Impact of Sensitization on Waiting Time Prior to Kidney Transplantation in Germany

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.

Imlifidase Desensitization in HLA-incompatible Kidney Transplantation: Finding the Sweet Spot

Imlifidase, derived from a Streptococcus pyogenes enzyme, cleaves the entire immunoglobulin G pool within hours after administration in fully cleaved antigen-binding and crystallizable fragments. These cleaved fragments can no longer exert their antibody-dependent cytotoxic functions, thereby creating a window to permit HLA-incompatible kidney transplantation. Imlifidase is labeled, in Europe only, for deceased donor kidney transplantation in highly sensitized patients, whose chances for an HLA-compatible transplant are negligible. This review discusses outcomes of preclinical and clinical studies on imlifidase and describes the phase III desensitization trials that are currently enrolling patients. A comparison is made with other desensitization methods. The review discusses the immunological work-up of imlifidase candidates and especially the "delisting strategy" of antigens that shift from unacceptable to acceptable with imlifidase desensitization. Other considerations for clinical implementation, such as adaptation of induction protocols, are also discussed. Imlifidase cleaves most of the currently used induction agents except for horse antithymocyte globulin, and rebound of donor-specific antibodies should be managed. Another consideration is the timing and interpretation of (virtual) crossmatches when bringing this novel desensitization agent into the clinic.

[Kidney transplantation]

Every patient with kidney failure requiring dialysis in Germany has the right to at least be evaluated for a transplantation. When an affected person can be considered for a transplantation, it must be clarified which allocation program is the right one for the person and whether a living organ donor can be considered. It should also be individually discussed with patients which type of donor organ should be accepted. Following a transplantation an individualized immunosuppression is relevant not only for the long-term survival of the transplant but also for the adherence of the patient.

The German Transplantation Registry Reveals Deficiencies in the Listing Process for Kidney Transplantation

Introduction

The time from dialysis onset to enrollment on the kidney waiting list (listing time) is a crucial step on the path to receiving a kidney allograft; however, this process has received very little research attention in the Eurotransplant (ET) area.

Methods

We retrospectively analyzed data from the German transplantation registry, including patients who were on the waiting list for a first kidney transplant in Germany between 2006 and 2016. Listing time was evaluated using a mixed linear model. The outcomes on the kidney waiting list were assessed using competing risk analyses.

Results

We assessed a total of 43,955 patients. Listing occurred at a higher pace in patients receiving living donor transplantations (median 0.4 years from dialysis onset) than in deceased donor transplantations (Eurotransplant Kidney Allocation System [ETKAS] 1.1 years, European Senior Program [ESP] 1.4 years, Acceptable Mismatch program 1.3 years), with 28.5% of living donor transplantations performed preemptively. There was only modest variation in listing time between the transplant centers. Patients with a history of viral infection, high immunization; hemodialysis patients; and patients with a higher body mass index (BMI) had a delayed listing process. Two of 3 patients listed in the ETKAS, excluding those with potential bonus points (pediatric, other organ transplantations), were eventually transplanted. Older patients, male patients, patients with blood type O, and patients with diabetic nephropathy as the underlying renal disease had the highest risk not to proceed to transplantation.

Conclusion

Although long waiting times remain the biggest hurdle for transplantation in Germany, there is ample room for improvement of the listing process.

Chimeric HLA antibody receptor T cells to target HLA-specific B cells in solid organ transplantation

HLA-sensitized patients on the transplant waiting list harbor antibodies and memory B cells directed against allogeneic HLA molecules, which decreases the chance to receive a compatible donor organ. Current desensitization strategies non-specifically target circulating antibodies and B cells, warranting the development of therapies that specifically affect HLA-directed humoral immune responses. We developed Chimeric HLA Antibody Receptor (CHAR) constructs comprising the extracellular part of HLA-A2 or HLA-A3 coupled to CD28-CD3ζ domains. CHAR-transduced cells expressing reporter constructs encoding T-cell activation markers, and CHAR-transduced CD8+ T cells from healthy donors were stimulated with HLA-specific monoclonal antibody-coated microbeads, and HLA-specific B cell hybridomas. CHAR T cell activation was measured by upregulation of T cell activation markers and IFNγ secretion, whereas CHAR T cell killing of B cell hybridomas was assessed in chromium release assays and by IgG ELISpot. HLA-A2- and HLA-A3-CHAR expressing cells were specifically activated by HLA-A2- and HLA-A3-specific monoclonal antibodies, either soluble or coated on microbeads, as shown by CHAR-induced transcription factors. HLA-A2 and HLA-A3 CHAR T cells efficiently produced IFNγ with exquisite specificity and were capable of specifically lysing hybridoma cells expressing HLA-A2- or HLA-A3-specific B-cell receptors, respectively. Finally, we mutated the α3 domain of the CHAR molecules to minimize any alloreactive T-cell reactivity against CHAR T cells, while retaining CHAR activity. These data show proof of principle for CHAR T cells to serve as precision immunotherapy to specifically desensitize (highly) sensitized solid organ transplant candidates and to treat antibody-mediated rejection after solid organ transplantation.

Immunized Patients Face Reduced Access to Transplantation in the Eurotransplant Kidney Allocation System

BACKGROUND

The presence of donor-specific HLA antibodies before transplantation is associated with poor transplantation outcomes. Unacceptable antigens can be assigned for Eurotransplant kidney transplant candidates to prevent kidney offers against which the candidate has developed clinically relevant HLA antibodies. This retrospective cohort study aimed to assess to what degree unacceptable antigens affect access to transplantation in the Eurotransplant Kidney Allocation System (ETKAS).

METHODS

Candidates who underwent kidney-only transplantation between 2016 and 2020 were included (n = 19 240). Cox regression was used to quantify the relationship between the relative transplantation rate and virtual panel-reactive antibodies (vPRAs), which is the percentage of the donor pool with unacceptable antigens. Models used accrued dialysis time as the timescale; were stratified by country and blood group of patient and were adjusted for nontransplantable status, patient age, sex, history of kidney transplantations, and prevalence of 0 HLA-DR-mismatched donors.

RESULTS

Transplantation rates were 23% lower for vPRA 0.1% to 50%, 51% lower for vPRA 75% to 85%, and decreased rapidly for vPRA of >85%. Prior studies showed significantly lower ETKAS transplantation rates only for highly sensitized patients (vPRA of >85%). The inverse relationship between transplantation rate and vPRA is independent of Eurotransplant country, listing time, and 0 HLA-DR-mismatched donor availability. Results were similar when quantifying the relationship between vPRA and attainment of a sufficiently high rank for an ETKAS offer, suggesting lower transplantation rates for immunized patients are due to current ETKAS allocation.

CONCLUSIONS

Immunized patients face lower transplantation rates across Eurotransplant. The current ETKAS allocation mechanism inadequately compensates immunized patients for reduced access to transplantation.

Regional Differences in Waiting Times for Kidney Transplantation in Germany

BACKGROUND

In order to achieve short ischemia times between organ donation and transplantation, regional organ allocation has been assigned priority in the development of allocation rules for kidney transplantation. It is unclear whether this leads to differences in regional waiting times in Germany.

METHODS

A retrospective cohort study over a 24-month observation period was conducted, including all patients who received a kidney-only graft allocated via the standard Eurotransplant Kidney Allocation System (ETKAS) (n = 1487) or the Eurotransplant Senior Program (ESP) (n = 566). Multiple linear regression analyses were performed to investigate differences in waiting times across the regions (ETKAS) or subregions (ESP) as defined by the German Organ Procurement Organization (DSO). Associations between the number of regionally procured kidneys (n = 1444) and regional waiting times were investigated.

RESULTS

In ETKAS, the median waiting time was 8.9 years (interquartile range [IQR] 6.7-10.6); in ESP, it was 3.9 (2.4 -5.3) years. Compared with the reference region with the shortest waiting time, waiting times in other regions were 0.6 to 1.7 years longer in ETKAS and 1.3 to 4.4 years longer in ESP. The ratio of the number of patients on the waiting list for a particular region to the number of organs donated in that region was associated with the waiting time in ETKAS (R2 = 0.70). In ESP, this association was markedly less pronounced (R2 = 0.45).

CONCLUSION

In Germany, waiting times depend strongly on the region where a patient is listed for kidney transplantation, especially in ESP. These findings call the current allocation algorithms into question and imply a need for suitable modification.