Facilitation of hematopoietic recovery by bone grafts with intra-bone marrow–bone marrow transplantation

We have previously shown that T cells can acquire donor-type major histocompatibility complex (MHC) restriction and can interact with both donor-type antigen-presenting cells (APCs) and B cells, when adult donor bones are co-grafted with intravenous (IV) injection of bone marrow cells (BMCs) in order to supply donor bone marrow (BM) stromal cells. We have also found that the direct injection of donor BMCs into recipient BM (intra-bone marrow–bone marrow transplantation: IBM–BMT) produces more rapid reconstitution (including T-cell functions) and higher survival rates than IV injection (IV-BMT) even in chimerism-resistant combinations. In the present study, we show that the co-administration of bones from suckling (2–3 days old) donor mice is also effective in the IBM–BMT system. Even when a relatively low number of BMCs were injected into adult (more than 15 weeks old) mice, complete reconstitution was achieved in the mice that had received IBM–BMT+bone grafts, but not in the mice that had received IBM–BMT alone. Most BM and splenic adherent cells obtained from the recipients that had received IBM–BMT+bone grafts were reconstituted by donor-type cells. Both T-cell proliferation and plaque-forming cell assays indicated that the T cells of such mice showed donor-type MHC restriction. Moreover, the analyses of thymic sections using confocal microscopy revealed that donor BM stromal cells had migrated into the thymus. Thus, the co-administration of donor bones has great advantages for allogeneic BMT in adult mice.