Helen Mah

Donor kidney exchanges.

Kidney transplantation from live donors achieves an excellent outcome regardless of human leukocyte antigen (HLA) mismatch. This development has expanded the opportunity of kidney transplantation from unrelated live donors. Nevertheless, the hazard of hyperacute rejection has usually precluded the transplantation of a kidney from a live donor to a potential recipient who is incompatible by ABO blood type or HLA antibody crossmatch reactivity. Region 1 of the United Network for Organ Sharing (UNOS) has devised an alternative system of kidney transplantation that would enable either a simultaneous exchange between live donors (a paired exchange), or a live donor/deceased donor exchange to incompatible recipients who are waiting on the list (a live donor/list exchange). This Regional system of exchange has derived the benefit of live donation, avoided the risk of ABO or crossmatch incompatibility, and yielded an additional donor source for patients awaiting a deceased donor kidney. Despite the initial disadvantage to the list of patients awaiting an O blood type kidney, as every paired exchange transplant removes a patient from the waiting list, it also avoids the incompatible recipient from eventually having to go on the list. Thus, this approach also increases access to deceased donor kidneys for the remaining candidates on the list.

Renal Transplantation in Patients With Positive Lymphocytotoxicity Crossmatches : One Center's Experience

Background. Sensitization to human leukocyte antigens remains an important barrier to successful renal transplantation. Materials and Methods. Herein we describe our center’s experience with a plasmapheresis-based desensitization protocol for highly sensitized patients. Twenty-nine patients had a positive T-cell or positive B-cell lymphocytotoxicity crossmatch against their donors. In some cases, baseline crossmatches were of high titer (e.g., 11 had baseline titers ≥1:32). Results. Twenty-eight of 29 patients were rendered T-cell crossmatch negative and B-cell crossmatch negative/low positive and transplanted. None had hyperacute rejection but 11 (39%) had acute antibody mediated rejection. Median follow-up is 22 months: 25 of the 28 (89%) of allografts are still functioning with mean plasma creatinine 1.5 mg/dL. There was one death because of the transplant or immunsuppression, one case of cytomegalovirus disease and no cases of lymphoproliferative disease. Conclusion. This series provides further evidence of the high efficacy of plasmapheresis-based desensitization protocols. Even patients with high baseline crossmatch titers can be successfully desensitized and transplanted. Short- and medium-term outcomes are encouraging but longer-term data are needed.

Long-term outcomes of kidney transplantation across a positive complement-dependent cytotoxicity crossmatch.

Background More than 30% of potential kidney transplant recipients have pre-existing anti–human leukocyte antigen antibodies. This subgroup has significantly lower transplant rates and increased mortality. Desensitization has become an important tool to overcome this immunological barrier. However, limited data is available regarding long-term outcomes, in particular for the highest risk group with a positive complement-dependent cytotoxicity crossmatch (CDC XM) before desensitization. Methods Between 2002 and 2010, 39 patients underwent living-kidney transplantation across a positive CDC XM against their donors at our center. The desensitization protocol involved pretransplant immunosuppression, plasmapheresis, and low-dose intravenous immunoglobulin±rituximab. Measured outcomes included patient survival, graft survival, renal function, rates of rejection, infection, and malignancy. Results The mean and median follow-up was 5.2 years. Patient survival was 95% at 1 year, 95% at 3 years, and 86% at 5 years. Death-censored graft survival was 94% at 1 year, 88% at 3 years, and 84% at 5 years. Uncensored graft survival was 87% at 1 year, 79% at 3 years, and 72% at 5 years. Twenty-four subjects (61%) developed acute antibody-mediated rejection of the allograft and one patient lost her graft because of hyperacute rejection. Infectious complications included pneumonia (17%), BK nephropathy (10%), and CMV disease (5%). Skin cancer was the most prevalent malignancy in 10% of patients. There were no cases of lymphoproliferative disorder. Mean serum creatinine was 1.7±1 mg/dL in functioning grafts at 5 years after transplantation. Conclusion Despite high rates of early rejection, desensitization in living-kidney transplantation results in acceptable 5-year patient and graft survival rates.

A new allocation plan for renal transplantation.

BACKGROUND A novel plan of renal allograft allocation has been conducted by United Network for Organ Sharing Region 1 transplant centers since September 3, 1996, based upon HLA matching, time waiting, and population distance points. The objectives of this plan were to achieve a balance between increasing the opportunity of renal transplantation for those patients listed with long waiting times and promoting local organ donor availability. METHODS A single list of candidates was formulated for each cadaver donor, assigning a maximum of 8 points for time waiting, a maximum of 8 points for population distance from the donor hospital, and HLA points based upon the degree of B/DR mismatch. Additional points were awarded to a cross-match-negative patient with a panel-reactive antibody of >80%, and to pediatric patients. RESULTS The total number of kidneys transplanted to patients who had waited >3 years was 100 (46%), and to patients who had waited >2.5-3 years was 29 (13%). However, the total number of kidneys transplanted to patients with the maximum population distance points was only 72 (33%). Thus, although the plan achieved a favorable distribution of kidneys to patients with longer waiting times (nearly 60%), the other, equally important objective of promoting local donor availability was not initially accomplished. Moreover, minor HLA B/DR differences between the donor and the recipient (i.e., not phenotypically matched) were unexpectedly consequential in determining allocation. As a result of these observations, the following adjustments were made in the plan (as of December 3, 1997): a maximum of 10 points for population distance, a maximum of 8 points for time waiting (both by a linear correlation), and the retention of HLA points for 0 B/DR mismatch only. After these interval changes, the percentage of patients receiving a kidney with some population distance points increased from 85% to 96%. Conclusions. We have shown that a heterogeneous region of multiple transplant centers can devise (and modify) an innovative and balanced plan that provides an equitable system of allocation for an ever-increasing number of patients.

Antibody depletion for the treatment of crossmatch-positive pediatric heart transplant recipients.

Sensitization to HLA is a risk factor for adverse outcomes after heart transplantation. Requiring a negative prospective CM results in longer waiting times and increased waitlist mortality. We report outcomes in a cohort of sensitized children who underwent transplant despite a positive CDC CM+ using a protocol of antibody depletion at time of transplant, followed by serial IVIG administration. All patients <21 yrs old who underwent heart transplantation at Boston Childrens Hospital from 1/1998 to 1/2011 were included. We compared freedom from allograft loss, allograft rejection, and serious infection between CM+ and CM− recipients. Of 134 patients in the cohort, 33 (25%) were sensitized prior to transplantation and 12 (9%) received a CM+ heart transplant. Serious infection in the first post‐transplant year was more prevalent in the CM+ patients compared with CM− patients (50% vs. 16%; p = 0.005), as was HD‐AMR (50% vs. 2%; p < 0.001). There was no difference in freedom from allograft loss or any rejection. At our center, children transplanted despite a positive CM had acceptable allograft survival and risk of any rejection, but a higher risk of HD‐AMR and serious infection.

A novel United Network for Organ Sharing region kidney allocation plan improves transplant access for minority candidates

BACKGROUND We report the consequences of a novel kidney allocation system on access of non-Caucasians (NC) to kidney transplantation. This new plan has provided a balance of allocation determinants between time waiting, HLA match, and geography (population density between donor and recipient center). METHODS Three sequential systems of regional allocation were analyzed: period I (September 1994 to September 1996), period II (September 1996 to November 1997), and period III (December 1997 to March 1 1999). Periods II and III are reflective of the new allocation plan. RESULTS During periods II and III, the NC rate of kidney transplantation increased closer to the NC proportion on the wait list, comparatively exceeding the national UNOS data. There was no statistical difference in regional mean wait time between Caucasian and NC. Improvements in access to transplantation for NCs between period I and periods II and III appear to be related to changes in geographic allocation weight from local unit to population density points, to the inclusion of the entire region in the plan, and to the deletion of intermediate degrees of B/DR mismatching in the revised plan. Despite the increased proportion of NCs on the wait list from period I to period III, the percentage difference between the proportion of NCs waiting on the list and the proportion NCs receiving a transplant fell from 7.8% to 4.9%. CONCLUSIONS These data demonstrate that this new allocation plan was associated with improved access of minority candidates to transplantation. The broadening of geographic allocation and the alteration of HLA points appear to permit a more favorable opportunity for renal transplantation to NC candidates. selection, compared to the UNOS formula. In this report, we analyze the consequences of the Region 1 allocation system on the access of non-Caucasian (NC) candidates to cadaver donor kidney transplantation.

RHD Zygosity Determination from Whole Genome Sequencing Data

In the Rh blood group system, the RHD gene is bordered by two homologous DNA sequences called the upstream and downstream Rhesus boxes. The most common cause of the D− phenotype in people of European descent is a deletion of the RHD gene region, which results in a hybrid combination of the two Rhesus boxes. PCRbased testing can detect the presence or absence of the hybrid box to determine RHD zygosity. PCR hybrid box testing on fathers can stratify risk for haemolytic disease of the fetus and new born in mothers with anti-D antibodies. Red blood cells and genomic DNA were isolated from 37 individuals of European descent undergoing whole genome sequencing as part of the MedSeq Project. A whole genome sequence-based RHD sequence read depth analysis was used to determine RHD zygosity (homozygous, hemizygous, or null states) with 100% agreement (n=37) when compared to conventional RhD serology and PCR-based hybrid box assay.

Impact of accidental discovery of renal cell carcinoma at time of renal transplantation on patient or graft survival.

Background. Renal tumors are common in the pretransplant end-stage renal disease population. Their impact on transplant outcome has not been well addressed. Methods. This study is a retrospective follow-up observational study conducted in 258 renal transplant recipients. All patients had an ipsilateral native nephrectomy at the time of transplantation. We reviewed the histopathology of all native nephrectomies to gauge the prevalence of renal cell carcinoma (RCC) and to investigate the impact of accidental discovery of RCC on graft and patient outcome. Results. RCC was found in 12 patients (4.7%): clear type in 9 patients, and chromophobe and combined clear and papillary type in 1 and 2 patients, respectively. There was no significant difference in human leukocyte antigen mismatch, primary immunosuppression, occurrence of rejection, graft function, and patient and graft survival between patients with or without RCC. RCC presented in the other native kidney in three patients (25%) posttransplantation and one of them developed metastasis 4 years after renal transplantation in the RCC group in comparison with eight patients in the control group (3.3%; P<0.001). The median follow-up period was 56 months for the RCC group and 65 months for the control group. Conclusions. We found that renal transplant outcome and patient survival were not adversely affected by the presence of accidently discovered RCC at the time of transplantation. These patients seem to be at significantly higher risk of the occurrence of RCC in the remaining native kidney. Further studies are warranted to confirm our results.

Automated typing of red blood cell and platelet antigens: a whole-genome sequencing study

BACKGROUND There are more than 300 known red blood cell (RBC) antigens and 33 platelet antigens that differ between individuals. Sensitisation to antigens is a serious complication that can occur in prenatal medicine and after blood transfusion, particularly for patients who require multiple transfusions. Although pre-transfusion compatibility testing largely relies on serological methods, reagents are not available for many antigens. Methods based on single-nucleotide polymorphism (SNP) arrays have been used, but typing for ABO and Rh-the most important blood groups-cannot be done with SNP typing alone. We aimed to develop a novel method based on whole-genome sequencing to identify RBC and platelet antigens. METHODS This whole-genome sequencing study is a subanalysis of data from patients in the whole-genome sequencing arm of the MedSeq Project randomised controlled trial (NCT01736566) with no measured patient outcomes. We created a database of molecular changes in RBC and platelet antigens and developed an automated antigen-typing algorithm based on whole-genome sequencing (bloodTyper). This algorithm was iteratively improved to address cis-trans haplotype ambiguities and homologous gene alignments. Whole-genome sequencing data from 110 MedSeq participants (30 × depth) were used to initially validate bloodTyper through comparison with conventional serology and SNP methods for typing of 38 RBC antigens in 12 blood-group systems and 22 human platelet antigens. bloodTyper was further validated with whole-genome sequencing data from 200 INTERVAL trial participants (15 × depth) with serological comparisons. FINDINGS We iteratively improved bloodTyper by comparing its typing results with conventional serological and SNP typing in three rounds of testing. The initial whole-genome sequencing typing algorithm was 99·5% concordant across the first 20 MedSeq genomes. Addressing discordances led to development of an improved algorithm that was 99·8% concordant for the remaining 90 MedSeq genomes. Additional modifications led to the final algorithm, which was 99·2% concordant across 200 INTERVAL genomes (or 99·9% after adjustment for the lower depth of coverage). INTERPRETATION By enabling more precise antigen-matching of patients with blood donors, antigen typing based on whole-genome sequencing provides a novel approach to improve transfusion outcomes with the potential to transform the practice of transfusion medicine. FUNDING National Human Genome Research Institute, Doris Duke Charitable Foundation, National Health Service Blood and Transplant, National Institute for Health Research, and Wellcome Trust.