Revisiting liver transplant immunology: from the concept of immune engagement to the dualistic pathway paradigm

Application of CD8+ Cells Count as a Guide of Immunosuppressive Regimen Introduction for Very Sick Patients Undergoing Liver Transplantation

BACKGROUND

Immunosuppression (IS) protocols should be individualized according to the individual recipient's immunity to minimize adverse effects. The aim of this study was to determine whether preoperative levels of CD8+ T lymphocytes could be used as a guide for the introduction of IS.

METHODS

Sixteen adult liver transplantations in our institute were retrospectively analyzed. The immunosuppressive agents were temporarily withheld for 8 patients with a lower (<10%) preoperative percentage of CD8+ cells after transplant (classified as group A). In this group, postoperative immunosuppressive agents had never been used until acute rejection was suspected. Another 8 patients receiving classic IS were classified as group B. We collected their demographic features and analyzed the clinical courses.

RESULTS

The postoperative IS-free period of group A was 5 to 120 days (median, 31 days). Our data showed an inverse correlation between CD8+ levels and the severity of liver disease. Although the IS-free protocol did not present a lower incidence of infection-related events, most of them were effectively treated with antibiotics. The 1-, 3-, and 5-year overall patient survival rates were not different between those with a short-term IS-free period and those with regular IS (87.5% vs 100%, 75% vs 100%, and 62.5% vs 87.5%; P = .468). No patient died of graft failure due to acute rejection.

CONCLUSIONS

Postoperative immunosuppressive agents can be safely withheld for a period of time to preserve proper immune responses against infections in very sick recipients guided by using the CD8+ levels.

Once daily calcineurin inhibitor monotherapy in pediatric liver transplantation

This report describes a group of pediatric liver transplant recipients who have undergone once daily calcineurin inhibitor (CNI) monotherapy at Children's Memorial Hospital, Chicago, between January 1, 2001 and November 30, 2008. We defined success as normal liver enzymes at 1 year after dose change, with normal enzymes throughout all follow-up. Patients who did not meet the set criteria or had lost an organ to chronic rejection were not considered for this therapeutic strategy. There were 147 patients in our organ transplant tracking record (OTTR) who were > or = 5 years post liver transplant. Of these, 56 underwent reduced dose, once daily CNI monotherapy. Patients who met the set criteria were placed on once daily calcineurin inhibitor at half their previous dose. Fifty patients successfully achieved this dose change, while six patients failed at a mean of 3.7 +/- 3.2 months following the dosing change. The mean interval from transplant was significantly longer in those patients who were successful compared to those who failed dose change (p < 0.05). Importantly, there have been no graft losses. Reduced dose, once daily CNI monotherapy is safe in carefully selected recipients, with a longer interval post liver transplantation increasing the likelihood of success.

Mechanistic insights into immunomodulation by hepatic stellate cells in mice: a critical role of interferon-gamma signaling

The liver is considered to be an immune-privileged organ that favors the induction of tolerance. The underlying mechanisms are not completely understood. Interestingly, liver transplants are spontaneously accepted in several animal models, but hepatocyte transplants are acutely rejected, suggesting that liver nonparenchymal cells may effectively protect the parenchymal cells from immune attack. We have shown the profound T cell inhibitory activity of hepatic stellate cells (HSCs). Thus, cotransplantation with HSCs effectively protects islet allografts from rejection in mice. In this study, using T cell receptor transgenic and gene knockout approaches, we provided definitive evidence that HSCs protected cotransplanted islet allografts by exerting comprehensive inhibitory effects on T cells, including apoptotic death in graft-infiltrating antigen-specific effector T cells and marked expansion of CD4(+) Forkhead box protein (Foxp)3(+) T regulatory (Treg) cells. All these effects required an intact interferon-gamma (IFN-gamma) signaling in HSCs, demonstrated by using HSCs isolated from IFN-gamma receptor 1 knockout mice. B7-H1 expression on HSCs, a product molecule of IFN-gamma signaling, was responsible for induction of T cells apoptosis, but had no effect on expansion of Treg cells, suggesting that undetermined effector molecules produced by IFN-gamma signaling is involved in this process.

CONCLUSION

Upon inflammatory stimulation, specific organ stromal cells (such as HSCs in the liver) demonstrate potent immune regulatory activity. Understanding of the mechanisms involved may lead to development of novel strategies for clinical applications in transplantation and autoimmune diseases.

Pre- and post-transplant monitoring of granzyme B enzyme-linked immunosorbent spot assay in pediatric liver recipients

This study aims to investigate potential role of granzyme B enzyme-linked immunosorbent spot (GrB ELISPOT) for immunological monitoring in pediatric liver transplantation.

PATIENTS AND METHODS

Peripheral blood mononuclear cells from 28 pediatric recipients were serially tested for GrB-producing donor-reactive cells at day 0 pre-transplantation (baseline) and days 7, 14, and 28 post-transplantation.

RESULTS

At baseline, no difference of GrB value was found in acute rejection (14/28) compared to normal graft function patients (day 0: 4(3.9) spots versus 5(2.9) spots, respectively: p=0.65). At day 7 post-transplantation, acute rejection patients showed frequencies of GrB ELISPOT higher than those with normal graft function, but the differences observed were not statistically significant (day 7: 15(4.9) spots versus 10(4.0) spots, respectively: p=0.55). GrB increased significantly at day 7 from baseline in the rejection group (15(4.9) spots versus 4(3.9), respectively p=0.04), whereas corresponding changes were not significant in the group without rejection (10(4.0) versus 5(2.9), respectively: p=0.15).

CONCLUSION

GrB ELISPOT pre-transplantation could not predict the occurrence of early post-transplant acute rejection; similarly frequencies at days 7, 14 and 28 could not be correlated with acute rejection in pediatric liver recipients. However, a kinetic study of GrB ELISPOT could be helpful to predict or confirm early rejection in the small group of liver allograft recipients analyzed in this study.

Impact of HLA-C and Bw epitopes disparity on liver transplantation outcome

The occurrence of graft rejection episodes after orthotopic liver transplantation (OLT) despite the use of immunosuppressive drugs designed to suppress T lymphocyte functions, indicates the involvement of other types of cells in this process. The activity of natural killer cells and their killer immunoglobulin-like receptors (KIR) is regulated by human leukocyte antigen (HLA) class I determinants; C and Bw epitopes. Because recipient/donor pairs are usually HLA mismatched, recipient natural killer alloreactivity may be the mediating factor in rejection. In this retrospective study, we have analyzed rejection occurrence and outcome in 66 OLT recipients, 42 with and 24 without C or Bw epitope disparity in the rejection direction. Recipients transplanted from donors with no C epitope disparity had significantly fewer rejection episodes in the first year after transplantation compared with recipients transplanted across C epitope disparity (p = 0.0002). Moreover, this effect was more pronounced when the outcome was analyzed in OLT recipients across negative crossmatching for the anti-HLA class I and II antibodies. In contrast, Bw epitope disparity did not affect the outcome. In conclusion, C epitopes disparity between recipients and donors in the rejection direction appears to influence posttransplant liver outcome. This finding may be helpful in the choice of appropriate liver donor and planning immune suppression.