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Keywords:

  • Antibody-mediated rejection;
  • clinical kidney transplantation;
  • donor-specific antibodies;
  • graft survival

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References

This study analyzes the influence of preformed DSA, identified by HLA-specific ELISA assays, on graft survival and evaluates the incidence of antibody-mediated rejection (AMR) in patients with and without pregraft desensitization.

Kidney graft survival at 8 years was significantly worse in patients with DSA (n = 43) than in those without DSA (n = 194)(p = 0.03). The incidence of AMR in patients with DSA is 9-fold higher than in patients without DSA (p < 0.001) and their graft survival is significantly worse than in DSA patients without AMR and in non-DSA patients (p = 0.005). The prevalence for AMR in patients with DSA detected on historic serum is 32.3% in nondesensitized patients and 41.7% in desensitized patients. The risk for AMR is significantly more elevated in patients with strongly positive DSA (score 6–8) compared to those with DSA score 4 (p < 0.001), and in patients with historic DSA+/CXM+ compared to those with DSA+/CXM− (p = 0.01).

The presence of preformed DSA is strongly associated with graft loss in kidney transplants, related to an increased risk of AMR. Our findings demonstrate the importance of detection and characterization of DSA before transplantation. Stratification of this risk could be used to determine kidney allocation and to devise specific strategies for these patients.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References

Patel and Terasaki first reported 38 years ago that the presence of recipient antibodies to antigens expressed on donor white cells was a major risk factor for immediate graft loss (1). Their finding, confirmed in many subsequent studies, was so compelling that even now the evaluation of immunologic risk for graft recipients and the decisions regarding allocation of renal grafts is based on lymphocytotoxicity assays. Patients awaiting renal transplantation are routinely tested for lymphocytotoxic panel-reactive antibodies (PRA), and graft allocation depends on the current T- and B-cell complement-dependent cytotoxicity (CDC) crossmatches. Much effort has been spent on increasing the sensitivity of the crossmatch assay such that weak anti-HLA sensitization can be detected (2,3), and new techniques for pretransplant antibody testing based on highly sensitive, strictly HLA-specific ELISAs have been developed (4,5). But up to now, no study has permitted evaluation of the clinical impact of donor-specific antibodies against HLA antigens (DSA) identified before transplantation by sensitive techniques. In an earlier study, we showed that 71.4% of patients who developed acute antibody-mediated rejection (AMR) presented DSA pretransplantation, as identified by ELISA (6). Other recent studies suggest that preformed DSA levels at the time of transplantation are clinically important and should be below the threshold of detection of low-level DSA for better outcomes (7).

To investigate the clinical relevance of DSA identified by highly sensitive, strictly HLA-specific assays, we retrospectively screened all renal transplant recipients by high-definition ELISA for their presence. Our graft strategy was the current worldwide strategy based on pretransplant antibody testing by complement-dependent lymphocytotoxicity assay. This study analyses the influence of pretransplant DSA status on transplant outcome and evaluates the predictive value for AMR of preformed DSA detected in a population of graft recipients desensitized prior to transplantation and in those without pregraft conditioning.

Patients and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References

Study design

A total of 237 consecutive ABO-compatible renal transplants (94 F, 143 M) were performed between 1998 and 2004 in our hospital, including 16 living donors (6.8%) and 221 deceased donors. A negative current T- and B-cell CDC crossmatches (CDCXM) was required for all kidney transplant recipients. To identify patients who might have preformed HLA DSA, not identified by routine lymphocytotoxicity assays, we retrospectively screened, by HLA-specific ELISAs, all kidney transplant recipients for the presence of DSA in historic sera and in that at the time of transplantation (D0). Based on the results of the screening of preformed DSA, patients were divided into two groups: (i) patients with DSA and (ii) patients with no DSA.

We analyzed the occurrence of rejection episodes and we compared the graft survival rates between the two groups. All data up through December 2006 were included, with a median follow-up of 46.5 ± 24.7 months (3–105 months) for the entire population of transplant patients.

Clinical protocols

Immunosuppression protocols were defined according to the immunologic risk, determined by the current system using lymphocytotoxic PRA and T- and B-cell based assays. Based on their pregraft conditioning, kidney recipients were divided into (i) patients without any pregraft conditioning (nondesensitized patients, n = 219) and (ii) desensitized patients (n = 18).

Patients without pregraft conditioning received classic protocols with induction therapy consisting of a polyclonal anti-T-lymphocyte globulin (Thymoglobuline, Genzyme) in 94.6% of cases or daclizumab (Zenapax®) in 5.4% of cases. Their maintenance immunosuppression consisted of tacrolimus (Prograf®, Astellas, Levallois-Perret, France) or cyclosporine (Neoral®, Novartis, Rueil-Malmaison, France), mycophenolate-mofetil (MMF) (CellCept®, Roche, Neuilly-sur-Seine, France) and steroids. Patients with remote positive IgG T- and B-cell crossmatches (CXM) received IVIg at the time of transplantation as prophylaxis against acute rejection (2 g/kg days 0–1, 20–21 and 40–41).

Desensitized patients had a PRA of the IgG class directed against HLA class I molecules equal to or greater than 50%. These patients received three courses of IVIg (Baxter Gammagard, Baxter, Belgium) at 4-week intervals, each course consisting of 2 g/kg of IVIg given over 48 h, according to a previously described protocol (8,9). Desensitization was considered a success if the level of antibodies fell by at least 50% and the patients were then transplanted with the first available ABO-matched kidney giving an IgG T-cell negative CXM with the post-IVIg serum. The immunosuppressive regimen at time of transplantation consisted of IVIg (2 g/kg days 0–1, 20–21 and 40–41), mycophenolate mofetil (2 g daily), steroids and thymoglobuline for 10 days at 1–1.5 mg/kg/day followed by tacrolimus.

Diagnosis and treatment of rejection

All rejection episodes were biopsy proven. Biopsy specimens were evaluated by light microscopy and immunofluorescence (C4d and immunoglobulins). Findings were graded according to the Banff 97 classification (10). For C4d detection, we used a two-step indirect immunofluorescence method with a monoclonal antibody specific for complement fragment C4d on frozen tissue (Quidel, Santa Clara, CA). Biopsies were considered positive for C4d (C4d+) when the peritubular capillaries (PTCs) stained diffusely and brightly linearly, excluding areas of necrosis. For all patients having acute rejection on graft biopsy, posttransplant DSA (at the time of biopsy) were evaluated by specific ELISA techniques (as described above).

Among the patients with clinical acute graft dysfunction, 21 patients (15 M, 6 F) had episodes of AMR, and 11 patients (7 M, 4 F) episodes of ACR. All AMR patients had characteristic histologic lesions of AMR (11), as described in a previous study (6) and positive C4d staining.

Patients with AMR were treated with specific protocols for antibody removal, a combination of steroid boluses, IVIg (2g/kg, monthly × 4 doses), associated with plasma exchange or muromonab-CD3 (OKT3®). Patients with ACR were treated by three steroid pulses (3 × 500 mg i.v.).

Screening algorithm for HLA antibodies

All pretransplant sera were screened by ELISA assays (LAT-M, One Lambda, Canoga Park, CA) to determine the presence or absence of anti-HLA class I or class II antibodies of the IgG isotype. Anti-HLA class I antibodies were then identified by complement-dependent cytotoxicity (CDC) on frozen cell tray of 30 selected HLA-typed lymphocytes (Serasreen FCT30 Frozen Cell Trays, Gen Trak, Liberty, NC). The presence of anti-HLA IgM antibodies was excluded by testing in the presence of DTT. Panel reactive antibodies (PRA) of the IgG class directed against HLA class I molecules were calculated from this CDC assay.

We retrospectively screened by HLA-specific ELISA assays all kidney transplant recipients for the presence of DSA in peak sera and in D0 sera. Identification of anti-HLA class I antibodies specificities were done using a high-definition (HD) single-antigen, ELISA (LAT-1HD, One Lambda), which uses 88 different HLA A and B alleles produced by recombinant technology. Antibodies are defined by a score of 4, 6 or 8 reactivity. For anti-HLA class II antibodies we performed an ELISA (LAT 2–40, One Lambda) test, which identified DR and DQ subtypes on a panel of purified HLA antigens. Both ELISA tests were performed as recommended by the manufacturer. All anti-HLA antibody testing was performed on nonpreabsorbed sera, drawn before the administration of Thymoglobuline or IVIg.

HLA typing of transplant recipients was performed by molecular biology (Innolipa HLA typing kit, Innogenetics, Belgium). For all kidney transplant donors, HLA A, B, DR and DQ tissue-typing was performed using the microlymphocytotoxicity technique with One Lambda INC tissue-typing trays and was controlled by molecular biology.

Criteria for accepting a donor: crossmatch techniques and interpretation

Crossmatches were performed by complement-dependent cytotoxicity (CDCXM) and T-cell antiglobulin-enhanced complement-dependent cytotoxicity (AHG-CDCXM) on lymph node and by CDC on separated B-lymphocytes or spleen cells, according to National Institutes of Health recommendations. Peak and current sera were tested according to EFI standards. Sera were tested both diluted and undiluted, with and without DTT. A current positive IgG T-Cell CDCXM was a contraindication to transplantation. A current positive AHG-CDCXM, negative IgG T-Cell CDCXM was not considered as a contraindication, but an immunosuppressive protocol using IVIg was used. CXMs positive only for IgM did not prevent transplantation. A current B-Cell positive CXM, in a patient whose current serum was positive for anti-HLA class II antibodies, was considered a contraindication to transplantation.

Statistical analysis

For categorical data, Fisher's exact test or Pearson's chi-square test was used. Kaplan–Meyer survival estimates were calculated for death or graft loss (dialysis) whichever came first. Survival curves were compared between patients with and without DSA using the Gehan–Wilcoxon test.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References

Pretransplant HLA antibodies in kidney transplant recipients

Historic (Peak) sera:  Among the 219 recipients who did not receive pregraft conditioning, 60 patients (27.4%) had antibodies against class I or class II HLA on historic sera: 19 patients (8.7%) with anti-HLA class I; 8 patients (3.7%) with anti-HLA class II and 33 patients (15.1%) with both anti-HLA class I + class II. In 51.7% (31/60 patients), these anti-HLA antibodies had anti-donor specificity (Table 1). The DSA identified on peak sera (peak DSA) had a score of 6–8 in 13 patients (42%), with DSA of score 4 in 18 patients (58%). Eleven patients (35.5%) had a remote positive CXM (4 pts with IgG T-cell CDCXM, 2 pts with B-cell CXM, and 5 pts with IgG T- and B-cell CXM of which 3 CDCXM and 2 AHG-CDCXM).

Table 1.  Relationship of pretransplant anti-HLA antibody status to AMR occurrence in kidney transplant recipients
 No pregraft conditioning (N = 219)Desensitized pretransplantation (N = 18)Total population (N = 237)
NAMR+ N%NAMR+ N%NAMR+ N%
  1. N = number of patients; %= percent; AMR = acute antibody-mediated rejection; DSA = anti-HLA donor-specific antibodies.

Peak serum
 No DSA188 6 (3.2)60194 6 (3.1)
 HLA-Ab class I and/or class II (ELISA)6013 (21.7)18 5 (27.8)7831 (39.7)
 DSA class I and/or class II (sc4–8)3110 (32.3)12 5 (41.7)4315 (34.9)
 DSA class I and/or class II (sc6–8)139 (69.2)10 5 (50)2314 (60.9)
 DSA class I and/or class II (sc 4)181 (5.6)20201 (5.0)
 HLA-Ab class I (± class II) (ELISA)5212 (23)18 5 (27.8)7017 (24.3)
 DSA class I (± class II) (sc4–8)258 (32)11 5 (45.5)3613 (36.1)
 DSA class I (± class II) (sc6–8) 97 (77.8)85 (62.5)1712 (70.6)
 DSA class I (± class II) (sc 4)161 (6.3)61 (16.7)222 (9.1)
 HLA-Ab class II (± class I) (ELISA)418 (19.5)16 5 (31.3)5713 (22.8)
 DSA class II (± class I) (sc4–8)115 (45.5)64 (66.7)179 (52.9)
 DSA class II (± class I) (sc6–8) 85 (62.5)64 (66.7)149 (64.3)
 DSA class II (± class I) (sc 4) 300030
D0 serum
 DSA class I and/or class II (sc4–8)155 (33.3)74 (57.1)229 (40.9)
 DSA class I and/or class II (sc6–8) 64 (66.7)54 (80)118 (72.7)
 DSA class I and/or class II (sc4) 91 (11.1)20111 (9.1)
 DSA class I (± class II) (sc4–8)112 (18.2)74 (57.1)186 (33.3)
 DSA class I (± class II) (sc6–8) 31 (33.3)54 (80) 85 (62.5)
 DSA class I (± class II) (sc4) 81 (12.5)20101 (10)
 DSA class II (± class I) (sc4–8) 43 (75)21 (50) 64 (66.7)
 DSA class II (± class I) (sc6–8) 33 (100)11 (100) 44 (100)
 DSA class II (± class I) (sc4) 1010 20

In the desensitized group of 18 patients, 12 patients (66.7%) had peak DSA (Table 1), 10 patients with DSA of score 6–8 and 2 patients of score 4. Six patients (33.3%) had a remote positive CXM (4 pts with IgG T-cell CDCXM, 1 pt with IgG T-cell AHG-CDCXM and 1 pt with IgG T- and B-cell CDCXM).

Current (D0) serum:  In the nondesensitized group, 15 patients (6.8%) showed DSA at the time of transplant (11 with DSA class I and 4 with DSA class II) (Table 1), with score 4 predominating (9/15 patients). All of the current IgG T- and B-cell CDCXM were negative. A single patient was transplanted with a current positive IgG T-cell AHG-CDCXM.

Among the desensitized patients, 7/18 (38.9%) had DSA at the time of transplant (Table 1). In 5/7 patients, the DSA identified at D0 were score 6–8. Two patients were transplanted with a current positive IgG T-cell AHG-CDCXM.

Pretransplant DSA in patients with acute AMR

Table 2 shows the evaluation of pretransplant DSA in the 21 patients with AMR. Retrospective studies for pretransplant DSA on the peak sera were positive in 71.4% (15/21 patients). In six patients with historic negative CXM, we identified pretransplant peak class I DSA by high-definition ELISA. Nine of 21 patients (42.9%) had a historic positive IgG T- or B-cell CXM. In 9 patients the DSA identified on the peak serum persisted at the time of the graft. Three patients had a current positive AHG-CDC CXM.

Table 2.  Pretransplant evaluation of DSA in patients with AMR
GroupSexDays to AMRSensitization historyPeak PRA (%)Remote CXMD0 CXMDSA peak serumDSA D0Functional graft (end of follow-up)
DSA class IDSA class IIDSA class IDSA class II
  1. RG = renal graft; BT = blood transfusion; P = pregnancy; M = male; F = female; IVIg = intravenous immunoglobulins; Ig = immunoglobulins; CDC = complement dependent cytotoxicity; AHG = antiglobulin-enhanced CDC crossmatch; Sc4 or Sc6–8 = score reactivity of antibody specificity; GF = graft failure.

  2. Desensitized = patients undergoing desensitization by IVIg before transplant.

DesensitizedM 9RG + BT95+ IgGT/CDCIgGT/AHGSc6–8Sc6–8Sc6–8Yes
M50RG93Sc6–8Sc6–8Yes
M 9RG + BT93+ IgGT/CDCSc6–8Sc6–8Sc6–8GF
M96BT90+ IgGT/AHGIgGT/AHGSc6–8Sc6–8Yes
M 9RG80+ IgGT/CDCSc6–8Sc6–8Sc6–8Sc6–8GF
NondesensitizedM18RG (2)90+ IgGT/AHGIgGT/AHGSc6–8Sc6–8Sc6–8GF
F16RG + P (3)88+ IgGT/CDCSc6–8Yes
F 7RG + BT85Sc4Sc4Yes
M51RG (2) + BT80+ IgGT/CDCSc6–8Yes
M10RG + BT66+ IgMT/CDCSc6–8Sc6–8Sc6–8Yes
F 3RG + BT + P (4)13+ IgGB/CDCSc6–8Sc6–8GF
M13RG36Sc6–8Yes
M11RG30+ IgGTB/CDCSc6–8Sc6–8Sc6–8GF
F34BT40Sc6–8Sc6–8GF
M15RG + BT17Yes
F58BT + P (3) 7Sc6–8Yes
M840BT 5Yes
F 8BT + P 0Yes
M57ND 0Yes
M730 BT 0-Yes
M1750    0-Yes

Course of patients with pretransplant DSA

Kidney graft survival was significantly worse in patients with preformed DSA than in those without DSA, with survivals at 8 years of 67.9% in patients with DSA and 77.3% in those with no DSA (p = 0.03) (Figure 1). This difference in graft survival appears to be uniquely due to occurrence of AMR in the DSA group, with 8-year survivals of 43.6% versus identical survivals for DSA patients without AMR (78.5%) and non-DSA patients (77.3%) (p < 0.001) (Figure 2). No graft loss related to an AMR episode was noted in the non-DSA group.

image

Figure 1. Eight-year grafts survival analysis of kidney transplants in relation to DSA status.

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image

Figure 2. Eight-year grafts survival analysis of kidney transplants according to DSA status and the occurrence of acute antibody-mediated rejection (AMR).

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The incidence of AMR among patients with preformed DSA was 34.9%, 9-fold higher than in patients without DSA (3.1%) (p < 0.00001). The incidence of ACR was not significantly different between the two groups (p = 0.23). In 18 of 21 patients (85.7%), AMR occurred shortly posttransplant, with a median onset of 16 days (range: 3–42 days). In three patients AMR was recognized late at 24, 28 and 58 months.

The prevalence of acute AMR in patients with pretransplant DSA

The presence of DSA (score 4–6–8) on historic serum had a prevalence of AMR of 32.3% in nondesensitized patients and of 41.7% in desensitized patients (Se 100%, Sp 46.2%). The prevalence of AMR in desensitized patients with peak DSA was not significantly different from that of nondesensitized patients (p = 0.8). The risk of AMR occurrence was significantly higher in anti-HLA positive/DSA positive patients than those who are anti-HLA positive/DSA negative (p = 0.01).

There was no significant difference between the prevalence of AMR in patients with peak DSA of class I versus those with class II (p = 0.75).

The distribution of pretransplant DSA and their relation to the development of AMR in desensitized and nondesensitized patients are showed in Table 1.

The significance of DSA strength:  The risk of AMR occurrence was significantly more elevated in patients with peak DSA scores 6–8 compared to those with peak DSA scores 4 (p < 0.001). In nondesensitized patients, the prevalence of AMR in patients with peak DSA scores 6–8 increased to 69.2% but was only 5.6% for score 4. In desensitized patients, the prevalence for AMR was 50% for strongly positive peak DSA (score 6–8). There was no significant difference in the incidence of AMR between those patients without DSA (3.1%) and those with DSA score 4 (5%) (p = 0.065).

The significance of the association DSA/CXM:  A total of 32.6% of the patients with DSA-identified pregraft had a remote positive IgG T- or B-cell CXM (52.2% of patients with peak DSA scores 6–8 and 10% of patients with peak DSA scores of 4). The relationships between peak or D0 DSA, the presence of historic positive CXM and AMR occurrence is shown in Table 3. The presence of peak complement-fixing DSA increased significantly the risk of AMR (peak DSA+/CXM+ vs. peak DSA+/CXM−, p = 0.01).

Table 3.  Pretransplant DSA, CXM status and AMR occurrence in the population of kidney transplant recipients
 CXM+CXM-
NAMR N (%)NAMR N (%)
  1. Peak DSA = donor-specific antibody identified on the peak serum; D0 DSA = donor-specific antibody identified on current serum; CXM = remote IgG T- or B-cell crossmatch; AMR = antibody-mediated rejection; N (%) = number and percent of patients.

Peak DSA+ (sc4–8)149 (64.3) 29 6 (20.7)
Peak DSA+ (sc6–8)129 (75)   11 6 (54.5)
No peak DSA 3 01916 (3.1)
D0 DSA+ (sc4–8) 76 (85.7) 153 (20) 
D0 DSA+ (sc6–8) 76 (85.7)  42 (50) 
No D0 DSA103 (30)  2159 (4.2)

In nondesensitized patients, the prevalence of AMR in patients with peak DSA (score 4–6–8) associated with a remote positive CXM (peak DSA+/CXM+) was 62.5%. This increased to 83.3% for strongly positive peak DSA (score 6–8)/CXM+. The high PPV for strongly positive peak DSA (score 6–8) was not greatly weakened by a negative CXM, the combination peak DSA+ (score 6–8)/CXM− having a PPV of 57.1%.

In desensitized patients, the prevalence of AMR in patients with peak DSA (score 6–8) with positive CXM was 66.7% and 25% with negative CXM.

The significance of D0 DSA:  The detection of D0 DSA in patients with prior positive DSA identified on historic sera did not confer an additional risk of humoral rejection (p = 0.33). In nondesensitized patients, 5 of 23 patients presented an episode of AMR despite disappearance of peak DSA at D0. None of the three patients with DSA identified only at D0-manifested AMR. In desensitized patients, AMR occurred in one of five patients in whom peak DSA disappeared at D0.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References

This study shows a highly significant association between the presence of DSA-detected pretransplant and the incidence of AMR, responsible for a diminution of graft survival. The importance of pretransplant DSA is only now being recognized, for historic reasons. Due to a series of studies in the 1980s (12–16) which failed to show evident diminution of survivals in patients transplanted with current negative but historic positive CDC T-cell crossmatches, the concept of graft allocation exclusively on the basis of current crossmatch was established. It was, in fact, the basis for graft allocation in our large cohort of nonselected renal transplant patients, using the traditional direct cytotoxicity assay (‘standard crossmatch’) and AHG-CDC crossmatch, with a negative current T- and B-cell crossmatch required as well. However, absence of proof is not proof of absence, and Gebel et al., later analyzing the literature on the role of preformed DSA, found the question unresolved because of nonhomogeneity of the crossmatch techniques utilized and lack of documentation of relations between the crossmatch, DSA and the course (16).

In our study, 18.1% of transplanted patients had evidence of DSA before the graft. Among them, 15 (34.9%) had an episode of AMR during their evolution, a 9-fold increase over DSA-negative patients. We found no difference in the incidence of AMR between class I and class II, taking into account the fact that the technique for detection of anti-HLA class II used here may have possibly underestimated the number of examples of DSA class II positivity. These results thus confirm the recent results of Pollinger et al. (17) and emphasize the importance of the detection of DSA class II by solid phase single HLA antigen assays. Technical limitations and the use of B-cell CXM as a ‘surrogate’ for the detection of class II DSA (16,18,19) had made the interpretation of the importance of antibodies against class II HLA confusing. Our results justify the close posttransplant surveillance of patients presenting class II DSA pregraft, in the same fashion as those with class I DSA. The risk of AMR was largely confined to patients with high (score 6–8) titers of DSA. Only 1/20 patients (5%) with a low (score 4) titer had AMR (this without loss of the graft). This incidence is comparable to that of patients without DSA, 3.1% (p = 0.75).

This study demonstrates the clinical significance of pregraft DSAs identified by the new techniques of HLA-specific ELISA assay. In our study, the predictive value of pregraft DSAs identified by ELISA with a negative historic crossmatch is 57.1% for high-titer (score 6–8) DSA, rising to 83.3% if these are associated with a historic positive CXM. For this population (DSA score 6–8 +/CXM+), the incidence of AMR remains quite high despite the posttransplant administration of prophylactic IVIg reported as efficacious for mid-term survivals in patients considered at immunologic risk (20). The stratification of immunologic risk will thus permit evaluation of other therapeutic strategies for these patients (transplantation with permitted antigens, anti-CD20 antibodies etc.). Similarly, it has been shown recently that patients with pretransplant HLA antibodies detected only by flow microparticles have a significantly higher risk of graft loss due to AMR than patients without detectable antibodies (21). Up to this point several studies have shown 15–35% discordance between crossmatches negative by various techniques and flow positive crossmatches (22–25). Moreover, recently Patel et al. have demonstrated in a cohort of 60 living donor renal transplant recipients that the presence of pretransplant DSA is associated with a significant rise in the incidence of AMR, despite negative pretransplant cytotoxicity testing and FCXMs (26). These data would suggest that in vitro CDC assays do not detect all relevant complement-fixing antibodies. Even if their presence is not a contraindication to transplantation, the DSA-identified pregraft uniquely by sensitive techniques and lacking cytotoxicity in vitro represent a significant risk factor, especially if they are present in high titer. They should thus be integrated into the decision algorithms for immunosuppressive treatment in patients at immunologic risk.

Our study underlines the clinical significance of HLA antibodies detected only on historic sera, overriding the importance of D0 sera, since no patient with AMR had DSA at D0 without prior DSA. It would appear that renal transplant recipients with a negative AHG-CDC crossmatch but a positive ELISA, possess an immunologic memory for donor antigens increasing the risk of both early graft loss and of suboptimal long-term outcomes as well (27). Another study has also reported early graft loss in patients with current negative but historic positive CDCCXM in whom flow cytometric approaches did not demonstrate DSA on current sera (21).

Desensitization protocols have been developed to allow successful kidney transplantation in sensitized recipients (8,28–33). Here we employed a desensitization protocol using high-dose IVIg (9,32,33). Recently, Stegall et al. (7) have compared three different techniques of desensitization: (i) plasmapheresis, low-dose IVIg, anti-CD20 antibody; (ii) a single infusion of high-dose IVIg and (iii) plasmapheresis, low-dose IVIg, anti-CD20 antibody and pretransplant Thymoglobulin combined with posttransplant DSA plasmapheresis. The three techniques diminish to varying degrees the DSA levels, as reflected by negatization of the CXM (84%, 38% and 88%, respectively). But even when the crossmatch became negative, rejection rates were 80% (IVIg), 37% (PP) and 29% (PP-monitoring). These desensitization techniques are efficacious and render transplantation possible in sensitized allograft recipients, but are not capable of preventing the appearance of humoral rejection. We found similar proportions of nondesensitized patients (37.5%) and desensitized patients (42.9%), who had disappearance of DSA at day 0, nonetheless had an episode of AMR.

This study demonstrates the importance of identifying and characterizing the strength of pregraft DSA by sensitive techniques, as well as their association to a remote positive crossmatch. The recognition of pregraft DSA identifies a group with a 9-fold increased risk of AMR. Since in the absence of AMR, graft survival of DSA-positive patients is the same as DSA-negative patients, it is to be hoped that vigilant monitoring will permit early identification and treatment of AMR.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. References
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