Objectives: Rituximab treatment strategies vary in ABO-incompatible pediatric kidney transplant recipients. Here, we present the efficacy of 2 doses of rituximab and subsequent outcomes in ABO-incompatible pediatric kidney transplant patients.
Materials and Methods: Our study of ABO-incompatible pediatric kidney transplant recipients included 21 who were pretreated with desensitization that included 2 doses of 100 mg rituximab (rituximab group) at 10 and 1 day pretransplant and 14 who received splenectomy without rituximab (splenectomy group). Both groups received immunosuppression. Basiliximab was admin-istered during transplant and 4 days posttransplant. Double-filtration plasmapheresis and/or plasma exchange procedures were performed pretransplant in those with higher antidonor antibody titers. CD19-positive and CD20-positive B cells were measured sequentially in the rituximab group. Maximum titers of antidonor antibody pre- and posttransplant, patient and graft survival, biopsy-proven rejection, and complications/infections were compared between groups.
Results: In the rituximab group, CD19- and CD20-positive B cells were depleted on transplant, per-sistently depleted at 3 months, and under 5% until 1 year posttransplant. Maximum titers of antidonor antibodies decreased significantly posttranplant in the rituximab (P < .001) but not in the splenectomy group (P = .174), with maximum titers posttransplant significantly lower than shown in the splenectomy group (P < .001). No rituximab patients had clinical rejection, but 5 splenectomy group patients had clinical T-cell-mediated rejection, with 2 also having antibody-mediated rejection. Six in the rituximab group had cytomegalovirus viremia but no cyto-megalovirus disease; however, 5 splenectomy group recipients had cytomegalovirus disease and viremia. In the rituximab group, 3 had late-onset neutropenia. One child died of hypertrophic cardio-myopathy with a functioning graft; all others survived with no failed grafts. All splenectomy group children survived, although 2 had deteriorated graft function.
Conclusions: Two doses of rituximab were effective in long-term B-cell depletion to suppress antidonor antibodies. The possibility of late-onset neutropenia must be considered.
Key words : Antibody-mediated rejection, CD19, CD20, Renal transplant
Rituximab is used to deplete B cells to suppress antidonor antibodies (ADAb) in ABO-incompatible pediatric kidney transplant recipients.1 Splenectomy requires surgery and may then induce serious pneumococcal infection in young children.2 Therefore, in our clinic, we have established a standard protocol since 2009 to use rituximab instead of splenectomy to suppress ADAb in ABO-incompatible pediatric kidney transplant patients. However, the optimal dose and timing of rituximab are still unknown in these patients. In most American3 and European4,5 transplant centers, the dose of rituximab is 375 mg/m2, and centers routinely perform intravenous immuno-globulin and plasmapheresis treatment or immuno-adsorption to reduce ADAb. In contrast, a single or double doses of rituximab of 150 to 200 mg is given as desensitization to suppress ADAb in adult ABO-incompatible pediatric kidney transplant patients in Japan.6-8 Double-filtration plasmapheresis (DFPP) and plasma exchange remove not only ADAb but also rituximab and thus results in lower serum rituximab concentration.9 Therefore, we planned to administer rituximab 100 mg twice as desensitization at 10 days before and 1 day before kidney transplant following plasma exchange. Recently, in our center, DFPP and plasma exchange have been avoided in children with a low titer of immunoglobulin G ADAb (< 64). Avoiding DFPP and plasma exchange main-tains higher serum concentrations of rituximab, which will subsequently improve B-cell depletion over a longer period.
Antibody-mediated rejection (AMR) should be avoided in ABO-incompatible pediatric kidney transplant patients within 2 weeks after transplant.10 AMR usually occurs due to a rebound of ADAb following transplant; therefore, the titer of ADAb should be as low as possible. Thus, we studied whether 2 doses of rituximab could be effective for desensitization in terms of CD19-positive and CD20-positive cell counts and subsequent titers of ADAb. In addition, outcomes such as com-plications, patient survival, and graft survival rates were also studied.
Materials and Methods
Twenty-one ABO-incompatible pediatric kidney transplant recipients were pretreated with a desensitization protocol that included 2 doses of rituximab (rituximab group). Background data of recipients and donors in the rituximab group and splenectomy group are shown in Tables 1 and 2. No recipients in the rituximab group underwent splenectomy. Fourteen ABO-incompatible pediatric kidney transplant recipients with splenectomy and not using rituximab were controls for comparison with the rituximab group.
Immunosuppression consisted of cyclosporine or tacrolimus (calcineurin inhibitor; CNI), myco-phenolate mofetil, and steroids in both groups. Mycophenolate mofetil 600 to 800 mg/m2 and CNI were administered 10 days before transplant. Rituximab 100 mg was administered 10 days and 1 day before transplant. Basiliximab 10 or 20 mg was administered on day of transplant and 4 days posttransplant. Plasma exchange and/or DFPP were performed before transplant; however, these procedures were recently excluded in recipients with a low titer (< ×64) of immunoglobulin G ADAb. Measurements of CD19-positive and CD20-positive B cells were performed only in the rituximab group sequentially. The maximum titers of ADAb pre- and posttransplant were compared between the rituximab and splenectomy groups.
Titers were analyzed with the paired t test, Welch t test, and chi-square test with Yates continuity correction. Patient and graft survival, biopsy-proven rejection, and complications, including infection, were compared between the rituximab group and the splenectomy group.
This study was conducted in accordance with the principles of the Declarations of Helsinki and Istanbul. All study procedures were approved by the Ethical Committee of the Toho University, Omori Medical Center (approval number: 27-236).
CD19-positive and CD20-positive B cells were depleted on transplant, and this depletion persisted for 3 months posttransplant in the rituximab group (Figures 1 and 2). The rates of CD19-positive and CD20-positive B cells in the peripheral blood of recipients in the rituximab group remained below 5% in 20 of 21 recipients until 1 year posttransplant. The maximum titers of the ADAb decreased significantly (P < .001) posttransplant in the rituximab group (log2n: n = 3.00 ± 2.74 pretransplant and n = 1.52 ± 1.83 posttransplant; Figure 3, a and b). In contrast, these titers did not decrease in the splenectomy group (log2n: n = 3.93 ± 2.76 pretransplant and n = 5.07 ± 1.14 posttransplant; P = .174). Pretransplant values were not significantly different between the 2 groups, but maximum titers posttransplant in the rituximab group were significantly lower than those in the splenectomy group (P < .001). Maximum titers in the rituximab group decreased or remained at 0 posttransplant in 20 of the 21 children in the rituximab group and decreased in 3 of the 14 children in the splenectomy group. Children in the rituximab group tended to have decreased ADAb compared with those in the splenectomy group (P < .001). Regarding these results, rituximab appeared to suppress ADAb production more than splenectomy.
In the rituximab group, there were no cases of clinical rejection, but protocol biopsies 3 months post-transplant revealed subclinical rejection (4 with borderline, 1 with AMR, and 1 with grade 2A) in 6 of the 21 recipients. In the splenectomy group, 5 recipients had clinical T-cell-mediated rejection (TMR; 4 with grade 1A, 1 with grade 2A, and 1 with grade 1B). Two of the 5 recipients with TMR also had clinical AMR. Protocol biopsies at 3 months posttransplant revealed subclinical rejections (4 with borderline, 1 with AMR, and 1 with grade 2A). The incidence of clinical acute rejection episodes, either of AMR or TMR, was higher in the splenectomy group than in the rituximab group (P < .001, chi-square test with Yates continuity correction).
In the rituximab group, 7 of the 21 recipients had cytomegalovirus (CMV) viremia but none had CMV disease. One child had Aspergillus pneumonia and one had adenovirus hemorrhagic cystitis. In contrast, 5 of the 14 transplant recipients in the splenectomy group had CMV disease with CMV viremia. One child had herpes zoster and 1 had adenovirus hemorrhagic cystitis. In the rituximab group, 3 children developed late-onset neutropenia (absolute neutrophil counts of 14/μL, 845/μL, and 126/μL) at 4, 2, and 4 months posttransplant, although all patients recovered from neutropenia after treatment with granulocyte colony-stimulating factor. One child died of hypertrophic cardiomyopathy with a functioning graft 8 months posttransplant. However, 20 patients survived without any failed grafts (follow-up period of 8-105 mo). In the splenectomy group, 2 patients had deteriorated graft function, but all 14 recipients survived (follow-up period of 180-300 mo).
The optimum dosage and timing of rituximab in ABO-incompatible pediatric kidney transplant recipients is still unknown. Tyden and associates5 reported a dose of rituximab of 375 mg/m2 once at 4 weeks before immunoadsorption. Stojanovic and associates4 also administered rituximab 1 month before transplant but only in children with a titer of ADAb ≥ ×8. Toki and associates11 demonstrated that spleen and peripheral B cells were depleted after a dose of 35 to 300 mg of rituximab. In addition, Kamburova and associates12 demonstrated that a single dose of rituximab does not deplete B cells in secondary lymphoid organs.
In our clinic, we still perform DFPP and/or plasma exchange to reduce ADAb in children with a high titer of > ×64 for ABO-incompatible pediatric kidney transplant patients. McDonald and associates9 showed that serum rituximab concentrations were significantly lower in patients with plasma exchange. We previously determined in an unpublished study that the removal rate of rituximab was 81.9% with DFPP and 50.5% with plasma exchange. Based on these findings, we decided to administer rituximab 100 mg twice at 10 days and 1 day before transplant following plasma exchange. In the rituximab group, 12 of the 21 children had no plasma exchange procedure pretransplant and thus may have maintained higher serum rituximab levels. The procedure of plasma exchange itself, including insertion of a blood access catheter and even immunoadsorption, poses a great risk and burden for children with peritoneal dialysis. However, ADAb-removal procedures such as DFPP, plasma exchange, and immunoadsorption are not more important than desensitization because these procedures never suppress the production ADAb but rather remove ADAb. Once AMR, including hyperacute rejection, occurs, ADAb production is accelerated by a complement-cascade reaction, and ADAb-removal procedures are not able to inhibit this reaction. Therefore, these procedures were excluded in 12 children with lower titers of ADAb (< ×64) in the rituximab group. Despite this, the 12 children had no clinical AMR.
The levels of CD19-positive and CD20-positive B cells remained depleted 3 months after transplant. Twenty of the 21 children had no rebound of the titer of ADAb posttransplant, and 1 patient had increased ADAb only to ×32. The cause of AMR was not ADAb against red blood cells but rather against the vascular endothelium in which the A or B blood group antigens are rich but are different from those in a red blood cell membrane.13 Therefore, rebound of the titer of ADAb posttransplant is likely due to an increase of antibodies against the vascular endothelium.
Suppression of ADAb in the rituximab group was significantly stronger than in the splenectomy group. However, there were no differences between groups in terms of the dose or timing of mycophenolate mofetil, steroids, and CNI except for rituximab dose. Therefore, 2 doses of rituximab seemed to improve B-cell depletion and ADAb suppression, thus lowering AMR incidence. Infection was controlled better in the rituximab group than in the splenectomy group. Lee and associates14 reported that standard-dose rituximab (375 mg/m2) was an independent risk factor for serious infections but had no relationship with rejection, renal function, graft survival, and patient survival compared with reduced-dose rituximab (200 mg). Incidence of CMV disease was much higher in the splenectomy group because antige-nemia monitoring was not strict and prophylactic use of valganciclovir was not adopted in the splenectomy group.
Late-onset neutropenia is a complication of rituximab, although it is curable with granulocyte colony-stimulating factor treatment. Two of the 21 children (9.5%) had late-onset neutropenia in this study, but this rate was much lower than shown in other studies.7,15 In addition, late-onset neutropenia did not induce serious bacterial or opportunistic infections in our pediatric patients. However, doctors and coordinators should note the recipients’ white blood cell counts in an outpatient transplant clinic.
Patient and graft survival rates in ABO-incompatible pediatric kidney transplant recipients were not different from those in ABO-compatible pediatric transplant recipients.16 In fact, only 1 of the 21 recipients died (of hypertrophic cardiomyopathy) but had a functioning graft; the remaining 20 children survived with a functioning graft.
Long-term dialysis is not a good option for children. Preemptive ABO-incompatible kidney transplant should be recom-mended as a first-line treatment for children with end-stage renal disease.
Two doses of rituximab are effective for B-cell depletion and for lowering the titer of ADAb in ABO-incompatible pediatric kidney transplant. In our study, there were no clinical AMR episodes, although protocol biopsies showed low incidence of subclinical AMR episodes. There were no serious complications, including infection, in the rituximab group posttransplant. Patient and graft survival outcomes were excellent. Antibody removal procedures in children with < ×64 ADAb are not necessary if 2 doses of rituximab are used for desensitization. This treatment is beneficial for children who receive preemptive ABO-incompatible kidney transplant and children on peritoneal dialysis without blood access.
Volume : 17
Issue : 1
Pages : 105 - 109
DOI : 10.6002/ect.MESOT2018.O43
From the 1Department of Nephrology and the 2Department of Pediatric Nephrology,
Toho University, Faculty of Medicine, Tokyo, Japan
Acknowledgements: The authors have no sources of funding for this study and have no conflicts of interest to declare. Yuko Hamasaki and Atsushi Aikawa collected and analyzed all data. Hideyo Oguchi and Ken Sakai studied pathologic findings of renal allograft biopsies. Other authors were clinically involved in pediatric kidney transplants.
Corresponding author: Atsushi Aikawa, Department of Nephrology, Toho University, Faculty of Medicine, 6-11-1, Omorinishi, Otaku, Tokyo 143-8541, Japan
Phone: +81 3 3762 4151
Figure 1. CD20-Positive B Cells in the Rituximab Group
Figure 2. CD19-Positive B Cells in the Rituximab Group
Figure 3. Maximum Titers of Antidonor Antibodies in the Splenectomy (A) and Rituximab (B) Groups
Table 1. Recipient and Donor Backgrounds in the Rituximab Group (N = 21)
Table 2. Recipient and Donor Backgrounds in the Splenectomy Group (N = 14)