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Inflammatory bowel disease following solid organ transplantation
Clinical Immunology (2008) 128, 287–293
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FOCIS Centers of Excellence Review
Inflammatory bowel disease following solid organ transplantation Daniel D. Hampton, Martin H. Poleski, Jane E. Onken⁎ Department of Medicine, Division of Gastroenterology, Inflammatory Bowel Disease Clinic, Duke University Medical Center, Durham, NC 27710, USA Received 2 June 2008; accepted with revision 25 June 2008 KEYWORDS Solid organ transplant Inflammatory bowel disease Immunosuppression Immune tolerance DAMPs PAMPs
Abstract Inflammatory bowel disease (IBD) is a T cell driven inflammatory condition of the gut. Following solid organ transplantation (SOT), de novo IBD has been reported despite anti-T cell therapy for the prevention of organ rejection. This paradox is illustrated with a case report, highlighting the difficult diagnostic criteria, the potential role of Damage or Pathogen Associated Molecular Pattern Molecules [DAMPs and PAMPs] that drives aspects of ongoing inflammation within the transplanted organ as well as the intestine, and the therapeutic strategies applied. Recurrent IBD is more common than de novo IBD following transplantation, with cumulative risks ten years after orthotopic liver transplantation of 70% and 30%, respectively. Furthermore, the annual incidence of de novo IBD following solid organ transplantation has been estimated to be 206 cases/ 100,000 or ten times the expected incidence of IBD in the general population (approximately 20 cases/100,000). The association of IBD with other autoimmune conditions such as primary sclerosing cholangitis and autoimmune hepatitis, both common indications for liver transplantation, may play a contributory role, particularly in view of the observation that IBD is more common following liver transplant than other solid organ transplants. Recurrent IBD following transplant appears to run a more aggressive course than de novo IBD, with a higher proportion requiring colectomy for medically refractory disease. Risk factors that have been associated with development of post-transplant IBD include acute CMV infection and the use of tacrolimus. © 2008 Elsevier Inc. All rights reserved.
⁎ Corresponding author. E-mail addresses: [email protected] (D.D. Hampton), [email protected] (J.E. Onken). 1521-6616/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.clim.2008.06.011
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Case presentation The patient, a 39-year-old African-American woman, presented to our institution in 1998 for evaluation and treatment of autoimmune hepatitis. Her history dated back to 1992 with the discovery of abnormal liver function tests on routine examination. Liver biopsy was performed and showed changes of chronic active hepatitis and evolving cirrhosis. Based on the clinical history, laboratory data, and pathology, a diagnosis of autoimmune hepatitis was made. She was treated with a prednisone taper followed by a maintenance dose of 10 mg/d in addition to azathioprine 50mg/d for the next 5 years. Her symptoms progressed, and in 1998, she was referred to our liver transplant center for evaluation. Laboratory studies at that time included an anti-neutrophilic antibody titer of 1:640. She was CMV antibody negative. Her transplant workup was completed and she was listed for transplantation in September 1998. Over the next 10months, her clinical condition deteriorated and she underwent orthotopic liver transplantation in July 1999. The donor was a 34-year-old male who suffered anoxic brain injury secondary to a gunshot wound. The donor was CMV negative. Explant pathology confirmed cirrhosis with ongoing chronic active hepatitis consistent with autoimmune hepatitis. The immediate post-operative course was complicated by a bile leak requiring surgical revision of the bile duct anastomosis within 24 h of transplant. Recovery was otherwise uneventful and she was discharged home on post-operative day seven. Discharge medications included ganciclovir prophylaxis as well as cyclosporine and prednisone. Within two weeks she was readmitted with biopsyproven acute cellular allograft rejection and treated with methylprednisolone. Cyclosporine was discontinued and tacrolimus initiated. She received another course of highdose steroids two weeks later and mycophenolate mofetil was added to her regimen. Despite high-dose steroids, her liver function failed to improve, and she was given a 10-day course of OKT3. She responded and was maintained on tacrolimus, mycophenolate mofetil, and prednisone. In February 2001 the patient was again hospitalized, this time with fever, diarrhea, and a 15 lb weight loss. CMV DNA was positive and she was treated with a course of IV ganciclovir. Her diarrhea improved initially but by July 2001, she returned complaining of bloody diarrhea with 12 stools/day. She was started empirically on ganciclovir. Colonoscopy was performed and revealed severe mucosal ulceration and friability. Although the appearance was felt consistent with CMV colitis, biopsies showed chronic active colitis and stains for CMV were negative. Her diarrhea improved but returned one month later despite ongoing ganciclovir. Flexible sigmoidoscopy showed improved but persistent colonic mucosal ulcerations. Stools were negative for pathogens, and a small bowel follow through was normal. The patient's diarrhea persisted and in October 2001, she developed a perirectal abscess associated with a perianal fistula. Her past medical history had included a simple rectal abscess drained in 1985. She developed another rectal abscess in June 2002, also with a fistula. Review of the previous colonic biopsies coupled with her history of diarrhea, recurrent rectal abscesses, perianal fistulas, and failure to improve despite ganciclovir were felt to be more
Figure 1 Endoscopic images from the patient's colonoscopy showing colitis with luminal narrowing, edema, erythema, granularity, loss of vascular pattern, and serpiginous ulcers.
consistent with a diagnosis of inflammatory bowel disease. Colonoscopy was repeated and revealed severe mucosal ulceration with skip lesions and relative rectal sparing consistent with Crohn's disease (Fig. 1). Prednisone was increased to 40mg/d and Ciprofloxacin 1g daily was added with prompt resolution of her diarrhea.
Discussion Clinical features and epidemiology of post-transplant IBD IBD following solid organ transplant (SOT) can be classified either as de novo disease or exacerbation of pre-existing disease. True de novo disease is uncommon, with most occurrences documented in case-report fashion [1]. However, interrogations of larger transplant databases have yielded some information regarding the epidemiology and risk factors for both de novo and recurrent IBD. Wörns et al. [1] reviewed all published reports of IBD postSOT and found that for de novo disease, 38 of 44 cases (86%) occurred following either liver transplantation (23) or combined liver/kidney transplantation (15), with the remaining 6 cases occurring after heart (4) or kidney (2)
Inflammatory bowel disease following solid organ transplantation transplant. Papadakis et al. reported a case of de novo Crohn's disease (CD) following living-donor liver transplantation from a donor with CD [2]. Taken together, these studies suggest that the liver, or the immune cells within it, may have a functional role in determining susceptibility to IBD. Furthermore, although stem-cell transplantation (SCT) is thought to be curative for CD, case reports exist [3] of relapse of CD following SCT. CD also frequently recurs following small bowel transplantation [4] suggesting that the underlying cellular dysfunction is likely outside the intestinal parenchyma and may be dependent on factors in addition to the immune cells in some cases. Using an electronic database search of 6800 liver and kidney transplants at the University of Pittsburgh, Riley et al. [5] identified 14 patients who developed IBD posttransplant. Twelve of the patients developed IBD following liver transplant; two were detected post kidney transplant. Based on their findings, the authors estimated the annual incidence of de novo IBD in the SOT population to be 206 cases/100,000, an order of magnitude higher than the expected incidence in the general population (20 cases/100,000), although it should be noted that IBD is associated with primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH), both common indications for liver transplantation. A U.S. study [5] looked at 870 OLT patients at a single center and found 91 cases of IBD. Forty-nine of these (54%) had a history of IBD prior to transplant. Of these, 32 (65%) had recurrence of IBD following transplant; all but four had UC. Five of the 32 patients (16%) who flared post-operatively had a poor response to medical therapy and required colectomy. Comparison of IBD therapies pre- and post-OLT demonstrated that the majority of patients (59%) required either an escalation in medical therapy or a colectomy postOLT, supporting the notion that induction and maintenance of remission of pre-existing IBD may be significantly more challenging once it relapses post-transplant. In the same study, de novo IBD developed in eight patients (42%) following OLT. Five of the eight (63%) were transplanted for AIH. This group tended to develop disease later in the post-transplant period than the patients with preexisting IBD whose disease was exacerbated post-OLT. In addition, the patients with de novo IBD post-transplant responded better to medical therapy; none required colectomy. Multivariate analysis identified only CMV mismatch (seropositive donor, seronegative recipient) as a significant risk factor for de novo IBD post-transplant. In the same analysis, the authors identified active IBD prior to transplant and the use of tacrolimus (FK506) to prevent allograft rejection as risk factors for the exacerbation of IBD posttransplant. The cumulative risks of recurrent versus de novo IBD 10 years after OLT were 70% and 30%, respectively. A series from the Netherlands reviewed 78 patients transplanted between 1979 and 2001 for PSC (n = 48) and AIH (n = 30) [6]. Nine of 25 (36%) patients diagnosed with IBD prior to OLT experienced a flare of disease posttransplant. De novo IBD developed in six of 53 (11%) patients post-OLT. The authors found IBD-free survival rates post-OLT were significantly higher in patients not receiving tacrolimus compared with those receiving tacrolimus, in patients receiving azathioprine (AZA) compared with those not receiving AZA, and in patients receiving a post-
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transplant regimen consisting of cyclosporine (CyA), prednisolone and azathioprine compared with a regimen of tacrolimus and prednisolone. Interestingly, five of the six patients in this series who developed de novo IBD had been treated with tacrolimus. Further subdividing the post-transplant IBD group, Papatheodoridis et al. reviewed 30 patients with PSC who underwent OLT [7]. Eighteen (60%) had IBD pre-OLT. None received long-term steroids after OLT. Four of 12 patients with ulcerative colitis in remission pre-OLT relapsed following transplant. All four patients with active UC prior to transplant remained active post-OLT. Three of the 8 patients with active disease post-OLT required colectomy. De novo IBD developed in 3 of 12 patients post-transplant; none required colectomy. These studies suggest that recurrent IBD tends to follow a more aggressive course post-transplant. The reviews by Verdonk and Haagsma raise the possibility that use of tacrolimus may play a role both in the recurrence of IBD post-OLT and the development of de novo disease as well. Drugs with proven efficacy for induction and maintenance of remission in IBD such as AZA may reduce the risk of disease exacerbation post-OLT, while acute CMV infection may increase the risk of de novo IBD in the post-transplant setting.
The role of immunosuppressive therapies How can therapy directed toward inducing tolerance of an organ fail to induce tolerance of the intestinal microflora? Certainly differences exist between various tissues including the gut associated lymphoid tissue and that resident in the liver with regard to tolerance, with widely differing immunosuppressive strategies between liver transplantation and IBD [8,9]. A closer look at the therapies used in both SOT and IBD may yield further insight as to the dichotomy between responses to therapy. Table 1 describes the systemic immunosuppressive medications used in IBD and SOT. At a cursory glance, a great deal of overlap is evident. However, when the efficacy, utilization, and mode of actions are compared it becomes clear that substantial differences exist. Although corticosteroids have proven efficacy in acute and chronic prevention of SOT rejection as well as in inducing clinical remission in IBD, they remain inadequate both for the maintenance of remission and for endoscopic healing in IBD [10,11] suggesting that the benefit may not be due entirely to disease modification. This inability to control chronic aspects of IBD may be related to the fact that corticosteroids do not cause apoptosis in mature T cells [12]. The calcineurin inhibitors CyA and tacrolimus are highly effective as chronic therapy in SOT and remain first-line agents in many institutions. In contrast, CyA has limited utility in IBD, with its primary use in acute, fulminant UC [13] and no proven efficacy in CD [14]. Tacrolimus is also largely ineffective in IBD, with only a marginal improvement in fistulizing CD [15]. Two other agents, mycophenolate mofetil (MMF) and mycophenolic acid (MPA), both have proven efficacy in SOT while their role in IBD is still a topic of debate [16,17]. Additionally, MMF is associated with an enterocolitis with features of CD leading many to question the risk–benefit balance.
290 Table 1
D.D. Hampton et al. Immunosuppresives commonly used in IBD and SOT
Class
Examples
Mechanism of Action
Corticosteroids
Prednisone, Methylprednisolone, Prednisolone, Hydrocortisone Cyclosporine, Tacrolimus
Down-regulate cytokine expression by T cells and APCs
mTOR inhibitors
Sirolimus, Everolimus
Anti-metabolites
6-mercaptopurine, Azathioprine
Anti-metabolites
Mycophenolate mofetil, Mycophenolic acid
Anti-metabolite
Methotrexate
Anti-IL-2 receptor antibodies
Daclizumab, Basiliximab
Inhibit B and T cell activation by arresting cell-cycle progression Interfere with purine synthesis causing interruption of DNA mechanisms; inhibit CD28 costimulation of T cell receptor Reduce de novo purine synthesis in lymphocytes by inhibiting IMPdehydrogenase Inhibit folate metabolism causing disruption of multiple folate dependent processes Block T cell proliferation by binding IL-2 receptor
Anti-T cell antibodies
OKT-3, Antithymocyte globulin
Anti-TNF antibodies
Infliximab, Adalimumab, Certolizumab
Calcineurin inhibitors
Selective adhesion Natalizumab molecule inhibitor
Clinical Utility in OLT
Clinical Utility in IBD
Induces T cell apoptosis?
Induction of remission in UC and CD
Not when mature [12]
Induction of remission in steroidrefractory UC None demonstrated
No [43]
Prevention of chronic rejection
Maintenance of remission in UC and CD
Yes [20]
Prevention of chronic rejection
Possibly maintenance of remission in CD
Possibly, but unclear [43,44,45]
None
Induction and maintenance of remission in CD
Yes [43,46]
Post-transplant to reduce steroid exposure Halting acute cellular rejection
None
No [47,48]
None
Yes [49]
Induction and maintenance of remission in UC and CD Induction and maintenance of remission in CD
Yes [21,22]
Immediately post-transplant; treatment of acute cellular rejection Inhibit calcineurin-induced Prevention of production of IL-2 and chronic rejection T cell activation
Deplete T cell pool via antibody mediated apoptosis or inhibition of activation Inhibit TNF-mediated inflammatory signaling
Prevention of chronic rejection
None
Inhibit T cell migration from the vasculature to target tissues by blocking α4β1 and α4β7
None
No [43]
Possibly [50]
Therapies with the ability to cause apoptosis of T cells consistently show the ability to maintain long-term remission in IBD whereas those that do not cause apoptosis do not.
Azathioprine and 6-mercaptopurine (6-MP) were among the first anti-rejection agents used in SOT and had reasonable efficacy. They have since fallen out of favor due in part to a perceived higher side-effect profile as doses required to prevent rejection often led to cytopenias and hepatotoxicity. In IBD, however, they remain among the most utilized drugs for maintenance of remission with proven efficacy in both CD and UC [18,19]. Their mechanism of action has traditionally been attributed to interference with purine metabolism causing disruptions in nucleic acid utility. However, it was recently demonstrated that 6-MP and AZA induce apoptosis in T cells by interfering with T cell receptor (TCR) signaling. When ligands bind TCR, a costimulatory signal is required through CD28 to activate T cells. If CD28 signaling is blocked,
then T cells become anergic or undergo apoptosis. Tiede, et al. [20] showed that 6-MP and AZA become incorporated into GTP to form 6-thio-GTP that in turn binds Rac-1 and alters the CD28 co-signal to favor anergy and apoptosis. Indeed, T cells isolated from patients with and without IBD were more likely to undergo apoptosis in the presence of 6-MP, while T cells from patients with IBD resistant to 6-MP showed no increase in apoptosis. Anti-TNF-α antibodies (infliximab, adalimumab, and certolizumab) have been a welcome addition to the armamentarium against IBD. Their exact mechanism of action is not entirely clear, although induction of T cell apoptosis has been widely cited [21,22]. Etanercept, an agent that binds soluble rather than membrane bound TNF,
Inflammatory bowel disease following solid organ transplantation is ineffective in IBD. It is ligation of membrane bound TNF that induces T cell apoptosis and it is this difference between etanercept and other anti-TNF agents that is one explanation for the observed difference in efficacy in IBD. In addition, patients with rheumatoid arthritis showed impaired function of CD4+CD25+ Tregs, specifically regarding suppression of effector T cells and monocytes as well as induction of Treg proliferation [23]. In these patients, infliximab was able to restore suppressive function to Tregs and to increase the number of peripheral Tregs, suggesting a novel mechanism of action. Taken as a whole, it seems that the ability to induce T cell apoptosis is critical for effective treatment of IBD but not necessarily for SOT. While this is not a new observation [24], the underlying mechanism has yet to be elucidated. As we discuss below, the uptake of apoptotic T cells by macrophages may be a link between the innate and adaptive immune systems in IBD.
DAMPs and their role in allograft rejection and chronic inflammation The concept of innate alloimmunity was introduced by Land et al. in 1994 with the results of a clinical trial involving intraoperative superoxide dismutase (SOD) in renal transplant recipients [25]. The authors observed a significant reduction in acute and chronic rejection and suggested that renal allograft reperfusion injury initiates acute allograft rejection and is also a factor in chronic rejection. They proposed an “injury hypothesis” in which reactive oxygen species (ROS)-mediated reperfusion injury to an allograft, in addition to its relative “foreignness,” triggers the adaptive alloimmune response (acute rejection). This hypothesis was later modified and the terms DAMPs (damage-associated molecular patterns) and PAMPs (pathogen-associated molecular patterns) introduced. PAMPs (e.g., LPS, peptidoglycan, CpG-rich DNA) are highly-conserved structures found on bacteria, fungi, and viruses. These bind to innate immune receptors such as toll-like receptors (TLR) and initiate an appropriate response. DAMPs (e.g., S100 proteins, alarmins) are endogenous ligands for TLR and the receptor for advanced glycation end products (RAGE) that are secreted by immune cells in inflamed sites. These molecules have a critical role as pro-inflammatory factors of innate immunity. Reperfusion injury has been shown to cause allograft destruction and generation of DAMPs. Subsequent activation of dendritic cells leads to an adaptive alloimmune response by the transplant recipient. [26] DAMPs have also been associated with a number of chronic diseases including rheumatoid arthritis, juvenile idiopathic arthritis, dermatomyositis, systemic lupus erythematosus, and IBD [27]. Released by phagocytes in response to cell stress, certain DAMPs can be found in high concentrations in inflamed tissue and their serum concentrations correlate well with disease activity. Measurement of fecal concentrations of the S100 family of calcium-binding proteins has become a diagnostic tool to help distinguish IBD from noninflammatory causes of gastrointestinal complaints [28]. Abreu et al. have proposed a TLR4-mediated derangement in the normal cooperative effort between the adaptive immune response in the intestine and the innate immune system in
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the clearance of pathogenic bacteria as a model for the development of inflammatory bowel disease [29], and deranged expression of TLR3 and TLR4 has been shown in biopsies from patients with active IBD [30]. The link between acute innate immune-induced inflammation and chronic adaptive immune-induced inflammation is an exciting topic, and the link between PAMPs, DAMPs, and tolerance is intriguing. Oral tolerance occurs through two mechanisms: T regulatory cells (Tregs) and anergy and deletion of effector T cells. When antigen is delivered orally in low doses the Treg pathway is favored [31]. In this case, antigen presenting cells (APC) present antigen to Tregs that then secrete downregulatory cytokines such as TGF-β, migrate to lymphoid organs and suppress T effector cells, and migrate to target tissues to produce downregulatory cytokines (e.g., TGF-β, IL-10). When higher doses of oral antigen are administered, anergy [32,33] and deletion [34] of effector T cells predominates. Deletion occurs, at least in part, by apoptosis of effector T cells as illustrated in mice in which suppression of experimental colitis is dependent on T cell apoptosis [35]. Intriguingly, when T cells undergo apoptosis and are taken up by macrophages, those macrophages then begin to secrete TGF-β and downregulate proinflammatory cytokine production [36], creating a Treg-like milieu in which further responses may occur. Thus, presentation of apoptotic T cells to the adaptive immune system seems to favor tolerance toward the respective antigens. Oral tolerance – more specifically a lack thereof – plays a role in the pathogenesis of inflammatory bowel disease. IL10 boosts Th3 function, and mice lacking IL-10 develop a well characterized form of chronic colitis in response to breaks in the epithelial barrier [37]. In the TNBS model of murine colitis, oral administration of both TNBS and extracts of colonic epithelial cells and mesenteric lymph nodes prevent colitis, all by TGF-β mediated pathways [38,39]. Another model of colitis uses the transfer of antigen naïve CD4+ CD45RBhigh T cells into SCID mice lacking functional B and T cells. Antigen experienced CD4+CD45RBlow T cells can prevent the development of colitis in this model, but not in the absence of TGF-β [40]. A delicate balance certainly exists between intestinal immune cells and the gut microflora, and when this balance tips toward an inflammatory response – i.e. away from oral tolerance – inflammatory bowel disease is the result. The role of oral tolerance in SOT is less clear, but some studies in mice have shown promising results. In one study, rejection of allografted livers in mice was completely prevented by injection of donor spleen cells into the recipient portal vein 10 days prior to liver transplantation [41]. Alternatively, in a study focusing on peripheral tolerance induced via oral tolerance, mice were fed high and low-dose ovalbumin (OVA) and their livers were subsequently transplanted into OVA-naïve mice. The recipient mice then showed tolerance to DTH challenge with OVA at 24h (high-dose OVA) and 4 days (low-dose OVA), suggesting that the liver plays a role as a tolerogenic site of immunity [42]. Taken together, the cascade of events appears to begin with bacterial initiation of an inflammatory response through PAMP recognition, followed by release of DAMPs by innate immune cells that in turn contribute to the response and initiate the adaptive immune system, and finally, deranged tolerance mechanisms perpetuate chronic inflammation. It
292 may be that presentation of apoptotic effector T cells (primed to PAMPs) by APCs is important for the induction of tolerance and that this is a yet unrecognized means by which anti-IBD therapies may work.
Conclusion The patient we presented illustrates the limitations of our knowledge of immune disorders and organ transplantation. Although a diagnosis of IBD did not exist prior to liver transplantation, in retrospect, our patient had at least one finding (prior rectal abscess) that may have suggested an underlying predisposition to the disease. Although de novo IBD following SOT is disproportionately reported following liver transplantation as opposed to other organ transplants, this might reflect a change in the balance of effector and regulatory cells as well as innate inflammatory cells in response to an individual's native microflora. Our patient may have had autoimmunity which was suitably suppressed by regulatory cells but revealed by panimmunosuppressives. The cause(s) of IBD following SOT is unknown, and some cases may represent the expected incidence of “naturally occurring” IBD. However, cases following liver transplantation may represent altered immunity, particularly as it relates to tolerance of the native microflora. Although post-transplant de novo IBD is uncommon, it has an incidence that is an order of magnitude higher than that seen in the general population, infrequently arises in the first year following transplant, and manifests as UC more commonly than CD. Rates are substantially higher following OLT relative to other solid organs, and this may reflect the associations of IBD with PSC and AIH. The only risk factor identified to date for de novo post-transplant IBD among patients with PSC or AIH is CMV serology mismatch, although there is some suggestion that biliary stasis may also play a role [1]. Pre-existing IBD has a tendency to worsen following SOT and is less responsive to therapy than de novo disease. Risk factors for recurrence of disease post-transplant include active disease at time of transplantation, a short duration of IBD prior to transplant, and the use of tacrolimus, while the use of AZA and 5aminosalicylates seems to be protective. The reasons underlying the disparity between response to anti-T cell therapy between IBD and SOT are not clear, although T cell apoptosis seems critical and we hypothesize that uptake of apoptotic primed T cells by APCs confers tolerance toward the antigens to which they were primed. Lastly, DAMPs and PAMPs appear to have a critical role in both allograft rejection and the chronic inflammation that characterizes IBD.
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Inflammatory bowel disease following solid organ transplantation
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FOCIS Centers of Excellence Review
Inflammatory bowel disease following solid organ transplantation Daniel D. Hampton, Martin H. Poleski, Jane E. Onken⁎ Department of Medicine, Division of Gastroenterology, Inflammatory Bowel Disease Clinic, Duke University Medical Center, Durham, NC 27710, USA Received 2 June 2008; accepted with revision 25 June 2008 KEYWORDS Solid organ transplant Inflammatory bowel disease Immunosuppression Immune tolerance DAMPs PAMPs
Abstract Inflammatory bowel disease (IBD) is a T cell driven inflammatory condition of the gut. Following solid organ transplantation (SOT), de novo IBD has been reported despite anti-T cell therapy for the prevention of organ rejection. This paradox is illustrated with a case report, highlighting the difficult diagnostic criteria, the potential role of Damage or Pathogen Associated Molecular Pattern Molecules [DAMPs and PAMPs] that drives aspects of ongoing inflammation within the transplanted organ as well as the intestine, and the therapeutic strategies applied. Recurrent IBD is more common than de novo IBD following transplantation, with cumulative risks ten years after orthotopic liver transplantation of 70% and 30%, respectively. Furthermore, the annual incidence of de novo IBD following solid organ transplantation has been estimated to be 206 cases/ 100,000 or ten times the expected incidence of IBD in the general population (approximately 20 cases/100,000). The association of IBD with other autoimmune conditions such as primary sclerosing cholangitis and autoimmune hepatitis, both common indications for liver transplantation, may play a contributory role, particularly in view of the observation that IBD is more common following liver transplant than other solid organ transplants. Recurrent IBD following transplant appears to run a more aggressive course than de novo IBD, with a higher proportion requiring colectomy for medically refractory disease. Risk factors that have been associated with development of post-transplant IBD include acute CMV infection and the use of tacrolimus. © 2008 Elsevier Inc. All rights reserved.
⁎ Corresponding author. E-mail addresses: [email protected] (D.D. Hampton), [email protected] (J.E. Onken). 1521-6616/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.clim.2008.06.011
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Case presentation The patient, a 39-year-old African-American woman, presented to our institution in 1998 for evaluation and treatment of autoimmune hepatitis. Her history dated back to 1992 with the discovery of abnormal liver function tests on routine examination. Liver biopsy was performed and showed changes of chronic active hepatitis and evolving cirrhosis. Based on the clinical history, laboratory data, and pathology, a diagnosis of autoimmune hepatitis was made. She was treated with a prednisone taper followed by a maintenance dose of 10 mg/d in addition to azathioprine 50mg/d for the next 5 years. Her symptoms progressed, and in 1998, she was referred to our liver transplant center for evaluation. Laboratory studies at that time included an anti-neutrophilic antibody titer of 1:640. She was CMV antibody negative. Her transplant workup was completed and she was listed for transplantation in September 1998. Over the next 10months, her clinical condition deteriorated and she underwent orthotopic liver transplantation in July 1999. The donor was a 34-year-old male who suffered anoxic brain injury secondary to a gunshot wound. The donor was CMV negative. Explant pathology confirmed cirrhosis with ongoing chronic active hepatitis consistent with autoimmune hepatitis. The immediate post-operative course was complicated by a bile leak requiring surgical revision of the bile duct anastomosis within 24 h of transplant. Recovery was otherwise uneventful and she was discharged home on post-operative day seven. Discharge medications included ganciclovir prophylaxis as well as cyclosporine and prednisone. Within two weeks she was readmitted with biopsyproven acute cellular allograft rejection and treated with methylprednisolone. Cyclosporine was discontinued and tacrolimus initiated. She received another course of highdose steroids two weeks later and mycophenolate mofetil was added to her regimen. Despite high-dose steroids, her liver function failed to improve, and she was given a 10-day course of OKT3. She responded and was maintained on tacrolimus, mycophenolate mofetil, and prednisone. In February 2001 the patient was again hospitalized, this time with fever, diarrhea, and a 15 lb weight loss. CMV DNA was positive and she was treated with a course of IV ganciclovir. Her diarrhea improved initially but by July 2001, she returned complaining of bloody diarrhea with 12 stools/day. She was started empirically on ganciclovir. Colonoscopy was performed and revealed severe mucosal ulceration and friability. Although the appearance was felt consistent with CMV colitis, biopsies showed chronic active colitis and stains for CMV were negative. Her diarrhea improved but returned one month later despite ongoing ganciclovir. Flexible sigmoidoscopy showed improved but persistent colonic mucosal ulcerations. Stools were negative for pathogens, and a small bowel follow through was normal. The patient's diarrhea persisted and in October 2001, she developed a perirectal abscess associated with a perianal fistula. Her past medical history had included a simple rectal abscess drained in 1985. She developed another rectal abscess in June 2002, also with a fistula. Review of the previous colonic biopsies coupled with her history of diarrhea, recurrent rectal abscesses, perianal fistulas, and failure to improve despite ganciclovir were felt to be more
Figure 1 Endoscopic images from the patient's colonoscopy showing colitis with luminal narrowing, edema, erythema, granularity, loss of vascular pattern, and serpiginous ulcers.
consistent with a diagnosis of inflammatory bowel disease. Colonoscopy was repeated and revealed severe mucosal ulceration with skip lesions and relative rectal sparing consistent with Crohn's disease (Fig. 1). Prednisone was increased to 40mg/d and Ciprofloxacin 1g daily was added with prompt resolution of her diarrhea.
Discussion Clinical features and epidemiology of post-transplant IBD IBD following solid organ transplant (SOT) can be classified either as de novo disease or exacerbation of pre-existing disease. True de novo disease is uncommon, with most occurrences documented in case-report fashion [1]. However, interrogations of larger transplant databases have yielded some information regarding the epidemiology and risk factors for both de novo and recurrent IBD. Wörns et al. [1] reviewed all published reports of IBD postSOT and found that for de novo disease, 38 of 44 cases (86%) occurred following either liver transplantation (23) or combined liver/kidney transplantation (15), with the remaining 6 cases occurring after heart (4) or kidney (2)
Inflammatory bowel disease following solid organ transplantation transplant. Papadakis et al. reported a case of de novo Crohn's disease (CD) following living-donor liver transplantation from a donor with CD [2]. Taken together, these studies suggest that the liver, or the immune cells within it, may have a functional role in determining susceptibility to IBD. Furthermore, although stem-cell transplantation (SCT) is thought to be curative for CD, case reports exist [3] of relapse of CD following SCT. CD also frequently recurs following small bowel transplantation [4] suggesting that the underlying cellular dysfunction is likely outside the intestinal parenchyma and may be dependent on factors in addition to the immune cells in some cases. Using an electronic database search of 6800 liver and kidney transplants at the University of Pittsburgh, Riley et al. [5] identified 14 patients who developed IBD posttransplant. Twelve of the patients developed IBD following liver transplant; two were detected post kidney transplant. Based on their findings, the authors estimated the annual incidence of de novo IBD in the SOT population to be 206 cases/100,000, an order of magnitude higher than the expected incidence in the general population (20 cases/100,000), although it should be noted that IBD is associated with primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH), both common indications for liver transplantation. A U.S. study [5] looked at 870 OLT patients at a single center and found 91 cases of IBD. Forty-nine of these (54%) had a history of IBD prior to transplant. Of these, 32 (65%) had recurrence of IBD following transplant; all but four had UC. Five of the 32 patients (16%) who flared post-operatively had a poor response to medical therapy and required colectomy. Comparison of IBD therapies pre- and post-OLT demonstrated that the majority of patients (59%) required either an escalation in medical therapy or a colectomy postOLT, supporting the notion that induction and maintenance of remission of pre-existing IBD may be significantly more challenging once it relapses post-transplant. In the same study, de novo IBD developed in eight patients (42%) following OLT. Five of the eight (63%) were transplanted for AIH. This group tended to develop disease later in the post-transplant period than the patients with preexisting IBD whose disease was exacerbated post-OLT. In addition, the patients with de novo IBD post-transplant responded better to medical therapy; none required colectomy. Multivariate analysis identified only CMV mismatch (seropositive donor, seronegative recipient) as a significant risk factor for de novo IBD post-transplant. In the same analysis, the authors identified active IBD prior to transplant and the use of tacrolimus (FK506) to prevent allograft rejection as risk factors for the exacerbation of IBD posttransplant. The cumulative risks of recurrent versus de novo IBD 10 years after OLT were 70% and 30%, respectively. A series from the Netherlands reviewed 78 patients transplanted between 1979 and 2001 for PSC (n = 48) and AIH (n = 30) [6]. Nine of 25 (36%) patients diagnosed with IBD prior to OLT experienced a flare of disease posttransplant. De novo IBD developed in six of 53 (11%) patients post-OLT. The authors found IBD-free survival rates post-OLT were significantly higher in patients not receiving tacrolimus compared with those receiving tacrolimus, in patients receiving azathioprine (AZA) compared with those not receiving AZA, and in patients receiving a post-
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transplant regimen consisting of cyclosporine (CyA), prednisolone and azathioprine compared with a regimen of tacrolimus and prednisolone. Interestingly, five of the six patients in this series who developed de novo IBD had been treated with tacrolimus. Further subdividing the post-transplant IBD group, Papatheodoridis et al. reviewed 30 patients with PSC who underwent OLT [7]. Eighteen (60%) had IBD pre-OLT. None received long-term steroids after OLT. Four of 12 patients with ulcerative colitis in remission pre-OLT relapsed following transplant. All four patients with active UC prior to transplant remained active post-OLT. Three of the 8 patients with active disease post-OLT required colectomy. De novo IBD developed in 3 of 12 patients post-transplant; none required colectomy. These studies suggest that recurrent IBD tends to follow a more aggressive course post-transplant. The reviews by Verdonk and Haagsma raise the possibility that use of tacrolimus may play a role both in the recurrence of IBD post-OLT and the development of de novo disease as well. Drugs with proven efficacy for induction and maintenance of remission in IBD such as AZA may reduce the risk of disease exacerbation post-OLT, while acute CMV infection may increase the risk of de novo IBD in the post-transplant setting.
The role of immunosuppressive therapies How can therapy directed toward inducing tolerance of an organ fail to induce tolerance of the intestinal microflora? Certainly differences exist between various tissues including the gut associated lymphoid tissue and that resident in the liver with regard to tolerance, with widely differing immunosuppressive strategies between liver transplantation and IBD [8,9]. A closer look at the therapies used in both SOT and IBD may yield further insight as to the dichotomy between responses to therapy. Table 1 describes the systemic immunosuppressive medications used in IBD and SOT. At a cursory glance, a great deal of overlap is evident. However, when the efficacy, utilization, and mode of actions are compared it becomes clear that substantial differences exist. Although corticosteroids have proven efficacy in acute and chronic prevention of SOT rejection as well as in inducing clinical remission in IBD, they remain inadequate both for the maintenance of remission and for endoscopic healing in IBD [10,11] suggesting that the benefit may not be due entirely to disease modification. This inability to control chronic aspects of IBD may be related to the fact that corticosteroids do not cause apoptosis in mature T cells [12]. The calcineurin inhibitors CyA and tacrolimus are highly effective as chronic therapy in SOT and remain first-line agents in many institutions. In contrast, CyA has limited utility in IBD, with its primary use in acute, fulminant UC [13] and no proven efficacy in CD [14]. Tacrolimus is also largely ineffective in IBD, with only a marginal improvement in fistulizing CD [15]. Two other agents, mycophenolate mofetil (MMF) and mycophenolic acid (MPA), both have proven efficacy in SOT while their role in IBD is still a topic of debate [16,17]. Additionally, MMF is associated with an enterocolitis with features of CD leading many to question the risk–benefit balance.
290 Table 1
D.D. Hampton et al. Immunosuppresives commonly used in IBD and SOT
Class
Examples
Mechanism of Action
Corticosteroids
Prednisone, Methylprednisolone, Prednisolone, Hydrocortisone Cyclosporine, Tacrolimus
Down-regulate cytokine expression by T cells and APCs
mTOR inhibitors
Sirolimus, Everolimus
Anti-metabolites
6-mercaptopurine, Azathioprine
Anti-metabolites
Mycophenolate mofetil, Mycophenolic acid
Anti-metabolite
Methotrexate
Anti-IL-2 receptor antibodies
Daclizumab, Basiliximab
Inhibit B and T cell activation by arresting cell-cycle progression Interfere with purine synthesis causing interruption of DNA mechanisms; inhibit CD28 costimulation of T cell receptor Reduce de novo purine synthesis in lymphocytes by inhibiting IMPdehydrogenase Inhibit folate metabolism causing disruption of multiple folate dependent processes Block T cell proliferation by binding IL-2 receptor
Anti-T cell antibodies
OKT-3, Antithymocyte globulin
Anti-TNF antibodies
Infliximab, Adalimumab, Certolizumab
Calcineurin inhibitors
Selective adhesion Natalizumab molecule inhibitor
Clinical Utility in OLT
Clinical Utility in IBD
Induces T cell apoptosis?
Induction of remission in UC and CD
Not when mature [12]
Induction of remission in steroidrefractory UC None demonstrated
No [43]
Prevention of chronic rejection
Maintenance of remission in UC and CD
Yes [20]
Prevention of chronic rejection
Possibly maintenance of remission in CD
Possibly, but unclear [43,44,45]
None
Induction and maintenance of remission in CD
Yes [43,46]
Post-transplant to reduce steroid exposure Halting acute cellular rejection
None
No [47,48]
None
Yes [49]
Induction and maintenance of remission in UC and CD Induction and maintenance of remission in CD
Yes [21,22]
Immediately post-transplant; treatment of acute cellular rejection Inhibit calcineurin-induced Prevention of production of IL-2 and chronic rejection T cell activation
Deplete T cell pool via antibody mediated apoptosis or inhibition of activation Inhibit TNF-mediated inflammatory signaling
Prevention of chronic rejection
None
Inhibit T cell migration from the vasculature to target tissues by blocking α4β1 and α4β7
None
No [43]
Possibly [50]
Therapies with the ability to cause apoptosis of T cells consistently show the ability to maintain long-term remission in IBD whereas those that do not cause apoptosis do not.
Azathioprine and 6-mercaptopurine (6-MP) were among the first anti-rejection agents used in SOT and had reasonable efficacy. They have since fallen out of favor due in part to a perceived higher side-effect profile as doses required to prevent rejection often led to cytopenias and hepatotoxicity. In IBD, however, they remain among the most utilized drugs for maintenance of remission with proven efficacy in both CD and UC [18,19]. Their mechanism of action has traditionally been attributed to interference with purine metabolism causing disruptions in nucleic acid utility. However, it was recently demonstrated that 6-MP and AZA induce apoptosis in T cells by interfering with T cell receptor (TCR) signaling. When ligands bind TCR, a costimulatory signal is required through CD28 to activate T cells. If CD28 signaling is blocked,
then T cells become anergic or undergo apoptosis. Tiede, et al. [20] showed that 6-MP and AZA become incorporated into GTP to form 6-thio-GTP that in turn binds Rac-1 and alters the CD28 co-signal to favor anergy and apoptosis. Indeed, T cells isolated from patients with and without IBD were more likely to undergo apoptosis in the presence of 6-MP, while T cells from patients with IBD resistant to 6-MP showed no increase in apoptosis. Anti-TNF-α antibodies (infliximab, adalimumab, and certolizumab) have been a welcome addition to the armamentarium against IBD. Their exact mechanism of action is not entirely clear, although induction of T cell apoptosis has been widely cited [21,22]. Etanercept, an agent that binds soluble rather than membrane bound TNF,
Inflammatory bowel disease following solid organ transplantation is ineffective in IBD. It is ligation of membrane bound TNF that induces T cell apoptosis and it is this difference between etanercept and other anti-TNF agents that is one explanation for the observed difference in efficacy in IBD. In addition, patients with rheumatoid arthritis showed impaired function of CD4+CD25+ Tregs, specifically regarding suppression of effector T cells and monocytes as well as induction of Treg proliferation [23]. In these patients, infliximab was able to restore suppressive function to Tregs and to increase the number of peripheral Tregs, suggesting a novel mechanism of action. Taken as a whole, it seems that the ability to induce T cell apoptosis is critical for effective treatment of IBD but not necessarily for SOT. While this is not a new observation [24], the underlying mechanism has yet to be elucidated. As we discuss below, the uptake of apoptotic T cells by macrophages may be a link between the innate and adaptive immune systems in IBD.
DAMPs and their role in allograft rejection and chronic inflammation The concept of innate alloimmunity was introduced by Land et al. in 1994 with the results of a clinical trial involving intraoperative superoxide dismutase (SOD) in renal transplant recipients [25]. The authors observed a significant reduction in acute and chronic rejection and suggested that renal allograft reperfusion injury initiates acute allograft rejection and is also a factor in chronic rejection. They proposed an “injury hypothesis” in which reactive oxygen species (ROS)-mediated reperfusion injury to an allograft, in addition to its relative “foreignness,” triggers the adaptive alloimmune response (acute rejection). This hypothesis was later modified and the terms DAMPs (damage-associated molecular patterns) and PAMPs (pathogen-associated molecular patterns) introduced. PAMPs (e.g., LPS, peptidoglycan, CpG-rich DNA) are highly-conserved structures found on bacteria, fungi, and viruses. These bind to innate immune receptors such as toll-like receptors (TLR) and initiate an appropriate response. DAMPs (e.g., S100 proteins, alarmins) are endogenous ligands for TLR and the receptor for advanced glycation end products (RAGE) that are secreted by immune cells in inflamed sites. These molecules have a critical role as pro-inflammatory factors of innate immunity. Reperfusion injury has been shown to cause allograft destruction and generation of DAMPs. Subsequent activation of dendritic cells leads to an adaptive alloimmune response by the transplant recipient. [26] DAMPs have also been associated with a number of chronic diseases including rheumatoid arthritis, juvenile idiopathic arthritis, dermatomyositis, systemic lupus erythematosus, and IBD [27]. Released by phagocytes in response to cell stress, certain DAMPs can be found in high concentrations in inflamed tissue and their serum concentrations correlate well with disease activity. Measurement of fecal concentrations of the S100 family of calcium-binding proteins has become a diagnostic tool to help distinguish IBD from noninflammatory causes of gastrointestinal complaints [28]. Abreu et al. have proposed a TLR4-mediated derangement in the normal cooperative effort between the adaptive immune response in the intestine and the innate immune system in
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the clearance of pathogenic bacteria as a model for the development of inflammatory bowel disease [29], and deranged expression of TLR3 and TLR4 has been shown in biopsies from patients with active IBD [30]. The link between acute innate immune-induced inflammation and chronic adaptive immune-induced inflammation is an exciting topic, and the link between PAMPs, DAMPs, and tolerance is intriguing. Oral tolerance occurs through two mechanisms: T regulatory cells (Tregs) and anergy and deletion of effector T cells. When antigen is delivered orally in low doses the Treg pathway is favored [31]. In this case, antigen presenting cells (APC) present antigen to Tregs that then secrete downregulatory cytokines such as TGF-β, migrate to lymphoid organs and suppress T effector cells, and migrate to target tissues to produce downregulatory cytokines (e.g., TGF-β, IL-10). When higher doses of oral antigen are administered, anergy [32,33] and deletion [34] of effector T cells predominates. Deletion occurs, at least in part, by apoptosis of effector T cells as illustrated in mice in which suppression of experimental colitis is dependent on T cell apoptosis [35]. Intriguingly, when T cells undergo apoptosis and are taken up by macrophages, those macrophages then begin to secrete TGF-β and downregulate proinflammatory cytokine production [36], creating a Treg-like milieu in which further responses may occur. Thus, presentation of apoptotic T cells to the adaptive immune system seems to favor tolerance toward the respective antigens. Oral tolerance – more specifically a lack thereof – plays a role in the pathogenesis of inflammatory bowel disease. IL10 boosts Th3 function, and mice lacking IL-10 develop a well characterized form of chronic colitis in response to breaks in the epithelial barrier [37]. In the TNBS model of murine colitis, oral administration of both TNBS and extracts of colonic epithelial cells and mesenteric lymph nodes prevent colitis, all by TGF-β mediated pathways [38,39]. Another model of colitis uses the transfer of antigen naïve CD4+ CD45RBhigh T cells into SCID mice lacking functional B and T cells. Antigen experienced CD4+CD45RBlow T cells can prevent the development of colitis in this model, but not in the absence of TGF-β [40]. A delicate balance certainly exists between intestinal immune cells and the gut microflora, and when this balance tips toward an inflammatory response – i.e. away from oral tolerance – inflammatory bowel disease is the result. The role of oral tolerance in SOT is less clear, but some studies in mice have shown promising results. In one study, rejection of allografted livers in mice was completely prevented by injection of donor spleen cells into the recipient portal vein 10 days prior to liver transplantation [41]. Alternatively, in a study focusing on peripheral tolerance induced via oral tolerance, mice were fed high and low-dose ovalbumin (OVA) and their livers were subsequently transplanted into OVA-naïve mice. The recipient mice then showed tolerance to DTH challenge with OVA at 24h (high-dose OVA) and 4 days (low-dose OVA), suggesting that the liver plays a role as a tolerogenic site of immunity [42]. Taken together, the cascade of events appears to begin with bacterial initiation of an inflammatory response through PAMP recognition, followed by release of DAMPs by innate immune cells that in turn contribute to the response and initiate the adaptive immune system, and finally, deranged tolerance mechanisms perpetuate chronic inflammation. It
292 may be that presentation of apoptotic effector T cells (primed to PAMPs) by APCs is important for the induction of tolerance and that this is a yet unrecognized means by which anti-IBD therapies may work.
Conclusion The patient we presented illustrates the limitations of our knowledge of immune disorders and organ transplantation. Although a diagnosis of IBD did not exist prior to liver transplantation, in retrospect, our patient had at least one finding (prior rectal abscess) that may have suggested an underlying predisposition to the disease. Although de novo IBD following SOT is disproportionately reported following liver transplantation as opposed to other organ transplants, this might reflect a change in the balance of effector and regulatory cells as well as innate inflammatory cells in response to an individual's native microflora. Our patient may have had autoimmunity which was suitably suppressed by regulatory cells but revealed by panimmunosuppressives. The cause(s) of IBD following SOT is unknown, and some cases may represent the expected incidence of “naturally occurring” IBD. However, cases following liver transplantation may represent altered immunity, particularly as it relates to tolerance of the native microflora. Although post-transplant de novo IBD is uncommon, it has an incidence that is an order of magnitude higher than that seen in the general population, infrequently arises in the first year following transplant, and manifests as UC more commonly than CD. Rates are substantially higher following OLT relative to other solid organs, and this may reflect the associations of IBD with PSC and AIH. The only risk factor identified to date for de novo post-transplant IBD among patients with PSC or AIH is CMV serology mismatch, although there is some suggestion that biliary stasis may also play a role [1]. Pre-existing IBD has a tendency to worsen following SOT and is less responsive to therapy than de novo disease. Risk factors for recurrence of disease post-transplant include active disease at time of transplantation, a short duration of IBD prior to transplant, and the use of tacrolimus, while the use of AZA and 5aminosalicylates seems to be protective. The reasons underlying the disparity between response to anti-T cell therapy between IBD and SOT are not clear, although T cell apoptosis seems critical and we hypothesize that uptake of apoptotic primed T cells by APCs confers tolerance toward the antigens to which they were primed. Lastly, DAMPs and PAMPs appear to have a critical role in both allograft rejection and the chronic inflammation that characterizes IBD.
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