT. When a third-party donor must be used for clinical IUHCT, the maternal serum should be screened for DSA to optimize the chance for successful engraftment.

Stem Cell Transplantation in the Fetus

BACKGROUND

In utero transplantation (IUT) of hematopoietic stem cells has the potential to treat a large number of hematologic and metabolic diseases amenable to partial replacement of the hematopoietic system.

METHODS

A review of the literature was conducted that focused on the clinical and experimental experience with IUT and, in this context, the development of the hematopoietic and immune systems.

RESULTS

Successful application of IUT has been limited to the treatment of various types of immunodeficiencies that affect lymphocyte development and function. Other congenital defects such as the thalassemias have not resulted in clinically significant engraftment. Recent efforts at understanding and overcoming the barriers to engraftment in the fetus have focused on providing a selective advantage to donor stem cells and fostering immune tolerance toward the donor cells. The critical cellular components of the graft that promote engraftment and tolerance induction are being evaluated in animal models. Improvements in engraftment have resulted from the inclusion of T cells and/or dendritic cells in the graft, as well as a strategy of combined prenatal and postnatal transplantation.

CONCLUSIONS

The advantages, necessity, and benefits of early treatment will continue to encourage development of IUT as a means to treat hematopoietic and other types of birth defects.

Postnatal xenogeneic B-cell tolerance in swine following in utero intraportal antigen exposure

BACKGROUND

The objective of this study was to investigate the humoral immune response to xenogeneic antigens administered during the fetal state utilizing a baboon-to-pig model.

METHODS

Nine fetuses from an alpha-1,3-galactosyltransferase gene knockout (GalT-KO) MGH-miniature swine sow underwent transuterine ultrasound-guided intraportal injection of T-cell depleted baboon bone marrow (B-BM) at mid-gestation. Two juvenile GalT-KO swine undergoing direct B-BM intraportal injection were used as controls.

RESULTS

Postnatal humoral tolerance was induced in the long-term surviving piglets as demonstrated by the absence of any antibody response to baboon donor cells. In addition, a second intraportal B-BM administration at 2.5 months post-birth led to no antibody formation despite re-exposure to xenogeneic antigens. This B-cell unresponsiveness was abrogated only when the animal was exposed subcutaneously to third-party xenogeneic and allogeneic antigens, suggesting that the previously achieved humoral non-responsiveness was donor specific. In comparison, the two juvenile GalT-KO control swine demonstrated increasing anti-baboon IgM and IgG levels following intraportal injection.

CONCLUSIONS

In summary, xenogeneic B-cell tolerance was induced through in utero intraportal exposure to donor cells and this tolerance persisted following postnatal rechallenge with donor B-BM, but was lost on exposure to third-party antigen, possibly as a result of cross-reactive antibody formation.

Correction of murine hemoglobinopathies by prenatal tolerance induction and postnatal nonmyeloablative allogeneic BM transplants

Sickle cell disease (SCD) and thalassemias (Thal) are common congenital disorders, which can be diagnosed early in gestation and result in significant morbidity and mortality. Hematopoietic stem cell transplantation, the only curative therapy for SCD and Thal, is limited by the absence of matched donors and treatment-related toxicities. In utero hematopoietic stem cell transplantation (IUHCT) is a novel nonmyeloablative transplant approach that takes advantage of the immunologic immaturity and normal developmental properties of the fetus to achieve mixed allogeneic chimerism and donor-specific tolerance (DST). We hypothesized that a combined strategy of IUHCT to induce DST, followed by postnatal nonmyeloablative same donor "booster" bone marrow (BM) transplants in murine models of SCD and Thal would result in high levels of allogeneic engraftment and donor hemoglobin (Hb) expression with subsequent phenotypic correction of SCD and Thal. Our results show that: (1) IUHCT is associated with DST and low levels of allogeneic engraftment in the murine SCD and Thal models; (2) low-level chimerism following IUHCT can be enhanced to high-level chimerism and near complete Hb replacement with normal donor Hb with this postnatal "boosting" strategy; and (3) high-level chimerism following IUHCT and postnatal "boosting" results in phenotypic correction in the murine Thal and SCD models. This study supports the potential of IUHCT, combined with a postnatal nonmyelablative "boosting" strategy, to cure Thal and SCD without the toxic conditioning currently required for postnatal transplant regimens while expanding the eligible transplant patient population due to the lack of a restricted donor pool.

Temporal definition of haematopoietic stem cell niches in a large animal model of in utero stem cell transplantation

The fetal sheep model has served as a biologically relevant and translational model to study in utero haematopoietic stem cell transplantation (IUHSCT), yet little is known about the ontogeny of the bone marrow (BM) niches in this model. Because the BMmicroenvironment plays a critical role in the outcome of haematopoietic engraftment, we have established the correlation between the fetal-sheep and fetal-human BM niche ontogeny, so that studies addressing the role of niche development at the time of IUHSCT could be accurately performed. Immunofluorescence confocal microscopic analysis of sheep fetal bone from gestational days (gd) 25-68 showed that the BM microenvironment commences development with formation of the vascular niche between 25 and 36 gd in sheep; correlating with the events at 10-11 gestational weeks (gw) in humans. Subsequently, between 45 and 51 gd in sheep (c. 14 gw in humans), the osteoblastic/endosteal niche started developing, the presence of CD34(+)  CD45(+) cells were promptly detected, and their number increased with gestational age. IUHSCT, performed in sheep at 45 and 65 gd, showed significant haematopoietic engraftment only at the later time point, indicating that a fully functional BM microenvironment improved engraftment. These studies show that sheep niche ontogeny closely parallels human, validating this model for investigating niche influence/manipulation in IUHSCT engraftment.

EphB2 isolates a human marrow stromal cell subpopulation with enhanced ability to contribute to the resident intestinal cellular pool

To identify human bone marrow stromal cell (BMSC) subsets with enhanced ability to engraft/contribute to the resident intestinal cellular pool, we transplanted clonally derived BMSCs into fetal sheep. Analysis at 75 d post-transplantation showed 2 of the 6 clones engrafting the intestine at 4- to 5-fold higher levels (5.03±0.089 and 5.04±0.15%, respectively) than the other clones (P<0.01), correlating with the percentage of donor-derived Musashi-1(+) (12.01-14.17 vs. 1.2-3.8%; P<0.01) or leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5)(+) cells within the intestinal stem cell (ISC) region. Phenotypic and transcriptome analysis determined that the clones with enhanced intestinal contribution expressed high levels of Ephrin type B receptor 2 (EphB2). Intestinal explants demonstrated proliferation of the engrafted cells and ability to generate crypt-like structures in vitro still expressing EphB2. Additional transplants based on BMSC EphB2 expression demonstrated that, at 7 d post-transplant, the EphB2(high) BMSCs engrafted in the ISC region at levels of 2.1 ± 0.2%, while control EphB2(low) BMSCs engrafted at 0.3 ± 0.1% (P<0.01). Therefore we identified a marker for isolating and culturing an expandable subpopulation of BMSCs with enhanced intestinal homing and contribution to the ISC region.

The case for intrauterine stem cell transplantation

The clinical burden imposed by the collective group of monogenic disorders demands novel therapies that are effective at achieving phenotypic cure early in the disease process before the development of permanent organ damage. This is important for lethal diseases and also for non-perinatally lethal conditions that are characterised by severe disability with little prospect of postnatal cure. Where postnatal treatments are limited to palliative options, intrauterine stem-cell therapies may offer the potential to arrest pathogenesis in the early undamaged fetus. Intrauterine stem-cell transplantation has been attempted for a variety of diseases, but has only been successful in immune deficiency states in the presence of a competitive advantage for donor cells. This disappointing clinical record requires preclinical investigations into strategies that improve donor cell engraftment, including optimising the donor cell source and manipulating the microenvironment to facilitate homing. This chapter aims to outline the current challenges of intrauterine stem-cell therapy.

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.

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.

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.

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.

In utero transplantation of human bone marrow-derived multipotent mesenchymal stem cells in mice

Mesenchymal stem cells (MSCs) are multipotent cells that can be isolated from human bone marrow and possess the potential to differentiate into progenies of embryonic mesoderm. However, current evidence is based predominantly on in vitro experiments. We used a murine model of in utero transplantation (IUT) to study the engraftment capabilities of human MSCs. MSCs were obtained from bone marrow by negative immunoselection and limiting dilution, and were characterized by flow cytometry and by in vitro differentiation into osteoblasts, chondrocytes, and adipocytes. MSCs were transplanted into fetal mice at a gestational age of 14 days. Engraftment of human MSCs was determined by flow cytometry, polymerase chain reaction, and fluorescence in situ hybridization (FISH). MSCs engrafted into tissues originating from all three germ layers and persisted for up to 4 months or more after delivery, as evidenced by the expression of the human-specific beta-2 microglobulin gene and by FISH for donor-derived cells. Donor-derived CD45+ cells were detectable in the peripheral blood of recipients, suggesting the participation of MSCs in hematopoiesis at the fetal stage. This model can further serve to evaluate possible applications of MSCs.

Tissue distribution of fetal liver cells following in utero transplantation in mice

Transplantation of hepatic stem cells in utero has been advanced as a potential clinical approach to a variety of diseases, including deficiencies of coagulation factors. Although syngeneic transplantation has met with some success, consideration needs to be given to the potential for transplanted cells to colonize nontarget tissues. Liver cells were harvested from Rosa26 embyros at embryonic age 12.5 days postconception (pc) and transplanted into the peritoneal cavity of syngeneic recipients in utero. Tissues were harvested from tissue recipients at various time points ranging from 1 to 328 days pc, and tissues were stained for beta-galactosidase to identify the existence of cells derived from Rosa26 donors. Beta-galactosidase-positive cells were found in the lung, liver, and brain as early as 20 days pc and through 328 days pc. Positive cells in these tissues existed as islands of cells that were morphologically similar to hepatocytes. In the spleen, individual beta-galactosidase-positive cells of both leukocytic and erythrocytic lineages were present, and suggest that hematopoietic cells were transferred to recipients along with hepatocytes. The lack of an inflammatory response to the beta-galactosidase-positive cells suggests that the donor cells were immunologically tolerated. In summary, the possibility that cells administered in utero may inadvertently colonize nontarget tissues suggests that clinical application of this method will need to be approached with diligence.

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.

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.

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.

Engraftment of human cord blood-derived stem cells in preimmune ovine fetuses after ultrasound-guided in utero transplantation

OBJECTIVE

The fetal sheep in utero transplantation model has developed into an important tool to study the efficacy of human in utero stem cell transplantation and gene therapy because of similarities in both the scale and development of immunocompetence relative to gestational age. The aim of this study was to determine whether human stem cells can be successfully transplanted to the first-trimester ovine fetus by use of a newly developed minimally invasive technique.

STUDY DESIGN

Human cord blood-derived, CD34(+)-enriched stem cells were injected into the peritoneal cavity of 45- to 60-day-old ovine fetuses by using ultrasound-guided transabdominal percutaneous needle puncture. Engraftment was determined 1 to 3 months after birth by flow cytometry with use of human-specific anti-CD45 antibodies.

RESULTS

In contrast to previous studies that used surgical techniques, we observed a fetal loss rate of 24%, significantly below previous values and only marginally higher than natural loss. Successful human cell engraftment was achieved in 18% of lambs available for analysis. Engraftment levels of human cells in bone marrow of the recipient were up to 0.8% of total nucleated cells.

CONCLUSION

Ultrasound-guided percutaneous transplantation of stem cells to fetal sheep in the first trimester is feasible. Although we were unable to observe a significant improvement in the level of engraftment of human cells in sheep, the decreased fetal loss rate associated with this technique allows greater use for further studies that use this model of in utero transplantation.

In vitro studies of the role of CD3+ and CD56+ cells in fetal liver cell alloreactivity

BACKGROUND

Previous functional studies have suggested that fetal liver cells (FLC) are capable of responding to allogeneic stimulation and have allostimulatory capacity by early in the second trimester. The present study was designed to analyze whether the allogenic response in human FLC is restricted to HLA class II expression and to evaluate the role of CD3+ cells (T cells) and CD56+ cells (natural killer cells) in the allogenic response.

METHODS

Mixed lymphocyte culture (MLC) experiments were performed on human FLC, at 14 to 18 gestational weeks, before and after depletion of HLA class II+ cells from the stimulator FLC pool (6-11 gestational weeks) and before and after depletion of CD3+ and CD56+ cells from the responder population.

RESULTS

Depletion of HLA class II+ cells from the stimulator FLC pool resulted in a decreased response in 9 of 12 initially positive MLCs. CD3+ cell depletion from responder FLC resulted in a decreased response in four of seven experiments with peripheral blood lymphocytes as stimulators and in two of five experiments with FLC as stimulators. Depletion of CD56+ cells from responder FLC resulted in a decreased response in five of seven initially positive MLCs with peripheral blood lymphocytes as stimulators and two of five with FLC as stimulators.

CONCLUSIONS

The results indicate that FLC are capable of alloresponsiveness when studied in MLC and that the response seems to be HLA class II dependent. Depletion of CD3+ or CD56+ cells led to a reduction in the MLC in a majority of the experiments. The question remains how these cells interact; it is likely that both cell types exhibit complementary effects in the early allogenic response.

Ultrasound-guided stem cell sampling from the early ovine fetus for prenatal ex vivo gene therapy

OBJECTIVE

Prenatal ex vivo gene therapy might be an effective and safe strategy with which to treat severe genetic disorders in utero. For this purpose, autologous fetal stem cells must be collected before the second trimester, transfected in vitro, and transplanted back to the fetus. The aim of this study was to determine whether stem cells can be sampled from the first trimester fetal liver in ongoing gestation.

STUDY DESIGN

Fetal liver stem cell sampling was performed in 21 ovine fetuses. Pregnant ewes at 57 +/- 2 gestational days were generally anesthesized. A 20-gauge needle was inserted transcutaneously into the fetal liver under ultrasound guidance. Fetal liver cells were sampled by suction. The numbers of nucleated cells and progenitor/stem cells were determined.

RESULTS

All 21 fetuses showed normal heart rate 5 minutes after the procedure. A mean (+/-SEM) of 2.07 +/- 0.5 x 10(7) nucleated cells and 172 +/- 53 colony-forming units per 10(5) cells (hematopoietic progenitors/stem cells) were collected. Fetal loss rate at term was 7 of 21 fetuses (33%).

CONCLUSION

This study shows that fetal liver cells can be collected in the early fetus with an ultrasound-guided technique. The number of fetal liver cells that are collectable is large enough for autologous transplantation and engraftment of genetically engineered (transfected) stem cells.

Transplantation of a fetus with paternal Thy-1(+)CD34(+)cells for chronic granulomatous disease

A fetus diagnosed with X-linked chronic granulomatous disease was transplanted with Thy-1(+)CD34(+) cells of paternal origin. The transplant was performed at 14 weeks gestation by ultrasound guided injection into the peritoneal cavity. The fetus was delivered at 38 weeks gestation after an otherwise uneventful pregnancy. Umbilical cord blood was collected and used to determine the level of peripheral blood chimerism as well as levels of functional engrafted cells. Flow cytometry was used to detect donor leukocytes identified as HLA-A2(-)B7(+) cells, whereas recipient cells were identified as HLA-A2(+)B7(-) cells. No evidence of donor cell engraftment above a level of 0.01% was found. PCR was used to detect HLA-DRB1*15(+) donor cells among the recipient's HLA-DRB1*15(-) cells, but no engraftment was seen with a sensitivity of 1:1000. The presence of functional, donor-derived neutrophils was assessed by flow cytometry using two different fluorescent dyes that measure reactive oxygen species generated by the phagocyte NADPH oxidase. No evidence of paternal-derived functional neutrophils above a level of 0.15% was observed. Peripheral blood and bone marrow samples were collected at 6 months of age. Neither sample showed engraftment by HLA typing using both flow cytometry and PCR. Functional phagocytes were also not observed. Furthermore, no indication of immunological tolerance specific for the donor cells was indicated by a mixed lymphocyte reaction assay performed at 6 months of age. While there appears to be no engraftment of the donor stem cells, the transplant caused no harm to the fetus and the child was healthy at 6 months of age. Analyses of fetal tissues, obtained from elective abortions, revealed that CD3(+) T cells and CD56(+)CD3(-) NK cells are present in the liver at 8 weeks gestation and in the blood by 9 weeks gestation. The presence of these lymphocytes may contribute to the lack of donor cell engraftment in the human fetus.

Transplantation of human peripheral blood stem cells into fetal rhesus monkeys (Macaca mulatta)

BACKGROUND

Methods for assessing engraftment efficiency have been explored in a primate xenogeneic model of in utero hematopoietic stem cell transplantation.

METHODS

Human peripheral blood stem cells (PBSC) were obtained by leukapheresis from a human male donor after 4 days of administration of recombinant human granulocyte-colony stimulating factor (5 microg/kg/ day). PBSC were enriched for the CD34+ population with and without T-cell depletion. The resulting mononuclear cells consisted of two cell populations, one that was stem cell enriched (0.83% CD3+ cells, 95% CD34+; group 1) and one that was stem cell enriched and T-cell depleted (<0.03% CD3+ cells, 98% CD34+; group 2). Four fetal monkeys (two per group) received either two or four i.p. injections (approximately 5x10(6) cells/injection) via ultrasound guidance every other day over a 7-day period (gestational days 50, 52, 54, and 56). One fetus in each group also received i.p. recombinant human stem cell factor (25 microg/kg) and recombinant human granulocyte-colony stimulating factor (10 microg/kg) posttransplant every 10 days from gestational day 60-150.

RESULTS

Four healthy newborns were delivered at term, and specimens were analyzed by polymerase chain reaction for the human Y chromosome (birth, monthly to 6 months; blood, marrow, progenitor assays). Polymerase chain reaction results were positive for all four newborns in all specimens assessed, and flow cytometric analysis for human CD45 in marrow showed engraftment ranging from 0.1-1.7%. There was no evidence of graft-versus-host disease in any of the animals.

CONCLUSION

These studies show that (1) multilineage engraftment of human PBSC can be achieved in the fetal rhesus recipient, (2) the rhesus fetus appears to tolerate relatively high numbers of human CD3+ cells, and (3) healthy chimeric rhesus infants can be delivered at term after multiple in utero procedures.

In utero transplantation of human fetal haemopoietic cells in NOD/SCID mice

We have previously demonstrated that high levels of allogeneic, donor-derived mouse haemopoietic progenitor cells engraft following in utero transplantation in NOD/SCID mice. To evaluate whether the fetal NOD/SCID haemopoietic microenvironment supports the growth and development of human fetal haemopoietic progenitor cells, we injected fetal liver mononuclear cells (FL) or fetal bone marrow (FBM) derived CD34+ cells into NOD/SCID mice on day 13/14 of gestation. At 8 weeks of age 12% of FBM recipients and 10% of FL recipients were found to have been successfully engrafted with CD45+ human cells. CD45+ cells were present in the BM of all chimaeric animals; 5/6 recipients showed engraftment of the spleen, and 4/6 recipients had circulating human cells in the peripheral blood (PB). The highest levels of donor cells were found in the BM, with up to 15% of the nucleated cells expressing human specific antigens. Multilineage human haemopoietic engraftment, including B cells (CD19), myelomonocytic cells (CD13/33) and haemopoietic progenitor cells (CD34), was detected in the BM of chimaeric mice. In contrast, no human CD3+ cells were detected in any of the tissues evaluated. When the absolute number of engrafted human cells in the PB, BM and spleens of chimaeric mice was determined, a mean 16-fold expansion of human donor cells was observed. Although multilineage engraftment occurs in these fetal recipients, both the frequency and the levels of engraftment are lower than those previously reported when human cells are transplanted into adult NOD/SCID recipients.

In utero transplantation for thalassemia

In utero hematopoietic stem cell transplantation is a promising approach for the treatment of a variety of congenital hematologic diseases. Although the approach has been successful for immunodeficiency syndromes, attempts thus far to treat the hemoglobinopathies have failed. In most of these cases the late gestational age at transplantation, source of donor cells, or procedure-related complications, provide an explanation for failure. Nevertheless the biology of thalassemia, in the context of prenatal transplantation, requires examination. In contrast to postnatal bone marrow transplant regimens, engraftment after in utero transplantation requires donor cells to effectively complete for developing receptive sites in the recipient hematopoietic microenvironment. Effective prenatal treatment of thalassemia will depend on the ability of normal cells to engraft and complete in the thalassemic microenvironment. Clinical observations after bone marrow transplantation of amelioration of anemia in beta-thalassemia by relatively low degrees of mixed chimerism, and the apparent selective advantage observed for donor erythropoiesis, suggest prenatal transplantation could succeed. Prenatal strategies involving multiple transplants, donor-specific tolerance induction, and postnatal same-donor transplants should be considered.

Sustained Multilineage Engraftment of Allogeneic Hematopoietic Stem Cells in NOD/SCID Mice After In Utero Transplantation

Substantial barriers exist to the engraftment of hematopoietic cells in mice after in utero transplantation. Although high levels of donor-derived hematopoiesis have been reported in SCID mice, the majority of chimeric recipients exhibit decreasing levels of donor cells over time. To directly test whether the natural killer cell and macrophage activity of the recipients represents a barrier to sustained engraftment, fetal NOD/SCID mice were injected on day 13.5 of gestation with an enriched congenic hematopoietic progenitor cell population. Forty-four percent of pups showed the presence of Ly5.1+ donor cells 4 weeks after transplantation. The mean number of donor-derived nucleated cells in the peripheral blood (PB) was 30%. Although the majority of circulating donor cells were lymphocytes, up to 15% expressed myelomonocytic markers. Serial PB samples from individual mice indicated that the percentage of circulating donor cells increased from 17% to 55% between 4 and 24 weeks. At 6 months posttransplantation, an increased frequency of multilineage, donor-derived cells was also observed in the bone marrow (BM) and the spleen of chimeric recipients. The engraftment of pluripotent hematopoietic stem cells was evaluated by transplanting BM from chimeric mice into irradiated congenic recipients. Irradiated secondary recipients also exhibited multilineage donor-derived hematopoiesis in the PB, BM, and spleen for up to 6 months. These results show that the in utero transplantation of lineage-depleted BM cells into NOD/SCID recipients produces a high frequency of sustained engraftment of allogeneic hematopoietic stem cells.