Highly sensitised patients awaiting deceased donor renal transplants are disadvantaged by the presence of denatured HLA antibody detected in routine HLA antibody testing

A modeling approach for mean fluorescence intensity value harmonization and cutoff prediction for luminex single antigen bead assays of two different vendors

Luminex single antigen bead (SAB) kits from One Lambda (OL) and Lifecodes (LC) are widely used for HLA antibody detection but have substantial differences in design and assay protocol resulting in different mean fluorescence intensity (MFI) values. Here, we present a non-linear modeling approach to accurately convert MFI values between two vendors and to establish user-independent MFI cutoffs when analyzing big datasets. HLA antibody data from a total of 47 EDTA-treated sera tested using both OL and LC SAB kits were analyzed. MFI comparisons were made for the common 84 HLA class I and 63 class II beads. In the exploration set (n = 24), a non-linear hyperbola model on raw MFI corrected by locus-specific highest self MFI subtraction yielded the highest correlation (class I r2 : 0.946, class II r2 : 0.898). Performance of the model was verified in an independent validation set (n = 12) (class I r2 : 0.952, class II r2 : 0.911). Furthermore, in an independent cohort of post-transplant serum samples (n = 11) using the vendor-specific MFI cutoffs dictated by the current model, we found 94% accuracy in bead-specific reactivity assignments by the two vendors. We recommend using the non-linear hyperbola modeling approach with self HLA correction and locus-specific analyzes to harmonize MFI values between two vendors in particular research datasets. As there are considerable variations between the two assays, using MFI conversion for individual patient samples is not recommended.

BSHI and BTS UK guideline on the detection of alloantibodies in solid organ (and islet) transplantation

Solid organ transplantation represents the best (and in many cases only) treatment option for patients with end-stage organ failure. The effectiveness and functioning life of these transplants has improved each decade due to surgical and clinical advances, and accurate histocompatibility assessment. Patient exposure to alloantigen from another individual is a common occurrence and takes place through pregnancies, blood transfusions or previous transplantation. Such exposure to alloantigen's can lead to the formation of circulating alloreactive antibodies which can be deleterious to solid organ transplant outcome. The purpose of these guidelines is to update to the previous BSHI/BTS guidelines 2016 on the relevance, assessment, and management of alloantibodies within solid organ transplantation.

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

BACKGROUND

Assignment of unacceptable HLA mismatches (UAMs) prevents transplantation of incompatible grafts but potentially prolongs waiting time. Whether this is true in the Eurotransplant Kidney Allocation System (ETKAS) and the Eurotransplant Senior Program in Germany is highly debated and relevant for UAM policies.

METHODS

Donor pool restriction due to UAM was expressed as percent virtual panel-reactive antibodies (vPRAs). Kaplan-Meier estimates and multivariable Cox regression models were used to analyze the impact of vPRA levels on waiting time and transplant probability during a period of 2 y in all patients eligible for a kidney graft unter standard circumstances in Germany on February 1, 2019 (n = 6533). Utility of the mismatch probability score to compensate for sensitization in ETKAS was also investigated.

RESULTS

In ETKAS, donor pool restriction resulted in significant prolongation of waiting time and reduction in transplant probability only in patients with vPRA levels above 85%. This was most evident in patients with vPRA levels above 95%, whereas patients in the acceptable mismatch program had significantly shorter waiting times and higher chances for transplantation than nonsensitized patients. In the Eurotransplant Senior Program, vPRA levels above 50% resulted in significantly longer waiting times and markedly reduced the chance for transplantation. Compensation for sensitization by the mismatch probability score was insufficient.

CONCLUSIONS

Donor pool restriction had no significant impact on waiting time in most sensitized patients. However, despite the existence of the acceptable mismatch program, the majority of highly sensitized patients is currently disadvantaged and would benefit from better compensation mechanisms.