Novel immune regulatory pathways and their role in immune reconstitution syndrome in organ transplant recipients with invasive mycoses

Cryptococcosis

Cryptococcosis is an invasive mycosis caused by pathogenic encapsulated yeasts in the genus Cryptococcus. Cryptococcus gained prominence as a pathogen capable of widespread disease outbreaks in vulnerable populations. We have gained insight into the pathobiology of Cryptococcus, including the yeast' s capacity to adapt to environmental pressures, exploit new geographic environments, and cause disease in both immunocompromised and apparently immunocompetent hosts. Inexpensive, point-of-care testing makes diagnosis more feasible than ever. The associated worldwide burden and mortality remains unacceptably high. Novel screening strategies and preemptive therapy offer promise at making a sustained and much needed impact on this sugar-coated opportunistic mycosis.

Therapeutics targeting inflammation in the immune reconstitution inflammatory syndrome

Immune reconstitution inflammatory syndrome (IRIS) is characterized by improvement in a previously incompetent human immune system manifesting as worsening of clinical symptoms secondary to the ability of the immune system to now mount a vigorous inflammatory response. IRIS was first recognized in the setting of human immunodeficiency virus, and this clinical setting continues to be where it is most frequently encountered. Hallmarks of the pathogenesis of IRIS, independent of the clinical presentation and the underlying pathogen, include excessive activation of the immune system, with increased circulating effector memory T cells, and elevated levels of serum cytokines and inflammatory markers. Patients with undiagnosed opportunistic infections remain at risk for unmasking IRIS at the time of active antiretroviral therapy (ART) initiation. Systematic screening for opportunistic infections before starting ART is a key element to prevent this phenomenon. Appropriate management of IRIS requires prompt recognition of the syndrome and exclusion of alternative diagnoses, particularly underlying infections and drug resistance. Controlled studies supporting the use of pharmacologic interventions in IRIS are scare, and recommendations are based on case series and expert opinions. The only controlled trial published to date, showed reduction in morbidity in patients with paradoxical tuberculosis-related IRIS with the use of oral corticosteroids. There are currently limited data to recommend other anti-inflammatory or immunomodulatory therapies that are discussed in this review, and further research is needed. Ongoing research regarding the immune pathogenesis of IRIS will likely direct future rational therapeutic approaches and clinical trials.

Immune reconstitution inflammatory syndrome associated with biologic therapy

The use of biologics in the treatment of autoimmune disease, cancer, and other immune conditions has revolutionized medical care in these areas. However, there are drawbacks to the use of these medications including increased susceptibility to opportunistic infections. One unforeseen risk once opportunistic infection has occurred with biologic use is the onset of immune reconstitution inflammatory syndrome (IRIS) upon drug withdrawal. Although originally described in human immunodeficiency virus (HIV) patients receiving highly active antiretroviral therapy, it has become clear that IRIS may occur when recovery of immune function follows opportunistic infection in the setting of previous immune compromise/suppression. In this review, we draw attention to this potential pitfall on the use of biologic drugs.

Cryptococcosis

Cryptococcosis is an infectious disease caused by the encapsulated fungi Cryptococcus neoformans and Cryptococcus gattii. Once a relatively uncommon cause of human disease, cryptococcal infection can develop in apparently immunocompetent hosts and has emerged as an important opportunistic infection in humans over the past several decades as immunocompromised populations expand in the setting of HIV/AIDS, organ transplantation, malignancies, and treatment for other conditions. Clinical manifestations are myriad but pulmonary and central nervous system (CNS) infections are the most common. Improvements in diagnostic testing and standardized approaches to antifungal therapy, when available, have made considerable impact in the management of this infection. While the widespread use of highly active antiretroviral therapy (HAART) has improved the outcome of cryptococcosis in many HIV-infected patients, cryptococcosis remains an entity of considerable morbidity and mortality in many parts of the world, and restoration of host immunity can present management challenges that require individualized management. As immunocompromised populations continue to expand, it is likely that cryptococcosis will remain an important opportunistic fungal infection of humans requiring ongoing investigation.

Neurological complications of solid organ transplantation

Solid organ transplantation (SOT) is the preferred treatment for an expanding range of conditions whose successful therapy has produced a growing population of chronically immunosuppressed patients with potential neurological problems. While the spectrum of neurological complications varies with the type of organ transplanted, the indication for the procedure, and the intensity of long-term required immunosuppression, major neurological complications occur with all SOT types. The second part of this 2-part article on transplantation neurology reviews central and peripheral nervous system problems associated with SOT with clinical and neuroimaging examples from the authors' institutional experience. Particular emphasis is given to conditions acquired from the donated organ or tissue, problems specific to types of organs transplanted and drug therapy-related complications likely to be encountered by hospitalists. Neurologically important syndromes such as immune reconstitution inflammatory syndrome (IRIS), posterior reversible encephalopathy syndrome (PRES), and posttransplantation lymphoproliferative disorder (PTLD) are readdressed in the context of SOT.

Dectin immunoadhesins and pneumocystis pneumonia

The opportunistic pathogen Pneumocystis jirovecii is a significant cause of disease in HIV-infected patients and others with immunosuppressive conditions. Pneumocystis can also cause complications in treatment following antiretroviral therapy or reversal of immunosuppressive therapy, as the newly reconstituted immune system can develop a pathological inflammatory response to remaining antigens or a previously undetected infection. To target β-(1,3)-glucan, a structural component of the Pneumocystis cell wall with immune-stimulating properties, we have developed immunoadhesins consisting of the carbohydrate binding domain of Dectin-1 fused to the Fc regions of the 4 subtypes of murine IgG (mIgG). These immunoadhesins bind β-glucan with high affinity, and precoating the surface of zymosan with Dectin-1:Fc can reduce cytokine production by macrophages in an in vitro stimulation assay. All Dectin-1:Fc variants showed specificity of binding to the asci of Pneumocystis murina, but effector activity of the fusion molecules varied depending on Fc subtype. Dectin-1:mIgG2a Fc was able to reduce the viability of P. murina in culture through a complement-dependent mechanism, whereas previous studies have shown the mIgG1 Fc fusion to increase macrophage-dependent killing. In an in vivo challenge model, systemic expression of Dectin-1:mIgG1 Fc significantly reduced ascus burden in the lung. When administered postinfection in a model of immune reconstitution inflammatory syndrome (IRIS), both Dectin-1:mIgG1 and Dectin-1:mIgG2a Fc reduced hypoxemia despite minimal effects on fungal burden in the lung. Taken together, these data indicate that molecules targeting β-glucan may provide a mechanism for treatment of fungal infection and for modulation of the inflammatory response to Pneumocystis and other pathogens.

Immune reconstitution reactions in human immunodeficiency virus-negative patients: report of a case and review of the literature

BACKGROUND

Immune reconstitution inflammatory syndrome (IRIS) is a phenomenon initially described in patients with human immunodeficiency virus. Upon initiation of combination antiretroviral therapy, recovery of cellular immunity triggers inflammation to a preexisting infection or antigen that causes paradoxical worsening of clinical disease. A similar phenomenon can occur in human immunodeficiency virus-negative patients, including pregnant women, neutropenic hosts, solid-organ or stem cell transplant recipients, and patients receiving tumor necrosis factor inhibitors.

OBSERVATIONS

We report a case of leprosy unmasking and downgrading reaction after stem cell transplantation that highlights some of the challenges inherent to the diagnosis of IRIS, especially in patients without human immunodeficiency virus infection, as well as review the spectrum of previously reported cases of IRIS reactions in this population.

CONCLUSIONS

The mechanism of immune reconstitution reactions is complex and variable, depending on the underlying antigen and the mechanism of immunosuppression or shift in immune status. Use of the term IRIS can aid our recognition of an important phenomenon that occurs in the setting of immunosuppression or shifts in immunity but should not deter us from thinking critically about the distinct processes that underlie this heterogeneous group of conditions.

Immune reconstitution inflammatory syndrome: the trouble with immunity when you had none

Some individuals who are infected with HIV rapidly deteriorate shortly after starting antiretroviral therapy, despite effective viral suppression. This reaction, referred to as immune reconstitution inflammatory syndrome (IRIS), is characterized by tissue-destructive inflammation and arises as CD4(+) T cells re-emerge. It has been proposed that IRIS is caused by a dysregulation of the expanding population of CD4(+) T cells specific for a co-infecting opportunistic pathogen. Here, we argue that IRIS instead results from hyper-responsiveness of the innate immune system to T cell help, a mechanism that may be shared by the many manifestations of IRIS that occur following the reversal of other types of immunosuppression in pathogen-infected hosts.

Opportunistic infection-associated immune reconstitution syndrome in transplant recipients

Reversal of pathogen-induced immunosuppression upon employment of effective antimicrobial therapy and withdrawal of iatrogenic immunosuppression has the potential to shift the host immune repertoire towards pathologic inflammatory responses conducive to immune reconstitution syndrome (IRS). Posttransplant IRS has been observed with fungi, M. tuberculosis, cytomegalovirus, and polyoma virus nephropathy. This review discusses the existing state of knowledge regarding IRS and the immune mechanisms that underlie its pathogenesis, with significant implications for developing reliable diagnostic biomarkers and optimal management strategies for post-transplant opportunistic infection-associated IRS.

Cutaneous cryptococcosis in solid organ transplant recipients

Clinical manifestations, treatment, and outcomes of cutaneous cryptococcosis in solid organ transplant (SOT) recipients are not fully defined. In a prospective cohort comprising 146 SOT recipients with cryptococcosis, we describe the presentation, antifungal therapy, and outcome of cutaneous cryptococcal disease. Cutaneous cryptococcosis was documented in 26/146 (17.8%) of the patients and manifested as nodular/mass (34.8%), maculopapule (30.4%), ulcer/pustule/abscess (30.4%), and cellulitis (30.4%) with 65.2% of the skin lesions occurred in the lower extremities. Localized disease developed in 30.8% (8/26), and disseminated disease in 69.2% (18/26) with involvement of the central nervous system (88.9%, 16/18), lung (33.3%, 6/18), or fungemia (55.6%, 10/18). Fluconazole (37.5%) was employed most often for localized and lipid formulations of amphotericin B (61.1%) for disseminated disease. Overall mortality at 90 days was 15.4% (4/26) with 16.7% in disseminated and 12.5% in localized disease (P = 0.78). SOT recipients who died were more likely to have renal failure (75.0% vs. 13.6%, P = 0.028), longer time to onset of disease after transplantation (87.5 vs. 22.6 months, P = 0.023), and abnormal mental status (75% vs. 13.6%, P = 0.028) than those who survived. Cutaneous cryptococcosis represents disseminated disease in most SOT recipients and preferentially involves the extremities. Outcomes with appropriate management were comparable between SOT recipients with localized and disseminated cryptococcosis.

Potential role of statins for the management of immune reconstitution syndrome

It has become evident that while a robust inflammatory response plays a critical role in eradicating invading microbes, dysregulated immunity can be detrimental to the host if an optimal balance between the inflammatory and anti-inflammatory reactions is disrupted. Opportunistic infection-associated immune reconstitution syndrome is characterized by an aggressive inflammatory immune response and its management remains challenging and largely unknown. Statins, in addition to their lipid lower effects have anti-inflammatory attributes and there is precedence for the use of these agents as a therapeutic modality for autoimmune inflammatory disorders which have similar underlying pathogenesis as immune reconstitution syndrome. We hypothesize that statins may have a potential role for the management of immune reconstitution syndrome. Our proposal has biologic and translational implications for optimizing outcomes in patients with immune reconstitution syndrome.

Updated principles and clinical caveats in the management of infection in renal transplant recipients

Renal transplantation is now considered the treatment of choice for patients with end-stage renal disease. In transplant recipients, infection and rejection are entwined and are unavoidable tribulations unless clinical tolerance becomes a reality. Although rejection rates have significantly decreased with the introduction of newer immunosuppressive agents, infections remain a major cause of morbidity and mortality, and the magnitude of the problem is on the rise. Newer infections are emerging and patterns of known infections are changing. The continuous evolution of donor and recipient characteristics also alters the landscape of infections. In clinical practice, establishing a definite diagnosis of infection in a timely manner remains a challenge in transplant recipients as compared to immunocompetent individuals. Hence a comprehensive knowledge of the principles of management of infections in renal transplant recipients is very essential. In this review, we would like to provide an overview of some of the key principles that we believe are essential in the management of infectious complications in renal transplant recipients with no focus on any individual infection.

Immune reconstitution inflammatory syndrome and solid organ transplant recipients: are children protected?

The IRIS was initially described in HIV-positive patients as a sudden clinical deterioration after the introduction of highly active retroviral therapy. It is believed that IRIS is caused by a restored and exaggerated inflammatory immune response to different infectious or non-infectious triggers. This abnormal response is the consequence of an imbalance between pro-inflammatory and anti-inflammatory states. Recently, IRIS has also been reported in adult SOT recipients, causing local and systemic manifestations, and compromising long-term graft function and patient survival. However, IRIS has to date not been reported in pediatric SOT recipients. Here we review what is known and speculated about the pathogenesis of IRIS and propose that children may be relatively protected from IRIS.

Genetic variability of innate immunity impacts human susceptibility to fungal diseases

Fungi are a major threat in immunocompromised patients. Despite presenting similar degrees of immunosuppression, not all individuals at-risk ultimately develop fungal diseases. The traditional view of immune suppression as a key risk factor for susceptibility to fungal infections needs to be accommodated within new conceptual advances on host immunity and its relationship to fungal disease. The critical role of the immune system emphasizes the contribution of host genetic polymorphisms to fungal disease susceptibility. This review highlights the present knowledge on innate immunity genetics that associates with susceptibility to fungal diseases.

Doxycycline enhances the Ras-MAPK signaling and proliferation of mouse thymic epithelial cells

Depletion of T-cell-dependent immunity is a major consideration for patients suffering from infections of human immunodeficiency virus (HIV), those undergoing organ transplantation, and those receiving anti-cancer chemotherapy and/or radiotherapy. In general, T-cell regeneration occurs in the thymus through thymopoiesis. We have found that doxycycline (Dox), a tetracycline derivative, enhances the proliferation of mouse thymic epithelial cells, which are unique in their capacity to support positive selection and are essential throughout the development of thymocytes. Cell cycle analysis indicates that the increased cell proliferation is due to a shortened G(0)/G(1) phase. To reveal the underlying mechanisms, we examined the expression of an array of molecules that regulate the cell cycle. The results show that in mouse thymic medullary-type epithelial cell line 1 (MTEC1) Dox leads to elevated levels of H-Ras, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), cyclin E, cyclin dependent kinase 4/2 (CDK4/CDK2), E2F3, and c-myc. These data, and the observation that the proliferation-enhancing effect is largely abolished following treatment with an ERK inhibitor support an active role of the Ras-ERK/mitogen-activated protein kinase (MAPK) signaling pathway. In conclusion, the present study reveals a new activity of an old family of antibiotics. The in vivo effect of Dox on immune reconstitution warrants further exploration.

Immune reconstitution inflammatory syndrome in non-HIV immunocompromised patients

PURPOSE OF REVIEW

In the era of highly active antiretroviral therapy, immune reconstitution inflammatory syndrome has become well recognized in the HIV-infected population. However, little is known about its occurrence in non-HIV immunocompromised hosts. The present review aims to propose the pathogenesis of immune reconstitution inflammatory syndrome, summarize its occurrence in immunocompromised patients without HIV infection, and suggest potential treatment options.

RECENT FINDINGS

Immune reconstitution inflammatory syndrome is exuberant and dysregulated inflammatory responses to invading microorganisms. It manifests when an abrupt shift of host immunity from an anti-inflammatory and immunosuppressive status towards a pathogenic proinflammatory state occurs as a result of rapid decreases or removal of factors promoting immunosuppression or inhibiting inflammation. In addition to HIV-infected patients, immune reconstitution inflammatory syndrome has also been observed in solid organ transplant recipients, women during the postpartum period, neutropenic patients, and tumor necrosis factor antagonist recipients. Corticosteroids are the most commonly employed treatment, whereas other potential agents based on its pathogenesis deserve further investigation.

SUMMARY

Non-HIV immunocompromised hosts develop immune reconstitution inflammatory syndrome when the sudden change in the dominant T helper responses to inflammation is not well balanced by anti-inflammatory responses. Judicious manipulation of host immunity and timely recognition of immune reconstitution inflammatory syndrome as we deal with the infections in these populations is critical to limit or avoid the harm by immune reconstitution inflammatory syndrome.

The enigmatic role of mast cells in dominant tolerance

PURPOSE OF REVIEW

The role of regulatory T cells (Treg) in peripheral tolerance has been studied extensively in transplantation research. Recently, mast cells have been shown to play an indispensable role in allograft tolerance. The purpose of this review is to inform the reader on the current standings of the role of mast cells in dominant tolerance with an emphasis on the interaction of mast cells with Treg.

RECENT FINDINGS

Mast cells are required to sustain peripheral tolerance via Treg. Treg can stabilize mast cells degranulation by contact-dependent mechanisms through the interaction of OX40 and its ligand OX40L, and by production of soluble factors, such as interleukin-10 and transforming growth factor-beta. Conversely, the activation and subsequent degranulation of mast cells break peripheral tolerance.

SUMMARY

Both mast cells and Treg are needed to create a local immunosuppressive environment in the transplant. Treg are not only necessary to suppress effector T-cell responses but also to stabilize mast cells. Mast cells in return could contribute to the immunosuppressive state by release of transforming growth factor-beta, interleukin-10 and specific proteases. However, the molecular basis for mast cells control of Treg suppression in organ transplantation is still unresolved.

Immune sensing of Aspergillus fumigatus proteins, glycolipids, and polysaccharides and the impact on Th immunity and vaccination

The ability of the fungus Aspergillus fumigatus to activate, suppress, or subvert host immune response during life cycle in vivo through dynamic changing of cell wall structure and secretion implicates discriminative immune sensing of distinct fungal components. In this study, we have comparatively assessed secreted- and membrane-anchored proteins, glycolipids, and polysaccharides for the ability to induce vaccine-dependent protection in transplanted mice and Th cytokine production by human-specific CD4(+) T cell clones. The results show that the different fungal components are endowed with the distinct capacity to activate Th cell responses in mice and humans, with secreted proteins inducing Th2 cell activation, membrane proteins Th1/Treg, glycolipids Th17, and polysaccharides mostly IL-10 production. Of interest, the side-by-side comparison revealed that at least three fungal components (a protease and two glycosylphosphatidylinositol-anchored proteins) retained their immunodominant Th1/Treg activating potential from mice to humans. This suggests that the broadness and specificity of human T cell repertoire against the fungus could be selectively exploited with defined immunoactive Aspergillus Ags.

Fungal infections after lung transplantation

PURPOSE OF REVIEW

Lung transplant's Achilles heel is chronic rejection. This is the reason why high immunosuppression is used, which leads to the development of infections. Fungal infections are a great obstacle in lung transplant patients' progress, not only because of their impact on patient survival, but also because fungal infections indirectly have an influence on the graft's progress. This review highlights the changing spectrum of invasive fungal infections as well as the most recent developments in diagnosis, prophylaxis, treatment and monitoring of lung transplantation.

RECENT FINDINGS

Fungal infections have a bimodal presentation: early onset, in relation to difficult postsurgeries and prior colonizations, and late onset, primarily in relation to chronic rejection and terminal renal insufficiency. The clinical impact of non-Aspergillus moulds is still unknown. Recent efforts have focused on nonculture-based methods to establish a rapid diagnosis. However, multicentre studies are needed to establish the diagnostic value of galactomannan antigen assay in invasive aspergillosis in lung transplantation. In addition, studies of the sensitivity and specificity of PCR assays are required to establish their diagnostic value. Unfortunately, only some advances in the diagnosis of aspergillosis have been achieved.

SUMMARY

Prophylaxis should be tailored according to the different individual patient's risk status. Combined treatments, including surgical therapy, may be useful in some patients.

Cryptococcosis in solid organ transplant recipients: current state of the science

Cryptococcosis remains a significant opportunistic infection in solid organ transplant recipients. Disease presentation and outcomes may be affected by, among other factors, the use of calcineurin inhibitor immunosuppressive agents. It is being increasingly recognized that rapid reversal of immunosuppression in transplant recipients treated for cryptococcosis incurs the risk of immune reconstitution inflammatory syndrome, which resembles worsening disease or relapse. This review summarizes the current state of knowledge regarding cryptococcosis in transplant recipients and highlights areas where future investigations are needed to further optimize outcomes for these patients.

Immune reconstitution syndrome after voriconazole treatment for cryptococcal meningitis in a liver transplant recipient

A new entity that comprises symptomatic worsening of an infectious or inflammatory process despite appropriate treatment was described a few years ago in human immunodeficiency virus-infected patients receiving highly active antiretroviral therapy. This entity was defined as immune reconstitution syndrome, and it is believed to result from an intense inflammatory reaction in patients with an appropriately treated infection who recover immunological status. Recently, immune reconstitution syndrome has also been described in transplant recipients, although information is scarce because of its low incidence. Here we describe a new case of immune reconstitution syndrome in a liver transplant recipient after successful treatment of cryptococcal meningitis.