Regulation of the earliest immune response to in utero hematopoietic cellular transplantation

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.

Fetoscopic versus Ultrasound-Guided Intravascular Delivery of Maternal Bone Marrow Cells in Fetal Macaques: A Technical Model for Intrauterine Haemopoietic Cell Transplantation

INTRODUCTION

Significant limitations with existing treatments for major haemoglobinopathies motivate the development of effective intrauterine therapy. We assessed the feasibility of fetoscopic and ultrasound-guided intrauterine haemopoietic cell transplantation (IUHCT) in macaque fetuses in early gestation when haemopoietic and immunological ontogeny is anticipated to enable long-term donor cell engraftment.

MATERIAL AND METHODS

Fluorescent-labelled bone marrow-derived mononuclear cells from 10 pregnant Macaca fascicularis were injected into their fetuses at E71-114 (18.9-170.0E+6 cells/fetus) by fetoscopic intravenous (n = 7) or ultrasound (US)-guided intracardiac injections, with sacrifice at 24 h to examine donor-cell distribution.

RESULTS

Operating times ranged from 35 to 118 min. Chorionic membrane tenting and intrachorionic haemorrhage were observed only with fetoscopy (n = 2). Labelled cells were stereoscopically visualised in lung, spleen, liver, and placenta. Donor-cell chimerism was highest in liver, spleen, and heart by flow cytometry, placenta by unique polymorphism qPCR, and was undetected in blood. Chimerism was 2-3 log-fold lower in individual organs by qPCR than by flow cytometry.

DISCUSSION

Both fetoscopic and US-guided IUHCT were technically feasible, but fetoscopy caused more intraoperative complications in our pilot series. The discrepancy in chimerism detection predicts the challenges in long-term surveillance of donor-cell chimerism. Further studies of long-term outcomes in the non-human primate are valuable for the development of clinical protocols for IUHCT.

Maternal and Fetal Immune Response to in Utero Stem Cell Transplantation

Purpose of Review

In Utero Hematopoietic Cellular Transplantation (IUHCT) is a promising intervention for the non-toxic treatment of congenital disease that hinges on the assumption of fetal immunologic immaturity and an inability to reject a hematopoietic allograft. However, clinical IUCHT has failed except in cases where the fetus is severely immunocompromised. The current review examines recent studies of engraftment barriers stemming from either the fetal or maternal immune system.

Recent Findings

New reports have illuminated roles for maternal humoral and cellular immunity and fetal innate cellular immunity in the resistance to allogeneic IUHCT. These experimental findings have inspired new approaches to overcome these barriers. Despite these advances, postulates regarding a maternal immune barrier to IUHCT provide an inadequate explanation for the well-documented clinical success only in the treatment of fetal immunodeficiency with normal maternal immunity.

Summary

Characterization of the maternal and fetal immune response to allogeneic IUHCT provides new insight into the complexity of prenatal tolerance. Future work in this area should aim to provide a unifying explanation for the observed patterns of success and failure with clinical IUHCT.

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.

NK cell tolerance as the final endorsement of prenatal tolerance after in utero hematopoietic cellular transplantation

The primary benefits of in utero hematopoietic cellular transplantation (IUHCT) arise from transplanting curative cells prior to the immunologic maturation of the fetus. However, this approach has been routinely successful only in the treatment of congenital immunodeficiency diseases that include an inherent NK cell deficiency despite the existence of normal maternal immunity in either setting. These observations raise the possibility that fetal NK cells function as an early barrier to allogeneic IUHCT. Herein, we summarize the findings of previous studies of prenatal NK cell allospecific tolerance in mice and in humans. Cumulatively, this new information reveals the complexity of the fetal immune response in the setting of rejection or tolerance and illustrates the role for fetal NK cells in the final endorsement of allospecific prenatal tolerance.

Immunological considerations in in utero hematopoetic stem cell transplantation (IUHCT)

In utero hematopoietic stem cell transplantation (IUHCT) is an attractive approach and a potentially curative surgery for several congenital hematopoietic diseases. In practice, this application has succeeded only in the context of Severe Combined Immunodeficiency Disorders. Here, we review potential immunological hurdles for the long-term establishment of chimerism and discuss relevant models and findings from both postnatal hematopoietic stem cell transplantation and IUHCT.

Differentiation and functional regulation of human fetal NK cells

The human fetal immune system is naturally exposed to maternal allogeneic cells, maternal antibodies, and pathogens. As such, it is faced with a considerable challenge with respect to the balance between immune reactivity and tolerance. Here, we show that fetal natural killer (NK) cells differentiate early in utero and are highly responsive to cytokines and antibody-mediated stimulation but respond poorly to HLA class I-negative target cells. Strikingly, expression of killer-cell immunoglobulin-like receptors (KIRs) did not educate fetal NK cells but rendered them hyporesponsive to target cells lacking HLA class I. In addition, fetal NK cells were highly susceptible to TGF-β-mediated suppression, and blocking of TGF-β signaling enhanced fetal NK cell responses to target cells. Our data demonstrate that KIR-mediated hyporesponsiveness and TGF-β-mediated suppression are major factors determining human fetal NK cell hyporesponsiveness to HLA class I-negative target cells and provide a potential mechanism for fetal-maternal tolerance in utero. Finally, our results provide a basis for understanding the role of fetal NK cells in pregnancy complications in which NK cells could be involved, for example, during in utero infections and anti-RhD-induced fetal anemia.