BACKGROUND: Hemopoietic chimerism may be essential for the induction of transplantation tolerance. Because a limb allograft provides bone marrow cells within a vascularized niche, it may be more efficient in the induction of chimerism than exogenously administered bone marrow. As such, the bone marrow of the limb allograft may be sufficient to establish a state of chimerism and thereby obviate the need to administer both exogenous free bone marrow and myeloablative therapy required for engraftment.

OBJECTIVE: The present study addressed the question of whether a higher level of hemopoietic chimerism is induced by the intact, vascularized bone marrow inherent to a limb allograft compared to a conventionally administered bone marrow transplant.

METHODS: Female C57BL/6J mice received either a vascularized limb allograft or intravenous injections of varying amounts of bone marrow from BALB/cJ male donors. Anti-CD40L, and CD4 and CD8 T-cell depleting antibodies were used to induce a state of immune unresponsiveness to allow the evaluation of the level of chimerism produced. Recipients were sacrificed after either one week or one month, and Y chromosome-specific quantitative PCR was used to detect and quantify the relative amounts of male donor cells in female recipients' bone marrow and splenocyte DNA extracts.

RESULTS: Our preliminary data demonstrate that neither the bone marrow of a limb allograft, nor the comparable dose of free bone marrow (5 million cells), can reproducibly induce chimerism at 1 week or 1 month. By contrast, the standard 20 million-cell dose of free bone marrow does produce macrochimerism in at least 50 percent of animals at 1 week and 1 month.

CONCLUSION: Our results suggest that the vascularized bone marrow within a limb allograft is not more effective at inducing hemopoietic chimerism than a comparable dose of exogenously administered free bone marrow. Since the quantity of bone marrow in a limb allograft is small, the production of chimerism in limb transplantation will still require the administration of exogenous donor bone marrow.