Disruption of murine cardiac allograft acceptance by latent cytomegalovirus

Trained immunity: A link between risk factors and cardiovascular disease

Cardiovascular diseases are significant contributors to human mortality, closely associated with inflammation. With the changing living conditions and the extension of human lifespan, greater attention has been directed towards understanding the impact of early, long-term events on the development of cardiovascular events. Lifestyle factors such as stress, unhealthy diet and physical inactivity can increase the risk of cardiovascular diseases. Interestingly, even if the risk factors are addressed later, their influence may persist. Recently, the concept of trained innate immunity (TRIM), defined as sustained alterations in the function of innate immunocyte that promote a more robust response to downstream stimuli, has been proposed to be involved in cardiovascular diseases. It is hypothesized that TRIM may serve as a mediator bridging the impacts of aforementioned risk factors. This review aims to elucidate the role of TRIM in cardiovascular diseases and highlight its significance in uncovering new mechanisms and therapeutic targets.

The Viral G-Protein-Coupled Receptor Homologs M33 and US28 Promote Cardiac Dysfunction during Murine Cytomegalovirus Infection

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that infects the majority of the world population and causes lifelong latent infection. HCMV has been shown to exacerbate cardiovascular diseases, including myocarditis, vascular sclerosis, and transplant vasculopathy. Recently, we have shown that murine CMV (MCMV) recapitulates the cardiovascular dysfunction observed in patients with HCMV-induced myocarditis. To understand the viral mechanisms involved in CMV-induced heart dysfunction, we further characterized cardiac function in response to MCMV and examined virally encoded G-protein-coupled receptor homologs (vGPCRs) US28 and M33 as potential factors that promote infection in the heart. We hypothesized that the CMV-encoded vGPCRs could exacerbate cardiovascular damage and dysfunction. Three viruses were used to evaluate the role of vGPCRs in cardiac dysfunction: wild-type MCMV, a M33-deficient virus (∆M33), and a virus with the M33 open reading frame (ORF) replaced with US28, an HCMV vGPCR (i.e., US28+). Our in vivo studies revealed that M33 plays a role in promoting cardiac dysfunction by increasing viral load and heart rate during acute infection. During latency, ΔM33-infected mice demonstrated reduced calcification, altered cellular gene expression, and less cardiac hypertrophy compared with wild-type MCMV-infected mice. Ex vivo viral reactivation from hearts was less efficient in ΔM33-infected animals. HCMV protein US28 expression restored the ability of the M33-deficient virus to reactivate from the heart. US28+ MCMV infection caused damage to the heart comparable with wild-type MCMV infection, suggesting that the US28 protein is sufficient to complement the function of M33 in the heart. Altogether, these data suggest a role for vGPCRs in viral pathogenesis in the heart and thus suggest that vGPCRs promote long-term cardiac damage and dysfunction.

Trained immunity - basic concepts and contributions to immunopathology

Trained immunity is a functional state of the innate immune response and is characterized by long-term epigenetic reprogramming of innate immune cells. This concept originated in the field of infectious diseases - training of innate immune cells, such as monocytes, macrophages and/or natural killer cells, by infection or vaccination enhances immune responses against microbial pathogens after restimulation. Although initially reported in circulating monocytes and tissue macrophages (termed peripheral trained immunity), subsequent findings indicate that immune progenitor cells in the bone marrow can also be trained (that is, central trained immunity), which explains the long-term innate immunity-mediated protective effects of vaccination against heterologous infections. Although trained immunity is beneficial against infections, its inappropriate induction by endogenous stimuli can also lead to aberrant inflammation. For example, in systemic lupus erythematosus and systemic sclerosis, trained immunity might contribute to inflammatory activity, which promotes disease progression. In organ transplantation, trained immunity has been associated with acute rejection and suppression of trained immunity prolonged allograft survival. This novel concept provides a better understanding of the involvement of the innate immune response in different pathological conditions, and provides a new framework for the development of therapies and treatment strategies that target epigenetic and metabolic pathways of the innate immune system.

Gallium containing bioactive materials: A review of anticancer, antibacterial, and osteogenic properties

The incorporation of gallium into bioactive materials has been reported to enhance osteogenesis, to influence blood clotting, and to induce anti-cancer and anti-bacterial activity. Gallium-doped biomaterials prepared by various techniques include melt-derived and sol-gel-derived bioactive glasses, calcium phosphate bioceramics, metals and coatings. In this review, we summarize the recently reported developments in antibacterial, anticancer, osteogenesis, and hemostasis properties of Ga-doped biomaterials and briefly outline the mechanisms leading to Ga biological effects. The key finding is that gallium addition to biomaterials has great potential for treating bone-related diseases since it can be efficiently transferred to the desired region at a controllable rate. Besides, it can be used as a potential substitute for antibiotics for the inhibition of infections during the initial and advanced phases of the wound healing process. Ga is also used as an anticancer agent due to the increased concentration of gallium around excessive cell proliferation (tumor) sites. Moreover, we highlight the possibility to design different therapeutic approaches aimed at increasing the efficiency of the use of gallium containing bioactive materials for multifunctional applications.

Don't Go Breaking My Heart: MCMV as a Model for HCMV-Associated Cardiovascular Diseases

Human Cytomegalovirus (HCMV) is a widespread pathogen that causes lifelong latent infection and is associated with the exacerbation of chronic inflammatory diseases in seropositive individuals. Of particular impact, HCMV infection is known to worsen many cardiovascular diseases including myocarditis, atherosclerosis, hypertension, and transplant vasculopathy. Due to its similarity to HCMV, murine CMV (MCMV) is an appropriate model to understand HCMV-induced pathogenesis in the heart and vasculature. MCMV shares similar sequence homology and recapitulates much of the HCMV pathogenesis, including HCMV-induced cardiovascular diseases. This review provides insight into HCMV-associated cardiovascular diseases and the murine model of MCMV infection, which has been used to study the viral pathogenesis and mechanisms contributing to cardiovascular diseases. Our new functional studies using echocardiography demonstrate tachycardia and hypertrophy in the mouse, similar to HCMV-induced myocarditis in humans. For the first time, we show long term heart dysfunction and that MCMV reactivates from latency in the heart, which raises the intriguing idea that HCMV latency and frequent virus reactivation perturbs long term cardiovascular function.

Acute murine cytomegalovirus disrupts established transplantation tolerance and causes recipient allo-sensitization

We have previously shown that acute cytomegalovirus (CMV) infection disrupts the induction of transplantation tolerance. However, what impact acute CMV infection would have on the maintenance of established tolerance and on subsequent recipient allo-sensitization is a clinically important unanswered question. Here we used an allogeneic murine islet transplantation tolerance model to examine the impact of acute CMV infection on: (a) disruption of established transplantation tolerance during tolerance maintenance; and (b) the possibility of recipient allo-sensitization by CMV-mediated disruption of stable tolerance. We demonstrated that acute CMV infection abrogated transplantation tolerance during the maintenance stage in 50%-60% recipients. We further demonstrated that acute CMV infection-mediated tolerance disruption led to recipient allo-sensitization by reverting the tolerant state of allo-specific T cells and promoting their differentiation to allo-specific memory cells. Consequently, a second same-donor islet allograft was rejected in an accelerated fashion by these recipients. Our study therefore supports close monitoring for allo-sensitization in previously tolerant transplant recipients in whom tolerance maintenance is disrupted by an episode of acute CMV infection.

Heart Dysfunction Following Long-Term Murine Cytomegalovirus Infection: Fibrosis, Hypertrophy, and Tachycardia

Human cytomegalovirus (HCMV) is associated with increased risk of chronic diseases of the heart and vasculature, including myocarditis, atherosclerosis, and transplant vasculopathy. To investigate CMV infection of the heart, murine cytomegalovirus (MCMV) was used to evaluate both acute and latent infection and the subsequent phenotypic and functional consequences of infection. Female BALB/c mice were intraperitoneally (i.p.) inoculated with 1 × 106 pfu of MCMV and evaluated at 14 and 50 days postinfection (dpi). At each time point, echocardiography was used to evaluate cardiac function and histology was conducted for phenotypic evaluation. MCMV replication in the heart was detected as early as 3 dpi and was no longer detectable at 14 dpi. Infected animals had significant cardiac pathology at 14 and 50 dpi when compared to uninfected controls. Histology revealed fibrosis of the heart as early as 14 dpi and the presence of white fibrous deposits on the surface of the heart. Functional evaluation showed significantly increased heart rate and muscle thickening in the latently infected animals when compared to the control animals. At 50 dpi, latent virus was measured by explant reactivation assay, demonstrating that MCMV establishes latency and is capable of reactivation from the heart, similar to other tissues such as spleen and salivary glands. Collectively, these studies illustrate that MCMV infection results in phenotypic alterations within the heart as early as 14 dpi, which progress to functional abnormalities during latency. These findings are similar to sinus tachycardia and hypertrophy of the heart muscle observed in cases of HCMV-induced acute myocarditis.

Trained immunity in organ transplantation

Consistent induction of donor-specific unresponsiveness in the absence of continuous immunosuppressive therapy and toxic effects remains a difficult task in clinical organ transplantation. Transplant immunologists have developed numerous experimental treatments that target antigen-presentation (signal 1), costimulation (signal 2), and cytokine production (signal 3) to establish transplantation tolerance. While promising results have been obtained using therapeutic approaches that predominantly target the adaptive immune response, the long-term graft survival rates remain suboptimal. This suggests the existence of unrecognized allograft rejection mechanisms that contribute to organ failure. We postulate that trained immunity stimulatory pathways are critical to the immune response that mediates graft loss. Trained immunity is a recently discovered functional program of the innate immune system, which is characterized by nonpermanent epigenetic and metabolic reprogramming of macrophages. Since trained macrophages upregulate costimulatory molecules (signal 2) and produce pro-inflammatory cytokines (signal 3), they contribute to potent graft reactive immune responses and organ transplant rejection. In this review, we summarize the detrimental effects of trained immunity in the context of organ transplantation and describe pathways that induce macrophage training associated with graft rejection.

Impact of infection on transplantation tolerance

Allograft tolerance is the ultimate goal of organ transplantation. Current strategies for tolerance induction mainly focus on inhibiting alloreactive T cells while promoting regulatory immune cells. Pathogenic infections may have direct impact on both effector and regulatory cell populations, therefore can alter host susceptibility to transplantation tolerance induction as well as impair the quality and stability of tolerance once induced. In this review, we will discuss existing data demonstrating the effect of infections on transplantation tolerance, with particular emphasis on the role of the stage of infection (acute, chronic, or latent) and the stage of tolerance (induction or maintenance) in this infection-tolerance interaction. While the deleterious effect of acute infection on tolerance is mainly driven by proinflammatory cytokines induced shortly after the infection, chronic infection may generate exhausted T cells that could in fact facilitate transplantation tolerance. In addition to pathogenic infections, commensal intestinal microbiota also has numerous significant immunomodulatory effects that can shape the host alloimmunity following transplantation. A comprehensive understanding of these mechanisms is crucial for the development of therapeutic strategies for robustly inducing and stably maintaining transplantation tolerance while preserving host anti-pathogen immunity in clinically relevant scenarios.

Cytokine-Mediated Induction and Regulation of Tissue Damage During Cytomegalovirus Infection

Human cytomegalovirus (HCMV) is a β-herpesvirus with high sero-prevalence within the human population. Primary HCMV infection and life-long carriage are typically asymptomatic. However, HCMV is implicated in exacerbation of chronic conditions and associated damage in individuals with intact immune systems. Furthermore, HCMV is a significant cause of morbidity and mortality in the immunologically immature and immune-compromised where disease is associated with tissue damage. Infection-induced inflammation, including robust cytokine responses, is a key component of pathologies associated with many viruses. Despite encoding a large number of immune-evasion genes, HCMV also triggers the induction of inflammatory cytokine responses during infection. Thus, understanding how cytokines contribute to CMV-induced pathologies and the mechanisms through which they are regulated may inform clinical management of disease. Herein, we discuss our current understanding based on clinical observation and in vivo modeling of disease of the role that cytokines play in CMV pathogenesis. Specifically, in the context of the different tissues and organs in which CMV replicates, we give a broad overview of the beneficial and adverse effects that cytokines have during infection and describe how cytokine-mediated tissue damage is regulated. We discuss the implications of findings derived from mice and humans for therapeutic intervention strategies and our understanding of how host genetics may influence the outcome of CMV infections.

Polymorphism in programmed cell death 1 gene is strongly associated with lung and kidney allograft survival in recipients from CMV-positive donors

BACKGROUND

Cytomegalovirus (CMV) has a role in chronic rejection and graft loss in kidney transplant (KTx) and lung transplant (LTx) recipients. In addition, donor CMV seropositivity is an independent risk factor for renal graft loss. The anti-CMV response might modulate this risk. Expression of programmed cell death 1 (PD-1), a receptor involved in viral-specific T-cell exhaustion, is influenced by a single nucleotide polymorphism called PD-1.3 (wild-type allele G, variant allele A).

METHODS

We performed a retrospective study to assess the impact of PD-1.3 on graft outcome in donor CMV seropositive (D+) and donor CMV seronegative (D-) KTx and LTx. We also performed a case-control study to evaluate the anti-CMVpp65 response according to genotype.

RESULTS

PD-1.3 was determined in 1,119 KTx and 181 LTx. In 481 D+ KTx, A allele carriers (24%) experienced significantly less graft failure compared with GG carriers (p = 0.001). Multivariate analysis showed that this association was independent of donor and recipient age, acute rejection episodes, and number of human leukocyte antigen mismatches (hazard ratio, 0.381; 95% confidence interval, 0.209-0.696; p = 0.002). Analysis in 85 D+ LTx showed similar results: A allele carriers had better survival (hazard ratio, 0.302; 95% confidence interval, 0.128-0.716; p = 0.006) and greater 6-month forced expiratory volume (71% ± 17% vs 54% ± 16%, p = 0.001). In D- recipients, PD-1.3 did not affect KTx or LTx outcome. Finally, AA recipients had a stronger anti-CMVpp65 T-cell response than matched GG recipients (p = 0.003).

CONCLUSIONS

The A variant allele in PD-1.3 single nucleotide polymorphism improved graft survival in kidney and lung transplant recipients receiving grafts from CMV-positive donors.

The Cell Biology of Cytomegalovirus: Implications for Transplantation

Interpretation of clinical data regarding the impact of cytomegalovirus (CMV) infection on allograft function is complicated by the diversity of viral strains and substantial variability of cellular receptors and viral gene expression in different tissues. Variation also exists in nonspecific (monocytes and dendritic cells) and specific (NK cells, antibodies) responses that augment T cell antiviral activities. Innate immune signaling pathways and expanded pools of memory NK cells and γδ T cells also serve to amplify host responses to infection. The clinical impact of specific memory T cell anti-CMV responses that cross-react with graft antigens and alloantigens is uncertain but appears to contribute to graft injury and to the abrogation of allograft tolerance. These responses are modified by diverse immunosuppressive regimens and by underlying host immune deficits. The impact of CMV infection on the transplant recipient reflects cellular changes and corresponding host responses, the convergence of which has been termed the "indirect effects" of CMV infection. Future studies will clarify interactions between CMV infection and allograft injury and will guide interventions that may enhance clinical outcomes in transplantation.

The composition of the microbiota modulates allograft rejection

Transplantation is the only cure for end-stage organ failure, but without immunosuppression, T cells rapidly reject allografts. While genetic disparities between donor and recipient are major determinants of the kinetics of transplant rejection, little is known about the contribution of environmental factors. Because colonized organs have worse transplant outcome than sterile organs, we tested the influence of host and donor microbiota on skin transplant rejection. Compared with untreated conventional mice, pretreatment of donors and recipients with broad-spectrum antibiotics (Abx) or use of germ-free (GF) donors and recipients resulted in prolonged survival of minor antigen-mismatched skin grafts. Increased graft survival correlated with reduced type I IFN signaling in antigen-presenting cells (APCs) and decreased priming of alloreactive T cells. Colonization of GF mice with fecal material from untreated conventional mice, but not from Abx-pretreated mice, enhanced the ability of APCs to prime alloreactive T cells and accelerated graft rejection, suggesting that alloimmunity is modulated by the composition of microbiota rather than the quantity of bacteria. Abx pretreatment of conventional mice also delayed rejection of major antigen-mismatched skin and MHC class II-mismatched cardiac allografts. This study demonstrates that Abx pretreatment prolongs graft survival, suggesting that targeting microbial constituents is a potential therapeutic strategy for enhancing graft acceptance.

CMV Primary Infection Is Associated With Donor-Specific T Cell Hyporesponsiveness and Fewer Late Acute Rejections After Liver Transplantation

Viral infections, including cytomegalovirus (CMV), abrogate transplantation tolerance in animal models. Whether this also occurs in humans remains elusive. We investigated how CMV affects T cells and rejection episodes after liver transplantation (LT). Phenotype and alloreactivity of peripheral and allograft-infiltrating T cells from LT patients with different CMV status were analyzed by flow cytometry. The association of CMV status with early and late acute rejection was retrospectively analyzed in a cohort of 639 LT patients. CMV-positivity was associated with expansion of peripheral effector memory T cell subsets after LT. Patients with CMV primary infection showed donor-specific CD8(+) T cell hyporesponsiveness. While terminally differentiated effector memory cells comprised the majority of peripheral donor-specific CD8(+) T cells in CMV primary infection patients, they were rarely present in liver allografts. Retrospective analysis showed that R(-) D(+) serostatus was an independent protective factor for late acute rejection by multivariate Cox regression analysis (hazard ratio [HR] = 0.18, 95% CI = 0.04-0.86, p = 0.015). Additionally, CMV primary infection patients showed the highest Vδ1/Vδ2 γδ T cell ratio, which has been shown to be associated with operational tolerance after LT. In conclusion, our data suggest that CMV primary infection may promote tolerance to liver allografts, and CMV status should be considered when tapering or withdrawing immunosuppression.

Clinical Implications of Basic Science Discoveries: Immune Homeostasis and the Microbiome-Dietary and Therapeutic Modulation and Implications for Transplantation

Links between the human microbiome and the innate and adaptive immune systems and their impact on autoimmune and inflammatory diseases are only beginning to be recognized. Characterization of the complex human microbial community is facilitated by culture-independent nucleic acid sequencing tools and bioinformatics systems. Specific organisms and microbial antigens are linked with initiation of innate immune responses that, depending on the context, may be associated with tolerogenic or effector immune responses. Further complexity is introduced by preclinical data that demonstrate the impacts of dietary manipulation on the prevention of genetically determined, systemic autoimmune disorders and on gastrointestinal microbiota. Investigation of interactions of complex microbial populations with the human immune system may provide new targets for clinical management in allotransplantation.

The efficacy and cost-effectiveness of valacyclovir in cytomegalovirus prevention in solid organ transplantation

Prevention of cytomegalovirus infection using antiviral prophylaxis or the pre-emptive therapy approach is an integral part of management of patients after solid organ transplantation. Regarding renal transplantation, valacyclovir is currently the only antiviral agent recommended for prophylaxis as an alternative to valganciclovir. This review article discusses studies documenting the efficacy and safety of valacyclovir prophylaxis as well as those comparing valacyclovir with other prophylactic regimens or with pre-emptive therapy. Also addressed are the economic aspects supporting the cost-effectiveness of valacyclovir prophylaxis and demonstrating lower costs compared with other cytomegalovirus preventive strategies.

T-cell activation and transplantation tolerance

Transplantation of allogeneic or "nonself" tissues stimulates a robust immune response leading to graft rejection, and therefore, most recipients of allogeneic organ transplants require the lifelong use of immune suppressive agents. Excellent outcomes notwithstanding, contemporary immunosuppressive medications are toxic, are often not taken by patients, and pose long-term risks of infection and malignancy. The ultimate goal in transplantation is to develop new treatments that will supplant the need for general immunosuppression. Here, we will describe the development and application of costimulation blockade to induce transplantation tolerance and discuss how the diverse array of signals that act on T cells will determine the balance between graft survival and rejection.

CD28 family and chronic rejection: "to belatacept...And beyond!"

Kidneys are one of the most frequently transplanted human organs. Immunosuppressive agents may prevent or reverse most acute rejection episodes; however, the graft may still succumb to chronic rejection. The immunological response involved in the chronic rejection process depends on both innate and adaptive immune response. T lymphocytes have a pivotal role in chronic rejection in adaptive immune response. Meanwhile, we aim to present a general overview on the state-of-the-art knowledge of the strategies used for manipulating the lymphocyte activation mechanisms involved in allografts, with emphasis on T-lymphocyte costimulatory and coinhibitory molecules of the B7-CD28 superfamily. A deeper understanding of the structure and function of these molecules improves both the knowledge of the immune system itself and their potential action as rejection inducers or tolerance promoters. In this context, the central role played by CD28 family, especially the relationship between CD28 and CTLA-4, becomes an interesting target for the development of immune-based therapies aiming to increase the survival rate of allografts and to decrease autoimmune phenomena. Good results obtained by the recent development of abatacept and belatacept with potential clinical use aroused better expectations concerning the outcome of transplanted patients.

The impact of infection and tissue damage in solid-organ transplantation

Investigations over the past two decades are revealing complexities in the regulation of the innate immune response, and how this response, in turn, controls adaptive immunity. Microbial exposure, infections and tissue damage that accompany solid-organ transplantation result in the release of pathogen- and damage-associated molecular patterns, as well as pathogen- or allograft-derived antigens. Here, we review these triggers of innate and adaptive immunity, and discuss emerging paradigms of the many ways in which infections and tissue damage might directly or indirectly affect alloreactivity and the outcome of transplanted allografts.

Early acceptance of renal allografts in mice is dependent on foxp3(+) cells

Mouse renal allografts have a remarkable ability to promote acceptance across full major histocompatibility complex incompatibilities in certain strain combinations without immunosuppression. The mechanism is unknown but is believed to involve immunoregulation. This study tests whether Foxp3(+) T-regulatory cells are responsible in the early phase of graft acceptance, using B6.Foxp3(DTR) mice that express diphtheria toxin receptor (DTR) in Foxp3(+) cells. The administration of DT to B6.Foxp3(DTR) recipients with accepted DBA/2 kidneys, 3 weeks to 3 months after transplantation, caused a marked depletion of Foxp3 cells and triggered acute cellular rejection, manifested by a sudden increase in blood urea nitrogen within a week. None of the controls showed an increase in blood urea nitrogen, including DT-treated B6 wild-type recipients of DBA/2 kidneys or B6.Foxp3(DTR) recipients of isografts. Accepted DBA/2 allografts showed prominent lymphoid sheaths around arteries containing numerous CD3(+)Foxp3(+) cells, CD4(+) cells, dedritic cells, and B cells, which was independent of CCR4. The lymphoid sheaths disintegrate after Foxp3 depletion, accompanied by widespread CD8 interstitial mononuclear inflammation, tubulitis, and endarteritis. The Foxp3 depletion caused an increased frequency of donor-reactive cells in the spleen by interferon (IFN) γ enzyme-linked immunosorbent spot (ELISPOT) assays and increased expression of the maturation markers, CD86 and IA(b), on dendritic cells in the spleen and kidney. We conclude that Foxp3(+) cells are needed to maintain acceptance of major histocompatibility complex-incompatible renal allografts in the first 3 months after transplantation and may act by inhibiting DC maturation.

Update and review: state-of-the-art management of cytomegalovirus infection and disease following thoracic organ transplantation

PURPOSE

Cytomegalovirus (CMV) is among the most important viral pathogens affecting solid organ recipients. The direct effects of CMV (eg, infection and its sequela; tissue invasive disease) are responsible for significant morbidity and mortality. In addition, CMV is associated with numerous indirect effects, including immunomodulatory effects, acute and chronic rejection, and opportunistic infections. Due to the potentially devastating effects of CMV, transplant surgeons and physicians have been challenged to fully understand this infectious complication and find the best ways to prevent and treat it to ensure optimal patient outcomes.

SUMMARY

Lung, heart, and heart-lung recipients are at considerably high risk of CMV infection. Both direct and indirect effects of CMV in these populations have potentially lethal consequences. The use of available treatment options depend on the level of risk of each patient population for CMV infection and disease. Those at the highest risk are CMV negative recipients of CMV positive organs (D+/R-), followed by D+/R+, and D-/R+. More than 1 guideline exists delineating prevention and treatment options for CMV, and new guidelines are being developed. It is hoped that new treatment algorithms will provide further guidance to the transplantation community. The first part describes the overall effects of CMV, both direct and indirect; risk factors for CMV infection and disease; methods of diagnosis; and currently available therapies for prevention and treatment. Part 2 similarly addresses antiviral-resistant CMV, summarizing incidence, risk factors, methods of diagnosis, and treatment options. Parts 3 and 4 present cases to illustrate issues surrounding CMV in heart and lung transplantation, respectively. Part 3 discusses the possible mechanisms by which CMV can cause damage to the coronary allograft and potential techniques of avoiding such damage, with emphasis on fostering strong CMV-specific immunity. Part 4 highlights the increased incidence of CMV infection and disease among lung transplant recipients and its detrimental effect on survival. The possible benefits of extended-duration anti-CMV prophylaxis are explored, as are those of combination prophylaxis with valganciclovir and CMVIG.

CONCLUSION

Through improved utilization of information regarding optimized antiviral therapy for heart and lung transplant recipients to prevent and treat CMV infection and disease and through increased understanding of clinical strategies to assess, treat, and monitor patients at high risk for CMV recurrence and resistance, the health care team will be able to provide the coordinated effort needed to improve patient outcomes.

Bacterial infections, alloimmunity, and transplantation tolerance

Transplantation of solid organs across histocompatibility barriers in the absence of immunosuppression is invariably followed by acute allograft rejection. Although several immunosuppressive regimens have been developed to prevent allograft rejection, these global immunosuppressive agents effectively inhibit all T cells, leaving the host vulnerable to infections. Thus, a major goal in transplantation immunology is to induce donor-specific tolerance that results in the extended suppression of allograft-specific immune responses, while leaving the remainder of the immune system competent to fight infections and malignancies. Initial successes in identifying approaches that successfully induce transplantation tolerance in experimental models have led to a newer research focus of identifying potential barriers to the induction of such tolerance as well as events that may reverse established allograft tolerance. Both clinical and experimental studies have identified bacterial infections as a possible trigger of allograft rejection. Recently, experimental models of transplantation tolerance have identified that bacterial signals can promote acute allograft rejection either by preventing the induction of transplantation tolerance or by reversing tolerance after it has been stably established. This review summarizes experimental and clinical literature supporting the hypothesis that bacterial infections and innate immunity can qualitatively and quantitatively alter adaptive alloreactivity through effects on innate immune responses.

RCMV increases intimal hyperplasia by inducing inflammation, MCP-1 expression and recruitment of adventitial cells to intima

Background

Cytomegalovirus (CMV) infection has been associated with accelerated transplant vasculopathy. In this study, we assessed the effects of acute rat CMV (RCMV) infection on vessel remodeling in transplant vasculopathy, focusing on allograft morphology, inflammation and contribution of adventitial cells to intimal hyperplasia.

Methods

Infrarenal aorta was locally infected with RCMV and transplanted from female F344 rats to male Lewis rats. Graft samples were collected 2 and 8 weeks after transplantation and analyzed for intimal hyperplasia, collagen degradation and inflammation. Transplantation of aorta followed by transplantation of RCMV infected and labeled isogenic adventitia were performed to study migration of adventitial cells towards the intima.

Results

Intimal hyperplasia was increased threefold in infected allografts. RCMV induced apoptosis in the media, expression of matrix metalloproteinase 2, and decreased collagen deposits. Macrophage infiltration was increased in the infected allografts and resulted in increased production of MCP-1. RCMV-infected macrophages were observed in the adventitia and intima. Cells derived from infected adventitia migrated towards the intima of the allograft.

Conclusions

RCMV enhances infiltration of macrophages to the allografts, and thereby increases MCP-1 production and inflammation, followed by recruitment of adventitial cells to the intima and accelerated intimal hyperplasia.

Revisiting the effects of CMV on long-term transplant outcome

PURPOSE OF THE REVIEW

Indirect effects of cytomegalovirus (CMV) in transplantation are of three types: increase in systemic immunosuppression, increased risk of malignancy (especially Epstein-Barr virus-related B-cell lymphoproliferative disease), and the possible contribution to allograft injury. Despite modern and potent antiviral drugs, the real impact of CMV in transplantation, especially kidney transplantation, remains a challenge because many confounding factors arise when analyzing this question.This review will fuel the discussion and review some of the recent data.

RECENT FINDINGS

A recent study on cardiac allograft in mice has shown that CMV in latently infected recipients could break graft acceptance. Although the exact nature of response was not addressed, this study suggested that CMV reactivation inside the graft played an important part in graft losses. Other recent results suggest that the quality of immune response against CMV influences graft outcome in both cardiac and kidney transplant patients. Other evidence suggests the link between CMV infection, immune senescence and vascular disease in the whole population. Studies have opened the perspective for new strategies to prevent indirect effects of CMV.

SUMMARY

Although a causal relationship between CMV reactivation and graft injury is supported by a large body of experimental and clinical data, definitive proof in clinical transplantation is still lacking to exclude an associative relationship. Large randomized clinical trials analyzing long-term graft survival and comparing prophylaxis with preemptive, especially D/R, is probably an efficient way to establish a causal relationship. Research on new antiviral strategies applicable over the long term is important.

Occult cytomegalovirus in vivarium-housed mice may influence transplant allograft acceptance

We have recently shown that latent murine cytomegalovirus (MCMV) can influence murine transplant allograft acceptance. During these studies we became aware that vivarium-housed control mice can acquire occult MCMV infection. The purpose of this investigation was to confirm occult MCMV transmission and determine the timing, vehicle, and possible consequences of transmission. Mice arriving from a commercial vendor were negative for MCMV both by commercial serologic testing and by our nested PCR. Mice housed in our vivarium became positive for MCMV DNA 30-60 days after arrival, but remained negative for MCMV by commercial serologic testing. To confirm MCMV we sequenced PCR products for several genes and showed >99% homology to MCMV. Further sequence analyses show that the occult MCMV is similar to a laboratory strain of MCMV, but the vehicle of transmission remains unclear. Control tissues from historical experiments with unexplained graft losses were evaluated for occult MCMV, and mice with unexplained allograft losses showed significantly higher incidence of occult MCMV than did allograft acceptors. Deliberate infection with very low titer MCMV confirmed that viral transmission can occur without measurable virus specific antibody or T-cell responses. These data suggest that vivarium-housed mice can develop occult MCMV that is missed by currently available commercial serologic testing, and that these infections may influence transplant allograft acceptance.

Antiviral prevention of sepsis induced cytomegalovirus reactivation in immunocompetent mice

INTRODUCTION

Immunocompetent patients can reactivate latent cytomegalovirus (CMV) during critical illness and reactivation is associated with significantly worse outcomes. Prior to clinical trials in humans to prove causality, we sought to determine an optimal antiviral treatment strategy.

METHODS

Mice latently infected with murine CMV (MCMV) received a septic reactivation trigger and were randomized to receive one of four ganciclovir regimens or saline. Lungs were evaluated for viral transcriptional reactivation and fibrosis after each regimen. Influences of ganciclovir on early sepsis-induced pulmonary inflammation and T-cell activation were studied after sepsis induction.

RESULTS

All ganciclovir regimens reduced measurable MCMV transcriptional reactivation, and 10mg/day for 7 or 21 days was most effective. Lower dose (5mg/kg/day) or delayed therapy was associated with significant breakthrough reactivation. Higher doses of ganciclovir given early were associated with the lowest incidence of pulmonary fibrosis, and delay of therapy for 1 week was associated with significantly worse pulmonary fibrosis. Although bacterial sepsis induced activation of MCMV-specific pulmonary T-cells, this activation was not influenced by ganciclovir.

CONCLUSION

These results suggest that antiviral treatment trials in humans should use 10mg/kg/day ganciclovir administered as early as possible in at-risk patients to minimize reactivation events and associated pulmonary injury.

Allogeneic stimulation causes transcriptional reactivation of latent murine cytomegalovirus

Cytomegalovirus (CMV) reactivation is a well-described complication of transplantation that may be caused by allogeneic stimulation, immunosuppression, or both. These studies were performed to determine if allogeneic stimulation alone is sufficient to reactivate latent CMV. BALB/c mice latently infected with Smith strain murine CMV (MCMV) received allograft (n = 8), allograft plus cortisol (n = 5), or isograft (n = 4) skin. All allograft recipients rejected their grafts within 9 to 12 days of transplantation. Three weeks after grafting, recipients were evaluated for MCMV reactivation, and all allograft recipients (8/8) showed MCMV reactivation, while no isografts had reactivation (0/4). Surprisingly, cortisol therapy blocked MCMV reactivation (0/5). These data suggested that allogeneic stimulation alone can trigger systemic reactivation of latent CMV. Although immunosuppression is thought to contribute to reactivation, certain agents that impair NF-kappaB activation may actually reduce reactivation.