Parathyroid Hormone Stimulates Human Mesenchymal Stem Cells to Enhance the Expansion of Hematopoietic Stem Cells,

Abstract 3407

Expanding hematopoietic stems cells (HSCs) has a great interest for successful engraftment of donor cells in hematopoietic stem cell transplantation (HSCT). In addition, mesenchymal stem cells (MSCs) show unique features with multi-differentiation, immune-modulation and tissue regeneration capabilities. Recent studies demonstrated the MSC-derived mature osteoblasts play important roles for the maintenance of HSC niche in the bone marrow (BM) microenvironment. We found that culture-expanded human MSCs support the expansion of HSCs and stimulation of MSCs with parathyroid hormone (PTH) further enhances the MSC-mediated expansion of HSCs.

Culture-expanded MSCs (2×10⁴ cells/well) were seeded on a 24-well culture plate. Autologous purified CD34⁺ HSCs (0.6×10³ cells/well) was applied on the MSC-grown plate and co-cultured in StemSpan Serum Free Expansion Medium (StemCell Technologies) supplemented with 100ng/mL SCF, 100ng/mL Flt-3 ligand, 50ng/mL TPO and 20ng/mL IL-3. After 10 days of co-culture of HSCs with MSCs, the number of CD34⁺ cells was increased to 9.0±1.6×10³ (Fig. culture condition #2), whereas that cultured in the absence of MSCs was 0.98–8, −1 and □ {7 of the irradiation. The number of leukocytes was decreased to the bottom level around 6–8 days after the irradiation in both PTH-treated and non-treated (control) mice. However, the number of leukocyte showed a steep increase in PTH-treated mice and it reached maximal level on day 14 at 16±5.2×10³/mL compared with that of 6.4±1.4×10³/mL in the control mice. In vitro experiments confirmed that PTH has no direct effects on the expansion of HSCs. It is suggested that PTH has supportive effects on hematopoietic recover in vivo, probably in part, through acting on MSCs in BM microenvironment.

In conclusion, PTH stimulated MSCs to enhance HSC expansion mainly through contribution of surface membrane molecules. A two-step manipulation of MSCs with culture expansion and subsequent PTH stimulation showed enhancement of MSC-mediated expansion of HSCs. This work revealed the novel mechanisms underlying HSC expansion mediated by MSCs. In addition, this novel concept of MSC manipulation could provide HSCT procedure with new technology for effective engraftment of donor hematopoietic cells.