Decreased expression of the interleukin 2 receptor on CD8 recipient lymphocytes in intestinal grafts rendered tolerant by liver transplantation in rats

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

Study of the impact of liver transplantation on the outcome of intestinal grafts in children

BACKGROUND

Successful small bowel transplantation remains a challenge due to the septic and immune content of the gut. The possible beneficial role of the liver was assessed in pediatric recipients of isolated intestinal and liver intestinal combined transplantation, receiving the same immunosuppressive therapy.

METHODS

Fifteen children who underwent small bowel transplantation (seven SbTx) or combined liver-small bowel transplantation (eight LSbTx) at a single center between 1994 and 1998 were retrospectively reviewed and compared with fifteen controls (eight normal and seven appendicitis as inflammatory control). Transplant and patient survival, acute rejection episodes were analyzed and compared. Epithelial apoptotic body counts (ABC) and NF-kB (p65), Caspase-3 and Bax intestinal immunostaining from days 0 to 20 after transplantation were assessed.

RESULTS

Graft and patient survivals at 5 years were respectively 75% and 75% in LSbTx; 43% and 57% in SbTx (NS). Histological analysis showed higher ABC in LSbTx intestinal mucosa (P = 0.05 on day 5, P < 0.01 thereafter). Immunostaining of biopsies on day 0 after reperfusion showed different expression of NF-kB, Caspase-3 and Bax on endothelial (P < 0.05 for NF-kB and Bax), mononuclear (P < 0.05 for Bax) and epithelial cells in LSbTx and SbTx.

CONCLUSIONS

Our results suggest a protective role of the liver toward intestinal transplantation even in absence of significative difference, probably due to the small number of children. Early changes in NF-kB immunostaining in the biopsies sampled on day 0, pointed to a possible beneficial effect of the liver in the very early phase following transplantation, perhaps through the differential control of ischemia-reperfusion.

Enhanced in situ expression of NF-kappaBp65 is an early marker of intestinal graft rejection in rats

BACKGROUND

Although intestinal transplantation provides a unique situation of free access to the graft because of the presence of temporary enterostomas, evaluation of local immunosuppression is still an unresolved issue and may constitute one of the causes of grafting failure.

AIMS

To study in a rat model of allogeneic intestinal transplantation the expression of transcription factors involved in lymphocyte activation in situ in the graft and to identify factors reflecting the efficiency of drug immunosuppression.

METHODS

Intestinal transplantation was performed in a Brown Norway (RT1n-donors)-Lewis (RT1(l)-recipients) rat strain combination. The animals were treated with tacrolimus to induce tolerance or left untreated. Syngeneic intestinal grafts and intestine from donor rats with peritonitis were used as controls. NF-kappaBp65, p-c-Jun, interleukin 2 receptor (CD25), and major histocompatibility complex class II antigen (OX-6) expression was studied in graft biopsies on days 2 and 5 by immunohistochemistry.

RESULTS

On day 2, before the onset of histologic signs of rejection, the number of cells expressing NF-kappaBp65 in the pericryptic lamina propria was significantly higher in untreated recipients of allogeneic grafts than in the other groups (P = .009). NF-kappaBp65 expression then fell between days 2 and 5 (P = .009). Classic markers of T-cell activation (CD25 and OX-6) were expressed during rejection in the lamina propria and on crypt enterocytes, respectively. p-c-Jun expression did not differ among the 3 groups.

CONCLUSION

NF-kappaBp65 expression in intestinal grafts is a precocious sign of local activation during rejection and could thus serve to optimize the management of immunosuppressive therapy.

Intragraft distribution of lymphocytes expressing β7 integrins after small bowel transplantation in mice

Lymphocytes with activated beta7 integrins (alphaEbeta7 and alpha4beta7) contribute to inflammatory reactions in the small bowel. Since the selective recruitment of lymphocytes to the lymphoid compartments of the small bowel is controlled by distinct adhesion molecule interactions, a compartment-dependent use of beta7 integrins may influence the rejection response within intestinal transplants. To further delineate the nature of beta7 integrin-mediated graft infiltration, we analysed their expression on T lymphocytes in the heterotopically transplanted small bowel of BALB/c and C57BL/6 mice. Lymphocytes isolated from the epithelium, lamina propria (LP), Peyer's patches (PP), and mesenteric lymph nodes (MLN) were analysed by three-color fluorescence flow cytometry using monoclonal antibodies (mAb) to integrin the subunits, lymphocyte markers, and MHC I of the donor and recipient strains. On postoperative day 5 (POD) after allogeneic small bowel transplantation (SBT), 43% of intraepithelial lymphocytes (IEL) and 63% of LP, 93% of MLN, and 93% of PP lymphocytes were of host origin. In the MLN and PP of allografts, a major infiltrating lymphocyte population consisted of CD8+ cells with increased expression of alpha4beta7 and decreased expression of L-selectin, an adhesion molecule profile characteristic of intestinal effector cell phenotypes. An increase in alpha4beta7 levels was also found on CD8+ host lymphocytes in the LP. The integrin profile of a number of host IEL suggests an ongoing transition from the phenotype of graft infiltrating lymphocytes with high levels of alpha4beta7 and low levels of alphaepsilonbeta7 to that of resident IEL with high levels of alphaepsilonbeta7 and low levels of alpha4beta7. The importance of beta7-mediated lymphocyte trafficking to the graft is attested by the significant reduction in the host lymphocyte population in the LP, PP, and epithelium following the administration of a beta7-blocking mAb to allograft recipients. In conclusion, while the infiltration patterns of lymphocytes may vary between the lymphoid compartments of intestinal allografts, host CD8+ lymphocytes with high levels of alpha4beta7 constitute a major effector cell population that affects the entire graft.

Irreversible intestinal failure

Intestinal failure (IF) can be defined as the reduction of functional gut mass below the minimal amount necessary for digestion and absorption adequate to satisfy the nutrient and fluid requirements for maintenance in adults or growth in children. In developed countries, IF mainly includes individuals with the congenital or early onset of conditions requiring protracted or indefinite parenteral nutrition (PN). Short bowel syndrome was the first commonly recognized cause of protracted IF. The normal physiologic process of intestinal adaptation after extensive resection usually allows for recovery of sufficient intestinal function within weeks to months. During this time, patients can be sustained on parenteral nutrition. Only a few children have permanent intestinal insufficiency and life-long dependency on PN. Non-transplant surgery including small bowel tapering and lengthening may allow weaning from PN in some cases. Hormonal therapy with recombinant human growth hormone has produced poor results while therapy with glucagon-like peptide-2 holds promise. Congenital diseases of enterocyte development such as microvillus inclusion disease or intestinal epithelial dysplasia cause permanent IF for which no curative medical treatment is currently available. Severe and extensive motility disorders such as total or subtotal intestinal aganglionosis (long segment Hirschsprung disease) or chronic intestinal pseudo-obstruction syndrome may also cause permanent IF. PN and home-PN remain are the mainstays of therapy regardless of the cause of IF. Some patients develop complications while receiving long-term PN for IF especially catheter related complications (thrombosis, sepsis) and liver disease. These patients may be candidates for intestinal transplantation. This review discusses the causes of irreversible IF and emphasizes the specific medico-surgical strategies for prevention and treatment of these conditions at several stages of IF.

FTY720 reduces T-cell recruitment into murine intestinal allograft and prevents activation of graft-infiltrating cells

BACKGROUND

Effective immunosuppression is a critical determinant of graft survival in small-bowel transplantation (SBTx). The present study was designed to determine the potency of FTY720, a newly synthesized immunosuppressant, in rat SBTx and examine the phenotype of graft-infiltrating cells to evaluate its effect on intestinal allografts.

MATERIALS AND METHODS

A segment of intestine of Dark Agouti rats was transplanted heterotopically into Lewis rats. The recipients were treated with or without oral FTY720 at a dose of 1 mg/kg per day. Six days after surgery, peripheral blood lymphocytes and lymphocytes from the mesenteric lymph nodes, Peyer's patches, intraepithelial site, and lamina propria of the intestinal allograft were isolated. After the number of lymphocytes in each site was counted, the lymphocyte subpopulations in the intestinal allograft were evaluated by means of a FACScan flow cytometer using several monoclonal antibodies.

RESULTS

FTY720 treatment significantly prolonged recipient survival and strongly inhibited rejection histologically in comparison with control rats. FTY720 immunosuppression resulted in a marked reduction of lymphocyte number in the graft epithelium and lamina propria and the proportion of CD8+ and CD25+ cells. FTY720 also significantly decreased T-cell receptors and increased B cells in the graft Peyer's patches.

CONCLUSION

FTY720 promoted long-term SBTx recipient survival and maintained the architecture of intestinal allografts. FTY720 immunosuppression may be associated with a reduction of T-cell recruitment subsequent to the redistribution of lymphocyte subpopulations to control the proliferation and activation of graft-infiltrating cells in intestinal allografts.

Intestinal transplantation: indications, results and strategy

The term 'intestinal failure' is now often used to describe gastrointestinal function insufficient to satisfy body nutrient and fluid requirements. The first recognized condition of intestinal failure was short bowel syndrome. Severe motility disorders such as chronic intestinal pseudo-obstruction syndrome in children as well as congenital intractable intestinal mucosa disorders are also forms of intestinal failure, because no curative treatment for these diseases is yet available. Parenteral nutrition and home parenteral nutrition remain the mainstay of therapy for intestinal failure, whether it is partial or total, provisional or permanent. However, some patients develop complications while receiving standard therapy for intestinal failure and are considered for intestinal transplantation. Indeed, recent advances in immunosuppressive treatment and the better monitoring and control of acute rejection have brought intestinal transplantation into the realm of standard treatment for intestinal failure. Although it has been used in humans for the past two decades, this procedure has had a slow learning curve. According to the current results, this challenging procedure may be performed in children or adults, only under certain conditions.