Protective immunity in macaques vaccinated with live attenuated, recombinant, and subunit measles vaccines in the presence of passively acquired antibodies

Sex and prior exposure jointly shape innate immune responses to a live herpesvirus vaccine

Background

Both sex and prior exposure to pathogens are known to influence responses to immune challenges, but their combined effects are not well established in humans, particularly in early innate responses critical for shaping subsequent outcomes.

Methods

We employed systems immunology approaches to study responses to a replication-defective, herpes simplex virus (HSV) 2 vaccine in men and women either naive or previously exposed to HSV.

Results

Blood transcriptomic and cell population profiling showed substantial changes on day 1 after vaccination, but the responses depended on sex and whether the vaccinee was naive or previously exposed to HSV. The magnitude of early transcriptional responses was greatest in HSV naive women where type I interferon (IFN) signatures were prominent and associated negatively with vaccine-induced neutralizing antibody titers, suggesting that a strong early antiviral response reduced the uptake of this replication-defective virus vaccine. While HSV seronegative vaccine recipients had upregulation of gene sets in type I IFN (IFN-α/β) responses, HSV2 seropositive vaccine recipients tended to have responses focused more on type II IFN (IFN-γ) genes.

Conclusions

These results together show that prior exposure and sex interact to shape early innate responses that then impact subsequent adaptive immune phenotypes.

Funding

Intramural Research Program of the NIH, the National Institute of Allergy and Infectious Diseases, and other institutes supporting the Trans-NIH Center for Human Immunology, Autoimmunity, and Inflammation. The vaccine trial was supported through a clinical trial agreement between the National Institute of Allergy and Infectious Diseases and Sanofi Pasteur. Clinical trial number: NCT01915212.

SARS-CoV-2-specicific humoral immunity in convalescent patients with mild COVID-19 is supported by CD4+ T-cell help and negatively correlated with Alphacoronavirus-specific antibody titer

This study aimed at investigating the nature of SARS-CoV-2-specific immunity in patients with mild COVID-19 and sought to identify parameters most relevant for the generation of neutralizing antibody responses in convalescent COVID-19 patients. In the majority of the examined patients a cellular as well as humoral immune response directed to SARS-CoV-2 was detected. The finding of an anti-SARS-CoV-2-reactive cellular immune response in healthy individuals suggests a pre-existing immunity to various common cold HCoVs which share close homology with SARS-CoV-2. The humoral immunity to the S protein of SARS-CoV-2 detected in convalescent COVID-19 patients correlates with the presence of SARS-CoV-2-reactive CD4⁺ T cells expressing T_h1 cytokines. Remarkably, an inverse correlation of SARS-CoV-2 S protein-specific IgGs with HCoV-NL63 and HCoV-229E S1 protein-specific IgGs suggests that pre-existing immunity to Alphacoronaviruses might have had an inhibitory imprint on the immune response to SARS-CoV-2-infection in the examined patients with mild COVID-19.

A recombinant VSV-vectored vaccine rapidly protects nonhuman primates against heterologous lethal Lassa fever

Lassa virus (LASV) is recognized by the World Health Organization as one of the top five pathogens likely to cause a severe outbreak. A recent unprecedented resurgence of LASV in Nigeria caused by genetically diverse strains underscores the need for licensed medical countermeasures. Single-injection vaccines that can rapidly control outbreaks and confer long-term immunity are needed. Vaccination of cynomolgus monkeys with a recombinant vesicular stomatitis virus vector expressing the glycoprotein precursor of LASV lineage IV strain Josiah (rVSVΔG-LASV-GPC) induces fast-acting protection in monkeys challenged 3 or 7 days later with a genetically heterologous lineage II isolate of LASV from Nigeria, while nonspecifically vaccinated control animals succumb to challenge. The rVSVΔG-LASV-GPC vaccine induces rapid activation of adaptive immunity and the transcription of natural killer (NK) cell-affiliated mRNAs. This study demonstrates that rVSVΔG-LASV-GPC may provide rapid protection in humans against LASV infections in cases where immediate public-health intervention is required.

Seroprevalence of Measles Antibodies in the Population of the Olomouc Region, Czech Republic—Comparison of the Results of Four Laboratories

Objectives: Although the incidence of measles has decreased globally since the introduction of regular vaccination, its frequency has increased again in recent years. The study is focused on data from the Olomouc Region in the Czech Republic analyzed in four laboratories. The obtained results were compared with already published data. Methods: The data were provided by individual laboratories in an anonymized form—age at the time of the examination, sex, and result of test. Samples were collected between June 2018 and September 2019 and evaluated on the scale positive–borderline–negative. Results: A total of 7962 sera samples were evaluated using three different methods—two types of ELISA tests and CLIA. Positive result was issued in a total of 62.6 percent of samples, but the results of individual laboratories varied widely from 55.5 to 70.8 percent. However, the same trend with the highest levels of antibodies in people born before beginning of vaccination was observed. Conclusions: Data show significantly different results depending on the individual laboratories and the detection kits used. The underestimation of the proportion of positive results can cause problems in selecting individuals for revaccination with a live vaccine, which may fail in weakly positive individuals.

Ginseng Stem-Leaf Saponins in Combination with Selenium Promote the Immune Response in Neonatal Mice with Maternal Antibody

Neonates acquire from their mothers maternal antibody (MatAb) which results in poor immune response to vaccination. We previously demonstrated that ginseng stem-leaf saponins in combination with selenium (GSe) had adjuvant effect on the immune response to an attenuated pseudorabies virus (aPrV) vaccine. The present study was to evaluate GSe for its effect on the immune response to aPrV vaccine in neonatal mice with MatAb. Results showed that GSe had adjuvant effect on the immune response to aPrV vaccine in neonates. When GSe was co-administered with aPrV vaccine (aP-GSe), specific gB antibody, Th1 cytokines (IL-2, IL-12 and IFN-γ) and Th2 cytokines (IL-4, IL-6 and IL-10) responses were significantly increased in association with enhanced protection of vaccinated neonates against the lethal PrV challenge even though MatAb existed when compared to the neonates immunized with aPrV vaccine alone. GSe-enhanced immune response depended on its use in the primary immunization. The mechanisms underlying the adjuvant effect of GSe may be due to more innate immune related pathways activated by GSe. Transcriptome analysis of splenocytes from neonates immunized with aP-GSe, aPrV or saline solution showed that there were 3976 differentially expressed genes (DEGs) in aP-GSe group while 5959 DEGs in aPrV group when compared to the control. Gene ontology (GO) terms and Kyoto encyclopedia of genes and genomes (KEGG) pathways analysis showed that innate immune responses and cytokine productions related terms or pathways were predominantly enriched in aP-GSe group, such as “NOD-like receptor signaling pathway”, “Natural killer cell mediated cytotoxicity”, “NF-κB signaling pathway”, “cytokine-cytokine receptor interaction”, and “Th1 and Th2 cell differentiation”. Considering the potent adjuvant effect of GSe on aPrV vaccine in neonatal mice with MatAb, it deserves further investigation in piglets.

The Effects of Pre-Existing Antibodies on Live-Attenuated Viral Vaccines

Live-attenuated vaccines (LAVs) have achieved remarkable successes in controlling virus spread, as well as for other applications such as cancer immunotherapy. However, with rapid increases in international travel, globalization, geographic spread of viral vectors, and widespread use of vaccines, there is an increasing need to consider how pre-exposure to viruses which share similar antigenic regions can impact vaccine efficacy. Pre-existing antibodies, derived from either from maternal–fetal transmission, or by previous infection or vaccination, have been demonstrated to interfere with vaccine immunogenicity of measles, adenovirus, and influenza LAVs. Immune interference of LAVs can be caused by the formation of virus–antibody complexes that neutralize virus infection in antigen-presenting cells, or by the cross-linking of the B-cell receptor with the inhibitory receptor, FcγRIIB. On the other hand, pre-existing antibodies can augment flaviviral LAV efficacy such as that of dengue and yellow fever virus, especially when pre-existing antibodies are present at sub-neutralizing levels. The increased vaccine immunogenicity can be facilitated by antibody-dependent enhancement of virus infection, enhancing virus uptake in antigen-presenting cells, and robust induction of innate immune responses that promote vaccine immunogenicity. This review examines the literature on this topic and examines the circumstances where pre-existing antibodies can inhibit or enhance LAV efficacy. A better knowledge of the underlying mechanisms involved could allow us to better manage immunization in seropositive individuals and even identify possibilities that could allow us to exploit pre-existing antibodies to boost vaccine-induced responses for improved vaccine efficacy.

Humanized Mice for Live-Attenuated Vaccine Research: From Unmet Potential to New Promises

Live-attenuated vaccines (LAV) represent one of the most important medical innovations in human history. In the past three centuries, LAV have saved hundreds of millions of lives, and will continue to do so for many decades to come. Interestingly, the most successful LAVs, such as the smallpox vaccine, the measles vaccine, and the yellow fever vaccine, have been isolated and/or developed in a purely empirical manner without any understanding of the immunological mechanisms they trigger. Today, the mechanisms governing potent LAV immunogenicity and long-term induced protective immunity continue to be elusive, and therefore hamper the rational design of innovative vaccine strategies. A serious roadblock to understanding LAV-induced immunity has been the lack of suitable and cost-effective animal models that can accurately mimic human immune responses. In the last two decades, human-immune system mice (HIS mice), i.e., mice engrafted with components of the human immune system, have been instrumental in investigating the life-cycle and immune responses to multiple human-tropic pathogens. However, their use in LAV research has remained limited. Here, we discuss the strong potential of LAVs as tools to enhance our understanding of human immunity and review the past, current and future contributions of HIS mice to this endeavor.

The effect of maternal antibodies on the cellular immune response after infant vaccination: A review

During the last few decades, maternal immunization as a strategy to protect young infants from infectious diseases has been increasingly recommended, yet some issues have emerged. Studies have shown that for several vaccines, such as live attenuated, toxoid and conjugated vaccines, high maternal antibody titers inhibit the infant's humoral immune response after infant vaccination. However, it is not clear whether this decreased antibody titer has any clinical impact on the infant's protection, as the cellular immune responses are often equally important in providing disease protection and may therefore compensate for diminished antibody levels. Reports describing the effect of maternal antibodies on the cellular immune response after infant vaccination are scarce, probably because such studies are expensive, labor intensive and utilize poorly standardized laboratory techniques. Therefore, this review aims to shed light on what is currently known about the cellular immune responses after infant vaccination in the presence of high (maternal) antibody titers both in animal and human studies. Overall, the findings suggest that maternally derived antibodies do not interfere with the cellular immune responses after infant vaccination. However, more research in humans is clearly needed, as most data originate from animal studies.

Vaccination Guidelines for Patients With Immune-Mediated Disorders on Immunosuppressive Therapies

BACKGROUND:

Patients with immune-mediated diseases on immunosuppressive therapies have more infectious episodes than healthy individuals, yet vaccination practices by physicians for this patient population remain suboptimal.

OBJECTIVES:

To evaluate the safety and efficacy of vaccines in individuals exposed to immunosuppressive therapies and provide evidence-based clinical practice recommendations.

METHODS:

A literature search for vaccination safety and efficacy in patients on immunosuppressive therapies (2009-2017) was conducted. Results were assessed using the Grading of Recommendation, Assessment, Development, and Evaluation system.

RESULTS:

Several immunosuppressive therapies attenuate vaccine response. Thus, vaccines should be administered before treatment whenever feasible. Inactivated vaccines can be administered without treatment discontinuation. Similarly, evidence suggests that the live zoster vaccine is safe and effective while on select immunosuppressive therapy, although use of the subunit vaccine is preferred. Caution regarding other live vaccines is warranted. Drug pharmacokinetics, duration of vaccine-induced viremia, and immune response kinetics should be considered to determine appropriate timing of vaccination and treatment (re)initiation. Infants exposed to immunosuppressive therapies through breastmilk can usually be immunized according to local guidelines. Intrauterine exposure to immunosuppressive agents is not a contraindication for inactivated vaccines. Live attenuated vaccines scheduled for infants and children ⩾12 months of age, including measles, mumps, rubella, and varicella, can be safely administered as sufficient time has elapsed for drug clearance.

CONCLUSIONS:

Immunosuppressive agents may attenuate vaccine responses, but protective benefit is generally maintained. While these recommendations are evidence based, they do not replace clinical judgment, and decisions regarding vaccination must carefully assess the risks, benefits, and circumstances of individual patients.

Beyond vaccine dosage, genetic modifications to the current measles vaccine to overcome maternal passive immunity

Pediatric measles infections still cause an unacceptable rate of childhood mortality. Despite the availability of an efficient preventative vaccine, measles virus can spread among the population of even developed countries. The availability of a reverse genetic system for measles, based on recombinant virus recovery from cDNA, allows application of the principles of intelligent vaccine design. Using this system, we recently demonstrated that a version of the current attenuated measles virus strain genetically modified to express higher levels of the viral hemagglutinin protein, the major target of neutralizing antibodies, is more immunogenic and resists passive immunity with a better immunogenicity profile in a mouse model than the current measles vaccine. The significance and practicality of this development are discussed.

Needle-free delivery of measles virus vaccine to the lower respiratory tract of non-human primates elicits optimal immunity and protection

Needle-free measles virus vaccination by aerosol inhalation has many potential benefits. The current standard route of vaccination is subcutaneous injection, whereas measles virus is an airborne pathogen. However, the target cells that support replication of live-attenuated measles virus vaccines in the respiratory tract are largely unknown. The aims of this study were to assess the in vivo tropism of live-attenuated measles virus and determine whether respiratory measles virus vaccination should target the upper or lower respiratory tract. Four groups of twelve cynomolgus macaques were immunized with 10⁴ TCID₅₀ of recombinant measles virus vaccine strain Edmonston-Zagreb expressing enhanced green fluorescent protein. The vaccine virus was grown in MRC-5 cells and formulated with identical stabilizers and excipients as used in the commercial MV^EZ vaccine produced by the Serum Institute of India. Animals were immunized by hypodermic injection, intra-tracheal inoculation, intra-nasal instillation, or aerosol inhalation. In each group six animals were euthanized at early time points post-vaccination, whereas the other six were followed for 14 months to assess immunogenicity and protection from challenge infection with wild-type measles virus. At early time-points, enhanced green fluorescent protein-positive measles virus-infected cells were detected locally in the muscle, nasal tissues, lungs, and draining lymph nodes. Systemic vaccine virus replication and viremia were virtually absent. Infected macrophages, dendritic cells and tissue-resident lymphocytes predominated. Exclusive delivery of vaccine virus to the lower respiratory tract resulted in highest immunogenicity and protection. This study sheds light on the tropism of a live-attenuated measles virus vaccine and identifies the alveolar spaces as the optimal site for respiratory delivery of measles virus vaccine.

Maternal antibodies protect offspring from severe influenza infection and do not lead to detectable interference with subsequent offspring immunization

BACKGROUND

Various studies have shown that infants under the age of 6 months are especially vulnerable for complications due to influenza. Currently there are no vaccines licensed for use in this age group. Vaccination of pregnant women during the last trimester, recommended by the WHO as protective measure for this vulnerable female population, may provide protection of newborns at this early age. Although it has been observed that maternal vaccination can passively transfer protection, maternal antibodies could possibly also interfere with subsequent active vaccination of the offspring.

METHODS

Using a mouse model, we evaluated in depth the ability of maternal influenza vaccination to protect offspring and the effect of maternal immunization on the subsequent influenza vaccination of the offspring. By varying the regimen of maternal immunization we explored the impact of different levels of maternal antibodies on the longevity of these antibodies in their progeny. We subsequently assessed to what extent maternal antibodies can mediate direct protection against influenza in their offspring, and whether these antibodies interfere with protection induced by active vaccination of the offspring.

RESULTS

The number of immunizations of pregnant mice correlates to the level and longevity of maternal antibodies in the offspring. When these antibodies are present at time of influenza challenge they protect offspring against lethal influenza challenge, even in the absence of detectable HAI titers. Moreover, no detectable interference of passively-transferred maternal antibodies on the subsequent vaccination of the offspring was observed.

CONCLUSION

In the absence of a licensed influenza vaccine for young children, vaccination of pregnant women is a promising measure to provide protection of young infants against severe influenza infection.

Antigenic Drift Defines a New D4 Subgenotype of Measles Virus

The measles virus hemagglutinin (MeV-H) protein is the main target of protective neutralizing antibodies. Using a panel of monoclonal antibodies (MAbs) that recognize known major antigenic sites in MeV-H, we identified a D4 genotype variant that escapes neutralization by MAbs targeting the neutralizing epitope (NE) antigenic site. By site-directed mutagenesis, L249P was identified as the critical mutation disrupting the NE in this genotype D4 variant. Forty-two available D4 genotype gene sequences were subsequently analyzed and divided into 2 groups according to the presence or absence of the L249P MeV-H mutation. Further analysis of the MeV-N gene sequences of these 2 groups confirmed that they represent clearly definable, sequence-divergent D4 subgenotypes, which we named subgenotypes D4.1 and D4.2. The subgenotype D4.1 MeVs were isolated predominantly in Kenya and Ethiopia, whereas the MAb-resistant subgenotype D4.2 MeVs were isolated predominantly in France and Great Britain, countries with higher vaccine coverage rates. Interestingly, D4.2 subgenotype viruses showed a trend toward diminished susceptibility to neutralization by human sera pooled from approximately 60 to 80 North American donors. Escape from MAb neutralization may be a powerful epidemiological surveillance tool to monitor the evolution of new MeV subgenotypes.IMPORTANCE Measles virus is a paradigmatic RNA virus, as the antigenic composition of the vaccination has not needed to be updated since its discovery. The vaccine confers protection by inducing neutralizing antibodies that interfere with the function of the hemagglutinin protein. Viral strains are indistinguishable serologically, although characteristic nucleotide sequences differentiate 24 genotypes. In this work, we describe a distant evolutionary branch within genotype D4. Designated subgenotype D4.2, this virus is distinguishable by neutralization with vaccine-induced monoclonal antibodies that target the neutralizing epitope (NE). The subgenotype D4.2 viruses have a higher predominance in countries with intermediary levels of vaccine coverage. Our studies demonstrate that subgenotype D4.2 lacks epitopes associated with half of the known antigenic sites, which significantly impacts our understanding of measles virus evolution.

Maternal antibody decay and antibody-mediated immune responses in chicken pullets fed prebiotics and synbiotics

Three experiments were conducted to evaluate the effect of yeast-derived carbohydrates (YDC), and a blend of probiotics and YDC (synbiotic, SNB) on serum IgG concentration, maternal-derived antibody (MDA) decay, and specific antibody-mediated immune response in chick pullets following immunization with T-cell dependent antigens. A total of 300 day-old pullet chicks were randomly assigned to 3 dietary treatments including: a basal diet (Control), and diets containing YDC, and SNB (Lactobacillus acidophilus, L. casei, Streptococcus faecium, and Bacillus subtilis, and YDC). In experiment one, on d 1 and wk 3, 4, 5, and 6, blood samples were collected and serum were analyzed by ELISA for total IgG (Y), and MDA against Newcastle disease virus (NDV) and infectious bursal disease virus (IBDV). The second experiment examined the specific antibody against infectious bronchitis virus (IBV) in pullet chicks following vaccination against IBV at d 1. Finally, in experiment 3, on d 21 and 28 posthatch, 10 birds per treatment were immunized intramuscularly with both sheep red blood cells (SRBC) and bovine serum albumin (BSA), and 11 after immunization serum samples were analyzed by hemagglutination assay for antibody response to SRBC, and by ELISA for serum IgM and IgG response to BSA. The results demonstrated that diet containing SNB increased serum IgG at wk 3 posthatch. However, the decay rate of MDA against NDV and IBDV were not affected by dietary treatments. Birds fed YDC showed higher specific antibody response against IBV in wk 4, while both diets containing YDC and SNB decreased antibody response to IBV in wk 6. In addition, specific antibody response against SRBC and BSA was not affected by diets. In conclusion, supplementation of diet with SNB improved humoral immunity by increasing IgG concentration in serum, and modulated the adaptive antibody-mediated immune response against IBV.

Generation of a More Immunogenic Measles Vaccine by Increasing Its Hemagglutinin Expression

Imported measles virus (MV) outbreaks are maintained by poor vaccine responders and unvaccinated people. A convenient but more immunogenic vaccination strategy would enhance vaccine performance, contributing to measles eradication efforts. We report here the generation of alternative pediatric vaccines against MV with increased expression of the H protein in the background of the current MV vaccine strain. We generated two recombinants: MVvac2-H2, with increased full-length H expression resulting in a 3-fold increase in H incorporation into virions, and MVvac2-Hsol, vectoring a truncated, soluble form of the H protein that is secreted into the supernatants of infected cells. Replication fitness was conserved despite the duplication of the H cistron for both vectors. The modification to the envelope of MVvac2-H2 conferred upon this virus a measurable level of resistance to in vitro neutralization by MV polyclonal immune sera without altering its thermostability. Most interestingly, both recombinant MVs with enhanced H expression were significantly more immunogenic than their parental strain in outbred mice, while MVvac2-H2 additionally proved more immunogenic after a single, human-range dose in genetically modified MV-susceptible mice.

IMPORTANCE

Measles incidence was reduced drastically following the introduction of attenuated vaccines, but progress toward the eradication of this virus has stalled, and MV still threatens unvaccinated populations. Due to the contributions of primary vaccine failures and too-young-to-be-vaccinated infants to this problem, more immunogenic measles vaccines are highly desirable. We generated two experimental MV vaccines based on a current vaccine's genome but with enriched production of the H protein, the main MV antigen in provoking immunity. One vaccine incorporated H at higher rates in the viral envelope, and the other secreted a soluble H protein from infected cells. The increased expression of H by these vectors improved neutralizing responses induced in two small-animal models of MV immunogenicity. The enhanced immunogenicity of these vectors, mainly from the MV that incorporates additional H, suggests their value as potential alternative pediatric MV vaccines.

Nonfebrile seizures after mumps, measles, rubella, and varicella-zoster virus combination vaccination with detection of measles virus RNA in serum, throat, and urine

We report the case of a child presenting with nonfebrile seizures 6 and 13 days after the first vaccination with a measles, mumps, rubella, and varicella (MMRV) combination vaccine. Measles virus RNA was detected in the patient's serum, throat, and urine. Genotyping revealed the Schwarz vaccine virus strain.

Vaxfectin adjuvant improves antibody responses of juvenile rhesus macaques to a DNA vaccine encoding the measles virus hemagglutinin and fusion proteins

DNA vaccines formulated with the cationic lipid-based adjuvant Vaxfectin induce protective immunity in macaques after intradermal (i.d.) or intramuscular (i.m.) delivery of 0.5 to 1 mg of codon-optimized DNA encoding the hemagglutinin (H) and fusion (F) proteins of measles virus (MeV). To characterize the effect of Vaxfectin at lower doses of H+F DNA, rhesus macaques were vaccinated twice with 20 μg of DNA plus Vaxfectin i.d., 100 μg of DNA plus Vaxfectin i.d., 100 μg of DNA plus Vaxfectin i.m. or 100 μg of DNA plus phosphate-buffered saline (PBS) i.m. using a needleless Biojector device. The levels of neutralizing (P = 0.036) and binding (P = 0.0001) antibodies were higher after 20 or 100 μg of DNA plus Vaxfectin than after 100 μg of DNA plus PBS. Gamma interferon (IFN-γ)-producing T cells were induced more rapidly than antibody, but were not improved with Vaxfectin. At 18 months after vaccination, monkeys were challenged with wild-type MeV. None developed rash or viremia, but all showed evidence of infection. Antibody levels increased, and IFN-γ- and interleukin-17-producing T cells, including cells specific for the nucleoprotein absent from the vaccine, were induced. At 3 months after challenge, MeV RNA was detected in the leukocytes of two monkeys. The levels of antibody peaked 2 to 4 weeks after challenge and then declined in vaccinated animals reflecting low numbers of bone marrow-resident plasma cells. Therefore, Vaxfectin was dose sparing and substantially improved the antibody response to the H+F DNA vaccine. This immune response led to protection from disease (rash/viremia) but not from infection. Antibody responses after challenge were more transient in vaccinated animals than in an unvaccinated animal.

Measles virus transmission from dendritic cells to T cells: formation of synapse-like interfaces concentrating viral and cellular components

Transmission of measles virus (MV) to T cells by its early CD150(+) target cells is considered to be crucial for viral dissemination within the hematopoietic compartment. Using cocultures involving monocyte-derived dendritic cells (DCs) and T cells, we now show that T cells acquire MV most efficiently from cis-infected DCs rather than DCs having trapped MV (trans-infection). Transmission involves interactions of the viral glycoprotein H with its receptor CD150 and is therefore more efficient to preactivated T cells. In addition to rare association with actin-rich filopodial structures, the formation of contact interfaces consistent with that of virological synapses (VS) was observed where viral proteins accumulated and CD150 was redistributed in an actin-dependent manner. In addition to these molecules, activated LFA-1, DC-SIGN, CD81, and phosphorylated ezrin-radixin-moesin proteins, which also mark the HIV VS, redistributed toward the MV VS. Most interestingly, moesin and substance P receptor, both implicated earlier in assisting MV entry or cell-to-cell transmission, also partitioned to the transmission structure. Altogether, the MV VS shares important similarities to the HIV VS in concentrating cellular components potentially regulating actin dynamics, conjugate stability, and membrane fusion as required for efficient entry of MV into target T cells.

The recombinant globular head domain of the measles virus hemagglutinin protein as a subunit vaccine against measles

Despite the availability of live attenuated measles virus (MV) vaccines, a large number of measles-associated deaths occur among infants in developing countries. The development of a measles subunit vaccine may circumvent the limitations associated with the current live attenuated vaccines and eventually contribute to global measles eradication. Therefore, the goal of this study was to test the feasibility of producing the recombinant globular head domain of the MV hemagglutinin (H) protein by stably transfected human cells and to examine the ability of this recombinant protein to elicit MV-specific immune responses. The recombinant protein was purified from the culture supernatant of stably transfected HEK293T cells secreting a tagged version of the protein. Two subcutaneous immunizations with the purified recombinant protein alone resulted in the production of MV-specific serum IgG and neutralizing antibodies in mice. Formulation of the protein with adjuvants (polyphosphazene or alum) further enhanced the humoral immune response and in addition resulted in the induction of cell-mediated immunity as measured by the production of MV H-specific interferon gamma (IFN-γ) and interleukin 5 (IL-5) by in vitro re-stimulated splenocytes. Furthermore, the inclusion of polyphosphazene into the vaccine formulation induced a mixed Th1/Th2-type immune response. In addition, the purified recombinant protein retained its immunogenicity even after storage at 37°C for 2 weeks.

A chimeric alphavirus replicon particle vaccine expressing the hemagglutinin and fusion proteins protects juvenile and infant rhesus macaques from measles

Measles remains a major cause of child mortality, in part due to an inability to vaccinate young infants with the current live attenuated virus vaccine (LAV). To explore new approaches to infant vaccination, chimeric Venezuelan equine encephalitis/Sindbis virus (VEE/SIN) replicon particles were used to express the hemagglutinin (H) and fusion (F) proteins of measles virus (MV). Juvenile rhesus macaques vaccinated intradermally with a single dose of VEE/SIN expressing H or H and F proteins (VEE/SIN-H or VEE/SIN-H+F, respectively) developed high titers of MV-specific neutralizing antibody and gamma-interferon (IFN-gamma)-producing T cells. Infant macaques vaccinated with two doses of VEE/SIN-H+F also developed neutralizing antibody and IFN-gamma-producing T cells. Control animals were vaccinated with LAV or with a formalin-inactivated measles vaccine (FIMV). Neutralizing antibody remained above the protective level for more than 1 year after vaccination with VEE/SIN-H, VEE/SIN-H+F, or LAV. When challenged with wild-type MV 12 to 17 months after vaccination, all vaccinated juvenile and infant monkeys vaccinated with VEE/SIN-H, VEE/SIN-H+F, and LAV were protected from rash and viremia, while FIMV-vaccinated monkeys were not. Antibody was boosted by challenge in all groups. T-cell responses to challenge were biphasic, with peaks at 7 to 25 days and at 90 to 110 days in all groups, except for the LAV group. Recrudescent T-cell activity coincided with the presence of MV RNA in peripheral blood mononuclear cells. We conclude that VEE/SIN expressing H or H and F induces durable immune responses that protect from measles and offers a promising new approach for measles vaccination. The viral and immunological factors associated with long-term control of MV replication require further investigation.

In vivo tropism of attenuated and pathogenic measles virus expressing green fluorescent protein in macaques

The global increase in measles vaccination has resulted in a significant reduction of measles mortality. The standard route of administration for the live-attenuated measles virus (MV) vaccine is subcutaneous injection, although alternative needle-free routes, including aerosol delivery, are under investigation. In vitro, attenuated MV has a much wider tropism than clinical isolates, as it can use both CD46 and CD150 as cellular receptors. To compare the in vivo tropism of attenuated and pathogenic MV, we infected cynomolgus macaques with pathogenic or attenuated recombinant MV expressing enhanced green fluorescent protein (GFP) (strains IC323 and Edmonston, respectively) via the intratracheal or aerosol route. Surprisingly, viral loads and cellular tropism in the lungs were similar for the two viruses regardless of the route of administration, and CD11c-positive cells were identified as the major target population. However, only the pathogenic MV caused significant viremia, which resulted in massive virus replication in B and T lymphocytes in lymphoid tissues and viral dissemination to the skin and the submucosa of respiratory epithelia. Attenuated MV was rarely detected in lymphoid tissues, and when it was, only in isolated infected cells. Following aerosol inhalation, attenuated MV was detected at early time points in the upper respiratory tract, suggesting local virus replication. This contrasts with pathogenic MV, which invaded the upper respiratory tract only after the onset of viremia. This study shows that despite in vitro differences, attenuated and pathogenic MV show highly similar in vivo tropism in the lungs. However, systemic spread of attenuated MV is restricted.

Current animal models: cotton rat animal model

The cotton rat (Sigmodon hispidus) model has proven to be a suitable small animal model for measles virus pathogenesis to fill the niche between tissue culture and studies in macaques. Similar to mice, inbred cotton rats are available in a microbiologically defined quality with an ever-increasing arsenal of reagents and methods available for the study of infectious diseases. Cotton rats replicate measles virus in the respiratory tract and (depending on virus strain) in lymphoid organs. They can be infected with vaccine, wild-type, and recombinant measles viruses and have been used to study viruses with genetic modifications. Other areas of study include efficacy testing of antivirals and vaccines. The cotton rat also has been an informative animal model to investigate measles virus-induced immune suppression and suppression of vaccination by maternal antibodies. In addition, the cotton rat promises to be a useful model for the study of polymicrobial disease (interaction between measles virus and secondary pathogens).

Measles studies in the macaque model

Much of our current understanding of measles has come from experiments in non-human primates. In 1911, Goldberger and Anderson showed that macaques inoculated with filtered secretions from measles patients developed measles, thus demonstrating that the causative agent of this disease was a virus. Since then, different monkey species have been used for experimental measles virus infections. Moreover, infection studies in macaques demonstrated that serial passage of the virus in vivo and in vitro resulted in virus attenuation, providing the basis for all current live-attenuated measles vaccines. This chapter will review the macaque model for measles, with a focus on vaccination and immunopathogenesis studies conducted over the last 15 years. In addition, recent data are highlighted demonstrating that the application of a recombinant measles virus strain expressing enhanced green fluorescent protein dramatically increased the sensitivity of virus detection, both in living and sacrificed animals, allowing new approaches to old questions on measles vaccination and pathogenesis.

Measles: old vaccines, new vaccines

Isolation of measles virus in tissue culture by Enders and colleagues in the 1960s led to the development of the first measles vaccines. An inactivated vaccine provided only short-term protection and induced poor T cell responses and antibody that did not undergo affinity maturation. The response to this vaccine primed for atypical measles, a more severe form of measles, and was withdrawn. A live attenuated virus vaccine has been highly successful in protection from measles and in elimination of endemic measles virus transmission with the use of two doses. This vaccine is administered by injection between 9 and 15 months of age. Measles control would be facilitated if infants could be immunized at a younger age, if the vaccine were thermostable, and if delivery did not require a needle and syringe. To these ends, new vaccines are under development using macaques as an animal model and various combinations of the H, F, and N viral proteins. Promising studies have been reported using DNA vaccines, subunit vaccines, and virus-vectored vaccines.

Use of Vaxfectin adjuvant with DNA vaccine encoding the measles virus hemagglutinin and fusion proteins protects juvenile and infant rhesus macaques against measles virus

A measles virus vaccine for infants under 6 months of age would help control measles. DNA vaccines hold promise, but none has provided full protection from challenge. Codon-optimized plasmid DNAs encoding the measles virus hemagglutinin and fusion glycoproteins were formulated with the cationic lipid-based adjuvant Vaxfectin. In mice, antibody and gamma interferon (IFN-gamma) production were increased by two- to threefold. In macaques, juveniles vaccinated at 0 and 28 days with 500 microg of DNA intradermally or with 1 mg intramuscularly developed sustained neutralizing antibody and H- and F-specific IFN-gamma responses. Infant monkeys developed sustained neutralizing antibody and T cells secreting IFN-gamma and interleukin-4. Twelve to 15 months after vaccination, vaccinated monkeys were protected from an intratracheal challenge: viremia was undetectable by cocultivation and rashes did not appear, while two naïve monkeys developed viremia and rashes. The use of Vaxfectin-formulated DNA is a promising approach to the development of a measles vaccine for young infants.

Immune responses to mumps vaccine in adults who were vaccinated in childhood

BACKGROUND

In a mumps outbreak in the United States, many infected individuals were adults who had received 2 doses of mumps vaccine. The persistence of cellular immunity to mumps vaccine has not been defined.

METHODS

This was an observational, nonrandomized cohort study evaluating cell-mediated and humoral immunity to mumps in 10 vaccinated and 10 naturally immune adults. Mumps-specific T cell activation and interferon (IFN)-gamma production were measured using lymphoproliferative and flow cytometry assays, and mumps immunoglobulin (Ig) G was measured using enzyme-linked immunosorbent assay.

RESULTS

T cell immunity to mumps was high in both groups; 70% of vaccinated and 80% of naturally immune individuals had a positive (> or =3) stimulation index (SI) (P = 1.0). The mean percentages of mumps-specific CD4+ T cells that expressed CD69 and produced IFN-gamma were equivalent in the 2 groups: 0.06% and 0.12%, respectively (P = .11). The mean SIs in the groups were also equivalent, although IFN-gamma concentrations from cultures stimulated with mumps antigen were higher in naturally immune adults than in vaccinated adults (P < or = .01). All adults were positive for mumps IgG.

CONCLUSION

T and B cell immunity to mumps was detected in adults at least 10 years after immunization. Except for IFN-gamma release, responses in vaccinated adults paralleled those observed in naturally immune individuals.

Expression of biologically active measles virus hemagglutinin glycoprotein by a recombinant baculovirus

In this study, one of the measles virus membrane proteins, named hemagglutinin (H) which has a key role in tropism, receptor binding, hemagglutinating activity and also induction of protective immunity against viral infection, was expressed by the baculovirus expression system using specific plasmid (pDONR221) to produce entry clone. Measles Virus (AIK-C strain) genome was extracted from infected Vero cells. H gene was amplified by specific primers during RT-PCR reaction and inserted into the specific plasmid (pDONR221) using BP recombination reaction. Recombinant baculovirus harboring H gene was consequently constructed by LR reaction. Insect cells (Sf9) were infected with recombinant baculovirus. In order to increase viral titer, recombinant baculoviruses were passaged four times in Sf9 cells. Synthesis of H protein was verified by SDS-PAGE, western-blot and indirect immunoflourescene using goat polyclonal antibody against Measles Virus. The results showed that H protein was partially glycosylated, but it appeared to be active in hemagglutination assay.

Dose-dependent protection against or exacerbation of disease by a polylactide glycolide microparticle-adsorbed, alphavirus-based measles virus DNA vaccine in rhesus macaques

Measles remains an important cause of vaccine-preventable child mortality. Development of a low-cost, heat-stable vaccine for infants under the age of 6 months could improve measles control by facilitating delivery at the time of other vaccines and by closing a window of susceptibility prior to immunization at 9 months of age. DNA vaccines hold promise for development, but achieving protective levels of antibody has been difficult and there is an incomplete understanding of protective immunity. In the current study, we evaluated the use of a layered alphavirus DNA/RNA vector encoding measles virus H (SINCP-H) adsorbed onto polylactide glycolide (PLG) microparticles. In mice, antibody and T-cell responses to PLG-formulated DNA were substantially improved compared to those to naked DNA. Rhesus macaques received two doses of PLG/SINCP-H delivered either intramuscularly (0.5 mg) or intradermally (0.5 or 0.1 mg). Antibody and T-cell responses were induced but not sustained. On challenge, the intramuscularly vaccinated monkeys did not develop rashes and had lower viremias than vector-treated control monkeys. Monkeys vaccinated with the same dose intradermally developed rashes and viremia. Monkeys vaccinated intradermally with the low dose developed more severe rashes, with histopathologic evidence of syncytia and intense dermal and epidermal inflammation, eosinophilia, and higher viremia compared to vector-treated control monkeys. Protection after challenge correlated with gamma interferon-producing T cells and with early production of high-avidity antibody that bound wild-type H protein. We conclude that PLG/SINCP-H is most efficacious when delivered intramuscularly but does not provide an advantage over standard DNA vaccines for protection against measles.

Predominant infection of CD150+ lymphocytes and dendritic cells during measles virus infection of macaques

Measles virus (MV) is hypothesized to enter the host by infecting epithelial cells of the respiratory tract, followed by viremia mediated by infected monocytes. However, neither of these cell types express signaling lymphocyte activation molecule (CD150), which has been identified as the receptor for wild-type MV. We have infected rhesus and cynomolgus macaques with a recombinant MV strain expressing enhanced green fluorescent protein (EGFP); thus bringing together the optimal animal model for measles and a virus that can be detected with unprecedented sensitivity. Blood samples and broncho-alveolar lavages were collected every 3 d, and necropsies were performed upon euthanasia 9 or 15 d after infection. EGFP production by MV-infected cells was visualized macroscopically, in both living and sacrificed animals, and microscopically by confocal microscopy and FACS analysis. At the peak of viremia, EGFP fluorescence was detected in skin, respiratory and digestive tract, but most intensely in all lymphoid tissues. B- and T-lymphocytes expressing CD150 were the major target cells for MV infection. Highest percentages (up to 30%) of infected lymphocytes were detected in lymphoid tissues, and the virus preferentially targeted cells with a memory phenotype. Unexpectedly, circulating monocytes did not sustain productive MV infection. In peripheral tissues, large numbers of MV-infected CD11c+ MHC class-II+ myeloid dendritic cells were detected in conjunction with infected T-lymphocytes, suggesting transmission of MV between these cell types. Fluorescent imaging of MV infection in non-human primates demonstrated a crucial role for lymphocytes and dendritic cells in the pathogenesis of measles and measles-associated immunosuppression.

Concomitant administration of Yersinia pestis specific monoclonal antibodies with plague vaccine has a detrimental effect on vaccine mediated immunity

Antibodies can be used to confer rapid immunity against infectious agents for short periods of time. By comparison, vaccine induced immunity is more protective, but takes a relatively long time to develop. Concomitant administration of antibody and vaccine by different routes was evaluated as a means of providing both rapid and long-term protection against plague. BALB/c mice were treated intraperitoneally with monoclonal antibodies, with specificities for Yersinia pestis LcrV and F1 antigens. A cohort of these mice was simultaneously vaccinated with rF1 and rLcrV by the intramuscular route. Antibody co-administration with vaccine reduced the level of vaccine mediated protection afforded against a high level Y. pestis challenge. Conversely, antibody-mediated protection was unaffected by vaccine co-administration and lasted for at least 8 weeks post administration. We also evaluated the effect of administering vaccine intradermally and antibody intratracheally and observed that, irrespective of administration route, concomitant administration of antibody reduced the effectiveness of vaccine mediated immunity. The results of passive transfer experiments supported the thesis that the development of protective antibody responses following vaccination is impaired by the presence of circulating monoclonal antibodies with specificities for important B-cell epitopes in the vaccine. We also noted that intradermal injection of LcrV antigen and cholera toxin adjuvant afforded good levels of protection against systemic and aerosol challenge with Y. pestis: intradermal injection might therefore be considered as a potential minimally invasive method of plague vaccine administration. These data have implications for the design of therapeutic strategies against plague infection.

Passive transmission and persistence of naturally acquired or vaccine-induced maternal antibodies against measles in newborns

This paper reviews literature on passively transferred maternal antibodies against measles in infants. The amount and decay of these antibodies can be a result of changing patterns in society: increasing cohorts of women are vaccinated against measles instead of having naturally acquired immunity, the age of first childbirth is increasing and young adults are less exposed to natural boosters. The concentration and persistence of maternal antibodies differ in infants of women vaccinated against measles versus infants of naturally immune women. The date for commencing universal measles vaccination should take into account the presence of these antibodies since they can hamper the immunological response to vaccination. Each country should therefore consider adapting the timing of vaccination in relation to its measles sero-epidemiological situation. The possibility of priming the immune system with an early vaccine dose and boosting later on offers opportunities for vaccination at very young age.

A vectored measles virus induces hepatitis B surface antigen antibodies while protecting macaques against measles virus challenge

Hepatitis B virus (HBV) acute and chronic infections remain a major worldwide health problem. Towards developing an anti-HBV vaccine with single-dose scheme potential, we engineered infectious measles virus (MV) genomic cDNAs with a vaccine strain background and expression vector properties. Hepatitis B surface antigen (HBsAg) expression cassettes were inserted into this cDNA and three MVs expressing HBsAg at different levels generated. All vectored MVs, which secrete HBsAg as subviral particles, elicited humoral responses in MV-susceptible genetically modified mice. However, small differences in HBsAg expression elicited vastly different HBsAg antibody levels. The two vectors inducing the highest HBsAg antibody levels were inoculated into rhesus monkeys (Macaca mulatta). After challenge with a pathogenic MV strain (Davis87), control naive monkeys showed a classic measles rash and high viral loads. In contrast, all monkeys immunized with vaccine or a control nonvectored recombinant vaccine or HBsAg-expressing vectored MV remained healthy, with low or undetectable viral loads. After a single vaccine dose, only the vector expressing HBsAg at the highest levels elicited protective levels of HBsAg antibodies in two of four animals. These observations reveal an expression threshold for efficient induction of HBsAg humoral immune responses. This threshold is lower in mice than in macaques. Implications for the development of divalent vaccines based on live attenuated viruses are discussed.

Measles vaccination of macaques by dry powder inhalation

Measles vaccination via the aerosol route has proven effective under field conditions, using vaccine reconstituted prior to nebulization. Inhalation of a dry powder aerosol vaccine would have additional benefits, including easier logistics of administration, reduced cold chain dependence and the potential of single dose administration. We have evaluated two candidate dry powder measles vaccine formulations in macaques. Specific immune responses were demonstrated, but levels of immunity were lower than in animals vaccinated by injection or by nebulized aerosol. These studies provide proof of principle that dry powder inhalation is a possible route for measles vaccination, but suggest that either the vaccine formulation or the method of delivery need to be improved for a better immune response.

High titers of circulating maternal antibodies suppress effector and memory B-cell responses induced by an attenuated rotavirus priming and rotavirus-like particle-immunostimulating complex boosting vaccine regimen

We investigated maternal antibody (MatAb) effects on protection and immune responses to rotavirus vaccines. Gnotobiotic pigs were injected intraperitoneally at birth with pooled serum from sows hyperimmunized with human rotavirus (HRV); control pigs received no sow serum. Pigs with or without MatAbs received either sequential attenuated HRV (AttHRV) oral priming and intranasal boosting with VP2/VP6 virus-like particle (VLP)-immunostimulating complex (ISCOM) (AttHRV/VLP) or intranasal VLP-ISCOM prime/boost (VLP) vaccines at 3 to 5 days of age. Subsets of pigs were challenged at 28 or 42 days postinoculation with virulent Wa HRV to assess protection. Isotype-specific antibody-secreting cell (ASC) responses to HRV were quantitated by enzyme-linked immunospot assay to measure effector and memory B-cell responses in intestinal and systemic lymphoid tissues pre- and/or postchallenge. Protection rates against HRV challenge (contributed by active immunity and passive circulating MatAbs) were consistently (but not significantly) lower in the MatAb-AttHRV/VLP groups than in the corresponding groups without MatAbs. Intestinal B-cell responses in the MatAb-AttHRV/VLP group were most suppressed with significantly reduced or no intestinal immunoglobulin A (IgA) and IgG effector and memory B-cell responses or antibody titers pre- and postchallenge. This suppression was not alleviated but was enhanced after extending vaccination/challenge from 28 to 42 days. In pigs vaccinated with nonreplicating VLP alone that failed to induce protection, MatAb effects differed, with intestinal and systemic IgG ASCs and prechallenge memory B cells suppressed but the low intestinal IgA and IgM ASC responses unaffected. Thus, we demonstrate that MatAbs differentially affect both replicating and nonreplicating HRV vaccines and suggest mechanisms of MatAb interference. This information should facilitate vaccine design to overcome MatAb suppression.

Aerosol measles vaccination in macaques: preclinical studies of immune responses and safety

The comparative efficacy and safety of measles vaccination via the aerosol route versus subcutaneous injection has not been fully resolved. We vaccinated cynomolgus monkeys (Macaca fascicularis) with the live-attenuated Edmonston-Zagreb measles virus (MV) vaccine and compared different routes of administration in the immunocompetent and the immunocompromised host. Immunogenicity and protective efficacy of aerosol vaccination using devices similar to those previously used in humans were comparable to those in animals vaccinated by injection. No evidence for a safety hazard associated with the route of vaccination was detected. The results of this study support further clinical evaluation of aerosol vaccination for measles.

Protective immunity provided by HLA-A2 epitopes for fusion and hemagglutinin proteins of measles virus

Natural infection and vaccination with a live-attenuated measles virus (MV) induce CD8(+) T-cell-mediated immune responses that may play a central role in controlling MV infection. In this study, we show that newly identified human HLA-A2 epitopes from MV hemagglutinin (H) and fusion (F) proteins induced protective immunity in HLA-A2 transgenic mice challenged with recombinant vaccinia viruses expressing F or H protein. HLA-A2 epitopes were predicted and synthesized. Five and four peptides from H and F, respectively, bound to HLA-A2 molecules in a T2-binding assay, and four from H and two from F could induce peptide-specific CD8+ T cell responses in HLA-A2 transgenic mice. Further experiments proved that three peptides from H (H9-567, H10-250, and H10-516) and one from F protein (F9-57) were endogenously processed and presented on HLA-A2 molecules. All peptides tested in this study are common to 5 different strains of MV including Edmonston. In both A2K(b) and HHD-2 mice, the identified peptide epitopes induced protective immunity against recombinant vaccinia viruses expressing H or F. Because F and H proteins induce neutralizing antibodies, they are major components of new vaccine strategies, and therefore data from this study will contribute to the development of new vaccines against MV infection.

Maternal antibody inhibits both cellular and humoral immunity in response to measles vaccination at birth

Maternal antibody prevents the use of live, attenuated measles vaccine (LAV) before 6-9 months of age, but vaccinated 6-month-old infants can mount a T cell response. An infant macaque model was used to study the immune response to LAV in the newborn in the presence or absence of maternal antibody. Four newborn monkeys without detectable maternal antibody and 9 newborns with passive measles antibody were vaccinated with LAV. Only the infants without passive antibody seroconverted after vaccination and 3 of 4 of these infants also developed measles-specific interferon gamma+ T cells. The monkeys were challenged with wild-type measles virus at 5 months of age, and 7 of 9 infants vaccinated in the presence of passive antibody had systemic infection and skin rash, while 3 of the 4 infants vaccinated in the absence of passive antibody were protected from viremia and rash. This suggests that the newborn can respond to LAV but that maternal antibody suppresses the priming of both humoral and cellular immunity at birth.

Inoculation of mares and very young foals with EHV-1 glycoproteins D and B reduces virus shedding following respiratory challenge with EHV-1

We have previously demonstrated that intramuscular inoculation of EHV-1 glycoprotein D (gD) and glycoprotein B (gB) produced by a recombinant baculovirus and formulated with the adjuvant Iscomatrix elicited virus-neutralizing antibody and gD- and gB-specific ELISA antibody in adult horses. In this study, 14 mares and their very young foals were inoculated with a combination of baculovirus-expressed EHV-1 gD and EHV-1 gB (EHV-1 gDBr) and challenged with a respiratory strain of EHV-1. Following experimental challenge, inoculated mares and foals shed virus in nasal secretions on significantly fewer occasions compared to uninoculated mares and foals. Uninoculated foals born from inoculated mares were no more protected against experimental challenge than uninoculated foals born from uninoculated mares. The results suggest that it is indeed possible to induce partial protection in very young foals through vaccination, and while the inoculation did not prevent infection, it did reduce the frequency of viral shedding with the potential to thereby reduce the risk and prevalence of infection in a herd situation.

Relative contributions of measles virus hemagglutinin- and fusion protein-specific serum antibodies to virus neutralization

The relative contribution of measles virus hemagglutinin (H)- or fusion protein (F)-specific antibodies to virus neutralization (VN) has not been demonstrated. We have depleted these specific antibodies from sera collected from young adults, who had been vaccinated during childhood, by prolonged incubation with viable transfected human melanoma cells expressing H or F. Simultaneous depletion of antibodies of both specificities completely abrogated VN activity. Depletion of F-specific antibodies only had a minimal effect, whereas removal of H-specific antibodies resulted in almost complete reduction of VN activity. These results demonstrate that measles virus neutralizing antibodies are mainly directed to the H protein.

A novel intranasal Protollin-based measles vaccine induces mucosal and systemic neutralizing antibody responses and cell-mediated immunity in mice

Protollin-MV is a vaccine produced by mixing split measles virus (MV) antigen with the novel adjuvant Protollin (Neisseria meningitidis outer membrane proteins non-covalently complexed with Shigella flexneri 2a lipopolysaccharide). Intranasal immunization of mice with two or three doses of Protollin-MV induces both serum IgG and mucosal IgA with strong neutralizing activity. There is a dose-dependent shift towards lower IgG1:IgG2a ratios and MV-specific IFNgamma production in splenocytes. Intranasal Protollin-MV can therefore induce systemic and mucosal neutralizing antibody responses as well as elicit a balanced TH1/TH2-type response.

Modulation of disease, T cell responses, and measles virus clearance in monkeys vaccinated with H-encoding alphavirus replicon particles

Measles remains a major worldwide problem partly because of difficulties with vaccination of young infants. New vaccine strategies need to be safe and to provide sustained protective immunity. We have developed Sindbis virus replicon particles that express the measles virus (MV) hemagglutinin (SIN-H) or fusion (SIN-F) proteins. In mice, SIN-H induced high-titered, dose-dependent, MV-neutralizing antibody after a single vaccination. SIN-F, or SIN-H and SIN-F combined, induced somewhat lower responses. To assess protective efficacy, juvenile macaques were vaccinated with a single dose of 10(6) or 10(8) SIN-H particles and infant macaques with two doses of 10(8) particles. A dose of 10(8) particles induced sustained levels of high-titered, MV-neutralizing antibody and IFN-gamma-producing memory T cells, and most monkeys were protected from rash when challenged with wild-type MV 18 months later. After challenge, there was a biphasic appearance of H- and F-specific IFN-gamma-secreting CD4+ and CD8+ T cells in vaccinated monkeys, with peaks approximately 1 and 3-4 months after challenge. Viremia was cleared within 14 days, but MV RNA was detectable for 4-5 months. These studies suggest that complete clearance of MV after infection is a prolonged, phased, and complex process influenced by prior vaccination.

ISCOM TM ‐based vaccines: The second decade

The immunostimulating complex or 'iscom' was first described 20 years ago as an antigen delivery system with powerful immunostimulating activity. Iscoms are cage-like structures, typically 40 nm in diameter, that are comprised of antigen, cholesterol, phospholipid and saponin. ISCOM-based vaccines have been shown to promote both antibody and cellular immune responses in a variety of experimental animal models. This review focuses on the evaluation of ISCOM-based vaccines in animals over the past 10 years, as well as examining the progress that has been achieved in the development of human vaccines based on ISCOM adjuvant technology.

The development of a plant-based vaccine for measles

Plant-based vaccination strategies have the potential to overcome the limitations of the current measles vaccine. The measles virus hemagglutinin (MV-H) protein has been expressed in tobacco. Oral immunisation of mice with plant-derived MV-H protein resulted in MV-specific antibodies and secretory IgA, indicative of humoral and mucosal immune responses. In addition, boosting with oral plant-derived MV-H protein following a MV-H DNA prime, resulted in a greater response than could be induced with either vaccine alone. Collectively, this research represents a significant step towards an effective oral measles vaccine that would be temperature-stable, easy to administer and amenable to inexpensive manufacture.