[IMMUNOGENICITY OF HUMAN UMBILICAL CORD BLOOD DERIVED MESENCHYMAL STEM CELLS AFTER OSTEOGENIC INDUCTION].

Objective: To study the immunological properties of osteogenically differentiated umbilical cord blood derived mesenchymal stem cells (UCB-MSCs).

Methods: UCB-MSCs were isolated from the umbilical cord vein, and were expanded; the cells at passage 3 were osteogenically induced for 2 weeks in vitro. The expressions of human leukocyte antigen I (HLA-I) and HLA-II molecules were observed by flow cytometry analysis before and after osteogenic induction. Peripheral blood T lymphocytes were isolated and cultured with osteoblastic induced or non-osteoblastic induced UCB-MSCs in different cell concentrations of 1 x 10(2), 1 x 10(3), 1 x 10(4), and 1 x 10(5) cells/well. The intake value of 3H-thymidine was calculated with luminescence counter. Then T lymphocytes were pretreated with PHA, and co-cultured with osteoblastic induced and non-osteoblastic induced UCB-MSCs as described above. IL-2 was further added to test the reversed effect of T lymphocytes proliferation stimulated by UCB-MSCs. Finally, to investigate whether the immunomodulatory effects on T lymphocytes proliferation depend on direct or indirect cell contact, the Transwell chamber culture system of UCB-MSCs and T lymphocytes was established.

Results: Flow cytometry analysis showed that non-osteoblastic induced UCB-MSCs expressed HLA-I but did not express HLA-II; the expression of HLA-II increased in osteoblastic induced UCB-MSCs. No T lymphocyte response was stimulated by non-osteoblastic induced UCB-MSCs, but osteoblastic induced UCB-MSCs could stimulate the proliferation of allogeneic T lymphocytes, especially after IFN-γ treatment. Non-osteoblastic induced UCB-MSCs of 1 x 10(4) and 1 x 10(5) cells/well could suppress the proliferation of T lymphocytes evoked by PHA, and this suppression could be reversed by the addition of IL-2. While osteoblastic induced UCB-MSCs did not have such suppressive effect. The results of the Transwell culture system also showed that non-osteoblastic induced UCB-MSCs could obviously inhibit the proliferation of T lymphocytes, but the osteoblastic induced UCB-MSCs could not.

Conclusion: The immunological properties of UCB-MSCs will change accordingly after osteogenic induction, so UCB-MSCs might not be suitable for the seed cells of bone tissue engineering.