Source of cell injected is a critical factors for short and long engraftment in xeno-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.

Assessment of Short-Term Engraftment Potential of Ex Vivo Expanded Hematopoietic Stem Cells Using Normal Fetal Mouse in Utero Transplantation Model

OBJECTIVE

Ex vivo expansion is a promising strategy to overcome the low number of human umbilical cord blood hematopoietic stem cells (hUCB-HSCs). Although based on the obtained results in unnatural physiological condition of irradiated genetically immune-deficient mouse models, there has always been concern that the expanded cells have less engraftment potential. The purpose of this study was to investigate effect of common ex vivo expansion method on engraftment potential of hUCB-mononuclear cells (MNCs), using normal fetal mouse, as a model with more similarity to human physiological conditions.

MATERIALS AND METHODS

In this experimental study, briefly, isolated hUCB-MNCs were cultured in common expansion medium containing stem cell factor, Flt3 ligand and thrombopoietin. The unexpanded and expanded cells were transplanted to the fetal mice on gestational days of 11.5-13.5. After administration of human hematopoiesis growth factors (hHGFs), presence of human CD45+ cells, in the peripheral blood of recipients, was assessed at various time points after transplantation.

RESULTS

The expanded MNCs showed 32-fold increase in the expression of CD34+38- phenotype and about 3-fold higher clonogenic potential as compared to the uncultured cells. Four weeks after transplantation, 73% (19/26) of expanded-cell recipients and 35% (7/20) of unexpanded-cell recipients were found to be successfully engrafted with human CD45+ cells. The engraftment level of expanded MNCs was significantly (1.8-fold) higher than unexpanded cells. After hHGFs administration, the level was increased to 3.2, 3.8 and 2.6-fold at respectively 8, 12, and 16 weeks of post transplantation. The increased expression of CXCR4 protein in expanded MNCs is a likely explanation for the present findings.

CONCLUSION

The presented data showed that expanded MNCs compared to unexpended cells are capable of more rapid and higher short-term engraftment in normal fetal mouse. It could also be suggested that in utero transplantation (IUT) of normal fetal mice could be an appropriate substitute for NOD/SCID mice in xenotransplantation studies.

Efficient biallelic mutation in porcine parthenotes using a CRISPR-Cas9 system

The parthenotes represent ideal models mimicking the embryonic development and characterizing the function of maternal genomes as well as an alternative source of pluripotent cell lines. Besides, parthenogenetically activated (PA) embryos serve as a rapid assay system to maximize the efficiency of generating genetically modified pig CRISPR/Cas9 system, an efficient and multiplex gene editing tool, has been utilized to modify the genome of porcine parthenotes. However, lower biallelic mutation rate and high mosaicism frequency were observed. Here, we aimed to enhance the biallelic mutation rate with reduced mosaicism by optimization of the concentration and injection time of the Cas9/sgRNA mixture in porcine parthenotes. The results showed that the efficient biallelic mutation (93%) and low mosaicism (33%) could be achieved in porcine parthenotes by cytoplasmic injection of Cas9 mRNA/sgRNA (125/12.5 ng/μl) after 8 h of parthenogenetical activation. Thus, our study provides an effective strategy for increasing the biallelic mutation rate and population homogeneity of genetically modified parthenotes, which will strengthen the role of parthenotes in uncovering early embryonic development and assessing the mutation efficiency due to the simplicity and adaptability of CRISPR/Cas9.

Long-term follow-up study on the engraftment of human hematopoietic stem cells in sheep

Xenograft models of human hematopoiesis are essential to the study of the engraftment and proliferative potential of human hematopoietic stem cells (HSCs) in vivo. Immunodeficient mice and fetal sheep are often used as xenogeneic recipients because they are immunologically naive. In this study, we transplanted human HSCs into fetal sheep and assessed the long-term engraftment of transplanted human HSCs after birth. Fourteen sheep were used in this study. In 4 fetal sheep, HSCs were transduced with homeo-box B4 (HOXB4) gene before transplantation, which promoted the expansion of HSCs. Another 4 fetal sheep were subjected to non-myeloablative conditioning with busulfan. Seven of these 8 sheep showed successful engraftment of human HSCs (1–3% of colony-forming units) as assessed after the birth of fetal sheep (5 months post-transplantation), although HOXB4-transduced HSCs showed sustained engraftment for up to 40 months. Intact HSCs were transplanted into six non-conditioned fetal sheep, and human colony-forming units were not detected in the sheep after birth. These results suggest that, as compared with mouse models, where the short lifespan of mice limits long-term follow-up of HSC engraftment, the fetal sheep model provides a unique perspective for evaluating long-term engraftment and proliferation of human HSCs.

Development and characterization of a novel CD34 monoclonal antibody that identifies sheep hematopoietic stem/progenitor cells

OBJECTIVE

We and many others have long used sheep as a predictive model system in which to explore stem cell transplantation. Unfortunately, while numerous markers are available to identify and isolate human hematopoietic stem cells (HSC), no reagents exist that allow HSC/progenitors from sheep to be identified or purified, greatly impeding the application of this well-established large animal model to the study of autologous or allogeneic HSC transplantation. The current studies were undertaken to create a monoclonal antibody to sheep CD34 that would enable isolation and study of sheep HSC/progenitors.

MATERIALS AND METHODS

A partial cDNA to the extracellular domain of the sheep CD34 antigen was polymerase chain reaction cloned, characterized, and used to genetically immunize mice and create hybridomas.

RESULTS

The resultant monoclonal antibody to sheep CD34 allows flow cytometric detection of sheep HSC/progenitors present within bone marrow, cord blood, and mobilized peripheral blood. Moreover, this antibody can be used to enrich for HSC/progenitors with enhanced in vitro colony-forming potential, and also identifies endothelial cells in situ within paraffin-embedded tissue sections, similarly to antibodies to human CD34.

CONCLUSIONS

The availability of this monoclonal antibody recognizing the stem cell antigen CD34 in sheep will greatly facilitate the study of autologous and allogeneic HSC transplantation using this clinically relevant large animal model.