Loss of maternally-acquired measles antibody during infancy in Ilorin, Nigeria

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.

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.

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.

Experimental vaccines against measles in a world of changing epidemiology

Vaccination with the current live attenuated measles vaccine is one of the most successful and cost-effective medical interventions. However, as a result of persisting maternal antibodies and immaturity of the infant immune system, this vaccine is poorly immunogenic in children <9 months old. Immunity against the live vaccine is less robust than natural immunity and protection less durable. There may also be some concern about (vaccine) virus spread during the final stage of an eventual measles eradication program. Opinions may differ with respect to the potential threat that some of these concerns may be to the World Health Organisation goal of measles elimination, but there is a consensus that the development of new measles vaccines cannot wait. Candidate vaccines are based on viral or bacterial vectors expressing recombinant viral proteins, naked DNA, immune stimulating complexes or synthetic peptides mimicking neutralising epitopes. While some of these candidate vaccines have proven their efficacy in monkey studies, aerosol formulated live attenuated measles vaccine are evaluated in clinical trials.

Placental transfer and decay of maternally acquired antimeasles antibodies in Nigerian children

BACKGROUND

In developing countries vaccination against measles virus (MV) is generally administered at 9 months of age, although it is well-documented that protection of most infants by passively acquired maternal MV antibodies is waning before immunization is given. The purpose of this study was to investigate the decay of maternally derived MV antibodies in Nigerian infants as well as to compare a German and Nigerian cohort of paired mothers and newborns regarding the placental transfer efficiency of MV-specific IgG and total IgG antibodies.

METHODS

MV-specific IgG antibodies were measured with a commercially available MV-enzyme-linked immunosorbent assay, a recombinant hemagglutinin enzyme-linked immunosorbent assay as well as a neutralization assay. Total IgG values were determined with a standard immunoturbidimetric test.

RESULTS

Anti-MV IgG titers were twice as high in German newborns as in Nigerian newborns. An increased concentration of immunoglobulins transferred via the placenta was found only in the German cohort. High concentrations of total maternal IgG reduced the concentration of MV-specific as well as total IgG that crossed the placenta. Furthermore only 17% of the 4-month-old Nigerian infants were still protected against measles. Antibodies had a biologic half-life of 33 days and a biochemical half-life of 48 days.

CONCLUSIONS

Our findings demonstrate that the decay of passively acquired MV antibodies occurred even more rapidly than expected resulting in susceptibility to MV in most of the 4-month-old infants in Nigeria. Furthermore transfer of maternal anti-MV IgG and total IgG antibodies to the newborn was more efficient in the German cohort compared with the Nigerian group. These findings suggest the use of alternative vaccination strategies in developing countries to possibly reduce the window of susceptibility against measles.

Factors determining prevalence of maternal antibody to measles virus throughout infancy: a review

The effectiveness of vaccination against measles, the leading cause of vaccine-preventable deaths in infants globally, is greatly impacted by the level of maternal antibody to measles virus (or "measles maternal antibody"; MMA) during infancy. Variation in the prevalence of maternal antibody to measles virus between infant populations across countries and sociodemographic strata is poorly understood. We reviewed the literature on the prevalence of MMA, focusing on 3 principal determinants: starting level of maternal antibody, placental transfer of maternal antibody, and rate of decay of maternal antibody after birth. Our review identified placental transfer as an important determinant, with greater efficiency found in studies performed in developed countries. Placental transfer was influenced by gestational age, human immunodeficiency virus infection, and malaria. Antibody levels in mothers varied widely between countries, although predictably according to vaccination status within populations. Rates of antibody decay across studies were similar. Future studies should evaluate the utility of the cord blood level of MMA as a predictor of vaccine efficacy in infancy; inclusion of World Health Organization international reference sera will facilitate comparisons. Greater understanding of the determinants of the prevalence of MMA will help national policy makers determine the appropriate age for measles vaccination.