Diagnosis of heart graft rejection

19F MRI detection of acute allograft rejection with in vivo perfluorocarbon labeling of immune cells

Current diagnosis of organ rejection following transplantation relies on tissue biopsy, which is not ideal due to sampling limitations and risks associated with the invasive procedure.We have previously shown that cellular magnetic resonance imaging (MRI) of iron-oxide labeled immune-cell infiltration can provide a noninvasive measure of rejection status by detecting areas of hypointensity on T 2*-weighted images. In this study, we tested the feasibility of using a fluorine-based cellular tracer agent to detect macrophage accumulation in rodent models of acute allograft rejection by fluorine-19 ((19) F) MRI and magnetic resonance spectroscopy. This study used two rat models of acute rejection, including abdominal heterotopic cardiac transplant and orthotopic kidney transplant models. Following in vivo labeling of monocytes and macrophages with a commercially available agent containing perfluoro-15-crown-5-ether, we observed (19) F-signal intensity in the organs experiencing rejection by (19) F MRI, and conventional (1) H MRI was used for anatomical context. Immunofluorescence and histology confirmed macrophage labeling. These results are consistent with our previous studies and show the complementary nature of the two cellular imaging techniques. With no background signal, (19) F MRI/magnetic resonance spectroscopy can provide unambiguous detection of fluorine labeled cells, and may be a useful technique for detecting and quantifying rejection grade in patients.

Noninvasive evaluation of cardiac allograft rejection by cellular and functional cardiac magnetic resonance

OBJECTIVES

We sought to use cardiac magnetic resonance (CMR) to establish sensitive and reliable indexes for noninvasive detection of acute cardiac allograft rejection.

BACKGROUND

Appropriate surveillance for acute allograft rejection is vitally important for graft survival. The current gold standard for diagnosing and staging rejection after organ transplantation is endomyocardial biopsy, which is not only invasive but also prone to sampling errors. The motivation of this study is to establish a CMR-based alternative that is noninvasive and sensitive for early detection of allograft rejection before irreversible damage occurs.

METHODS

We employed a noninvasive 2-pronged approach to detect acute cardiac allograft rejection using a rodent working heart and lung transplantation model. We used CMR to detect immune-cell infiltration at sites of rejection by monitoring the accumulation of dextran-coated ultra-small superparamagnetic-iron-oxide-labeled immune cells (in particular macrophages) in vivo. Simultaneously, we used CMR tagging and strain analysis to detect regional myocardial function loss resulting from acute rejection.

RESULTS

Immune cells infiltration, mainly macrophages and monocytes, could be identified with CMR by in vivo labeling with ultra-small superparamagnetic-iron-oxide. Our data show that immune-cell infiltration in cardiac allograft rejection was highly heterogeneous. Thus, it is not surprising to find inconsistencies between rejection and endomyocardial biopsy results because of the limited number and small samples available. Tagged CMR and strain analysis showed that, as with immune-cell infiltration, ventricular functional loss was also heterogeneous. Although changes in global systolic function were generally not observed until the later stages of rejection, our data revealed that a functional index derived from local strain analysis correlated well with rejection grades, which may be a more sensitive parameter for detecting early rejection.

CONCLUSIONS

CMR is noninvasive and provides a 3-dimensional, whole-heart perspective of the rejection status, potentially allowing more reliable detection of acute allograft rejection.

Cardiovascular magnetic resonance in the diagnosis of acute heart transplant rejection: a review

BACKGROUND

Screening for organ rejection is a critical component of care for patients who have undergone heart transplantation. Endomyocardial biopsy is the gold standard screening tool, but non-invasive alternatives are needed. Cardiovascular magnetic resonance (CMR) is well suited to provide an alternative to biopsy because of its ability to quantify ventricular function, morphology, and characterize myocardial tissue. CMR is not widely used to screen for heart transplant rejection, despite many trials supporting its use for this indication. This review summarizes the different CMR sequences that can detect heart transplant rejection as well as the strengths and weaknesses of their application.

RESULTS

T2 quantification by spin echo techniques has been criticized for poor reproducibility, but multiple studies show its utility in screening for rejection. Human and animal data estimate that T2 quantification can diagnose rejection with sensitivities and specificities near 90%. There is also a suggestion that T2 quantification can predict rejection episodes in patients with normal endomyocardial biopsies.T1 quantification has also shown association with biopsy proven rejection in a small number of trials. T1 weighted gadolinium early enhancement appeared promising in animal data, but has had conflicting results in human trials. Late gadolinium enhancement in the diagnosis of rejection has not been evaluated.CMR derived measures of ventricular morphology and systolic function have insufficient sensitivity to diagnose mild to moderate rejection. CMR derived diastolic function can demonstrate abnormalities in allografts compared to native human hearts, but its ability to diagnose rejection has not yet been tested.There is promising animal data on the ability of iron oxide contrast agents to illustrate the changes in vascular permeability and macrophage accumulation seen in rejection. Despite good safety data, these contrast agents have not been tested in the human heart transplant population.

CONCLUSION

T2 quantification has demonstrated the best correlation to biopsy proven heart transplant rejection. Further studies evaluating diastolic function, late gadolinium enhancement, and iron oxide contrast agents to diagnose rejection are needed. Future studies should focus on combining multiple CMR measures into a transplant rejection scoring system which would improve sensitivity and possibly reduce, if not eliminate, the need for endomyocardial biopsy.

In situ labeling of immune cells with iron oxide particles: an approach to detect organ rejection by cellular MRI

In vivo cell tracking by MRI can provide means to observe biological processes and monitor cell therapy directly. Immune cells, e.g., macrophages, play crucial roles in many pathophysiological processes, including organ rejection, inflammation, autoimmune diseases, cancer, atherosclerotic plaque formation, numerous neurological disorders, etc. The current gold standard for diagnosing and staging rejection after organ transplantation is biopsy, which is not only invasive, but also prone to sampling errors. Here, we report a noninvasive approach using MRI to detect graft rejection after solid organ transplantation. In addition, we present the feasibility of imaging individual macrophages in vivo by MRI in a rodent heterotopic working-heart transplantation model using a more sensitive contrast agent, the micrometer-sized paramagnetic iron oxide particle, as a methodology to detect acute cardiac rejection.

Cytokine gene polymorphisms in heart transplantation: association of low IL-10 production genotype with Quilty effect

BACKGROUND

Cytokines are important modulators of post-transplant, allogeneic immune responses. In heart transplantation, endomyocardial biopsies allow monitoring of histologic and immunologic events that occur inside the graft; their correlation with risk factors condition graft outcome. Recent reports indicate that various cytokine gene allelic polymorphisms control the number of cytokines produced and may be associated with graft outcome.

METHODS

We studied 71 heart transplant recipients between December 1985 and December 2000. We used sequence-specific primers (SSP) polymerase chain reaction to study interleukin-10 (IL-10) polymorphisms at -1082 (G/A), -819 (C/T), and -592 (C/A); tumor necrosis factor alpha (TNF-alpha) at -308 (G/A) and -238 (G/A); transforming growth factor beta (TGF-beta) variants at codon 10 (C/T) and codon 25 (G/C); and interferon-gamma (IFN-gamma) polymorphisms at +874 (T/A). We determined the association of allele, genotype, and haplotype frequencies with the presence of histologically proven rejection episodes (according to International Society for Heart and Lung Transplantation criteria) and the presence of Quilty lesions in endomyocardial biopsy specimens.

RESULTS

We found no association between the polymorphisms studied and the frequency and severity of acute and chronic rejection episodes. However, the gene frequency of allele A at IL-10 -1082, associated with decreased IL-10 production, was increased in patients with Quilty lesions (p = 0.0027, odds ratio = 2.98). Similarly, we found more AA homozygous individuals, compared with AG heterozygous and GG homozygous individuals (p = 0.0017), among patients with Quilty effect. The ATA and ACC IL-10 haplotypes also were associated with Quilty effect (p = 0.0051).

CONCLUSIONS

These results suggest that genetically controlled decreased IL-10 production predisposes to the development of Quilty lesions. The decreased negative regulatory effect of IL-10 on T cells and macrophages may result in enhanced graft infiltration.

Cardiac apoptosis: from organ failure to allograft rejection

Cardiac myocyte apoptosis has been extensively studied in the last few years. Increased interest in the field stems from the hope that pharmacological manipulation of apoptosis may become a valuable tool for preventing excessive cell death observed in different pathological conditions. This paper is not intended as a comprehensive overview of current research about life and death in the cardiovascular system, but rather as a concise update on new developments in areas that were highlighted in a recent series of excellent reviews. A short inventory of unsolved issues concerning the significance of cardiac myocyte loss through apoptosis in both physiological and pathological circumstances is addressed.