Adenovirus infections in stem cell transplant recipients: recent developments in understanding of pathogenesis, diagnosis and management

An interesting case of adenoviral hepatitis in a cardiac transplant recipient

Adenoviral infections are commonly described in pediatric transplant populations. However, much less information is available regarding the incidence of infection and clinical spectrum of disease in adult transplant recipients. Moreover, this infection usually manifests as involvement of the transplanted organ in one pathologic form or the other, in addition to other systemic manifestations. We present a case of adenoviral infection of a nontransplanted organ in a solid organ transplant recipient.

Disseminated adenovirus infection in renal transplant recipients: the role of cidofovir and intravenous immunoglobulin

Disseminated adenovirus (ADV) infection in solid organ transplant patients is associated with high mortality. Limited studies have shown benefit from using cidofovir (CDV), as well as intravenous immunoglobulin (IVIG). In this study, we report 2 renal transplant patients who presented with fever and pulmonary infiltrates. Both patients continued to worsen despite antibiotic therapy. Bronchoalveolar lavage viral culture and serum polymerase chain reaction (PCR) were positive for ADV. Patients were treated with CDV, IVIG, and reduction in immunosuppression. A progressive decline in serum ADV DNA by PCR correlated with clinical improvement and pulmonary infiltrates improved. Both patients recovered. Allograft function was preserved although reversible acute kidney injury was observed in both patients. To the best of our knowledge, this is the first successful use of CDV and IVIG in renal transplant patients with disseminated ADV infection.

Clinical features and treatment of adenovirus infections

Adenoviruses (Ads) are common opportunistic pathogens that are rarely associated with severe clinical symptoms in healthy individuals. In contrast, in patients with compromised immunity, Ad infections often result in disseminated and potentially life-threatening disease. Among these are AIDS patients, individuals with hereditary immunodeficiencies and recipients of solid organ or haematopoietic stem cell transplants (HSCT) who receive immunosuppressive therapy. The latter account for the largest number of severe Ad infections. There is currently no formally approved antiviral therapy for the treatment of severe Ad keratoconjunctivitis and life-threatening Ad infections in immunocompromised patients. Here we update current knowledge on Ad biology, the clinical features observed in different patient groups and specific immune responses towards Ad infections. In addition, we review current and future treatment options, including: (i) the antiviral drugs cidofovir, ribavirin and new investigational compounds, as evaluated in the clinic or in relevant animal models, as well as (ii) novel immunotherapeutic strategies.

Adenoviruses in immunocompromised hosts

SUMMARY

The number of patients with acquired immunodeficiency has grown steadily as a result of both a larger number of patients receiving solid organ and hematopoietic stem cell transplants and their longer survival times. The use of newer, more potent immunosuppressive regimens has increased the frequency of severe adenovirus infections. Human adenoviruses are a large group of viruses, represented by at least 52 serotypes with various genotypes divided into genomic clusters, and these may cause a broad variety of clinical manifestations. The development of molecular methods has increased the sensitivity and rapidity of adenovirus infection diagnosis. The implementation of PCR assays has significantly contributed to the identification of patients with disseminated adenovirus disease. More recently, the development of real-time PCR assays has permitted virus quantification and patient follow-up. There is no treatment for adenovirus with demonstrated efficacy, although cidofovir is widely used. Sensitive diagnostic tests for adenovirus can contribute to the early diagnosis and successful treatment of life-threatening adenovirus infections, especially in complex immunocompromised patients. The development of improved adenovirus therapy still remains a challenge. Adenovirus genetic diversity should be considered for diagnosis, typing, and therapeutic interventions.

T-cell lines specific for peptides of adenovirus hexon protein and devoid of alloreactivity against recipient cells can be obtained from HLA-haploidentical donors

Human adenovirus (HAdV) infection may cause life-threatening complications in recipients of hematopoietic stem cell transplantation (HSCT), the highest risk being observed in children given T-cell depleted haploidentical allografts. The effectiveness of pharmacologic therapy for HAdV infection is suboptimal. Recently, cell therapy was demonstrated to offer a unique opportunity to restore antiviral immune surveillance, leading to clearance of infection and prevention/treatment of disease. However, infusion of insufficiently selected HAdV-specific T cells in haplo-HSCT may increase the risk of graft-versus-host disease. We conducted scale-up experiments to validate a method of in vitro culture to expand T cells specific for HAdV from donor peripheral blood mononuclear cells (PBMC), based on stimulation with a pool of five 30-mer peptides derived from HAdV5 hexon protein, for use in recipients of haplo-HSCT. A total of 21 T-cell lines that included a majority of CD4 T lymphocytes, were generated. Nineteen of the 21 T-cell lines proliferated specifically against HAdV. The 2 nonspecific, and 3 T-cell lines with lower specific activity, included a median of 48% CD8 T cells. The 19 HAdV-specific T-cell lines showed a median 357-fold decrease in alloreactivity, compared with proliferation of noncultured donor PBMC in response to recipient PBMC, only 4/19 T-cell lines showing residual alloreactivity. Our data indicate that HAdV-specific CD4 T-cell lines with efficient in vitro antiviral response and low/undetectable alloreactivity against recipient targets may be expanded from PBMC of most human leukocyte antigen-haploidentical HSCT donors after stimulation with HAdV hexon protein-derived peptides. These T cells may be safely employed for adoptive treatment of HAdV complications.

High-risk adenovirus-infected pediatric allogeneic hematopoietic progenitor cell transplant recipients and preemptive cidofovir therapy

ADV has emerged as an important pathogen in children undergoing allogeneic HPCT. A prospective study of the epidemiology of ADV infection and preemptive therapy of high risk ADV infections in children undergoing HPCT was undertaken. Cultures of throat, urine, and stool for viral pathogens and plasma for ADV PCR were obtained prior to transplantation, weekly for the first 100 days, and then monthly for one yr. Children developing high-risk ADV infections were treated preemptively with cidofovir 1 mg/kg/day given three times weekly for three wk. A case-controlled study was performed to identify risk factors for high-risk ADV infections. Seven (18%) of the 38 subjects developed high-risk ADV infections usually within 100 days of HPCT and were preemptively treated with i.v. cidofovir at a dose of 1 mg/kg/dose three times weekly for nine doses. High-risk ADV infections resolved in all seven patients without renal toxicity. CMV viremia occurred in two of seven patients during or shortly after therapy with cidofovir. A case-control study did not identify any risk factors that achieved statistical significance. Treatment with a modified dosing regimen of cidofovir was well-tolerated and high-risk ADV infections resolved in all patients.

Identification of adenoviruses in specimens from high-risk pediatric stem cell transplant recipients and controls

Adenovirus infection is an important cause of morbidity and mortality in stem cell transplant recipients. We report species and type-specific analysis from a prospective study of high-risk adenovirus infections following hematopoietic progenitor cell transplantation prior to, during, and after treatment with cidofovir, as well as species analysis of contemporaneously collected samples from control patients. Nine different adenovirus types representing all six recognized species were identified, and mixed infections were commonly found in this group of patients.

Quantification of adenovirus species B and C viremia by real-time PCR in adults and children undergoing stem cell transplantation

Adenovirus infection during stem cell transplantation is associated with high morbidity and mortality. Adenovirus species B and C have been the main causes for these infections; however, epidemiological details about the species are still unclear. To clarify the contributions of species B and C adenovirus, the DNA was tested serially by quantitative real-time PCR in peripheral blood, stool and urine of 32 patients (16 adults and 16 children) undergoing stem cell transplantation. Adenovirus species B viremia was detected in 10 of 16 adult and 6 of 16 pediatric transplant recipients. Adenovirus species C viremia was also detected simultaneously in five adult and three pediatric recipients. The stool and urine of patients with adenovirus viremia were also positive for the same adenovirus species as in blood. In contrast, in none of 50 healthy adult controls was adenovirus species B or C viremia detected. Among patients who developed adenovirus viremia, one adult recipient developed disseminated disease and died from multiple organ failure. The remaining patients experienced fever of several degrees and/or diarrhea during the period of adenovirus viremia; however, they all recovered without antiviral therapy. The results indicated that stem cell transplantation was frequently associated with adenovirus species B or C viremia, although it did not always cause serious infectious complications.

Treatment of adenovirus disease in stem cell transplant recipients with cidofovir

Invasive adenovirus (AdV) disease is fatal in >50% of allogeneic hematopoietic stem cell transplant (SCT) recipients. Treatment with cidofovir may improve outcomes based on in vitro susceptibility data and case reports. Six consecutive cases of invasive AdV disease treated with cidofovir were reviewed among 84 allogeneic adult SCT recipients (incidence, 7.1%). Cidofovir was administered intravenously at 5 mg/kg per dose (1-7 doses). All patients received intravenous immune globulin. Blood AdV DNA levels (viral loads, VLs) were monitored with a real-time quantitative polymerase chain reaction assay. Published reports of cidofovir treatment of AdV disease in SCT recipients were critically reviewed. The primary manifestations of AdV disease were hepatitis (n = 3), colitis (n = 2), and nephritis (n = 1). All patients had detectable AdV VLs, with peak values from 5 x 10(5) to 2 x 10(8) copies/mL. All patients received CD34+ selected grafts (n = 3) and/or had graft-versus-host disease (n = 4) and had CD4 counts <100 cells/mm3. Only 1 of 5 patients (20%) who received >or=2 doses of cidofovir died with active AdV disease. Four patients exhibited improvement within days of treatment with cidofovir as documented by clinical criteria and declines in AdV VLs (without a change in immunosuppression). In contrast, 1 patient treated late after onset of AdV disease died after 1 dose of cidofovir. In our review of 70 published cases treated with >or=2 doses of cidofovir, 13 (19%) died from AdV disease. In conclusion, early treatment of AdV disease with cidofovir inhibits viral replication in vivo and reduces mortality in allogeneic SCT recipients compared with historical data.

Respiratory Viral Infections in Transplant Recipients

A wide range of viruses affect the respiratory tract of transplant recipients, including adenovirus, influenza, human metapneumovirus, parainfluenza virus, respiratory syncytial virus (RSV) and rhinovirus. Prospective studies using contemporary diagnostic techniques have recently improved our understanding of the epidemiology and importance of these respiratory viruses among transplant recipients. From these studies, rhinovirus, in particular, has been shown to be one of the most common causes of infection in stem cell and lung transplant recipients. In addition to epidemiological data, recent studies have also advanced our understanding of management of influenza, adenovirus, and RSV infections among transplant recipients.

Adenoviral infections in pediatric transplant recipients: a hospital-based study

OBJECTIVE

To assess the disease burden and outcomes resulting from adenoviral infections among pediatric transplant recipients.

METHODS

This was a retrospective study of adenoviral infections among pediatric transplant recipients who were hospitalized at our center between 1993 and 2003. Patients were defined as having adenoviral infection if the virus was demonstrated in stool, urine, respiratory, blood, or biopsy tissue samples in the presence of attributable clinical findings. Data were obtained from the hospital's medical records and laboratory databases.

RESULTS

There were 55 patients with single episodes of adenovirus infection: 28 (50.9%) solid organ transplant (SOT) and 27 (49.1%) hematopoietic stem cell transplant (HSCT) recipients. The prevalence rates among SOT and HSCT recipients were 1 per 16 and 1 per 24 transplants performed, respectively. The median age of patients with adenovirus infections was 3.66 years (range, 0.25-17.25). Infection occurred at a median of 1.6 months posttransplantation (range, 0.03-153.). Adenovirus was most frequently demonstrated from the gastrointestinal tract (78%). Other sites infected included the respiratory tract, liver, blood and urinary tract. Overall mortality was 14.6%. All deaths occurred among HSCT recipients (mortality, 29.6%). Deaths were more likely among patients with adenovirus identified at >or=2 sites than in those having localized disease (P < 0.01).

CONCLUSION

Mortality from adenoviral infection was a greater risk for HSCT than SOT recipients. Early onset of infection after transplantation suggests the possibility of reactivation of adenovirus rather than new acquisition in at least of proportion of cases. This is important for surveillance of this infection in transplant recipients.

Adenovirus infections in transplant recipients

Adenoviruses are increasingly recognized as contributors to morbidity and mortality among stem cell and solid-organ transplant recipients. Clinical presentations range from asymptomatic viremia to respiratory and gastrointestinal disease, hemorrhagic cystitis, and severe disseminated illness. The limited clinical data available support the use of cidofovir for many of these illnesses. Prospective studies are needed to better understand the pathogenesis of and therapeutic options for adenoviral infections in this patient population.

Clinical and In Vitro Evaluation of Cidofovir for Treatment of Adenovirus Infection in Pediatric Hematopoietic Stem Cell Transplant Recipients

Post-hematopoietic stem cell transplantation (HSCT) adenovirus infections were identified in 31 of 204 consecutive pediatric HSCT patients, 18 of whom had severe manifestations of infection. Cidofovir treatment led to clinical improvement in 8 of 10 patients with severe infection and to virologic clearance in 9 patients. In vitro susceptibility to cidofovir was demonstrated in 12 clinical adenovirus isolates. Cidofovir is a promising treatment option for this population.

Identification of quantitative trait loci for susceptibility to mouse adenovirus type 1

Adult SJL/J mice are highly susceptible to mouse adenovirus type 1 (MAV-1) infections, whereas other inbred strains, including BALB/cJ, are resistant (K. R. Spindler, L. Fang, M. L. Moore, C. C. Brown, G. N. Hirsch, and A. K. Kajon, J. Virol. 75:12039-12046, 2001). Using congenic mouse strains, we showed that the H-2(s) haplotype of SJL/J mice is not associated with susceptibility to MAV-1. Susceptibility of MAV-1-infected (BALB/cJ x SJL/J)F(1) mice was intermediate between that of SJL/J mice and that of BALB/cJ mice, indicating that susceptibility is a genetically controlled quantitative trait. We mapped genetic loci involved in mouse susceptibility to MAV-1 by analysis of 192 backcross progeny in a genome scan with 65 simple sequence length polymorphic markers. A major quantitative trait locus (QTL) was detected on chromosome 15 (Chr 15) with a highly significant logarithm of odds score of 21. The locus on Chr 15 alone accounts for 40% of the total trait variance between susceptible and resistant strains. QTL modeling of the data indicated that there are a number of other QTLs with small effects that together with the major QTL on Chr 15 account for 54% of the trait variance. Identification of the major QTL is the first step in characterizing host genes involved in susceptibility to MAV-1.

Prospects for adenovirus antivirals

Adenoviruses cause a number of self-limiting but often highly infectious diseases that affect multiple organs, most commonly those associated with respiratory, genitourinary and gastrointestinal tracts and the ocular surface. Many factors have driven a search for effective topical and systemic antivirals to adenoviruses. These include patient morbidity, economic losses and chronic visual disturbances associated with epidemic keratoconjunctivitis; and the startling recent trend of high morbidity and rising mortality associated with systemic adenoviral infections in the immunosuppressed, particularly paediatric bone marrow transplant recipients. The development of effective antivirals has proven to be a complex task, owing to the fact that multiple and often genetically divergent adenovirus serotypes can cause similar diseases. Currently, there remains no licensed systemic or topical treatment in the USA or Europe. However, many compounds have been explored for activity against adenoviruses, and some have been evaluated clinically in either a topical setting for ocular disease or in the setting of systemic treatment in the face of life-threatening adenovirus infections. This article outlines such compounds, discusses the potential for their clinical development, and highlights some problems that may be faced in evaluating their efficacy clinically.