Influenza antibody in human respiratory secretions after subcutaneous or respiratory immunization with inactivated virus

Mucosal correlates of protection after influenza viral challenge of vaccinated and unvaccinated healthy volunteers

The induction of systemic antibody titers against hemagglutinin has long been the main focus of influenza vaccination strategies, but mucosal immunity has also been shown to play a key role in the protection against respiratory viruses. By vaccinating and challenging healthy volunteers, we demonstrated that inactivated influenza vaccine (IIV) modestly reduced the rate of influenza while predominantly boosting serum antibody titers against hemagglutinin (HA) and HA stalk, a consequence of the low neuraminidase (NA) content of IIV and the intramuscular route of administration. The viral challenge induced nasal and serum responses against both HA and NA. Correlations between mucosal IgA and serum IgG against specific antigens were low, whether before or after challenge, suggesting a compartmentalization of immune responses. Even so, volunteers who developed viral shedding for multiple days had lower baseline titers across both systemic and mucosal compartments as compared to those with no shedding or a single day of shedding. Regression analysis showed that pre-challenge HA inhibition titers were the most consistent correlate of protection across clinical outcomes combining shedding and symptoms, with NA inhibition titers and HA IgG levels only predicting the duration of shedding. Despite the inclusion of data from multiple binding and functional antibody assays against HA and NA performed on both serum and nasal samples, multivariate models were unable to account for the variability in outcomes, emphasizing our imperfect understanding of immune correlates in influenza and the importance of refining models with assessments of innate and cellular immune responses.IMPORTANCEThe devastating potential of influenza has been well known for over 100 years. Despite the development of vaccines since the middle of the 20th century, influenza continues to be responsible for substantial global morbidity and mortality. To develop next-generation vaccines with enhanced effectiveness, we must synthesize our understanding of the complex immune mechanisms culminating in protection. Our study outlines the differences in immune responses to influenza vaccine and influenza infection, identifying potential gaps in vaccine-induced immunity, particularly at the level of the nasal mucosa. Furthermore, this research underscores the need to refine our imperfect models while recognizing potential pitfalls in past and future attempts to identify and measure correlates of protection.

Intranasal inactivated influenza vaccines for the prevention of seasonal influenza epidemics

INTRODUCTION

Intranasal influenza vaccines are expected to confer protection among vaccine recipients by successful induction of mucosal immune response in the upper respiratory tract. Though only live attenuated influenza virus vaccines (LAIVs) are licensed and available for intranasal use in humans today, intranasal inactivated influenza vaccines (IIVs) are currently under reconsideration as a promising intranasal influenza vaccine.

AREAS COVERED

This review addresses the history of intranasal IIV research and development, along with a summary of the studies done so far to address the mechanism of action of intranasal IIVs.

EXPERT COMMENTARY

From numerous in vitro and in vivo studies, it has been shown that intranasal IIVs can protect hosts from a broad spectrum of influenza virus strains. In-depth studies of the mucosal antibody response following intranasal IIV administration have also elucidated the detailed functions of secretory IgA (immunoglobulin A) antibodies which are responsible for the mechanism of action of intranasal vaccines. Safe and effective intranasal IIVs are expected to be an important tool to combat seasonal influenza.

Intranasal Inactivated Influenza Vaccines: a Reasonable Approach to Improve the Efficacy of Influenza Vaccine?

Influenza is a contagious, acute respiratory disease caused by the influenza virus. The mucosal lining in the host respiratory tract is not only the site of virus infection, but also the site of defense; it is at this site that the host immune response targets the virus and protects against reinfection. One of the most effective methods to prevent influenza is to induce specific antibody (Ab) responses in the respiratory tract by vaccination. Two types of influenza vaccines, intranasal live attenuated influenza virus (LAIV) vaccines and parenteral (injectable) inactivated vaccines, are currently used worldwide. These vaccines are approved by the European Medicines Agency (EMA) and the US Food and Drug Administration. Live attenuated vaccines induce both secretory IgA (S-IgA) and serum IgG antibodies (Abs), whereas parenteral vaccines induce only serum IgG Abs. However, intranasal administration of inactivated vaccines together with an appropriate adjuvant induces both S-IgA and IgG Abs. Several preclinical studies on adjuvant-combined, nasal-inactivated vaccines revealed that nasal S-IgA Abs, a major immune component in the upper respiratory tract, reacted with homologous virus hemagglutinin (HA) and were highly cross-reactive with viral HA variants, resulting in protection and cross-protection against infection by both homologous and variant viruses, respectively. Serum-derived IgG Abs, which are present mainly in the lower respiratory tract, are less cross-reactive and cross-protective. In addition, our own clinical trials have shown that nasal-inactivated whole virus vaccines, including a built-in adjuvant (single-stranded RNA), induced serum hemagglutination inhibition (HI) Ab titers that fulfilled the EMA criteria for vaccine efficacy. The nasal-inactivated whole virus vaccines also induced high levels of nasal HI and neutralizing Ab titers, although we have not yet evaluated the nasal HI titers due to the lack of official criteria to establish efficacy based on this parameter. Data suggest that adjuvant-combined nasal-inactivated vaccines have advantages over the current injectable vaccine because the former induce both S-IgA and serum IgG Abs. In addition, nasal-inactivated vaccines seem to be superior to the LAIV vaccines, because non-infectious preparations could be used in high-risk groups. Thus, the development of intranasal inactivated vaccines is recommended, because such vaccines are expected to improve the efficacy of influenza vaccines.

Chimeric virus-like particles containing influenza HA antigen and GPI-CCL28 induce long-lasting mucosal immunity against H3N2 viruses

Influenza virus is a significant cause of morbidity and mortality, with worldwide seasonal epidemics. The duration and quality of humoral immunity and generation of immunological memory to vaccines is critical for protective immunity. In the current study, we examined the long-lasting protective efficacy of chimeric VLPs (cVLPs) containing influenza HA and GPI-anchored CCL28 as antigen and mucosal adjuvant, respectively, when immunized intranasally in mice. We report that the cVLPs induced significantly higher and sustainable levels of virus-specific antibody responses, especially IgA levels and hemagglutination inhibition (HAI) titers, more than 8-month post-vaccination compared to influenza VLPs without CCL28 or influenza VLPs physically mixed with sCCL28 (soluble) in mice. After challenging the vaccinated animals at month 8 with H3N2 viruses, the cVLP group also demonstrated strong recall responses. On day 4 post-challenge, we measured increased antibody levels, ASCs and HAI titers with reduced viral load and inflammatory responses in the cVLP group. The animals vaccinated with the cVLP showed 20% cross-protection against drifted (Philippines) and 60% protection against homologous (Aichi) H3N2 viruses. Thus, the results suggest that the GPI-anchored CCL28 induces significantly higher mucosal antibody responses, involved in providing long-term cross-protection against H3N2 influenza virus when compared to other vaccination groups.

Intranasal administration of influenza vaccines: current status

AbstractThis review article focuses on intranasal immunisation against influenza,although it also encompasses antigen uptake and processing in the nasopharyngealpassages, host defence from influenza and current influenza vaccination practices.Improvement of current vaccination strategies is clearly required; current proceduresinvolve repeated annual injections that sometimes fail to protect the recipient. It isenvisaged that nonpercutaneous immunisation would be more attractive to potentialvaccinees, thus improving uptake and coverage. As well as satisfying noninvasivecriteria, intranasal influenza immunisation has a number of perceived immunologicaladvantages over current procedures. Perhaps one of the greatest attributes of thisapproach is its potential to evoke the secretion of haemagglutinin-specific IgAantibodies in the upper respiratory tract, the main site of viral infection. Inactivated influenza vaccines have the advantage that they have a long historyof good tolerability as injected immunogens, and in this respect are possibly morelikely to be licensed than attenuated viruses. Inert influenza vaccines are poormucosal immunogens, requiring several administrations, or prior immunologicalpriming, in order to engender significant antibody responses. The use of vaccinedelivery systems or mucosal adjuvants serves to appreciably improve theimmunogenicity of mucosally applied inactivated influenza vaccines. As is the casewhen they are introduced parenterally, inactivated influenza vaccines are relativelypoor stimulators of virus-specific cytotoxic T lymphocyte activity following nasalinoculation. Live attenuated intranasal influenza vaccines are at a far moreadvanced stage of clinical readiness (phase III versus phase I). With the use of liveattenuated vaccines, it is possible to stimulate mucosal and cell-mediatedimmunological responses of a similar kind to those elicited by natural influenzainfection. In children, recombinant live attenuated cold-adapted influenza viruses arewell tolerated. Moreover, cold-adapted influenza viruses usually stimulate protectiveimmunity following only a single nasal inoculation. Safety of recombinant liveattenuated cold-adapted influenza viruses has also been demonstrated in high riskindividuals with cystic fibrosis, asthma, cardiovascular disease and diabetes mellitus.They are not suitable for immunising immunocompromised patients, however, andare poorly efficacious in individuals with pre-existing immunity to strains closelyantigenically matched with the recombinant virus. According to the reviewedliterature, it is apparent that intranasal administration of vaccine as an aerosol issuperior to administration as nose drops. The information reviewed in this papersuggests that nasally administered influenza vaccines could make a substantialimpact on the human and economic cost of influenza.

Dry powder vaccines for mucosal administration: critical factors in manufacture and delivery

Dry powder vaccine formulations have proved effective for induction of systemic and mucosal immune responses. Here we review the use of dry vaccines for immunization in the respiratory tract. We discuss techniques for powder formulation, manufacture, characterization and delivery in addition to methods used for evaluation of stability and safety. We review the immunogenicity and protective efficacy of dry powder vaccines as compared to liquid vaccines delivered by mucosal or parenteral routes. Included is information on mucosal adjuvants and mucoadhesives that can be used to enhance nasal or pulmonary dry vaccines. Mucosal immunization with dry powder vaccines offers the potential to provide a needle-free and cold chain-independent vaccination strategy for the induction of protective immunity against either systemic or mucosal pathogens.

Needle-free influenza vaccination

Vaccination is the cornerstone of influenza control in epidemic and pandemic situations. Influenza vaccines are typically given by intramuscular injection. However, needle-free vaccinations could offer several distinct advantages over intramuscular injections: they are pain-free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs. Moreover, vaccine delivery via the respiratory tract, alimentary tract, or skin might elicit mucosal immune responses at the site of virus entry and better cellular immunity, thus improving effectiveness. Although various needle-free vaccination methods for influenza have shown preclinical promise, few have progressed to clinical trials-only live attenuated intranasal vaccines have received approval, and only in some countries. Further clinical investigation is needed to help realise the potential of needle-free vaccination for influenza.

Viral infections of the respiratory tract: prevention and treatment

The rapid discovery of specific viral agents as the cause of many acute respiratory diseases was accompanied by considerable optimism that vaccines or other control measures could be developed quickly. Subsequent experience has demonstrated that effective control of these important public health problems has been an elusive goal. However, recent exciting developments in our understanding of the molecular biology and immunology of these viruses may provide the basis for more effective strategies in the future.

Influenza vaccines have a short but illustrious history

Isolation of the causative virus of influenza in 1933, followed by the discovery of embryonated hen eggs as a substrate, quickly led to the formulation of vaccines. Virus-containing allantoic fluid was inactivated with formalin. The phenomenon of antigenic drift of the virus HA was soon recognized and, as WHO began to coordinate the world influenza surveillance, it became easier for manufacturers to select an up-to-date virus. Influenza vaccines remain unique in that the virus strain composition is reviewed yearly but modern attempts are being made to free manufacturers from this yolk by investigating internal virus proteins including M2e and NP as “universal” vaccines covering all virus sub types. Recent technical innovations have been the use of Vero and MDCK cells as the virus cell substrate, the testing of two new adjuvants and the exploration of new presentations to the nose or epidermal layers as DNA or antigen mixtures. The international investment into public health measures for a global human outbreak of avian H5N1 influenza is leading to enhanced production of conventional vaccine and to a new research searchlight on T cell epitope vaccines, viral live attenuated carriers of influenza proteins and even more innovative substrates to cultivate virus, including plant cells.

A dose-response evaluation of inactivated influenza vaccine given intranasally and intramuscularly to healthy young adults

Epidemic influenza occurs annually throughout the world and is accompanied by excess morbidity and mortality. Increasing the antigen content and topical administration of vaccine are two strategies being explored to improve the immune responses to trivalent inactivated influenza vaccine (TIV). We conducted a randomized, double-blind, placebo-controlled trial to compare the immunogenicity and reactogenicity of intramuscular (IM), intranasal (IN), or combined IM and IN administration of a contemporary US vaccine formulation at escalating dosage levels in young healthy adults. Two hundred forty three healthy adults between the ages of 18 and 45 years received 15, 30, or 60mcg of trivalent inactivated influenza vaccine by either IN, IM or both routes, 120mcg of vaccine IM, or placebo IN and IM. All dosages and routes of vaccine administration were well-tolerated. A bad taste and mild nasal discomfort were more likely to be reported when influenza vaccine was administered IN, while arm tenderness was more common after IM administration. Significant increases in geometric mean serum antibody titers in both HAI and Nt assays were seen in all of the groups receiving influenza vaccine for all test antigens (P<or=.025, paired t-test), except for the B HAI antibody titer in the group that received 30mcg IN (P=.055, paired t-test). Postvaccination geometric mean serum antibody titers, the frequency of seroresponses, and the percentage achieving postvaccination serum HAI antibody titers of >or=32 were higher following delivery of the study vaccines by an IM route than by the IN route, but significant increases in serum antibody were seen after IN vaccination. Nasal IgA antibody responses were more common when vaccine was administered IN; and, when the IN dosage was increased, the primary benefit from IN vaccine over IM vaccine appeared to be greater induction of nasal secretory antibody.

Intranasal administration of a proteosome-influenza vaccine is well-tolerated and induces serum and nasal secretion influenza antibodies in healthy human subjects

Two randomized, blinded, active comparator-controlled trials of a prototype monovalent A/Beijing/262/95 (H1N1) - proteosome vaccine delivered by intranasal spray were performed in healthy adults. Overall, the intranasal proteosome-adjuvanted vaccine was well-tolerated with only mild stuffy nose and rhinorrhea seen more frequently in recipients of vaccine than in recipients of intranasal saline, and there were no serious adverse events. The intranasal proteosome-adjuvanted vaccine induced serum hemagglutination inhibiting (HAI) and nasal secretory IgA (sIgA) responses specific for the influenza antigen. Serum HAI responses were most influenced by the dosage level, whereas mucosal sIgA responses, although demonstrable with both single-dose and two-dose vaccine regimens, appeared to be greater in response to two-dose regimens (regardless of dose level). Further evaluation of mucosal influenza immunization using the proteosome adjuvant/delivery system is clearly warranted.

Is there a role for a mucosal influenza vaccine in the elderly?

Influenza infection is an acute respiratory disease with a high morbidity and significant mortality, particularly among the elderly and individuals with chronic diseases. The majority of countries now recommend annual influenza vaccination for all people aged 65 years or older, and for those with high risk conditions. Most commercially available influenza vaccines are administered systemically and while these are effective in children and young adults, efficacy levels in elderly individuals have been reported to be much lower. Mucosal vaccines may offer an improved vaccine strategy for protection of the elderly. As the influenza virus causes a respiratory infection, it is potentially more beneficial to administer a vaccine that will boost protection in the mucosal surfaces of the upper and lower respiratory tract. Mucosal influenza vaccines are aimed at stimulating protective immunity in the respiratory tract via oral or intranasal immunisation. This review examines our present knowledge of mucosal immunity and current strategies for mucosal vaccination. It also stresses that the use of serum antibody levels as a 'surrogate marker' for protection against influenza is potentially misleading; serum antibody, for example, may be a quite inappropriate marker to assess a mucosal vaccine. This marker does not reflect other immune responses to vaccination that are crucial for protection.

Clinical and immunological characteristics of the emulsion form of inactivated influenza vaccine delivered by oral immunization

Prophylaxis of human respiratory diseases caused by influenza viruses is actually a problem of infectious pathology because of their wide prevalence. In our investigations, safety, reactogenicity and immunological activity of the orally administered emulsion-inactivated influenza vaccine prepared from influenza virus strains of types A(H1N1), A(H3N2) and B have been studied. Clinical studies of the emulsion-inactivated influenza vaccine on volunteers has shown its safety and nonreactogenicity. The orally administered vaccine did not cause weak, middle or strong general or local reactions including clinical, biochemical, haemotological and immunological reactions. The emulsion-inactivated vaccine has high immunological activity and induces reliable increases in the level of secretory immunoglobulin A to influenza viruses A and B in protective titers in nasal secretions and saliva of volunteers after one oral administration. The obtained results indicate the expediency of further investigation and improvement of inactivated influenza vaccine for oral administration.

Enhancing effects of pertussis toxin B oligomer on the immunogenicity of influenza vaccine administered intranasally

Influenza vaccines together with pertussis toxin B oligomer (PTB) purified from a culture supernatant of Bordetella pertussis were administered intranasally into mice to test for an adjuvant effect of the PTB. An inactivated virus vaccine and an ether-treated HA vaccine prepared from influenza virus A/Yamagata/120/86 (H1N1) and formulated with PTB, stimulated production of serum haemagglutinin inhibition (HI) antibody and pulmonary and endotracheal secretory IgA antibody to high titres. In addition, mice immunized with the influenza vaccines formulated with PTB were protected against exposure with a challenge virus. These results demonstrate that PTB can enhance the immunogenicity of influenza vaccines administered intranasally.

High doses of purified influenza A virus hemagglutinin significantly augment serum and nasal secretion antibody responses in healthy young adults

The reactogenicity and immunogenicity of purified influenza virus hemagglutinin (HA) vaccines administered intramuscularly were evaluated in two placebo-controlled clinical trials. A total of 139 healthy young adults were randomized to receive increasing doses of monovalent influenza A/Taiwan/1/86 (H1N1) virus HA (range, 0 to 405 micrograms per dose [study 1]). An additional 139 subjects were given increasing doses of a trivalent HA vaccine containing equal amounts of A/H1N1 virus, A/Shanghai/16/89 (H3N2) virus, and influenza B/Yamagata/16/88 virus HA (range, 0 to 135 micrograms of HA per strain, 0 to 405 micrograms per dose) or a standard dose of commercial influenza vaccine (study 2). Increasing doses of HA were associated with increasing frequencies of symptoms at the vaccination site early after vaccination, but all doses were well tolerated. Occurrence of systemic symptoms was unrelated to dose. Increasing the dose of HA resulted in increasingly higher postimmunization levels of serum hemagglutination inhibiting and neutralizing antibody levels versus influenza A/H1N1 virus in study 1 (P < 0.05); these enhanced responses persisted for up to 6 months. Nasal secretory immunoglobulin A and G antibody responses were assessed 2 weeks after immunization with monovalent H1N1 virus HA; the frequencies of significant responses also increased in a dose-related fashion. Similar increases in serum antibody levels were noted for both A/H1N1 and A/H3N2 viruses in study 2. These data provide a basis for proceeding with the evaluation of high doses of purified HA in the elderly.

Influenza immunization: intranasal live vaccinia recombinant contrasted with parenteral inactivated vaccine

To compare the efficacy and duration of the immune response to local and systemic vaccination, Balb/c mice were vaccinated either intraperitoneally (i.p.) with an inactivated A/PR/8/34 (H1N1) vaccine or intranasally (i.n.) with a vaccinia recombinant containing the H1 gene of influenza. The i.p. inactivated vaccine stimulated high serum IgG anti-influenza titres and protected the lungs against viral challenge for the duration of the experiment (17 months). Little nasal wash IgA was induced and the noses were susceptible to challenge. Animals vaccinated i.n. with the recombinant had lower serum IgG titres and the lungs showed poor protection against challenge. Nasal wash IgA titres were higher, however, and the noses were largely protected from viral challenge for 17 months.

Comparison of intranasal inoculation of influenza HA vaccine combined with cholera toxin B subunit with oral or parenteral vaccination

The antibody responses to influenza virus A/PR/8/34 HA vaccine and protection against virus challenge in mice given the vaccine together with the B subunit of cholera toxin (CTB) intranasally were compared with those in mice given the vaccine with CTB perorally, intraperitoneally or subcutaneously. Intranasal vaccination induced remarkably higher levels of antiviral IgA antibodies in both respiratory washings and serum than did other routes of vaccination. The titres of antiviral IgG antibodies in respiratory washings and serum, and haemagglutination-inhibiting (HI) antibodies in serum, were similar after intranasal and parenteral vaccination. Oral vaccination, however, induced low levels of antiviral IgG antibodies but no detectable HI antibodies. Moreover, intranasal immunization elicited significantly higher titres of antiviral IgA antibodies in intestinal secretions in comparison with oral immunization. In contrast, parenteral immunization failed to induce these IgA antibodies. In virus challenge studies, a greater protective effect was seen after intranasal and intraperitoneal vaccination than after other routes of vaccination. These results suggest that intranasal inoculation of combined HA vaccine and CTB is superior to oral or parenteral inoculation in protecting mice. Furthermore, the intestinal antiviral IgA responses suggest that intranasal administration of CTB-combined vaccines could be effective not only against respiratory pathogens but also against enteropathogens.

Comparison of inactivated, live and recombinant DNA vaccines against influenza virus in a mouse model

The protective efficacy of influenza hemagglutinin expressed from recombinant vaccinia virus was compared with that induced by inactivated or infectious influenza vaccines. Intraperitoneal and intranasal routes of vaccination were compared. All the vaccines except the intranasally administered, inactivated vaccine induced detectable levels of neutralizing and hemagglutination-inhibiting antibodies in the serum of mice at 28 days postvaccination. Immunization with any of the intranasally administered vaccines reduced the amount of influenza virus nucleoprotein antigen in lungs after challenge with a homologous, mouse-adapted strain of influenza virus. Intraperitoneally administered vaccines failed to provide such protection. These results indicated that the route of vaccine administration may be the most critical factor for inducing protective immunity. The results also showed that in this mouse model a recombinant DNA-based vaccine could provide protection equivalent to that provided by conventional attenuated and inactivated influenza vaccines.

Enhancement of DTH response by cholera toxin B subunit inoculated intranasally together with influenza HA vaccine

The effects of B subunit of cholera toxin (CTB) on delayed-type hypersensitivity (DTH) response to influenza vaccine derived from influenza virus A/PR/8/34 (PR-8, HlNl) virus were investigated in B10 mice that were immunized intranasally with both influenza vaccine and CTB. The result showed that intranasal inoculation of this combination augmented DTH response to influenza vaccine, which reached its peak 6 days after inoculation, and also induced accelerated DTH response upon a second inoculation of influenza vaccine alone 4 weeks later, that the cross-reactive DTH response to PR-8 vaccine was elicited by the injection of the different influenza A-type virus vaccine into the footpad of the vaccinated mice, but was not by influenza B-type virus vaccine, that the DTH-mediating T cells were detected selectively in the lungs of mice that received the nasal inoculation of the vaccine and CTB together, but that subcutaneous inoculation of this combination failed to induce DTH-mediating T cells in the lungs. These results, together with the previous papers (Tamura et al, Vaccine 7: 257-262; 314-320, 1989), suggest that CTB could augment both humoral and DTH responses against influenza vaccine in the respiratory mucosal tract.

Immune responses to influenza virus in orally and systemically immunized mice

In our studies on the induction of an immune response by oral immunization, we have explored the potential of a novel approach for antigen delivery by microencapsulation. This procedure preserved the immunogenicity of the influenza virus introduced by either systemic or oral routes. Furthermore, the levels of specific antibodies in serum and in saliva were enhanced and lasted longer (up to 4 months) in animals immunized with of antigens in microencapsulated form than in animals immunized with equal doses of free suspension. Preliminary challenge experiments showed a correlation between levels of antibodies and protection. All mice systemically immunized were protected against the virus, while mice orally immunized with lower doses of microencapsulated antigen had better survival rates than those immunized with higher doses. Additional experiments suggested that low doses of immunogen were able to generate better protective immunity than high doses, which may instead be tolerogenic. Further experiments with a well characterized microencapsulated antigen (size of microcapsules, time of release of antigen, as well as its dose and form) will be necessary to establish conditions for optimal immunization protocols applicable for the oral or systemic routes.

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.

Active synthesis of hemagglutinin-specific immunoglobulin A by lung cells of mice that were immunized intragastrically with inactivated influenza virus vaccine

Intragastric inoculation with whole-virion vaccine of inactivated influenza virus resulted in production of hemagglutinin (HA)-specific immunoglobulin A (IgA) and IgG both in lung lavage fluids and in serum samples of mice. HA-specific IgA was the predominant isotypic antibody secreted in the lung lavage fluids (average IgA/IgG ratio, 13:1), whereas HA-specific IgG was the major antibody class in serum (average IgA/IgG ratio, 0.3:1). These responses were similar to the antibody responses stimulated by intranasal infection with live influenza virus. In vitro cultures of lymphoid cells from lungs and Peyer's patches, but not from spleens, in the presence of homologous antigen, from mice vaccinated intragastrically synthesized mostly HA-specific IgA. Mice immunized parenterally with inactivated influenza virus produced only IgG in lung lavage fluids and sera. Cultures of lymphoid cells from their spleens, but not their lungs, synthesized HA-specific IgG upon antigenic stimulation in vitro; neither synthesized IgA. These in vitro cell culture results, as well as the inverse relationship of IgA/IgG ratios in lung lavage fluids and sera, demonstrated that the IgA antibody in lung lavage fluids was actively synthesized locally in the lungs of intragastrically immunized mice. This finding was consistent with the migratory distribution of antigen-primed lymphoid cells from Peyer's patches to distant lymphoid tissue such as lung. Intragastric vaccination conferred protection against intranasal challenge with a lethal dose of virulent virus.

Age-dependent antibody response in mice and humans following oral influenza immunization

In order to compare the antibody response in serum and secretions from healthy young subjects and the elderly (greater than 60 years), volunteers were immunized with the commercial inactivated influenza virus vaccine, by the usual (parenteral) route or orally. Also, young and old mice (mean age, 20 months) were orally immunized with live influenza virus. The older mice responded with a very slight rise in their serum and respiratory tract antibody levels compared with the young mice but showed no diminution in protection against lethal viral challenge. Elderly volunteers showed only slight serum antibody responses after parenteral immunization compared with the young. Neither group demonstrated a rise in serum antibody following oral immunization. With respect to the secretory IgA (SIgA) antibody response, certain differences were noted between the young and the elderly: the preimmunization levels of antibody to influenza virus were significantly greater in nasal secretions and saliva in the elderly as compared to the young volunteers, and the salivary antibody response was diminished in the elderly. This lack of a salivary antibody response in the elderly was explicable by the inverse relationship between the preimmunization SIgA antibody titers and the response to immunization. Oral immunization led to no more side effects than observed in the placebo control group.

Protective effects of nasal immunization in mice with various kinds of inactivated Sendai virus vaccines

The immunoprophylactic effects of nasal vaccination with 13 different kinds of inactivated Sendai virus vaccines were compared by contact exposure to infector mice. Efficacies of the vaccines were evaluated on the basis of the presence of virus-infected cells by immunofluorescent examination of the entire respiratory tract, including the nasal mucosa. A single or double inoculations of B-propiolactone (0.5%)-vaccine promoted the infection in the respiratory tract, particularly in the nasal mucosa, whereas three inoculations of B-propiolactone (0.2%)-vaccine provided considerable protection throughout the respiratory tract with only slight development of serum HI titer. Formalin (0.1%)-vaccine and UV irradiated-vaccine strongly protected the nasal mucosa from infection, but did not sufficiently safeguard the lower respiratory tract even with three vaccinations despite adequate development of serum antibody. Nearly complete protection of the entire respiratory tract was induced with six to eight inoculations of a vaccine treated excessively with both UV rays and 1% formalin, without significant development of serum antibody. Out of eight thermal vaccines, five (inactivated at 23 C, 30 C, 37 C and 7 C, and 30 C and 7 C) provided strong protection against infection when inoculated three times. The others inactivated at higher temperatures (37 C, 50 C, or 60 C) were not so protective. High serum HI titers developed, on the whole, with the drop in the temperature required for inactivating the virus. In eight immune mouse groups in which infection was strongly suppressed in the entire respiratory tract, most of the mice harbored less than 50 viral antigen-positive cells in their nasal mucosa in the postexposure period. The number of the cells was assumed to be a useful criterion for evaluation of vaccine efficacy.

Comparison of long-term systemic and secretory antibody responses in children given live, attenuated, or inactivated influenza A vaccine

A comparison of inactivated intramuscular and live intranasal influenza A vaccines in young children undergoing primary immunization might be expected to show differences in serum and local mucosal antibody responses. To demonstrate such differences, serum and local respiratory tract antibody responses of young children vaccinated with intranasal live, attenuated, cold-adapted (H3N2 or H1N1), or intramuscular inactivated (H3N2) influenza A vaccines were examined for one year after vaccination. Antibody responses were measured by hemagglutination-inhibition (HAI) and class-specific enzyme-linked immunosorbent assay (ELISA). One year after vaccination, live intranasal vaccinees had significantly less decay of serum HAI (p = 0.025) and IgG antibody (p = 0.01) directed against the influenza hemagglutinin and neuraminidase than did intramuscular inactivated vaccinees. Nasal secretory IgA developed almost exclusively in live vaccinees and persisted for up to one year. Persistent nasal secretory IgG was detected in both live and inactivated vaccinees. Live vaccination not only stimulates a more durable serum antibody response, but also induces long-lasting local respiratory tract IgA antibody that may play an important role in host protection.

A comparison of live and inactivated influenza A (H1N1) virus vaccines. 1. Short-term immunity

Groups of volunteers were immunized subcutaneously with one of three inactivated influenza virus A/USSR/77 (H1N1) vaccine preparations; a whole virus vaccine, a surface-antigen subunit adsorbed vaccine, or an aqueous surface-antigen subunit vaccine. The reactions to immunization were recorded, and the antibody response was measured 1 month later. A fourth group of volunteers were inoculated intranasally with live attentuated A/USSR/77 (H1N1) influenza virus; the reactions and antibody response of these volunteers were also measured. One month after immunization, the incidence of infection by challenge with homologous live attentuated virus was determined for all groups of volunteers. The results showed that all four vaccines used were relatively non-reactogenic, and that inactivated vaccines induced higher titres of serum antibody than the live attenuated vaccine. All the vaccines induced significant protection against challenge virus infection which was directly related to the level of serum HI antibody response.

A comparison of live and inactivated influenza A (H1N1) virus vaccines. 2. Long-term immunity

Groups of volunteers were immunized with one of three influenza virus vaccines, and the resistance to challenge infection with attenuated influenza A (H1N1) virus was measured 8 months later. The vaccines were aqueous subunit influenza A/USSR/77 (H1N1) vaccine, aqueous subunit influenza B/Hong Kong/73 vaccine, or attenuated influenza virus A (H1N1) vaccine. The B virus vaccine was included as a control to assess the incidence of natural A virus infection during the study period. A proportion of the B virus vaccinees had pre-existing A (H1N1) virus antibody and were used to study the immunity conferred by natural infection to the live virus challenge. The serum antibody responses were measured at 1 and 8 months after immunization. The results showed that all the vaccines induced serum HI antibody in a proportion of the volunteers; however, after 1 month, higher titres of serum antibody were found in volunteers given inactivated A vaccine than in those given live attenuated A virus vaccine. Eight months post-immunization the titres of serum antibody in volunteers given inactivated vaccine had declined significantly, but there were no changes in the antibody titres of those given live virus vaccine. The incidence of infection by the challenge virus at 8 months post-immunization was directly related to the serum antibody titres 1 month post-immunization; no evidence was obtained to suggest that those given live virus vaccine had a more solid immunity than those given inactivated vaccine.

Immune responses in serum and respiratory secretions following vaccination with a live cold-recombinant (CR35) and inactivated A/USSR/77 (H1N1) influenza virus vaccine

One hundred adult volunteers were administered inactivated vaccine (20 micrograms/0.5 cc) intramuscularly (IM) or intranasally (IN), or 10(4.7) TCID50 of a live cold-adapted vaccine (CR35) IN. Microneutralization (Nt) and radioimmunoprecipitation methods were employed to measure hemagglutinin antibody responses in sera, nasal washes, and in bronchopulmonary lavage fluids. In unprimed recipients, the relative frequency of serum antibody response and magnitude of rise was highest following the IM-inactivated vaccine (100%) and lowest after IN-live vaccine (29%). However, in individuals with pre-existing antibody, the three vaccines given were comparably immunogenic. Occurrences of secretory IgA hemagglutinin antibody in nasal washings were more frequently associated with topical administration of live or inactivated vaccine, whereas, IgG hemagglutinin antibody responses occurred with equal frequency in nasal washings in all three vaccine groups. Analysis of the hemagglutinin antibody responses in the lower respiratory tract showed that the IN-live vaccine favored the induction of secretory IgA hemagglutinin antibody and the IM-inactivated vaccine stimulated a more frequent IgG hemagglutinin antibody response.

Nasal secretory IgA circadian rhythm: a single-dose suppression test

The existence of a clear circadian rhythm in the local secretion of nasal IgA is well-known phenomenon which is confirmed in the present research. Since the temporal pattern of secretory IgA (SIgA) strictly parallels the ACTH-cortisol cycle, a dependence was hypothesized in previous research, but the suppression of adrenal rhythm by means of massive doses of exogenous corticosteroids showed no influence on the SIgA cycle. In the present research a more sophisticated method of corticoid-incretion suppression was used; the single-dose suppression test with dexamethasone, which influences only the impulsive phase of the rhythm. In this case too, however, no influence was demonstrated on nasal SIgA secretion.

Modulation of the lung local immune response by systemic immunization

The present study describes the respiratory immune response of mice to locally administered antigen, and the modulation of this response by systemic immunization. Intranasal immunization of mice with the A/PR/8/34 strain of influenza virus evoked local antibody response of the IgA type. The titer of the IgA antibodies declined to a nondetectable level in 40--50 days. If at that time a second intranasal dose was administered, a secondary IgA response was evoked. On the other hand, administration by the intramuscular route resulted in a mixed population of IgA and IgG antibodies. The relevance of this finding to problems of immunization against respiratory viral infections is discussed.

Immunoglobulins and their relative neutralizing efficiency in cattle immunized with infectious bovine rhinotracheitis--parainfluenza-3 (IBR-PI-3) virus vaccine

The localization of anti-IBR and anti-PI-3 activity in the serum and nasal secretory immunoglobulins following intranasal immunization of cattle with a mixed vaccine (IBR-PI-3, MLV, TCO) was studied and was found to reside in the nasal secretory IgA, serum IgM and IgG fractions. The computation of their relative virus neutralizing efficiencies from kinetic data revealed their order of neutralizing efficiencies to be IgM greater than IgA greather than IgG.

Humoral and secretory antibody responses to immunization with low and high dosage split influenza virus vaccine

Tri (n-butyl) phosphate (TNBP)-split vaccine containing 6400 CCA units of influenza virus A/Aichi/68 (H3N2) was given intramuscularly to a group of volunteers. The changes in serum haemagglutination-inhibiting (HI) and nasal wash neutralizing antibody were measured, and the results compared with that of volunteers given a TNBP-split vaccine containing 400 CCA of the same virus. More volunteers given the high-dose vaccine developed a fourfold rise in serum HI antibody, and there was a greater increase in geometric mean titre in this group. In addition, more volunteers given the high-dose vaccine developed detectable nasal wash neutralizing and anti-neuraminidase antibodies. Following low-dose vaccine, the production of nasal wash antibody was not related to the serum antibody response. For both groups given vaccine, antibody was detected most frequently in nasal washings with relatively high levels of protein and IgA; the concentration of IgA was also directly related to the protein concentration.

Immunity following intranasal administration of an inactivated, freeze-dried A/England/42/72 vaccine

A group of 23 student volunteers were each inoculated intranasally with 400 IU of inactivated, freeze-dried A/England/42/72 vaccine. Only one volunteer showed a four-fold rise in serum HI antibody following immunization, and the mean increase in serum HI antibody (gmt) for all volunteers did not increase two-fold. Thirteen of the volunteers developed detectable levels of nasal wash neutralizing antibody after immunization; local antibody was most commonly found in volunteers who produced a detectable but less than four-fold fise in serum antibody titre, and who produced nasal washings with relatively high concentrations of protein and secretory IgA. Four weeks after immunization, the vaccinees and a matched group of control subjects were inoculated with attenuated A/England/42/72 (MRC-7) virus. Evidence of infection was found in 14 of 23 (61 per cent) of control subjects and in seven of 23 (30 per cent) of immunized volunteers. This result showed a significant protection (P = 0.04) against challenge virus infection for volunteers given intranasal vaccine.

Neutralizing antibody response in bovine serum and nasal and salivary secretions after immunization with live or inactivated food-and-mouth disease virus

Calves develop nasal and salivary neutralizing antibodies against foot-and-mouth disease virus after nasal inoculation with live virus. Nasal and salivary antibody was not detected after exposure to inactive virus. Serum antibodies were induced by live and inactive virus given subcutaneously. Passively acquired antibodies were detected as long as 7 months after birth.