The Theoretical Basis of In Utero Hematopoietic Stem Cell Transplantation and Its Use in the Treatment of Blood Disorders

Transamniotic Delivery of Hematopoietic Stem Cells Genetically Modified to Carry a Human Hemoglobin Subunit Beta Gene (HBB) in a Healthy Rodent Model

BACKGROUND

We sought to determine whether transamniotic stem cell therapy (TRASCET) could be a viable alternative for the fetal administration of genetically modified hematopoietic stem cells (HSCs) carrying a human hemoglobin subunit beta gene (hHBB) in a healthy syngeneic rat model.

METHODS

Time-dated pregnant Lewis dams underwent volume-matched intra-amniotic injections in all their fetuses (n = 61) of a suspension of donor HSCs genetically modified with either both a hHBB gene and a firefly luciferase reporter gene (n = 42) or the firefly luciferase reporter gene alone to control for HBB-derived protein interspecies homology (n = 19) on gestational day 17 (E17; term = E21). Donor HSCs consisted of syngeneic cells phenotyped by flow cytometry with successful hHBB transduction confirmed by ELISA prior to administration in vivo. At term, fetal samples from five anatomical sites relevant to hematopoiesis were screened for the presence of human hemoglobin subunit beta by ELISA and by digital droplet PCR (ddPCR).

RESULTS

When controlled by HSCs without hHBB injections, human hemoglobin subunit beta production was documented at term in the fetal bone marrow and spleen (p < 0.001 and p = 0.028 respectively). Positive hHBB expression by ddPCR was detected in the spleen (54 %), bone marrow (46 %), blood (46 %), liver (23 %), and thymus (15 %).

CONCLUSIONS

Genetically modified hematopoietic stem cells carrying a human hemoglobin subunit beta gene can reach fetal hematopoietic sites after simple intra-amniotic injection in a healthy syngeneic rat model. Transamniotic hematopoietic stem cell-based gene therapy could become a novel strategy for the perinatal management of select hemoglobinopathies.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

TYPE OF STUDY

animal and laboratory study.

Development of molecular diagnostic platform for α0 -thalassemia 44.6 kb (Chiang Rai, --CR ) deletion in individuals with microcytic red blood cells across Thailand

INTRODUCTION

The α⁰ -thalassemia 44.6 kb or Chiang Rai (--^CR ) deletion has been reported in northern Thailand and is capable of causing hemoglobin (Hb) H disease and a lethal α-thalassemia genotype, Hb Bart's hydrops fetalis, in this region. However, there are no current data regarding the frequency of --^CR nationwide due to a lack of effective diagnostic assay. Therefore, this study aimed to develop a reliable platform for simultaneous genotyping of --^CR and two common α⁰ -thalassemias in Thailand (--^SEA and --^THAI ) and investigate the frequency of --^CR across Thailand.

METHODS

Multiplex gap-PCR assay and five renewable plasmid DNA controls for --^CR , --^SEA , --^THAI , α2-globin (HBA2), and β-actin (ACTB) were newly developed and validated with reference methods. The developed assay was further tested on 1046 unrelated individuals with a reduced mean corpuscular volume (MCV) of less than 75 fl for investigating genotypic and allelic spectrum of --^CR .

RESULTS

Our developed assay showed 100% concordance with reference methods. The results were valid and reproducible throughout hundreds of reactions. Comparison of the genotypic and allelic spectra revealed that heterozygous --^SEA (--^SEA /αα) and --^SEA alleles were dominant with the frequency of 22.85% (239/1046) and 13.34% (279/2092), respectively. Of these, --^THAI and --^CR were relatively rare in this population and comparable to each other with the allelic frequency of 0.14% (3/2092).

CONCLUSION

This study successfully established a reliable molecular diagnostic platform for genotyping of --^CR , --^SEA , and --^THAI in a single reaction. Additionally, we demonstrated the frequency of --^CR in Thailand for the first time and provided knowledge basis for the planning of severe α-thalassemia prevention and control programs in Thailand, where thalassemia is endemic.

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.

Regenerative medicine: prenatal approaches

This two-paper Series focuses on recent advances and applications of regenerative medicine that could benefit paediatric patients. Innovations in genomic, stem-cell, and tissue-based technologies have created progress in disease modelling and new therapies for congenital and incurable paediatric diseases. Prenatal approaches present unique opportunities associated with substantial biotechnical, medical, and ethical obstacles. Maternal plasma fetal DNA analysis is increasingly adopted as a noninvasive prenatal screening or diagnostic test for chromosomal and monogenic disorders. The molecular basis for cell-free DNA detection stimulated the development of circulating tumour DNA testing for adult cancers. In-utero stem-cell, gene, gene-modified cell (and to a lesser extent, tissue-based) therapies have shown early clinical promise in a wide range of paediatric disorders. Fetal cells for postnatal treatment and artificial placenta for ex-utero fetal therapies are new frontiers in this exciting field.