A2 to B Kidney Transplantation in the Post-Kidney Allocation System Era: A 3-year Experience with Anti-A Titers, Outcomes, and Cost

A2/A2B to B deceased donor kidney transplantation in the Kidney Allocation System era

Kidney transplantation from blood type A2/A2B donors to type B recipients (A2→B) has increased dramatically under the current Kidney Allocation System (KAS). Among living donor transplant recipients, A2-incompatible transplants are associated with an increased risk of all-cause and death-censored graft failure. In light of this, we used data from the Scientific Registry of Transplant Recipients from December 2014 until June 2022 to evaluate the association between A2→B listing and time to deceased donor kidney transplantation (DDKT) and post-DDKT outcomes for A2→B recipients. Among 53 409 type B waitlist registrants, only 12.6% were listed as eligible to accept A2→B offers ("A2-eligible"). The rates of DDKT at 1-, 3-, and 5-years were 32.1%, 61.4%, and 72.1% among A2-eligible candidates and 14.1%, 29.9%, and 44.1% among A2-ineligible candidates, with the former experiencing a 133% higher rate of DDKT (Cox weighted hazard ratio (wHR) = 2.192.332.47; P < .001). The 7-year adjusted mortality was comparable between A2→B and B-ABOc (type B/O donors to B recipients) recipients (wHR 0.780.941.13, P = .5). Moreover, there was no difference between A2→B vs B-ABOc DDKT recipients with regards to death-censored graft failure (wHR 0.771.001.29, P > .9) or all-cause graft loss (wHR 0.820.961.12, P = .6). Following its broader adoption since the implementation of the kidney allocation system, A2→B DDKT appears to be a safe and effective transplant modality for eligible candidates. As such, A2→B listing for eligible type B candidates should be expanded.

A2/A2B to B kidney transplantation outcomes: A single center 7-year experience

INTRODUCTION

Data on long-term outcomes following A2/A2B to B kidney transplants since the 2014 kidney allocation system (KAS) changes are few. The primary aim of this study is to report our 7-year experience with A2/A2B to B kidney transplants and to compare post-transplant outcomes of A2/A2B to a concurrent group of B to B kidney transplants. Additionally, the study evaluates the impact of pre-transplant anti-A1 titers on survival outcomes in A2/A2B transplants.

METHODS

This retrospective, single-center analysis included all adults who received A2/A2B to B deceased donor kidney transplants from December 2014 to June 2021 compared to B to B recipients. The effects of pre-transplant IgM/IgG titers, stratified as ≤1:8 and ≥1:16, on death-censored, rejection-free, and overall graft survival were tested.

RESULTS

Fifty-three A2/A2B and 114 B to B adults were included with a median follow-up time of 32 months. Overall graft survival, patient survival, and rejection-free graft survival did not differ between the two groups. There were no differences between the groups' overall kidney function values (p > .80) or their temporal trajectories (time by group interaction p > .11). Unadjusted death-censored graft survival was lower in A2/A2B to B compared to B recipients (p = .03), but the effect was not significant (p = .195) after adjusting for any readmissions (p = .96), rejection episodes (p < .001) or BK infection (p = .76). We did not detect an effect of pre-transplant titer group on death-censored (p = .59), rejection-free (p = .61), or overall graft survival (p = .26) CONCLUSIONS: A2/A2B to B kidney transplants have comparable overall patient and graft survival, rejection-free graft survival, and longitudinal renal function compared to B to B transplants at our center. Allograft survival outcomes were not significantly different between patients with low and high pre-transplant anti-A1 IgM/IgG titers.

Impact of sensitization and ABO blood types on the opportunity of deceased-donor kidney transplantation with prolonged waiting time

The waiting time to deceased-donor kidney transplantation (DDKT) is long in Asian countries. We investigated the impact of sensitization and ABO blood type (ABO) on DDKT opportunity using two Korean cohorts: a hospital cohort from two centers and a national database. The impact of panel reactive antibody (PRA) based on the maximal PRA% and ABO on DDKT accessibility was analyzed using a competing risks regression model. In the hospital cohort (n = 4722), 88.2%, 8.7%, and 3.1% of patients belonged to < 80%, 80-99%, and ≥ 99% PRA groups, respectively, and 61.1%, 11.6%, and 27.3% belonged to A or B, AB, and O blood types, respectively. When PRA and ABO were combined, PRA < 80%/A or B and 80 ≤ PRA < 99%/AB had fewer DDKT opportunities (median, 12 years; subdistribution hazard ratio [sHR], 0.71) compared with PRA < 80%/AB (median, 11 years). Also, PRA < 80%/O, 80 ≤ PRA < 99%/A or B, and PRA ≥ 99%/AB had a much lower DDKT opportunity (median, 13 years; sHR, 0.49). Furthermore, 80 ≤ PRA < 99%/O and PRA ≥ 99%/non-AB had the lowest DDKT opportunity (sHR, 0.28). We found similar results in the national cohort (n = 18,974). In conclusion, an integrated priority system for PRA and ABO is needed to reduce the inequity in DDKT opportunities, particularly in areas with prolonged waiting times.

Increasing Access to Kidney Transplantation for Black and Asian Patients Through Modification of the Current A2 to B Allocation Policy

Key Points

A2 to B incompatible transplantation is not fully practiced in the country, and further policies should encourage centers to perform more blood incompatible transplants. Centers that currently practice A2 to B incompatible transplants should give priority to blood type B patients who are willing to accept an A organ. This will benefit Asian and Black patients.

Background

The rate of A2 to B incompatible (ABO-i) kidney transplant continues to be low despite measures in the new kidney allocation system (KAS) to facilitate such transplants. This study shows how the number of ABO-i transplants could increase if KAS policies were used to their fullest extent through a boost in ABO-i priority points.

Method

Transplant outcomes were predicted using the Kidney Pancreas Simulated Allocation Model, preloaded with national data of 2010. We used this simulation to compare KAS with a new intervention in which priority equal to cPRA=100 has been given to blood type B candidates who are willing to accept an A blood type organ.

Results

The number of Black recipients increased by 375 (from 35% of the total recipient population to 38.7%), the number of blood type B Blacks increased by 65 (from 8% of the total recipient population to 9%), and the number of blood type B Black patients receiving blood type A kidneys increased by 49 (from 2% of the total recipient population to 2.5%). The same change occurred for Asians, particularly blood type B Asians (from 0.54% of the total recipient population to 0.7%). The average wait time notably decreased by 27 days for blood type B Black patients. In the proposed scenario, 263 blood type B Black patients received a blood type A organ (2.5% of the total recipient population) while only 181 (1.1%) of such transplants were performed in 2021. These results signify a considerable opportunity loss of ABO-i transplants for Black patients.

Conclusions

If this policy was universally adopted, we would expect to see an overall increase in A2 to B transplantation, but in reality, not all centers perform ABO-i transplantation. Thus, adopting this policy would incentivize other centers to perform more subtyping of A-type kidneys, and it would increase access to organs for blood type B Asian and Black patients in centers where ABO-i transplantation already takes place.

Comparative analysis of Basiliximab and Alemtuzumab induction therapies in blood type A2-to-B kidney transplantation: Impact on kidney function and de novo donor-specific HLA antibodies

PURPOSE

Blood group B kidney transplant candidates have lower transplantation rates and longer waiting times compared to other blood groups. Kidney transplantation from blood group A2-to-B has offered a solution for these patients. This study aimed to investigate the impact of Basiliximab and Alemtuzumab induction therapies on kidney function and de novo donor-specific antibodies (DSA) in blood type A2-to-B kidney transplant recipients within the first 12 months of post-transplant.

METHODS

A retrospective analysis was conducted on 110 consecutive A2-to-B kidney transplant recipients between January 2015 and December 2022. Of these, 46 (41.8%) received Basiliximab, while 64 (58.2%) received Alemtuzumab as induction therapy. Demographics and comorbidities data were collected and compared between the two groups. Serum samples collected at 4- and 12-month intervals post-transplant were used to assess the presence of de novo DSA. Kidney allograft function was evaluated by monitoring serum creatinine levels and assessing Creatinine Clearance based on 24-h urine collection at various time points.

RESULTS

During the follow-up period, 20.00% of patients who received Alemtuzumab developed de novo DSA, whereas none of the patients induced with Basiliximab developed de novo DSA (p = 0.038). Recipients who received Basiliximab were older (mean age = 72.00) and received higher Kidney Donor Profile Index (KDPI) kidneys (mean = 75) compared to those induced with Alemtuzumab (mean age = 58.00, mean KDPI = 49) (p < 0.001), with no significant difference observed in the last follow-up creatinine clearance or creatinine levels between the two groups (p = 0.28).

CONCLUSION

The use of Basiliximab as induction immunosuppression in A2-to-B kidney transplant recipients is associated with a lower incidence of de novo HLA DSA formation without significant differences in overall renal function compared to Alemtuzumab.

ABO-Incompatible Living Donor Liver Transplant From a Blood Type A2 Donor to a Type B Recipient: A Note of Caution

Standardization of immunomodulation protocols has enabled ABO-incompatible liver transplants with outcomes similar to those of ABO-compatible liver transplants. Patients with the A2 blood group are unique because they have a diminished expression of the A antigen. Despite rare immune complications, this phenomenon of diminished expression has led to treatment of type A2 donors according to the regimen for type O blood group donors in ABO-incompatible liver transplants. Additionally, the requirement for pretransplant recipient immunomodulation is consi dered minimal when considering these donors. The transplant of a type A2 donor kidney to a type B recipient is well recognized; however, for liver donation the A2-to-B transplant is rare. Here, we present a case of 48-year-old male patient with blood group type B who underwent ABO-incompatible liver transplant of a right lobe liver graft from a type A2 donor. Postoperatively, despite adequate immunosuppression and initiation of thera - peutic plasma exchange, the patient developed severe and refractory antibody-mediated rejection that ultimately abated with a splenectomy. This report highlights the low but tangible risk of antibody-mediated rejection in ABO-incompatible liver transp lants from type A2 donors and emphasizes the importance of serial monitoring of anti-A isohemag glutinin titers and posttransplant splenectomy to ensure that liver grafts with antibody-mediated rejection can be rescued.

Discrepant subtyping of blood type A2 living kidney donors: Missed opportunities in kidney transplantation

BACKGROUND

Despite the institution of a new Kidney Allocation System in 2014, A2/A2B to B transplantation has not increased as expected. The current Organ Procurement and Transplantation Network policy requires subtyping on two separate occasions, and in the setting of discrepant results, defaulting to the A1 subtype. However, there is significant inherent variability in the serologic assays used for blood group subtyping and genotyping is rarely done.

METHODS

The National Kidney Registry, a kidney paired donation (KPD) program, performs serological typing on all A/AB donors, and in cases of non-A1/non-A1B donors, confirmatory genotyping is performed.

RESULTS

Between 2/18/2018 and 9/15/2020, 13.0% (145) of 1,111 type A donors registered with the NKR were ultimately subtyped as A2 via genotyping. Notably, 49.6% (72) of these were subtyped as A1 at their donor center, and in accordance with OPTN policy, ineligible for allocation as A2.

CONCLUSION

Inaccurate A2 subtyping represents a significant lost opportunity in transplantation, especially in KPD where A2 donors can not only facilitate living donor transplantation for O and highly sensitized candidates, but can also facilitate additional living donor transplants. This study highlights the need for improved accuracy of subtyping technique, and the need for policy changes encouraging optimal utilization of A2 donor kidneys.

Impact of the 2014 kidney allocation system changes on trends in A2/A2B into B kidney transplantation and organ procurement organization reporting of donor subtyping

The current kidney allocation system (KAS) preferentially allocates kidneys from blood type A2 or A2B (A/A2B) donors to blood type B candidates. We used national data to evaluate center-level performance of A2/A2B to B transplants, and organ procurement organization (OPO) reporting of type A or AB donor subtyping, in 5-year time periods prior to (2009-2014) and following (2015-2019) KAS implementation. The number of centers performing A2/A2B to B transplants increased from 17 pre-KAS to 76 post-KAS, though this still represents only a minority of centers (7.3% pre-KAS and 32.6% post-KAS). For high-performing centers, the median net increase in A2/A2B to B transplants was 19 cases (range -2-72) per center in the 5 years post-KAS. The median net increase in total B recipient transplants was 21 cases (range -17-119) per center. Despite requirements for performance of subtyping, in 2019 subtyping was reported on only 56.4% of A/AB donors. This translates into potential missed opportunities for B recipients, and even post-KAS up to 2322 A2/A2B donor kidneys may have been allocated for transplantation as A/AB. Further progress must be made both at center and OPO levels to broaden implementation of A2/A2B to B transplants for the benefit of underserved recipients.

A Safe Anti-A2 Titer for a Successful A2 Incompatible Kidney Transplantation: A Single-center Experience and Review of the Literature

Background.

Kidney allocation system allows blood type B candidates accept kidneys from A2/A2B donors. There is no mandate by UNOS on which the anti-A2 level is acceptable. We aimed to investigate the safety of kidney transplant in blood group B patients with anti-A2 titers ≤16.

Methods.

We performed 41 A2-incompatible kidney transplants in blood group B recipients between May 2015 and September 2019. Clinical outcomes were compared with a control group of 75 blood group B recipients who received blood group compatible kidney transplantation at the same period.

Results.

Of the 41 recipients, 85% were male, 48% African American, with a median age of 53 (20–73) y. Thirty-eight (93%) were deceased-donor and 3 (7%) were living-donor kidney transplant recipients. Pretransplant anti-A2 IgG titers were 2 in 16, 4 in 9, 8 in 6, and 16 in 5 and too weak to titer in 5 recipients. Eight patients had pretransplant donor-specific antibodies. During a median follow-up of 32.6 mo (6–57.3) patient and graft survival were 100% and 92% in the A2-incompatible kidney transplant group, and 91% and 92% in the blood group compatible group, respectively. Twelve A2-incompatible recipients underwent a 21 clinically indicated kidney biopsies at a median 28 d (6–390) after transplantation. None of the patients developed acute antibody-mediated rejection and 2 patients (5%) had acute T-cell–mediated rejection. Interestingly, peritubular capillary C4d positivity was seen in 7 biopsies which did not have any findings of acute rejection or microvascular inflammation but not in any of the rejection-free biopsies in the control group. C4d positivity was persistent in 5 of those patients who had follow-up biopsies.

Conclusions.

A2-incompatible transplantation is safe in patients with anti-A2 titers ≤16 with excellent short-term kidney allograft outcomes. C4d positivity is frequent in allograft biopsies without acute rejection.