A Comparison of Splenectomy versus Intensive Posttransplant ... : Transplantation (original) (raw)
ABO-incompatible kidney transplantation is an increasingly attractive option for renal allograft candidates whose only living donor is blood group incompatible (1) To remove and durably control antiblood group antibody, most protocols have employed a combination of pretransplant plasmapheresis and intravenous immunoglobulin (2–5). To remove antibody-producing plasma cells, many protocols also have included splenectomy either pretransplant or at the time of transplantation for non-A2 blood group ABOI kidney transplants (4, 5). However, the evidence that splenectomy is necessary to the success of ABOI kidney transplants is predominantly historical (6). Currently, more effective immunosuppression may be adequate to permit transplantation of ABOI kidneys obviating the need for splenectomy.
The purpose of this study was to compare the outcomes of ABO-incompatible living donor kidney transplants using a protocol without splenectomy involving intensive pre- and posttransplant PP/IVIG plus anti-CD20 antibody to a protocol using less-intensive plasmapheresis plus splenectomy. The major outcomes assessed were patient and graft survival, humoral rejection, and the level of antidonor blood group antibody following transplantation.
METHODS
Patients
This study was conducted with informed consent according to a protocol approved by the Mayo Foundation Institutional Review Board. The protocol was offered to candidates whose only potential living donor was ABO incompatible (ABOI).
Between September 1999 and May 2004, 34 ABOI kidney transplants were performed. Prior to May 2003, all patients were transplanted using a protocol involving pretransplant plasmapheresis and splenectomy at the time of the transplant (n=23). After May 2003, splenectomy was not performed (n=11) and a protocol that involved pretransplant anti-CD20 antibody and a more intensive posttransplant plasmapheresis regimen aimed at maintaining low levels of antiblood group antibody was utilized.
ABO Blood Group and Antibody Titers
Red blood cell group was determined with commercially available antisera with positive and negative controls according to standard American Association of Blood Banks immunohematologic techniques. Blood group A donors were designated as the A1 subgroup on the basis of reactivity of their red blood cells with the anti-A1 lectin Dolichos biflorus.
Anti-A or anti-B antibody titers were determined with direct and indirect isoagglutination assays (7). A1 or B blood group red blood cells were suspended in serial doubling dilutions of recipient serum, incubated at 37°C for 30 min and washed with normal saline and antihuman globulin (Coombs reagent) was added. The specimen was then centrifuged and analyzed for agglutination. This assay was defined as representing IgG activity. By standard red cell agglutination readings the most dilute unequivocally positive reaction was defined as the anti-A or anti-B IgG antibody titer.
Immunosuppression
The immunosuppressive regimen used has previously been reported in detail (3). In brief, all patients received antibody induction with rabbit anti-human T-cell polyclonal antibody (Thymoglobulin; Sangstadt, Menlo Park, CA) 1.5 mg/kg body weight, 5–7 doses following transplantation. Maintenance immunosuppression consisted of Tacrolimus (Prograf, Fujisawa, Deerfield, IL), mycophenolate mofetil (Cellcept, Roche, Nutley, NJ) and prednisone. Tacrolimus was given within the first 3 days after transplantation with an initial dosage of 3 mg twice daily, with trough levels of 12–15 ng/ml in the first month, 10–12 until 3 months posttransplantation and 6-8 thereafter. MMF was started during the preconditioning period, initially 750 mg twice daily, and then adjusted to a target mycophenolic acid level 1.0–3.5 ng/ml. All patients received prednisone tapered to 5 mg/day by 3 months posttransplant.
Pretransplantation Preconditioning
Prior to transplant patients received a series of plasmapheresis treatments followed by intravenous immunoglobulin, 100-mg/kg-body weight to prevent hypogammaglobulinemia. The PP/IVIG protocol which was utilized has been reported in detail (8). In brief, PP consisted of 1 plasma volume exchange using 5% albumin as replacement solution, supplemented by 4 units of fresh frozen plasma to replenish coagulation factors when PP was performed within 48 hr of surgery or biopsy. The number of PP/IVIG treatments was determined by the baseline antidonor blood group antibody titer, and the goal of PP/IVIG was to achieve a titer of ≪ 1:8 at the time of the transplant.
Patients not undergoing splenectomy received the anti-CD20 antibody rituximab (Rituxan; Genentech, Inc. San Francisco, CA) immediately prior to initiating the preconditioning regimen.
Posttransplant Management
Recipients underwent protocol biopsies one half-hour following renal allograft reperfusion (time 0), and postoperative days 3, 7, 14, 90 and 1 year. Biopsies were also performed at times of allograft dysfunction.
Splenectomized Patients
Patients treated with splenectomy had no posttransplant plasmapheresis/IVIG therapy unless renal biopsies documented humoral rejection, whether associated with allograft dysfunction or subclinical.
Nonsplenectomized Patients
Patients who were not splenectomized received posttransplant plasmapheresis/IVIG therapy on postoperative days 1 and 3 by protocol. In addition, isoagglutinin titers were measured daily during the first 2 weeks after transplantation. Plasmapheresis/IVIG was administered as needed to maintain the antidonor blood group isoagglutinin IgG titer ≪ 1:8 during the first and ≪ 1:16 during the second postoperative week. Following week 2, PP/IVIG was administered only for rejection.
Detection and Treatment of Humoral Rejection
All rejection episodes were biopsy proven. In addition to light microscopic evaluation, staining for the complement degradation product C4d was performed with standard immunofluorescence techniques. Histologic criteria for humoral rejection included proliferative and mesangiolytic glomerulopathy, glomerular and arterial thrombi, peritubular capillary neutrophilic infiltration, and peritubular capillary C4d deposition (9, 10). C4D immunostaining in the absence of other histologic abnormalities was not considered sufficient for the diagnosis of humoral rejection. Humoral rejection (whether associated with allograft dysfunction or subclinical) was treated with a series of two to six one-plasma volume exchanges with 5% albumin followed by 100 mg/kg IVIG. In addition, patients received bolus methylprednisolone 1 g intravenously for 3 days followed by corticosteroids tapered over one week to the previous dose.
Statistical Analysis
Donor specific blood group isoagglutinins titers and dilutions were compared in splenectomized and non-splenectomized groups at baseline, day of transplantation, 3 and 12 months posttransplant using Student’s t test. Patient and allograft survival were calculated using the Kaplan-Meier method.
RESULTS
Demographic data is presented in Table 1. In all, 23 patients underwent transplantation with splenectomy while 11 nonsplenectomized patients received posttransplant PP/IVIG and rituximab induction. Blood group combinations are listed in Table 1. Patient survival and patient survival with functioning allograft at 2 years in non-SPX and SPX groups are 91% vs. 96% and 82% vs. 87%, respectively (Fig. 1). One patient in each group died within 2 weeks of transplant of myocardial infarction. Both individuals were known to have significant coronary artery disease prior to transplantation. In the nonsplenectomized group a mean of 3.6±1.5 posttransplant PP/IVIG treatments were administered, while in the splenectomized group PP/IVIG was administered only as treatment for humoral rejection. Serum creatinine concentrations are 1.4±0.4 and 1.6±0.5 mg/dl (mean ± SD) at a mean follow up of 399 and 1056 days, respectively.
Patient demographics
Patient survival with functioning graft.
Antidonor blood group antibody data are presented in Table 2 and Figures 2 and 3. No difference in antibody titer was seen between splenectomized and nonsplenectomized groups at baseline, day of transplantation, 3 and 12 months (_P_=0.9, 0.53, 0.43, and 0.69, respectively). Compared to baseline titers, antidonor antibody titer was significantly lower at time of transplantation (after pretransplant plasmapheresis) and at 3 and 12 months posttransplantation (_P_=0.002, 0.001, and 0.005, respectively). Data regarding antibody levels expressed in terms of dilutions is presented in Figure 3 (one dilution equals a change in antibody titer by one increment, i.e. titer 1:64 to 1:32 or 1:4 to 1:2 equals 1 dilution change). No difference was seen between splenectomized and nonsplenectomized groups in terms of dilution change from baseline to day of transplant, 3 or 12 months posttransplant (_P_=0.17, 0.85, 0.87, respectively).
Antidonor antibody titers at baseline and follow-up
Frequency of antidonor blood group antibody titers.
Change in antidonor antibody dilutions from baseline. Points, mean change in dilutions from baseline; bars, 95% confidence intervals for the mean; point and line to the left in each group, no splenectomy group.
Humoral rejection was diagnosed in 2/11 (18%) nonsplenectomized and 7/23 (30%) of splenectomized patients using our published criteria (_P_=0.68) (9). The relationship between baseline anti donor blood group antibody titer and humoral rejection is presented in Table 3. The incidence of HR was 12-13% in patients with baseline titers <1:128 regardless of splenectomy or posttransplant therapy, while patients with titers >1:256 uniformly developed rejection. Neither of 2 patients with titers 128-256 who were treated with posttransplant PP/IVIG and rituximab induction developed HR, while 4/5 (80%) of splenectomized patients not treated with posttransplant PP/IVIG or rituximab induction had humoral rejection (_P_=0.14).
Incidence of humoral rejection versus antidonor blood group antibody titer
DISCUSSION
Early attempts of kidney transplantation across the ABO blood group barrier led to a high rate of early graft loss due to humoral rejection (11). However, more recent reports have demonstrated remarkable success using novel pretransplant conditioning protocols—most of which have included splenectomy (2–5). In some cases, successful ABO-incompatible kidney transplants have been shown to be possible without concurrent splenectomy. ABOI transplants using A2 donors are commonly performed without splenectomy in recipients with low levels of anti-A antibody (12–14). Successful ABOI transplants have also been performed without splenectomy using non-A2 kidneys in small series of patients with low levels of donor specific blood group antibodies, particularly in blood group B donors (15). Tyden et al. report a series of 4 ABOI kidney transplants in which the anti-CD20 antibody rituximab has been used in combination with donor antigen-specific immunoadsorption both pre- and posttransplant. Immunoadsorption was performed three times during the first 9 days after transplantation with further treatments as needed to maintain low antibody levels (16). Sonnenday et al. have reported another series of six ABOI transplants in which posttransplant PP/IVIG was given by protocol on postoperative days 1, 3, and 5 combined with CMV hyperimmune globulin and rituximab, with none of the patients developing rejection (17).
In the current investigation, we compared outcomes in splenectomized and non-splenectomized ABOI kidney transplant recipients. Patient and allograft survival as well as renal function were equivalent in the two groups. Although the humoral rejection rate was lower in the non-splenectomized group treated with intensive posttransplant PP/IVIG and rituximab this difference was not statistically significant (_P_=0.68). Individuals with antibody titer <1:128 at baseline rarely experienced humoral rejection regardless of which therapy was used. Conversely, both recipients with baseline antibody titers >1:256 experienced humoral rejection. This is consistent with a previous report of a high incidence of humoral rejection in splenectomized ABOI recipients with high baseline antibody titer (18). In the current series, graft loss occurred in one patient with a baseline titer 1:512 despite intensive posttransplant PP/IVIG therapy (daily treatment POD 1–14), suggesting that splenectomy may be necessary in certain high-titer candidates. An important observation in the current study is that while 4/5 splenectomized patients with baseline antibody titer 128–256 developed humoral rejection, 0/2 nonsplenectomized patients treated with posttransplant PP/IVIG rejected. Although this association was not statistically significant (_P_=0.14), this low incidence of humoral rejection is consistent with the findings observed by both Tyden et al. and Sonnenday et al., and suggests that posttransplant PP/IVIG, rituximab and no splenectomy may actually be more effective than splenectomy without posttransplant therapy in individuals with moderate baseline antibody titers. Prior investigations in which aggressive posttransplant therapy was not utilized have reported humoral rejection rates of 30-40% (2–5).
The major reason for splenectomy in recipients of ABO incompatible kidney transplants is to remove antibody-producing plasma cells and/or memory B cells that might contribute to humoral rejection either at the time of transplant or in the immediate posttransplant period. While there are indeed plasma cells and memory B cells in the spleen, these cells also exist in large number in other parts of the body including the lymph nodes and bone marrow. Thus, there may be theoretical reasons why systemic therapy might lead to improved control of antibody production compared to splenectomy alone. Sykes et al. have demonstrated that plasma cells producing antibody to the carbohydrate antigen gal α1-3 gal21, 3 GAL in mice reside primarily in the spleen (19). While the actual site of anti-blood group antibody secreting plasma cells in humans has not been identified, it is possible that these plasma cells might also be abundant in the spleen. However, the similarity in posttransplant antidonor blood group antibody titers seen in splenectomized and nonsplenectomized patients in the current study suggests that antibody-producing cells exist in other lymphoid compartments.
In this investigation, nonsplenectomized patients underwent rituximab induction. It is not clear from the current data whether anti-CD20 antibody is actually necessary or even beneficial in ABO-incompatible kidney transplant recipients. The single dose used in the current protocol is sufficient to cause depletion of B lymphocytes in the peripheral blood for weeks after transplantation (data not shown). However, most plasma cells do not express detectable levels of CD20 and thus it is unlikely that this therapy has a major impact on plasma cells. A recent study that demonstrated that anti-CD20 had only minimal impact on HLA antibody levels in sensitized renal allograft candidates supports this view (20). Conversely, memory B cells express CD20 and thus might be an important target for anti-CD20 therapy. However, the role of memory B cells in humoral rejection in ABO-incompatible kidney transplants is unclear. Further studies are needed to verify the exact role, if any, of anti-CD20 antibody in these patients.
We believe that the most important facet of the nonsplenectomy protocol is the close monitoring of antiblood group antibody levels combined with prompt initiation of plasmapheresis when the levels rise in the first 2 weeks after transplantation. Humoral rejection was rare when the antidonor blood group antibody levels were maintained less than 1:8 in the first and 1:16 in the second weeks after transplantation. Conversely, in the splenectomized group not aggressively treated in the posttransplant period, we commonly saw evidence of antibody mediated damage when the antibody levels rose above these levels. It is our current practice to maintain levels ≪1:16 for the first 2 weeks after transplantation and then allow them to rise thereafter if graft function and surveillance biopsies remain normal.
In both splenectomized and nonsplenectomized groups, the pretransplant conditioning regimen successfully lowered the antibody titer 3–4 dilutions below baseline. Although antibody levels increased by 3 months following transplantation, the mean titer remained 2–3 dilutions below baseline, and this effect persisted at 12 months. No difference in antibody level was noted between splenectomized and nonsplenectomized groups following transplantation. The mechanism by which antidonor antibodies are decreased following transplantation compared to baseline is not clear. Uchida et al. report a disconjugation of blood group antibody levels, with donor specific antibodies persisting at low titers while third party antibody returns to baseline following ABOI kidney transplants (21). West et al. report the disappearance of donor specific antibody secreting cells from peripheral blood in some ABOI pediatric heart transplant recipients suggesting that tolerance to blood group incompatibility may occur (22).
In conclusion, ABOI kidney transplantation may be safely performed without splenectomy in some individuals. The risk for humoral rejection appears to be relatively low in patients with low level of antidonor blood group antibody at baseline. Rituximab induction combined with intensive posttransplant plasmapheresis/IVIG and antibody monitoring may be more effective than splenectomy in preventing humoral rejection in recipients with moderately elevated baseline titers. Individuals with markedly elevated baseline antidonor blood group antibody titers are at high risk for humoral rejection, and in these patients splenectomy combined with intensive posttransplant therapy may be necessary.
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Keywords:
ABO incompatible; Plasmapheresis; Splenectomy; Kidney transplantation
© 2005 Lippincott Williams & Wilkins, Inc.