The use of severely immunodeficient mice engrafted with human hematopoietic stem cells (HSCs) to recontitute immune system humanized mice has provided researchers with powerful tools for virus research and cellular immunotherapy preclinical evaluation of the human immune system and related primates. However, the maintenance, differentiation, and function of human hematopoietic cells are not ideal in these hosts. Human thrombopoietin (THPO) promotes functional human hematopoietic stem cells to maintain their multilineage differentiation potential and promote their long-term engraftment in mouse bone marrow.
 

Biocytogen developed B-NDG hTHPO mice in which the full-length THPO gene sequence of mice was replaced with the full-length coding sequence of the human THPO gene to obtain severely immunodeficient mice expressing human THPO. Humanization of THPO can promote the long-term maintenance and self-renewal of human HSCs in mice. So mice without irradiation pretreatment can also well reconstitute the human immune system, and can promote the multi-lineage differentiation of hematopoietic cells.

Strain specific analysis of THPO gene expression in C57BL/6 mice, B-NDG mice and B-NDG hTHPO mice by RT-PCR. Mouse Thpo mRNA was detectable in liver and kidney of C57BL/6 mice (+/+) and B-NDG mice (+/+). Human THPO mRNA was detectable only in homozygous B-NDG hTHPO mice (H/H) but not in wild-type C57BL/6 mice and B-NDG mice.

Complete blood count (CBC) of B-NDG hTHPO mice. Values are expressed as mean ± SD.

Human CD34+ HSCs (1.5E5) were intravenous engrafted into wild-type B-NDG mice and homozygous B-NDG hTHPO mice (female, 6 week-old, n=20). B-NDG mice were treated with 2Gy-irradiation. B-NDG hTHPO mice were not irradiated. Flow cytometric analysis of peripheral blood lymphocyte from the two mice after engraftment with human CD34+ HSCs were shown in the figure above. Results showed that the survival rate of B-NDG hTHPO mice was higher than that of B-NDG mice. The percentages of human CD45+ leukocytes, T cells, B cells, NK cells, myeloid cells, monocytes, macrophages and neutrophils in B-NDG hTHPO mice were similar to those in B-NDG mice, demonstrating that the humanized mouse model engrafted with human CD34+ HSCs was successfully constructed. Values are expressed as mean ± SEM. HSCs: hematopoietic stem cells.