Donor selection in pediatric kidney transplantation using DR and DQ eplet mismatching: A new histocompatibility paradigm.

It is now appreciated that more HLA-DR mismatching at the time of the first renal transplant is associated with higher degrees of sensitization, lower rates and longer times to retransplantation, and worse graft outcomes in children who are subsequently retransplanted. As such, our pediatric renal transplant program preferentially uses 0 or 1 HLA-DR-mismatched kidneys and reserves 2 DR-mismatched kidneys for recipients with an eminent need for a kidney. Based on a new HLA class II epitope matching strategy that is designed to minimize dnDSA production to DR and DQ antigens, we evaluated the prevalence of DR and DQ eplet mismatching for dd offers made to our pediatric wait-listed candidates. Each candidate/dd pair were HLA-DR (ß1 and ß3 and/or ß5) and DQ (α1 and ß1) allele typed by rSSO and were then evaluated for eplet mismatches by the HLAMatchmaker program. We evaluated 78 offers made to 16 children on our UNOS waiting list from 27 consecutive dd from 4/14/14 to 3/23/15. The data show that 40% (8/20) of the 1 DR-mismatched dd offers and 64% (37/58) of the 2 DR-mismatched offers were in the high-risk category for both DR and DQ dnDSA development. Whereas only 15% (3/20) of the 1 DR-mismatched offers and 5% (3/58) of the 2 DR-mismatched offers were in the low-risk category for both DR and DQ dnDSA development, 55% and 33% of the 1 DR- and 2 DR-mismatched offers, respectively, had a favorable DQ eplet mismatch threshold. In summary, HLA class II eplet mismatching is common in potential pediatric transplant recipient/donor pairs. Additional study will be necessary to validate the DR and DQ eplet threshold levels in children and to determine whether eplet mismatching strategies in donor selection result in improved transplant outcome and decreased dnDSA production.

Donor-specific antibodies present at the time of kidney transplantation in immunologically unmodified patients increase the risk of acute rejection.

BACKGROUND: Human leukocyte antigens (HLA) class II donor-specific antibodies (DSAs) are associated with microcirculation inflammation, transplant glomerulopathy and ultimately graft loss. There is however no data on allograft outcomes in deceased donor kidney transplant recipients who have not received any desensitization prior to transplantation. METHODS: We prospectively evaluated the association of HLA DR and DQ DSAs on rejection and short-term graft survival in patients who did not receive desensitization prior to transplantation. On the basis of their cumulative strength of HLA DR and/or DQ DSA, the patients were dichotomized into: 1) median fluorescence intensity (MFI)<1000 and 2) MFI≥1000. RESULTS: In the two year study period, 50 consecutive patients with HLA DR and/or DQ sensitization were transplanted in our two centers. Post-transplantation, the incidence of acute rejection was significantly greater in the MFI≥1000 group (35%; 8/22) compared to the MFI<1000 group (7%; 2/28) (p<0.001). There were two graft losses, both in the MFI≥1000 group. CONCLUSION: The strength of DR and/or DQ DSA at the time of renal transplantation influences the risk of rejection in non-desensitized recipients with HLA class II DSA.

Sharing kidneys across donor-service area boundaries with sensitized candidates can be influenced by HLA C.

The United Network for Organ Sharing (UNOS) implemented the virtual crossmatch system in UNet as a way to improve the likelihood of a negative crossmatch when kidneys are shared with HLA-sensitized candidates across donor service area (DSA) boundaries. The role of HLA C in that process is not universally appreciated. We recently experienced an unexpected positive flow T and B cell crossmatch for an imported, HLA zero-mismatched kidney because of donor-specific HLA C antibodies and transplanted it into the backup candidate. HLA C locus antigens were not typed by the OPO's laboratory that sent the kidney so the UNet virtual crossmatch could not "strike" our candidate from the UNOS match run. HLA C locus typing data of donors for kidneys our DSA imported from other DSAs revealed that C typing was not performed in 23% (14/60) and was discrepant with our molecular type for 10% (6/60) and was concordant in 67% (40/60) of cases. The rate of positive donor-specific crossmatches was higher (83%) for HLA C discrepantly typed donors than for concordantly typed donors (44%). Sensitization for HLA C (42%) is less frequent than for A (80%) or B (83%) locus antigens but the immunogenicity of C locus antigens in patients who make C locus antibodies is equivalent in black and white patients. Finally, the transplant rate of imported kidneys into class I-sensitized candidates was 24%, and C locus-sensitized candidates comprised 55% of those transplanted.

Renal graft survival is not influenced by a positive flow B-cell crossmatch.

INTRODUCTION: The influence of a positive B-cell crossmatch on graft outcome in renal transplantation is controversial. METHODS: We analyzed graft survival using Kaplan-Meier estimates for recipients of deceased donor kidneys who were either regraft transplant patients (n = 198) from 1990 to August 20, 2004, or primary transplant patients (n = 361) from December 15, 2000 to August 8, 2004, each of whom had a flow T- and B-cell IgG crossmatch performed before transplantation. The flow B-cell crossmatch (FBXM) was not used to decide whether or not to transplant. Graft survival was analyzed by whether the patient's FBXM was positive or negative. We also evaluated creatinine levels and graft survival of 131 transplant patients (June 1, 2004 to July 1, 2005) by their FBXM result and by their HLA class II flow-defined IgG PRA. RESULTS: One- and three-yr graft survival for the primary transplant patient group with a positive FBXM (98% and 84%) was not significantly different from the group with a negative FBXM (96% and 93%) (log-rank = 0.9). Similarly, graft survival at one, five, and 10 yr for the regraft transplant group whose FBXM was positive (91%, 76%, and 61%) was not significantly different from the group whose FBXM was negative (91%, 79%, and 77%) (log-rank = 0.4). Creatinine levels in the group of patients whose FBXM was positive (1.4 +/- 0.4 mg/dL; n = 76) were not significantly different from the group with a negative FBXM (1.4 +/- 0.4 mg/dL; n = 42). Even in the presence of class II PRA, a positive FBXM did not impact a patient's creatinine levels or graft outcome. CONCLUSION: Neither short nor long-term graft survival of deceased donor kidneys is influenced by a positive flow B-cell IgG crossmatch, even when caused by HLA class II antibody.

Successful renal transplantation despite low levels of donor-specific HLA class I antibody without IVIg or plasmapheresis.

We prospectively transplanted 10 primary kidney recipients with deceased donor organs (nine kidney and one pancreas/kidney) when their flow cytometric T-cell IgG, HLA class I donor-specific crossmatch was positive but the AHG T-cell crossmatch was negative, with a median follow-up of 1.8 yr. No pre- or peri-operative IVIg or plasmapheresis was administered to any patient. All but one of the 11 organs transplanted into patients with a flow T(+)/AHG(-) crossmatch is currently functioning despite the continued presence of circulating low levels of HLA class I antibody. Flow HLA class I antigen-coated beads showed the presence of at least one donor-specific HLA class I antibody at transplantation in each of the 10 cases. No rejections were observed in seven of the 10 cases (70%). Six rejection episodes, four cellular and two humoral, occurred in three patients. Each rejection was successfully treated. The only graft loss occurred in a kidney recipient on day 667 secondary to ischemia to the kidney because of cardiac surgery. Thus, short-term (one to two years) graft survival in primary transplants was not influenced by low levels of donor-specific HLA class I antibody present at transplantation and no prophylactic treatment such as IVIg, plasmapheresis, anti-CD20 or splenectomy was needed peri-operatively.

Improving access to kidney transplantation without decreasing graft survival: long-term outcomes of blood group A2/A2B deceased donor kidneys in B recipients.

BACKGROUND: The transplantation of blood group A2/A2B deceased donor kidneys into B recipients could improve access to transplantation for blood group B recipients. However, this practice is controversial, and long-term data are lacking. This study analyzed the long-term outcomes of A2/A2B deceased donor kidneys transplanted into selected B recipients. METHODS: We retrospectively assessed the outcomes (graft survival, transplant rates, and acute rejection) of deceased-donor kidneys using an allocation system that transplanted A2/A2B donors into B recipients with low anti-A blood group antibody titers between 1994 and 2003. Patients received conventional immunosuppression without any specific antibody reduction procedures. We further assessed the impact this system had on access to transplantation by blood group. RESULTS: Of 1,400 kidney transplants, 56 (4.0%) were A2/A2B to B recipients. The system reduced waiting time for all B recipients, even shorter than for blood group A recipients (median waiting times of A2/A2B to B transplants=182 days vs. B to B transplants=297 days; and A to A=307 days). Although there was a trend toward increased acute rejection in A2/A2B to B transplants, the actuarial 7-year death censored graft survival was 72% for B recipients regardless of donor type. CONCLUSIONS: Transplanting A2/A2B deceased donor kidneys into B recipients leads to an equalization of waiting time between blood groups with similar patient and graft survival using conventional immunosuppression. This protocol could lead to more equal access to kidney transplantation in blood group B recipients.

The risk for Chagas' disease in the Midwestern United States organ donor population is low.

PURPOSE: Several recent publications have increased awareness that transplanted organs can transmit infectious diseases. In light of the recent report describing the transmission of Trypanosoma cruzi infection by an organ donor in the United States (MMWR 2002: 51: 210), we have tested archived serum samples from our Organ Procurement Organization's (OPO's) deceased organ donors and live donors from 23 October 1995 through 1 March 2002. METHODS: A total of 1117 serum samples from 558 locally recovered deceased donors, 178 imported deceased donors, and 212 live donors were tested (several duplicates were included). Samples were screened for antibodies to T. cruzi, the protozoan parasite that causes Chagas' disease, with a passive particle agglutination assay (Fujirebio, Inc., Tokyo, Japan). Indeterminate samples (those agglutinating both sensitized and control particles) were absorbed with control antigen and re-tested. Inconclusive samples (those not yielding clearly negative or positive results) were re-tested using the original test format, and if persistently inconclusive, were assayed by radio-immune precipitation (RIPA). RESULTS: Of the 770 local OPO donors (deceased and live donor) and the 178 imported donors tested, 52 (5.5%) were indeterminate, but following absorption, all were negative. Forty-four samples (4.6%) were inconclusive and after re-testing 34 were negative while 10 remained inconclusive. Those 10 samples were found to be negative by RIPA. CONCLUSIONS: The risk of transmission of Chagas' disease by organ transplantation in the Midwestern United States is low because during a 6.5 year period, none of our deceased or live donors tested positive for antibodies to T. cruzi. Although the passive particle agglutination test is simple to perform, easy to interpret and rapid enough to be used in screening organ donors, because of the rate of false positive results, it should only be utilized when the donor population is at high risk for previous exposure to T. cruzi.