Hepatic parenchymal replacement in mice by transplanted allogeneic hepatocytes is facilitated by bone marrow transplantation and mediated by CD4 cells.

UNLABELLED: The lack of adequate donor organs is a major limitation to the successful widespread use of liver transplantation for numerous human hepatic diseases. A desirable alternative therapeutic option is hepatocyte transplantation (HT), but this approach is similarly restricted by a shortage of donor cells and by immunological barriers. Therefore, in vivo expansion of tolerized transplanted cells is emerging as a novel and clinically relevant potential alternative cellular therapy. Toward this aim, in the present study we established a new mouse model that combines HT with prior bone marrow transplantation (BMT). Donor hepatocytes were derived from human alpha(1)-antitrypsin (hAAT) transgenic mice of the FVB strain. Serial serum enzyme-linked immunosorbent assays for hAAT protein were used to monitor hepatocyte engraftment and expansion. In control recipient mice lacking BMT, we observed long-term yet modest hepatocyte engraftment. In contrast, animals undergoing additional syngeneic BMT prior to HT showed a 3- to 5-fold increase in serum hAAT levels after 24 weeks. Moreover, complete liver repopulation was observed in hepatocyte-transplanted Balb/C mice that had been transplanted with allogeneic FVB-derived bone marrow. These findings were validated by a comparison of hAAT levels between donor and recipient mice and by hAAT-specific immunostaining. Taken together, these findings suggest a synergistic effect of BMT on transplanted hepatocytes for expansion and tolerance induction. Livers of repopulated animals displayed substantial mononuclear infiltrates, consisting predominantly of CD4(+) cells. Blocking the latter prior to HT abrogated proliferation of transplanted hepatocytes, and this implied an essential role played by CD4(+) cells for in vivo hepatocyte selection following allogeneic BMT. CONCLUSION: The present mouse model provides a versatile platform for investigation of the mechanisms governing HT with direct relevance to the development of clinical strategies for the treatment of human hepatic failure.

Donor-derived, liver-specific protein expression after bone marrow transplantation.

BACKGROUND: Bone marrow transplantation (BMT) may represent a novel mechanism to deliver a functional gene to a deficient liver. Bone marrow-derived hepatocytes are rare and without a defined contribution to liver function. Consequently, the clinical significance of BMT to treat liver disease is unclear. We sought to quantify bone marrow-derived hepatocyte protein expression after BMT and determine whether the process is inducible with liver injury. METHODS: Mice transgenic for human alpha-1 antitrypsin (hAAT) under a hepatocyte-specific promoter were used as bone marrow donors. Adenoviral transduction of modified urokinase plasminogen activator (Ad-muPA) was used to induce liver injury. Eight weeks after lethal irradiation and BMT, recipients were stratified into two groups: BMT alone (n = 5) and BMT + Ad-muPA (n= 10). Both groups of animals were bled before (t = 0) and at 2, 4, 8, and 16 weeks after Ad-muPA administration, and the serum samples were assessed for hAAT by enzyme-linked immunosorbent assay. RESULTS: Transgenic donor mice expressed 5 to 10 mg/mL of hAAT. Recipients of BMT alone expressed less than 80 ng/mL of hAAT over all time periods. Animals receiving BMT + Ad-muPA showed sustained and stable hAAT expression of approximately 200 ng/mL. Differences were statistically significant at each time point. CONCLUSION: Serum protein levels from liver-specific transgene expression are detectable and persist after BMT. Expression is low, but inducible with liver injury. We are currently developing strategies to augment donor-derived, liver-specific protein expression after BMT.

Tissue engineering and regenerative medicine.

Regenerative medicine is evolving toward a powerful new paradigm of functional restoration. With the ethical use of gene therapy or through the manipulation of autologous tissues, improved tissue replacements may soon be available. The promise of engineered whole organs, although fraught with technical hurdles, remains on the horizon. As these advances occur, physicians and surgeons of the twenty-first century will possess ever more powerful tools to restore form and function.

Cardiac allograft aortic dissection: successful repair using a composite valve graft and modified-Cabrol coronary reconstruction.

We report a 55-year-old man, the recipient of a cardiac allograft for ischemic cardiomyopathy 9 years earlier, who presented with progressive aortic root dilation, worsening aortic insufficiency, and an incidentally discovered chronic type A aortic dissection limited to the donor aorta. The patient was taken to the operating room, and the aortic dissection successfully repaired using standard reoperative techniques. This is the sixth case reported in the literature, and only the fourth survivor. To our knowledge, this case represents the first successful repair, of a limited aortic dissection of the donor aorta postcardiac transplantation, using a composite valve graft and modified-Cabrol coronary reconstruction.