Intestinal transplantation has evolved to be a standard therapeutic option and the only chance of cure for patients with intestinal failure who fail parenteral nutrition (1–3). Even though the combination of tacrolimus and corticosteroids continues to be the keystone in intestinal transplant immunosuppression, an initial immunosuppression induction course using antilymphocyte agents such as rabbit antithymocyte globulin (rATG), alemtuzamab, and daclizumab have been implemented by most centers (4–8). Modifications in the initial immunosuppression regimen, along with changes in timing of the immunosuppression, have translated into decreased episodes of acute cellular rejection in the first 90 days posttransplant. These changes have improved short-term patient and graft survival, which now approaches the reported survival for other solid abdominal organs at 1-year (9).
Although early transplant outcomes have improved dramatically in the last 5 years, graft loss due to chronic rejection, long-term drug toxicity, and malignancy continue to hamper long-term survival for intestinal transplant recipients (9). In patients with chronic rejection, indolent but progressive infiltration and damage to the transplanted intestine by leukocytes and antibodies results in increasing fibrosis and disruption of the villae (10). Early depletion of lymphocytes may limit this effect. To induce an acute lymphocyte depletion (B- and T-lymphocytes), our center has included rituximab in our immunosuppression induction protocol, along with rATG and corticosteroids. Rituximab is a chimeric anti-CD 20 monoclonal antibody and primarily depletes B-cells, whereas rATG primarily depletes T-cells. Our center has modified its immunosuppression induction protocol in an attempt to improve both short- and long-term outcomes. We now report the results of this induction protocol in 29 adult intestinal transplants.
MATERIALS AND METHODS
We performed a retrospective review of 27 adult patients who underwent 29 intestinal transplants from July 2004 to March 2007 at Indiana University. The following three types of procedures were performed: isolated intestinal transplantation (Itx, n=7) for patients with intestinal failure and with viable liver function; modified multivisceral transplantation (MMVtx, n=3) for patients with functional disease of the intestinal tract and/or extensive Crohn’s disease, and multivisceral transplantation (n=19) for patients with coexisting intestinal and liver failure, nonresectable tumors of the abdominal cavity, or complete mesenteric venous thrombosis. In addition, four patients underwent simultaneous transplantation of a cadaveric renal allograft.
Induction therapy was performed using rATG (10 mg/kg) divided into five equivalent doses (2 mg/kg), which were given on postoperative days 0, 2, 4, 6, and 8. Rituximab (150 mg/m2) was given as a single dose on postoperative day 3. Methylprednisolone was given in decreasing doses as premedication for both rATG and rituximab, and was subsequently tapered off over 1 to 6 months. Intravenous tacrolimus was initiated posttransplant on arrival to the intensive care unit and was dosed to maintain initial serum levels of 14 to 18 ng/dL. Enteral tacrolimus was added between postoperative days 3 and 5. When enteral absorption of tacrolimus was adequate, the intravenous tacrolimus was stopped. Rejection was treated with an increase in the baseline tacrolimus levels combined with one to three doses of intravenous solumedrol (500 mg), depending on initial severity of the rejection episode and clinical response to treatment. For steroid resistant rejection, patients were dosed with additional thymoglobulin or with Campath. All patients received cytomegalovirus and Pneumocystis carinii pneumonia prophylaxis therapy with valganciclovir, cytogam, and septra. Posttransplant intestinal allograft surveillance was performed with serial magnification endoscopy with mucosal biopsy.
All of the intestinal transplant allografts in this series were procured by a team from our center. Intestinal donor demographic and clinical data were obtained from the original donor charts as recorded by the on-site OPO representative. Graft and patient survival data were collected from the transplant database at our center. Patients are closely followed posttransplant by our center, and no patients were lost to follow-up. All recipients were listed for transplantation according to standard procedures and protocols as established by the United Network for Organ Sharing. For this cohort, there were no ABO mismatches.
Transplant outcomes included graft and patient survival, episodes of rejection of the intestine, incidence of posttransplant lymphoproliferative disorder (PTLD), and incidence of graft-versus-host disease (GVHD). All patients received a minimum of twice weekly magnification endoscopy with biopsy in the first 4 weeks posttransplant. All occurrences of graft loss or patient death were included in the final analysis regardless of the causative factors. There were no exclusions for intraoperative or perioperative mortality or graft loss or for nontransplant-related deaths. Minimum follow-up time was 2 months, with median follow-up time of 15 months. This study was reviewed and approved by the Indiana University School of Medicine institutional review board.
Statistical analysis was conducted using commercially available software (SPSS, SPSS Inc., Version 15.0, 2006). Graft and patient survival outcomes were analyzed using the Chi-square test and the Fisher’s Exact test, as indicated.
Patient demographics and indications for transplant are listed in Table 1. There were 7 Itx (24%), 3 MMVtx (10%), and 19 multivisceral transplant (66%). The primary indications for intestinal transplant included short gut syndrome (38%), diffuse mesenteric thrombosis (38%), nonresectable tumor (10%), and pseudoobstruction (7%). The median recipient age at transplant was 41, with 59% being men and 97% being white. Donor characteristics included a median age of 17, with 76% being men. The primary cause of death for donors was trauma (72%).
Overall graft and patient survival was 72% (21 of 29) and 78% (21 of 27), respectivley. One-year graft and patient survival was 76% (13 of 17) and 81% (13 of 16), respectively (Table 2). The most successful transplant type was isolated small bowel transplant (86% overall survival) followed by multivisceral transplant (79% overall survival). Survival by indication was best for nonresectable tumors and pseudoobstruction (100% overall survival), followed by short gut syndrome (75% overall survival).
Thirteen patients (48%) experienced 19 episodes of acute rejection (9 mild episodes, 2 moderate, and 8 severe). Two patients who underwent MMVtx, presented with exfoliative severe rejection of the intestinal component during the first month after transplant. The rejection was unresponsive to steroid pulse and rATG. In both patients, the small bowel component of the graft was resected and retransplantation with a multivisceral graft was performed at a later date. Both these patients had no further episodes of rejection. Chronic rejection was seen in only one isolated intestinal graft 18 months after transplant. Patients with a multivisceral graft experienced less episodes of severe acute rejection (1 of 19, 5%) when compared with isolated intestinal transplants and modified multivisceral transplants (7 of 10, 70%).
Two patients had episodes of skin GVHD that responded to steroid boluses. PTLD was not seen in our series. Two patients developed cytomegalovirus enteritis that responded to long-term intravenous ganciclovir therapy.
The intestine remains the most challenging abdominal solid organ to transplant because of its distinctive capability of causing a strong immunological response that can be translated into rejection or GVHD. Even though tacrolimus-based immunosuppression continues to be the mainstay in maintenance immunosuppression after intestinal transplantation, efforts have focused on the development of new agents capable of avoiding rejection with fewer long-term side effects. In general, average serum levels of tacrolimus are maintained at higher levels in intestinal transplant patients when compared with those for recipients of other organs. A decline in renal function has been well-described in patients undergoing solid organ transplantation and this decline may be more precipitous in intestinal transplant patients. Kato et al. (11) described the incidence of renal insufficiency (glomerular filtration rate <90 mL/min) in children to be 13% at transplant, 48% at 1-year, and 35% at 2-years posttransplant.
Targeting cell surface antigens using monoclonal and polyclonal antibodies represents an attractive therapy in the prevention of acute rejection after solid organ transplantation minimizing initial high doses of tacrolimus. The use of anti-T-cell preparations is now a common practice in the majority of intestinal transplant centers (4, 12).
Thymoglobulin is prepared by immunizing rabbits with cells derived from fragments of the human thymus gland. Unlike the previous monoclonal preparations directed against specific T-cell antigens, thymoglobulin is a polyclonal preparation containing antibodies to a variety of T- and B-cell antigens. Studies have shown that the human thymus, in addition to the thymocytes that usually express T-cell antigens, also consists of 5% to 10% plasma cells (13). Therefore, the rabbit inoculation results in a preparation that contains antibodies against plasma cell/B-cell antigens, as well as the expected T-cell antigens. In addition to T- and B-cell depletion, studies have shown a possible protective effect against reperfusion injury when thymoglobulin is administered before reperfusion of solid organs (14, 15). Several mechanisms have been proposed to explain this finding, including a blockade of adhesion molecules, decreased cell surface expression of β1 and β2 integrins, as well as endothelial inflammatory cells such as intercellular adhesion molecule-1 (16).
Acute cellular rejection remains the most common complication after intestinal transplantation, and occurs with a higher frequency when compared with transplantation of other solid abdominal organs. In two recent large center reports, the incidence of acute cellular rejection ranged between 50% and 70% in the first 90-days posttransplant (17, 18). In 2005, Reyes et al. reported induction therapy with thymoglobulin in 36 intestinal transplant recipients with excellent patient and graft survival. In the study, the incidence of acute cellular rejection was 55% in the first 90 days posttransplant. With a median follow-up of 15.8±5.3 months, no clinical or histopathological signs of chronic rejection were identified (4).
The presence of anti-HLA class I and II antibodies has not been correlated with higher incidence of rejection after small bowel transplantation even though several studies have showed poor graft function in kidney, lung, and heart transplantation in patients with high levels of panel reactive antibodies. In 2003, Ruiz et al. (19) examined 188 biopsies of 21 postintestinal transplant patients. Different degrees of mucosal vascular changes were observed with small-vessel congestion and red cell extravasation being the most common findings. The vascular changes described had no correlation with the presence of acute cellular rejection, HLA type, or HLA antigen mismatches. However, patients with vascular changes had significantly higher PRA levels and a higher incidence of positive T- and B-cell crossmatch with lower graft survival rates.
We have added rituximab to rATG attempting to minimize the possible injury caused by pre- and posttransplant formed antibodies against the intestinal graft. Rituximab, a chimeric anti-CD20 monoclonal antibody, efficiently removes B cells with few side effects. The elimination of B cells occurs by three potential mechanisms: (1) antibody dependent cell-mediated cytotoxity, (2) complement dependent cytotoxicity, and (3) apoptosis (20). B-cells that recover are significantly depleted of memory CD 27+ B cells for as long as 2 years after a single dose. In our series, 13 (48%) patients experienced 19 episodes of rejection; however, only eight (30%) episodes occurred in the first 90 days posttransplant. Also, only one episode of severe rejection occurred in the multivisceral transplant group. The reasons for a lower incidence of severe rejection in multivisceral patients have not been established. A possible explanation for the protective effect of a multivisceral graft could be in the massive removal of the native lymphoid tissue, which is significantly more extensive than in any other intra abdominal organ transplant. In a recent publication by Tzakis et al. (17), a lower incidence of severe rejection among multivisceral transplant grafts was observed when compared with intestinal or liver/intestinal transplant grafts. Finally, another potential benefit of the use of rituximab is a possible reduction in the incidence of PLTD. The rate of PTLD is higher in intestinal transplant patients (6%–8%) when compared with other solid abdominal organ recipients (21–23). This increased rate may be related to the increased immunosuppression used routinely in intestinal transplant recipients. In almost 4 years since the initiation of our intestinal transplant program, we have not documented a single case of PTLD.
Although less frequent than acute cellular rejection, chronic rejection occurs as an indolent process with nonspecific symptoms. Clinically, recurrent diarrhea with a worsening of the patient’s nutritional status is usually associated with the motility disorder seen in chronic rejection. Histological findings consist of differing degrees of change in villae architecture, interstitial fibrosis, leukocyte infiltration, and obliterative arteriopathy (24). One theory suggests that chronic rejection may be associated with a slowly progressive antibody mediated injury. However, with little available evidence, the mechanism for chronic rejection remains to be determined. We report only one case of chronic rejection in this series, which occurred 2 years after an isolated intestinal transplant. However, chronic rejection occurs years after transplantation and we anticipate future cases of chronic rejection as predicted by the published literature.
In conclusion, induction immunosuppression has developed as a mainstay in the early clinical management of intestinal transplant recipients. Our induction regimen of rATG, rituximab, and corticosteroids, accompanied by maintenance tacrolimus and low-dose steroids has resulted in an incidence of rejection similar to those previously published with a low incidence of PTLD and chronic rejection. There was a very low incidence of rejection in all intestinal transplant patients undergoing simultaneous transplantation of a liver allograft. Two of three patients undergoing modified multivisceral transplantation did develop severe exfoliative rejection and required removal of the transplant bowel. Both these patients subsequently underwent a full multivisceral transplantation and had not further episodes of rejection. Therefore, the combination of rATG and rituximab is an effective induction therapy based on our preliminary data. The number and severity of rejection episodes increased when the liver was not included as part of the graft. An immunosuppression regimen including rATG, rituximab, and steroids may have a protective effect against PTLD and chronic rejection.
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