Contemporary outcomes of pediatric cardiac transplantation with a positive retrospective crossmatch

BACKGROUND

A positive crossmatch (+ XM) has traditionally been associated with adverse outcomes following pediatric heart transplantation. However, more recent studies suggest that favorable intermediate-term outcomes may be achieved despite a + XM. This study's hypothesis is that children with a + XM have similar long-term survival, but higher rate of complications such as rejection, coronary allograft vasculopathy (CAV), and infection, compared to patients with a negative (-) XM.

METHODS

The Pediatric Heart Transplant Society Registry (PHTS) database was queried from 2010-2021 for all patients <18 years of age with a known XM. Baseline demographics were compared between + XM and - XM groups using appropriate parametric and non-parametric group comparisons. Cox Proportional Hazards Modeling was used to identify risk factors for post-transplant graft loss, rejection, and CAV.

RESULTS

Of 4599 pediatric heart transplants during the study period, XM results were available for 3914 (85%), of which 373 (9.5%) had a + XM. Univariate analysis showed lower 10-year survival for patients with + XM (HR = 1.3, p = .04). Multivariate analyses revealed no significant difference in 10-year survival in the 2 groups; however, time to first rejection (p = .0001) remained significantly shorter in the + XM group.

CONCLUSIONS

Pediatric patients transplanted across a + XM experience earlier rejection; however, after multivariate adjustment, + XM is not independently associated with intermediate-term graft loss. The risk of heart transplantation against a + XM must be balanced with the ongoing risk of waitlist mortality.

Imlifidase for Kidney Transplantation of Highly Sensitized Patients With a Positive Crossmatch: The French Consensus Guidelines

Imlifidase recently received early access authorization for highly sensitized adult kidney transplant candidates with a positive crossmatch against an ABO-compatible deceased donor. These French consensus guidelines have been generated by an expert working group, in order to homogenize patient selection, associated treatments and follow-up. This initiative is part of an international effort to analyze properly the benefits and tolerance of this new costly treatment in real-life. Eligible patients must meet the following screening criteria: cPRA ≥ 98%, ≤ 65-year of age, ≥ 3 years on the waiting list, and a low risk of biopsy-related complications. The final decision to use Imlifidase will be based on the two following criteria. First, the results of a virtual crossmatch on recent serum, which shall show a MFI for the immunodominant donor-specific antibodies (DSA) > 6,000 but the value of which does not exceed 5,000 after 1:10 dilution. Second, the post-Imlifidase complement-dependent cytotoxicity crossmatch must be negative. Patients treated with Imlifidase will receive an immunosuppressive regimen based on steroids, rATG, high dose IVIg, rituximab, tacrolimus and mycophenolic acid. Frequent post-transplant testing for DSA and systematic surveillance kidney biopsies are highly recommended to monitor post-transplant DSA rebound and subclinical rejection.

Imlifidase therapy: exploring its clinical uses

INTRODUCTION

Imlifidase, the IgG-degrading enzyme derived from Streptococcus pyogenes, can cleave all four human IgG subclasses with precise specificity. All IgG molecules can be inactivated for ~1-to-2 weeks, until new IgG synthesis is detected.

AREAS COVERED

Imlifidase was first studied for the desensitization of highly HLA-sensitized patients to enable kidney transplantation. It is currently being evaluated for kidney transplant recipients who have antibody-mediated rejection (AMR), those with acute kidney injury in the setting of anti-glomerular basement membrane disease, and those with Guillain-Barré syndrome. In 2020, imlifidase received conditional approval from the European Medicines Agency for use to desensitize deceased-donor kidney transplant recipients with a positive crossmatch. Literature search through PubMed revealed that so far, 39 crossmatched-positive patients, i.e. in the presence of donor-specific alloantibodies (DSA) on the transplantation day, have received imlifidase prior to kidney transplantation in four single-arm, open-label, phase II studies. Results at 3-year follow-up are good, i.e. allograft survival is 84%, despite 38% of patients presenting with acute AMR. Mean estimated glomerular filtration rate at 3 years was 55 mL/min/1.73 m².

EXPERT OPINION

The major hurdle now is how to prevent/avoid DSA rebound within days 5-15 post-transplantation. Thus, imlifidase represents a major breakthrough for highly HLA-sensitized kidney transplant candidates, particularly those that have calculated panel-reactive alloantibodies of ≥90%.

Positive Crossmatch Kidney Transplantation: State of the Art and Future Perspectives

The organ shortage for kidney transplantation remains a challenging issue worldwide. Incompatibility between donor-recipient pairs, commonly occurring among transplant candidates who were sensitized from prior antigen exposure, serves as a significant barrier to kidney transplantation. In efforts to overcome this obstacle, living and deceased donor kidney transplantation across human leukocyte antigen barriers following desensitization has been pursued via positive crossmatch transplantation. The goal of desensitization therapy is to remove or denigrate donor-specific alloantibodies prior to transplantation in order to permit transplantation across the human leukocyte antigen barrier and prevent rejection. Various desensitization regimens have been utilized, including the use of plasmapheresis, intravenous immunoglobulin, and or immunoadsorption. Although long-term allograft outcomes for positive crossmatch kidney transplantation following desensitization therapy have been shown to be inferior to compatible transplantation, particularly with increasing strength of the crossmatch, there is an established survival benefit for positive crossmatch transplant recipients compared with remaining on the transplant waitlist. However, positive crossmatch transplantation may confer higher risks of infection and malignancy. Despite the fact that some of these heightened risks, positive crossmatch transplantation has also been demonstrated to have cost-savings compared with remaining on dialysis and may, therefore, be a cost-effective treatment option for sensitized patients who would face long waiting times and may never be able to achieve compatible transplantation. This review highlights both the risks and benefits of positive crossmatch transplantation and its role in the broader field of kidney transplantation.

Charges and resource utilization for pediatric heart transplantation across a positive virtual and/or cytotoxicity crossmatch

There is growing acceptance of transplantation across a positive crossmatch for highly allosensitized pediatric HT candidates. While survival may be similar to patients transplanted across a negative crossmatch, costs are unknown. Among 60 HT recipients at our center from 5/07 to 6/12, we analyzed hospital charges and length of stay from the day of HT to discharge and through the first year after transplant. Median age at HT was 6.2 years (15 days-20.5 years). Charges in the first year post-HT were greater for crossmatch-positive patients ($907 678 vs $549 754; P = .017), with a trend toward higher charges for the HT hospitalization ($537 640 vs $407 374; P = .07). Plasmapheresis was more common in crossmatch-positive patients during the HT hospitalization (80% vs 4%, P < .001). In the first year after HT, crossmatch-positive patients had a greater number of endomyocardial biopsies (10 vs 7.5, P = .03) and episodes of treated rejection (2 vs 0, P = .004). Pediatric HT across a positive crossmatch is associated with higher first-year costs, including increased use of plasmapheresis and care around an increased number of rejections. These novel data will help inform decision and policymaking regarding care practices for the growing population of highly sensitized pediatric HT candidates.

Biopsy findings on a stable recipient after secondary donor specific antibody (DSA) positive and ABO incompatible kidney transplantation

Using desensitization protocol, we performed a secondary donor specific antibody (DSA) positive and ABO incompatible kidney transplantation. One-hour biopsy showed no C4d deposition. The protocol biopsy after 2 weeks showed diffuse C4d deposition with peritubulitis. After 12 weeks, however, the protocol biopsy showed disappearance of tubulitis in spite of remaining C4d deposition. The recipient was in stable condition with excellent graft function despite high titer of the DSA. Monitoring of protocol biopsy is critical while antibody titer and the interpretation of the histological findings correlating with clinical markers must be considered.