Racial Differences in Donor-Derived Cell-Free DNA and Mitochondrial DNA After Heart Transplantation, on Behalf of the GRAfT Investigators

BACKGROUND

Black heart transplant patients are at higher risk of acute rejection (AR) and death than White patients. We hypothesized that this risk may be associated with higher levels of donor-derived cell-free DNA (dd-cfDNA) and cell-free mitochondrial DNA.

METHODS

The Genomic Research Alliance for Transplantation is a multicenter, prospective, longitudinal cohort study. Sequencing was used to quantitate dd-cfDNA and polymerase chain reaction to quantitate cell-free mitochondrial DNA in plasma. AR was defined as ≥2R cellular rejection or ≥1 antibody-mediated rejection. The primary composite outcome was AR, graft dysfunction (left ventricular ejection fraction <50% and decrease by ≥10%), or death.

RESULTS

We included 148 patients (65 Black patients and 83 White patients), median age was 56 years and 30% female sex. The incidence of AR was higher in Black patients compared with White patients (43% versus 19%; P=0.002). Antibody-mediated rejection occurred predominantly in Black patients with a prevalence of 20% versus 2% (P<0.001). After transplant, Black patients had higher levels of dd-cfDNA, 0.09% (interquartile range, 0.001-0.30) compared with White patients, 0.05% (interquartile range, 0.001-0.23; P=0.003). Beyond 6 months, Black patients showed a persistent rise in dd-cfDNA with higher levels compared with White patients. Cell-free mitochondrial DNA was higher in Black patients (185 788 copies/mL; interquartile range, 101 252-422 133) compared with White patients (133 841 copies/mL; interquartile range, 75 346-337 990; P<0.001). The primary composite outcome occurred in 43% and 55% of Black patients at 1 and 2 years, compared with 23% and 27% in White patients, P<0.001. In a multivariable model, Black patient race (hazard ratio, 2.61 [95% CI, 1.35-5.04]; P=0.004) and %dd-cfDNA (hazard ratio, 1.15 [95% CI, 1.03-1.28]; P=0.010) were associated with the primary composite outcome.

CONCLUSIONS

Elevated dd-cfDNA and cell-free mitochondrial DNA after heart transplant may mechanistically be implicated in the higher incidence of AR and worse clinical outcomes in Black transplant recipients.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02423070.

Sex-specific patterns of donor-derived cell-free DNA in heart transplant rejection: An analysis from the Genomic Research Alliance for Transplantation (GRAfT)

BACKGROUND

Noninvasive methods for surveillance of acute rejection are increasingly used in heart transplantation (HT), including donor-derived cell-free DNA (dd-cfDNA). As other cardiac biomarkers differ by sex, we hypothesized that there may be sex-specific differences in the performance of dd-cfDNA for the detection of acute rejection. The purpose of the current study was to examine patterns of dd-cfDNA seen in quiescence and acute rejection in male and female transplant recipients.

METHODS

Patients enrolled in the Genomic Research Alliance for Transplantation who were ≥18 years at the time of HT were included. Rejection was defined by endomyocardial biopsy with acute cellular rejection (ACR) grade ≥2R and/or antibody-mediated rejection ≥ pAMR 1. dd-cfDNA was quantitated using shotgun sequencing. Median dd-cfDNA levels were compared between sexes during quiescence and rejection. The performance of dd-cfDNA by sex was assessed using area under the receiver operator characteristic (AUROC) curve. Allograft injury was defined as dd-cfDNA ≥0.25%.

RESULTS

One hundred fifty-one unique patients (49 female, 32%) were included in the analysis with 1,119 available dd-cfDNA measurements. Baseline characteristics including demographics and comorbidities were not significantly different between sexes. During quiescence, there were no significant sex differences in median dd-cfDNA level (0.04% [IQR 0.00, 0.16] in females vs 0.03% [IQR 0.00, 0.12] in males, p = 0.22). There were no significant sex differences in median dd-cfDNA for ACR (0.33% [0.21, 0.36] in females vs 0.32% [0.21, 1.10] in males, p = 0.57). Overall, median dd-cfDNA levels were higher in antibody-mediated rejection (AMR) than ACR but did not significantly differ by sex (0.50% [IQR 0.18, 0.82] in females vs 0.63% [IQR 0.32, 1.95] in males, p = 0.51). Elevated dd-cfDNA detected ACR/AMR with an AUROC of 0.83 in females and 0.89 in males, p-value for comparison = 0.16.

CONCLUSIONS

There were no significant sex differences in dd-cfDNA levels during quiescence and rejection. Performance characteristics were similar, suggesting similar diagnostic thresholds can be used in men and women for rejection surveillance.

Hannah A. Valantine, M.D., Stanford University School of Medicine

Dr. Hannah Valantine is renowned for her work in transplantation medicine, leadership, and mentoring as well as her efforts to improve scientific workforce diversity. In this interview with Cell, she discusses her research; what Juneteenth means to her; the persistent gender, race, and ethnicity leadership gaps that exist in academic medicine; and the importance of equitable, inclusive, and diverse science.

Applying Genomics to Unravel Health Disparities in Organ Transplantation: Paul I. Terasaki State-of-the-art Lecture; American Transplant Congress 2021

An extensive body of research about team science provides empirical evidence that diverse teams outperform homogenous teams in creating more innovative solutions to complex problems. At the core of diverse and inclusive teams is a rich diversity of perspectives, experiences, and backgrounds that invite new questions and broaden the scope of research. Diverse perspectives are especially relevant for biomedicine, which seeks to find solutions for challenging problems affecting the human condition. It is essential that diversity and inclusion in biomedicine is prioritized as a key driver of innovation, both through the people who conduct the research and the science itself. Key questions have been articulated as important drivers for funding research: (1) Who is doing the science and who is building the tools? (2) What science and technology is being done and how? and (3) Who has access to the knowledge and benefits of scientific innovation? I will briefly review the empirical evidence supporting diversity as a powerful enhancer of the quality and outputs of research and clinical care. I offer my own research as a case study of incorporating a framework of diversity, equity, and inclusion into research that uses new emerging genomic tools for earlier and more precise diagnosis of organ transplant rejection. I will demonstrate how these same tools hold great promise for accelerating the discovery of hitherto unexplored mechanisms that drive the poor outcomes for African ancestry organ transplant recipients, which in turn will identify new diagnostics and therapeutic targets that benefit transplant recipients across all ancestries.

Plasma Cell-Free DNA Predicts Survival and Maps Specific Sources of Injury in Pulmonary Arterial Hypertension

BACKGROUND

Cell-free DNA (cfDNA) is a noninvasive marker of cellular injury. Its significance in pulmonary arterial hypertension (PAH) is unknown.

METHODS

Plasma cfDNA was measured in 2 PAH cohorts (A, n=48; B, n=161) and controls (n=48). Data were collected for REVEAL 2.0 (Registry to Evaluate Early and Long-Term PAH Disease Management) scores and outcome determinations. Patients were divided into the following REVEAL risk groups: low (≤6), medium (7-8), and high (≥9). Total cfDNA concentrations were compared among controls and PAH risk groups by 1-way analysis of variance. Log-rank tests compared survival between cfDNA tertiles and REVEAL risk groups. Areas under the receiver operating characteristic curve were estimated from logistic regression models. A sample subset from cohort B (n=96) and controls (n=16) underwent bisulfite sequencing followed by a deconvolution algorithm to map cell-specific cfDNA methylation patterns, with concentrations compared using t tests.

RESULTS

In cohort A, median (interquartile range) age was 62 years (47-71), with 75% female, and median (interquartile range) REVEAL 2.0 was 6 (4-9). In cohort B, median (interquartile range) age was 59 years (49-71), with 69% female, and median (interquartile range) REVEAL 2.0 was 7 (6-9). In both cohorts, cfDNA concentrations differed among patients with PAH of varying REVEAL risk and controls (analysis of variance P≤0.002) and were greater in the high-risk compared with the low-risk category (P≤0.002). In cohort B, death or lung transplant occurred in 14 of 54, 23 of 53, and 35 of 54 patients in the lowest, middle, and highest cfDNA tertiles, respectively. cfDNA levels stratified as tertiles (log-rank: P=0.0001) and REVEAL risk groups (log-rank: P<0.0001) each predicted transplant-free survival. The addition of cfDNA to REVEAL improved discrimination (area under the receiver operating characteristic curve, 0.72-0.78; P=0.02). Compared with controls, methylation analysis in patients with PAH revealed increased cfDNA originating from erythrocyte progenitors, neutrophils, monocytes, adipocytes, natural killer cells, vascular endothelium, and cardiac myocytes (Bonferroni adjusted P<0.05). cfDNA concentrations derived from erythrocyte progenitor cells, cardiac myocytes, and vascular endothelium were greater in patients with PAH with high-risk versus low-risk REVEAL scores (P≤0.02).

CONCLUSIONS

Circulating cfDNA is elevated in patients with PAH, correlates with disease severity, and predicts worse survival. Results from cfDNA methylation analyses in patients with PAH are consistent with prevailing paradigms of disease pathogenesis.

Circulating microRNAs in cellular and antibody-mediated heart transplant rejection

BACKGROUND

Noninvasive monitoring of heart allograft health is important to improve clinical outcomes. MicroRNAs (miRs) are promising biomarkers of cardiovascular disease and limited studies suggest they can be used to noninvasively diagnose acute heart transplant rejection.

METHODS

The Genomic Research Alliance for Transplantation (GRAfT) is a multicenter prospective cohort study that phenotyped heart transplant patients from 5 mid-Atlantic centers. Patients who had no history of rejection after transplant were compared to patients with acute cellular rejection (ACR) or antibody-mediated rejection (AMR). Small RNA sequencing was performed on plasma samples collected at the time of an endomyocardial biopsy. Differential miR expression was performed with adjustment for clinical covariates. Regression was used to develop miR panels with high diagnostic accuracy for ACR and AMR. These panels were then validated in independent samples from GRAfT and Stanford University. Receiver operating characteristic curves were generated and area under the curve (AUC) statistics calculated. Distinct ACR and AMR clinical scores were developed to translate miR expression data for clinical use.

RESULTS

The GRAfT cohort had a median age of 52 years, with 35% females and 45% Black patients. Between GRAfT and Stanford, we included 157 heart transplant patients: 108 controls and 49 with rejection (50 ACR and 38 AMR episodes). After differential miR expression and regression analysis, we identified 12 miRs that accurately discriminate ACR and 17 miRs in AMR. Independent validation of the miR panels within GRAfT led to an ACR AUC 0.92 (95% confidence interval [CI]: 0.86-0.98) and AMR AUC 0.82 (95% CI: 0.74-0.90). The externally validated ACR AUC was 0.72 (95% CI: 0.59-0.82). We developed distinct ACR and AMR miR clinical scores (range 0-100), a score ≥ 65, identified ACR with 86% sensitivity, 76% specificity, and 98% negative predictive value, for AMR score performance was 82%, 84% and 97%, respectively.

CONCLUSIONS

We identified novel miRs that had excellent performance to noninvasively diagnose acute rejection after heart transplantation. Once rigorously validated, the unique clinical ACR and AMR scores usher in an era whereby genomic biomarkers can be used to screen and diagnose the subtype of rejection. These novel biomarkers may potentially alleviate the need for an endomyocardial biopsy while facilitating the initiation of targeted therapy based on the noninvasive diagnosis of ACR or AMR.

Ending Sexual Harassment in Science: Designing and Administering a Survey That Can Lead to an Improved Organizational Climate

Workplace harassment, particularly sexual harassment, has substantial negative implications for individuals and organizations and for scientific advancement. The National Institutes of Health (NIH) is uniquely positioned to lead the effort to prevent sexual harassment in the scientific community and mitigate its detrimental effects. Recognizing the need for benchmark data, NIH developed and validated the 2019 NIH Workplace Climate and Harassment Survey. The goal was to use best practices in survey design methods to create an instrument for rigorous assessment of harassment incidence and organizational climate predictors of sexual harassment in scientific research environments. This article summarizes the processes used to design and administer the NIH survey and provides brief descriptions of 3 products of the process developed to guide scientific institutions wishing to embark on a data-driven approach to assess and prevent harassment: a document detailing survey development and methods, a survey implementation guide, and the key findings obtained from the survey, including recommendations for interventions targeting the organizational climate at NIH and limitations of the survey. The survey identified that 1 in 5 respondents had experienced sexual harassment in the 12 months preceding their participation in the survey and that women, sexual and gender minorities, younger respondents, trainees/students, and individuals with a disability were more likely to have experienced sexual harassment. Those who had experienced sexual harassment during that period were also more likely to have experienced incivility, bullying, and intimidating behaviors in the workplace. NIH intends to use the survey findings as a quality assurance and quality improvement guide to inform future activities to prevent and address harassment across NIH.

NIH's scientific approach to inclusive excellence

The representation of women and scientists from underrepresented groups (URGs), including Black/African Americans, Hispanic/Latinx, Pacific Islanders, and American Indians, diminishes as individuals advance in their careers from training to senior leadership positions. Correcting this imbalance requires integrated strategies to achieve inclusive excellence within the scientific workforce reflected by creating and sustaining environments, in which diverse talent thrives. The National Institutes of Health (NIH) Scientific Workforce Diversity office has led the charge to develop and implement evidence-informed interventions toward achieving this goal that undergirds NIH's mission to improve the nation's health. Past and current efforts aiming to enhance workforce diversity but targeted to individuals are necessary but insufficient for lasting change. Thus, NIH-funded institutions should develop and prioritize integrated, systems-targeted efforts as foundational components of a well-supported, productive workforce. At the heart of these endeavors is institutional accountability that ties progress toward inclusive excellence to institutional values and reward systems.

Cell-Free DNA to Detect Heart Allograft Acute Rejection

BACKGROUND

After heart transplantation, endomyocardial biopsy (EMBx) is used to monitor for acute rejection (AR). Unfortunately, EMBx is invasive, and its conventional histological interpretation has limitations. This is a validation study to assess the performance of a sensitive blood biomarker-percent donor-derived cell-free DNA (%ddcfDNA)-for detection of AR in cardiac transplant recipients.

METHODS

This multicenter, prospective cohort study recruited heart transplant subjects and collected plasma samples contemporaneously with EMBx for %ddcfDNA measurement by shotgun sequencing. Histopathology data were collected to define AR, its 2 phenotypes (acute cellular rejection [ACR] and antibody-mediated rejection [AMR]), and controls without rejection. The primary analysis was to compare %ddcfDNA levels (median and interquartile range [IQR]) for AR, AMR, and ACR with controls and to determine %ddcfDNA test characteristics using receiver-operator characteristics analysis.

RESULTS

The study included 171 subjects with median posttransplant follow-up of 17.7 months (IQR, 12.1-23.6), with 1392 EMBx, and 1834 %ddcfDNA measures available for analysis. Median %ddcfDNA levels decayed after surgery to 0.13% (IQR, 0.03%-0.21%) by 28 days. Also, %ddcfDNA increased again with AR compared with control values (0.38% [IQR, 0.31-0.83%], versus 0.03% [IQR, 0.01-0.14%]; P<0.001). The rise was detected 0.5 and 3.2 months before histopathologic diagnosis of ACR and AMR. The area under the receiver operator characteristic curve for AR was 0.92. A 0.25%ddcfDNA threshold had a negative predictive value for AR of 99% and would have safely eliminated 81% of EMBx. In addition, %ddcfDNA showed distinctive characteristics comparing AMR with ACR, including 5-fold higher levels (AMR ≥2, 1.68% [IQR, 0.49-2.79%] versus ACR grade ≥2R, 0.34% [IQR, 0.28-0.72%]), higher area under the receiver operator characteristic curve (0.95 versus 0.85), higher guanosine-cytosine content, and higher percentage of short ddcfDNA fragments.

CONCLUSIONS

We found that %ddcfDNA detected AR with a high area under the receiver operator characteristic curve and negative predictive value. Monitoring with ddcfDNA demonstrated excellent performance characteristics for both ACR and AMR and led to earlier detection than the EMBx-based monitoring. This study supports the use of %ddcfDNA to monitor for AR in patients with heart transplant and paves the way for a clinical utility study. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02423070.

Where Are We in Bridging the Gender Leadership Gap in Academic Medicine?

In nearly all walks of life, leadership sets the tone for what gets done, who does it, and how it is achieved. In 2020, the top ranks of academic medicine have not yet attained gender parity-an aspirational goal set 7 years ago in this journal as "50:50 by 2020," and a vital aim for the United States' productivity and innovation as a leader in biomedical research. Parity in academic leadership for women and other groups underrepresented in science and medicine will seed the culture change necessary for inclusive excellence: environments in which individuals from all backgrounds thrive in their pursuit of new knowledge to benefit human health.In this Invited Commentary, the author describes the National Institutes of Health's (NIH's) current system-wide framework and tools for creating cultures of inclusive excellence through a set of guiding principles and integrated strategies. Successful efforts will recognize that individually focused solutions are necessary but not sufficient for institutional culture change. In keeping with a systems approach are implementing accountability and transparency; establishing clear metrics of inclusion, diversity, and equity; tracking and evaluating such metrics; as well as tying these metrics to institutional reward systems. These essential steps to institutional culture transformation require strong partnerships between NIH and the academic community. The author argues that with committed vision, focus, and energy, success is attainable, and soon.

Topic choice contributes to the lower rate of NIH awards to African-American/black scientists

Despite efforts to promote diversity in the biomedical workforce, there remains a lower rate of funding of National Institutes of Health R01 applications submitted by African-American/black (AA/B) scientists relative to white scientists. To identify underlying causes of this funding gap, we analyzed six stages of the application process from 2011 to 2015 and found that disparate outcomes arise at three of the six: decision to discuss, impact score assignment, and a previously unstudied stage, topic choice. Notably, AA/B applicants tend to propose research on topics with lower award rates. These topics include research at the community and population level, as opposed to more fundamental and mechanistic investigations; the latter tend to have higher award rates. Topic choice alone accounts for over 20% of the funding gap after controlling for multiple variables, including the applicant's prior achievements. Our findings can be used to inform interventions designed to close the funding gap.

Donor-derived cell-free DNA predicts allograft failure and mortality after lung transplantation

Background

Allograft failure is common in lung-transplant recipients and leads to poor outcomes including early death. No reliable clinical tools exist to identify patients at high risk for allograft failure. This study tested the use of donor-derived cell-free DNA (%ddcfDNA) as a sensitive marker of early graft injury to predict impending allograft failure.

Methods

This multicenter, prospective cohort study enrolled 106 subjects who underwent lung transplantation and monitored them after transplantation for the development of allograft failure (defined as severe chronic lung allograft dysfunction [CLAD], retransplantation, and/or death from respiratory failure). Plasma samples were collected serially in the first three months following transplantation and assayed for %ddcfDNA by shotgun sequencing. We computed the average levels of ddcfDNA over three months for each patient (avddDNA) and determined its relationship to allograft failure using Cox-regression analysis.

Findings

avddDNA was highly variable among subjects: median values were 3·6%, 1·6% and 0·7% for the upper, middle, and low tertiles, respectively (range 0·1%–9·9%). Compared to subjects in the low and middle tertiles, those with avddDNA in the upper tertile had a 6·6-fold higher risk of developing allograft failure (95% confidence interval 1·6–19·9, p = 0·007), lower peak FEV1 values, and more frequent %ddcfDNA elevations that were not clinically detectable.

Interpretation

Lung transplant patients with early unresolving allograft injury measured via %ddcfDNA are at risk of subsequent allograft injury, which is often clinically silent, and progresses to allograft failure.

Fund

National Institutes of Health.

Impact of Asymmetric Dimethylarginine on Coronary Physiology Early After Heart Transplantation

Cardiac allograft vasculopathy is a major cause of long-term graft failure following heart transplantation. Asymmetric dimethylarginine (ADMA), a marker of endothelial dysfunction, has been mechanistically implicated in the development of cardiac allograft vasculopathy, but its impact on coronary physiology early after transplantation is unknown. Invasive indices of coronary physiology, namely, fractional flow reserve (FFR), the index of microcirculatory resistance, and coronary flow reserve, were measured with a coronary pressure wire in the left anterior descending artery within 8 weeks (baseline) and 1 year after transplant. Plasma levels of ADMA were concurrently assayed using high-performance liquid chromatography. In 46 heart transplant recipients, there was a statistically significant correlation between elevated ADMA levels and lower FFR values at baseline (r = -0.33; p = 0.024); this modest association persisted 1 year after transplant (r = -0.39; p = 0.0085). Patients with a baseline FFR <0.90 (a prognostically validated cutoff) had significantly higher baseline ADMA levels (0.63 ± 0.16 vs 0.54 ± 0.12 µM; p = 0.034). Baseline ADMA (odds ratio 1.80 per 0.1 µM; 95% confidence interval 1.07 to 3.03; p = 0.027) independently predicted a baseline FFR <0.90 after multivariable adjustment. Even after dichotomizing ADMA (≥0.60 µM, provides greatest diagnostic accuracy by receiver operating characteristic curve), this association remained significant (odds ratio 7.52, 95% confidence interval 1.74 to 32.49; p = 0.006). No significant relationship between ADMA and index of microcirculatory resistance or coronary flow reserve was detected. In conclusion, baseline ADMA was a strong independent predictor of FFR <0.90, suggesting that elevated ADMA levels are associated with abnormal epicardial function soon after heart transplantation.

The effect of negative remodeling on fractional flow reserve after cardiac transplantation

BACKGROUND

Negative remodeling is a common occurrence early after cardiac transplantation. Its impact on the development of myocardial ischemia is not well documented. The aim of this study is to investigate the impact of negative remodeling on fractional flow reserve after cardiac transplantation.

METHODS

Thirty-four cardiac transplant recipients underwent intravascular ultrasound (IVUS) and fractional flow reserve (FFR) assessment soon after transplantation and one year later. Patients were divided into those with and without negative remodeling based on IVUS, and the impact on FFR was assessed. In the 19 patients with negative remodeling, there was no significant change in plaque volume (119.3±82.0 to 131.3±91.2mm³, p=0.21), but vessel volume (775.6±212.0 to 621.9±144.1mm³, p<0.0001) and lumen volume (656.3±169.1 to 490.7±132.0mm³, p<0.0001) decreased significantly and FFR likewise decreased significantly (0.88±0.06 to 0.84±0.07, p=0.04). In the 15 patients without negative remodeling, vessel volume did not change (711.7±217.6 to 745.7±198.5, p=0.28), but there was a significant increase in plaque volume (126.8±88.3 to 194.4±92.7, p<0.001) and a resultant significant decrease in FFR (0.89±0.05 to 0.85±0.05, p=0.01).

CONCLUSION

Negative remodeling itself, without any change in plaque volume can cause a significant decrease in fractional flow reserve after cardiac transplantation and appears to be another possible mechanism for myocardial ischemia.

Angiotensin-Converting Enzyme Inhibition Early After Heart Transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) remains a leading cause of mortality after heart transplantation (HT). Angiotensin-converting enzyme inhibitors (ACEIs) may retard the development of CAV but have not been well studied after HT.

OBJECTIVES

This study tested the safety and efficacy of the ACEI ramipril on the development of CAV early after HT.

METHODS

In this prospective, multicenter, randomized, double-blind, placebo-controlled trial, 96 HT recipients were randomized to undergo ramipril or placebo therapy. They underwent coronary angiography, endothelial function testing; measurements of fractional flow reserve (FFR) and coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR); and intravascular ultrasonography (IVUS) of the left anterior descending coronary artery, within 8 weeks of HT. At 1 year, the invasive assessment was repeated. Circulating endothelial progenitor cells (EPCs) were quantified at baseline and 1 year.

RESULTS

Plaque volumes at 1 year were similar between the ramipril and placebo groups (162.1 ± 70.5 mm³ vs. 177.3 ± 94.3 mm³, respectively; p = 0.73). Patients receiving ramipril had improvement in microvascular function as shown by a significant decrease in IMR (21.4 ± 14.7 to 14.4 ± 6.3; p = 0.001) and increase in CFR (3.8 ± 1.7 to 4.8 ± 1.5; p = 0.017), from baseline to 1 year. This did not occur with IMR (17.4 ± 8.4 to 21.5 ± 20.0; p = 0.72) or CFR (4.1 ± 1.8 to 4.1 ± 2.2; p = 0.60) in the placebo-treated patients. EPCs decreased significantly at 1 year in the placebo group but not in the ramipril group.

CONCLUSIONS

Ramipril does not slow development of epicardial plaque volume but does stabilize levels of endothelial progenitor cells and improve microvascular function, which have been associated with improved long-term survival after HT. (Angiotensin Converting Enzyme [ACE] Inhibition and Cardiac Allograft Vasculopathy; NCT01078363).

From the NIH: A Systems Approach to Increasing the Diversity of the Biomedical Research Workforce

The National Institutes of Health (NIH) is committed to attracting, developing, and supporting the best scientists from all groups as an integral part of excellence in training. Biomedical research workforce diversity, capitalizing on the full spectrum of skills, talents, and viewpoints, is essential for solving complex human health challenges. Over the past few decades, the biomedical research workforce has benefited from NIH programs aimed at enhancing diversity. However, there is considerable room for improvement, particularly at the level of independent scientists and within scientific leadership. We provide a rationale and specific opportunities to develop and sustain a diverse biomedical research workforce through interventions that promote the successful transitions to different stages on the path toward completion of training and entry into the biomedical workforce.

Attenuated-Signal Plaque Progression Predicts Long-Term Mortality After Heart Transplantation: IVUS Assessment of Cardiac Allograft Vasculopathy

BACKGROUND

Although cardiac allograft vasculopathy (CAV) is typically characterized by diffuse coronary intimal thickening with pathological vessel remodeling, plaque instability may also play an important role in CAV. Previous studies of native coronary atherosclerosis have demonstrated associations between attenuated-signal plaque (ASP), plaque instability, and adverse clinical events.

OBJECTIVES

This study's aim was to characterize the association between ASP and long-term mortality post-heart transplantation.

METHODS

In 105 heart transplant recipients, serial (baseline and 1-year post-transplant) intravascular ultrasound was performed in the first 50 mm of the left anterior descending artery. The ASP score was calculated by grading the measured angle of attenuation from grades 0 to 4 (specifically, 0°, 1° to 90°, 91° to 180°, 181° to 270°, and >270°) at 1-mm intervals. The primary endpoint was all-cause death or retransplantation.

RESULTS

At 1-year post-transplant, 10.5% of patients demonstrated ASP progression (newly developed or increased ASP). Patients with ASP progression had a higher incidence of acute cellular rejection during the first year (63.6% vs. 22.3%; p = 0.006) and tendency for greater intimal growth (percent intimal volume: 9.2 ± 9.3% vs. 4.4 ± 5.3%; p = 0.07) than those without. Over a median follow-up of 4.6 years, there was a significantly lower event-free survival rate in patients with ASP progression at 1-year post-transplant compared with those without. In contrast, maximum intimal thickness did not predict long-term mortality.

CONCLUSIONS

ASP progression appears to reflect chronic inflammation related to acute cellular rejection and is an independent predictor of long-term mortality after heart transplantation. Serial assessments of plaque instability may enhance identification of high-risk patients who may benefit from closer follow-up and targeted medical therapies.

Single-stranded DNA library preparation uncovers the origin and diversity of ultrashort cell-free DNA in plasma

Circulating cell-free DNA (cfDNA) is emerging as a powerful monitoring tool in cancer, pregnancy and organ transplantation. Nucleosomal DNA, the predominant form of plasma cfDNA, can be adapted for sequencing via ligation of double-stranded DNA (dsDNA) adapters. dsDNA library preparations, however, are insensitive to ultrashort, degraded cfDNA. Drawing inspiration from advances in paleogenomics, we have applied a single-stranded DNA (ssDNA) library preparation method to sequencing of cfDNA in the plasma of lung transplant recipients (40 samples, six patients). We found that ssDNA library preparation yields a greater portion of sub-100 bp nuclear genomic cfDNA (p 10⁻⁵, Mann-Whitney U Test), and an increased relative abundance of mitochondrial (10.7x, p 10⁻⁵) and microbial cfDNA (71.3x, p10⁻⁵). The higher yield of microbial sequences from this method increases the sensitivity of cfDNA-based monitoring for infections following transplantation. We detail the fragmentation pattern of mitochondrial, nuclear genomic and microbial cfDNA over a broad fragment length range. We report the observation of donor-specific mitochondrial cfDNA in the circulation of lung transplant recipients. A ssDNA library preparation method provides a more informative window into understudied forms of cfDNA, including mitochondrial and microbial derived cfDNA and short nuclear genomic cfDNA, while retaining information provided by standard dsDNA library preparation methods.

Monitoring pharmacologically induced immunosuppression by immune repertoire sequencing to detect acute allograft rejection in heart transplant patients: a proof-of-concept diagnostic accuracy study

BACKGROUND

It remains difficult to predict and to measure the efficacy of pharmacological immunosuppression. We hypothesized that measuring the B-cell repertoire would enable assessment of the overall level of immunosuppression after heart transplantation.

METHODS AND FINDINGS

In this proof-of-concept study, we implemented a molecular-barcode-based immune repertoire sequencing assay that sensitively and accurately measures the isotype and clonal composition of the circulating B cell repertoire. We used this assay to measure the temporal response of the B cell repertoire to immunosuppression after heart transplantation. We selected a subset of 12 participants from a larger prospective cohort study (ClinicalTrials.gov NCT01985412) that is ongoing at Stanford Medical Center and for which enrollment started in March 2010. This subset of 12 participants was selected to represent post-heart-transplant events, with and without acute rejection (six participants with moderate-to-severe rejection and six without). We analyzed 130 samples from these patients, with an average follow-up period of 15 mo. Immune repertoire sequencing enables the measurement of a patient's net state of immunosuppression (correlation with tacrolimus level, r = -0.867, 95% CI -0.968 to -0.523, p = 0.0014), as well as the diagnosis of acute allograft rejection, which is preceded by increased immune activity with a sensitivity of 71.4% (95% CI 30.3% to 94.9%) and a specificity of 82.0% (95% CI 72.1% to 89.1%) (cell-free donor-derived DNA as noninvasive gold standard). To illustrate the potential of immune repertoire sequencing to monitor atypical post-transplant trajectories, we analyzed two more patients, one with chronic infections and one with amyloidosis. A larger, prospective study will be needed to validate the power of immune repertoire sequencing to predict rejection events, as this proof-of-concept study is limited to a small number of patients who were selected based on several criteria including the availability of a large number of samples and the absence or presence of rejection events.

CONCLUSIONS

If confirmed in larger, prospective studies, the method described here has potential applications in the tailored management of post-transplant immunosuppression and, more broadly, as a method for assessing the overall activity of the immune system.

Teaching corporate in college

By applying the strengths of corporate models for effective teamwork, academic scientists can drive transdisciplinary research and accelerate biomedical translation.

Circulating cell-free DNA enables noninvasive diagnosis of heart transplant rejection

Monitoring allograft health is an important component of posttransplant therapy. Endomyocardial biopsy is the current gold standard for cardiac allograft monitoring but is an expensive and invasive procedure. Proof of principle of a universal, noninvasive diagnostic method based on high-throughput screening of circulating cell-free donor-derived DNA (cfdDNA) was recently demonstrated in a small retrospective cohort. We present the results of a prospective cohort study (65 patients, 565 samples) that tested the utility of cfdDNA in measuring acute rejection after heart transplantation. Circulating cell-free DNA was purified from plasma and sequenced (mean depth, 1.2 giga-base pairs) to quantify the fraction of cfdDNA. Through a comparison with endomyocardial biopsy results, we demonstrate that cfdDNA enables diagnosis of acute rejection after heart transplantation, with an area under the receiver operating characteristic curve of 0.83 and sensitivity and specificity that are comparable to the intrinsic performance of the biopsy itself. This noninvasive genome transplant dynamics approach is a powerful and informative method for routine monitoring of allograft health without incurring the risk, discomfort, and expense of an invasive biopsy.

Gene expression profiling to study racial differences after heart transplantation

Background

The basis for increased mortality after heart transplantation in African Americans and other non-Caucasian racial groups is poorly defined. We hypothesized that increased risk of adverse events is driven by biological factors. To test this hypothesis in the IMAGE study, we determined whether the event rate of the primary outcome of acute rejection, graft dysfunction, death, or re-transplantation varied by race as a function of calcineurin inhibitor levels and gene expression profile (GEP) scores.

Methods

We determined the event rate of the primary outcome, comparing racial groups, stratified by time post-transplant. Logistic regression was used to compute the relative risk across racial groups and linear modeling was used to measure the dependence of CNI levels and GEP score on race.

Results

In 580 patients followed for a median of 19 months, the incidence of the primary endpoint in African Americans, other non-Caucasians, and Caucasians was 18.3%, 22.2%, and 8.5%, respectively (p<0.001). There were small but significant correlations of race and tacrolimus trough levels to GEP score. Tacrolimus levels were similar between races. Of patients receiving tacrolimus, other non-Caucasians had higher GEP scores than the other racial groups. African American recipients demonstrated a unique decrease in expression of the FLT3 gene in response to higher tacrolimus levels.

Conclusions

African Americans and other non-Caucasian heart transplant recipients were 2.5–3 times more likely than Caucasians to experience outcome events in IMAGE. The increased risk of adverse outcomes may be partly due to the biology of the alloimmune response, which is less effectively inhibited at similar tacrolimus levels in minority racial groups.

The gender gap in academic medicine: comparing results from a multifaceted intervention for stanford faculty to peer and national cohorts

PURPOSE

To assess whether the proportion of women faculty, especially at the full professor rank, increased from 2004 to 2010 at Stanford University School of Medicine after a multifaceted intervention.

METHOD

The authors surveyed gender composition and faculty satisfaction five to seven years after initiating a multifaceted intervention to expand recruitment and development of women faculty. The authors assessed pre/post relative change and rates of increase in women faculty at each rank, and faculty satisfaction; and differences in pre/post change and estimated rate of increase between Stanford and comparator cohorts (nationally and at peer institutions).

RESULTS

Post intervention, women faculty increased by 74% (234 to 408), with assistant, associate, and full professors increasing by 66% (108 to 179), 87% (74 to 138), and 75% (52 to 91), respectively. Nationally and at peer institutions, women faculty increased by about 30% (30,230 to 39,200 and 4,370 to 5,754, respectively), with lower percentages at each rank compared with Stanford. Estimated difference (95% CI) in annual rate of increase was larger for Stanford versus the national cohort: combined ranks 0.36 (0.17 to 0.56), P = .001; full professor 0.40 (0.18 to 0.62), P = .001; and versus the peer cohort: combined ranks 0.29 (0.07 to 0.51), P = .02; full professor 0.37 (0.14 to 0.60), P = .003. Stanford women faculty satisfaction increased from 48% (2003) to 71% (2008).

CONCLUSIONS

Increased satisfaction and proportion of women faculty, especially full professors, suggest that the intervention may ameliorate the gender gap in academic medicine.

Utility of gene expression profiling score variability to predict clinical events in heart transplant recipients

BACKGROUND

Gene expression profiling test scores have primarily been used to identify heart transplant recipients who have a low probability of rejection at the time of surveillance testing. We hypothesized that the variability of gene expression profiling test scores within a patient may predict risk of future events of allograft dysfunction or death.

METHOD

Patients from the IMAGE study with rejection surveillance gene expression profiling tests performed at 1- to 6-month intervals were selected for this cohort study. Gene expression profiling score variability was defined as the standard deviation of an individual's cumulative test scores. Gene expression profiling ordinal score (range, 0-39), threshold score (binary value=1 if ordinal score ≥ 34), and score variability were studied in multivariate Cox regression models to predict future clinical events.

RESULTS

Race, age at time of transplantation, and time posttransplantation were significantly associated with future events in the univariate analysis. In the multivariate analyses, gene expression profiling score variability, but not ordinal scores or scores over threshold, was independently associated with future clinical events. The regression coefficient P values were <0.001, 0.46, and 0.773, for gene expression profiling variability, ordinal, and threshold scores, respectively. The hazard ratio for a 1 unit increase in variability was 1.76 (95% CI, 1.4-2.3).

DISCUSSION

The variability of a heart recipient's gene expression profiling test scores over time may provide prognostic utility. This information is independent of the probability of acute cellular rejection at the time of testing that is rendered from a single ordinal gene-expression profiling test score.

Temporal response of the human virome to immunosuppression and antiviral therapy

There are few substantive methods to measure the health of the immune system, and the connection between immune strength and the viral component of the microbiome is poorly understood. Organ transplant recipients are treated with posttransplant therapies that combine immunosuppressive and antiviral drugs, offering a window into the effects of immune modulation on the virome. We used sequencing of cell-free DNA in plasma to investigate drug-virome interactions in a cohort of organ transplant recipients (656 samples, 96 patients) and find that antivirals and immunosuppressants strongly affect the structure of the virome in plasma. We observe marked virome compositional dynamics at the onset of the therapy and find that the total viral load increases with immunosuppression, whereas the bacterial component of the microbiome remains largely unaffected. The data provide insight into the relationship between the human virome, the state of the immune system, and the effects of pharmacological treatment and offer a potential application of the virome state to predict immunocompetence.

Transdisciplinary translational science and the case of preterm birth

Medical researchers have called for new forms of translational science that can solve complex medical problems. Mainstream science has made complementary calls for heterogeneous teams of collaborators who conduct transdisciplinary research so as to solve complex social problems. Is transdisciplinary translational science what the medical community needs? What challenges must the medical community overcome to successfully implement this new form of translational science? This article makes several contributions. First, it clarifies the concept of transdisciplinary research and distinguishes it from other forms of collaboration. Second, it presents an example of a complex medical problem and a concrete effort to solve it through transdisciplinary collaboration: for example, the problem of preterm birth and the March of Dimes effort to form a transdisciplinary research center that synthesizes knowledge on it. The presentation of this example grounds discussion on new medical research models and reveals potential means by which they can be judged and evaluated. Third, this article identifies the challenges to forming transdisciplines and the practices that overcome them. Departments, universities and disciplines tend to form intellectual silos and adopt reductionist approaches. Forming a more integrated (or 'constructionist'), problem-based science reflective of transdisciplinary research requires the adoption of novel practices to overcome these obstacles.

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.

Gene-expression profiling for rejection surveillance after cardiac transplantation

BACKGROUND

Endomyocardial biopsy is the standard method of monitoring for rejection in recipients of a cardiac transplant. However, this procedure is uncomfortable, and there are risks associated with it. Gene-expression profiling of peripheral-blood specimens has been shown to correlate with the results of an endomyocardial biopsy.

METHODS

We randomly assigned 602 patients who had undergone cardiac transplantation 6 months to 5 years previously to be monitored for rejection with the use of gene-expression profiling or with the use of routine endomyocardial biopsies, in addition to clinical and echocardiographic assessment of graft function. We performed a noninferiority comparison of the two approaches with respect to the composite primary outcome of rejection with hemodynamic compromise, graft dysfunction due to other causes, death, or retransplantation.

RESULTS

During a median follow-up period of 19 months, patients who were monitored with gene-expression profiling and those who underwent routine biopsies had similar 2-year cumulative rates of the composite primary outcome (14.5% and 15.3%, respectively; hazard ratio with gene-expression profiling, 1.04; 95% confidence interval, 0.67 to 1.68). The 2-year rates of death from any cause were also similar in the two groups (6.3% and 5.5%, respectively; P=0.82). Patients who were monitored with the use of gene-expression profiling underwent fewer biopsies per person-year of follow-up than did patients who were monitored with the use of endomyocardial biopsies (0.5 vs. 3.0, P<0.001).

CONCLUSIONS

Among selected patients who had received a cardiac transplant more than 6 months previously and who were at a low risk for rejection, a strategy of monitoring for rejection that involved gene-expression profiling, as compared with routine biopsies, was not associated with an increased risk of serious adverse outcomes and resulted in the performance of significantly fewer biopsies. (ClinicalTrials.gov number, NCT00351559.)

Effect of rapamycin therapy on coronary artery physiology early after cardiac transplantation

BACKGROUND

Rapamycin has been shown to reduce anatomical evidence of cardiac allograft vasculopathy, but its effect on coronary artery physiology is unknown.

METHODS

Twenty-seven patients without angiographic evidence of coronary artery disease underwent measurement of fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR) within 8 weeks and then 1 year after transplantation using a pressure sensor/thermistor-tipped guidewire. Measurements were compared between consecutive patients who were on rapamycin for at least 3 months during the first year after transplantation (rapamycin group, n = 9) and a comparable group on mycophenolate mofetil (MMF) instead (MMF group, n = 18).

RESULTS

At baseline, there was no significant difference in FFR, CFR, or IMR between the 2 groups. At 1 year, FFR declined significantly in the MMF group (0.87 +/- 0.06 to 0.82 +/- 0.06, P = .009) but did not change in the rapamycin group (0.91 +/- 0.05 to 0.89 +/- 0.04, P = .33). Coronary flow reserve and IMR did not change significantly in the MMF group (3.1 +/- 1.7 to 3.2 +/- 1.0, P = .76; and 27.5 +/- 18.1 to 19.1 +/- 7.6, P = .10, respectively) but improved significantly in the rapamycin group (2.3 +/- 0.8 to 3.8 +/- 1.4, P < .03; and 27.0 +/- 11.5 to 17.6 +/- 7.5, P < .03, respectively). Multivariate regression analysis revealed that rapamycin therapy was an independent predictor of CFR and FFR at 1 year after transplantation.

CONCLUSION

Early after cardiac transplantation, rapamycin therapy is associated with improved coronary artery physiology involving both the epicardial vessel and the microvasculature.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.

Outcome in cardiac recipients of donor hearts with increased left ventricular wall thickness

The ongoing shortage of donors for cardiac transplantation has led to a trend toward acceptance of donor hearts with some structural abnormalities including left ventricular hypertrophy. To evaluate the outcome in recipients of donor hearts with increased left ventricular wall thickness (LVWT), we retrospectively analyzed data for 157 cardiac donors and respective recipients from January 2001 to December 2004. There were 47 recipients of donor heart with increased LVWT >or=1.2 cm, which constituted the study group and 110 recipients of a donor heart with normal LVWT < 1.2 cm that formed the control group. At 3 +/- 1.5 years, recipient survival was lower (50% vs. 82%, p = 0.0053) and incidence of allograft vasculopathy was higher (50% vs. 22%, p = 0.05) in recipients of donor heart with LVWT > 1.4 cm as compared to LVWT <or= 1.4 cm. By Cox regression, donor LVWT > 1.4 cm (p = 0.003), recipient preoperative ventricular assist device (VAD) support (p = 0.04) and bypass time > 150 min (p = 0.05) were predictors of reduced survival. Our results suggest careful consideration of donor hearts with echocardiographic evidence of increased LVWT in the absence of hypovolemia, because they may be associated with poorer outcomes; such hearts should potentially be reserved only for the most desperately ill recipients.

Cytomegalovirus-associated allograft rejection in heart transplant patients

PURPOSE OF REVIEW

Modern antiviral strategies are effective in controlling the clinical syndromes associated with acute cytomegalovirus infection in heart transplant recipients. Despite this effectiveness, subclinical cytomegalovirus infection is a common finding in these patients and its impact on long-term graft outcome is currently underestimated.

RECENT FINDINGS

Recent studies provide evidence implicating subclinical cytomegalovirus infection in the pathogenesis of allograft rejection and cardiac allograft vasculopathy. In this process, cytomegalovirus interacts with local inflammatory pathways, and systemic immune-regulation mechanisms, which may lead to graft damage, even in the absence of cytomegalovirus replication within the graft. Consequently, in addition to pharmacologic strategies that inhibit viral replication, immune-based therapies that abrogate host immune response may provide an effective tool to prevent the indirect impact of cytomegalovirus on graft function.

SUMMARY

Current evidence suggests that subclinical cytomegalovirus infection plays an important role in the pathogenesis of long-term graft dysfunction in heart transplant recipients and in other solid organ transplant recipients. Pending the availability of definitive data from randomized trials, we propose that the use of pharmacologic and immune-based approaches, directed at complete suppression of cytomegalovirus infection, represents the best strategy for prevention of cytomegalovirus-induced rejection, cardiac allograft vasculopathy and chronic allograft damage.

Changes in coronary anatomy and physiology after heart transplantation

Cardiac allograft vasculopathy (CAV) is a progressive process involving the epicardial and microvascular coronary systems. The timing of the development of abnormalities in these 2 compartments and the correlation between changes in physiology and anatomy are undefined. The invasive evaluation of coronary artery anatomy and physiology with intravascular ultrasound, fractional flow reserve, coronary flow reserve, and the index of microcirculatory resistance (IMR) was performed in the left anterior descending coronary artery during 151 angiographic evaluations of asymptomatic heart transplant recipients from 0 to >5 years after heart transplantation (HT). There was no angiographic evidence of significant CAV, but during the first year after HT, fractional flow reserve decreased significantly (0.89 +/- 0.06 vs 0.85 +/- 0.07, p = 0.001), and percentage plaque volume derived by intravascular ultrasound increased significantly (15.6 +/- 7.7% to 22.5 +/- 12.3%, p = 0.0002), resulting in a significant inverse correlation between epicardial physiology and anatomy (r = -0.58, p <0.0001). The IMR was lower in these patients compared with those > or =2 years after HT (24.1 +/- 14.3 vs 29.4 +/- 18.8 units, p = 0.05), suggesting later spread of CAV to the microvasculature. As the IMR increased, fractional flow reserve increased (0.86 +/- 0.06 to 0.90 +/- 0.06, p = 0.0035 comparing recipients with IMRs < or =20 to those with IMRs > or =40), despite no difference in percentage plaque volume (21.0 +/- 11.2% vs 20.5 +/- 10.5%, p = NS). In conclusion, early after HT, anatomic and physiologic evidence of epicardial CAV was found. Later after HT, the physiologic effect of epicardial CAV may be less, because of increased microvascular dysfunction.