Immunoglobulin administration and ribavirin therapy: efficacy in respiratory syncytial virus infection of the cotton rat

Fc-mediated functions and the treatment of severe respiratory viral infections with passive immunotherapy - a balancing act

Passive immunotherapies have been used to treat severe respiratory infections for over a century, with convalescent blood products from recovered individuals given to patients with influenza-related pneumonia as long ago as the Spanish flu pandemic. However, passive immunotherapy with convalescent plasma or hyperimmune intravenous immunoglobulin (hIVIG) has not provided unequivocal evidence of a clinical benefit for severe respiratory infections including influenza and COVID-19. Efficacy trials, primarily conducted in late-stage disease, have demonstrated inconsistent efficacy and clinical benefit for hIVIG treatment of severe respiratory infections. To date, most serological analyses of convalescent plasma and hIVIG trial samples have focused on the measurement of neutralizing antibody titres. There is, however, increasing evidence that baseline antibody levels and extra-neutralizing antibody functions influence the outcome of passive immunotherapy in humans. In this perspective, findings from convalescent plasma and hIVIG trials for severe influenza, COVID-19 and respiratory syncytial virus (RSV) will be described. Clinical trial results will be discussed in the context of the potential beneficial and deleterious roles of antibodies with Fc-mediated effector functions, with a focus on natural killer cells and antibody-dependent cellular cytotoxicity. Overall, we postulate that treating respiratory viral infections with hIVIG represents a delicate balance between protection and immunopathology.

From animal studies into clinical trials: the relevance of animal models to develop vaccines and therapies to reduce disease severity and prevent hRSV infection

INTRODUCTION

Human respiratory syncytial virus (hRSV) is an important cause of lower respiratory tract infections in the pediatric and the geriatric population worldwide. There is a substantial economic burden resulting from hRSV disease during winter. Although no vaccines have been approved for human use, prophylactic therapies are available for high-risk populations. Choosing the proper animal models to evaluate different vaccine prototypes or pharmacological treatments is essential for developing efficient therapies against hRSV.

AREAS COVERED

This article describes the relevance of using different animal models to evaluate the effect of antiviral drugs, pharmacological molecules, vaccine prototypes, and antibodies in the protection against hRSV. The animal models covered are rodents, mustelids, bovines, and nonhuman primates. Animals included were chosen based on the available literature and their role in the development of the drugs discussed in this manuscript.

EXPERT OPINION

Choosing the correct animal model is critical for exploring and testing treatments that could decrease the impact of hRSV in high-risk populations. Mice will continue to be the most used preclinical model to evaluate this. However, researchers must also explore the use of other models such as nonhuman primates, as they are more similar to humans, prior to escalating into clinical trials.

Respiratory Viral Infections in Patients With Cancer or Undergoing Hematopoietic Cell Transplant

Survival rates for pediatric cancer have steadily improved over time but it remains a significant cause of morbidity and mortality among children. Infections are a major complication of cancer and its treatment. Community acquired respiratory viral infections (CRV) in these patients increase morbidity, mortality and can lead to delay in chemotherapy. These are the result of infections with a heterogeneous group of viruses including RNA viruses, such as respiratory syncytial virus (RSV), influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (HMPV), rhinovirus (RhV), and coronavirus (CoV). These infections maintain a similar seasonal pattern to those of immunocompetent patients. Clinical manifestations vary significantly depending on the type of virus and the type and degree of immunosuppression, ranging from asymptomatic or mild disease to rapidly progressive fatal pneumonia Infections in this population are characterized by a high rate of progression from upper to lower respiratory tract infection and prolonged viral shedding. Use of corticosteroids and immunosuppressive therapy are risk factors for severe disease. The clinical course is often difficult to predict, and clinical signs are unreliable. Accurate prognostic viral and immune markers, which have become part of the standard of care for systemic viral infections, are currently lacking; and management of CRV infections remains controversial. Defining effective prophylactic and therapeutic strategies is challenging, especially considering, the spectrum of immunocompromised patients, the variety of respiratory viruses, and the presence of other opportunistic infections and medical problems. Prevention remains one of the most important strategies against these viruses. Early diagnosis, supportive care and antivirals at an early stage, when available and indicated, have proven beneficial. However, with the exception of neuraminidase inhibitors for influenza infection, there are no accepted treatments. In high-risk patients, pre-emptive treatment with antivirals for upper respiratory tract infection (URTI) to decrease progression to LRTI is a common strategy. In the future, viral load and immune markers may prove beneficial in predicting severe disease, supporting decision making and monitor treatment in this population.

Respiratory Syncytial Virus and Human Metapneumovirus Infection in Transplant Recipients

Respiratory viral infections due to respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) cause infections in immunocompromised transplant patients ranging from mild upper respiratory infections to severe lower respiratory tract disease with respiratory failure. These viruses are more readily diagnosed due to improvements in sensitive molecular diagnostic methods. The epidemiology of RSV and hMPV is similarly becoming more readily appreciated in hematopoietic stem cell transplant (HSCT) patients of all ages as well as solid organ transplant (SOT) patients, with lung transplant recipients having evidence of more frequent and severe complications related to these viruses. RSV and hMPV infection typically but not always present with upper respiratory signs and symptoms that progress to lower respiratory tract disease. Treatment options for RSV are limited, with aerosolized, intravenous, and oral ribavirin all studied in HSCT and lung transplant patients. No antiviral therapy for the treatment of hMPV is available, although ribavirin has shown some effectiveness in vitro. New antiviral agents including RSV fusion inhibitors and nucleoside analogs are being developed, with some under clinical evaluation.

Management of respiratory viral infections in hematopoietic cell transplant recipients and patients with hematologic malignancies

Despite preventive strategies and increased awareness, a high incidence of respiratory viral infections still occur in patients with hematologic malignancies (HMs) and in recipients of hematopoietic cell transplant (HCT). Progression of these viral infections to lower respiratory tract may prove fatal, especially in HCT recipients. Increasing evidence on the successful use of ribavirin (alone or in combination with immunomodulators) for the treatment of respiratory syncytial virus infections in HM patients and HCT recipients is available from retrospective studies; however, prospective clinical trials are necessary to establish its efficacy with confidence. The impact on progression to pneumonitis and/or mortality of treating parainfluenza virus infections with available (ribavirin) or investigational (DAS181) antiviral agents still needs to be determined. Influenza infections have been successfully treated with neuraminidase inhibitors (oseltamivir or zanamivir); however, the efficacy of these agents for influenza pneumonia has not been established, and immunocompromised patients are highly susceptible to emergence of antiviral drug resistance, most probably due to prolonged viral shedding. Infection control measures and an appreciation of the complications following respiratory viral infections in immunocompromised patients remain crucial for reducing transmission. Future studies should focus on strategies to identify patients at high risk for increased morbidity and mortality from these infections and to determine the efficacy of novel or available antiviral drugs.

Efficacy of oral ribavirin in hematologic disease patients with paramyxovirus infection: analytic strategy using propensity scores

Few antiviral agents are available for treating paramyxovirus infections, such as those involving respiratory syncytial virus (RSV), parainfluenza virus (PIV), and human metapneumovirus (hMPV). We evaluated the effect of oral ribavirin on clinical outcomes of paramyxovirus infections in patients with hematological diseases. All adult patients with paramyxovirus were retrospectively reviewed over a 2-year period. Patients who received oral ribavirin were compared to those who received supportive care without ribavirin therapy. A propensity-matched case-control study and a logistic regression model with inverse probability of treatment weighting (IPTW) were performed to reduce the effect of selection bias in assignment for oral ribavirin therapy. A total of 145 patients, including 64 (44%) with PIV, 60 (41%) with RSV, and 21 (15%) with hMPV, were analyzed. Of these 145 patients, 114 (78%) received oral ribavirin and the remaining 31 (21%) constituted the nonribavirin group. Thirty-day mortality and underlying respiratory death rates were 31% (35/114) and 12% (14/114), respectively, for the oral ribavirin group versus 19% (6/31) and 16% (5/31), respectively, for the nonribavirin group (P = 0.21 and P = 0.56). In the case-control study, the 30-day mortality rate in the ribavirin group was 24% (5/21) versus 19% (4/21) in the nonribavirin group (P = 0.71). In addition, the logistic regression model with IPTW revealed no significant difference in 30-day mortality (adjusted hazard ratio of 1.3; 95% confidence interval [95% CI] of 0.3 to 5.8) between the two groups. Steroid use (adjusted odds ratio, 5.67; P = 0.01) and upper respiratory tract infection (adjusted odds ratio, 0.07; P = 0.001) was independently associated with mortality. Our data suggest that oral ribavirin therapy may not improve clinical outcomes in hematologic disease patients infected with paramyxovirus.

Respiratory syncytial virus disease: prevention and treatment

Respiratory syncytial virus (RSV) is one of the most clinically important viruses infecting young children, the elderly, and the immunocompromised. Over the past decade, the most significant advance in the prevention of RSV disease has been the development of high-titered antibody products. Infection control is the only other strategy to prevent RSV disease. A humanized monoclonal antibody directed against the fusion (F) protein palivizumab, (Synagis®, MedImmune, Inc., Gaithersburg, MD), is given routinely on a monthly basis to premature infants and young children less than 24 months of age with underlying medical problems including prematurity, chronic lung disease, or cardiac disease to prevent RSV disease and hospitalization. Other products utilizing polyclonal or monoclonal antibodies or antibody fragments against the F protein have been developed and some already tested in patient populations. The only licensed antiviral treatment available today is ribavirin, a guanosine analogue generally administered as a small particle aerosol to immunocompromised patients with lower respiratory tract disease due to RSV. This drug has also been utilized in oral and intravenous forms, again mainly in immunocompromised patients. Promising new antiviral agents under development by multiple pharmaceutical and biotechnology companies include small molecule fusion inhibitors, attachment inhibitors, inhibitors of RNA synthesis, and small interfering RNA particles (siRNA).

Prophylaxis and treatment of respiratory syncytial virus in adult immunocompromised patients

OBJECTIVE

To review the literature regarding current strategies and strategies under active development for the prevention and treatment of respiratory syncytial virus (RSV) infections in immunocompromised adults.

DATA SOURCES

The MEDLINE/PubMed, EMBASE, and Cochrane databases were queried from January 1980 to December 2011 for articles in English using these associated search terms: respiratory syncytial virus, ribavirin, intravenous immunoglobulin, IVIG, palivizumab, motavizumab, lung, pneumonia, transplantation, bone marrow, cancer, malignancy, and vaccine.

STUDY SELECTION AND DATA EXTRACTION

All relevant original studies, meta-analyses, systematic reviews, and review articles were assessed for inclusion. References from pertinent articles were examined for additional content not found during the initial search.

DATA SYNTHESIS

RSV in the immunocompromised adult can lead to significant morbidity and mortality. Treatment of RSV-infected adults is limited to antiviral therapy with ribavirin (aerosolized, oral, intravenous) and immunomodulation with intravenous immunoglobulins, corticosteroids, and palivizumab. Existing literature is predominantly case reports, small trials, and retrospective reviews of patients infected with RSV who have undergone lung or hematopoietic stem cell transplantation (HSCT). Palivizumab may be a viable option for prophylaxis against RSV in high-risk adults. Ribavirin is the most studied treatment option and should remain the backbone of multidrug regimens. Of the routes of administration, aerosolized ribavirin carries the preponderance of evidence and, though challenging, is preferred to limit systemic toxicities in the infected patient. Addition of an immunomodulator to ribavirin may provide a survival benefit over ribavirin alone; however, this has only been studied in a subset of HSCT patients with lower respiratory tract RSV infection.

CONCLUSIONS

Research most strongly supports the use of aerosolized ribavirin as the treatment strategy for immunocompromised adults with RSV. Addition of an immunomodulator may provide a survival benefit over ribavirin alone. Strategies and supportive data for the prevention of RSV infection in the high-risk adult are critically needed.

Management of RSV infections in adult recipients of hematopoietic stem cell transplantation

Respiratory syncytial virus (RSV) is a common cause of seasonal respiratory viral infection in patients who have undergone hematopoietic stem cell transplantation. RSV usually presents as an upper respiratory tract infection in this patient population but may progress rapidly to lower respiratory tract infection. Available therapies that have been used for the treatment of RSV infections are limited to ribavirin, intravenous immunoglobulin, and palivizumab. The use of aerosolized ribavirin, alone or in combination with either palivizumab or intravenous immunoglobulin, remains controversial. In this comprehensive review, we present and discuss the available literature on management of RSV infections in adult hematopoietic stem cell transplantation recipients with a focus on therapeutic modalities and outcomes.

Immunoprophylaxis and immunotherapy: role in the prevention and treatment of repiratory syncytial virus

It is now apparent that neutralizing antibody may play an important role in ameliorating RSV lower repiratory tract illness. At the present time immunoprophylaxis and immunotherapy with polyclonal antibodies show the most promise in the prevention and treatment of RSV illness. Several questions remained to be answered. These include the practical application of IGIV in prevention and treatment of RSV illness. Intravenous lines are often difficult to place and maintain. With the further development of polyclonal or monoclonal antibodies it may be possible to immunize prospective donors and boost their anti RSV titers to the degree that a hyper-immune IGIV with sufficient antibody to be given intramuscularly could be produced. The role for RSV-specific monoclonal antibodies for disease prevention or treatment must be defined as well as the appropriatee viral epitopes to target. In the absence of a safe and effective vaccine, it is clear that, despite these questions passive immunotherapy and immunoprophylaxis offers the greatest hope for the prevention and treatment of RSV disease in high risk infants and children.

The cotton rat (Sigmodon hispidus) is a permissive small animal model of human metapneumovirus infection, pathogenesis, and protective immunity

Human metapneumovirus (hMPV) is a newly described paramyxovirus that is an important cause of acute respiratory tract disease. We undertook to develop a small animal model of hMPV infection, pathogenesis, and protection. Hamsters, guinea pigs, cotton rats, and nine inbred strains of mice were inoculated intranasally with hMPV. The animals were sacrificed, and nasal and lung tissue virus yields were determined by plaque titration. None of the animals exhibited respiratory symptoms. The quantity of virus present in the nasal tissue ranged from 4.6 x 10(2) PFU/gram tissue (C3H mice) to greater than 10(5) PFU/gram (hamster). The amount of virus in the lungs was considerably less than in nasal tissue in each species tested, ranging from undetectable (<5 PFU/g; guinea pigs) to 1.8 x 10(5) PFU/gram (cotton rat). The peak virus titer in cotton rat lungs occurred on day 4 postinfection. hMPV-infected cotton rat lungs examined on day 4 postinfection exhibited histopathological changes consisting of peribronchial inflammatory infiltrates. Immunohistochemical staining detected virus only at the luminal surfaces of respiratory epithelial cells throughout the respiratory tract. hMPV-infected cotton rats mounted virus-neutralizing antibody responses and were partially protected against virus shedding and lung pathology on subsequent rechallenge with hMPV. Viral antigen was undetectable in the lungs on challenge of previously infected animals. This study demonstrates that the cotton rat is a permissive small animal model of hMPV infection that exhibits lung histopathology associated with infection and that primary infection protected animals against subsequent infection. This model will allow further in vivo studies of hMPV pathogenesis and evaluation of vaccine candidates.

Animal pneumoviruses: molecular genetics and pathogenesis

Pneumoviruses are single-stranded, negative-sense, nonsegmented RNA viruses of the family Paramyxoviridae, subfamily Pneumovirinae, and include pathogens that infect humans (respiratory syncytial virus and human metapneumovirus), domestic mammals (bovine, ovine, and caprine respiratory syncytial viruses), rodents (pneumonia virus of mice), and birds (avian metapneumovirus). Among the topics considered in this review are recent studies focused on the roles of the individual virus-encoded components in promoting virus replication as well as in altering and evading innate antiviral host defenses. Advances in the molecular technology of pneumoviruses and the emergence of recombinant pneumoviruses that are leading to improved virus-based vaccine formulations are also discussed. Since pneumovirus infection in natural hosts is associated with a profound inflammatory response that persists despite adequate antiviral therapy, we also review the recent experimental treatment strategies that have focused on combined antiviral, anti-inflammatory, and immunomodulatory approaches.

Severe respiratory syncytial virus pneumonia complicating fludarabine and cyclophosphamide treatment of chronic lymphocytic leukemia

The potential for life-threatening pneumonia due to respiratory syncytial virus (RSV) infection is recognised among patients with acute leukaemia and recipients of allogeneic or autologous bone marrow transplantation. RSV pneumonia has a high mortality rate in these settings. Less intensively treated patients are not usually considered to be at risk for serious RSV pneumonia. We describe the case of a 62-yr-old patient with chronic lymphocytic leukaemia (CLL) treated with fludarabine and cyclophosphamide who developed severe RSV pneumonia and recovered following treatment including intravenous ribavirin.

Respiratory syncytial virus infections in autologous blood and marrow transplant recipients with breast cancer: combination therapy with aerosolized ribavirin and parenteral immunoglobulins

Scant data are available concerning the impact and response to therapy of respiratory syncytial virus (RSV) infections in patients undergoing autologous blood and marrow transplantation (BMT) for breast cancer. During eight winter seasons from 1992-1993 to 1999-2000, nine (4%) of 249 such patients were hospitalized with RSV infections. Six patients, including all five patients who were early post transplant in the pre-engraftment period, developed pneumonia and were treated with a combination of aerosolized ribavirin and IVIG. Among five patients with pneumonia in whom therapy was initiated prior to respiratory failure, one (20%) died. The sixth patient, in whom therapy was initiated after respiratory failure developed, also died. In total, two (1%) patients, both of whom were in the pre-engraftment period, died of progressive pneumonia. In conclusion, RSV is a significant cause of life-threatening pneumonia in autologous BMT recipients with breast cancer during the early post-transplant period, and accounted for a substantial portion of the overall transplant-related mortality, which in recent years has been minimal.

Respiratory syncytial virus immune globulin treatment of lower respiratory tract infection in pediatric patients undergoing bone marrow transplantation - a compassionate use experience

Respiratory syncytial virus (RSV) pneumonia in BMT recipients carries a mortality rate of approximately 50-70% despite ribavirin (Virazole) treatment. In both immunocompetent and immunocompromised animal models, RSV neutralizing antibodies rapidly reduce pulmonary virus load after a single dose. RSV-IGIV (RespiGam) is an IgG immune globulin with high concentrations of RSV neutralizing antibody (>19 200 MU/ml). From June 1991 to February 1996, a compassionate-use protocol using RSV-IGIV for treatment of RSV infections was conducted. Eleven children at multiple centers, mean age 3.3 years (4 months to 9 years), were undergoing BMT and met the protocol criteria. They received a single 1500 mg/kg dose of RSV-IGIV infused over 12 h at a median of 5 days (1-37 days) after RSV symptom onset. Ten of these patients received prior or concurrent aerosolized ribavirin. Serum RSV neutralizing titers were measured in five patients and showed a 3- to 30-fold increase 24 h after RSV-IGIV infusion. Adverse events were mild. One of 11 (9.1%) patients died from their RSV illness (91% RSV survival). In comparison to previously published reports, RSV-IGIV treatment of RSV pneumonia in BMT patients may increase survival above that in such patients treated with ribavirin alone. Bone Marrow Transplantation (2000) 25, 161-165.

Chemotherapy of respiratory viruses: prospects and challenges

Billions of people are infected with respiratory viruses annually. Infants and young children, the elderly, immunocompromised individuals and those debilitated by other diseases or nutritional deficiencies are most at risk for serious disease. There are few vaccines available for use against these viruses, and even where there are (influenza, measles and adenovirus), infections remain common. The continued prevalence of respiratory virus infections has lead to renewed efforts to find safe agents effective against the most medically important respiratory viruses: influenza, respiratory syncytial, parainfluenza, measles, rhino- and adenovirus. Copyright 1999 Harcourt Publishers Ltd.

Mouse model of respiratory syncytial virus infection to evaluate antiviral activity in vivo

In this study, we have developed a practical mouse model for evaluating in vivo the antiviral activity of compounds against respiratory syncytial virus (RSV) infection. BALB/c mice are not particularly susceptible to RSV infection; however, infection rates were improved by pretreatment with the immunosuppressive agent cyclophosphamide (CYP). When mice were inoculated intranasally with RSV A2 strain, the pulmonary RSV titres of CYP-pretreated 10-week-old mice were higher than those of untreated 10-week-old and 28-week-old mice, peaking on days 4 and 5 post-infection. Sections of lung from RSV-infected mice pretreated with CYP, taken on day 4 post-inoculation, showed widespread evidence of interstitial pneumonia and other significant pathological changes. We also confirmed that ribavirin, a representative antiviral agent, significantly reduced the pulmonary RSV titres of mice pretreated with CYP when administered intraperitoneally.

Efficacy of RD3-0028 aerosol treatment against respiratory syncytial virus infection in immunosuppressed mice

RD3-0028, a benzodithiin compound, has antiviral activity against respiratory syncytial virus (RSV) in cell culture. We used a mouse model of RSV infection to determine the in vivo effect of RD3-0028. Cyclophosphamide (CYP)-treated, immunosuppressed mice were inoculated intranasally. The lungs of the mice were removed on day 4. The virus titers of the lungs of RD3-0028-treated mice were compared to the virus titers of the lungs of virus-inoculated, untreated control mice. In an effort to increase the therapeutic effectiveness of this compound, RD3-0028 was administered by aerosol to RSV-infected mice by using a head-exposure system. Aerosols generated from reservoirs containing RD3-0028 (7 mg/ml) administered for 2 h twice daily for 3 days significantly reduced the pulmonary titer of RSV-infected mice. It is clear that the minimal effective dose of RD3-0028 for RSV-infected mice is significantly less than that of ribavirin, the only compound currently available for use against RSV disease. Furthermore, the RD3-0028 aerosol administration appeared to protect the lungs of infected, CYP-treated mice against tissue damage, as evidenced by the preservation of the lung architecture and a reduction in pulmonary inflammatory infiltrates. RD3-0028 aerosol was not toxic for mice at the therapeutic dose. The present study demonstrates the effectiveness of aerosol administration of RD3-0028 for RSV-infected mice.

Respiratory syncytial virus infection: immune response, immunopathogenesis, and treatment

Respiratory syncytial virus (RSV) is the single most important cause of lower respiratory tract infection during infancy and early childhood. Once RSV infection is established, the host immune response includes the production of virus-neutralizing antibodies and T-cell-specific immunity. The humoral immune response normally results in the development of anti-RSV neutralizing-antibody titers, but these are often suboptimal during an infant's initial infection. Even when the production of RSV neutralizing antibody following RSV infection is robust, humoral immunity wanes over time. Reinfection during subsequent seasons is common. The cellular immune response to RSV infection is also important for the clearance of virus. This immune response, vital for host defense against RSV, is also implicated in the immunopathogenesis of severe lower respiratory tract RSV bronchiolitis. Many details of the immunology and immunopathologic mechanisms of RSV disease known at present have been learned from rodent models of RSV disease and are discussed in some detail. In addition, the roles of immunoglobulin E, histamine, and eosinophils in the immunopathogenesis of RSV disease are considered. Although the treatment of RSV bronchiolitis is primarily supportive, the role of ribavirin is briefly discussed. Novel approaches to the development of new antiviral drugs with promising anti-RSV activity in vitro are also described.

Respiratory syncytial virus (RSV) disease and prospects for its control

Respiratory syncytial virus (RSV) is a major virus pathogen of infants and young children, an important cause of disease in adults and is responsible for a significant amount of excess morbidity and mortality in the elderly. It also can be devastating in immunosuppressed populations. Vaccines are being developed, but none are currently licensed. Moreover, even if one or more are approved, they may not be suitable for some populations vulnerable to RSV (e.g. very young infants and the immunosuppressed). Ribavirin and immunoglobulin preparations with high titers of RSV-specific neutralizing antibodies are currently approved for use to treat and prevent RSV infection. However, neither of these is cost-effective or simple to administer. New agents are needed to reduce the impact of RSV. This review is concerned with the means currently available for controlling RSV, the search for new agents effective against this virus, and future prospects for preventing and treating RSV infections.

Intravenous ribavirin therapy in a neonate with disseminated adenovirus infection undergoing extracorporeal membrane oxygenation: pharmacokinetics and clearance by hemofiltration

Intravenously administered ribavirin (20 mg/kg per day) was given to a neonate with disseminated adenovirus infection requiring extracorporeal membrane oxygenation and hemofiltration. Plasma concentrations at steady state were 4.81 to 8.47 micrograms/ml, hemofiltration sieving-coefficient was 0.85, and hemofiltration clearance (0.046 L/kg per hour) was similar to the renal clearance reported with normal kidney function. Despite low plasma concentrations, results of viral cultures were negative within 48 hours of initiation of ribavirin therapy, suggesting that plasma concentrations may not adequately predict inhibition of adenovirus replication in vivo.

Prevention and treatment of respiratory syncytial virus and parainfluenza viruses in immunocompromised patients

Immunocompromised patients are vulnerable to severe infections due to respiratory syncytial virus (RSV) and parainfluenza viruses (PIV), and therefore prevention and treatment strategies must be considered. The prevention of RSV disease with high-titer RSV-specific immune globulin has been documented in very young children but has not been systematically studied in high-risk adults. Vaccines against RSV and PIV are under development, but their use in immunocompromised patients is problematic. Ribavirin aerosol therapy is licensed for the treatment of RSV in pediatric patients and has also been used to treat RSV disease in adults and PIV disease in severely immunocompromised children and adults. Uncontrolled trials show that early therapy with ribavirin aerosol may be beneficial, but treatment of pneumonia in patients with respiratory failure is rarely successful. Other potential treatments for RSV or PIV disease include high-dose, short-duration ribavirin therapy; combined immunoglobulin and ribavirin therapy; polyclonal and monoclonal antibodies; and, potentially, immunomodulators.

Community respiratory virus infections in immunocompromised patients with cancer

Community respiratory viruses, such as respiratory syncytial virus (RSV), influenza viruses, parainfluenza viruses, adenoviruses, and picornaviruses, are an important cause of respiratory disease in the immunocompromised adult with cancer. Recent studies have demonstrated that a minimum of 31% of adult bone marrow transplant (BMT) recipients and 18% of adults with leukemia who are hospitalized with an acute respiratory illness have a community respiratory virus infection. The temporal occurrence of these infections in immunocompromised patients tends to mirror their occurrence in the community. The clinical illnesses range from self-limited upper respiratory illnesses to fatal pneumonias, depending on the type of virus and the type and degree of immunosuppression. The pneumonias may be viral, bacterial/fungal, or mixed. The highest frequency of progression to fatal viral pneumonia has been reported for RSV infections in recently transplanted BMT recipients and myelosuppressed patients with leukemia. Studies have suggested that early therapy for RSV pneumonia with a combination of aerosolized ribavirin and intravenous immunoglobulin may be of benefit. Defining effective prophylactic and therapeutic strategies will be a challenge, given the diversity of viruses, the wide spectrum of immunocompromised patients with varying vulnerability to serious community respiratory virus disease, and the frequent presence of other opportunistic infections and medical problems. A combination of antiviral drugs and immunotherapy may need to be considered for their potential additive effect as well as to prevent the emergence of resistant virus, as occurs during monotherapy for influenza with amantadine or rimantadine. The optimal therapies need to be defined in controlled trials; however, it appears that a favorable response will hinge on the initiation of therapy at an early stage of the respiratory illness.

Respiratory syncytial virus (RSV) immune globulin intravenous therapy for RSV lower respiratory tract infection in infants and young children at high risk for severe RSV infections: Respiratory Syncytial Virus Immune Globulin Study Group

OBJECTIVES

To evaluate the efficacy of high-titer intravenous respiratory syncytial virus immune globulin (RSVIG) in the treatment of children at high risk for severe RSV infection who were hospitalized with proven RSV.

METHODS

Infants and young children younger than 2 years with bronchopulmonary dysplasia, chronic lung disease, congenital heart disease, or prematurity (<32 weeks' gestational age), hospitalized with a history of lower respiratory tract infection (LRI) of less than 4 days, were enrolled in this study. Patients were randomized in a blinded fashion to receive either 1500 mg/kg RSVIG or placebo in equal volumes. They were evaluated daily for safety and respiratory scores and for RSV nasal shedding.

RESULTS

One hundred seven high-risk children were randomized--54 in the RSVIG group and 53 in the placebo group. Of these children, 51 in each group were considered evaluable. Children with pulmonary disease, congenital heart disease, or prematurity were equally distributed between the two treatment groups. However, two important differences were found in baseline variables between the two groups: there were more patients in the placebo group who had histories of previous LRI and there was a trend toward more severe disease at study entry in the RSVIG group. This was manifested by a higher entry respiratory score in the RSVIG group than in the placebo group (3.4 +/- 0.2 vs 3.1 +/- .01). A higher proportion of children in the RSVIG group (47%) than in the placebo group (28%) required intensive care at entry and mechanical ventilation at study entry (31% RSVIG-treated vs 18% placebo-treated patients). No significant difference was found between groups in the mean unadjusted duration of hospitalization (RSVIG group, 9.10 +/- 1.18 days; control group, 8.17 +/- 1.08 days). When the mean was adjusted for entry respiratory score, likewise, no difference was observed between each group (8.41 +/- 0.97 vs 8.89 +/- .99 days). The lack of efficacy observed in the study primary endpoint was observed in all diagnostic groups. No differences between the RSVIG and placebo groups were observed in the following secondary endpoints: duration of intensive care unit stay, duration of intensive care unit stay for RSV, mechanical ventilation, or supplemental oxygen. No significant differences in adverse events were reported in the RSVIG group (16 children) when compared with the control group (10 children).

CONCLUSION

RSVIG treatment was safe but not efficacious in the treatment of children with bronchopulmonary dysplasia, congenital heart disease, or premature gestation who were hospitalized with RSV LRI.

Cloning, expression and functional activities of a single chain antibody fragment directed to fusion protein of respiratory syncytial virus

BACKGROUND

HNK20 is a murine IgA which is currently being investigated in clinical trials against respiratory syncytial virus (RSV) infections in infants and young children.

OBJECTIVE

To produce a single chain antibody fragment (scFv) from HNK20 hybridoma cells and assess its functional activities in vitro and in vivo (mouse model).

STUDY DESIGN

The V regions of heavy and light chains were cloned and linked by a sequence encoding for (Gly4 Ser)3 and expressed in Escherichia coli.

RESULTS

Over 100 mg/l of the HNK20-scFv was produced in shake flasks after induction with isopropyl (beta-D-thiogalactopyranoside (IPTG). ScFv was purified under native conditions on a Ni2+ affinity column and migrated as a single band of 34 kDa on sodium dodecyl sulfate (SDS)-gels. ScFv demonstrated similar affinity as its parent IgA molecule, neutralized RSV in vitro and significantly reduced RSV titers in lungs of mice when administered intranasally shortly before or a day after RSV challenge.

CONCLUSION

It is possible that this scFv or its derivatives, when applied by intranasal or pulmonary route, will be useful for treatment of RSV infections in infants and young children.

Combination antiviral therapy for respiratory virus infections

A limited number of antiviral drug combinations have been shown to have enhanced activity for important human respiratory viruses. Rimantadine or amantadine combined with ribavirin shows increased antiviral effects in vitro and in experimental animal models. This combination warrants testing in human influenza. Immunoglobulin containing neutralizing anti-RSV antibody combined with ribavirin shows enhanced antiviral effects in experimental animal infections and provides clinical benefit in severe RSV infections of transplant patients. Generally, more effective treatments for acute respiratory viral infections will likely involve combinations of both antivirals and agents that modulate host inflammatory responses to infection.

Pathogenesis of respiratory syncytial virus vaccine-augmented pathology

Respiratory syncytial virus (RSV) is an important respiratory pathogen for which vaccine development has been thwarted by the legacy of vaccine-enhanced illness. A formalin-inactivated, alum-precipitated, whole virus vaccine did not protect children from infection and was associated with severe illness. Clues from clinical studies of RSV and vaccine-induced atypical measles illness suggest that an aberrant CD4+ lymphocyte response occurred in vaccinees. There is a growing body of evidence from murine models that show vaccine formulations can selectively activate different populations of CD4+ T helper lymphocytes that produce distinct cytokine expression patterns. The cytokine milieu in turn can influence the composition of the immune response and thereby impact the efficiency of virus clearance, type of pathology, and magnitude of illness. Major priorities of current vaccine development are to define the optimal combination of T lymphocyte subsets to safely clear RSV and to learn ways to modulate the composition of the immune response to vaccine antigens.

Hyperimmune globulins in prevention and treatment of respiratory syncytial virus infections

Respiratory syncytial virus (RSV) is an important community and nosocomial respiratory pathogen for infants and young children. RSV causes especially severe disease in the prematurely born or those with chronic cardiopulmonary diseases. Elderly persons and those with T-cell deficiencies, such as bone marrow transplant recipients, are also at high risk for serious lower respiratory tract infections. To date, prevention of RSV infections by vaccination has proven elusive and no preventive drugs exist. Studies in animals and humans have shown that the lower respiratory tract can be protected from RSV infection by sufficient circulating RSV neutralizing antibody levels. Recently, an RSV hyperimmune immune globulin (RSVIG) was developed and tested for the prevention of RSV infections or reduction of disease severity. Passive immunization of high-risk children with RSVIG during the respiratory disease season effected significant reductions in RSV infections, hospitalizations, days of hospitalization, intensive care unit admissions, days in the intensive care unit, and ribavirin use. Studies in cotton rats and owl monkeys show that RSV infections can also be treated with inhalation of immune globulin at doses substantially smaller than required for parenteral treatment. Therapeutic trials of parenteral RSVIG have been completed and are pending analysis. The use of polyclonal, hyperimmune globulins and perhaps human monoclonal antibodies provides an additional approach to the prevention and perhaps the treatment of certain viral lower respiratory tract infections such as those caused by RSV.

Treatment and prevention options for respiratory syncytial virus infections

Although the therapeutic antiviral agents ribavirin and amantadine ameliorate illness caused by influenza A and respiratory syncytial virus (RSV) in children, these agents are used infrequently because they are not cost-effective. Research currently is directed toward defining the high-risk groups for which these antiviral drugs should be used. Treatment of severe respiratory infection with specific immune globulin, either alone or in combination with antiviral drugs, is another therapeutic approach. Prevention of viral respiratory diseases is preferable because some lung damage occurs before the beginning of treatment, and damage resulting from the immune response may continue even after the virus is inhibited. As natural history and animal studies suggest, passive immunization can be achieved for neonates through active immunization of the mother during pregnancy. However, this approach is limited by the half-life of the transferred antibodies and the lack of antibody in premature infants. Standard immune globulin does not contain sufficient RSV neutralizing antibody titer to fully protect against severe RSV illness. Passive immunization with RSV immune globulin in infants and children has been shown to prevent or attenuate RSV in high-risk groups. Active immunization against some respiratory viruses has been achieved by administration of inactive virus (or their subunits), recombinant viral antigens, and live attenuated virus. Large trials are under way to determine the safety and immunogenicity of these vaccines for children in whom young age and serious underlying illness are significant barriers to primary immune response. The current research environment is suitable for the development of an immunization strategy to prevent many of the significant respiratory infections in children.

The role of RSV neutralizing antibodies in the treatment and prevention of respiratory syncytial virus infection in high-risk children

Studies assessing the use of RSV immune globulin in the treatment of RSV illness are not yet completed. However, a large multicenter trial demonstrated that prophylaxis with RSV immune globulin was safe and efficacious in prevention of serious RSV disease in high-risk infants. Refinements in the practical application of RSVIG are needed, as intravenous lines are difficult to place and maintain in these fragile infants. With the development of concentrated polyclonal and/or effective monoclonal antibody preparations, it may be possible to immunize intramuscularly (Tempest et al., 1993; Barbas et al., 1992). The efficacy of RSV-specific monoclonal antibodies must still be defined, and the appropriate viral epitopes targeted. While these issues still need to be addressed, it is exciting to have finally produced a safe and effective way to prevent severe RSV disease in high-risk young children.

The antiviral activity of SP-303, a natural polyphenolic polymer, against respiratory syncytial and parainfluenza type 3 viruses in cotton rats

SP-303, a naturally occurring polyphenolic polymer (average M.W. = 2100 Da), was tested in cotton rats (Sigmoden hispidus) for antiviral activity against respiratory syncytial (RSV) and parainfluenza type 3 (PIV3) viruses, and for acute toxicity. Significant reductions in pulmonary RSV titers, compared to pulmonary RSV titers in comparably treated control animals, were seen in cotton rats given 1-10 mg SP-303/kg/day intraperitoneally (i.p.) on days 1 through to 3, after experimental inoculation with RSV. The minimum efficacious dose of SP-303 against PIV3, when given i.p. for 3 days, was 3 mg/kg/day. Higher doses of SP-303 could not be given i.p., as doses > or = 30 mg/kg/day given once daily by this route for 3 or more consecutive days caused both significant weight loss and death in infected or uninfected animals. Although no toxicity was observed following oral administration of up to 270 mg of SP-303 daily for 3 days, this compound had variable antiviral activity when given by this route.

Toxicity and antiviral activity of LY253963 against respiratory syncytial and parainfluenza type 3 viruses in tissue culture and in cotton rats

LY253963, the sodium salt of 1,3,4-thiadiazol-2-ylcyanamide, was evaluated in tissue culture and in cotton rats for toxicity and antiviral efficacy against respiratory syncytial (RSV) and parainfluenza type 3 (PIV3) viruses. The selective index (ratio of the median toxic dose: median efficacious dose) of LY253963 in HEp2 tissue culture cells was greater than 100 against both RSV and PIV3. When given intraperitoneally to cotton rats, the minimum protective dose of LY253963 against both of these viruses was between 1 and 3 mg/kg/day. In contrast, doses of LY253963 as high as 30 mg/kg/day, administered orally after experimental inoculation of virus, did not significantly reduce pulmonary virus titers in treated animals compared to control animals given placebo. No toxic effects were noted in cotton rats, even in those given 20 mg/kg/day for eight consecutive days.

Enhancement of the protective efficacy of inactivated influenza A virus vaccine in aged mice by IL-2 liposomes

A dose-dependent, vaccine-induced protection of aged and young Balb/c mice against lethal influenza A virus challenge has been demonstrated. Low dose formalin-inactivated influenza A virus vaccine was protective in young mice, but not in aged mice, while a higher dose was protective in both. Administration of low dose vaccine with IL-2 liposomes conferred protection comparable to the high dose in aged mice. Serum neutralizing antibody responses were stimulated by vaccine in a dose-dependent manner while IL-2 liposomes significantly enhanced responses in the low dose paralleled protection in young but not in aged mice. Lung interferon levels paralleled lung virus titres in young but not in aged mice. CTL responses in infected mice were generally higher in young than aged mice. These results demonstrate efficacy of IL-2 liposomes as an adjuvant for influenza virus vaccines in the aged.

Gastro-oesophageal reflux in preterm infants

Gastro-oesophageal reflux in very low birthweight infants was studied using a new 1 mm monocrystalline antimony oesophageal pH electrode. Gastro-oesophageal reflux was detected in 30 (85%) subjects. The mean (SEM) number of episodes of reflux in 24 hours was 12.1 (2.1), and 3.2 (0.6) lasted over five minutes. The mean reflux index was 4.5 (1.0)%, and the longest episode 17.1 (4.6) 17.1. Reflux was unrelated to postconceptional age or to resting lower oesophageal sphincter pressure. The mean reflux index was low at rest before feeds, being 1.8 (0.6)%, and increased slightly after feeds (3.8 (1.0)%), but was significantly increased after nursing care to 16.4 (3.0)%, and while xanthines were being given (5.9 (1.6)%. A subgroup of seven infants with xanthine resistant apnoea had severe gastro-oesophageal reflux that was not clinically apparent (reflux index 27.4 (3.6)%). Successful treatment of the reflux (reflux index: 3.6 (1.2)%) was associated with cessation of the apnoea. We conclude that gastro-oesophageal reflux is common, and is usually not clinically apparent, even when severe. It is important to consider gastro-oesophageal reflux in the differential diagnosis of xanthine resistant apnoea in preterm infants.

Intravenous immunoglobulin treatment of respiratory syncytial virus infections in infants and young children

Respiratory syncytial virus (RSV)-infected cotton rats (Sigmadon hispidus) and owl monkeys (Aotus trivirgatus) showed significant reductions in RSV shedding from their respiratory tracts following parenteral therapy with human intravenous immunoglobulin (IVIG) containing high titers of RSV-neutralizing antibody. Because this therapy was well tolerated and appeared safe, a double-blind, placebo-controlled IVIG immunotherapy pilot study was performed on 35 hospitalized, RSV-infected infants and children. The treatment was well tolerated and resulted in significant reductions in nasal RSV shedding and in improvements in transcutaneous oximetry readings. However, the mean duration of hospitalization was not reduced by IVIG treatment. Followup to date has revealed no harmful effects resulting from immunotherapy of RSV infections. These studies appear to refute the hypothesis that passively acquired antibody may exacerbate RSV bronchiolitis or pneumonia in infants. Studies with larger numbers of seriously ill children will be required to determine if immunoglobulin G immunotherapy of RSV infections in infants is of clinical value.