Serologic response of children to in-activated measles vaccine

Successful Vaccines

Vaccines are considered one of the most important advances in modern medicine and have greatly improved our quality of life by reducing or eliminating many serious infectious diseases. Successful vaccines have been developed against many of the most common human pathogens, and this success has not been dependent upon any one specific class of vaccine since subunit vaccines, non-replicating whole-virus or whole-bacteria vaccines, and attenuated live vaccines have all been effective for particular vaccine targets. After completing the initial immunization series, one common aspect of successful vaccines is that they induce long-term protective immunity. In contrast, several partially successful vaccines appear to induce protection that is relatively short-lived and it is likely that long-term protective immunity will be critical for making effective vaccines against our most challenging diseases such as AIDS and malaria.

An orally available, small-molecule polymerase inhibitor shows efficacy against a lethal morbillivirus infection in a large animal model

Measles virus is a highly infectious morbillivirus responsible for major morbidity and mortality in unvaccinated humans. The related, zoonotic canine distemper virus (CDV) induces morbillivirus disease in ferrets with 100% lethality. We report an orally available, shelf-stable pan-morbillivirus inhibitor that targets the viral RNA polymerase. Prophylactic oral treatment of ferrets infected intranasally with a lethal CDV dose reduced viremia and prolonged survival. Ferrets infected with the same dose of virus that received post-infection treatment at the onset of viremia showed low-grade viral loads, remained asymptomatic, and recovered from infection, whereas control animals succumbed to the disease. Animals that recovered also mounted a robust immune response and were protected against rechallenge with a lethal CDV dose. Drug-resistant viral recombinants were generated and found to be attenuated and transmission-impaired compared to the genetic parent virus. These findings may pioneer a path toward an effective morbillivirus therapy that could aid measles eradication by synergizing with vaccination to close gaps in herd immunity due to vaccine refusal.

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.

Comparison of the immune responses induced by chimeric alphavirus-vectored and formalin-inactivated alum-precipitated measles vaccines in mice

A variety of vaccine platforms are under study for development of new vaccines for measles. Problems with past measles vaccines are incompletely understood and underscore the need to understand the types of immune responses induced by different types of vaccines. Detailed immune response evaluation is most easily performed in mice. Although mice are not susceptible to infection with wild type or vaccine strains of measles virus, they can be used for comparative evaluation of the immune responses to measles vaccines of other types. In this study we compared the immune responses in mice to a new protective alphavirus replicon particle vaccine expressing the measles virus hemagglutinin (VEE/SIN-H) with a non-protective formalin-inactivated, alum-precipitated measles vaccine (FI-MV). MV-specific IgG levels were similar, but VEE/SIN-H antibody was high avidity IgG2a with neutralizing activity while FI-MV antibody was low-avidity IgG1 without neutralizing activity. FI-MV antibody was primarily against the nucleoprotein with no priming to H. Germinal centers appeared, peaked and resolved later for FI-MV. Lymph node MV antibody-secreting cells were more numerous after FI-MV than VEE/SIN-H, but were similar in the bone marrow. VEE/SIN-H-induced T cells produced IFN-gamma and IL-4 both spontaneously ex vivo and after stimulation, while FI-MV-induced T cells produced IL-4 only after stimulation. In summary, VEE/SIN-H induced a balanced T cell response and high avidity neutralizing IgG2a while FI-MV induced a type 2 T cell response, abundant plasmablasts, late germinal centers and low avidity non-neutralizing IgG1 against the nucleoprotein.

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.

Atypical measles and enhanced respiratory syncytial virus disease (ERD) made simple

Atypical measles and enhanced respiratory syncytial virus disease (ERD) were serious diseases that resulted from exposure of children immunized with inactivated vaccines against measles virus (MV) and respiratory syncytial virus (RSV) to the respective wild-type agents in the 1960s. Although the clinical manifestations of both illnesses were different, the immune responses elicited and primed for by the vaccines shared important similarities. Both vaccines failed to elicit long-lived protective antibody and to promote cytotoxic T lymphocyte responses. In both cases, postvaccination exposure to wild type virus during community outbreaks was associated with immune complex deposition in affected tissues, vigorous CD4 T lymphocyte proliferative responses, and a Th2 bias of the immune response. No relapses of atypical measles or ERD were ever reported. In this manuscript, the pathogeneses of both enhanced diseases and the requirements for the generation of protective antibodies against MV and RSV are discussed, to contribute to the development of newer safe and effective vaccines against these important pathogens.

Involvement of antibody, complement and cellular immunity in the pathogenesis of enhanced respiratory syncytial virus disease

In 1966, infants and children in the USA were immunized with a formalin-inactivated vaccine against respiratory syncytial virus. The vaccine was immunogenic but elicited mainly nonprotective antibody. Upon exposure to respiratory syncytial virus in the community, immunized children developed severe pulmonary disease characterized by bronchoconstriction and pneumonia. Two immunized infants died as toddlers after respiratory syncytial virus infection. Exploration of the mechanisms of disease has dominated the literature for decades. In this review, the pathogenesis of enhanced respiratory disease is discussed and the characteristics of protective and pathogenic respiratory syncytial virus vaccines are examined.

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.

Emerging diseases: Measles

High vaccination coverage rates and the administration of a second dose of measles vaccine have resulted in a significant decline in the incidence of measles and neurologic diseases due to measles in many countries. However, intermittent outbreaks of measles still occur even in countries with excellent vaccination coverage, suggesting the existence of high rates of measles virus introduction from endemic regions and/or waning of vaccine-induced immunity. Strategies to sustain high levels of global immunity to measles virus by increasing vaccine coverage with routine and supplementary vaccination campaigns must be supported.

A role for nonprotective complement-fixing antibodies with low avidity for measles virus in atypical measles

In the 1960s, a formalin-inactivated measles vaccine (FIMV) predisposed recipients to atypical measles, an immune complex-mediated disease. To identify characteristics of the immune priming that leads to atypical measles, responses of monkeys to FIMV were compared with responses to live attenuated virus (LAV) and hemagglutinin (H-DNA) vaccines that do not prime for atypical measles. Antibodies induced by FIMV were transient and avidity did not mature. Antibodies induced by LAV and H-DNA vaccines were sustained and avidity matured over time. After challenge with measles virus, FIMV and H-DNA recipients developed high titers of complement-fixing antibodies. In FIMV recipients, the antibodies were of low avidity, whereas in H-DNA vaccine recipients, the antibodies were of high avidity. Neutralizing capacity in B958 cells correlated with avidity. Only FIMV recipients had immune complex deposition. Failure of FIMV to induce affinity maturation results in anamnestic production of nonprotective, complement-fixing antibodies, immune complex deposition and atypical measles.

Immune responses to measles and measles vaccine: challenges for measles control

Most strategies for reducing global measles morbidity and mortality and eliminating measles are based on the ability to enhance immune responses to measles virus. Challenges to measles elimination and eradication are based in part on the need to sustain high levels of population immunity to interrupt transmission of measles virus. We review aspects of the immunology of measles and measles vaccination with the aim of demonstrating how knowledge of the immune responses is essential to furthering the goals of reducing measles morbidity and mortality and the elimination of measles. Better understanding of the mechanisms of immune suppression after measles, the potential for alternative vaccination strategies to induce immunity in young infants, and the immunologic basis of atypical measles, increased mortality after high-titer measles vaccine, and waning immunity will lead to improved strategies for measles control and elimination.

Production of atypical measles in rhesus macaques: evidence for disease mediated by immune complex formation and eosinophils in the presence of fusion-inhibiting antibody

The severe disease atypical measles occurred when individuals immunized with a poorly protective inactivated vaccine contracted measles, and was postulated to be due to a lack of fusion-inhibiting antibodies. Here, rhesus macaques immunized with formalin-inactivated measles vaccine developed transient neutralizing and fusion-inhibiting antibodies, but no cytotoxic T-cell response. Subsequent infection with measles virus caused an atypical rash and pneumonitis, accompanied by immune complex deposition and an increase in eosinophils. Fusion-inhibiting antibody appeared earlier in these monkeys than in non-immunized monkeys. These data indicate that atypical measles results from previous priming for a nonprotective type 2 CD4 T-cell response rather than from lack of functional antibody against the fusion protein.

Immune responses during measles virus infection

The characteristic disease features of measles--fever and rash--are associated with the immune response to infection and are coincident with virus clearance. MV-specific antibody and CD4 and CD8 T cell responses are generated and contribute to virus clearance and protection from reinfection. During this same phase of immune activation immunologic abnormalities are also apparent. There is a generalized suppression of cellular immune responses that may contribute to increased susceptibility to other infections. Autoimmune disease may appear in the form of acute disseminated encephalomyelitis. If virus-specific immune responses are inadequate infection may progress with pulmonary or CNS manifestations, but without a rash. The pathogenesis of the rare disease SSPE, that occurs many years after primary infection is not clear, but immune responses show increased antibody to measles and cellular immune responses similar to those seen after uncomplicated infection.

[Induction of specific antibodies by measles vaccine. Study in normal and undernourished infants 6 to 24-months old]

Foi estudada a indução de anticorpos anti-sarampo em 223 crianças nutridas e desnutridas vacinadas entre 6 e 24 meses e naquelas que permaneceram soronegativas com 1 dose da vacina realizada antes dos 12 meses que foram revacinadas após os 12 meses. A determinação de anticorpos anti-sarampo foi realizada pelas técnicas de inibição da hemaglutinação e de soroneutralização. Observamos que a taxa de soroconversão aumentou progressivamente com a idade, sendo de 43% aos 6 meses e de 80% aos 15 meses. A taxa de soroconversão em crianças marasmáticas foi semelhante à obtida em crianças nutridas, concordando com a literatura que vem demonstrando que crianças desnutridas não apresentam alteração na capacidade de resposta humoral à vacina. Utilizando os dados de mortalidade por sarampo e as taxas de soroconversão à vacina, idealizou-se um modelo hipotético para a avaliação da aplicação da vacina em diferentes idades e suas conseqüências em têrmos de mortalidade, e observou-se que quando a vacina é realizada em idades precoces (6-7 meses) o número de óbito esperado é inferior ao esperado quando a vacina é realizada em idades posteriores (9-11 meses), indicando que a proposta atual do Ministério da Saúde de aplicar dose única aos 9 meses, teoricamente aumentaria o risco de mortalidade. Considerando o número de crianças protegidas com 1 dose de vacina aplicada antes dos 12 meses e o número de crianças protegidas com a revacinação a taxa de soroconversão foi de 84,3%.

Purification of measles virus H polypeptide and of F polypeptide

Measles virus was disrupted by Tween 80 and ether and subjected to isoelectric focusing in granular gel. The two surface envelope polypeptides, the one showing haemagglutinating activity (H) and the one making up the structural basis of the haemolytic and fusion activity (F) banded together at pH 5.2. The two envelope polypeptides were also isolated together after adsorption to a Lentil-lectin column. Separation of the two polypeptides was performed by gel filtration on Sephadex G-150 in the presence of 8 M urea. After separation both the H and F polypeptides fixed to the lectin column. It was demonstrated that the column, after having fixed the two polypeptides, absorbed anti-H and anti-F antibodies from a rabbit anti-measles virus immune serum. Thus the antigenic reactivity of the isolated surface polypeptides remained intact.

Revaccination of previous recipients of killed measles vaccine: clinical and immunologic studies

Clinical and immunologic studies were performed in association with revaccination with live measles vaccine in 75 adolescents 11 to 14 years after immunization with killed measles vaccine. Ten subjects had local pain with swelling or erythema or both at the injection site; in three, the local reactions were severe and disturbing systemic complaints were also noted. These marked reactions were more common in subjects in whom the interval between the last dose of killed vaccine and the dose of live vaccine of the primary immunization series was less than or equal to 2 months, in subjects with prevaccination serum HAI antibody titers of less than or equal to 5, and in subjects with high measles antigen specific lymphocyte stimulation ratios. Serum complement levels could not be correlated with clinical reactions. Measles specific lymphocyte stimulation ratios were significantly higher in recipients of killed vaccine than in three compara,ive groups, in subjects with a killed-live interval in the initial vaccine series of less than or equal to 2 months as compared with greater than or equal to 3 months, and in subjects with prevaccination HAI antibody titers of less than or equal to 5 as compared with titers greater than or equal to 10. Although both low serum antibody and high measles specific lymphocyte reactivity were associated with marked local reactions, and probably indicative of susceptibility to atypical measles, our findings suggest that exaggerated lymphocyte reactivity is of greater importance in the adverse clinical response.