Fulminant Acute Cellular Rejection With Negative Findings on Endomyocardial Biopsy

Unsupervised mRNA-seq classification of heart transplant endomyocardial biopsies

BACKGROUND

Endomyocardial biopsy (EMB) is currently considered the gold standard for diagnosing cardiac allograft rejection. However, significant limitations related to histological interpretation variability are well-recognized. We sought to develop a methodology to evaluate EMB solely based on gene expression, without relying on histology interpretation.

METHODS

Sixty-four EMBs were obtained from 47 post-heart transplant recipients, who were evaluated for allograft rejection. EMBs were subjected to mRNA sequencing, in which an unsupervised classification algorithm was used to identify the molecular signatures that best classified the EMBs. Cytokine and natriuretic peptide peripheral blood profiling was also performed. Subsequently, we performed gene network analysis to identify the gene modules and gene ontology to understand their biological relevance. We correlated our findings with the unsupervised and histological classifications.

RESULTS

Our algorithm classifies EMBs into three categories based solely on clusters of gene expression: unsupervised classes 1, 2, and 3. Unsupervised and histological classifications were closely related, with stronger gene module-phenotype correlations for the unsupervised classes. Gene ontology enrichment analysis revealed processes impacting on the regulation of cardiac and mitochondrial function, immune response, and tissue injury response. Significant levels of cytokines and natriuretic peptides were detected following the unsupervised classification.

CONCLUSION

We have developed an unsupervised algorithm that classifies EMBs into three distinct categories, without relying on histology interpretation. These categories were highly correlated with mitochondrial, immune, and tissue injury response. Significant cytokine and natriuretic peptide levels were detected within the unsupervised classification. If further validated, the unsupervised classification could offer a more objective EMB evaluation.

Multi-modal imaging of the pediatric heart transplant recipient

The assessment of pediatric patients after orthotropic heart transplantation (OHT) relies heavily on non-invasive imaging. Because of the potential risks associated with cardiac catheterization, expanding the role of non-invasive imaging is appealing. Echocardiography is fast, widely available, and can provide an accurate assessment of chamber sizes and function. Advanced echocardiographic methods, such as myocardial deformation, have potential to assess for acute rejection or cardiac allograft vasculopathy (CAV). While not currently part of routine care, cardiac magnetic resonance imaging (CMR) and computed tomography may potentially aid in the detection of graft complications following OHT. In particular, CMR tissue characterization holds promise for diagnosing rejection, while quantitative perfusion and myocardial late gadolinium enhancement may have a role in the detection of CAV. This review will evaluate standard and novel methods for non-invasive assessment of pediatric patients after OHT.

Evaluation of the Graft Mechanical Function Using Speckle-Tracking Echocardiography During the First Year After Orthotropic Heart Transplantation

Background

Recent advances in ultrasound strain imaging facilitate more precise monitoring of subtle myocardial changes and thus may allow for more appropriate assessment of myocardium after orthotopic heart transplantation (OHT). This study aimed to explore longitudinal left ventricular (LV) and right ventricular (RV) function by speckle-tracking echocardiography (STE) during a 12-month follow-up period in relation to acute cellular rejection (ACR) degree ≥2R and the response to intense immunosuppressive therapy with intravenous steroids.

Material/Methods

Forty-five adult heart transplant recipients were prospectively assessed at a single center from January 2016 until June 2017. Echocardiography was performed serially at baseline and together with routine biopsies at 2 weeks and 1, 2, 3, 6, 9, and 12 months after OHT. Changes in graft function were evaluated using STE before and during ACR and in the resolving period of ACR.

Results

A total of 220 pairs of biopsy specimens and strain recordings were analyzed. Moderate ACR was seen in 30 biopsies (13.6%). In the serial assessment, longitudinal strain parameters of the LV (global and 4-, 2-, 3-chamber longitudinal strain) and RV (global and free wall longitudinal strain) were decreased at baseline and improved significantly (P<0.001) within 12 months after OHT. The degree of improvement was not influenced by ACR. There were no significant differences in circumferential, radial, or longitudinal strain rate, or mechanical dyssynchrony. Reduced LV and RV longitudinal strain was related to ACR degree 2R and increased significantly (P<0.0005) during 3 days of intravenous methylprednisolone therapy.

Conclusions

Using the STE technique, we have documented an acute improvement in mechanical myocardial function following ACR steroid therapy and a progressive recovery of LV and RV longitudinal function during the first year after OHT.

Three-Dimensional Self-Navigated T2 Mapping for the Detection of Acute Cellular Rejection After Orthotopic Heart Transplantation

BACKGROUND

T₂ mapping is a magnetic resonance imaging technique measuring T₂ relaxation time, which increases with the myocardial tissue water content. Myocardial edema is a component of acute cellular rejection (ACR) after heart transplantation. This pilot study compares in heart transplantation recipients a novel high resolution 3-dimensional (3D) T₂-mapping technique with standard 2-dimensional (2D) T₂-mapping for ACR detection.

METHODS

Consecutive asymptomatic patients (n = 26) underwent both 3D T₂ mapping and reference 2D T₂ mapping magnetic resonance imaging on the day of endomyocardial biopsy (EMB). 3D T₂ maps were obtained at an isotropic spatial resolution of 1.72 mm (voxel volume 5.1 mm³). 2D and 3D maps were matched anatomically, and maximum segmental T₂ values were compared blinded to EMB results. In addition, all 3D T₂ maps were rendered as 3D images and inspected for foci of T₂ elevation.

RESULTS

T₂ values of segments from 2D and reformatted 3D T₂ maps agreed (p > 0.5). The highest 2D segmental T₂ values were 49.9 ± 4.0 ms (no ACR = 0R, n = 18), 48.9 ± 0.8 ms (mild ACR = 1R, n = 3), and 65.0 ms (moderate ACR = 2R). Rendered 3D T₂ maps of cases with 1R showed foci with significantly elevated T₂ signal (T₂ = 58.2 ± 3.6 ms); 5 cases (28%) in the 0R group showed foci with increased T₂ values (>2 SD above adjacent tissue) that were not visible on the 2D T₂ maps.

CONCLUSIONS

This pilot study in a small cohort suggests equivalency of standard segmental analysis between 3D and 2D T₂-mapping. 3D T₂ mapping provides a spatial resolution that permits detection of foci with elevated T₂ in patients with mild ACR.

Quantification of CD4(+) T Cell Alloreactivity and Its Control by Regulatory T Cells Using Time-Lapse Microscopy and Immune Synapse Detection

Assays designed to select transplant recipients for immunosuppression withdrawal have met with limited success, perhaps because they measure events downstream of T cell-alloantigen interactions. Using in vitro time-lapse microscopy in a mouse transplant model, we investigated whether transplant outcome would result in changes in the proportion of CD4(+) T cells forming prolonged interactions with donor dendritic cells. By blocking CD4-MHC class II and CD28-B7 interactions, we defined immunologically relevant interactions as those ≥500 s. Using this threshold, T cell-dendritic cell (T-DC) interactions were examined in rejection, tolerance and T cell control mediated by regulatory T cells. The frequency of T-DC contacts ≥500 s increased with T cells from mice during acute rejection and decreased with T cells from mice rendered unresponsive to alloantigen. Regulatory T cells reduced prolonged T-DC contacts. Importantly, this effect was replicated with human polyclonally expanded naturally occurring regulatory T cells, which we have previously shown can control rejection of human tissues in humanized mouse models. Finally, in a proof-of-concept translational context, we were able to visualize differential allogeneic immune synapse formation in polyclonal CD4(+) T cells using high-throughput imaging flow cytometry.

The natural history of biopsy-negative rejection after heart transplantation

Purpose. The most recent International Society for Heart and Lung Transplantation (ISHLT) biopsy scale classifies cellular and antibody-mediated rejections. However, there are cases with acute decline in left ventricular ejection fraction (LVEF ≤ 45%) but no evidence of rejection on biopsy. Characteristics and treatment response of this biopsy negative rejection (BNR) have yet to be elucidated. Methods. Between 2002 and 2012, we found 12 cases of BNR in 11 heart transplant patients as previously defined. One of the 11 patients was treated a second time for BNR. Characteristics and response to treatment were noted. Results. 12 cases (of 11 patients) were reviewed and 11 occurred during the first year after transplant. 8 cases without heart failure symptoms were treated with an oral corticosteroids bolus and taper or intravenous immunoglobulin. Four cases with heart failure symptoms were treated with thymoglobulin, intravenous immunoglobulin, and intravenous methylprednisolone followed by an oral corticosteroids bolus and taper. Overall, 7 cases resulted in return to normal left ventricular function within a mean of 14 ± 10 days from the initial biopsy. Conclusion. BNR includes cardiac dysfunction and can be a severe form of rejection. Characteristics of these cases of rejection are described with most cases responding to appropriate therapy.

Identification and classification of acute cardiac rejection by intragraft transcriptional profiling

BACKGROUND

Treatment of acute rejection (AR) in heart transplantation relies on histopathological grading of endomyocardial biopsies according to International Society for Heart and Lung Transplantation guidelines. Intragraft gene expression profiling may be a way to complement histological evaluation.

METHODS AND RESULTS

Transcriptional profiling was performed on 26 endomyocardial biopsies, and expression patterns were compared with the 1990 International Society for Heart and Lung Transplantation AR grades. Importantly, transcriptional profiles from settings with an equivalent AR grade appeared the same. In addition, grade 0 profiles could not be distinguished from 1A profiles, and grade 3A profiles could not be distinguished from 3B profiles. Comparing the AR groupings (0+1A, 1B, and 3A+3B), 0+1A showed more striking differences from 1B than from 3A+3B. When these findings were extrapolated to the 2005 revised guidelines, the combination of 1A and 1B into a single category (1R) appears to have brought together endomyocardial biopsies with different underlying processes that are not evident from histological evaluation. Grade 1B was associated with upregulated immune response genes, as 1 categorical distinction from grade 1A. Although grade 1B was distinct from the clinically relevant AR grades 3A and 3B, all of these grades shared a small number of overlapping pathways consistent with common physiological underpinnings.

CONCLUSION

The gene expression similarities and differences identified here in different AR settings have the potential to revise the clinical perspective on acute graft rejection, pending the results of larger studies.