Hepatitis A Antibodies in Liver Transplant Recipients: Evidence for Loss of Immunity Posttransplantation

Transcription

1 Hepatitis A Antibodies in Liver Transplant Recipients: Evidence for Loss of Immunity Posttransplantation Mehmet Arslan, Russell H. Wiesner, John J. Poterucha, John B. Gross, Jr, and Nizar N. Zein Liver transplant recipients frequently have chronic liver diseases and should be considered for vaccination against hepatitis A virus (HAV). However, persistence of protective antibodies after orthotopic liver transplantation (OLT) has not been shown in this population, which may have implications for future vaccine recommendations. We evaluated the prevalence and epidemiological significance of immunoglobulin G (IgG) antibody to HAV (anti-hav) in a nonvaccinated population before OLT (immunity from previous exposure) and determined the persistence of IgG anti-hav at 1 and 2 years after OLT. One hundred consecutive patients were identified who underwent OLT and had at least 2 years of follow-up post-olt. They were not vaccinated against HAV infection at any time. Clinical data were summarized from medical records, and stored sera were tested for IgG anti-hav before OLT and at 1 and 2 years after OLT by a commercially available enzyme immunoassay. Of 100 patients, 24 had IgG anti-hav before OLT. No epidemiological differences were noted between those with or without detectable IgG anti-hav before OLT. Among patients with detectable IgG anti-hav before OLT, 4 of 22 patients (18%) and 7 of 24 patients (29%) became negative for IgG anti-hav at 1 and 2 years post-olt, respectively. None of the patients with undetectable IgG anti-hav before OLT became positive at any time. Most of our patients with end-stage liver disease had no serological evidence for immunity against HAV. A significant proportion of patients with detectable protective antibodies before OLT lost their antibodies at 2 years after OLT. Copyright 2000 by the American Association for the Study of Liver Diseases H epatitis A virus (HAV) has a worldwide distribution. More than 1.4 million infections are reported annually. 1 In the United States, approximately 134,000 infections occur each year, of which 80,000 result in clinical disease, and 80 to 100 deaths caused by fulminant hepatitis are reported. 1 Mortality is seen mainly in the older population and in subjects with chronic liver disease (CLD). 2,3 The Third National Health and Nutrition Examination Survey, conducted in the United States between 1988 and 1991, showed a seroprevalence of HAV antibodies of approximately 33%. 1 However, more recent data suggested a declining rate of infection and gradual change in the epidemiological characteristics of HAV. 4 Although the declining rate of infection is reassuring, it suggests an increase in susceptible individuals in this country. Although seroprevalence of HAV antibodies has been evaluated in several specific populations, no data exist for patients with end-stage liver disease awaiting orthotopic liver transplantation (OLT). The initial antibody response to HAV infection consists of immunoglobulin M (IgM), IgA, and IgG antibodies. However, IgG antibody is the major class of antibodies found during convalescence and is the primary defense against reinfection. 5 IgG antibody to HAV (anti-hav) is critical and clearly sufficient by itself to prevent reinfection, and it frequently persists, providing a lifelong immunity against reinfection with HAV. 5,6 Persistence of these antibodies, however, has not been shown in the setting of immune deficiency, such as in organ transplant recipients. Human pooled immune serum globulin was introduced many years ago and has been used for passive immunoprophylaxis against HAV in susceptible individuals. The level of IgG anti-hav detected after immune serum globulin infusion is typically much less than levels detected in the serum of previously infected individuals, and protection is short lived (3 to 5 months). 6 More recently, inactivated hepatitis A vaccines became available and proved to be safe and effective. 7,8 These vaccines provide a serum level of protective IgG anti-hav that is much less than levels seen after natural infection. 9 The longevity of protection after vaccination is not completely known, but protection appears to last for several years in immunocompetent hosts The increased morbidity and mortality of HAV infection led the Advisory Committee on Immunization Practices in 1996 to recommend immunization of From the Division of Gastroenterology and Hepatology and Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, MN. Presented in part at the 49th Annual Meeting of the American Association for the Study of Liver Diseases, Chicago, IL, November 6-10, Supported in part by a grant from the American Liver Foundation (N.N.Z.). Address reprint requests to Nizar N. Zein, MD, Division of Gastroenterology and Hepatology and Internal Medicine, Mayo Clinic, 200 First St SW, Rochester, MN Copyright 2000 by the American Association for the Study of Liver Diseases /00/ $3.00/0 Liver Transplantation, Vol 6, No 2 (March), 2000: pp

2 192 Arslan et al all patients with CLD (without evidence for previous exposure) against HAV infection. 1 Liver transplant recipients are generally elderly and frequently have CLD related to rejection or recurrence of pre-olt disease or caused by such post-olt complications as vascular insufficiency or biliary strictures. These patients may be at risk for liver failure associated with acute HAV infection and may therefore benefit from immunization against HAV. Liver transplant recipients represent a special group of patients with CLD. They are heavily immunosuppressed, which may alter the kinetics and persistence of protective antibodies against HAV after OLT, whether these antibodies were from a natural infection or after vaccination. Understanding the kinetics of HAV antibodies after OLT may have implications for the selection of appropriate candidates for vaccination against HAV and for optimal timing of booster immunization. The objectives of this study are to define the prevalence and epidemiological characteristics of IgG anti-hav in a cohort of nonvaccinated individuals with end-stage liver disease undergoing OLT to identify subsets of patients likely to require vaccination. We determined the rate of decline in the detectability of these antibodies over 2 years after OLT, which may have implications for future vaccine recommendations in this specific population of patients with CLD. Materials and Methods Selection of Patients One hundred consecutive liver transplant recipients were identified who underwent OLT at the Mayo Clinic between 1990 and 1994 and had at least 2 years of follow-up post-olt. Clinical data for these patients were obtained from medical records and included age, sex, ethnic background, potential risk factors for HAV acquisition, and underlying liver disease. Patients were excluded if they received immunization against HAV at any time before or after OLT; if they had more than one underlying liver disease at transplantation, such as primary biliary cirrhosis and hepatitis C simultaneously; and if pretransplantation HAV serological status was not known and stored sera were not available for testing. Serological Assay for IgG Anti-HAV Detection Stored sera were tested for antibodies against HAV before OLT (within 1 year before transplantation) and at 1 and 2 years after OLT. Sera were stored at 80 C. Antibody titers in stored sera at this temperature are stable over a long time. 13 IgG anti-hav was detected by means of a commercially available enzyme immunoassay (IMx HAVAB; Abbott Laboratories, Abbott Park, IL), following the manufacturer s instructions. The reproducibility, sensitivity, and specificity of this assay have been validated, and the results have been used to assess immune status or for epidemiological studies. 8,14-22 Specificity and sensitivity of this assay were reported to be 100% and 99.8% to 100%, respectively. 23 Patients who had detectable IgG anti-hav based on this assay have been regarded as immune against reinfection. However, the absence of HAV antibody by this assay may indicate the lack of immunity or antibody titers less than detection limits. 24,25 Statistical Analyses The SAS statistical analysis package (SAS Institute, Cary, NC) was used for all calculations. Fisher s exact test was used for testing independence of categorical variables. Wilcoxon s rank-sum test was used to compare variables for those with and without detectable antibodies to HAV. The McNemar chi-squared test was used to compare the rate of positivity of HAV antibodies before and after transplantation because samples at each time represented the same patients. Results Epidemiological features of these patients are listed in Table 1. Of 100 patients, 52 were women. Mean age of the entire group was years (range, 15 to 71 years at transplantation). Cholestatic liver disease (primary biliary cirrhosis or primary sclerosing cholangitis) was the most common underlying cause of liver failure requiring transplantation in this group. Of 100 pre-olt samples, 24 were positive for IgG anti-hav, suggesting immunity from previous expo- Table 1. Epidemiological Features of Patients With and Without Detectable Antibodies Against Hepatitis A Virus Feature IgG Anti-HAV ( )(n 24) IgG Anti-HAV ( ) (n 76) Total (n 100) Age (y) Women 11 (46) 41 (54) 52 (52) White 23 (96) 74 (97) 97 (97) History of BT 12 (50) 40 (53) 52 (52) Child s score PBC or PSC 9 (37.5) 42 (55) 51 (51) Alcoholic liver disease 3 (12.5) 7 (9.2) 10 (10) Viral hepatitis B or C 5 (21) 8 (11) 13 (13) Child s class C cirrhosis 5 (21) 28 (37) 33 (33) NOTE. Values expressed as mean SE or number (percent). Abbreviations: ( ), positive; ( ), negative; BT, blood transfusion; PBC, primary biliary cirrhosis; PSC, primary sclerosing cholangitis.

3 Hepatitis A and Liver Transplantation 193 sure. There were no significant epidemiological differences between samples positive and negative for IgG anti-hav, including mean age, sex distribution, ethnic background, history of blood transfusion, severity of liver disease, and underlying liver disease (Table 1). Interestingly, the prevalence of anti-hav was not different in patients aged older than 40 years at the time of OLT (77 patients) than in patients aged younger than 40 years (23 patients; P.61). Seroprevalence of IgG anti-hav was not significantly dependent on the stage of liver cirrhosis. The prevalence of these antibodies in patients with Child s class C cirrhosis (33 patients) was not different than that in patients with Child s class A or B cirrhosis (67 patients; P.146). Only 10 patients were believed to have alcoholic liver disease, and they had a similar prevalence of IgG anti-hav compared with patients without alcoholic liver disease (P.4). Fifty-nine of our patients lived in a midwestern state of the United States (Iowa, Minnesota, North and South Dakota, Wisconsin, and Illinois), and the rest were from other parts of the United States. We did not observe a statistically significant difference in the seroprevalence of HAV antibodies based on the geographic origin of these patients (P.9). Stored sera were available for 96 patients at 1 year and 100 patients at 2 years. Of 22 patients with detectable pre-olt IgG anti-hav who had sera samples at 1 year post-olt (2 patients had no sera available at this time), 18 patients (82%) remained positive and 4 patients (18%) lost their antibodies according to this assay (P.001; Fig. 1). Similarly, of 24 patients with detectable IgG anti-hav before transplantation, only 17 patients (71%) remained positive at 2 years after transplantation and 7 patients Figure 1. Anti-hepatitis A virus antibody positivity before and after liver transplantation. P 0.001, McNemar chi-squared test (between pre-olt and post-olt year 2). (29%) became negative, suggesting either loss of immunity or significant decrease in antibody titers (P.001; Fig. 1). We then compared the immunosuppressive regimen at 2 years of those who lost detectable IgG anti-hav (7 patients) and those who continued to have detectable antibodies (17 patients). The mean prednisone dose at 2 years for those who lost detectable antibodies was mg compared with mg for those who maintained detectable antibodies (P.3). The mean serum cyclosporine level in those who lost detectable antibodies was ng/ml compared with ng/ml in those who maintained detectable antibodies (P 0.1). The mean azathioprine dose for those who lost detectable antibodies was mg compared with mg for those who maintained detectable antibodies (P.3). Finally, none of the 76 patients without detectable IgG anti-hav pre-olt became positive for these antibodies at 1 or at 2 years post-olt. Discussion The prognosis of HAV infection for patients with underlying chronic hepatitis is less favorable than that for otherwise healthy individuals. In the Shanghai outbreak in 1988, the fatality rate of HAV disease in patients with hepatitis B virus infection was estimated to be 5.6-fold greater than the fatality rate of those without chronic hepatitis B virus infection. 26,27 In the United States, preexisting liver disease was shown to contribute to the mortality for acute hepatitis A. Between 1983 and 1988, 0.3% of patients with acute HAV infection who were reported to the Centers for Disease Control died. 27 However, the case fatality rate of acute hepatitis A in the non hepatitis B virus carriers was 58-fold less than in the hepatitis B virus carriers. 27 More recently, Vento et al 28 reported that 7 of 17 patients (41%) with chronic hepatitis C virus infection had fulminant hepatitis after a superinfection with HAV. It was suggested that vaccination against HAV should be recommended for all patients with chronic hepatitis C virus. Although it has not been reported to date that HAV infection is associated with fulminant hepatic failure or death in liver transplant recipients, these patients frequently have CLD. It is therefore reasonable to consider vaccination against HAV in this population. However, it is important to understand the kinetics of HAV antibodies in the setting of immuno-

4 194 Arslan et al suppression because it may have implications for vaccine strategy. The prevalence of HAV infection is related to the quality of the water supply, level of sanitation, age, sex, and ethnic background. In the United States, evidence for HAV exposure in males is 20% greater than that in females, and it increases with age. 29 The prevalence of HAV antibody is 10% among children aged younger than 10 years and 75% in people aged older than 70 years. Anti-HAV prevalence is greater among Mexican Americans (67%) than blacks (37%) and whites (29%). 30 The seroprevalence of HAV antibodies in our patients (24%) was similar to that in the white population of the United States. This was expected because 97% of our patients were white. However, the seroprevalence of HAV antibodies was almost identical in patients aged younger or older than 40 years. This may be owing to the small number of patients in each group or it may reflect selection bias. All these patients were aged older than 18 years and younger than 68 years at the time of OLT, which may have contributed to the lack of an age-dependent difference in HAV antibody prevalence in our patients. IgG anti-hav is protective against reinfection with HAV, and it remains detectable for several decades after acute infection. 31 Although certain epidemiological features, such as age and sex, may predict the likelihood of having protective antibodies against HAV, these features were not useful in our patients. We found no specific features to identify those with evidence of antibodies compared with those without. Screening all patients with liver disease for anti-hav antibodies using serological assays is therefore the only practical means to identify vaccine candidates. Persistence of anti-hav antibodies in liver transplant recipients is not known. IgG anti-hav is the major class of antibody found during convalescence, and it appears to be the primary defense against reinfection. 6 IgG anti-hav remains detectable for several decades after acute HAV infection and reflects resistance to reinfection. 32 In this study, we found that IgG anti-hav became undetectable within 2 years in a significant number of patients who had detectable antibodies before OLT. This rate of loss of antibodies is greater than would be expected in immunocompetent patients after acute HAV infection and may suggest loss of immunity and the need for prophylaxis. Furthermore, the titers of vaccine-induced antibody, although protective, are usually much less than those present after natural infection and would be more likely to decline at a faster rate in liver transplant recipients. More frequent booster immunizations may be necessary to maintain protection against HAV in liver transplant recipients. Standard commercially available immunoassays for the detection of IgG anti-hav, including the assay used in this study, have detection thresholds of approximately 40 to 100 miu/ml. 15,33 The minimum level of neutralizing antibody that protects against infection and disease is not known. 6 However, it has been suggested that a minimal protective level is approximately 20 miu/ml. It is possible that our patients who lost detectable antibodies are still protected against reinfection and that they have antibody titers less than the detection limits for these assays. Although serological assays with greater sensitivity for the detection of low antibody titers have been used, these assays are not well validated, are not used in clinical practice, and remain experimental. Finally, it is also possible that some of the individuals who lost detectable IgG anti-hav after OLT maintained immune memory cells. These memory cells may rapidly increase antibody titers after viral antigen reexposure, providing protection regardless of the detectability of IgG anti-hav before reexposure. 34 This remains a hypothesis and may need to be investigated in future studies related to HAV infection after OLT. In summary, most patients in our study with end-stage liver disease had no serological evidence for immunity to HAV. A significant proportion of those with detectable immunity pre-olt lost antibodies at 2 years post-olt. References 1. Centers for Disease Control and Prevention. Prevention of hepatitis A through active or passive immunization: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 1996;45: Lednar WM, Lemon SM, Kirkpatrick JW, Redfield RR, Fields ML, Kelley PW. Frequency of illness associated with epidemic hepatitis A virus infections in adults. Am J Epidemiol 1985;122: Romero R, Lavine JE. Viral hepatitis in children. 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