Marian D. Witvliet

The Dutch national living donor kidney exchange program

The wait time for deceased‐donor kidney transplantation has increased to 4–5 years in the Netherlands. Strategies to expand the donor pool include a living donor kidney exchange program. This makes it possible that patients who cannot directly receive a kidney from their intended living donor, due to ABO blood type incompatibility or a positive cross match, exchange donors in order to receive a compatible kidney. All Dutch kidney transplantation centers agreed on a common protocol. An independent organization is responsible for the allocation, cross matches are centrally performed and exchange takes place on an anonymous basis. Donors travel to the recipient centers. Surgical procedures are scheduled simultaneously. Sixty pairs participated within 1 year. For 9 of 29 ABO blood type incompatible and 17 of 31 cross match positive combinations, a compatible pair was found. Five times a cross match positive couple was matched to a blood type incompatible one, where the recipients were of blood type O. The living donor kidney exchange program is a successful approach that does not harm any of the candidates on the deceased donor kidney waitlist. For optimal results, both ABO blood type incompatible and cross match positive pairs should participate.

Hurdles, barriers, and successes of a national living donor kidney exchange program.

Background. Living donor kidney exchange is now performed in several countries. However, no information is available on the practical problems inherent to these programs. Here, we describe our experiences with 276 couples enrolled in the Dutch program. Methods. Our protocol consists of five steps: registration, computerized matching, crossmatching, donor acceptation, and transplantation. We prospectively collected data of each step of the procedure. Results. Of the 276 registered pairs we created 183 computer-matched combinations. However, 62 of 183 recipients proved to have a positive crossmatch with their new donor, which was not predicted by the screening results of the recipient centers. Alternative solutions were found for 39 couples, resulting in a total of 160 new combinations with negative crossmatches. Thereafter, because of 22 individual clinical problems, the exchange procedure had to be discontinued for 51 couples while only for 19 of them alternative solutions were found. At the end of day, 128 patients had received exchange kidneys, 55 were transplanted outside the program, 59 are still on the crossover waitlist, and 34 had left the program for medical or psychological reasons. Conclusion. A living donor kidney exchange program is a dynamic process. Many clinical hurdles and barriers are encountered that for a large part were not foreseen but should be taken into account when programs are initiated based on computer simulations. Success is dependent on a flexible organization able to create alternative solutions when problems arise. Centralized allocation and crossmatch procedures are instrumental in this respect.

A highly efficient living donor kidney exchange program for both blood type and crossmatch incompatible donor-recipient combinations

Background. Lack of deceased donors for kidney transplant patients in the Netherlands encouraged alternative options to expand the living donor pool for recipients who have a willing donor but cannot donate directly because of a positive crossmatch or ABO blood type incompatibility. A national donor kidney exchange was considered as a possible solution. Methods. From January 2004 until June 2006, 146 couples from seven kidney transplantation centers were enrolled and participated in 10 match procedures. The Dutch Transplant Foundation was responsible for the allocation and the National Reference Laboratory for Histocompatibility in Leiden performed all the serological crossmatches. Results. For 72 out of the 146 (49%) donor-recipient combinations, a match was found. The success rate in the positive crossmatch group was significantly (P=0.0015) higher than in the ABO-incompatible group (44/69 vs. 28/77); median panel reactive antibodies of the matched recipients in the positive crossmatch group was 38% (0–100) and in the ABO-incompatible group 0% (0–27; P<0.001). We were least successful for ABO blood type incompatible pairs with blood type O recipients, but for 9/53 (17%) there were possibilities. These nine blood type incompatible pairs were coupled to nine positive crossmatch pairs, which reflects the efficiency of combining the two categories of donor-recipient combinations into one program. Conclusion. The donor kidney exchange program in the Netherlands, in which all seven kidney transplantation centers participated, proved to be a successful program to expand the number of living donor kidney transplantations.

The presence of HLA-antibodies in recurrent miscarriage patients is associated with a reduced chance of a live birth

Anti-paternal HLA-antibodies are considered a harmless phenomenon during most pregnancies, whereas their role in recurrent miscarriage (RM) patients is disputed. In contrast to primary RM, patients with secondary RM have carried a fetus to term pregnancy prior to a series of miscarriages, which increases the chance that allogeneic fetal cells appear in the maternal circulation. This study investigates the frequency of HLA-antibodies in secondary RM, primary RM patients and parous controls and analyzes whether the presence of HLA-antibodies in early pregnancy is associated with pregnancy outcome. Sera from women with secondary RM (n=56), primary RM (n=13) and parous controls (n=24) were tested for HLA-antibodies using an ELISA assay and complement dependent cytotoxicity. Samples were taken at gestational week 4-5 in 62 (90%) of the patients. HLA-antibodies were significantly more frequent in secondary RM patients with a boy prior to the miscarriages (62%) compared to secondary RM patients with a firstborn girl (29%, p=0.03), primary RM patients (23%, p=0.02) and parous controls (25%, p=0.005). Forty-one percent of HLA-antibody positive pregnant RM patients had a live birth compared to 76% of HLA-antibody negative RM patients, p=0.006 (adjusted OR: 0.22 (0.07-0.68), p=0.008). In conclusion, HLA-antibodies are significantly more frequent in secondary RM patients with a firstborn boy than in other RM patients and controls. The presence of these antibodies in early pregnancy is associated with a reduced chance of a live birth. Further exploring this association may increase our understanding of maternal acceptance of the fetal allograft.

A broad and strong humoral immune response to donor HLA after implantation of cryopreserved human heart valve allografts

Cryopreserved human heart valves are used for valve replacement in patients with congenital or acquired heart disease. Although no blood group or human leukocyte antigens (HLA) matching is performed and no immunosuppression is administered, the clinical results are relatively good. After valve replacement, the majority of the patients develop HLA antibodies, whereas a smaller group of patients shows valve-related events at the long term after right ventricular outflow tract reconstruction. Therefore, we hypothesized that not the mere presence, but rather the titers of antidonor HLA antibodies may be related to valve allograft failure. The presence and specificity of HLA class I antibodies were determined by complement-dependent microlymphocytotoxicity (CDC) test in longitudinally taken peripheral blood samples of 35 valve allograft recipients. In eight patients with an antibody response specific against donor-HLA class I, the titers were measured by this CDC method after stepwise dilution of the plasma. Panel reactive antibodies of more than 10% were found in 31 of 35 (89%) valve allograft recipients. From these 31 patients, 24 (77%) developed donor-specific HLA class I antibodies. All eight selected patients had detectable donor-specific antibody titers, ranging from 1:2 to 1:8,000. Two donor valve recipients before retransplantation had (donor-specific) HLA antibodies and showed high titers of 1:256 and 1:8,000 shortly after the second allograft valve replacement, which was associated with an early graft failure in the latter patient. We conclude that transplantation of cryopreserved human heart valve allografts leads to a broad and strong humoral response, which is probably the result of a lack of immunosuppressive therapy after valve transplantation. Patients receiving a second or following valve allograft appeared to be sensitized and developed early and high allo-antibody titers after second valve allograft implantation. Valve failure was diagnosed in a patient with extremely high titers. These findings suggest that preoperative cross-matching may identify patients with high donor-specific HLA antibody titers and may reduce the risk for early recurrent graft failure.

The 25th anniversary of the Eurotransplant Acceptable Mismatch program for highly sensitized patients

In 2014, the Eurotransplant Acceptable Mismatch (AM) program celebrated its 25th anniversary. The AM program was initiated to enhance transplantation of highly sensitized patients awaiting a renal transplant within the Eurotransplant region. Unlike the regular renal transplant allocation, in which the histocompatibility parameters consist of the degree of compatibility with the patients human leucocyte antigen (HLA) type and the absence of unacceptable antigens, the AM program is based on compatibility of the possible donor with the combination of the patients HLA type and the acceptable antigens. These acceptable antigens are defined as HLA antigens to which the patient has never made antibodies. This strategy aims at the prediction of a negative cross match. Since the start of the program almost 2000 patients participated and more than 1000 patients were transplanted with excellent transplant outcome, comparable to that of non-immunized transplant recipients within Eurotransplant. Progressive insights have led to fine-tuning of the AM program through the years, as well as to novel initiatives, including a recent consortium study to determine the feasibility of a Europe-wide AM program. The current review will tell the story of the AM program in a historical perspective, but will also provide an open-minded look into the future of transplanting highly sensitized patients.

Differential immunogenicity of paternal HLA Class I antigens in pregnant women

More insight into the differential immunogenicity of human leukocyte antigen (HLA) mismatches will be beneficial for donor selection in clinical transplantation. In this study the immunogenicity of HLA antigens was analyzed by examining the antibody profiles in women who have been pregnant. In total 888 women, who had pregnancy induced HLA alloantibodies, were included in this study, while 413 women who had not been immunized by their pregnancy, served as controls. First it was analyzed whether women expressing particular HLA antigens are more likely to produce HLA alloantibodies. Next we determined whether certain HLA mismatches of their children are more immunogenic than other ones. Finally we studied whether the immunogenicity of specific HLA mismatches is dependent on the HLA phenotype of the women. Women expressing HLA-A3, HLA-A32, and HLA-B21 are more likely to produce alloantibodies whereas women expressing HLA-B13 and HLA-B17 have a significantly lower incidence of alloantibodies compared with women expressing other HLA antigens. Children with HLA-A2 or HLA-B5 mismatches induced alloantibodies significantly more often whereas children with HLA-A30, -A31 or -A33 and HLA-A28 induced alloantibodies significantly less often than children with other HLA class I mismatches. Finally we could demonstrate that the immunogenicity of a particular HLA mismatch is dependent on the HLA phenotype of the women. Information on the differential immunogenicity of HLA mismatches may be of benefit for the determination of acceptable and taboo mismatches in the case of donor selection for (highly sensitized) patients.

The optimal chain length for kidney paired exchanges: an analysis of the Dutch program

Living donor kidney exchange programs offer incompatible donor–recipient pairs the opportunity to be transplanted. To increase the number of these transplants, we examined in our actual donor–recipient couples how to reach the maximum number of matches by using different chain lengths. We performed 20 match procedures in which we constructed four different chain lengths: two, up to three, up to four and unlimited. The actual inflow and outflow of donor–recipient couples for each run were taken into consideration in this analysis. The total number of matched pairs increased from 148 pairs for only two‐way exchanges to 168 for three‐way exchanges. When a chain length of 4 was allowed five extra couples could be matched over a period of 5 years. Unlimited chain length did not significantly affect the results. The optimal chain length for living donor kidney exchange programs is 3. Longer chains with their inherent logistic burden do not lead to significantly more transplants.

Formation of donor-specific human leukocyte antigen antibodies after kidney transplantation: Correlation with acute rejection and tapering of immunosuppression

Background. Before kidney transplantation, a serological crossmatch is routinely performed between donor and recipient to prevent hyperacute rejection by donor-specific anti-human leukocyte antigen (HLA) antibodies. After transplantation, the presence of these antibodies is not routinely monitored. We wanted to know whether donor-specific anti-HLA antibodies are detectable during acute rejection (AR), before or after reduction of immunosuppression in kidney transplant recipients who were converted from cyclosporine A (CsA) to the less nephrotoxic azathioprine (AZA) or mycophenolate mofetil (MMF) at 1 year after transplantation. Methods. Plasma samples were collected before transplantation, at several time points after transplantation, and during AR. Antibodies were measured in 29 patients: 5 patients with AR during the first year after transplantation (before conversion), 14 patients with AR after conversion or dose-reduction of AZA or MMF, and a control group of 10 patients without AR during a follow-up of 2 years (1 year before and 1 year after conversion of immunosuppression). Antibodies were measured by complement-dependent cytotoxicity assay, enzyme-linked immunosorbent assay (ELISA), and flow-cytometry in a crossmatch with donor spleen cells. Results. Donor-specific antibodies were not detectable after transplantation in the control group without AR, nor in patients with AR shortly after transplantation during CsA therapy. After conversion from CsA to AZA or MMF, antibodies appeared only in one patient after graft failure followed by transplantectomy and in patients during AR on AZA but not on MMF therapy. Conclusion. In this patient group, we could not detect donor-specific antibodies during CsA treatment, not even at the time of AR using three different techniques. Donor-specific antibodies were primarily present during AR in patients converted from CsA to AZA and were not found in the sera from patients converted to MMF.

Kidney allocation based on proven acceptable antigens results in superior graft survival in highly sensitized patients

Highly sensitized renal transplant candidates accumulate on transplant waiting lists since they produce antibodies to many HLA antigens, which in this way become unacceptable. Organ allocation to these patients is usually based on avoiding transplantation of organs bearing these unacceptable antigens. In contrast, allocation through the Eurotransplant Acceptable Mismatch (AM) program is based on extension of the patients own HLA type with so-called acceptable HLA antigens to which strictly no antibodies are formed, as shown by extensive laboratory testing. We questioned which type of allocation results in the best long-term graft survival. Therefore, we selected 58,727 cadaveric single renal transplant recipients transplanted within Eurotransplant between 1996 and 2015 and determined factors influencing graft survival for patients transplanted through the AM program. Next, we compared ten-year graft survival of patients with various sensitization grades who received a renal transplant through regular allocation to that of highly sensitized patients transplanted through the AM program. Unlike regular allocation, no effect for HLA mismatches existed for AM patients, while factors that did affect graft survival were similar to those of the general kidney transplant population. AM patients had significantly superior ten-year graft survival compared to highly sensitized patients transplanted on the basis of avoidance of unacceptable mismatches. Strikingly, graft survival of AM patients receiving a repeat transplant was similar to that of nonsensitized repeat transplant recipients. Thus, allocation of kidneys to highly sensitized patients based on proven acceptable antigens results in a significantly better graft survival compared to mere avoidance of unacceptable mismatches.