The fate of allogeneic grafts of intact bone marrow in immunologically tolerant recipients and after abrogation of the tolerance.

In ossicles derived from grafts of compatible intact bone marrow in the subcapsular renal site the ectopic bone remains of donor provenance but the haemopoietic elements are partially replaced with tissue by host cells derived from stem cells migrating from the blood. Ossicles derived from incompatible intact bone marrow grafted in immunologically tolerant recipients are morphologically identical to those derived from compatible intact bone marrow. On abolition of the tolerance the allogeneic ectopic bone and donor microenvironment for haemopoiesis became manifest: haemopoietic marrow, even the host elements, was rapidly lost, bone disappearing rapidly if recently established, slowly if long established. Provided the state of immunological tolerance persists, the histoincompatible bone and microenvironment of the donor co-exist with marrow derived from the circulating haemopoietic stem cells of the tolerant recipient.