In vivo transplantation of N-BMSCs and TBD-BMSCs. (A) Cells (N-BMSCs, AAA-BMSCs, and TBD-BMSCs) were attached to hydroxyapatite/tricalcium phosphate ceramic particles as a scaffold (labeled “s” in panels B-G) and transplanted under the skin of immunocompromised mice. After 8 weeks, the transplants were harvested, fixed and decalcified, and used for histologic examination after H&E staining. (B) When N-BMSCs (even from donors of advanced age) were transplanted, they formed an ectopic bone/marrow organ, with bone (labeled “b”), hematopoiesis-supportive stroma (which cannot be seen due to the high density of hematopoietic cells), and marrow adipocytes (labeled “a”) of human origin, whereas hematopoiesis (labeled “hp”) was of mouse origin (n = 8 different normal donors, 2 transplants/donor). (C) Similar bone/marrow organs were formed by AAA-BMSCs (n = 8 different AAA donors, 2 transplants/donor), although these cells were derived from aplastic marrow (D) (AAA Pt - NHLBI-64-1). (E-F) Under the same conditions, TBD-BMSCs were not capable of forming bone or of supporting hematopoiesis, but instead formed dense fibrotic tissue (labeled “ft”) in association with the scaffold. In addition, extensive areas of marrow adipocytes (labeled “a”) were noted in the TBD-BMSC transplants (n = 8 donors, 2 transplants each for TBD patients 1 [TERC], 2 [TINF2], 3 [RTEL1], 4 [TERC], 5 [TERT], 6 [RTEL1], 9 [WRAP53], 10 [no mutation in known telomere-related genes found to date], 11 [TINF2]). (G) The transplants generated by TBD-BMSCs are highly reminiscent of a BM biopsy taken from TBD patient 5 (TERT), showing marrow aplasia and large fields of adipocytes. (Biopsy images were obtained using an Olympus BX-41 microscope with UPlan 10×/0.30 or Uplan 20×/0.50 lenses, and an Olympus DP72 digital camera and software [Olympus], courtesy of Dr. Irina Maric, Warren G. Magnuson Clinical Center, NIH, DHHS).