The maternal immune response inhibits the success of in utero hematopoietic cell transplantation

Preexisting maternal immunity to AAV but not Cas9 impairs in utero gene editing in mice

In utero gene editing (IUGE) is a potential treatment for inherited diseases that cause pathology before or soon after birth. Preexisting immunity to adeno-associated virus (AAV) vectors and Cas9 endonuclease may limit postnatal gene editing. The tolerogenic fetal immune system minimizes a fetal immune barrier to IUGE. However, the ability of maternal immunity to limit fetal gene editing remains a question. We investigated whether preexisting maternal immunity to AAV or Cas9 impairs IUGE. Using a combination of fluorescent reporter mice and a murine model of a metabolic liver disease, we demonstrated that maternal anti-AAV IgG antibodies were efficiently transferred from dam to fetus and impaired IUGE in a maternal titer-dependent fashion. By contrast, maternal cellular immunity was inefficiently transferred to the fetus, and neither maternal cellular nor humoral immunity to Cas9 impaired IUGE. Using human umbilical cord and maternal blood samples collected from mid- to late-gestation pregnancies, we demonstrated that maternal-fetal transmission of anti-AAV IgG was inefficient in midgestation compared with term, suggesting that the maternal immune barrier to clinical IUGE would be less relevant at midgestation. These findings support immunologic advantages for IUGE and inform maternal preprocedural testing protocols and exclusion criteria for future clinical trials.

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

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

Regulatory T cells promote alloengraftment in a model of late-gestation in utero hematopoietic cell transplantation

In utero hematopoietic cell transplantation (IUHCT) has the potential to cure congenital hematologic disorders including sickle cell disease. However, the window of opportunity for IUHCT closes with the acquisition of T-cell immunity, beginning at approximately 14 weeks gestation, posing significant technical challenges and excluding from treatment fetuses evaluated after the first trimester. Here we report that regulatory T cells can promote alloengraftment and preserve allograft tolerance after the acquisition of T-cell immunity in a mouse model of late-gestation IUHCT. We show that allografts enriched with regulatory T cells harvested from either IUHCT-tolerant or naive mice engraft at 20 days post coitum (DPC) with equal frequency to unenriched allografts transplanted at 14 DPC. Long-term, multilineage donor cell chimerism was achieved in the absence of graft-versus-host disease or mortality. Decreased alloreactivity among recipient T cells was observed consistent with donor-specific tolerance. These findings suggest that donor graft enrichment with regulatory T cells could be used to successfully perform IUHCT later in gestation.

In utero Therapy for the Treatment of Sickle Cell Disease: Taking Advantage of the Fetal Immune System

Sickle Cell Disease (SCD) is an autosomal recessive disorder resulting from a β-globin gene missense mutation and is among the most prevalent severe monogenic disorders worldwide. Haematopoietic stem cell transplantation remains the only curative option for the disease, as most management options focus solely on symptom control. Progress in prenatal diagnosis and fetal therapeutic intervention raises the possibility of in utero treatment. SCD can be diagnosed prenatally in high-risk patients using chorionic villus sampling. Among the possible prenatal treatments, in utero stem cell transplantation (IUSCT) shows the most promise. IUSCT is a non-myeloablative, non-immunosuppressive alternative conferring various unique advantages and may also offer safer postnatal management. Fetal immunologic immaturity could allow engraftment of allogeneic cells before fetal immune system maturation, donor-specific tolerance and lifelong chimerism. In this review, we will discuss SCD, screening and current treatments. We will present the therapeutic rationale for IUSCT, examine the early experimental work and initial human experience, as well as consider primary barriers of clinically implementing IUSCT and the promising approaches to address them.

Immune-tolerance to human iPS-derived neural progenitors xenografted into the immature cerebellum is overridden by species-specific differences in differentiation timing

We xeno-transplanted human neural precursor cells derived from induced pluripotent stem cells into the cerebellum and brainstem of mice and rats during prenatal development or the first postnatal week. The transplants survived and started to differentiate up to 1 month after birth when they were rejected by both species. Extended survival and differentiation of the same cells were obtained only when they were transplanted in NOD-SCID mice. Transplants of human neural precursor cells mixed with the same cells after partial in vitro differentiation or with a cellular extract obtained from adult rat cerebellum increased survival of the xeno-graft beyond one month. These findings are consistent with the hypothesis that the slower pace of differentiation of human neural precursors compared to that of rodents restricts induction of immune-tolerance to human antigens expressed before completion of maturation of the immune system. With further maturation the transplanted neural precursors expressed more mature antigens before the graft were rejected. Supplementation of the immature cells suspensions with more mature antigens may help to induce immune-tolerance for those antigens expressed only later by the engrafted cells.

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

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

In Utero Gene Therapy (IUGT) Using GLOBE Lentiviral Vector Phenotypically Corrects the Heterozygous Humanised Mouse Model and Its Progress Can Be Monitored Using MRI Techniques

In utero gene therapy (IUGT) to the fetal hematopoietic compartment could be used to treat congenital blood disorders such as β-thalassemia. A humanised mouse model of β-thalassemia was used, in which heterozygous animals are anaemic with splenomegaly and extramedullary hematopoiesis. Intrahepatic in utero injections of a β globin-expressing lentiviral vector (GLOBE), were performed in fetuses at E13.5 of gestation. We analysed animals at 12 and 32 weeks of age, for vector copy number in bone marrow, peripheral blood liver and spleen and we performed integration site analysis. Compared to noninjected heterozygous animals IUGT normalised blood haemoglobin levels and spleen weight. Integration site analysis showed polyclonality. The left ventricular ejection fraction measured using magnetic resonance imaging (MRI) in treated heterozygous animals was similar to that of normal non-β-thalassemic mice but significantly higher than untreated heterozygous thalassemia mice suggesting that IUGT ameliorated poor cardiac function. GLOBE LV-mediated IUGT normalised the haematological and anatomical phenotype in a heterozygous humanised model of β-thalassemia.

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.

Long-Term Hematopoietic Engraftment of Congenic Amniotic Fluid Stem Cells After in Utero Intraperitoneal Transplantation to Immune Competent Mice

Clinical success of in utero transplantation (IUT) using allogeneic hematopoietic stem cells (HSCs) has been limited to fetuses that lack an immune response to allogeneic cells due to severe immunological defects, and where transplanted genetically normal cells have a proliferative or survival advantage. Amniotic fluid (AF) is an autologous source of stem cells with hematopoietic potential that could be used to treat congenital blood disorders. We compared the ability of congenic and allogeneic mouse AF stem cells (AFSC) to engraft the hematopoietic system of time-mated C57BL/6J mice (E13.5). At 4 and 16 weeks of age, multilineage donor engraftment was higher in congenic versus allogeneic animals. In vitro mixed lymphocyte reaction confirmed an immune response in the allogeneic group with higher CD4 and CD8 cell counts and increased proliferation of stimulated lymphocytes. IUT with congenic cells resulted in 100% of donor animals having chimerism of around 8% and successful hematopoietic long-term engraftment in immune-competent mice when compared with IUT with allogeneic cells. AFSCs may be useful for autologous cell/gene therapy approaches in fetuses diagnosed with congenital hematopoietic disorders.

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

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

Sheep CD34+ amniotic fluid cells have hematopoietic potential and engraft after autologous in utero transplantation

Unmatched allogeneic in utero stem cell transplantation (IUSCT) produces poor engraftment unless the fetus has congenital immunodeficiency, probably because of maternal and fetal immune responses to injected cells. We studied the functional hematopoietic potential of transduced green fluorescent protein (GFP+) sheep amniotic fluid (AF) stem cells, before and after autologous IUSCT. CD34+ cells were selected from first trimester sheep AF, transduced overnight, and injected intravenously into NOD-SCID-gamma (NSG) mice. At 3 months, primary recipient bone marrow (BM) was injected into secondary NSG recipients. GFP+ cells were detected in the hematopoietic organs and peripheral blood of primary and secondary recipients at 3 months. Autologous IUSCT (transduced GFP+CD34+AF) was performed in fetal sheep. Six months postnatally, lamb BM was injected into secondary NSG recipients. GFP+ cells were detected in the peripheral blood of primary and secondary recipients. This confirms the hematopoietic potential of AF stem cells supporting the concept of autologous IUSCT to treat congenital hematopoietic disease.

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

BACKGROUND AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Neonatal immune-tolerance in mice does not prevent xenograft rejection

Assessing the efficacy of human stem cell transplantation in rodent models is complicated by the significant immune rejection that occurs. Two recent reports have shown conflicting results using neonatal tolerance to xenografts in rats. Here we extend this approach to mice and assess whether neonatal tolerance can prevent the rapid rejection of xenografts. In three strains of neonatal immune-intact mice, using two different brain transplant regimes and three independent stem cell types, we conclusively show that there is rapid rejection of the implanted cells. We also address specific challenges associated with the generation of humanized mouse models of disease.