Transient-mixed Chimerism With Nonmyeloablative Conditioning Does Not Induce Liver Allograft Tolerance in Nonhuman Primates

Abstract

Background. Although short-term outcomes for liver transplantation have improved, patient and graft survival are limited by infection, cancer, and other complications of immunosuppression. Rapid induction of tolerance after liver transplantation would decrease these complications, improving survival and quality of life. Tolerance to kidneys, but not thoracic organs or islets, has been achieved in nonhuman primates and humans through the induction of transient donor chimerism. Since the liver is considered to be tolerogenic, we tested the hypothesis that the renal transplant transient chimerism protocol would induce liver tolerance. Methods. Seven cynomolgus macaques received immune conditioning followed by simultaneous donor bone marrow and liver transplantation. The more extensive liver surgery required minor adaptations of the kidney protocol to decrease complications. All immunosuppression was discontinued on postoperative day (POD) 28. Peripheral blood chimerism, recipient immune reconstitution, liver function tests, and graft survival were determined. Results. The level and duration of chimerism in liver recipients were comparable to those previously reported in renal transplant recipients. However, unlike in the kidney model, the liver was rejected soon after immunosuppression withdrawal. Rejection was associated with proliferation of recipient CD8 T effector cells in the periphery and liver, increased serum interleukin (IL)-6 and IL-2, but peripheral regulatory T cell (Treg) numbers did not increase. Antidonor antibody was also detected. Conclusions. These data show the transient chimerism protocol does not induce tolerance to livers, likely due to greater CD8 T cell responses than in the kidney model. Successful tolerance induction may depend on greater control or deletion of CD8 T cells in this model.

Strategies for Liver Transplantation Tolerance

“…Similar observations of CD8 + T-cell expansion in LT clinical trials and comparable NHP models demonstrate the necessary enhanced suppression of memory lymphocytes in LT tolerance induction [132,133]. Whereas at least transient mixed hematopoietic chimerism is the only method that has induced transplantation tolerance in both animals (mice, pigs, primates) and humans in kidney transplantation [134], mixed chimerism has so far been insufficient to allow early IS withdrawal in LT [7]. It can however not be ruled out that MC level, duration and composition may still be important for a successful liver tolerance outcome, and further studies are required.…”

“…(A) Successful immunosuppression withdrawal can, at least in part, be explained by the balance between early triggered alloreactivity (orange) and a gradually re-establishing tolerogenic liver environment (green). When immunosuppression withdrawal is attempted 1-2 years post liver transplantation success is rare, likely due to activation of large numbers of alloreactive memory T-cells [7], enhanced by post-surgery inflammation. After the initial insult has subsided, the natural tolerogenic influence of the liver can contribute to clonal deletion and peripheral regulatory control of alloreactive T-cells.…”

“…Effector memory CD8 + T-cells pose a particular threat towards transplanted organs with rapid expression of IFN-γ and cytotoxic molecules upon allostimulation, mediated by lower co-stimulation requirements for re-activation such as, for example, reduced CD28 expression [51]. The enhanced memory CD8 + T-cell barrier both in the periphery and in the liver allograft has been described in a non-human primate model attempting to induce early liver tolerance [7]. Functionally active memory CD8 + T-cells have a low activation threshold, high proliferative capacity, can track to tissues, constitute about 40-50% of T-cells, and express high levels of CD2 [52][53][54][55][56][57][58][59].…”

“…NHP studies may in this regard offer additional insight into the mechanisms of tolerance induction in LT. A clinically established strategy for tolerance induction has been demonstrated in recipients of combined kidney and bone marrow cell transplantation (CKBMT) [4], relying on early Treg-mediated peripheral tolerance and long-term deletion of anti-donor T-cells (central tolerance) [129][130][131]. In a study of NHP to translate the CKBMT protocol to LT, the recipients rejected the graft rapidly after IS withdrawal despite developing multilineage mixed chimerism (MC) [7]. The rejections were associated with expansion of intra-graft and circulating effector memory CD8 + T-cells.…”

Precision medicine in transplantation and hemodialysis

“…With such an approach, sufficient T-cell chimerism rates for tolerance induction are achievable in the first weeks after transplantation [ 13 ]. It is of note, however, that no absolute threshold of chimerism for tolerance has been established yet, and furthermore, rates may be different in other solid organ transplants [ 14 ]. Such an approach may be especially appealing for young recipients of live donor organs with an expected long lifetime.…”