BIOLOGY OF LIMB TRANSPLANTATION- I. MIGRATION OF TRANSPLANTED BONE MARROW CELLS INTO RECIPIENT:

A220 Introduction: The transplanted limb contains bone marrow (BM) tissue. The hematopoietic cells contained in the bone of the graft normally differentiate after transplantation and can be released to the recipient. They migrate to the recipient bone marrow cavities and lymphoid organs. This causes that the immune reaction between the donor and recipient develops not only in the graft itself but also in the recipient immune organs, into which donor bone marrow cells (BMC) home. Aim: The purpose of this study was to investigate the process of emigration of the hematopoietic cells from the donor limb to the recipient bone marrow cavities and lymphoid tissues. The questions we asked were: what is the rate of release of BMC from the transplanted bone, where do the released BMC home in the recipient, how fast are donor BMC rejected by the recipient and whether some BMC homing in the recipient tissues can survive and create a state of microchimerism. Study design. Experiments were performed on BN and LEW inbred rat strains (n=30). Limb donors received i.v. 51Cr-labelled BMC. Twenty-four hours later limb with homing labelled BMC was transplanted to an allogeneic or syngeneic recipient. The rate of radioactivity of BMC released from the graft and homing in recipient tissues was measured after another 24 hours. In order to eliminate factors adversely affecting homing as the “crowding effect” and allogeneic elimination of BMC by NK cells, total body irradiation and antiasialo-GM1 antiserum was applied to recipients prior to limb transplanation. In rats surviving with the limb grafts for 7 and 30 days homing of donor BMC was studied by specific labelling of donor cells and flow cytometry as well as by detecting donor male Y chromosome. Results: We found that (i) transplantation of limb with bone marrow in its natural spatial relationship with stromal cells and blood perfusion brings about immediate but low rate release of BMC and their migration to recipient BM and lymphoid tissues, (ii) a large portion of allogeneic BMC is rapidly destroyed in the mechanism of allogeneic elimination by radioresistant but anti-asialoGM1-sensitive NK cells, (iii) some transplanted BMC remain in the recipient tissues and create a state of cellular and DNA microchimerism. Low number of physiologically released donor BMC does not seem to adversely affect the clinical outcome of limb grafting. A slight prolongation of the graft survival time was observed.