Artificial intelligence for detection of microsatellite instability in colorectal cancer-a multicentric analysis of a pre-screening tool for clinical application.

BACKGROUND: Microsatellite instability (MSI)/mismatch repair deficiency (dMMR) is a key genetic feature which should be tested in every patient with colorectal cancer (CRC) according to medical guidelines. Artificial intelligence (AI) methods can detect MSI/dMMR directly in routine pathology slides, but the test performance has not been systematically investigated with predefined test thresholds. METHOD: We trained and validated AI-based MSI/dMMR detectors and evaluated predefined performance metrics using nine patient cohorts of 8343 patients across different countries and ethnicities. RESULTS: Classifiers achieved clinical-grade performance, yielding an area under the receiver operating curve (AUROC) of up to 0.96 without using any manual annotations. Subsequently, we show that the AI system can be applied as a rule-out test: by using cohort-specific thresholds, on average 52.73% of tumors in each surgical cohort [total number of MSI/dMMR = 1020, microsatellite stable (MSS)/ proficient mismatch repair (pMMR) = 7323 patients] could be identified as MSS/pMMR with a fixed sensitivity at 95%. In an additional cohort of N = 1530 (MSI/dMMR = 211, MSS/pMMR = 1319) endoscopy biopsy samples, the system achieved an AUROC of 0.89, and the cohort-specific threshold ruled out 44.12% of tumors with a fixed sensitivity at 95%. As a more robust alternative to cohort-specific thresholds, we showed that with a fixed threshold of 0.25 for all the cohorts, we can rule-out 25.51% in surgical specimens and 6.10% in biopsies. INTERPRETATION: When applied in a clinical setting, this means that the AI system can rule out MSI/dMMR in a quarter (with global thresholds) or half of all CRC patients (with local fine-tuning), thereby reducing cost and turnaround time for molecular profiling.

COVID-19 effects on the kidney.

Apart from pulmonary disease, acute kidney injury (AKI) is one of the most frequent and most severe organ complications in severe coronavirus disease 2019 (COVID-19). The SARS-CoV­2 virus has been detected in renal tissue. Patients with chronic kidney disease (CKD) before and on dialysis and specifically renal transplant patients represent a particularly vulnerable population. The increasing number of COVID-19 infected patients with renal involvement led to an evolving interest in the analysis of its pathophysiology, morphology and modes of virus detection in the kidney. Meanwhile, there are ample data from several autopsy and kidney biopsy studies that differ in the quantity of cases as well as in their quality. While the detection of SARS-CoV­2 RNA in the kidney leads to reproducible results, the use of electron microscopy for visualisation of the virus is difficult and currently critically discussed due to various artefacts. The exact contribution of indirect or direct effects on the kidney in COVID-19 are not yet known and are currently the focus of intensive research.

[COVID-19 effects on the kidney]. / COVID-19-Auswirkungen auf die Niere.

Apart from pulmonary disease, acute kidney injury (AKI) is one of the most frequent and most severe organ complications in severe coronavirus disease 2019 (COVID-19). The SARS-CoV­2 virus has been detected in renal tissue. Patients with chronic kidney disease (CKD) before and on dialysis and specifically renal transplant patients represent a particularly vulnerable population. The increasing number of COVID-19 infected patients with renal involvement led to an evolving interest in the analysis of its pathophysiology, morphology and modes of virus detection in the kidney. Meanwhile, there are ample data from several autopsy and kidney biopsy studies that differ in the quantity of cases as well as in their quality. While the detection of SARS-CoV­2 RNA in the kidney leads to reproducible results, the use of electron microscopy for visualisation of the virus is difficult and currently critically discussed due to various artefacts. The exact contribution of indirect or direct effects on the kidney in COVID-19 are not yet known and are currently the focus of intensive research.

[COVID-19 and kidney involvement]. / COVID-19 und Nierenbefall: Pathologie.

Apart from the pulmonary disease, acute kidney injury is one of the most frequent and most severe organ complications in severe coronavirus disease 2019 (COVID-19). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could also be detected in renal tissue. Patients with chronic kidney disease and on dialysis as well as kidney transplantation patients represent a particularly vulnerable population. The increasing number of patients infected with SARS-CoV­2 has aroused increased interest in the exact pathophysiology and morphology of kidney damage as well as the direct detection of the virus in the kidneys, which in contrast to the lungs is overall more difficult to perform. Meanwhile, data from several large autopsy and kidney biopsy studies are now available. While the detection of SARS-CoV­2 RNA in tissue leads to consistently reproducible results, the use of electron microscopy for visualization of the virus is critically discussed due to various artefacts. The exact and direct effects of SARS-CoV­2 on the kidneys are not yet known in detail and are currently the focus of intensive research.

[Late Breaking Session Pathology and COVID-19 Report]. / Bericht zur Late-Breaking Session Pathologie und COVID-19.

This paper briefly summarizes the late-breaking session "Pathology and COVID-19" that took place at the virtual congress of the German Society of Pathology on June 6, 2020. The lectures tackled a broad variety of aspects, including the German Registry for COVID-19 autopsies (DeRegCOVID), the detection methods of SARS-CoV­2 in pathological material, the typical lung findings in severe COVID-19 cases, the distinct (micro)vascular changes and the cardiac and gastrointestinal involvement in COVID-19. In summary, in this first scientific meeting in German pathology on the COVID-19 pandemic, it became clear that pathologists in Germany, Austria and Switzerland have reacted very quickly to the pandemic and have established an autopsy program that has led to medically highly relevant findings.

MIF in kidney diseases : A story of Dr. Jekyll and Mr. Hyde.

BACKGROUND: Macrophage migration-inhibitory factor (MIF) is a cytokine best known for its proinflammatory and disease-aggravating role in a number of conditions, including atherosclerosis, autoimmune diseases, sepsis, and glomerulonephritides. OBJECTIVES: In our studies we aimed to define the role of MIF on local renal resident cells, in particular the renal epithelium. RESULTS: We have shown that MIF exerts local effects on glomerular cells, in particular the parietal epithelial cells and mesangial cells, promoting their pathological proliferation and aggravating disease course of a murine model of immune-mediated glomerulonephritis. In contrast, in a large set of animal and in vitro experiments, we have shown that in the setting of chronic kidney disease, MIF had an unexpected and potent antifibrotic and anti-inflammatory effect. This was mediated by enhanced regeneration and reduced cell-cycle arrest of tubular epithelial cells. Finally, in a combined approach using clinical studies, animal models, and in vitro experiments, we have shown that MIF is also renoprotective in the setting of acute kidney injury. In this setting, MIF-modulated programmed cell death of tubular cells and thereby reduced necroinflammation and kidney injury. CONCLUSIONS: Taken together, MIF has a dual role in kidney diseases, promoting (auto)immune glomerular diseases and limiting tubular cell injury in the setting of acute and chronic kidney diseases. These data suggest potential safety issues of systemic MIF targeted therapies, but also open new therapeutic options by targeting MIF or its analogues to tubular cells.

[MIF in kidney diseases : A story of Dr. Jekyll and Mr. Hyde (German version)]. / MIF in Nierenerkrankungen : Eine Geschichte über Dr. Jekyll und Mr. Hyde.

BACKGROUND: Macrophage migration-inhibitory factor (MIF) is a cytokine best known for its proinflammatory and disease-aggravating role in a number of conditions, including atherosclerosis, autoimmune diseases, sepsis, and glomerulonephritides. OBJECTIVES: In our studies we aimed to define the role of MIF on local renal resident cells, in particular the renal epithelium. RESULTS: We have shown that MIF exerts local effects on glomerular cells, in particular the parietal epithelial cells and mesangial cells, promoting their pathological proliferation and aggravating disease course of a murine model of immune-mediated glomerulonephritis. In contrast, in a large set of animal and in vitro experiments, we have shown that in the setting of chronic kidney disease, MIF had an unexpected and potent antifibrotic and anti-inflammatory effect. This was mediated by enhanced regeneration and reduced cell-cycle arrest of tubular epithelial cells. Finally, in a combined approach using clinical studies, animal models, and in vitro experiments, we have shown that MIF is also renoprotective in the setting of acute kidney injury. In this setting, MIF-modulated programmed cell death of tubular cells and thereby reduced necroinflammation and kidney injury. CONCLUSIONS: Taken together, MIF has a dual role in kidney diseases, promoting (auto)immune glomerular diseases and limiting tubular cell injury in the setting of acute and chronic kidney diseases. These data suggest potential safety issues of systemic MIF targeted therapies, but also open new therapeutic options by targeting MIF or its analogues to tubular cells.

[What is certain in the treatment of glomerulonephritis?] / Was ist gesichert in der Therapie der Glomerulonephritis?

Glomerulonephritides essentially all belong to the rare diseases; however, they are the most common cause of end-stage renal disease in young adults. Besides obtaining a specific diagnosis via a renal biopsy, assessing the prognosis constitutes the other essential step in the work-up, since this enables a decision to be made on whether supportive care with relatively few adverse effects is sufficient or whether additional immunosuppressive therapy is required. The latter is discussed focusing on the most common European types of glomerulonephritis: immunoglobulin A nephropathy, membranous glomerulonephritis, minimal change nephropathy and focal segmental glomerulosclerosis.

Prednisolone does not affect direct-acting antivirals against hepatitis C, but inhibits interferon-alpha production by plasmacytoid dendritic cells.

BACKGROUND: Chronic hepatitis C virus (HCV) infection compromises long-term outcomes of liver transplantation. Although glucocorticosteroid-based immunosuppression is commonly used, discussion is ongoing on the effect of prednisolone (Pred) on HCV recurrence and response to antiviral therapy post transplantation. Recently, new drugs (direct-acting antivirals) have been approved for the treatment of HCV, however, it remains unknown whether their antiviral activity is affected by Pred. The aim of this study was to investigate the effects of Pred on the antiviral activity of asunaprevir (Asu), daclatasvir (Dac), ribavirin (RBV), and interferon-alpha (IFN-α), and on plasmacytoid dendritic cells (PDCs), the main IFN-α-producing immune cells. METHODS: The effects of Pred and antiviral compounds were tested in both a subgenomic and infectious HCV replication model. Furthermore, effects were tested on human PDCs stimulated with a Toll-like receptor-7 ligand. RESULT: Pred did not directly affect HCV replication and did not inhibit the antiviral action of Asu, Dac, RBV, or IFN-α. Stimulated PDCs potently suppressed HCV replication. This suppression was reversed by treating PDCs with Pred. Pred significantly decreased IFN-α production by PDCs without affecting cell viability. When Asu and Dac were combined with PDCs, a significant cooperative antiviral effect was observed. CONCLUSION: This study shows that Pred acts on the antiviral function of PDCs. Pred does not affect the antiviral action of Asu, Dac, RBV, or IFN-α. This implies that there is no contraindication to combine antiviral therapies with Pred in the post-transplantation management of HCV recurrence.

Renal allograft fibrosis: biology and therapeutic targets.

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3-6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor-related factors, in particular in case of expanded criteria donors, ischemia-reperfusion injury, immune-mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non-transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.

Rapamycin has suppressive and stimulatory effects on human plasmacytoid dendritic cell functions.

Plasmacytoid dendritic cells (PDC) are involved in innate immunity by interferon (IFN)-α production, and in adaptive immunity by stimulating T cells and inducing generation of regulatory T cells (Treg ). In this study we studied the effects of mammalian target of rapamycin (mTOR) inhibition by rapamycin, a commonly used immunosuppressive and anti-cancer drug, on innate and adaptive immune functions of human PDC. A clinically relevant concentration of rapamycin inhibited Toll-like receptor (TLR)-7-induced IFN-α secretion potently (-64%) but TLR-9-induced IFN-α secretion only slightly (-20%), while the same concentration suppressed proinflammatory cytokine production by TLR-7-activated and TLR-9-activated PDC with similar efficacy. Rapamycin inhibited the ability of both TLR-7-activated and TLR-9-activated PDC to stimulate production of IFN-γ and interleukin (IL)-10 by allogeneic T cells. Surprisingly, mTOR-inhibition enhanced the capacity of TLR-7-activated PDC to stimulate naive and memory T helper cell proliferation, which was caused by rapamycin-induced up-regulation of CD80 expression on PDC. Finally, rapamycin treatment of TLR-7-activated PDC enhanced their capacity to induce CD4(+) forkhead box protein 3 (FoxP3)(+) regulatory T cells, but did not affect the generation of suppressive CD8(+) CD38(+) lymphocyte activation gene (LAG)-3(+) Treg . In general, rapamycin inhibits innate and adaptive immune functions of TLR-stimulated human PDC, but enhances the ability of TLR-7-stimulated PDC to stimulate CD4(+) T cell proliferation and induce CD4(+) FoxP3(+) regulatory T cell generation.

[New approaches in progressive kidney diseases]. / Neue Ansätze bei progressiven Nierenerkrankungen.

Renal fibrosis, i.e. the replacement of functional tissue with scar tissue, represents the pathological correlate for chronic kidney disease (CKD). A great number of renal diseases lead to CKD and thereby to renal fibrosis. Therefore, renal fibrosis represents an excellent treatment option for patients with CKD. Here we discuss the problems with the preclinical identification and testing of potential factors and therapeutic approaches for renal fibrosis as well as obstacles in the translation of these results to clinical practice. We present the preclinical evidence for the role of novel molecules involved in renal fibrosis, e.g. platelet-derived growth factors (PDGF), C5a or peroxisome proliferator-activated receptor-α (PPAR-α).

Association of biochemical parameters and RAGE gene polymorphisms in healthy infants and their mothers.

BACKGROUND: The receptor for advanced glycation end-products (RAGEs) and its gene polymorphisms are implicated in the pathogenesis of different chronic diseases including diabetes and its complications. Infant formulas contain high amounts of advanced glycation end-products (AGEs) - the ligands of RAGE. METHODS: In this cross-sectional study, we examined the impact of G82S and -374 A/T polymorphisms in the gene encoding RAGE on standard blood chemistry, soluble (s)RAGE and inflammatory markers in 244 healthy infants (3-16months of age) and in 119 healthy mothers. Children were subdivided according to age (younger and older than 8months) and for the -374 A/T polymorphism according to the feeding regimen (breast-fed vs. infant formula-fed). RESULTS: Minor allele of the RAGE gene polymorphism G82S was associated with reduced plasma sRAGE in all age groups and with increased sICAM-1 in older children and mothers. Minor allele carrying mothers had decreased insulin sensitivity and HDL. The A allele of the RAGE gene promoter polymorphism -374 A/T was associated with higher indices of insulin resistance in young infant formula-fed, but not breast-fed children. In older, formerly infant formula-fed children signs of insulin resistance diminished, while formerly breast-fed children with A allele were more insulin sensitive. CONCLUSIONS: The phenotype of minor allele carriers in G82S is associated with reduced levels of protective sRAGE in healthy infants. With increasing age sICAM-1 levels increased and insulin resistance developed. In early childhood the phenotype of the -374 A/T polymorphism was diet-dependently associated with changes in glucose metabolism, which diminished with increasing age.

Neuronal activation in the CNS during different forms of acute renal failure in rats.

The effect of experimentally induced acute renal failure (ARF) on neuronal cell activation was investigated by immunohistochemistry for Fos and Fra-2 in the rat brain. ARF in rats was induced by bilateral nephrectomy (BNX), bilateral ureter ligature (BUL) and uranyl acetate injection with proper controls (sham-operation or saline injections, respectively). To follow the effect of the development of ARF, rats were killed 30 and 60 min, and 3, 12, 24 and 72 h after surgery, or 3 h to 12 days after uranyl acetate injections. In the BUL and BNX rats, urea and creatinine rose markedly in the plasma within 72 h, while in the uranyl acetate-injected rats the highest levels were observed on the 7th day, followed by a marked decline. At each time-point of the three different, experimentally induced ARF, the presence of Fos- and/or Fra-2-immunoreactive neurons was determined in 120 different brain areas and nuclei. In general, the 73 of 120 brain areas that showed time and intensity dependent activation in response to ARF can be classified into four groups: 1) biogenic amine (noradrenaline, adrenaline, histamine and 5-HT) expressing cell groups in the lower brainstem, 2) "stress-sensitive" forebrain areas, with regard to certain hypothalamic, limbic and cortical areas, 3) neuronal cell groups that participate in the central regulation of body and brain water and electrolyte homeostasis, including the circumventricular organs, and 4) central autonomic cell groups, especially visceral sensory cell groups in the brain, which are in primary, secondary or tertiary connections with renal afferents. Data presented here indicate that a wide variety of neurons in several regulatory mechanisms is affected by ARF-induced peripheral and central alterations.

CCN3 is a novel endogenous PDGF-regulated inhibitor of glomerular cell proliferation.

CCN proteins affect cell proliferation, migration, attachment, and differentiation. We identified CCN3 as a suppressed gene following platelet-derived growth factor (PDGF)-BB or -DD stimulation in a cDNA-array analysis of mesangial cells. In vitro growth-arrested mesangial cells overexpressed and secreted CCN3, whereas the addition of the recombinant protein inhibited cell growth. Induction of mesangial cell proliferation by PDGF-BB or the specific PDGF beta-receptor ligand PDGF-DD led to downregulation of CCN3 mRNA, confirming the array study. Specific PDGF alpha-receptor ligands had no effect. CCN3 protein was found in arterial smooth muscle cells, the medullary interstitium, and occasional podocytes in the healthy rat kidney. Glomerular CCN3 was low prior to mesangial proliferation but increased as glomerular cell proliferation subsided during mesangioproliferative glomerulonephritis (GN). Inhibition of PDGF-B in mesangioproliferative disease led to overexpression of glomerular CCN3 mRNA. CCN3 localized mostly to podocytes in human glomeruli, but this expression varied widely in different human glomerulonephritides. Glomerular cell proliferation negatively correlated with CCN3 expression in necrotizing GN. Our study identifies CCN3 as an endogenous inhibitor of mesangial cell growth and a modulator of PDGF-induced mitogenesis.

Glutathione-S-transferase protects against oxidative injury of endothelial cell tight junctions.

Oxidative damage of endothelial tight junction permeability is involved in the pathophysiology of a variety of vascular diseases. The authors studied the role of the antioxidant enzyme, human glutathione-S-transferase A4-4 (hGSTA4-4), in regulating expression of major molecules of tight junction in vascular endothelial cells under oxidative stress induced by H(2)O(2). A vascular endothelial cell line, mouse pancreatic endothelial cells (MS1), was transduced with recombinant adenoviral vector containing hGSTA4-4 gene. hGSTA4-4 induced expression of tight junction proteins occludin and zonula occludens (ZO)-1 under oxidative stress. Increased hGSTA4-4 expression correlated with increased transepithelial electrical resistance and decreased tyrosine phosphorylation of occludin and ZO-1 following exposure to H(2)O(2). In addition, morphologic dissociation of occludin, ZO-1, and F-actin during oxidative stress was reduced in hGSTA4-4-expressing cells. To explore a genetic approach for vascular diseases associated with disruption of tight junction proteins, we introduced the same viral vector to blood vessels of mice, rats, and rabbits ex vivo and found strong expression of hGSTA4-4 in endothelial cells. These results demonstrate that oxidative stress mediated disruption of tight junctions in endothelial cells may be attenuated by hGSTA4-4 expression.

Allele-sharing of cytokine genes in familial inflammatory bowel disease.

BACKGROUND/AIMS: The pathogenesis of inflammatory bowel disease is complex, multifactorial, and involves genetic predisposition. This predisposition is likely to include various chromosomal loci, but simple Mendelian inheritance cannot be excluded in a subset of families with inflammatory bowel disease. METHODOLOGY: We evaluated allele-sharing in 17 sib-pairs with inflammatory bowel disease as an approach to select candidate genes for further studies in individual families. It was determined whether each sib-pair had inherited the same alleles for interleukin-2, interleukin-2 receptor beta, interleukin-4, interleukin-4 receptor, interleukin-10, interleukin-10 receptor, tumor necrosis factor alpha, tumor necrosis factor alpha receptor 1 and 2. RESULTS: The results were very different per individual family. The estimated probability of sharing both alleles identical-by-descent at interleukin-4 receptor, interleukin-10, interleukin-10 receptor, and tumor necrosis factor alpha were 50%, 39%, 40%, and 33% respectively. The LOD score was significant for interleukin-4 receptor (p = 0.04). CONCLUSIONS: In this small group of sib-pairs with inflammatory bowel disease a modestly increased allele-sharing was found for some inflammatory related genes. Different results per family may suggest genetic heterogeneity. This method can be useful as a first step to further evaluation of specific candidate genes which may play a pathogenetic role in individual families.

Acrolein generation stimulates hypercontraction in isolated human blood vessels.

Increased risk of vasospasm, a spontaneous hyperconstriction, is associated with atherosclerosis, cigarette smoking, and hypertension-all conditions involving oxidative stress, lipid peroxidation, and inflammation. To test the role of the lipid peroxidation- and inflammation-derived aldehyde, acrolein, in human vasospasm, we developed an ex vivo model using human coronary artery bypass graft (CABG) blood vessels and a demonstrated acrolein precursor, allylamine. Allylamine induces hypercontraction in isolated rat coronary artery in a semicarbazide-sensitive amine oxidase activity (SSAO) dependent manner. Isolated human CABG blood vessels (internal mammary artery, radial artery, saphenous vein) were used to determine: (1) vessel responses and sensitivity to acrolein, allylamine, and H(2)O(2) exposure (1 microM-1 mM), (2) SSAO dependence of allylamine-induced effects using SSAO inhibitors (semicarbazide, 1 mM; MDL 72274-E, active isomer; MDL 72274-Z, inactive isomer; 100 microM), (3) the vasoactive effects of two other SSAO amine substrates, benzylamine and methylamine, and (4) the contribution of extracellular Ca(2+) to hypercontraction. Acrolein or allylamine but not H(2)O(2), benzylamine, or methylamine stimulated spontaneous and pharmacologically intractable hypercontraction in CABG blood vessels that was similar to clinical vasospasm. Allylamine-induced hypercontraction and blood vessel SSAO activity were abolished by pretreatment with semicarbazide or MDL 72274-E but not by MDL 72274-Z. Allylamine-induced hypercontraction also was significantly attenuated in Ca(2+)-free buffer. In isolated aorta of spontaneously hypertensive rat, allylamine-induced an SSAO-dependent contraction and enhanced norepinephrine sensitivity but not in Sprague-Dawley rat aorta. We conclude that acrolein generation in the blood vessel wall increases human susceptibility to vasospasm, an event that is enhanced in hypertension.

Prednisolone suppresses the function and promotes apoptosis of plasmacytoid dendritic cells.

Organ transplant recipients are highly susceptible to viral infections early after transplantation. Plasmacytoid dendritic cells (PDC) play a major role in antiviral immunity. Therefore, we determined the numbers of circulating PDC after liver transplantation (LTX) and established the effects of immunosuppressive drugs on PDC survival and function. PDC were determined longitudinally in 13 LTX recipients treated with prednisone and cyclosporin or tacrolimus. Purified PDC were cultured with or without clinically relevant concentrations of cyclosporin, tacrolimus or prednisolone. Apoptosis induction was monitored by determination of active caspase-3, nuclear condensation and annexin-V/7AAD staining. After LTX, a 4-fold reduction in the number of circulating PDC was observed (p < 0.01), which recovered partially after discontinuation of prednisone treatment. In vitro, prednisolone induced apoptosis in PDC, while cyclosporin and tacrolimus did not. Higher doses of prednisolone were needed to induce apoptosis in Toll-like receptor (TLR)-stimulated PDC. However, non-apoptosis inducing concentrations of prednisolone suppressed interferon-alpha production, upregulation of co-stimulatory molecules and allo-stimulatory capacity of TLR-stimulated PDC. In conclusion, prednisolone induces apoptosis in PDC, which explains the decline in circulating PDC numbers after transplantation. Moreover, prednisolone suppresses the functions of TLR-stimulated PDC. Therefore, corticosteroid-free immunosuppressive therapy may reduce the number and severity of viral infections after transplantation.