Humoral and cell-mediated immune responses of humans to inactivated influenza vaccine with or without QS21 adjuvant.

To evaluate humoral (antibody) and cell mediated immune (CMI) responses, 30 healthy young adults were either given inactivated influenza vaccine with or without QS21 adjuvant. Vaccination site pain and postvaccination myalgias were greater in the QS21 group. Serum antibody increases occurred in 73-93% of subjects for each vaccine and antigen at 2 weeks and 4 weeks but frequencies and mean titers for the two vaccines were not different. No differences in T cell cytotoxicity were detected for either vaccine for influenza A or B infected cells. IFN-gamma for both vaccine groups was increased in supernates after 3 days but not 7 days of stimulation in the cytotoxicity tests; amounts for the two vaccines were similar. To further evaluate CMI, remaining PBMCs were stimulated overnight with cells infected with each vaccine strain; an increase in spot forming cells (sfc) for Granzyme B and IFN-gamma was found for all subjects and in 51 of 54 sfc tests. A slightly higher response in the Gran B test for QS21 subjects was suggested, but no clear immune response advantage was identified among healthy adults for QS21 adjuvanted influenza vaccine.

An overview of serum antibody responses to influenza virus antigens.

Serum antibody responses after exposure to influenza virus antigens follow expected patterns for protein antigens. Induction of primary responses occurs in organized lymphoid tissues while secondary responses may occur in the periphery; in primary responses, IgM antibody is initially dominant whereas IgG antibody is dominant in secondary responses. Serum antibody responses have been ascribed to the HA, NA, M2, NP, and M1 proteins. Only the HA and NA antibodies have been shown to provide immunity in humans. Anti-HA antibody mediates neutralization and serum IgG anti-HA antibody is the dominant antibody in the lower respiratory tract. Since evidence indicates that most infections are acquired by the airborne route with deposition of virus in the lower respiratory tract, serum IgG anti-HA antibody is the primary mediator of immunity to influenza. Homotypic immunity is high for decades. Both antigenic drift and shift of the surface antigens reduce the effectiveness of antibody to the HA and NA and lead to renewed susceptibility to infection. Nevertheless, heterotypic antibody can convey substantial immunity with the degree dependent upon the extent of cross-reactivity for the infecting virus antigens. While serum anti-HA antibody is the major need for optimal immunity to influenza, a full complement of immune modalities is desirable to ensure maximum immunity.

Immunization against influenza: comparison of various topical and parenteral regimens containing inactivated and/or live attenuated vaccines in healthy adults.

Methods for enhancing immune responses to influenza were explored in 2 double-blind, placebo-controlled trials. Intranasal (inl) immunization with monovalent, live attenuated, cold-adapted recombinant (CR) or inactivated influenza virus (MIV) vaccine and intramuscular (im) immunization with MIV were evaluated in various combinations. Healthy susceptible adults were assigned randomly to receive 10(7.1) TCID(50) of CR (A/H1N1 or A/H3N2), homologous MIV (15 microg), or placebo inl and placebo or homologous MIV im (6 groups in each study). Serum antibody responses were greatest in groups given im vaccine (with or without inl vaccine). A 2-fold increase in nasal wash antibody response frequencies was seen in groups given combined inl (CR or MIV) and im vaccine, compared with subjects given a single im (MIV) or inl (CR or MIV) vaccine. Combined inl and im immunization is a promising approach for enhancing both local and systemic immune responses against influenza.

Influenza: prospects for control.

Influenza is a disease of antiquity that annually imposes a major burden of morbidity and mortality. The available inactivated vaccine is effective for preventing influenza and the serious disease and death that can accompany it. However, annual recommendations for vaccination among persons at risk have never been adequately implemented. This remains the most pressing current need for control of influenza. Amantadine, rimantadine, and the newly available drugs zanamivir and oseltamivir are effective for influenza prevention and treatment (the former two for influenza A only). The availability of four antiviral agents that effectively prevent and treat influenza provides the physician with considerable flexibility for their use in influenza control. Optimal application of the currently available vaccine and antiviral agents should substantially reduce the impact of influenza. Other methods for influenza treatment and control are under development, and a live attenuated vaccine with substantial potential for control is nearing approval. However, better inactivated vaccines, better rapid diagnostic tests, and an increased understanding of options for use of antiviral agents are still needed. When all of these things are available and optimally applied, effective control of influenza should result. The prospect is compelling. Full participation by the practicing physician will be necessary to achieve this goal.

Impact of respiratory virus infections on persons with chronic underlying conditions.

CONTEXT: While hospitalization rates have declined overall, hospitalizations for acute lower respiratory tract infections have increased steadily since 1980. Development of new approaches for prevention of acute respiratory tract conditions requires studies of the etiologies of infections and quantification of the risk of hospitalization for vulnerable patients. OBJECTIVE: To determine the frequency of specific virus infections associated with acute respiratory tract conditions leading to hospitalization of chronically ill patients. DESIGN: Analysis of viral etiology of patients hospitalized with acute respiratory tract conditions between July 1991 and June 1995. SETTING: Four large clinics and related hospitals serving diverse populations representative of Harris County, Texas. PATIENTS: A total of 1029 patients who were hospitalized for pneumonia, tracheobronchitis, bronchiolitis, croup, exacerbations of asthma or chronic obstructive pulmonary disease, and/or congestive heart failure. MAIN OUTCOME MEASURE: Virus infection, defined by culture, antigen detection, and significant rise in serum antibodies, by underlying condition; hospitalization rates by low- vs middle-income status. RESULTS: Ninety-three percent of patients older than 5 years had a chronic underlying condition; a chronic pulmonary condition was most common. Patients with chronic pulmonary disease from low-income populations were hospitalized at a rate of 398.6 per 10000, almost 8 times higher than the rate for patients from middle-income groups (52.2 per 10000; P<.001). Of the 403 patients (44.4% of adults and 32.3% of children) who submitted convalescent serum specimens for antibody testing, respiratory tract virus infections were detected in 181 (44.9%). Influenza, parainfluenza, and respiratory syncytial virus (RSV) infections accounted for 75% of all virus infections. CONCLUSIONS: Our study suggests that respiratory virus infections commonly trigger serious acute respiratory conditions that result in hospitalization of patients with chronic underlying conditions, highlighting the need for development of effective vaccines for these viruses, especially for parainfluenza and RSV.

Human interleukin-12 enhances interferon-gamma-producing influenza-specific memory CD8+ cytotoxic T lymphocytes.

Interferon (IFN)-gamma synthesis of CD45RO+ (memory) and CD45RA+ (naive) CD8+ cytotoxic T lymphocytes (CTLs) and the role of interleukin (IL)-12 in the regulation of human CTL functions in virus-specific immunity were investigated. After culture with influenza virus, CD45RO+ CD8+ T cells from human peripheral blood mononuclear cells increased in frequency and exhibited significant major histocompatibility complex class I-mediated CTL activity, whereas CD45RA+ CD8+ T cells did not. Influenza virus-stimulated CD45RO+ CD8+ T cells contained significantly higher levels of IFN-gamma-producing cells and IFN-gamma-specific mRNA than did CD45RA+ CD8+ T cells. Recombinant human IL-12 further enhanced CTL activity and IFN-gamma production by CD45RO+ CD8+ T cells. These data clearly show that human virus-specific CTL activity and coproduction of IFN-gamma are associated with the CD45RO+ CD8+ T cells that are modulated by the cell-mediated, immunity-inducible cytokine IL-12 in humans.

Measures for control of influenza.

Influenza viruses cause recurring illnesses among individuals and recurring epidemics among populations. The major effective control measure for preventing infection and illness is inactivated vaccine, which can prevent influenza illnesses and their complications when given before exposure to the virus. While inactivated vaccine is effective for preventing influenza in most individuals, recommendations for its use focus on the prevention of severe disease and death among those who are at high risk of complications. Live attenuated cold-adapted influenza vaccines are nearing availability. They are given by nasal spray and are particularly effective for preventing influenza among young children, but also for preventing influenza among young adults, and enhancing protection against influenza when given with inactivated vaccine to elderly persons. The antiviral agents amantadine and rimantadine are related compounds that are effective for the prevention and treatment of influenza A virus infections and illnesses. Disadvantages are the rapid development of resistance during treatment and CNS adverse effects with amantadine. These drugs are also effective for outbreak control. Ribavirin is an antiviral given by small particle aerosol that is approved for the treatment of respiratory syncytial virus disease; it is also effective for the treatment of influenza. Two new antiviral agents inhibit influenza viral neuraminidase activity; one is given by inhalation or intranasally (zanamivir) and the other orally (GS4104). The former is free of adverse effects, while the latter induces nausea and vomiting in some individuals. Both are effective for the prevention as well as the treatment of influenza A and B illnesses. Thus, various measures for preventing and treating influenza are nearing availability. Their optimal use should further improve the control of influenza in individuals and populations as well as permit efforts to prevent community epidemics.

Improvement of inactivated influenza virus vaccines.

Inactivated influenza virus vaccines (IVVs) are used for prevention of influenza and its complications. Present vaccines are immunogenic, of low reactogenicity, and protective, but protection has varied between 0% and 100%. Increasing the dose of hemagglutinin and neuraminidase antigens with purified proteins significantly increased serum and nasal antibody responses; however, trials with newer adjuvants have not shown increased serum antibody to levels comparable with those in earlier studies using oil emulsion adjuvants. IgA antibody responses in respiratory secretions were enhanced by the respiratory administration of IVVs, but IVVs by the oral route yielded varying results. IVVs appeared less effective for pandemic influenza in 1968 than in 1957. Since IVVs will be the major preventative measure for pandemic influenza in most countries, they need to be improved to provide better protection against pandemic and interpandemic influenza. Increasing the doses of hemagglutinin and neuraminidase, using adjuvants or immunomodulators, and administering IVVs by the mucosal route could improve the performance of these vaccines.

Efficacy of repeated annual immunization with inactivated influenza virus vaccines over a five year period.

Some reports have suggested that influenza virus vaccine is less effective in persons that have received prior annual vaccination(s) than in those receiving it for the first time. This issue was addressed by evaluating the efficacy of annual influenza vaccinations over a 5 year period in healthy adults employing commercially-available, inactivated whole-virus vaccine. Influenza vaccination had minimal effects on overall respiratory illnesses during epidemic periods. However, it reduced influenza virus shedding by an average of 38.8% and conferred protection against influenza virus infection during each epidemic. Some variation in infection rates were noted between vaccine groups given one or more than one annual immunization, and between years, but no consistent pattern of differences was noted in relation to number of successive years of vaccination. These results suggest that the current recommendation for annual influenza vaccination of persons at special risk of serious disease and complications is appropriate, but that continued efforts to improve the effectiveness of our prophylactic measures against influenza are needed.

Cytokines and impaired CD8+ CTL activity among elderly persons and the enhancing effect of IL-12.

We have previously demonstrated that about 70% of elderly persons exhibit deficient cytotoxic T lymphocyte (CD8+ CTL) responses against influenza viruses when compared to young persons. Since IFN-gamma, a Th1 cytokine and IL-4, a Th2 cytokine, stimulate and inhibit CD8+ CTL responses respectively, their role(s) in the age-related CTL deficiency was investigated. Lymphocytes from young adults (34 +/- 5 years old) and elderly subjects (71 +/- 1 years old) were stimulated in vitro with influenza A/H3N2, A/H1N1 or influenza B virus for 6-7 days. The CD8+ CTL activity against virus-infected autologous target cells was significantly lower among the elderly than the young subjects (P < 0.01). Following stimulation with influenza virus, IL-4 production in both age groups was similar on day 3 but significantly higher among elderly persons on day 6 (P < 0.05). In contrast, T cells from the elderly produced significantly lower IFN-gamma than did those from young persons on both days (P < 0.05). Treatment of T cells from young and elderly adults with recombinant human IL-12, a pivotal cytokine that stimulates Th1 cytokines, resulted in enhancement of CD8+ CTL activity and IFN-gamma production in a dose dependent manner (P < 0.01). IL-12-dependent enhancement of CTL activity was not always abrogated by anti-IFN-gamma antibody treatment. These results suggest that deficient influenza virus-specific CTL activity among the elderly is attributable to a Th1 to Th2 cytokine production switch. Immunotherapy with IL-12 could represent a useful approach to correct the CD8+ CTL deficiency and cytokine imbalance among elderly humans.

Respiratory viral infections in immunocompetent and immunocompromised persons.

The acute respiratory illnesses are the most common type of acute illness in the United States today. The respiratory viruses--which include influenza viruses, parainfluenza viruses, respiratory syncytial virus (RSV), rhinoviruses, coronaviruses, and adenoviruses--cause the majority of these illnesses. Some of these viruses cause illness throughout the year, whereas others are most common in winter. All population groups experience these infections and illnesses. As the number of elderly persons and those with underlying disease increases, awareness is growing that these common infections can have serious consequences. This has recently been emphasized for immunocompromised persons. At the M.D. Anderson Cancer Center (MDACC), infection surveillance of mostly hospitalized adults with leukemia or a recent bone marrow transplant yielded a respiratory virus from 181 of 668 (27.1%) respiratory illness episodes. In descending order of frequency, infections with RSV, rhinoviruses, influenza viruses, parainfluenza viruses, and adenoviruses were detected in each of three surveillance years. High frequencies of nosocomial acquisition occurred, as has been noted in prior reports. Similarly, persistence of infection and high frequencies of pneumonia and death among infected patients occurred, which have also been noted earlier. At MDACC, pneumonia occurred in 58-78% of infected patients, and 22-44% died. The role of the virus infection in many cases of pneumonia is uncertain, but death from pure viral pneumonia is well documented. A number of immune deficiencies in this patient population and options for control of these infections have been described that can, respectively, account for the medical problem and provide ways to approach prevention and treatment.

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.

Cytotoxic T lymphocyte responses of infants after natural infection or immunization with live cold-recombinant or inactivated influenza A virus vaccine.

The cytotoxic T lymphocyte (CTL) response of infants after immunization with either inactivated trivalent subvirion vaccine (TIV) or bivalent attenuated cold-recombinant (CR) vaccine or occurrence of natural influenza virus infection were compared in a blinded, placebo-controlled study during the 1987-1988 and 1988-1989 influenza epidemic seasons. Healthy infants between 6 and 13 months of age were randomly assigned and administered a single dose of intranasal bivalent (A/H3N2/A/H1N1) CR vaccine, a two-dose regimen of TIV (A/H3N2/A/H1N1/B) influenza vaccine, or placebo. Peripheral blood lymphocytes were obtained prior to and 2-8 weeks after vaccination and at the end of the epidemic season and stimulated with virus in vitro for 6 or 7 days. Lysis of autologous virus-infected target cells was assessed in a 4 hr 51Cr release assay. MHC class I-restricted influenza A-specific CTL was stimulated following natural influenza A virus infection but not after immunization with CR influenza A virus vaccine or TIV. These results demonstrate for the first time induction of influenza virus-specific CTL activity in infants under 1 year of age.