Osteogenic potential of allogeneic rat marrow cells in porous hydroxyapatite ceramics: a histological study

Hydroxyapatite ceramics facilitate osteogenesis but cannot induce bone formation by themselves. We studied the feasibility of bone formation supported by allogeneic bone marrow cells in porous hydroxyapatite ceramics. Coralline hydroxyapatite discs were soaked in a marrow cell suspension harvested from either ACI (RT1a), Lewis (RT1(1)), or Fischer 344 (RT1(1v)) male rats, and these discs were implanted subcutaneously into 56 male Fischer 344 rats. FK-506 (tacrolimus hydrate), an immunosuppressant, or saline was injected intramuscularly into the recipients every day for 2 weeks after surgery, and additional injections were given to 19 of the rats every 2 days for 2 more weeks. Neither of the mismatched major (ACI rat) or minor (Lewis rat) marrow cell transplants showed any bone formation without administration of FK-506. However, in rats treated with FK-506, bone formed in the pores of all the three types of ceramics implanted, which each contained the marrow cells from one of the three kinds of rats used. There were no differences among the three groups of donors with regard to the bone formation ratio. We previously reported that subcutaneous implantation of porous hydroxyapatite combined with isogeneic marrow cells resulted in consistent bone formation, even at ectopic sites. Since it would be difficult to harvest a large number of autologous marrow cells in clinical cases, we attempted to use allogeneic marrow cells and have shown the allogeneic murine marrow cells to have osteogenic potential.