Evaluation of cotton rats as a model for severe acute respiratory syndrome

Experimental studies were conducted to evaluate two species of cotton rats, Sigmodon hispidus and Sigmodon fulviventer, as a model for severe acute respiratory syndrome (SARS). Blood and turbinate wash samples, and lung tissue were collected from each animal at different time points after SARS coronavirus (CoV) infection for determining the growth curve of virus, if any, by the standard infectivity assay in Vero E6 cells. In addition, sections of the lung, liver, spleen, and kidney were taken and used for histology analysis. All animals were observed daily for signs of illness, and in some experiments, animals were weighed on the day when they were sacrificed. The results indicated that the cotton rat species, S. hispidus and S. fulviventer, were not a useful model for either SARS-CoV infection or disease. This observation was supported by the absence of any signs of illness, the failure to consistently demonstrate virus in the blood and tissues, and the absent of any notable histopathology. However, infected animals were capable of producing neutralizing antibodies against SARS-CoV, suggesting the seroconversion did occur. Further studies are warranted to consider other animal species in efforts to find better animal models for the evaluation of SARS-CoV vaccines and antiviral drugs.

Use of cotton rats for preclinical evaluation of measles vaccines

The continued prevalence and medical impact of measles worldwide has created interest in the development of new generations of measles vaccines. Monkeys can be used for preclinical testing of these vaccines. However, a more practical and less expensive animal model is highly desirable, particularly for initial vaccine development and evaluation. Cotton rats have been shown to support the replication of different strains of measles virus (MV), and thus may be useful for these purposes. To test this concept, the immunogenicity and protective efficacy of two standard (Moraten and trivalent measles, mumps, rubella) and four experimental (two recombinant ALVAC, one ISCOM subunit and live attenuated Edmonston-Zagreb) MV vaccines were evaluated in naïve cotton rats, and cotton rats with passively acquired MV-specific neutralizing serum antibodies. All of the test vaccines were immunogenic and protected naíve animals from pulmonary infection and viral dissemination. However, under the conditions utilized, only the Edmonston-Zagreb vaccine provided such protection to animals with significant levels of passively acquired MV-specific neutralizing antibodies. The results of these tests and the potential of using cotton rats as an animal model for preliminary testing of MV vaccines are discussed.

Use of cotton rats to evaluate the efficacy of antivirals in treatment of measles virus infections

No practical animal models for the testing of chemotherapeutic or biologic agents identified in cell culture assays as being active against measles virus (MV) are currently available. Cotton rats may serve this purpose. To evaluate this possibility, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and poly(acrylamidomethyl propanesulfonate) (PAMPS), two compounds that have been reported to inhibit MV in vitro, and ribavirin, an established antiviral drug with MV-inhibitory activity, were evaluated for their antiviral activities against MV and respiratory syncytial virus (RSV) in tissue culture and in hispid cotton rats. A single administration of PAMPS markedly inhibited pulmonary RSV or MV replication (>3 log(10) reduction in pulmonary titer compared to that for controls), but only if this compound was administered intranasally at about the time of virus inoculation. Both EICAR and ribavirin exhibited therapeutic activity against RSV and MV in cotton rats when they were administered parenterally. However, both of these compounds were less effective against MV. On the basis of the pulmonary virus titers on day 4 after virus inoculation, the minimal efficacious dose of EICAR against MV (120 mg/kg of body weight/day when delivered intraperitoneally twice daily) appeared to be three times lower against this virus than that of ribavirin delivered at a similar dose (i.e., 360 mg/kg/day). These findings correlated with those obtained in vitro. The data obtained suggest that cotton rats may indeed be useful for the initial evaluation of the activities of antiviral agents against MV.

Phase I study of adenoviral delivery of the HSV-tk gene and ganciclovir administration in patients with current malignant brain tumors

Between December 1996 and September 1998, 13 patients with advanced recurrent malignant brain tumors (9 with glioblastoma multiforme, 1 with gliosarcoma, and 3 with anaplastic astrocytoma) were treated with a single intratumoral injection of 2 x 10(9), 2 x 10(10), 2 x 10(11), or 2 x 10(12) vector particles (VP) of a replication-defective adenoviral vector bearing the herpes simplex virus thymidine kinase gene driven by the Rous sarcoma virus promoter (Adv.RSVtk), followed by ganciclovir (GCV) treatment. The VP to infectious unit ratio was 20:1. Our primary objective was to determine the safety of this treatment. Injection of Adv.RSVtk in doses <==2 x 10(11) VP, followed by GCV, was safely tolerated. Patients treated with the highest dose, 2 x 10(12) VP, exhibited central nervous system toxicity with confusion, hyponatremia, and seizures. One patient is living and stable 29.2 months after treatment. Two patients survived >25 months before succumbing to tumor progression. Ten patients died within 10 months of treatment, 9 from tumor progression and 1 with sepsis and endocarditis. Neuropathologic examination of postmortem tissue demonstrated cavitation at the injection site, intratumoral foci of coagulative necrosis, and variable infiltration of the residual tumor with macrophages and lymphocytes.

Replication of clinical measles virus strains in hispid cotton rats

An alternative model to nonhuman primates to study measles virus (MV) pathogenesis, to evaluate potential MV vaccines, or to screen for potential antivirals effective against this virus is highly desirable. The laboratory-adapted Edmonston strain of MV has been reported to replicate in the lungs of hispid cotton rats following intranasal inoculation, immunosuppress infected animals, and disseminate widely from the lungs, making these animals a candidate model. However, clinical MV strains have generally not been found to grow in these animals, limiting the utility and acceptance of this model. In the present studies we demonstrate reproducible replication of several clinical MV strains in hispid cotton rats. As with the Edmonston strain, leukocytes appear to be the primary target cells of these viruses following intranasal inoculation, and extrapulmonary dissemination is common. It is also demonstrated that prior MV infection or immunization of test animals with MV vaccine prevents pulmonary tract infection. These findings should make the MV-cotton rat model more acceptable.

Distribution, persistency, toxicity, and lack of replication of an E1A-deficient adenoviral vector after intracardiac delivery in the cotton rat

Adenoviral vectors were inoculated via intracardiac injection into 5- to 1O-week-old cotton rats (Sigmodon hispidus) to evaluate the effects of systemic delivery. Cotton rats were chosen as a model because they are semipermissive to the replication of human adenoviruses. The vector used was AdV.RSV-tk, a replication-deficient adenovirus with a herpes simplex virus thymidine kinase gene inserted in the E1 region. Vector doses were 3 x 10(8), 3 x 10(9), and 3 x 10(10) viral particles per animal with and without ganciclovir at 10 mg/kg twice a day. Animals were sacrificed and necropsied at 24 hours, 7 days, and 14 days postinoculation. Gross and microscopic pathologic observations in dosed groups were compared with an unmanipulated control group. From each animal, 10 different organ systems were analyzed for histopathology and vector distribution. The only significant microscopic lesions observed were epicardial inflammation and splenic hemosiderosis. Vector sequences persisted throughout the 14-day assay with preponderance in the heart, lung, and lymphoid organs. Infectious virions were detected for 24 hours, and these virions were only detected at the site of injection of two animals in the highest dose group. No viral replication was detected. Therefore, systemic delivery of up to 3 x 10(11) viral particles/kg was well tolerated in this semipermissive host model and did not result in any significant pathology.

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.

Common emergence of amantadine- and rimantadine-resistant influenza A viruses in symptomatic immunocompromised adults

The importance and significance of amantadine- or rimantadine-resistant influenza viruses in immunocompromised patients was studied in a population of adult bone marrow transplant (BMT) recipients and patients with leukemia prospectively cultured for respiratory viruses. Influenza A viruses were isolated from 29 patients with acute respiratory illness (14 BMT recipients and 15 patients with leukemia). Fifteen patients (52%) received amantadine (n = 4) or rimantadine (n = 11) therapy. All influenza isolates recovered from six patients shedding virus for > or = 3 days were screened for antiviral susceptibility; resistant isolates were further genetically characterized. Initial influenza isolates were susceptible to amantadine or rimantadine, but subsequent isolates from five of six patients were resistant. Influenza-associated mortality was similar among patients with and without documented antiviral resistance (2 of 5 vs. 5 of 24). We conclude that development of antiviral resistance in immunocompromised individuals should be considered when they have been treated with antivirals and have shed influenza virus for a prolonged period. Isolation procedures should be instituted for all immunocompromised patients with influenza, both during and after therapy with amantadine or rimantadine.

CL387626 exhibits marked and unusual antiviral activity against respiratory syncytial virus in tissue culture and in cotton rats

CL387626 (4,4'-Bis[4,6-di[3-aminophenyl-N,N-bis(2-carbamoylethyl)-sulfon ilimino]-1,3,5-triazine-2-ylamino-bi-phenyl-2,2'-disulfonic acid, disodium salt), a compound synthesized by Wyeth-Ayerst Research Laboratories, was tested for its cytotoxicity and antiviral activity against respiratory syncytial virus (RSV) in tissue culture and in cotton rats. The median cell inhibitory (IC50) and median efficacious (EC50) concentrations of CL387626 against RSV in proliferating HEp2 or Vero tissue culture cells were determined to be 375 and 0.25 microg/ml, respectively, giving the compound an apparent selective index (S.I.) of 1500. This compound also exhibited uncommon antiviral activity against RSV in cotton rats. In multiple experiments, a single 30 mg/kg dose of CL387626 administered intranasally 4 or 5 days prior to virus challenge, significantly inhibited pulmonary replication of RSV compared to that seen in control animals inoculated similarly with placebo (i.e. water). In contrast to these results, most lots of CL387626 failed to significantly inhibit pulmonary RSV replication when administered utilizing therapeutic administration schedules. Although some cytotoxicity was noted in tissue culture assays, no overt toxic effects were noted in any test animal, including those inoculated with > 300 mg CL387626/kg, a dose approximately 150 times the apparent minimal efficacious dose (i.e. 1.9 mg/kg).

Genetic inactivation of an extracellular cysteine protease (SpeB) expressed by Streptococcus pyogenes decreases resistance to phagocytosis and dissemination to organs

Streptococcal pyrogenic exotoxin B (SpeB), a conserved cysteine protease expressed by virtually all Streptococcus pyogenes strains, has recently been shown to be an important virulence factor (S. Lukomski, S. Sreevatsan, C. Amberg, W. Reichardt, M. Woischnik, A. Podbielski, and J. M. Musser, J. Clin. Invest. 99:2574-2580, 1997). Genetic inactivation of SpeB significantly decreased the lethality of a serotype M49 strain for mice and abolished the lethality of a serotype M3 strain after intraperitoneal (i.p.) injection. In the present study, a wild-type M3 isolate and an M3 speB mutant derivative were used to investigate the mechanism responsible for altered virulence. Following i.p. injection, the mutant and wild-type strains induced virtually identical cellular inflammatory responses, characterized largely by an influx of polymorphonuclear leukocytes (PMNs). In addition, the mutant and wild-type strains rapidly entered the blood and were recovered from all organs examined. However, significantly fewer (P < 0.05) CFUs of the isogenic mutant derivative than of the wild-type parent strain were recovered from blood and organs. PMNs effectively cleared the M3 speB mutant from the peritoneum by 22 h, thereby sparing the host. In contrast, the wild-type M3 strain continued to replicate intraperitoneally and had the ability to kill phagocytes. This process allowed the wild-type strain to continuously disseminate, resulting in host death. Our results indicate that genetic inactivation of the cysteine protease decreased the resistance of the mutant to phagocytosis and impaired its subsequent dissemination to organs. These results provide insight into the detrimental effect of SpeB inactivation on virulence.

Neurotoxicity of intracerebral injection of a replication-defective adenoviral vector in a semipermissive species (cotton rat)

The neurotoxicity of an adenoviral vector (Adv.RSVtk) carrying the gene for herpes simplex virus thymidine kinase (HSVtk) was tested in the cotton rat, a semipermissive host. Adv.RSVtk was injected intracerebrally in cotton rats at a dose of 5.0 x 10(6) or 7.5 x 10(7) p.f.u. No signs of illness were observed. Histological inspection at 12 and 28 days after injection showed inflammation of the ependyma and choroid plexus and at the injection site. No demyelination, viral inclusions, cerebral edema, necrosis, cavities or vascular necrosis were seen in the brains. There was no significant difference between animals injected with 5.0 x 10(6) or 7.5 x 10(7) p.f.u., nor was there a difference between animals analyzed at 12 or 28 days after vector injection. This inflammation was similar in animals that had been preimmunized with wild-type virus and in animals that had been treated with ganciclovir. No histopathology, was observed in the lungs of the animals and no replication-competent virus was detected. These experiments indicate that Adv.RSVtk has limited neurotoxicity which would not prohibit its use in a limited phase I clinical trial in humans that have malignant tumors of the central nervous system.

Recombinant superoxide dismutase (SOD) administered by aerosol inhibits respiratory syncytial virus infection in cotton rats

Recombinant (r) human (hu) manganese (Mn) and copper-zinc (CuZn) superoxide dismutase (SOD) were evaluated for their cytotoxicity and antiviral activity against respiratory syncytial virus (RSV) in tissue culture and in cotton rats. No apparent cytotoxicity or inhibition of RSV was observed in the tissue culture studies (both compounds had IC50 and EC50 values > or = 1000 micrograms/ml and a selective index = 1). However, significant reductions in mean pulmonary RSV titers (ranging between 0.5 and 1.9 log10/g of lung compared with the mean pulmonary viral titers detected in similarly inoculated, placebo-treated control animals) were seen in most of the experiments, in which experimentally infected cotton rats were exposed to continuous small-particle aerosols (reservoir concentrations > or = 20 mg/ml) containing either rhuMnSOD or rhuCuZnSOD. This protective effect was dose dependent and not observed when either rSOD compound was administered parenterally (intraperitoneally) or intranasally. No toxic effects were noted in any of the cotton rats exposed to aerosols of either rhuMn or CuZnSOD; nor was any evidence of drug-induced histopathology observed in sections of lung prepared from these animals.

Evaluation of the protective efficacy of reshaped human monoclonal antibody RSHZ19 against respiratory syncytial virus in cotton rats

Reshaped human MAb RSHZ19, which is specific for the surface fusion protein of respiratory syncytial virus (RSV) is in clinical development for the prevention and treatment of RSV-induced disease in human infants. The current studies profile lung virus clearance and evaluate lung histopathology in MAb-treated, RSV-infected cotton rats, a well characterized model of RSV infection. The highest dose of this MAb (10 mg/kg) administered parenterally 24 h before infection decreased subgroup A or B RSV lung titers to below detectable levels (> or = 2.3 log10 reduction), and significantly reduced lung virus titers (> or = 2.0 log10 reduction) when administered 96 h postinfection. Prophylactic administration of 10 mg/kg RSHZ19 was significantly more protective than 1000 mg/kg conventional human immune serum globulin (HSIg), and protective serum-neutralizing titers in MAb-treated animals (1:32, which correlated with approximately 40 micrograms/ml determined by anti-idiotype ELISA) were significantly lower than those reported previously for HSIg or for convalescent human serum (1:200-1:400). MAb concentration in lung lavages was determined by ELISA to be approximately 1% of the serum MAb concentration, but was not detectable by neutralization assay. The degree of lung histopathology in MAb-treated cotton rats was proportional to lung virus titer, and inversely proportional to the RSHZ19 dose administered. There was no evidence of exacerbated disease in the lungs of MAb-treated animals. These studies thus support the potential clinical utility of RSHZ19 MAb in the prevention and treatment of RSV-induced disease in humans.

Evidence that measles virus hemagglutinin initiates modulation of leukocyte function-associated antigen 1 expression

Measles virus (MV), human immunodeficiency virus, Epstein-Barr virus, and other leukotropic viruses can modulate the expression of leukocyte function antigen 1 (LFA-1) on the surface of infected and nearby leukocytes. This ability to induce changes in LFA-1 expression may play an important role in the pathogenesis of these viruses. However, the mechanism(s) involved in virus-mediated regulation of LFA-1 is unknown. Evidence is presented in this report that it is the MV hemagglutinin (H) protein that initiates up-regulation of LFA-1 expression in leukocyte cultures infected with this virus. Indeed, comparison of the abilities of different MV strains to modulate LFA-1 expression, examination of published nucleotide sequences for the H proteins of different vaccine strains, and competitive inhibition assays using oligopeptides homologous or heterologous to a region of the H protein gene encompassing amino acid 116 (from the amino terminus) all suggest that it is this portion of the H protein that is responsible for MV-induced alteration of LFA-1. These comparisons also support the hypothesis that there is a relationship between the abilities of different MV strains to alter LFA-1 expression and their pathogenic potentials.

Protection of mice against lethal viral infection by synthetic peptides corresponding to B- and T-cell recognition sites of influenza A hemagglutinin

Previously, we reported 12 synthetic T- and B-cell recognition regions representing surface areas of the hemagglutinin (HA) of X31 influenza virus. In the present study, four of these peptides were examined in Balb/c mice for their ability to produce protective immunity against lethal infection with a dose equivalent to 10 LD50 of influenza virus. These peptides corresponded to the following sequences: 23-36 (HA1-1); 138-152 (HA1-3); 183-199 (HA1-6) and 1-11 (HA2-10). Each of the selected peptides, in their free form, evoked anti-peptide antibodies that cross-react with intact X31 virus. Two of the peptides, HA1-1 and HA1-3, also elicited virus-specific delayed type hypersensitivity (DTH) responses. These two peptides, when injected into mice, not only failed to protect the immunized mice against challenge with influenza virus, but in fact caused greater susceptibility to viral infection as compared to control animals that had been injected with saline. In contrast, peptides HA1-6 and HA2-10, which were unable to induce adequate virus-specific DTH responses, conferred 42-46% and 54-73% protection, respectively, compared to the control group that received only saline (P < 0.03 to P < 0.01).

Evaluation of the antiviral activity of N-(phosphonoacetyl)-L-aspartate against paramyxoviruses in tissue culture and against respiratory syncytial virus in cotton rats

N-(phosphonoacetyl)-L-aspartate (PALA), a potent inhibitor of L-aspartic acid transcarbamoylase, was evaluated for cytotoxicity and antiviral activity against three different paramyxoviruses in tissue culture, and for antiviral efficacy and toxicity in vivo using a cotton rat-respiratory syncytial virus (RSV) model. Significant in vitro cytotoxicity was observed in proliferating cultures of HEp-2 (IC50 = 250 micrograms/ml) and Vero cells (IC50 = 32 micrograms/ml), but was less evident in cultures containing confluent monolayers (i.e., stationary cells) of these cells, or in cultures of Madin Darby canine kidney (MDCK) cells (these IC50 values were all > or = 750 micrograms/ml, with 1000 micrograms/ml being the maximum concentration tested). Mean selective indices (ratio of the median cytotoxic dose: median efficacious dose) of 1, 72 and 146 were obtained against parainfluenza virus type 3, RSV and measles virus, respectively, when PALA was tested against these viruses using confluent HEp-2 and Vero cell monolayers. In cotton rats, significant reductions in pulmonary titers (0.8-1.4 log10/g lung) compared to pulmonary viral titers in placebo-treated control animals, were consistently seen in cotton rats given > or = 10 mg of PALA/kg/day (b.i.d.) intraperitoneally on days 1-3 postinfection with either subtype A or B RSV. No toxic effects were noted even in animals given 100 mg of PALA/kg/day for 7 consecutive days.

A prototype recombinant vaccine against respiratory syncytial virus and parainfluenza virus type 3

We have produced a genetically-engineered chimeric protein composed of the external domains of the respiratory syncytial virus (RSV) fusion (F) protein and the parainfluenza virus type 3 (PIV-3) hemagglutinin-neuraminidase (HN) protein in insect cells using the baculovirus expression system. The yield of the soluble chimeric FRSV-HNPIV-3 protein could be increased approximately 2-fold by using Trichoplasia ni (High Five) insect cells in place of Spodoptera frugiperda (Sf9) for expression. The chimeric protein, purified from the supernatant of baculovirus-infected High Five cells by immunoaffinity chromatography was correctly processed at the F2-F1 proteolytic cleavage site. Immunochemical analysis of the chimera with a panel of anti-F and anti-HN monoclonal antibodies suggested that the antigenicity of the major F and HN neutralization epitopes of the chimeric protein was preserved. Immunization of cotton rats with two 1 or 10 micrograms doses of the chimeric protein adsorbed to aluminum phosphate elicited strong PIV-3 specific HAI responses as well as PIV-3 and RSV specific neutralizing antibodies, and at either dose completely protected against challenge with live RSV and PIV-3.

Infection of leucocytes by measles vaccine viruses Edmonston-Zagreb and Enders-Moraten has different consequences: potential mechanism for increased vaccine efficacy or aberrant activity in field trials

The abilities of two measles vaccine virus strains, Edmonston-Zagreb (E-Z) and Enders-Moraten (E-M), to infect and modify the activities of U937 monocytoid and peripheral blood mononuclear leucocytes (PBMLs) were compared with each other and with changes resulting from infection of these cells by a wild-type measles virus (MV). Both the E-Z and wild-type MV were shown to infect U937 and PBMLs and (1) to markedly increase expression of leucocyte function antigen 1 (LFA-1) on leucocytes present in infected cultures; (2) to increase cell-cell interaction; (3) to grow and disseminate readily in both types of leucocyte cultures; and (4) to persist for more than 7 days in these cultures despite the presence of MV-specific neutralizing antibodies. In contrast, the E-M virus did not grow well in unstimulated PBMLs and, although it did grow well in U937 cells, it did not noticeably alter the expression of LFA-1 on these cells, did not induce significant cell-cell interaction, and was rapidly eliminated from these cultures if MV-specific neutralizing antibodies were present. The possible relationship of these findings to the increased protective efficacy and untoward effects associated with the E-Z MV vaccine is discussed.

Aerosolized amphotericin B-liposomes for treatment of systemic Candida infections in mice

Mice lethally infected with Candida albicans were exposed to small-particle aerosols containing amphotericin B-liposomes. The drug, when administered twice daily for 2 h (0.58 mg/kg of body weight per day) on days 1, 2, and 3 postinoculation, significantly reduced the numbers of Candida organisms in the kidneys. Aerosol treatment increased the survival time of mice given 2 2-h treatments once a week for 4 weeks. A twice-weekly, 2-h small-particle aerosol administration of amphotericin B-liposomes for 1, 2, or 3 weeks significantly increased both the mean time of survival and percent survival.

Enhanced pulmonary pathology associated with the use of formalin-inactivated respiratory syncytial virus vaccine in cotton rats is not a unique viral phenomenon

The specificity of viral antigens in the formalin-inactivated, alum-precipitated respiratory syncytial virus (FI-RSV) vaccine in augmenting the pulmonary inflammatory response was evaluated. Cotton rats were immunized with a FI-RSV vaccine derived from Vero cells, a monkey cell line, or HEp-2 cells, a human cell line. The FI-RSV/Vero and the FI-RSV/HEp-2 vaccines were prepared similarly to the original Lot-100 FI-RSV vaccine that was associated with enhanced disease in the mid-1960s field trials. Each vaccine was administered intramuscularly at various doses and intervals. At 1, 4 or 7 weeks after the last vaccine dose, cotton rats were challenged with 10(6) plaque-forming units of live RSV grown in HEp-2 cells. For controls, FI-parainfluenza, FI-HEp-2 and alum vaccines, and live RSV primary infection were used. For measuring virus replication and histopathology, lungs were harvested at 4 and 8 days postchallenge. A dose-response relationship to vaccine dose was observed for ELISA, neutralizing and antifusion antibodies. All animals given three doses or two of the higher doses of FI-RSV/Vero vaccine developed significant neutralizing antibody, were protected against pulmonary virus replication and had similar low levels of histopathology compared with live RSV and controls. Two immunizations of the lowest dose of FI-RSV/Vero vaccine did not induce neutralizing antibody, did not provide protection of the lung against RSV and did not enhance the pulmonary cellular response. However, FI-RSV/HEp-2 vaccine was associated with significant enhanced pulmonary histopathology despite inducing high titres of neutralizing antibody and protecting the lungs against RSV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and administration of cyclosporine liposomes as a small-particle aerosol

Systemically administered CsA has not consistently suppressed the pulmonary immunoreactivity that leads to rejection in lung transplant patients. Pulmonary T cells from patients given CsA systemically still retain their immunoreactivity, which can be suppressed with added CsA. Direct application of CsA by aerosol to the respiratory epithelium should achieve high lung concentrations with minimum systemic effects. In the present study, CsA was most efficiently incorporated into liposomes composed of egg yolk phosphatidylcholine at a molar ratio of CsA to egg yolk phosphatidylcholine of 1:20. These CsA liposomes retained their biological activity and were as effective as free CsA in the suppression of anti-CD3-stimulated [3H]thymidine incorporation by mouse spleen cells. The generation of a small-particle aerosol of CsA liposomes had no effect on this biological activity. CsA liposome aerosol particles have a mass median aerodynamic diameter of 2 microns, which allows for distribution of drug throughout the respiratory tract. Quantitation of CsA in the lungs and blood of mice exposed to CsA liposome aerosols for 4 days showed that as little as 15 min daily (0.11 mg/kg/day) was sufficient to achieve an estimated concentration of CsA in respiratory secretions of 6 micrograms/ml without detectable blood levels. Thus, CsA liposomes can be produced and aerosolized that achieve pulmonary concentrations with sufficient immunosuppressive activity to be effective in the treatment of lung diseases.

Induction of CD8+ cytotoxic T cells by immunization with killed influenza virus and effect of cholera toxin B subunit

The MHC class I cytotoxic T-lymphocyte (CTL) response in mice given formalin-inactivated influenza whole-virus vaccine (WVV) with or without cholera toxin B subunit (CTB) was studied. Intraperitoneal injection of Balb/c (H-2d) mice with high doses of A/Taiwan/1/86 (H1N1) WVV stimulated influenza A virus-specific CTL response in a dose-dependent manner. A dose of 4.4 or 44 micrograms induced CTL response equal to or greater than live influenza virus infection. Coadministration of vaccine with 5 or 25 micrograms of CTB resulted in a higher level of CTL than with vaccine alone. CTL lysed A/Taiwan and A/Shanghai (H3N2) virus-infected class I-expressing P815 (H-2d) but not virus-infected EL-4 (H-2b) target cells nor B/Yamagata virus-infected target cells. Virus-infected MHC class II- and class I-expressing A20 (H-2d) targets were also lysed. Depletion of Lyt-2+ (CD8+) T cells with monoclonal antibody completely abrogated lysis of P815 target cells and resulted only in a slight reduction of lysis of A20 target cells. Depletion of L3T4+ (CD4+) T cells or NK cells had minimal effect on lysis of either P815 or A20 target cells. Using limiting dilution analysis, the precursor CTL (pCTL) frequency paralleled CTL activity. Significant CTL activity was detected 7 months after immunization. These results demonstrate that adequate doses of influenza WVV with or without CTB can induce long-lasting influenza A cross-reactive MHC class I-restricted CD8+ CTL response in mice. Thus, coadministration of influenza WVV with CTB may lead to an effective vaccine that stimulates both CTL and antibody responses.

SP-303 small-particle aerosol treatment of influenza A virus infection in mice and respiratory syncytial virus infection in cotton rats

A natural plant product, SP-303, was administered by small-particle aerosol to influenza A/HK virus-infected mice and RSV-infected cotton rats. Aqueous SP-303 at 2 mg/ml in the Collison nebulizer reservoir generated an aerosol with an output of 26 micrograms/l and a particle size distribution of 1.4 microns +/- 4.6 (MMAD +/- GSD). SP-303 at a dosage of 0.5-9.4 mg/kg per day administered for 3-4 days significantly increased both the rate and duration of survival of mice lethally infected with influenza A/HK virus. SP-303 was toxic to mice at 16 mg/kg per day as indicated by weight loss and a decrease in the duration of survival compared to control animals. From these data, a maximum therapeutic index (T.I.) of 12 was calculated. SP-303 given 3-4 days at dosages of 1.3-9.8 mg/kg per day was effective in reducing the pulmonary titer of RSV in infected cotton rats. However, at the 18.7 mg/kg per day dose a significant weight loss compared to control animals was observed; a T.I. of < or = 14 was estimated. These experiments demonstrate that aerosol administration of SP-303 was effective in the treatment of influenza A-infected mice and of RSV-infected cotton rats.

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.

Measles virus-induced changes in leukocyte function antigen 1 expression and leukocyte aggregation: possible role in measles virus pathogenesis

Measles virus (MV) infection of U937 cell or peripheral blood leukocyte cultures was shown to induce changes in the expression of leukocyte function antigen 1 (LFA-1) and cause marked aggregation of these cells. Addition of selected monoclonal antibodies specific for LFA-1 epitopes that did not neutralize MV in standard neutralization assays were found to block both virus-induced leukocyte aggregation and virus dissemination. These data suggest that MV modulation of LFA-1 expression on leukocytes may be an important step in MV pathogenesis.

Parainfluenza virus type 3 (PIV3)-specific and non-virus-specific delayed type hypersensitivity responses in cotton rats given different PIV3 antigen preparations

Virus-specific, T-lymphocyte-mediated delayed type hypersensitivity (DTH) responses were studied in cotton rats using replicating (wild-type parainfluenza virus type 3 (PIV3) and recombinant vaccinia virus expressing PIV3 haemagglutinin-neuraminidase (HN) or fusion (F) glycoproteins), and non-replicating (detergent-solubilized, affinity chromatography purified HN and F glycoproteins or inactivated whole PIV3) virus preparations. Significant virus-specific DTH responses were observed in all test groups 1-2 weeks after a single antigen inoculation or 5 days after two inoculations given 3 weeks apart. Peak swelling of ear pinnas in these animals generally occurred 24 h after elicitation and was marked by a cellular infiltration consisting of mono- and polymorphonuclear leucocytes. A considerable non-virus-specific inflammatory response, presumably due to tissue culture or media components in the priming antigen preparations, was observed 3 weeks after priming. No significant differences in DTH responses were observed in cotton rats primed with any of the PIV3 preparations. The possible roles and significance of both the virus-specific and non-virus-specific DTH responses in paramyxovirus-induced disease in humans and cotton rats are discussed.

Measles virus replication in lungs of hispid cotton rats after intranasal inoculation

Hispid cotton rats were inoculated intranasally with either measles virus (MV) Edmonston, a multipassaged, tissue culture-adapted strain of MV, or with one of three clinical MV isolates that had limited passages (three to five times) in tissue culture cells. MV Edmonston was recovered from the lungs of every (n = 37) hispid cotton rat inoculated with this virus for at least 7 days after virus inoculation. Peak pulmonary titers occurred on Day +4 (3.3-4.4 log10/g lung). Scattered areas of inflammation were observed interstitially in lung sections from infected animals stained with hematoxylin and eosin, and a similar pattern of diffuse fluorescence was seen in cryostat sections stained with an indirect fluorescent antibody procedure specific for virus antigens. Fluorescent antibody and virus isolation studies on lung lavage cells both suggested that lung leukocytes were a primary target of the virus. In contrast to these findings, virus was isolated only sporadically from hispid cotton rats inoculated with any of the clinical measles virus isolates. Despite the restricted growth of MV in these animals, cotton rats may be useful for studying certain aspects of measles virus pathogenesis and for screening potential antiviral compounds in vivo.

Aerosolized liposomal amphotericin B for treatment of pulmonary and systemic Cryptococcus neoformans infections in mice

Cryptococcus infections of the lung and central nervous system have become major problems in immuno-compromised patients, leading to the need for additional treatment protocols. We have utilized a Cryptococcus-mouse model that mimics human cryptococcal disease to evaluate the efficacy of amphotericin B-liposomes (AmpB-Lip) when delivered by small-particle aerosol (SPA). In the model, initial intranasal inoculation leads to a pulmonary infection that spreads after 2 to 3 weeks to distant organs, including the brain. Aerosols of AmpB-Lip that were generated by a Collison nebulizer had mass median aerodynamic diameters of 1.8 microns and contained 10.3 micrograms of AmpB per liter. When AmpB-Lip SPA was begun at 24 h postinoculation, a single 2-h treatment (0.3 mg of AmpB per kg of body weight) was effective in reducing pulmonary Cryptococcus infection. This regimen was more effective than intravenous administration of AmpB-Lip given for 3 continuous days. This single 2-h exposure to AmpB-Lip also was effective in reducing pulmonary Cryptococcus infection when treatment was delayed for 7 or 14 days. At day 21, when organisms had spread to the brain in all animals, the single 2-h aerosol treatment reduced the number of cryptococci in the brain as well as in the lungs. AmpB-Lip SPA administered once for 2 h on days 7, 14, and 21 also was effective in increasing the duration of survival of infected animals. These results demonstrate that aerosolized AmpB-Lip can be effective in treating both local, pulmonary Cryptococcus disease and systemic disease.

Further studies with short duration ribavirin aerosol for the treatment of influenza virus infection in mice and respiratory syncytial virus infection in cotton rats

Ribavirin aerosol administration has been shown to be effective in the treatment of respiratory syncytial virus (RSV) infections in infants and in influenza A and B virus infections in young adults. Long treatment schedules and potential for environmental contamination have stimulated the search for alternative dosing schedules. Thus, we attempted to determine the length of time of ribavirin aerosol necessary for effective treatment of influenza and RSV. In RSV-infected cotton rats, aerosolization for just 30 min with high-dose ribavirin (HDR:60 mg ribavirin/ml in reservoir), 3 times daily, reduced viral lung titers/gm of tissue by 1.1 log10. In influenza virus-infected mice, 15 min of aerosolized HDR, 3 times daily, was effective in reducing both mortality and pulmonary virus titers (1.1 log10 reduction). When the intervals between aerosol administration each day were equally divided (i.e., q.8 h), the treatments were most effective. Treatment for 45 min, once daily, was not as effective as divided doses. Calculations of ribavirin concentrations in respiratory secretions following 15 min treatment in mice with HDR indicated that drug levels dropped below the ED50 for influenza viruses after about 9 h. A daily dosage of ribavirin, estimated to be 8-15 mg/kg, was effective for the treatment of influenza and RSV infections.

Evaluation of the immunogenicity and protective efficacy of a candidate parainfluenza virus type 3 subunit vaccine in cotton rats

A parainfluenza virus type 3 (PIV3) subunit vaccine consisting of detergent-solubilized, affinity-purified haemagglutinin-neuraminidase (HN) and fusion (F) surface glycoproteins was tested in cotton rats for immunogenicity, short-term effects on virus-induced immunopathology and protective efficacy. Groups of animals were immunized twice, 4 weeks apart, with graded doses of vaccine administered either alone or with aluminium phosphate (AlPO4). The minimum immunogenic dose of vaccine was 0.1 microgram HN and F when the vaccine was given alone and 0.01 microgram when the vaccine was administered with AlPO4 adjuvant. Antibody responses in animals immunized with 1 microgram HN and F mixed with adjuvant were similar to those in control animals infected with live PIV3 intranasally. Pulmonary and nasal wash PIV3 titres generally were inversely correlated with serum antibody levels. Virus titres were significantly reduced in all groups of animals immunized with greater than or equal to 0.1 microgram HN and F compared with control animals immunized with vehicle only. Four days after virus challenge, there was no evidence of enhanced histopathology in lung sections from animals immunized with the candidate vaccine.

Aerosol and intraperitoneal administration of ribavirin and ribavirin triacetate: pharmacokinetics and protection of mice against intracerebral infection with influenza A/WSN virus

Ribavirin is active in vitro but not in vivo against a number of viruses capable of causing encephalitis. Ribavirin triacetate (RTA), a lipophilic derivative, has been reported to be more effective than ribavirin in protecting animals from encephalitis. By using an influenza A/WSN virus encephalitis model, we demonstrated that RTA administered by small-particle aerosol was able to decrease the death rate and increase the time of survival. To determine if this beneficial effect was due to increased delivery of drug, the pharmacokinetic properties of ribavirin and RTA when administered as an aerosol or by intraperitoneal injection were examined. Aerosol administration of ribavirin or RTA gave significantly higher concentrations of ribavirin in the lungs and serum of mice than did intraperitoneal injection. There was no difference, however, in ribavirin levels when either ribavirin or RTA was administered by small-particle aerosol. In brain tissue, ribavirin concentrations increased with time and did not appear to decrease as rapidly as in lungs and serum. Mean peak ribavirin concentrations in the brain were higher following aerosol administration of ribavirin than RTA, and both were higher than that following intraperitoneal injection of either drug. Administration of ribavirin or RTA by intraperitoneal injection failed to protect mice from a lethal intracerebral inoculation of influenza A/WSN virus, while aerosolized RTA did protect mice. The pharmacokinetics of ribavirin in brain tissue following aerosol administration of either drug did not explain the advantage of RTA over ribavirin in protecting mice from intracerebral infection with influenza A/WSN virus.

High dose-short duration ribavirin aerosol treatment--a review

A high-dose, short-duration treatment with ribavirin aerosol consisting of a three-fold increase in concentration of drug (60 mg versus 20 mg of ribavirin per mL in the liquid reservoir of the generator administered for about one-third the time of the standard treatment) was as effective as the standard dosage in the treatment of experimental influenza A and B infections in mice and in the treatment of experimental respiratory syncytial virus infection in cotton rats. Despite some minor pulmonary intolerance, it was considered to be suitable for use in treatment of patients with severe chronic pulmonary disease, and it was well-tolerated and apparently effective in the treatment (by face mask and endotracheal tube) of infants with bronchiolitis principally caused by respiratory syncytial virus infection. Pharmacokinetic studies in mice revealed very high concentrations of drug in the lungs, about triple the level with the standard dose, with similar blood and brain concentrations. Ribavirin concentrations were similarly high in respiratory secretions of infants given the triple dose.

Mutational analysis of regulation of MHC and anti-viral genes

CTL-mediated selection for loss of expression of Mta by H-2-heterozygous SV40-transformed mouse fibroblasts (line 24SV) produced an unusual phenotypic class of maternally transmitted Ag negative mutants defective in both MHC expression and in anti-viral activity. Severely reduced surface expression of class I MHC Ag from multiple loci of both haplotypes correlated with low levels of MHC H chain and beta 2-microglobulin mRNA. Inasmuch as IFN can up-regulate class I expression and some fibroblasts elaborate autocrine IFN-beta, we examined whether IFN could restore wild-type expression of class I MHC Ag. However, IFN could not restore wild-type expression. Moreover, the fold-increases in class I Ag and mRNA expression were significantly reduced in mutant cells compared to wild-type cells. These results suggested that the mutants might have generalized defects in IFN response. Inasmuch as the induction of an anti-viral state is a hallmark of IFN responses, we exposed cells to IFN-alpha, -beta, or -gamma and challenged with virus. 24SV cells, exposed to any of the three IFNs, were completely protected from destruction by vesicular stomatitis, mengovirus or respiratory syncytial viruses. In contrast, MHC and anti-viral defective mutants could not be protected from virus-induced lysis by any IFN. Somatic cell hybridization analyses indicated that both basal MHC and IFN-inducible phenotypes were recessive to wild-type, and that a trans-acting regulatory factor required for basal MHC expression is defectively expressed in the mutants. Such a factor may integrate the organismal response to virus infection, encompassing both immune and nonimmune anti-viral responses.

Mutational analysis of regulation of MHC and anti-viral genes

CTL-mediated selection for loss of expression of Mta by H-2-heterozygous SV40-transformed mouse fibroblasts (line 24SV) produced an unusual phenotypic class of maternally transmitted Ag negative mutants defective in both MHC expression and in anti-viral activity. Severely reduced surface expression of class I MHC Ag from multiple loci of both haplotypes correlated with low levels of MHC H chain and beta 2-microglobulin mRNA. Inasmuch as IFN can up-regulate class I expression and some fibroblasts elaborate autocrine IFN-beta, we examined whether IFN could restore wild-type expression of class I MHC Ag. However, IFN could not restore wild-type expression. Moreover, the fold-increases in class I Ag and mRNA expression were significantly reduced in mutant cells compared to wild-type cells. These results suggested that the mutants might have generalized defects in IFN response. Inasmuch as the induction of an anti-viral state is a hallmark of IFN responses, we exposed cells to IFN-alpha, -beta, or -gamma and challenged with virus. 24SV cells, exposed to any of the three IFNs, were completely protected from destruction by vesicular stomatitis, mengovirus or respiratory syncytial viruses. In contrast, MHC and anti-viral defective mutants could not be protected from virus-induced lysis by any IFN. Somatic cell hybridization analyses indicated that both basal MHC and IFN-inducible phenotypes were recessive to wild-type, and that a trans-acting regulatory factor required for basal MHC expression is defectively expressed in the mutants. Such a factor may integrate the organismal response to virus infection, encompassing both immune and nonimmune anti-viral responses.

Evaluation of the toxicity and antiviral activity of carbocyclic 3-deazaadenosine against respiratory syncytial and parainfluenza type 3 viruses in tissue culture and in cotton rats

The toxicity and antiviral efficacy of carbocyclic 3-deazaadenosine (Cc3Ado) against respiratory syncytial (RSV) and parainfluenza type 3 (PIV3) virus infections were tested in tissue culture and in cotton rats. The mean median efficacious dose (ED50) of Cc3Ado in HEp2 cells against RSV and PIV3 was 9 and 14 micrograms/ml, respectively. These values were 85- and 55-fold less than the median inhibitory (toxic) dose (ID50) of Cc3Ado in this cell line (750 micrograms/ml), and similar to values obtained for ribavirin. Cc3Ado exhibited no significant antiviral activity against influenza A, influenza B, adeno type 5 or adeno type 7 viruses (all ED50 were greater than 1000 micrograms/ml). In cotton rats, animals given greater than or equal to 1 mg/kg/day Cc3Ado intraperitoneally on days 1, 2 and 3 after experimental challenge with virus, consistently had significant reductions in pulmonary RSV and PIV3 titers compared to pulmonary virus titers in comparably treated control animals. The minimum efficacious dose of ribavirin given under the same conditions was 30 mg/kg/day. Cc3Ado was also efficacious in cotton rats when given orally by gavage, or when different administration schedules were used. The median efficacious dose of Cc3Ado when given orally was 10 mg/kg/day. No significant toxic effects were noted in cotton rats, even in animals given 20 mg/kg daily for eight consecutive days.

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.

Influenza virus infection and bacterial clearance in young adult and aged mice

The effects of influenza A/Hong Kong/68 (H3N2) virus infection on clearance of bacteria (Staphylococcus aureus or Serratia marcescens) from lungs of young adult (8-week-old) and aged (2-year-old) CBA/2N mice were studied. No consistent differences in pulmonary bacterial clearance were observed in uninfected animals of either age group. However, both young and aged virus-infected mice consistently exhibited significantly reduced ability to clear challenge bacteria from their lungs compared to age-matched nonvirus-infected controls; this deficit was markedly more pronounced in virus-infected aged mice. The extra deficit seen in virus-infected aged animals did not correlate with pulmonary virus or interferon titers, or with severity of pulmonary histopathology. Moreover, the phagocytic and bactericidal activities of pulmonary macrophages and polymorphonuclear neutrophiles from virus-infected young and aged mice were comparable.

Comparison of the anti-respiratory syncytial virus activity and toxicity of papaverine hydrochloride and pyrazofurin in vitro and in vivo

Based on reports describing their broad antiviral activity, the toxicity and antiviral efficacy of papaverine hydrochloride and pyrazofurin against respiratory syncytial virus (RSV) infection were tested in vitro in tissue culture cells and in vivo in cotton rats. Papaverine inhibited RSV replication in vitro; however, the median minimal toxic dose-median minimal inhibitory concentration ratios (MTD50:MIC50) in vitro and in vivo for papaverine were less than 4. Further work with this compound was discontinued. In contrast, pyrazofurin inhibited RSV replication in vitro (a mean MIC50 of 0.04 microgram/ml was obtained) and in vivo (RSV pulmonary titers were significantly reduced consistently in cotton rats given daily 10 mg/kg doses compared to untreated control animals). However, some toxic effects were observed in both the in vitro and in vivo tests of this compound. The remaining potential of pyrazofurin as an anti-RSV compound is discussed.

Cytotoxic and helper T-lymphocyte responses to antibody recognition regions on influenza virus hemagglutinin

We have previously localized and synthesized twelve antibody recognition sites on influenza virus hemagglutinin (HA). These peptides correspond to exposed surface areas in the 3-D structure of HA. Using intact X31 virus as the immunogen, we have determined the recognition of these synthetic peptides by proliferative T-helper lymphocytes (ThL), delayed type hypersensitivity (DTH), and cytotoxic T-lymphocytes (CTL) responses. The responses to the individual determinants in each of these immune compartments were under separate Ir gene control. Conversely, using the peptides as immunogens, we have determined the ability of various peptide-specific antibodies (in outbred mice) and ThLs (in H-2k, H-2d, H-2s and H-2b mice) to recognize intact virus. Whereas most of the peptides primed the mice for an anti-peptide proliferative ThL response, only very few of these cross-reacted with the virus. The identity of the peptide(s) eliciting virus cross-reactive ThLs varied with the strain. The importance of antibody, ThL, CTL and DTH responses in protection against viral infection and in vaccine design is discussed.

Cytotoxic T lymphocyte recognition sites on influenza virus hemagglutinin

When influenza virus infection occurs, part of the cytotoxic T lymphocyte responses induced are directed to the major surface molecule of the virus, the hemagglutinin. However, despite their potential use as a peptide vaccine, little information is available concerning the submolecular areas in the hemagglutinin that are responsible for its immunologic recognition by cytotoxic T lymphocytes. The primary goal of this study is to determine whether submolecular areas recognized by antibodies and helper T cells are also important in the virus-specific, T lymphocyte-mediated cytotoxic responses generated towards virus-infected cells. A panel of synthetic peptides representing areas of the hemagglutinin, homologous to those in influenza AX-31 virus which have previously been shown to bind anti-influenza virus antibodies and provoke proliferation of virus-primed T-helper lymphocytes, was tested in two different cytotoxicity assays. In the experiments presented here, it was found that when selected peptides were incubated with appropriate L929 target cells, lysis by virus-specific cytotoxic T cells was observed. In addition, AX-31-primed lymphocytes preincubated with these synthetic peptides (both individually and as an equimolar mixture) exhibited enhanced lysis of virus-infected syngeneic targets. The cytotoxic responses showed dose-response characteristics in all cases, and in each of the two assays used the same patterns of cytotoxic induction were observed. The recognition of peptides was MHC-restricted since virus-specific cytotoxic T cells from C3H/He mice (H-2k) lysed L929 (H-2k) target cells after incubation with peptides or viruses, but did not lyse P815 (H-2d) targets under the same conditions.

Small particle aerosols of enviroxime-containing liposomes

Enviroxime inhibits the replication of all rhinoviruses tested in vitro at very low concentrations (10-100 ng/ml), but evaluations in humans have not consistently shown efficacy. Lack of an appropriate method for administering this water-insoluble drug may have contributed to the latter result. The present report describes the characteristics and utilization of small particle aerosols to continuously deliver enviroxime-containing liposomes (LE) throughout the respiratory tract. The enviroxime content of liposomes and biological fluids of exposed individuals was quantified by high performance liquid chromatography using C18 resin, a mobile phase of 60:40 acetonitrile:water, and monitoring at 215 nm. Small particle aerosols of LE generated by Puritan-Bennett nebulizers had mass median diameters ranging from 2.4 to 3.1 microns. The concentration of enviroxime in aerosol particles was proportional to the reservoir concentration; during the first hour of operation, the mean concentration was 20 micrograms of enviroxime/l of aerosol. Liposome particles in the reservoir, although initially heterogeneous in size (less than 0.1 to greater than 1 micron), were processed by passage through the nebulizer to smaller, more homogeneous particles; the majority were less than 0.2 micron. In a preliminary study to evaluate short term tolerance and toxicity, five volunteers were exposed to small particle aerosol of LE for 1 h. At 1 h post-treatment, large amounts of enviroxime were still present in the nasal wash as determined both by HPLC and biological assay. Enviroxime was not detected in any urine sample and was detected in only 1 of 5 serum samples. No side effects were noted. This data suggest that liposome aerosols offer a method for the delivery of hydrophobic compounds for the treatment of respiratory diseases.

Activity against rhinoviruses, toxicity, and delivery in aerosol of enviroxime in liposomes

Enviroxime has been shown to inhibit the replication of rhinoviruses and other enteroviruses in concentrations as low as nanograms per milliliter in in vitro assays but is markedly less effective in clinical trials. The marked hydrophobicity and water insolubility of this compound may be a factor for this disparity. To overcome this handicap, we incorporated enviroxime into liposomes and then tested the antirhinovirus activity and toxicity of the liposome-incorporated enviroxime (LE) in cell culture and studied its administration by small-particle aerosol. Free enviroxime and LE were found to have equivalent efficacies against rhinovirus strains 1A and 13 in in vitro assays; however, preparations of LE were 10- to greater than or equal to 50-fold less toxic to tissue culture cells than was free enviroxime. In contrast to free enviroxime, which could not be delivered by small-particle aerosol because of its water insolubility, LE (4 mg/ml) was readily and successfully delivered by small-particle aerosol to the upper and lower respiratory tracts of mice; after just 20 min, significant levels of enviroxime were detected in the lungs and noses of exposed mice. Moreover, mice exposed to aerosols of liposomes containing both enviroxime and fluorescein isothiophosphatidylethanolamine showed accumulations of the fluorescent marker in the lungs, particularly in or around the tall columnar epithelial cells lining the bronchi and bronchioles.

Immunogenicity and efficacy of orally administered inactivated influenza virus vaccine in mice

The immunogenicity and protective efficacy of formalin-inactivated whole influenza A/Bangkok/79 virus vaccine given to unprimed Swiss mice orally in capsules, in their drinking water, or by direct injection into the duodenum were studied. Virus-specific IgG and IgA antibody responses to all these methods were dose-dependent and varied according to immunization conditions. Following intranasal challenge with live A/Bangkok influenza virus, mice given greater than or equal to 66 micrograms haemagglutinin (HA) of vaccine in drinking water or capsules, and mice injected into the duodenum with greater than or equal to 0.66 microgram HA, had significantly lower virus titres in their noses and lungs than control mice comparably inoculated.

Pharmacokinetics of ribavirin aerosol in mice

The pharmacokinetics of ribavirin administered in single or multiple treatments to mice by small-particle aerosol were monitored in lung, serum, and brain tissues. ribavirin aerosol was administered with a standard drug concentration (20 mg/ml) in the reservoir for 12 h or a high dose (60 mg/ml) for 2 or 4 h. After single or 3-day treatments, ribavirin rapidly accumulated in the lungs at concentrations sufficient to inhibit influenza virus or respiratory syncytial virus (1 to 5 mM). While peak levels of ribavirin in the lungs after the high-dose administration were about three times those found with the standard dose, ribavirin was rapidly cleared from the lungs. There was no accumulation of drug in the lungs after multiple treatments. Ribavirin cleared from the lungs was detected in the blood within 15 min. Concentrations in the serum were similar (20 to 30 microM) for standard- and high-dose treatments with either single or multiple treatments. Ribavirin clearance from the serum after treatment was similar for each regimen. Ribavirin also rapidly accumulated in the brain to a similar level (ca. 6 nmol per brain) after standard- or high-dose treatment for 3 days. In contrast to ribavirin in the serum, ribavirin in the brain appeared to be slowly cleared, allowing levels to remain relatively constant during and after treatment. With the interest in viral encephalopathies, further evaluation of the possible advantages of this method of drug administration is warranted.

Efficacy of high dose-short duration ribavirin aerosol in the treatment of respiratory syncytial virus infected cotton rats and influenza B virus infected mice

Fifteen to 20 mg/ml ribavirin administered as a small particle aerosol for 10-18 h per day is currently the regimen generally used to treat experimental or naturally-occurring respiratory syncytial (RS) or influenza virus infections in humans. To determine if such prolonged treatment schedules could be reduced, cotton rats and mice were inoculated with RS or influenza B virus, respectively, and then treated with different concentrations of ribavirin small particle aerosols. Aerosols generated from reservoirs containing 60 mg/ml ribavirin given 2 h twice daily, protected cotton rats from RS virus and mice from influenza B virus as well as aerosols generated from reservoirs containing 20 mg/ml ribavirin given 11 h daily. Aerosols generated from reservoirs containing 40 or 20 mg/ml given 2 h daily were less efficacious. There was no evidence of intolerance or pulmonary histopathology in infected or uninfected animals exposed to any of the doses of ribavirin tested. These studies indicate that use of aerosols containing higher concentrations of ribavirin than generally used to treat respiratory virus diseases may permit significantly shorter treatment schedules without loss of efficacy or increase in toxicity.

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

We studied the effects of combined administration of human immunoglobulin (IVIG) and ribavirin aerosol on respiratory syncytial virus (RSV) infection in cotton rats (Sigmodon hispidus). Cotton rats assigned to receive combined therapy were administered Gamimune, a preparation of purified IVIG with a high titer of anti-RSV neutralizing activity, intraperitoneally 24 h prior to intranasal RSV challenge and then treated with ribavirin aerosol 3 days after challenge. Lung viral titers from these cotton rats (geometric mean titers [GMT] log10 = 0.15 +/- 0.5) were lower than titers from untreated animals (GMT, log10 = 3.7 +/- 0.6) and animals treated with either IVIG alone (GMT, log10 = 1.8 +/- 0.9) or ribavirin alone (GMT, log10 = 1.9 +/- 1.1). Only one of 12 cotton rats treated with both IVIG and ribavirin had a demonstrable titer of virus after RSV challenge. When IVIG administration was delayed until day 3 after virus challenge, lung viral titers were still lowest in animals receiving both IVIG and ribavirin. In comparison, there was no additive antiviral effect between IVIG and ribavirin against RSV infections of HEp-2 cells in vitro. Pathologic changes on histologic examination of pulmonary tissues from animals challenged with RSV were least prominent in animals treated with both IVIG and ribavirin. Despite the apparent absence of in vitro additive antiviral effect, combined use of IVIG and ribavirin was more efficacious against RSV infection in the cotton rat than use of either agent alone.

Protection of mice from lethal influenza virus infection with high dose-short duration ribavirin aerosol

An aerosol generated from a reservoir containing 60 mg of ribavirin per ml given for 2 h twice daily for 4 days afforded the same high level of protection against lethal influenza virus infection of mice as a longer, conventional treatment schedule (20 mg/ml given for 11 h daily for 4 days). Incremental decreases in ribavirin concentration made while maintaining the 2-h intermittent schedule provided progressively less protection of mice. Mice exposed to the 60-mg/ml doses had significantly increased pulmonary and serum drug levels when compared with mice given 20 mg of drug per ml, these increases were transient, and no evidence of pulmonary intolerance was detected. These studies suggest that protective effects of ribavirin against influenza virus infection can be achieved without untoward effects if higher doses and shorter periods of administration are used.

Limited efficacy of aerosolized recombinant alpha interferon against virulent influenza A/HK infection in mice

Hybrid recombinant human alpha interferon A/D (rIFN A/D) is unusual in that it has equivalent antiviral activity in in vitro assays using mouse or human tissue cells. This interferon was delivered to outbred Swiss mice in small particle aerosols before and/or after these mice were inoculated with virulent influenza A/HK/68 virus. Although rIFN A/D was effective in inhibiting influenza virus replication in vitro in primary mouse embryo cells, it had only a limited degree of effectiveness in the in vivo tests; only animals exposed to rIFN A/D for 4 hr and inoculated with influenza virus 4 hr later exhibited a significant decrease in mortality (approximately 25% reduction in deaths; P less than 0.025) compared with that of the untreated control animals. The limited effectiveness of rIFN A/D seen in these studies indicated that the use of this or similar recombinant alpha interferons alone to prevent or treat influenza virus infection in humans is not promising.