Nonhuman leukocyte antigen antibodies that have impact in the heart transplant patient

The role of non-HLA antibodies in solid organ transplantation: a complex deliberation

PURPOSE OF REVIEW

There is tremendous interest in understanding when, if, and how non-HLA antibodies contribute to allograft injury. Numerous non-HLA target antigens have been identified and sensitization to these targets have been associated with delayed allograft function, rejection, and allograft failure. This review focuses on the clinical utility of HLA antibody testing, highlighting the strengths and limitations of current clinical studies, and the need for defining characteristics to inform non-HLA antibody pathogenicity.

RECENT FINDINGS

Clinical studies continue to show associations between non-HLA antibodies and rejection and reduced allograft survival across multiple transplanted organ types. The worst clinical outcomes continue to be observed among recipients testing positive for both non-HLA and donor-specific HLA antibodies. Mechanistic insights from both animal and clinical studies support a model in which tissue injury accompanied by an inflammatory environment influence non-HLA antibody formation and pathogenicity.

SUMMARY

Immune triggers that lead to non-HLA antibody formation and pathogenicity are complex and poorly understood. The ability of non-HLA antibodies to mediate allograft injury may depend upon their affinity and strength (titer), target specificity, density of the target antigen, and synergy with donor-specific HLA antibodies.

Antibody-medicated rejection after heart transplantation: diagnosis and clinical implications

PURPOSE OF REVIEW

The present article will review the diagnosis of antibody-mediated rejection in heart transplant recipients and further explore the clinical implications.

RECENT FINDINGS

Improved diagnostic techniques have led to increased recognition of antibody-mediated rejection and better understanding of the long-term consequences in heart transplant recipients. Endomyocardial biopsy remains the gold standard for the diagnosis of antibody-medicated ejection; however, several advances in molecular testing have emerged, including the use of gene expression profiling, messenger RNA, and microRNA. Routine surveillance of donor-specific antibodies identifies recipients at high risk for graft compromise. Additionally, new monoclonal antibody therapies have broadened our repertoire in the treatment of rejection.

SUMMARY

Advances in molecular testing for antibody-mediated rejection may improve the associated long-term complication, while minimizing risk to the patient.

Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

Upregulation of Endothelial HLA Class II is a Marker of Antibody-Mediated Rejection in Heart Allograft Biopsies

In 2013, the International Society of Heart and Lung Transplant (ISHLT) introduced the working classification for pathologic changes associated with antibody-mediated rejection (AMR) of the heart allograft, known as pathologic AMR (pAMR). With 2 components associated with AMR, histopathologic changes) and immunopathologic markers, the proposed classification also suggests the use of class II HLA as a marker of endothelial integrity. It is known that during allograft rejection, endothelial cells are activated, therefore, we hypothesized that endothelial class II HLA rather than a marker of mere endothelial presence, is a marker of endothelial activation and becomes upregulated in AMR. Eight hundred thirty-eight heart allograft biopsies, collected from January 2016 to September 2018 at a single institution from patients with a current or recent diagnosis of AMR, were evaluated for both histopathologic and immunopathologic changes of AMR. Biopsies were labeled with immunofluorescence with antibodies against C4d and for immunohistochemistry with antibodies against C3d, CD68, and class II HLA. ISHLT criteria were used to classify the biopsies, and for class II HLA, both the percentage and the stain intensity were evaluated. Biopsies (74.8%) from our cohort showed either histopathologic pAMR-1, immunopathologic pAMR-1, or combined histopathologic and immunopathologic pAMR-2 evidence of AMR. Expression of endothelial HLA class II was significantly correlated with the diagnosis of AMR by percentage area (P < .0001) and intensity of staining (P < .0001). The diagnosis of AMR significantly correlated with moderate (+2) and strong (+3) staining intensity for class II HLA as follows: histopathologic and immunopathologic pAMR-2 with odds ratio (OR) = 28.3 (P < .0001);histopathologic pAMR-1 alone with OR = 22.7 (P < .0001); and immunopathologic pAMR-1 alone with OR = 32.6 (P < .0001). Interestingly, our study also suggested that the inclusion of C4d focally positive cases also significantly correlates with the diagnosis of AMR (P < .003). We confirmed our hypothesis that in heart allograft biopsies, there is a spectrum of both percentage and intensity of HLA class II expression due to endothelial activation, and that class II HLA by immunohistochemistry is a marker significantly correlated with the diagnosis of AMR. In addition, the group of focally positive C4d biopsies (10%-50%) should be considered positive for the immunopathologic component of the 2013 ISHLT classification, as this group of biopsies also correlated with the diagnosis of AMR.