Section 5 -

Areas of Emphasis and Developments in Liver Allograft Pathology Anthony J. Demetris

A. Areas of Emphasis and Developments in Liver Allograft Pathology Syndromes unique to reduced-size and living donor liver allografts. Causes late liver allograft dysfunction and consequences of long term engraftment: Autoimmune hepatitis vs rejection Progression of fibrosis in HCV Distinguishing between various causes of chronic hepatitis Findings in recipients enrolled in "immunosuppressive minimization protocols", including immunosuppressive drug withdrawal B. Immunological Considerations that Impact Histopathologic Findings Rejection reactions, like all other immune responses, evolve and diversify over time via "epitope spreading": Tissue damage during the initial phases of an immune response leads to release of cryptic antigens, which results in development of auto-antibodies and cell mediated immunity directed against non-MHC determinants, including various cytoplasmic, nuclear, and matrix proteins shared by the donor and recipient. Likely explains histopathological differences between "early" (<6 months) and "late" onset acute cellular rejection. Immune responses against a self-antigen constitute an autoimmune response, and those against a foreign antigen constitute an anti-graft response: Since donor livers contain antigens not expressed in the native liver, many forms of AIH after transplantation could be classified as rejection. No conventional clinical tests reliably differentiate AIH from rejection and distinctions based on clinical and histopathological findings that may not reflect the true pathogenic nature C. Practical Problems in Determining the Cause of Late Liver Allograft Dysfunction Most late causes of liver allograft injury are first detected because of abnormalities in routinely monitored liver tests; clinical signs and symptoms are much less common. Distinguishing among the various causes of late liver allograft dysfunction is difficult because of overlapping clinical, serological, and histopathological features. Many late post-transplant biopsies show portal-based chronic inflammation with variable interface activity . Laboratory tests used to establish a diagnosis before transplantation may not have the same significance after transplantation. More than one insult can contribute to late post-transplant dysfunction. Levels of immunosuppression can influence biopsy findings and the severity of recurrent viral hepatitis, AIH, and rejection. D. Generalized Criteria for Determination of Causes of Late Liver Allograft Dysfunction Histopathologic and serologic evidence of liver injury showing a pattern compatible with the diagnosis. Positive serologic, molecular biologic, immunologic, or radiographic evidence of pathogen or possible cause of injury CHCVHCV. Other causes of similar histopathologic changes and elevated liver tests, if present, have been reasonably excluded. Figure 2. Algorithm for determining the most likely diagnosis in biopsies with prominent central perivenulitis (from [1] with permission). Table 1. Incidence, risk factors, and clinical observations (from [1] with permission) Diagnosis Incidence at 5 Years of Recurrent Disease Risk Factors for Disease Recurrence and/or severe Recurrent Disease Clinical/Immunological/Radiological Observations Recurrent AIH 30% - suboptimal immunosuppression; type I > type II disease; severe inflammation in native liver before transplantation; longer duration of follow-up - HLA DR3 or DR4 recipient status may reflect more severe disease - usually need higher baseline immunosuprression (see text) - HLA DR3 and/or DR4 genotype often present De novo AIH < 5% - may be more common in children, but this assumption has been questioned recently - same as above Recurrent HBV - 100 % if HBV DNA pos. - Less frequent if HBV DNA is neg. - anti-HBc+ donor - inadequate anti-HBV treatment - HBV mutants - recurrent HBV disease not usually significant problem because of treatment with effective anti-viral drugs Recurrent HCV Nearly universal in those with HCV replication before transplantation - HCV RNA in blood helpful in differential diagnosis: > 30,000,000 IU/L increased risk of cholestatic hepatitis; - significant acute or chronic rejection usually occurs only in association with relatively low HCV RNA levels < 5,000,000 IU/L - greater viral burden and more rapid progression of fibrosis than in general population - severity of hepatitis often worse with genotype 1 viruses - variable disease progression - subset of recipients with late onset rapid progression Recurrent PBC 20 - 30 % increases with time - Tacrolimus as baseline immunosuppression; living-related donor; steroid and other immunosuppression withdrawal - may recur as AIH - initial diagnosis often made by biopsy in asymptomatic recipient with/out increased liver tests Recurrent PSC 20 - 30 % increases with time - male sex; donor-recipient gender mismatch - intact colon at time of transplantation - patients at increased risk of rejection - cholangiographically-confirmed biliary strictures occurring > 90 days after OLTx - mural irregularity, diverticulum-like outpouchings, and an overall appearance resembling PSC - patient and allograft survival not adversely affected up 5 years; later outcome uncertain Acute Rejection Variable < 30% of causes of late dysfunction - inadequate immunosuppression - treatment with immune activating drugs (e.g. interferon) - history of autoimmune liver disease - much less common than early after transplantation - may be more difficult to treat, perhaps related to delay in diagnosis. Chronic Rejection 3 % - inadequate immunosuppression - treatment with immune activating drugs (e.g. interferon) - refractory acute rejection - chronic rejection in a previous failed allograft - important cause of late dysfunction - most cases occur within first year - does not appear to increase with time after transplantation, but more follow-up is needed. Idiopathic post-transplant hepatitis 5 - 60 % wide variation - 5 - 15% of patients followed for a minimum of 10 years will develop progressive fibrosis resulting in established cirrhosis - incidence varies widely among centers Table 2. Histopathologic features most commonly detected with various causes of late liver allograft dysfunction (from [1] with permission) . Histopathologic Features1 Autoimmune Hepatitis2 Acute Rejection Chronic Rejection Chronic Viral Hepatitis types B and C Primary Biliary Cirrhosis PSC/BD Strictures Distribution, severity and composition of portal inflammation Usually diffuse predominantly mononuclear of varying intensity. Often prominent plasma cell component Usually diffuse, variable intensity Mixed "rejection-type" (see text) infiltrate Patchy, usually minimal or mild lymphoplasmacytic Patchy, variable intensity; predominantly mononuclear; nodular aggregates Noticeably patchy and variable intensity; predominantly mononuclear; nodular aggregates and granulomas Usually patchy to diffuse depending on stage; mild neutrophilic, eosinophilic, or occasionally mononuclear predominant Presence and type of interface activity Usually prominent and defining feature: necro-inflammatory-type; often plasma cell rich Focally present and mild necro-inflammatory type Minimal to absent Variable, usually not prominent: necro-inflammatory and (ductular-type) Important feature later in disease development: ductular and necro-inflammatory-type with copper deposition Prominent and defining feature: ductular-type with portal and peri-portal edema Bile duct inflammation and damage Variable; if present involves a minority of bile ducts Present and usually involves a majority of bile ducts Focal ongoing lymphocytic bile duct damage; inflammation wanes with duct loss Variable; if present involves a minority of bile ducts Granulomatous or focally severe lymphocytic cholangitis is diagnostic in proper setting Periductal lamellar edema, "fibrous cholangitis", acute cholangitis, multiple intra-portal ductal profiles Biliary epithelial senescence changes and small bile loss Absent or involves only a minority of ducts/portal tracts, but may be focally severe Absent or involves only a minority of ducts Senescence/atrophy/ atypia involve a majority of remaining ducts (see text) Absent or involves only a minority of ducts Small bile duct loss associated with ductular reaction Small bile duct loss associated with ductular reaction Perivenular mononuclear inflammation and/or hepatocyte dropout Variable, can involve a majority of perivenular regions, similar to rejection (see text); may be plasma cell rich. Variable, if defining feature should involve a majority of perivenular regions; may also show subendothelial inflammation of vein (see text) Usually present, but variable Variable, but generally mild, if present involves a minority of perivenular regions Variable, but generally mild, if present involves a minority of perivenular regions Absent Lobular findings and necro-inflammatory activity Variable severity; rosettes may be present and/or prominent Variable, if present, concentrated in perivenular regions Variable; if present, concentrated in perivenular regions Disarray variable Variable severity necro-inflammatory activity Mild disarray, parenchymal granulomas Periportal copper deposition and cholatestasis are late features Disarray unusual Neutrophils clusters ± Cholestasis Pattern of fibrosis during progression toward cirrhosis Usually macronodular, post-hepatitic pattern Rare Uncommon, if present usually a veno-centric pattern; may evolve to biliary pattern over time Usually macronodular, hepatitic pattern; may be micronodular (see text) Biliary pattern Biliary pattern 1 The histopathologic findings in this table should be combined with clinical, serological, radiographic and important exclusionary criteria listed in Table 2 to arrive at a final diagnosis. 2 The same findings apply to recurrent and de novo autoimmune hepatitis. Table 3. Inclusionary and exclusionary criteria for the diagnosis of recurrent and new onset chronic necro-inflammatory diseases after liver transplantation and timing of first onset and pattern of liver test elevations (from [1] with permission). Diagnosis Original Disease Serology/Molecular Testing2 Timing3 and Liver Injury Test Profile4 Important Exclusionary Criteria Recurrent AIH AIH - auto-antibodies** (ANA, ASMA, ALKM) usually in high titers (>1:80); raised serum IgG > 6 months Hepatocellular - acute and chronic rejection, HBV, HCV infection, as determined by third generation ELISA assay and/or by serum PCR De novo AIH Other than AIH -Same as above > 6 months Hepatocellular - same as above Recurrent HBV or HCV HBV- or HCV-induced cirrhosis HBV or HCV infection using standard, third generation serologic criteria and/or positive molecular testing for HBV or HCV nucleic acids usually 6-8 weeks, but as early as 10 days. - usually hepatocellular; but may be cholestatic - acute and chronic rejection - AIH Recurrent PBC PBC - positive AMA, but little additional benefit because AMA remains elevated in the majority of patients after transplantation > one year - Cholestatic - biliary tract obstruction/strictures Recurrent PSC PSC NA - usually > 1 yr - Cholestatic HA thrombosis/stenosis, chronic (ductopenic) rejection, abnormal surgical anatomy, anastomotic strictures alone, non-anastomotic strictures occurring < 90 d after OLTx, and ABO incompatibility Acute Rejection NA (see text for risk factors) NA - any time - Usually hepatocellular; may be mixed if superimposed on chronic rejection - inadequate immunosuppression usually, but not always present (see text) Important exclusions: biliary tract obstruction/strictures, HBV, HCV, AIH Chronic Rejection NA (see text for risk factors) NA - any time, but usually < 1 year - Cholestatic; rarely hepatocellular in veno-occlusive variant (see text). - inadequate immunosuppression usually, but not always present (see text) Important exclusions: biliary tract obstruction/strictures, HBV, HCV, AIH Idiopathic post-transplant hepatitis Non-viral and non-autoimmune hepatitis Negative testing for HBV and HCV infection and autoantibodies > one year - Usually hepatocellular - acute and chronic rejection, all other causes of chronic hepatitis, and biliary tract obstruction/strictures reasonably excluded. All attempts should be made to determine a cause. 1 See Table 1 for compatible histopathologic findings. 2 Timing= usual timing of first onset; 3 ANA= anti-nuclear antibodies; ASMA = anti-smooth muscle antibodies; ALKM = anti-liver-kidney microsomal antibodies; 4 sustained elevation for more than one month, Hepatocellular = ALT and/or AST > ALP and/or GGTP; Cholestatic = ALP and/or GGTP > AST and/or ALT; Abbreviations: AIH: autoimmune hepatitis; PBC: primary biliary cirrhosis; PSC: primary sclerosing cholangitis References Banff Working Group. Liver biopsy interpretation for causes of late liver allograft dysfunction. Hepatology 2006 (in press).