Spatio-Temporal Bone Remodeling after Hematopoietic Stem Cell Transplantation

• Main Authors: Constanze S. Schwarz, Christian H. Bucher, Claudia Schlundt, Sarah Mertlitz, Katarina Riesner, Martina Kalupa, Lydia Verlaat, Oskar Schmidt-Bleek, Radost A. Sass, Katharina Schmidt-Bleek, Georg N. Duda, Olaf Penack, Il-Kang Na
• Format: Article
• Language: English
• Published: MDPI AG 2021-12-01
• Series: International Journal of Molecular Sciences
• Subjects: hematopoietic stem cell transplantation; T lymphocytes; bone remodeling
• Online Access: https://www.mdpi.com/1422-0067/22/1/267
• ISSN: 1661-6596; 1422-0067

The interaction of hematopoietic cells and the bone microenvironment to maintain bone homeostasis is increasingly appreciated. We hypothesized that the transfer of allogeneic T lymphocytes has extensive effects on bone biology and investigated trabecular and cortical bone structures, the osteoblast reconstitution, and the bone vasculature in experimental hematopoietic stem cell transplantations (HSCT). Allogeneic or syngeneic hematopoietic stem cells (HSC) and allogeneic T lymphocytes were isolated and transferred in a murine model. After 20, 40, and 60 days, bone structures were visualized using microCT and histology. Immune cells were monitored using flow cytometry and bone vessels, bone cells and immune cells were fluorescently stained and visualized. Remodeling of the bone substance, the bone vasculature and bone cell subsets were found to occur as early as day +20 after allogeneic HSCT (including allogeneic T lymphocytes) but not after syngeneic HSCT. We discovered that allogeneic HSCT (including allogeneic T lymphocytes) results in a transient increase of trabecular bone number and bone vessel density. This was paralleled by a cortical thinning as well as disruptive osteoblast lining and loss of B lymphocytes. In summary, our data demonstrate that the adoptive transfer of allogeneic HSCs and allogeneic T lymphocytes can induce profound structural and spatial changes of bone tissue homeostasis as well as bone marrow cell composition, underlining the importance of the adaptive immune system for maintaining a balanced bone biology.