What's new and what's hot in transplantation: basic science ATC 2003

Donor and recipient HLA/KIR genotypes do not predict liver transplantation outcome

Whether or not Natural Killer (NK) cells affect the immune response to solid organ allografts is still controversial. Main determinants of NK-cell activation are specific HLA/killer-cell immunoglobulin-like receptors (KIR) interactions that, in transplantation, may induce NK-cell alloreactivity. So far, in liver transplantation (LTX) donor-versus-recipient alloreactivity has not been investigated; in addition, studies of predicted recipient-versus-donor NK-cell alloreactivity have led to contradicting results. We typed a cohort of LTX donors and recipients for HLA-C/Bw4 and KIRs. We estimated the effect of NK-cell alloreactivity, as predicted by classically used models, in the donor-versus-recipient direction. The results indicate that HLA/KIR mismatches in the donor-versus-recipient direction do not predict graft rejection nor graft or patient survival, suggesting that donor-derived NK cells do not play a major role in LTX outcome. In addition, when considering predicted NK-cell alloreactivity in the reverse direction (recipient-versus-donor), we first confirmed that donor HLA-C genotype was not associated with acute rejection, graft or patient survival and secondly we found that none of the models describing NK-cell alloreactivity could predict LTX outcome. Overall our observations suggest that, in contrast to what is shown in haematopoietic stem cell transplantation, donor-derived NK cells may not contribute in preventing liver graft rejection, and that recipient-versus-donor NK-cell alloreactivity does not predict LTX outcome.

Multiple costimulatory blockade in the peripheral nerve allograft

BACKGROUND

In the nerve allograft model, costimulation blockade has permitted good regeneration but is still inferior to the nerve isograft. We hypothesize that a short course of multiple costimulatory pathway blockade will be more effective in inhibiting the redundancy of the immune response and improve nerve regeneration through the nerve allograft.

METHODS

The murine sciatic nerve allograft model was used to reconstruct a 1 cm sciatic nerve gap. Treatment consisted of the inhibition of the CD40, CD28/B7 and ICOS pathways and was compared with only single or double costimulation blockade. Assessment methods included quantitative histomorphometry and ELISPOT assay to quantify the host immune response after 3 weeks post-operatively.

RESULTS

Triple costimulation blockade permitted regeneration through the nerve allograft that was equivalent to the nerve isograft. A short course of three doses was more effective than a single dose for all combinations tested. ELISPOT assay demonstrated minimal in vitro immune response with a short course of double or triple pathway-blocking agents.

CONCLUSION

Costimulation blockade, especially with the simultaneous inhibition of multiple pathways, remains a promising strategy to promote regeneration through the peripheral nerve allograft, and may be uniquely suited to the temporary immunosuppressive requirements of the peripheral nerve allograft.

New concepts in organ transplantation

Over the past several decades, many factors have led to higher rates of patient and graft survival in organ transplantation. These factors include enhanced immunosuppressants available in recent years such as Neoral, Prograf, sirolimus, mycophenolate mofetil and anti-interleukin-2 receptor monoclonal antibodies. In addition, other new drugs, such as FTY 720, FK 778, anti-CD20, anti-CD40, and anti-CH52 monoclonal antibodies, are now being tested in clinical studies. Furthermore, there have been advances in surgical techniques, such as the piggyback method without venovenous bypass, side-to-side anastomosis of the hepatic veins, use of vascular staplers, biliary duct-to-duct anastomosis with or without tube drainage, microsurgical hepatic artery anastomosis and laparoscopic donor nephrectomy. Finally, better patient and donor selection criteria with regard to HBV- and HCV-seropositive donors, diabetic donors, donors with malignancies, older donors, ABO-incompatible donors, and non-heart-beating donors have been combined with optimal timing of transplantation, better options for treating early surgical and late medical complications, and improved management in intensive-care units. Other noteworthy scientific and social development are on the horizon namely genetic advances in xenografting and cell transplantation, and induction of immunologic tolerance. This article reviews the current developments that have significantly improved graft and patient survival among solid-organ transplants.