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Vaccination against tick-borne encephalitis under therapeutic immunosuppression. Reduced efficacy in heart transplant recipients
Vaccine 17 (1999) 867±874
Vaccination against tick-borne encephalitis under therapeutic immunosuppression. Reduced ecacy in heart transplant recipients Thomas J. Dengler a, *, Rainer Zimmermann a, Joachim Meyer a, Falk-U. Sack b, Otto Girgsdies c, Wolfgang E. KuÈbler a a
Department of Cardiology, University of Heidelberg, Bergheimerstr. 58, 69115 Heidelberg, Germany Department of Cardiac Surgery, University of Heidelberg, Bergheimerstr. 58, 69115 Heidelberg, Germany c Chiron Behring, Clinical Research, 35006 Marburg, Germany
b
Received 12 May 1998; received in revised form 3 July 1998; accepted 7 July 1998
Abstract Patients after organ transplantation are at an increased risk of microbial infections and might bene®t from active vaccination. Due to therapeutic immunosuppression the ecacy of immunizations is, however, reduced and dicult to predict. Ecacy of vaccination against tick-borne encephalitis (TBE) using an abbreviated immunization schedule was compared in 31 heart transplant recipients (age: 54.5 2 11.5 years, mean time after transplantation: 53.5 2 23.7 months) under cyclosporine-based immunosuppression and 29 controls. TBE vaccination was well tolerated by the transplant recipients; spectrum and frequency of adverse events were similar to controls. In the transplant patients, seroconversion rate (35% versus 100%; p < 0.001) and the geometric mean of post-vaccinal antibody titres (0.98 (SF: 2.3) U/ml versus 5.46 (2.2) U/ml; p < 0.001) were markedly reduced in comparison to the control group. No clinical or demographic predictors of vaccination success could be established in the transplant patients. Due to the limited ecacy, TBE vaccination cannot be recommended as a routine procedure in heart transplant recipients at risk of TBE virus infection. TBE vaccination may be performed safely in selected cases, but repeated titre controls to con®rm vaccination success would be required. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Tick-borne encephalitis; Vaccination; Heart transplantation; Immunosuppression
1. Introduction Patients after the transplantation of solid organs are at an increased risk of bacterial, viral and protozoal infections due to the required therapeutic immunosuppresion. Protective vaccination might prevent infection-related morbidity and death after organ transplantation, but immunizations in transplant recipients have been hampered by reduced and unpredictable ecacy under therapeutic immunosuppression [1± 4]. Few controlled studies on the ecacy and safety of protective vaccinations have been performed in solid * Corresponding author. Present address: Boyer Center for Molecular Medicine, Yale School of Medicine, New Haven, CT 06510, USA. Tel.: +1-203-737-2294; fax: +1-203-737-2293. 0264-410X/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 9 8 ) 0 0 2 7 2 - 2
organ transplant recipients and currently vaccinations are not routinely performed in these patients. Tick-borne encephalitis is one of the most frequent arthropod-transmitted infections in Central and Eastern European countries [5]. In Germany the causative RNA-¯avivirus is endemic in the southern and central parts of the country, in some areas infesting up to 25% of all ticks [6]. Human infection following a tick bite is characterized by two clinical stages: initial symptoms include lethargy, malaise and ¯u-like symptoms, aecting approximately 10±20% of infected subjects. After 10 days meningitis, encephalitis and myelitis develop in 1±2% of patients that were originally infected [7]. In 1997, approximately 350 cases of tick-borne encephalitis were registered in Germany. No data on the clinical course of TBE in immunosup-
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pressed adults are available, but the severity of symptoms or the proportion of patients with manifest disease might be increased in patients with endogenous or therapeutic immunosuppression including recipients of solid organ grafts. For several years inactivated TBE virus particle vaccines have been available [8±11], oering excellent protection even when employing a short immunization schedule over 21 days [12]. To date, the ecacy of TBE vaccination in transplant recipients has not been studied. In the present study the serological ecacy of TBE vaccination in heart transplant recipients under cyclosporine-based immunosuppression was compared to control subjects. In addition, potential predictors of vaccination success in the transplant patients were investigated. As most ecacy data on TBE vaccines have so far been generated in healthy, young adults, the control group included also subjects above 50 years of age and patients with mild or moderate concomitant illnesses. The results of this study should provide useful data for counseling recipients of solid organ grafts concerning TBE vaccination. 2. Materials and methods 2.1. Vaccine and antigen contents The TBE vaccine used in this study (Encepur1, Chiron-Behring, Marburg, Germany) contains formalin-inactivated K23 virus adsobed to Al(OH)3. After propagation in chick embryo ®broblasts, virus is puri-
®ed and stabilized by polygeline. One approved dose of 0.5 ml contains 1.5 mg of antigen [12] including a maximum of 0.01 mg formaldehyde and 5 mg polygeline and traces of neomycin, gentamycin and chlortetracycline. 2.2. Heart transplant recipients 31 heart transplant recipients were studied, clinical data are shown in Table 1. To ensure stable clinical conditions and levels of immunosuppression, only patients beyond 12 months post-operatively were included in the study. Exclusion criteria were signs of graft failure, renal failure (serum creatinine concentration >4 mg/dl), acute infections or fever of unknown origin, ongoing acute graft rejection episodes, malignancy, antibody de®ciency states, previous vaccination against tick-borne encephalitis and hypersensitivity against chicken proteins. After cytolytic induction therapy with anti-thymocyte globulin for 5 days, patients received standard immunosuppression with cyclosporine A (1 patient received FK506), optional corticosteroids and azathioprine, azathioprine being withheld with blood leucocyte counts below 4000/mm3 (4/nl). Standard outpatient follow-up continued during the study period, including routine endomyocardial biopsies. Signi®cant acute rejection episodes (rgrade 3 according to the classi®cation [13] of the International Society for Heart and Lung Transplantation (ISHLT)) were treated with increased immunosuppression (steroid bolus: 1 g of prednisolone for 3 days, cytolytic agents as required). As a timeindependent measure of rejection frequency in individ-
Table 1 Demographics and clinical characteristics of heart transplant patients (n = 31) at study entry Male/Female Age (mean2S.D. (range); (years)) > 50 years > 60 years Time after transplantation (mean2S.D. (range); (months)) Rejection indexa (mean2 S.D., (range)) Pre-operative diagnoses (n, (%)) Dilated cardiomyopaty Ischaemic heart disease Valvular heart disease Diabetes (n (%)) None Dietary management Insulin therapy Daily cyclosporine dose (mean2S.D. (range); (mg)) Cyclosporine blood level (mean2S.D. (range); (mg/l)) Daily steroid dose (mean2S.D. (range); (mg)) Azathioprine medication n (%) Daily dose (mean2S.D. (range); (mg)) a
25/6 54.5 211.5 (26±67) 22/31 (70.9%) 10/31 (32.2%) 53.5 223.7 (14.7±103.8) 0.87 20.29 (0.24±1.6) 23/31 (74.2%) 6/31 (19.6%) 2/31 (6.2%) 24/31 (77.4%) 4/31 (12.9%) 3/31 (9.7%) 226.7257.6 (150±400) 180.7227.9 (98±228) 3.2 22.4 (0±7.5) 22/31 (70.9%) 77.3 236.9 (25±150)
Measure of incidence of acute rejection episodes, independent of post-operative time and frequency of biopsy (cf. Section 2).
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ual patients, a rejection index was calculated: each result of endomyocardial biopsy was graded with a point system (ISHLT grades 0±4 receiving 0, 1, 1.5, 3 and 4 points, respectively) and normalized to the number of post-operative biopsies. Written, informed consent for the study was obtained from all participants and the study was approved by the local ethics committee. Routine laboratory screening, cyclosporine whole blood levels (by monoclonal ¯uorescence polarisation immunoassay) and speci®c immunoglobulin concentrations was measured at study entry and completion. Patients received a study diary to record adverse events. 2.3. Control subjects The control group comprised 29 subjects (11 male, 18 female) with a mean age of 47.7 2 14.4 years (range: 22±67; >50 years: n = 16, >60 years: n = 6). Several subjects in the control group suered from concomitant illnesses. 7 subjects had diseases of mild severity: soft tissue rheumatism, lower back pain, peripheral artery disease, arterial hypertension (n = 2), hyperthyroidism and Gilbert's disease. 5 patients had illnesses of moderate severity: severe psoriasis with diabetes mellitus, symptomatic ischaemic heart disease (n = 2), epilepsy and chronic hepatitis (non-immunological). 11 subjects took regular medication (including antihypertensives, b-blockers, analgesics), none of the control subjects received any immunosuppressive agents (e.g. steroids, methotrexate, cyclosporine). 2.4. Schedule of immunization Study patients were immunized according to the abbreviated TBE vaccination schedule [12] receiving 3 injections of one standard dose of 1.5 mg antigen on days 0, 7 and 21. Injections were given intramuscularly into the deltoid muscle. Blood samples for antibody assays were drawn before the ®rst immunization on day 0 and on day 42 2 5. 2.5. Antibody assay FSME-speci®c antibody titres in human serum were assayed in a newly developed enzyme linked immunosorbent assay (PEV-ELISA), measuring antibody levels on a continuous scale in U/ml. Microtiter plates were coated with 2 mg/ml inactivated TBE virus in 0.05 M sodium phosphate buer (pH 7.5) for 24 h at room temperature and then washed three times with 0.05 M sodium citrate buer (pH 7.4). Sera were tested in triplicates (100 ml/well). Samples were incubated for 2 h at room temperature. After washing, bound antibodies were detected with rabbit-anti-human antiserum conjugated to horseradish peroxidase (2.5 mg/ml, 100 ml/
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well, 1 h at room temperature). Afterwards, TMB substrate (Behring Diagnostics, Marburg, Germany) was added for 30 min. The reaction was stopped by 0.25 M H2SO4 and measured at 450 nm in an ELISA reader (BEP III, Behring Diagnostics). Cross calculation with data obtained by the previous ELISA according to Heinz (QKV-ELISA) [14] expressed in reciproke titres was performed according to the following regression equation for log 2-transformed data: PEV-ELISA (U/ml) = 0.8645*QKVELISA (1/titre) ÿ 6.2580. Seroconversion in terms of this new PEV-ELISA was de®ned as antibody titres r1.27 U/ml (equivalent to a titre r1:200 in the previous QKV-ELISA). At this antibody level, all sera had previously been found to be positive in the TBE virus neutralization test [14]. 2.6. Ecacy variables Ecacy variable was the TBE antibody titre measured by PEV-ELISA. The primary ecacy criterion was the seroconversion rate (see Section 2.5) on day 42 2 5 after the ®rst vaccination. Subjects with signi®cant pre-vaccinal titres (1 patient of the control group) were excluded from the ecacy evaluation and were analysed separately. Equivalence of titres was chosen as the secondary ecacy criterion: titres were regarded as equivalent if the geometric mean titre in the transplant recipients was at the most one titre step (=factor 1/2) below the mean titre in the controls. 2.7. Statistics Vaccinated subjects were characterized by means of demographic data and information from their medical histories. Adherence to inclusion/exclusion criteria was also checked. Vaccination results were primarily evaluated by intention-to-treat analysis. Statistical analysis of demographic and serological data and associations between vaccination data and clinical parameters was performed using Mann±Whitney±Wilcoxon U-test and analysis of variance as appropriate. Statistical signi®cance was assumed for p < 0.05, data analysis was performed using the SAS statistical software package. 3. Results 3.1. Patient characteristics The control group comprised signi®cantly more women (62.1%) than the transplant group (20.7%). The transplant patients were older than the control subjects with a mean age of 54.5 211.5 years (range: 26±67) versus 47.7 214.4 years (range: 22±67). This dierence, however, reached only borderline statistical
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signi®cance ( p = 0.05). The proportion of subjects older than 50 or 60 years was not dierent between the groups (Table 1). Mean body weight in the transplant group was higher than in the controls (82.92 20.1 versus 73.5 213.7 kg; p < 0.05), however no in¯uence of weight on TBE vaccination has previously been demonstrable (unpublished observation).
oped; in the control patient, seroconversion was demonstrated as scheduled at 7 weeks after vaccination. Formally, seroconversion following clinically silent infection in the absence of vaccination response cannot be excluded, but appears very unlikely in this setting.
3.2. Adverse events
3.3. Serious adverse events
TBE vaccination was well tolerated by the heart transplant recipients and control patients. The most frequently noted side eects were local pain and swelling for 24±48 h at the injection site. General reactions like fever (below 398C), arthralgias, headache and tiredness occurred with much lower frequency. Similar to previous studies [15], the frequency of adverse events was higher after the ®rst vaccination than after the second and third injection. A detailed analysis of adverse events is shown in Table 2; overall the spectrum and frequency of side eects were similar to ®ndings in earlier studies [12, 15]. There was no signi®cant dierence in the quality and frequency of adverse events between transplant patients and the control group. Moreover, no infectious complications or increased incidence of rejection episodes were noted in the transplant recipients. One transplant recipient developed a gastric ulcer during the period of the study, which was considered to be unrelated to vaccination. One transplant patient and one control patient had tick bites after the second vaccination: in both cases, no clinical disease devel-
One serious adverse event occurred in a 56 year old female in the control group. She had a long history of psoriasis, severe osteoarthritis in both hip joints and diet-controlled diabetes mellitus. After the third vaccination she developed nausea, asthenia, diarrhea and progressive swelling, pain with paresthesias and weakness in both hands, most markedly in the ®nger joints. After extensive neurological, rheumatological and radiological investigation, polyneuritis and infection could be excluded and a diagnosis of an exacerbation of pre-existing psoriatic arthropathy was made. A causal relation with TBE vaccination was considered unlikely, but could not formally be ruled out. A course of tapered corticosteroids with additional non-steroidal analgesics as required was started and after 3 weeks symptoms had subsided without residual limitations. The incident was reported accordingly and classi®ed as serious adverse events, as an initial hospitalization phase was required. As the adverse event occurred after the third vaccination, the patient remained in the study and antibody titres at 42 25 days were analysed according to protocol.
Table 2 Adverse events TBE vaccination in heart transplant recipients and controls, speci®ed after each of 3 injections. Results are presented as patient number (n) and percentage of group (in parentheses) Patient group (vaccination) control (n = 29)
heart transplant recipients (n = 31)
1st
2nd
3rd
1st
2nd
3rd
Local reactions Pain (injection site) Pain (limb) Swelling/hematoma
9 (31%) 3 (10.3%) 3 (10.3%)
5 (17.2%) 2 (6.9%) 1 (3.4%)
1 (3.4%) 0 1 (3.4%)
4 (12.9%) 3 (9.6%) 2 (6.4%)
4 (12.9%) 1 (3.2%) 0
3 (9.6%) 1 (3.2%) 1 (3.2%)
General reactions Fever 38±398C Fever >398C Asthenia/tiredness Arthralgia Headache Nausea/vomiting Diarrhoea Others
1 0 0 0 3 2 1 0
0 0 1 0 3 2 1 2
1 (3.4%) 0 0 1 (3.4%) 0 0 1 (3.4%) 0
1 0 3 2 1 0 1 0
0 0 2 1 1 0 0 1
0 0 2 (6.4%) 0 0 0 0 0
(3.4%)
(10.3%) (6.9%) (3.4%)
(3.4%) (10.3%) (6.9%) (3.2%) (6.9%)
(3.2%) (9.6%) (6.4%) (3.2%) (3.2%)
(6.4%) (3.2%) (3.2%) (3.2%)
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Table 3 Results of TBE vaccination in controls and heart transplant recipients. TBE-speci®c antibody titres were determined by ELISA, seroconversion was de®ned as post-vaccinal increase of antibody titres above 1.27 U/ml. Results are presented as antibody concentration in U/ml and equivalent titre levelsa
Patient number (n) Pre-vaccinal antibody titres, geometric mean (SFc) Pre-vaccinal titre levelsa, geometric mean Post-vaccinal antibody titres, geometric mean (SFc) Post-vaccinal titre levelsa, geometric mean Seroconversion (n, (%))
Controls
Heart transplant recipients
28b 0.29 (1.8) 1:30 5.46 (2.3) 1:1080 28/28 (100%)
31 0.28 (1.9) 1:30 0.98 (2.2)d 1:150d 11/31 (35.5%)d
a Equivalent titre levels were cross-calculated from ELISA results with a regression equation for log 2-transformed data (cf. Section 2). bOne pre-immune subject (pre-vaccinal titre 1.45 U/ml) was excluded from analysis of ecacy. c SF = scatter factor. dp < 0.001 for dierence to controls.
3.4. Ecacy of TBE vaccination The results of the study were primarily analysed in an intention-to-treat fashion: mean TBE antibody titres before vaccination were not dierent between transplant recipients and controls (geometric mean: 0.29 U/ml (Scatter factor (SF): 1.8) versus 0.28 U/ml (1.9), p = n.s). One pre-immune subject in the control group (pre-vaccinal titre: 1.45 U/ml) was excluded from ecacy analysis and was evaluated separately. The seroconversion rate in the transplant patients (35.4%) was signi®cantly reduced compared to the control subjects (100%, p < 0.001; Table 3), using 1.27 U/ml as the threshold for seroconversion (equivalent to a titre of 1:200). The geometric means of the postvaccinal antibody titres determined by ELISA were also signi®cantly lower in the transplant recipients (0.98 (SF = 2.3) U/ml versus 5.46 (SF = 2.2) U/ml, p < 0.001; Table 3). The individual pre- and post-vaccinal titres of all participants are presented in Fig. 1. In addition, it could be shown that the criterion for equivalent ecacy of the vaccine was not ful®lled in the transplant patients: the geometric mean of postvaccinal titres in transplant recipients was more than 1 titre step (factor = 1/2) below the mean titre in controls (1:150 versus 1:1080 for cross-calculated values, p < 0.001; Table 3). In both groups seroconversion rate and antibody titres were not associated with sex, age or weight; no signi®cant changes in routine laboratory values were seen after vaccination. In the transplant group, predictors of vaccination success were sought by correlation of seroconversion status or post-vaccinal titres with demographic, clinical or laboratory parameters. There was, however, no signi®cant correlation of the responder status with time after transplantation, pre-operative diagnosis, presence of diabetes mellitus or other concomitant diseases, routine laboratory parameters, cyclosporine dosage and blood levels, (cumulative and current) azathioprine and steroid medication, immunoglobulin concen-
trations, rejection index and number of steroid bolus treatments. In addition, no association with other laboratory values (electrolytes, renal and liver function tests, serum lipids, full blood count) could be established. In the transplant recipients there was a statistical trend for higher pre-vaccinal titres in subjects with successful seroconversion, but previous exposure to TBE virus and a possible `booster' eect on vaccination was unlikely based on patient history and geographical location.
Fig. 1. Semilogarithmic representation of individual pre- and postvaccinal TBE antibody titres including limit of seroconversion (1.27 U/ml). HTX: heart transplant recipients; pre: titres before vaccination; post: titres after vaccination. Short thick lines: geometric means of FSME titres.
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In the control subjects the presence of concomitant disease or medication did not in¯uence seroconversion or post-vaccinal antibody titres. The patient experiencing a serious adverse event and receiving a course of steroids also demonstrated seroconversion. The only pre-immune subject (excluded from the general analysis of ecacy above) displayed a signi®cant rise in post-vaccinal antibody titre, not exceeding the mean titre of the control group. 4. Discussion Patients after transplantation of solid organs are at an increased risk of microbial infections due to therapeutic immunosuppression. Eective immunization would, therefore, be a helpful adjunct in post-operative care of these patients, but ecacy of active immunization is doubtful and dicult to predict due to immunosuppression [16, 17]. TBE represents the most important arthropod-transmitted disease in Central Europe, causing neurologic morbidity and even mortality in approximately 1% of infected subjects [6]. Protective vaccination is available [11, 18], but both the eects of infection and vaccination in immunosuppressed patients are largely unknown. To date, there have only been two episodic reports on reduced ecacy of TBE immunization in 4 HIV infected subjects [19] and 5 women with breast cancer receiving chemotherapy [20]. 4.1. Ecacy In the present study, TBE vaccination using the abbreviated immunization schedule [12] was well tolerated, but signi®cantly less eective serologically in immunosuppressed heart transplant recipients than in control subjects. Predictive parameters for vaccination success in this patient group could not be identi®ed, in particular, time after transplantation, dose or blood levels of immunosuppressive drugs and concomitant diseases were not associated with the ecacy of vaccination. The reduced serological ecacy of TBE vaccination in heart transplant recipients is mainly accounted for by therapeutic immunosuppression, which not only suppresses allograft rejection, but also immune reactions against all other exogenous antigens. Patients received cyclosporine-based immunosuppression (1 patient: FK 506) including also azathioprine and corticosteroids in most cases. After heart transplantation, higher levels of immunosuppression are required than following liver or kidney transplantation, but the level of immunosuppression is reduced over time. Only patients more than 1 year after transplantation were included in the present study but, when extrapolating from other studies [21], the ecacy
of vaccination would probably have been even further reduced in patients earlier after transplantation. The individual level of immunosuppression (as opposed to immunosuppression as such) was, however, not associated with vaccination success in the transplant patients. Considering the rather narrow range in the parameters of immunosuppression, it may be assumed that other factors apart from these rather crude indicators of immunosuppression in¯uence the immune response to vaccination in these patients. The slightly higher age of the transplant patients is unlikely to account for the dierence in vaccination ecacy, as no in¯uence of age between 14±59 years on the seroconversion rate could be demonstrated here or in previous studies [15]. Higher weight and dierent sex ratio in the transplant group also does not in¯uence the ecacy of vaccination with the standard 1.5 mg dose (unpublished observation). The reduced serological ecacy of TBE vaccination con®rms other studies of protein-based vaccines in transplant recipients: the immune response to measles vaccine was drastically reduced in children after liver transplantation [22]. In adults after heart, liver or renal transplantation hepatitis B vaccination has been disappointingly unsuccessful [1±3] and has been abandoned clinically. In several studies, the immune response to in¯uenza vaccination was reduced in recipients of solid organ transplants, though not completely abolished [4, 23]. Interestingly, the immune response against T-cell-independent polysaccharide pneumococcal vaccine (Pneumovax-23) is fully preserved in heart and liver transplant patients receiving cyclosporine-based immunosuppression [24]. The high ecacy of TBE vaccination in the control subjects corresponds to previous data [12, 15]. The control group of the present study is, however, noteworthy for the high age (16 subjects >50 years) and the presence of mild and moderate concomitant illnesses. Despite the small size of the study, the serological ecacy of TBE vaccination in these patients seems to indicate that successful immunization can also be achieved in people above 60 years and with relevant concomitant disease. 4.2. Tolerance TBE vaccination was well tolerated and safe in the transplant recipients. The spectrum and frequency of adverse events corresponds to earlier reports [15, 25] and was not signi®cantly dierent from the control subjects. Similar to other immunizations in transplant patients [26], infection or undue stimulation of the immune system resulting in more frequent acute rejection episodes after vaccination did not occur. In the control group, TBE vaccination was generally well tolerated, also by those patients with mild or
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moderate concomitant disease, including one patient with epilepsy. One serious adverse event occurred in a 56 year old woman with pre-existing psoriasis, who developed an exacerbation of pre-existing psoriatic arthritis in the ®nger joints, requiring hospitalization and treatment with corticosteroids. A causal relation with TBE vaccination appears unlikely based on the patient's history and radiological ®ndings of longstanding disease, but cannot formally be ruled out. Exacerbation, but not causation, of autoimmune disease has, however, previously been described after vaccination [27] but, similar to the case in the current study, symptoms subsided rapidly and without residual lesions. As these incidents appear to be exceedingly rare, pre-existing autoimmune disease need not be considered a formal contraindication to vaccination [28]. 4.3. Clinical implications TBE vaccination in heart transplant recipients is safe, but serological ecacy is markedly reduced. It should be noted that protection from disease was not investigated in the present study but, based on available clinical and experimental data [12, 15], antibody levels below the serological cut-o used in this study will not be able to prevent the development of clinical disease. Unknown cellular defects in the immune response to TBE virus in transplant patients might even further impair the potential protection conferred by TBE speci®c antibody titres. Thus, even transplant patients with successful seroconversion might not be fully protected from clinical disease. In addition, the post-vaccinal time course of antibody titres may be dierent in immunosuppressed transplant recipients. Before speci®c data on antibody persistence will become available, seroconverted transplant patients should receive the recommended booster dose after one year with the abbreviated immunization schedule [12]. Moreover, investigation of the eect of an additional booster dose at one year in non-seroconverters appears worthwhile. Based on the limited ecacy demonstrated in the present study TBE vaccination cannot be recommended as a routine procedure in heart transplant recipients at risk of TBE virus infection (residence in endemic area, travel to high risk areas). TBE vaccination may be performed safely in selected cases, but repeated controls of serum antibody titres to con®rm successful vaccination and persistence of antibody titres appear imperative. Patients should be informed that, due to unknown cellular immune defects through therapeutic immunosuppression, seroconversion might still not confer adequate protection from TBE. Therefore, other protective measures against TBE virus infection (clothing, avoiding high-risk areas for travel) are advisable.
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[24] Dengler TJ, Strnad N, Zimmermann R, Allers C, Markus BH, Nessen SV, Kubler W, Zielen S. Pneumococcal vaccination after heart and liver transplantation. Immune responses in immunosuppressed patients and in healthy controls. Dtsch Med Wochenschr 1996;121:1519±25. [25] von Hedenstrom M, Heberle U, Theobald K. Vaccination against tick-borne encephalitis (TBE): in¯uence of simultaneous application of TBE immunoglobulin on seroconversion and rate of adverse events. Vaccine 1995;13:759±62. [26] Kobashigawa JA, Warner Stevenson L, Johnson BL, Moriguchi JD, Kawata N, Drinkwater DC, Laks H. In¯uenza vaccine does not cause rejection after cardiac transplantation. Transplant Proc 1993;25:2738±9. [27] Cohen AD, Shoenfeld Y. Vaccine-induced autoimmunity. J Autoimmun 1996;9:699±703. [28] Chalmers A, Scheifele D, Patterson C, Williams D, Weber J, Shuckett R, Teufel A. Immunization of patients with rheumatoid arthritis against in¯uenza: a study of vaccine safety and immunogenicity. J Rheumatol 1994;21:1203±6.
Vaccination against tick-borne encephalitis under therapeutic immunosuppression. Reduced ecacy in heart transplant recipients Thomas J. Dengler a, *, Rainer Zimmermann a, Joachim Meyer a, Falk-U. Sack b, Otto Girgsdies c, Wolfgang E. KuÈbler a a
Department of Cardiology, University of Heidelberg, Bergheimerstr. 58, 69115 Heidelberg, Germany Department of Cardiac Surgery, University of Heidelberg, Bergheimerstr. 58, 69115 Heidelberg, Germany c Chiron Behring, Clinical Research, 35006 Marburg, Germany
b
Received 12 May 1998; received in revised form 3 July 1998; accepted 7 July 1998
Abstract Patients after organ transplantation are at an increased risk of microbial infections and might bene®t from active vaccination. Due to therapeutic immunosuppression the ecacy of immunizations is, however, reduced and dicult to predict. Ecacy of vaccination against tick-borne encephalitis (TBE) using an abbreviated immunization schedule was compared in 31 heart transplant recipients (age: 54.5 2 11.5 years, mean time after transplantation: 53.5 2 23.7 months) under cyclosporine-based immunosuppression and 29 controls. TBE vaccination was well tolerated by the transplant recipients; spectrum and frequency of adverse events were similar to controls. In the transplant patients, seroconversion rate (35% versus 100%; p < 0.001) and the geometric mean of post-vaccinal antibody titres (0.98 (SF: 2.3) U/ml versus 5.46 (2.2) U/ml; p < 0.001) were markedly reduced in comparison to the control group. No clinical or demographic predictors of vaccination success could be established in the transplant patients. Due to the limited ecacy, TBE vaccination cannot be recommended as a routine procedure in heart transplant recipients at risk of TBE virus infection. TBE vaccination may be performed safely in selected cases, but repeated titre controls to con®rm vaccination success would be required. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Tick-borne encephalitis; Vaccination; Heart transplantation; Immunosuppression
1. Introduction Patients after the transplantation of solid organs are at an increased risk of bacterial, viral and protozoal infections due to the required therapeutic immunosuppresion. Protective vaccination might prevent infection-related morbidity and death after organ transplantation, but immunizations in transplant recipients have been hampered by reduced and unpredictable ecacy under therapeutic immunosuppression [1± 4]. Few controlled studies on the ecacy and safety of protective vaccinations have been performed in solid * Corresponding author. Present address: Boyer Center for Molecular Medicine, Yale School of Medicine, New Haven, CT 06510, USA. Tel.: +1-203-737-2294; fax: +1-203-737-2293. 0264-410X/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 4 - 4 1 0 X ( 9 8 ) 0 0 2 7 2 - 2
organ transplant recipients and currently vaccinations are not routinely performed in these patients. Tick-borne encephalitis is one of the most frequent arthropod-transmitted infections in Central and Eastern European countries [5]. In Germany the causative RNA-¯avivirus is endemic in the southern and central parts of the country, in some areas infesting up to 25% of all ticks [6]. Human infection following a tick bite is characterized by two clinical stages: initial symptoms include lethargy, malaise and ¯u-like symptoms, aecting approximately 10±20% of infected subjects. After 10 days meningitis, encephalitis and myelitis develop in 1±2% of patients that were originally infected [7]. In 1997, approximately 350 cases of tick-borne encephalitis were registered in Germany. No data on the clinical course of TBE in immunosup-
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pressed adults are available, but the severity of symptoms or the proportion of patients with manifest disease might be increased in patients with endogenous or therapeutic immunosuppression including recipients of solid organ grafts. For several years inactivated TBE virus particle vaccines have been available [8±11], oering excellent protection even when employing a short immunization schedule over 21 days [12]. To date, the ecacy of TBE vaccination in transplant recipients has not been studied. In the present study the serological ecacy of TBE vaccination in heart transplant recipients under cyclosporine-based immunosuppression was compared to control subjects. In addition, potential predictors of vaccination success in the transplant patients were investigated. As most ecacy data on TBE vaccines have so far been generated in healthy, young adults, the control group included also subjects above 50 years of age and patients with mild or moderate concomitant illnesses. The results of this study should provide useful data for counseling recipients of solid organ grafts concerning TBE vaccination. 2. Materials and methods 2.1. Vaccine and antigen contents The TBE vaccine used in this study (Encepur1, Chiron-Behring, Marburg, Germany) contains formalin-inactivated K23 virus adsobed to Al(OH)3. After propagation in chick embryo ®broblasts, virus is puri-
®ed and stabilized by polygeline. One approved dose of 0.5 ml contains 1.5 mg of antigen [12] including a maximum of 0.01 mg formaldehyde and 5 mg polygeline and traces of neomycin, gentamycin and chlortetracycline. 2.2. Heart transplant recipients 31 heart transplant recipients were studied, clinical data are shown in Table 1. To ensure stable clinical conditions and levels of immunosuppression, only patients beyond 12 months post-operatively were included in the study. Exclusion criteria were signs of graft failure, renal failure (serum creatinine concentration >4 mg/dl), acute infections or fever of unknown origin, ongoing acute graft rejection episodes, malignancy, antibody de®ciency states, previous vaccination against tick-borne encephalitis and hypersensitivity against chicken proteins. After cytolytic induction therapy with anti-thymocyte globulin for 5 days, patients received standard immunosuppression with cyclosporine A (1 patient received FK506), optional corticosteroids and azathioprine, azathioprine being withheld with blood leucocyte counts below 4000/mm3 (4/nl). Standard outpatient follow-up continued during the study period, including routine endomyocardial biopsies. Signi®cant acute rejection episodes (rgrade 3 according to the classi®cation [13] of the International Society for Heart and Lung Transplantation (ISHLT)) were treated with increased immunosuppression (steroid bolus: 1 g of prednisolone for 3 days, cytolytic agents as required). As a timeindependent measure of rejection frequency in individ-
Table 1 Demographics and clinical characteristics of heart transplant patients (n = 31) at study entry Male/Female Age (mean2S.D. (range); (years)) > 50 years > 60 years Time after transplantation (mean2S.D. (range); (months)) Rejection indexa (mean2 S.D., (range)) Pre-operative diagnoses (n, (%)) Dilated cardiomyopaty Ischaemic heart disease Valvular heart disease Diabetes (n (%)) None Dietary management Insulin therapy Daily cyclosporine dose (mean2S.D. (range); (mg)) Cyclosporine blood level (mean2S.D. (range); (mg/l)) Daily steroid dose (mean2S.D. (range); (mg)) Azathioprine medication n (%) Daily dose (mean2S.D. (range); (mg)) a
25/6 54.5 211.5 (26±67) 22/31 (70.9%) 10/31 (32.2%) 53.5 223.7 (14.7±103.8) 0.87 20.29 (0.24±1.6) 23/31 (74.2%) 6/31 (19.6%) 2/31 (6.2%) 24/31 (77.4%) 4/31 (12.9%) 3/31 (9.7%) 226.7257.6 (150±400) 180.7227.9 (98±228) 3.2 22.4 (0±7.5) 22/31 (70.9%) 77.3 236.9 (25±150)
Measure of incidence of acute rejection episodes, independent of post-operative time and frequency of biopsy (cf. Section 2).
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ual patients, a rejection index was calculated: each result of endomyocardial biopsy was graded with a point system (ISHLT grades 0±4 receiving 0, 1, 1.5, 3 and 4 points, respectively) and normalized to the number of post-operative biopsies. Written, informed consent for the study was obtained from all participants and the study was approved by the local ethics committee. Routine laboratory screening, cyclosporine whole blood levels (by monoclonal ¯uorescence polarisation immunoassay) and speci®c immunoglobulin concentrations was measured at study entry and completion. Patients received a study diary to record adverse events. 2.3. Control subjects The control group comprised 29 subjects (11 male, 18 female) with a mean age of 47.7 2 14.4 years (range: 22±67; >50 years: n = 16, >60 years: n = 6). Several subjects in the control group suered from concomitant illnesses. 7 subjects had diseases of mild severity: soft tissue rheumatism, lower back pain, peripheral artery disease, arterial hypertension (n = 2), hyperthyroidism and Gilbert's disease. 5 patients had illnesses of moderate severity: severe psoriasis with diabetes mellitus, symptomatic ischaemic heart disease (n = 2), epilepsy and chronic hepatitis (non-immunological). 11 subjects took regular medication (including antihypertensives, b-blockers, analgesics), none of the control subjects received any immunosuppressive agents (e.g. steroids, methotrexate, cyclosporine). 2.4. Schedule of immunization Study patients were immunized according to the abbreviated TBE vaccination schedule [12] receiving 3 injections of one standard dose of 1.5 mg antigen on days 0, 7 and 21. Injections were given intramuscularly into the deltoid muscle. Blood samples for antibody assays were drawn before the ®rst immunization on day 0 and on day 42 2 5. 2.5. Antibody assay FSME-speci®c antibody titres in human serum were assayed in a newly developed enzyme linked immunosorbent assay (PEV-ELISA), measuring antibody levels on a continuous scale in U/ml. Microtiter plates were coated with 2 mg/ml inactivated TBE virus in 0.05 M sodium phosphate buer (pH 7.5) for 24 h at room temperature and then washed three times with 0.05 M sodium citrate buer (pH 7.4). Sera were tested in triplicates (100 ml/well). Samples were incubated for 2 h at room temperature. After washing, bound antibodies were detected with rabbit-anti-human antiserum conjugated to horseradish peroxidase (2.5 mg/ml, 100 ml/
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well, 1 h at room temperature). Afterwards, TMB substrate (Behring Diagnostics, Marburg, Germany) was added for 30 min. The reaction was stopped by 0.25 M H2SO4 and measured at 450 nm in an ELISA reader (BEP III, Behring Diagnostics). Cross calculation with data obtained by the previous ELISA according to Heinz (QKV-ELISA) [14] expressed in reciproke titres was performed according to the following regression equation for log 2-transformed data: PEV-ELISA (U/ml) = 0.8645*QKVELISA (1/titre) ÿ 6.2580. Seroconversion in terms of this new PEV-ELISA was de®ned as antibody titres r1.27 U/ml (equivalent to a titre r1:200 in the previous QKV-ELISA). At this antibody level, all sera had previously been found to be positive in the TBE virus neutralization test [14]. 2.6. Ecacy variables Ecacy variable was the TBE antibody titre measured by PEV-ELISA. The primary ecacy criterion was the seroconversion rate (see Section 2.5) on day 42 2 5 after the ®rst vaccination. Subjects with signi®cant pre-vaccinal titres (1 patient of the control group) were excluded from the ecacy evaluation and were analysed separately. Equivalence of titres was chosen as the secondary ecacy criterion: titres were regarded as equivalent if the geometric mean titre in the transplant recipients was at the most one titre step (=factor 1/2) below the mean titre in the controls. 2.7. Statistics Vaccinated subjects were characterized by means of demographic data and information from their medical histories. Adherence to inclusion/exclusion criteria was also checked. Vaccination results were primarily evaluated by intention-to-treat analysis. Statistical analysis of demographic and serological data and associations between vaccination data and clinical parameters was performed using Mann±Whitney±Wilcoxon U-test and analysis of variance as appropriate. Statistical signi®cance was assumed for p < 0.05, data analysis was performed using the SAS statistical software package. 3. Results 3.1. Patient characteristics The control group comprised signi®cantly more women (62.1%) than the transplant group (20.7%). The transplant patients were older than the control subjects with a mean age of 54.5 211.5 years (range: 26±67) versus 47.7 214.4 years (range: 22±67). This dierence, however, reached only borderline statistical
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signi®cance ( p = 0.05). The proportion of subjects older than 50 or 60 years was not dierent between the groups (Table 1). Mean body weight in the transplant group was higher than in the controls (82.92 20.1 versus 73.5 213.7 kg; p < 0.05), however no in¯uence of weight on TBE vaccination has previously been demonstrable (unpublished observation).
oped; in the control patient, seroconversion was demonstrated as scheduled at 7 weeks after vaccination. Formally, seroconversion following clinically silent infection in the absence of vaccination response cannot be excluded, but appears very unlikely in this setting.
3.2. Adverse events
3.3. Serious adverse events
TBE vaccination was well tolerated by the heart transplant recipients and control patients. The most frequently noted side eects were local pain and swelling for 24±48 h at the injection site. General reactions like fever (below 398C), arthralgias, headache and tiredness occurred with much lower frequency. Similar to previous studies [15], the frequency of adverse events was higher after the ®rst vaccination than after the second and third injection. A detailed analysis of adverse events is shown in Table 2; overall the spectrum and frequency of side eects were similar to ®ndings in earlier studies [12, 15]. There was no signi®cant dierence in the quality and frequency of adverse events between transplant patients and the control group. Moreover, no infectious complications or increased incidence of rejection episodes were noted in the transplant recipients. One transplant recipient developed a gastric ulcer during the period of the study, which was considered to be unrelated to vaccination. One transplant patient and one control patient had tick bites after the second vaccination: in both cases, no clinical disease devel-
One serious adverse event occurred in a 56 year old female in the control group. She had a long history of psoriasis, severe osteoarthritis in both hip joints and diet-controlled diabetes mellitus. After the third vaccination she developed nausea, asthenia, diarrhea and progressive swelling, pain with paresthesias and weakness in both hands, most markedly in the ®nger joints. After extensive neurological, rheumatological and radiological investigation, polyneuritis and infection could be excluded and a diagnosis of an exacerbation of pre-existing psoriatic arthropathy was made. A causal relation with TBE vaccination was considered unlikely, but could not formally be ruled out. A course of tapered corticosteroids with additional non-steroidal analgesics as required was started and after 3 weeks symptoms had subsided without residual limitations. The incident was reported accordingly and classi®ed as serious adverse events, as an initial hospitalization phase was required. As the adverse event occurred after the third vaccination, the patient remained in the study and antibody titres at 42 25 days were analysed according to protocol.
Table 2 Adverse events TBE vaccination in heart transplant recipients and controls, speci®ed after each of 3 injections. Results are presented as patient number (n) and percentage of group (in parentheses) Patient group (vaccination) control (n = 29)
heart transplant recipients (n = 31)
1st
2nd
3rd
1st
2nd
3rd
Local reactions Pain (injection site) Pain (limb) Swelling/hematoma
9 (31%) 3 (10.3%) 3 (10.3%)
5 (17.2%) 2 (6.9%) 1 (3.4%)
1 (3.4%) 0 1 (3.4%)
4 (12.9%) 3 (9.6%) 2 (6.4%)
4 (12.9%) 1 (3.2%) 0
3 (9.6%) 1 (3.2%) 1 (3.2%)
General reactions Fever 38±398C Fever >398C Asthenia/tiredness Arthralgia Headache Nausea/vomiting Diarrhoea Others
1 0 0 0 3 2 1 0
0 0 1 0 3 2 1 2
1 (3.4%) 0 0 1 (3.4%) 0 0 1 (3.4%) 0
1 0 3 2 1 0 1 0
0 0 2 1 1 0 0 1
0 0 2 (6.4%) 0 0 0 0 0
(3.4%)
(10.3%) (6.9%) (3.4%)
(3.4%) (10.3%) (6.9%) (3.2%) (6.9%)
(3.2%) (9.6%) (6.4%) (3.2%) (3.2%)
(6.4%) (3.2%) (3.2%) (3.2%)
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Table 3 Results of TBE vaccination in controls and heart transplant recipients. TBE-speci®c antibody titres were determined by ELISA, seroconversion was de®ned as post-vaccinal increase of antibody titres above 1.27 U/ml. Results are presented as antibody concentration in U/ml and equivalent titre levelsa
Patient number (n) Pre-vaccinal antibody titres, geometric mean (SFc) Pre-vaccinal titre levelsa, geometric mean Post-vaccinal antibody titres, geometric mean (SFc) Post-vaccinal titre levelsa, geometric mean Seroconversion (n, (%))
Controls
Heart transplant recipients
28b 0.29 (1.8) 1:30 5.46 (2.3) 1:1080 28/28 (100%)
31 0.28 (1.9) 1:30 0.98 (2.2)d 1:150d 11/31 (35.5%)d
a Equivalent titre levels were cross-calculated from ELISA results with a regression equation for log 2-transformed data (cf. Section 2). bOne pre-immune subject (pre-vaccinal titre 1.45 U/ml) was excluded from analysis of ecacy. c SF = scatter factor. dp < 0.001 for dierence to controls.
3.4. Ecacy of TBE vaccination The results of the study were primarily analysed in an intention-to-treat fashion: mean TBE antibody titres before vaccination were not dierent between transplant recipients and controls (geometric mean: 0.29 U/ml (Scatter factor (SF): 1.8) versus 0.28 U/ml (1.9), p = n.s). One pre-immune subject in the control group (pre-vaccinal titre: 1.45 U/ml) was excluded from ecacy analysis and was evaluated separately. The seroconversion rate in the transplant patients (35.4%) was signi®cantly reduced compared to the control subjects (100%, p < 0.001; Table 3), using 1.27 U/ml as the threshold for seroconversion (equivalent to a titre of 1:200). The geometric means of the postvaccinal antibody titres determined by ELISA were also signi®cantly lower in the transplant recipients (0.98 (SF = 2.3) U/ml versus 5.46 (SF = 2.2) U/ml, p < 0.001; Table 3). The individual pre- and post-vaccinal titres of all participants are presented in Fig. 1. In addition, it could be shown that the criterion for equivalent ecacy of the vaccine was not ful®lled in the transplant patients: the geometric mean of postvaccinal titres in transplant recipients was more than 1 titre step (factor = 1/2) below the mean titre in controls (1:150 versus 1:1080 for cross-calculated values, p < 0.001; Table 3). In both groups seroconversion rate and antibody titres were not associated with sex, age or weight; no signi®cant changes in routine laboratory values were seen after vaccination. In the transplant group, predictors of vaccination success were sought by correlation of seroconversion status or post-vaccinal titres with demographic, clinical or laboratory parameters. There was, however, no signi®cant correlation of the responder status with time after transplantation, pre-operative diagnosis, presence of diabetes mellitus or other concomitant diseases, routine laboratory parameters, cyclosporine dosage and blood levels, (cumulative and current) azathioprine and steroid medication, immunoglobulin concen-
trations, rejection index and number of steroid bolus treatments. In addition, no association with other laboratory values (electrolytes, renal and liver function tests, serum lipids, full blood count) could be established. In the transplant recipients there was a statistical trend for higher pre-vaccinal titres in subjects with successful seroconversion, but previous exposure to TBE virus and a possible `booster' eect on vaccination was unlikely based on patient history and geographical location.
Fig. 1. Semilogarithmic representation of individual pre- and postvaccinal TBE antibody titres including limit of seroconversion (1.27 U/ml). HTX: heart transplant recipients; pre: titres before vaccination; post: titres after vaccination. Short thick lines: geometric means of FSME titres.
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In the control subjects the presence of concomitant disease or medication did not in¯uence seroconversion or post-vaccinal antibody titres. The patient experiencing a serious adverse event and receiving a course of steroids also demonstrated seroconversion. The only pre-immune subject (excluded from the general analysis of ecacy above) displayed a signi®cant rise in post-vaccinal antibody titre, not exceeding the mean titre of the control group. 4. Discussion Patients after transplantation of solid organs are at an increased risk of microbial infections due to therapeutic immunosuppression. Eective immunization would, therefore, be a helpful adjunct in post-operative care of these patients, but ecacy of active immunization is doubtful and dicult to predict due to immunosuppression [16, 17]. TBE represents the most important arthropod-transmitted disease in Central Europe, causing neurologic morbidity and even mortality in approximately 1% of infected subjects [6]. Protective vaccination is available [11, 18], but both the eects of infection and vaccination in immunosuppressed patients are largely unknown. To date, there have only been two episodic reports on reduced ecacy of TBE immunization in 4 HIV infected subjects [19] and 5 women with breast cancer receiving chemotherapy [20]. 4.1. Ecacy In the present study, TBE vaccination using the abbreviated immunization schedule [12] was well tolerated, but signi®cantly less eective serologically in immunosuppressed heart transplant recipients than in control subjects. Predictive parameters for vaccination success in this patient group could not be identi®ed, in particular, time after transplantation, dose or blood levels of immunosuppressive drugs and concomitant diseases were not associated with the ecacy of vaccination. The reduced serological ecacy of TBE vaccination in heart transplant recipients is mainly accounted for by therapeutic immunosuppression, which not only suppresses allograft rejection, but also immune reactions against all other exogenous antigens. Patients received cyclosporine-based immunosuppression (1 patient: FK 506) including also azathioprine and corticosteroids in most cases. After heart transplantation, higher levels of immunosuppression are required than following liver or kidney transplantation, but the level of immunosuppression is reduced over time. Only patients more than 1 year after transplantation were included in the present study but, when extrapolating from other studies [21], the ecacy
of vaccination would probably have been even further reduced in patients earlier after transplantation. The individual level of immunosuppression (as opposed to immunosuppression as such) was, however, not associated with vaccination success in the transplant patients. Considering the rather narrow range in the parameters of immunosuppression, it may be assumed that other factors apart from these rather crude indicators of immunosuppression in¯uence the immune response to vaccination in these patients. The slightly higher age of the transplant patients is unlikely to account for the dierence in vaccination ecacy, as no in¯uence of age between 14±59 years on the seroconversion rate could be demonstrated here or in previous studies [15]. Higher weight and dierent sex ratio in the transplant group also does not in¯uence the ecacy of vaccination with the standard 1.5 mg dose (unpublished observation). The reduced serological ecacy of TBE vaccination con®rms other studies of protein-based vaccines in transplant recipients: the immune response to measles vaccine was drastically reduced in children after liver transplantation [22]. In adults after heart, liver or renal transplantation hepatitis B vaccination has been disappointingly unsuccessful [1±3] and has been abandoned clinically. In several studies, the immune response to in¯uenza vaccination was reduced in recipients of solid organ transplants, though not completely abolished [4, 23]. Interestingly, the immune response against T-cell-independent polysaccharide pneumococcal vaccine (Pneumovax-23) is fully preserved in heart and liver transplant patients receiving cyclosporine-based immunosuppression [24]. The high ecacy of TBE vaccination in the control subjects corresponds to previous data [12, 15]. The control group of the present study is, however, noteworthy for the high age (16 subjects >50 years) and the presence of mild and moderate concomitant illnesses. Despite the small size of the study, the serological ecacy of TBE vaccination in these patients seems to indicate that successful immunization can also be achieved in people above 60 years and with relevant concomitant disease. 4.2. Tolerance TBE vaccination was well tolerated and safe in the transplant recipients. The spectrum and frequency of adverse events corresponds to earlier reports [15, 25] and was not signi®cantly dierent from the control subjects. Similar to other immunizations in transplant patients [26], infection or undue stimulation of the immune system resulting in more frequent acute rejection episodes after vaccination did not occur. In the control group, TBE vaccination was generally well tolerated, also by those patients with mild or
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moderate concomitant disease, including one patient with epilepsy. One serious adverse event occurred in a 56 year old woman with pre-existing psoriasis, who developed an exacerbation of pre-existing psoriatic arthritis in the ®nger joints, requiring hospitalization and treatment with corticosteroids. A causal relation with TBE vaccination appears unlikely based on the patient's history and radiological ®ndings of longstanding disease, but cannot formally be ruled out. Exacerbation, but not causation, of autoimmune disease has, however, previously been described after vaccination [27] but, similar to the case in the current study, symptoms subsided rapidly and without residual lesions. As these incidents appear to be exceedingly rare, pre-existing autoimmune disease need not be considered a formal contraindication to vaccination [28]. 4.3. Clinical implications TBE vaccination in heart transplant recipients is safe, but serological ecacy is markedly reduced. It should be noted that protection from disease was not investigated in the present study but, based on available clinical and experimental data [12, 15], antibody levels below the serological cut-o used in this study will not be able to prevent the development of clinical disease. Unknown cellular defects in the immune response to TBE virus in transplant patients might even further impair the potential protection conferred by TBE speci®c antibody titres. Thus, even transplant patients with successful seroconversion might not be fully protected from clinical disease. In addition, the post-vaccinal time course of antibody titres may be dierent in immunosuppressed transplant recipients. Before speci®c data on antibody persistence will become available, seroconverted transplant patients should receive the recommended booster dose after one year with the abbreviated immunization schedule [12]. Moreover, investigation of the eect of an additional booster dose at one year in non-seroconverters appears worthwhile. Based on the limited ecacy demonstrated in the present study TBE vaccination cannot be recommended as a routine procedure in heart transplant recipients at risk of TBE virus infection (residence in endemic area, travel to high risk areas). TBE vaccination may be performed safely in selected cases, but repeated controls of serum antibody titres to con®rm successful vaccination and persistence of antibody titres appear imperative. Patients should be informed that, due to unknown cellular immune defects through therapeutic immunosuppression, seroconversion might still not confer adequate protection from TBE. Therefore, other protective measures against TBE virus infection (clothing, avoiding high-risk areas for travel) are advisable.
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