Neonatal DNA immunization with a plasmid encoding an internal viral protein is effective in the presence of maternal antibodies and protects against subsequent viral challenge

T cells in the brain enhance neonatal mortality during peripheral LCMV infection

In adult mice the severity of disease from viral infections is determined by the balance between the efficiency of the immune response and the magnitude of viral load. Here, the impact of this dynamic is examined in neonates. Newborns are highly susceptible to infections due to poor innate responses, lower numbers of T cells and Th2-prone immune responses. Eighty-percent of 7-day old mice, immunologically equivalent to human neonates, succumbed to extremely low doses (5 PFU) of the essentially non-lethal lymphocytic choriomeningitis virus (LCMV-Armstrong) given intraperitoneally. This increased lethality was determined to be dependent upon poor early viral control, as well as, T cells and perforin as assessed in knockout mice. By day 3, these neonatal mice had 400-fold higher viral loads as compared to adults receiving a 10,000-fold (5X104 PFU) higher dose of LCMV. The high viral load in combination with the subsequent immunological defect of partial CD8 T cell clonal exhaustion in the periphery led to viral entry and replication in the brain. Within the brain, CD8 T cells were protected from exhaustion, and thus were able to mediate lethal immunopathology. To further delineate the role of early viral control, neonatal mice were infected with Pichinde virus, a less virulent arenavirus, or LCMV was given to pups of LCMV-immune mothers. In both cases, peak viral load was at least 29-fold lower, leading to functional CD8 T cell responses and 100% survival.

Nucleoside-modified mRNA vaccination partially overcomes maternal antibody inhibition of de novo immune responses in mice

Maternal antibodies provide short-term protection to infants against many infections. However, they can inhibit de novo antibody responses in infants elicited by infections or vaccination, leading to increased long-term susceptibility to infectious diseases. Thus, there is a need to develop vaccines that are able to elicit protective immune responses in the presence of antigen-specific maternal antibodies. Here, we used a mouse model to demonstrate that influenza virus-specific maternal antibodies inhibited de novo antibody responses in mouse pups elicited by influenza virus infection or administration of conventional influenza vaccines. We found that a recently developed influenza vaccine, nucleoside-modified mRNA encapsulated in lipid nanoparticles (mRNA-LNP), partially overcame this inhibition by maternal antibodies. The mRNA-LNP influenza vaccine established long-lived germinal centers in the mouse pups and elicited stronger antibody responses than did a conventional influenza vaccine approved for use in humans. Vaccination with mRNA-LNP vaccines may offer a promising strategy for generating robust immune responses in infants in the presence of maternal antibodies.

Immunization of pregnant women: Future of early infant protection

Children in early infancy do not mount effective antibody responses to many vaccines against commons infectious pathogens, which results in a window of increased susceptibility or severity infections. In addition, vaccine-preventable infections are among the leading causes of morbidity in pregnant women. Immunization during pregnancy can generate maternal immune protection as well as elicit the production and transfer of antibodies cross the placenta and via breastfeeding to provide early infant protection. Several successful vaccines are now recommended to all pregnant women worldwide. However, significant gaps exist in our understanding of the efficacy and safety of other vaccines and in women with conditions associated with increased susceptible to high-risk pregnancies. Public acceptance of maternal immunization remained to be improved. Broader success of maternal immunization will rely on the integration of advances in basic science in vaccine design and evaluation and carefully planned clinical trials that are inclusive to pregnant women.

Maternal vaccination: moving the science forward

BACKGROUND

Infections remain one of the leading causes of morbidity in pregnant women and newborns, with vaccine-preventable infections contributing significantly to the burden of disease. In the past decade, maternal vaccination has emerged as a promising public health strategy to prevent and combat maternal, fetal and neonatal infections. Despite a number of universally recommended maternal vaccines, the development and evaluation of safe and effective maternal vaccines and their wide acceptance are hampered by the lack of thorough understanding of the efficacy and safety in the pregnant women and the offspring.

METHODS

An outline was synthesized based on the current status and major gaps in the knowledge of maternal vaccination. A systematic literature search in PUBMED was undertaken using the key words in each section title of the outline to retrieve articles relevant to pregnancy. Articles cited were selected based on relevance and quality. On the basis of the reviewed information, a perspective on the future directions of maternal vaccination research was formulated.

RESULTS

Maternal vaccination can generate active immune protection in the mother and elicit systemic immunoglobulin G (IgG) and mucosal IgG, IgA and IgM responses to confer neonatal protection. The maternal immune system undergoes significant modulation during pregnancy, which influences responsiveness to vaccines. Significant gaps exist in our knowledge of the efficacy and safety of maternal vaccines, and no maternal vaccines against a large number of old and emerging pathogens are available. Public acceptance of maternal vaccination has been low.

CONCLUSIONS

To tackle the scientific challenges of maternal vaccination and to provide the public with informed vaccination choices, scientists and clinicians in different disciplines must work closely and have a mechanistic understanding of the systemic, reproductive and mammary mucosal immune responses to vaccines. The use of animal models should be coupled with human studies in an iterative manner for maternal vaccine experimentation, evaluation and optimization. Systems biology approaches should be adopted to improve the speed, accuracy and safety of maternal vaccine targeting.

A Plasmid Encoding Japanese Encephalitis Virus PrM and E Proteins Elicits Protective Immunity in Suckling Mice

A plasmid encoding Japanese encephalitis virus (JEV) prM and E proteins was constructed, and its efficacy as a candidate vaccine against JEV was evaluated in suckling mice. Groups of 10 BALB/c mice (5-7 days old) were immunized twice via muscular injection with this DNA vaccine, an empty vector or PBS at an interval of 3 weeks, and were challenged with a lethal dose of JEV 3 weeks after the second inoculation. Both cellular and humoral immune responses were examined before the challenge. Two animals from each group were sacrificed to detect the JEV-specific cytotoxic T lymphocyte activity. JEV-specific lactate dehydrogenase release in the DNA vaccine, empty vector and PBS groups was 37.5%, 18% and 8.5% respectively. JEV-specific antibody was detected in 8 of 10 animals in DNA vaccine group with a geometrical mean titer of 1: 28.3. The pooled serum from the same group also showed a neutralizing activity. Six of 8 mice in the DNA vaccine group survived the challenge, with a protection rate of 75%, but all the mice died in the two control groups. These results show that this JEV prM and E DNA vaccine is immunogenic and protective against JEV infection in the mouse model.

Oral antigen exposure in extreme early life in lambs influences the magnitude of the immune response which can be generated in later life

BACKGROUND

Previous investigations in newborn lambs determined that adenovirus-mediated expression of antigen to a localized region of the gut induced antigen-specific mucosal and systemic immunity. These experiments were limited in that the localized region of the gut to which antigen was introduced was sterile and the influence of colostrum on the antigen was not assessed but they do suggest that mucosal vaccines may be an effective vaccination strategy to protect neonatal lambs. We propose that persistent oral antigen exposure introduced in extreme early life can induce immunity in lambs, despite the presence of commensal bacteria and colostrum.

RESULTS

To test this hypothesis, conventionally raised newborn lambs (n = 4 per group) were gavaged with ovalbumin (OVA) starting the day after birth for either a single day (2.27 g), every day for 3 days (0.23 g/day), or every day for 3 days then every second day until nine days of age (0.023 g/day). Lambs gavaged with OVA for 3 to 9 days developed significant serum anti-OVA IgG titres (p < 0.05), but not IgA titres, relative to control lambs (n = 4) after 3 and 4 weeks. At 4 weeks of age, lambs were immunized with OVA in Incomplete Freund's Adjuvant via intraperitoneal (i.p.) injection then lambs were euthanized at 7 weeks. Serum anti-OVA IgG titres were further augmented after i.p. immunization indicating immunity persisted and tolerance was not induced. Serum IgA titres remained low regardless of treatment. It is known that i.p. priming of sheep with antigen in Freund's complete adjuvant leads to an enhanced number of IgA and IgG antibody containing cells in the respiratory mucosa (Immunology 53(2):375-384, 1984). Lambs gavaged with a single bolus of 2.27 g OVA prior to i.p. immunization showed very low titres of anti-OVA IgA in the lung lavage. These data suggest that a single, high dose exposure to OVA can promote tolerance which impacts response to systemic vaccination in later life. Lambs gavaged with 0.023 g OVA for 9 days (Group C) generated significant anti-OVA IgA titres in lung (p < 0.001) compared to negative control lambs but no additive effect was observed compared to parenteral control lambs. When splenocytes were re-stimulated with OVA ex vivo, all groups failed to show increased lymphocyte proliferation or interferon (IFN)-γ production relative to the parenteral control group.

CONCLUSIONS

In agreement with our hypothesis, persistent low dose antigen exposure primes humoral antibody production in serum in conventionally raised newborn lambs. In contrast, a single high dose bolus of antigen triggered oral tolerance which negatively impacted the quality and magnitude of the immune response to i.p. immunization in later life. These tangential responses are important as they indicate that the dose and/or repeated oral exposure to antigen, such as that which may be found in the neonate's environment, may promote immunity or alternatively it may negatively impact responses to parenteral vaccination.

Maternal LAMP/p55gagHIV-1 DNA immunization induces in utero priming and a long-lasting immune response in vaccinated neonates

Infants born to HIV-infected mothers are at high risk of becoming infected during gestation or the breastfeeding period. A search is thus warranted for vaccine formulations that will prevent mother-to-child HIV transmission. The LAMP/gag DNA chimeric vaccine encodes the HIV-1 p55gag fused to the lysosome-associated membrane protein-1 (LAMP-1) and has been shown to enhance anti-Gag antibody (Ab) and cellular immune responses in adult and neonatal mice; such a vaccine represents a new concept in antigen presentation. In this study, we evaluated the effect of LAMP/gag DNA immunization on neonates either before conception or during pregnancy. LAMP/gag immunization of BALB/c mice before conception by the intradermal route led to the transfer of anti-Gag IgG1 Ab through the placenta and via breastfeeding. Furthermore, there were an increased percentage of CD4+CD25+Foxp3+T cells in the spleens of neonates. When offspring were immunized with LAMP/gag DNA, the anti-Gag Ab response and the Gag-specific IFN-γ-secreting cells were decreased. Inhibition of anti-Gag Ab production and cellular responses were not observed six months after immunization, indicating that maternal immunization did not interfere with the long-lasting memory response in offspring. Injection of purified IgG in conjunction with LAMP/gag DNA immunization decreased humoral and cytotoxic T-cell responses. LAMP/gag DNA immunization by intradermal injection prior to conception promoted the transfer of Ab, leading to a diminished response to Gag without interfering with the development of anti-Gag T- and B-cell memory. Finally, we assessed responses after one intravenous injection of LAMP/gag DNA during the last five days of pregnancy. The intravenous injection led to in utero immunization. In conclusion, DNA vaccine enconding LAMP-1 with Gag and other HIV-1 antigens should be considered in the development of a protective vaccine for the maternal/fetal and newborn periods.

Maternal immunization to modulate the development of allergic response and pathogen infections

This article reviews recent experimental approaches of preventive strategies regarding allergy and infections by pathogens, particularly in early childhood, by targeting maternal immunomodulation. Basic research is essential to understand maternal vaccination as a strategy to control allergic disease and bacterial and viral infections; thus, providing support for future translational research. The environmental stimuli and host genetic factors, along with maternal influences in early life when immune systems are developing and during postnatal life, are essential for the decision between tolerance induction or allergen sensitization. Maternal immunomodulation strategies should serve as a challenge when attempting to halt the spread of allergy responses and viral infections, until the innate and adaptive arms of the immune system of the neonates are competent.

Vaccines: the fourth century

Vaccine development, which began with Edward Jenner's observations in the late 18th century, has entered its 4th century. From its beginnings, with the use of whole organisms that had been weakened or inactivated, to the modern-day use of genetic engineering, it has taken advantage of the tools discovered in other branches of microbiology. Numerous successful vaccines are in use, but the list of diseases for which vaccines do not exist is long. However, the multiplicity of strategies now available, discussed in this article, portends even more successful development of vaccines.

Development and evaluation of a recombinant DNA vaccine candidate expressing porcine circovirus 2 structural protein

Porcine circovirus 2 (PCV2) is generally associated with the porcine circovirosis syndrome, which is considered an important disease of swine and has potentially serious economic impact on the swine industry worldwide. This article describes the construction of a recombinant plasmid expressing the PCV2 structural protein and the evaluation of cellular and humoral immune responses produced by this recombinant vaccine in BALB/c mice. The vaccine candidate was obtained and analyzed in vivo, in an effort to determine the ability to induce a specific immune response in mice. DNA was extracted from a Brazilian PCV2 isolate and the gene coding for Cap protein was amplified by PCR and inserted into an expression plasmid. Groups of BALB/c mice were inoculated intra-muscularly and intradermally in a 15-day interval, with 100 µg and 50 µg of the vaccine construct, respectively. Another group was inoculated intramuscularly with 100 µg of empty plasmid, corresponding to the control group. Seroconversion and cellular response in BALB/c mice were compared and used for vaccine evaluation. Seroconversion was analyzed by ELISA. After a series of 3 immunizations the spleen cells of the immunized animals were used to perform lymphocyte proliferation assays. Seroconversion to PCV2 was detected by ELISA in the animals inoculated with the vaccine construct when compared with control groups. Lymphocyte proliferation assays showed a stronger cell proliferation in the inoculated animals compared with the control group. Thus, the vaccine candidate construct demonstrated to be able to induce both humoral and cellular responses in inoculated mice.

Strategies for induction of protective immunity to bovine herpesvirus-1 in newborn calves with maternal antibodies

The objective of this study was to evaluate Th1 promoting strategies for vaccination of neonates against bovine herpesvirus-1 (BHV-1). A plasmid encoding a secreted truncated version of glycoprotein D (tgD) and tgD protein formulated with CpG oligodeoxynucleotide (ODN) effectively primed the immune system of newborn lambs, whereas without CpG ODN the tgD protein was less effective. Furthermore, a heterologous DNA prime-protein/CpG boost induced stronger and more balanced immune responses than either the DNA vaccine or a protein/CpG prime-DNA boost. Three of these strategies were compared as an approach to induce protective immunity in newborn calves with BHV-1-specific maternal antibodies. Whereas the DNA vaccine induced minimal protection, the DNA prime-protein boost resulted in reduced temperature response, weight loss and virus shedding in comparison to the placebo group. Close to complete protection against BHV-1 challenge was elicited in the calves immunized with the protein/CpG formulation, as these animals lost very little weight, had only slightly elevated temperatures and shed almost no virus.

Recent advances in the development of recombinant vaccines against classical swine fever virus: cellular responses also play a role in protection

Classical swine fever virus (CSFV) is the causative agent of one of the most devastating porcine haemorrhagic viral diseases, classical swine fever (CSF). CSFV mainly infects endothelial cells and macrophages and at the same time promotes bystander apoptosis of the surrounding T cells, causing strong immune suppression and high mortality rates. Most animals experience acute infection, during which they either die or survive by producing neutralising antibodies to the virus. However, in a few cases, the impaired immune system cannot control viral progression, leading to chronic infection. Efficient live attenuated vaccines against CSFV exist and are routinely used only in endemic countries. The ability of these vaccines to replicate in the host, even at very low rates, makes it extremely difficult to distinguish vaccinated from infected animals, favouring a restricted policy regarding vaccination against CSFV in non-endemic countries. There is a clear need for efficient and safer marker vaccines to assist in the control of future CSF outbreaks. In this review article, some of the most recent advances in the field of recombinant vaccines against CSFV are presented and the nature of the protective immune responses they induce is discussed.

DNA vaccination against pseudorabies virus and bovine respiratory syncytial virus infections of young animals in the face of maternally derived immunity

DNA vaccination represents a unique opportunity to overcome the limitations of conventional early life vaccine strategy which is restricted by the effects of maternally derived immunity. The pseudorabies virus (PRV) infection model in neonatal piglets was employed to demonstrate that a single DNA vaccination was able to prime memory humoral immune responses in the face of high concentrations of maternally derived antibodies. Immunity induced under these conditions protected against challenge with virulent PRV at the end of the fattening period, but long-term protective responses were not correlated with the kinetics of the initial serological responses. The bovine respiratory syncytial virus (BRSV) infection model in young calves was similarly studied, however the ability of DNA vaccination to prime memory humoral responses in the face of high concentrations of maternally derived antibodies was not confirmed, illustrating that the performance of DNA vaccination varies between species and/or infectious disease targets. However, in the BRSV model system it was evident that DNA vaccination could prime cell-mediated immunity in the face of high concentrations of maternally derived antibodies. Although not sufficient to ensure protection against clinical disease or viral excretion as a standalone vaccination strategy, priming by DNA vaccination was proven to establish cell-mediated immune responses for subsequent recall with an inactivated vaccine booster. Under these conditions, protection against challenge virus re-excretion was correlated with interferon (IFN) gamma-producing T-cell responses. The safety and the efficacy of DNA vaccine priming in very young animals in the face of high concentrations of maternally derived antibody provides a unique opportunity to design innovative and flexible vaccination programs to ensure uninterrupted protection under field conditions.

Immunopathology of RSV infection: prospects for developing vaccines without this complication

Respiratory syncytial virus is the most important cause of lower respiratory tract infection in infants and young children. RSV clinical disease varies from rhinitis and otitis media to bronchiolitis and pneumonia. An increased incidence of asthma later in life has been associated with the more severe lower respiratory tract infections. Despite its importance as a pathogen, there is no licensed vaccine against RSV. This is due to a number of factors complicating the development of an effective and safe vaccine. The immunity to natural RSV infection is incomplete as re-infections occur in all age groups, which makes it challenging to design a protective vaccine. Second, the primary target population is the newborn infant, which has a relatively immature immune system and maternal antibodies that can interfere with vaccination. Finally, some vaccines have resulted in a predisposition for exacerbated pulmonary disease in infants, which was attributed to an imbalanced Th2-biased immune response, although the exact cause has not been elucidated. This makes it difficult to proceed with vaccine testing in infants. It is likely that an effective and safe vaccine needs to elicit a balanced immune response, including RSV-specific neutralising antibodies, CD8 T-cells, Th1/Th2 CD4 T-cells and preferably secretory IgA. Subunit vaccines formulated with appropriate adjuvants may be adequate for previously exposed individuals. However, intranasally delivered genetically engineered attenuated or vectored vaccines are currently most promising for newborns, as they are expected to induce a balanced immune response similar to that elicited to natural infection and not be subject to interference from maternal antibodies. Maternal vaccination may be the optimal strategy to protect the very young infants.

Comparison of immune responses in parenteral FaeG DNA primed pigs boosted orally with F4 protein or reimmunized with the DNA vaccine

We previously showed that an intradermal (i.d.) FaeG DNA prime (2x)-oral F4 protein boost immunization induces a systemic response and weakly primes a mucosal IgG response in pigs, especially when plasmid vectors encoding the A and B subunit of the E. coli thermo-labile enterotoxin (LT) are added to the DNA vaccine. In the present study, we evaluated whether addition of 1alpha,25-dihydroxyvitamin D(3) (vitD(3)) to the DNA vaccine could further enhance this mucosal priming and/or modulate the antibody response towards IgA. To further clarify priming of systemic and mucosal responses by the i.d. DNA vaccination, we firstly compared the localization of the F4-specific antibody response in pigs that were orally boosted with F4 to that in pigs that received a third i.d. DNA immunization and secondly evaluated cytokine mRNA expression profiles after i.d. DNA vaccination. The i.d. DNA prime (2x)-oral F4 boost immunization as well as the 3 i.d. DNA vaccinations induced mainly a systemic response, with a higher response observed following the heterologous protocol. Co-administration of vitD(3), and especially of the LT vectors, enhanced this response. Furthermore, only the heterologous immunization resulted in a weak mucosal priming, which appeared to require the presence of the LT vectors or vitD(3) as adjuvants. In addition, the LT vectors strongly enhanced the FaeG-specific lymphocyte proliferation and this was accompanied by the absence of a clear IL-10 response. However, despite two DNA immunizations in the presence of these adjuvants and an oral F4 boost, we failed to demonstrate the secretory IgA response needed to be protective against enterotoxigenic E. coli.

DNA vaccines for poultry: the jump from theory to practice

DNA vaccines could offer a solution to a number of problems faced by the poultry industry; they are relatively easy to manufacture, stable, potentially easy to administer, can overcome neonatal tolerance and the deleterious effects of maternal antibody, and do not cause disease pathology. Combined with this, in ovo vaccination offers the advantage of reduced labor costs, mass administration and the induction of an earlier immune response. Together, this list of advantages is impressive. However, this combined technology is still in its infancy and requires many improvements. The potential of CpG motifs, DNA vaccines and in ovo vaccination, however, can be observed by the increasing number of recent reports investigating their application in challenge experiments. CpG motifs have been demonstrated to be stimulatory both in vitro and in vivo. In addition, DNA vaccines have been successfully delivered via the in ovo route, albeit not yet through the amniotic fluid. Lastly, a recent report has demonstrated that a DNA vaccine against infectious bronchitis virus administered via in ovo vaccination, followed by live virus boost, can slightly improve on the protective effect induced by the live virus alone. Therefore, DNA vaccination via the in ovo route is promising and offers potential as a poultry vaccine, however, efficacy needs to be improved and the costs of production reduced before it is likely to be beneficial to the poultry industry in the long term.

Formulation with CpG oligodeoxynucleotides increases cellular immunity and protection induced by vaccination of calves with formalin-inactivated bovine respiratory syncytial virus

Vaccination of calves with formalin-inactivated bovine respiratory syncytial virus (FI-BRSV) induces low levels of cellular immunity that may not be protective. Since inactivated and subunit vaccines formulated with CpG oligodeoxynucleotides (ODNs) have been shown to induce cellular immune responses, we studied the ability of a FI-BRSV vaccine formulated with CpG ODN to elicit cellular immunity against BRSV. Neonatal calves were immunized with FI-BRSV, FI-BRSV formulated with CpG ODN or medium and challenged with BRSV after two immunizations. Calves vaccinated with FI-BRSV formulated with CpG ODN developed increased numbers of IFN-gamma secreting cells in the peripheral blood and broncho-tracheal lymph nodes and enhanced BRSV-specific serum IgG2 in comparison to FI-BRSV immunized animals. Calves that received the FI-BRSV vaccine formulated with CpG ODN also experienced a reduction in the amount of BRSV in the lung tissue. Based on these observations, CpG ODN appears to be a suitable candidate adjuvant for inactivated BRSV vaccines.

Carriers for the delivery of a vaccine against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and pneumonia in young children and the elderly. Despite its clinical importance, there is no licensed vaccine available at present. Vaccine development has been hampered by observations of increased pathology after RSV infection in infants vaccinated with formalin-inactivated RSV; incomplete immunity following natural infection; and the need to be effective during the neonatal period when levels of maternal antibody are high. Four categories of RSV vaccine carriers--live-attenuated RSVs, recombinant vectors expressing the protective antigens of RSV, DNA vaccines and subunit vaccines--have been evaluated in animal models and/or clinical trials. So far, studies with live-attenuated virus vaccines highlight the need to improve immunogenicity whilst maintaining a suitable level of attenuation. Studies with recombinant vectors, DNA and subunit vaccines illustrate the pivotal nature of the vaccine carrier in determining the balance between immune-mediated protection against infection and the induction of immune-mediated pulmonary pathology.

Assessment in mice of vapA–DNA vaccination against Rhodococcus equi infection

There is a need to produce a vaccine against Rhodococcus equi pneumonia in foals in which immunity against infection is largely based on a type 1, cell-mediated, immune response. The VapA protein of the virulence plasmid of R. equi is highly immunogenic. To assess the potential of vapA-DNA to produce immunity, C57BL/6 and BALB/c mice were immunized with a DNA vaccine constructed from vapA incorporated into pcDNA3.1. The plasmid construct expressed VapA in a COS-7 cell line. Intramuscular immunization of mice resulted in enhanced clearance of R. equi from the liver of intravenously challenged mice compared to non-immunized controls. This effect was more marked when pORF-IL-12, a plasmid expressing murine IL12, was included with the vaccine. Antibody developed to VapA, with an IgG2a response being more marked in mice immunized with pcDNA-vapA than in non-immunized or in mice immunized with the mixed vapA and IL-12 plasmid constructs. In conclusion, this study has shown for the first time that DNA immunization with vapA enhances the immune responses of mice against R. equi infection, that the IgG subisotype response is consistent with a type 1-based immune response, and that this can be enhanced by injection of the IL-12 gene.

Six revolutions in vaccinology

The history of vaccine development can be divided into 5 waves, produced by revolutions in technology. They are attenuation, inactivation, cell culture of viruses, genetic engineering and methods to induce cellular immune responses. This division is somewhat artificial, and all of the past strategies continue to be useful. I discuss the candidates for the sixth revolution, which include combination vaccines, new adjuvants, proteomics, reverse vaccinology and vaccines for noninfectious diseases, among others. I propose new delivery systems as the most likely to succeed, although humbly admitting that prediction is always subject to error.

CD80 and CD86, but not CD154, augment DNA vaccine-induced protection in experimental bovine tuberculosis

DNA vaccination is known to elicit robust cellular and humoral responses to encoded antigen. The co-administration of costimulatory molecules CD80 (B7-1), CD86 (B7-2) and CD154 (CD40L) has been shown to enhance immune responses in several murine models. The role of specific costimulatory molecules in non-rodent species remains incompletely characterized. In these studies, we demonstrate that the co-administration of CD80 and CD86, but not CD154, to an existing candidate subunit DNA vaccine (ESAT-6) against bovine tuberculosis, enhances protection after aerosol challenge with virulent Mycobacterium bovis. Additionally, we have shown that vaccination with M. bovis BCG is protective against tuberculosis following aerosol challenge in cattle. Two independent trials were conducted in cattle to determine the adjuvant effect of encoded antigen + CD80/CD86 and directly compare the adjuvant activities of CD80/CD86 to those of CD154. Co-administration of either CD80/CD86 or CD154 enhanced ESAT-6-specific IFN-gamma responses as compared to animals vaccinated with ESAT-6 DNA alone. However, following aerosol challenge, only animals vaccinated with CD80/CD86 possessed decreased pathology of the lungs and associated lymph nodes, as measured by gross examination, radiographic lesion morphometry and bacterial recovery. Collectively, these results demonstrate that the co-administration of costimulatory molecules with a protective antigen target enhances bovine immune responses to DNA vaccination, and that CD80/CD86 is superior to CD154 in augmenting DNA vaccine-induced protection in experimental bovine tuberculosis.

Mucosally delivered Salmonella live vector vaccines elicit potent immune responses against a foreign antigen in neonatal mice born to naive and immune mothers

The development of effective vaccines for neonates and very young infants has been impaired by their weak, short-lived, and Th-2 biased responses and by maternal antibodies that interfere with vaccine take. We investigated the ability of Salmonella enterica serovars Typhi and Typhimurium to mucosally deliver tetanus toxin fragment C (Frag C) as a model antigen in neonatal mice. We hypothesize that Salmonella, by stimulating innate immunity (contributing to adjuvant effects) and inducing Th-1 cytokines, can enhance neonatal dendritic cell maturation and T-cell activation and thereby prime humoral and cell-mediated immunity. We demonstrate for the first time that intranasal immunization of newborn mice with 10(9) CFU of S. enterica serovar Typhi CVD 908-htrA and S. enterica serovar Typhimurium SL3261 carrying plasmid pTETlpp on days 7 and 22 after birth elicits high titers of Frag C antibodies, previously found to protect against tetanus toxin challenge and similar to those observed in adult mice. Salmonella live vectors colonized and persisted primarily in nasal tissue. Mice vaccinated as neonates induced Frag C-specific mucosal and systemic immunoglobulin A (IgA)- and IgG-secreting cells, T-cell proliferative responses, and gamma interferon secretion. A mixed Th1- and Th2-type response to Frag C was established 1 week after the boost and was maintained thereafter. S. enterica serovar Typhi carrying pTETlpp induced Frag C-specific antibodies and cell-mediated immunity in the presence of high levels of maternal antibodies. This is the first report that demonstrates the effectiveness of Salmonella live vector vaccines in early life.

Inhibition of 19-kDa C-terminal region of merozoite surface protein-1-specific antibody responses in neonatal pups by maternally derived 19-kDa C-terminal region of merozoite surface protein-1-specific antibodies but not whole parasite-specific antibodies

Immunizing pregnant women with a malaria vaccine is one approach to protecting the mother and her offspring from malaria infection. However, specific maternal Abs generated in response to vaccination and transferred to the fetus may interfere with the infant's ability to respond to the same vaccine. Using a murine model of malaria, we examined the effect of maternal 19-kDa C-terminal region of merozoite surface protein-1 (MSP1(19)) and Plasmodium yoelii Abs on the pups' ability to respond to immunization with MSP1(19). Maternal MSP1(19)-specific Abs but not P. yoelii-specific Abs inhibited Ab production following MSP1(19) immunization in 2-wk-old pups. This inhibition was correlated with the amount of maternal MSP1(19) Ab present in the pup at the time of immunization and was due to fewer specific B cells. Passively acquired Ab most likely inhibited the development of an Ab response by blocking access to critical B cell epitopes. If a neonate's ability to respond to MSP1(19) vaccination depends on the level of maternal Abs present at the time of vaccination, it may be necessary to delay immunization until Abs specific for the vaccinating Ag have decreased.

An assessment of different DNA delivery systems for protection against respiratory syncytial virus infection in the murine model: gene-gun delivery induces IgG in the lung

Immunization with plasmid DNA (pDNA) has the potential to overcome the difficulties of neonatal vaccination that may be required for protection against infection with respiratory syncytial virus (RSV); however, little is known about optimal delivery modalities. In this pilot study we compared mucosal delivery of pDNA encoding RSV F protein encapsulated in poly(DL-lactide-co-glycolide) with delivery of pDNA by gene-gun for the induction of immunity in mice. Intra-gastric or intra-nasal immunization with various doses of microparticles induced weak low levels of RSV-specific serum antibodies in a proportion of mice; in contrast, gene-gun vaccination led to protective immunity associated with a humoral response. Interestingly, RSV-specific antibody was detected in lung fragment cultures following intradermal vaccination with the gene-gun.

Priming of piglets against enterotoxigenic E. coli F4 fimbriae by immunisation with FAEG DNA

Early vaccination is necessary to protect pigs against postweaning diarrhoea caused by enterotoxigenic Escherichia coli (ETEC). However, at present no commercial vaccine allows successful vaccination. This is partly due to the presence of maternally derived antibodies. Since DNA vaccines are suggested to be superior to protein vaccines in young animals with maternal antibodies, we determined whether the fimbrial adhesin (FaeG) of F4ac(+) ETEC could be used as a plasmid DNA vaccine to prime piglets in a heterologous prime-boost approach. Hereto, pcDNA1/faeG19 was constructed and expression of rFaeG in Cos-7 cells was demonstrated. Thereafter, pigs were immunised (days 0, 21 and 42) intramuscularly by injection or intradermally by gene gun and humoral and cellular immune responses were analysed. Even though responses were low, results demonstrated that intramuscular injection was superior to gene gun delivery for priming the humoral immune response since higher antibody titres were raised, whereas gene gun delivery better induced a cellular response, evaluated by a lymphocyte proliferation assay. Effective priming of the humoral immune response was evidenced by high IgG titres 1 week after a protein boost with purified F4. The low responses to the pcDNA1/faeG19 DNA vaccination suggest that delivery of the DNA and/or the expression of the faeG gene should be improved.

Influence of maternal antibodies on Chlamydophila psittaci-specific immune responses in turkeys elicited by naked DNA

Plasmid DNA (pcDNA1::MOMP D) expressing the major outer membrane protein (MOMP) of an avian Chlamydophila psittaci serovar D strain was tested for its ability to induce protective immunity against C. psittaci challenge in the presence of maternal antibodies. A combined parenteral (intramuscular injection) and mucosal route (DNA drops administered to the nares) of DNA inoculation was used. Following pcDNA1::MOMP vaccination, both T helper and B cell memory were primed. However, high maternal antibodies titres affected the induction of vaccine-specific antibody responses as assessed by MOMP-specific antibody levels in enzyme-linked immunosorbent assay (ELISA). Cell-mediated immunity was unaltered as demonstrated by the significantly heightened proliferative responses of peripheral blood lymphocytes (PBL) following vaccination. DNA vaccination could significantly reduce clinical symptoms, pharyngeal and cloacal excretion as well as Chlamydophila replication, even in the presence of maternal antibodies.

Immunisation against PCV2 structural protein by DNA vaccination of mice

Porcine circovirus type 2 (PCV2) is the causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome (PMWS). The disease affects primarily 5-12-weeks-old pigs which might suggest that infection with PCV2 occurs when the level of maternal antibodies have declined to sub-protective levels around weaning at 3-5-weeks of age. If immunoprophylaxis is to be effective, an immunisation method capable of breaking through maternal immunity must be employed. In this study, we have developed and investigated the potential of a DNA vaccination approach to be one such method. The gene encoding the capsid protein of PCV2 was cloned in a DNA vaccination plasmid and expression of capsid protein was demonstrated in vitro. Mice were gene gun vaccinated three timesand all mice responded serologically by raising antibodies against PCV2. The results suggest, that DNA based vaccination might offer opportunities for vaccination of piglets against PCV2.

Prior DNA vaccination does not interfere with the live-attenuated measles vaccine

The currently used live-attenuated measles vaccine is very effective although maternal antibody prevents its administration prior to 6 months of age. We are investigating the ability of a DNA vaccine encoding the measles viral hemagglutinin, fusion and nucleoprotein to protect newborn infants from measles. Here, we show that a measles DNA vaccine protects juvenile macaques from pathogenic measles virus challenge and that macaques primed and boosted with this DNA vaccine have anemnestic antibody and cell-mediated responses after vaccination with a live-attenuated canine distemper-measles vaccine. Therefore, this DNA vaccine administered to newborn infants may not hinder the subsequent use of live-attenuated measles vaccine.

Coxsackievirus B3 and the neonatal CNS: the roles of stem cells, developing neurons, and apoptosis in infection, viral dissemination, and disease

Neonates are particularly susceptible to coxsackievirus infections of the central nervous system (CNS), which can cause meningitis, encephalitis, and long-term neurological deficits. However, viral tropism and mechanism of spread in the CNS have not been examined. Here we investigate coxsackievirus B3 (CVB3) tropism and pathology in the CNS of neonatal mice, using a recombinant virus expressing the enhanced green fluorescent protein (eGFP). Newborn pups were extremely vulnerable to coxsackievirus CNS infection, and this susceptibility decreased dramatically by 7 days of age. Twenty-four hours after intracranial infection of newborn mice, viral genomic RNA and viral protein expression were detected in the choroid plexus, the olfactory bulb, and in cells bordering the cerebral ventricles. Many of the infected cells bore the anatomical characteristics of type B stem cells, which can give rise to neurons and astrocytes, and expressed the intermediate filament protein nestin, a marker for progenitor cells. As the infection progressed, viral protein was identified in the brain parenchyma, first in cells expressing neuron-specific class III beta-tubulin, an early marker of neuronal differentiation, and subsequently in cells expressing NeuN, a marker of mature neurons. At later time points, viral protein expression was restricted to neurons in specific regions of the brain, including the hippocampus, the entorhinal and temporal cortex, and the olfactory bulb. Extensive neuronal death was visible, and appeared to result from virus-induced apoptosis. We propose that the increased susceptibility of the neonatal CNS to CVB infection may be explained by the virus' targeting neonatal stem cells; and that CVB is carried into the brain parenchyma by developing neurons, which continue to migrate and differentiate despite the infection. On full maturation, some or all of the infected neurons undergo apoptosis, and the resulting neuronal loss can explain the longer-term clinical picture.

DNA vaccination of neonate piglets in the face of maternal immunity induces humoral memory and protection against a virulent pseudorabies virus challenge

DNA vaccination represents a unique opportunity to overcome the limitations of conventional vaccine strategy in early life in the face of maternal-derived immunity. We used the model of pseudorabies virus (PRV) infection in pigs to further explore the potential of DNA vaccination in piglets born to sows repeatedly vaccinated with a PRV inactivated vaccine. A single immunisation of 8-week-old piglets with a DNA vaccine expressing secreted forms of PRV gB, gC, and gD, triggered an active serological response, confirming that DNA vaccination can over-ride significant residual maternal-derived immunity. A clear anamnestic response was evidenced when a secondary DNA vaccination was performed at 11 weeks of age, suggesting that DNA vaccination, performed in the face of passive immunity, elicited a strong humoral memory. We subsequently explored the potential of DNA vaccination in neonate piglets (5-6 days of age) in the face of very high titres of maternal antibodies and demonstrated that very high titres of passive antibodies selectively inhibited serological responses but not the establishment of potent memory responses. Finally, we demonstrated that DNA vaccination provided protection against an infectious PRV challenge at the end of the fattening period (i.e. at approximately 5 months of age). Collectively, our results pave the way for a new flexible vaccination program, which could ensure uninterrupted protection of fattening pigs over their entire economical life under field conditions.

DNA vaccination of infants in the presence of maternal antibody: a measles model in the primate

To eradicate measles in developing nations a vaccine capable of being administered at birth may be necessary. We immunized newborn rhesus macaques with naked DNA encoding the measles virus hemagglutinin, fusion and nucleoprotein genes. Prior to vaccination we passively transferred measles immunoglobulin to mimic maternal antibody. In the presence or absence of measles immunoglobulin, 23 of 25 infant macaques had detectable cell mediated immunity and 16 had protective levels of neutralizing antibody. The co-administration of an IL-2/IgG plasmid augmented the vaccine, increasing cell mediated immunity in all infants and increasing the antibody response in infants vaccinated without immunoglobulin. We show for the first time that DNA vaccination can protect a newborn primate from the high-level viremia that correlates with severe measles, even in the presence of maternal antibody. Further, the addition of a molecular IL-2 adjuvant augments this DNA vaccine.

Neonates mount robust and protective adult-like CD8(+)-T-cell responses to DNA vaccines

Neonates are thought to mount less vigorous adaptive immune responses than adults to antigens and infectious agents. This concept has led to a delay in the administration of many currently available vaccines until late infancy or early childhood. It has recently been shown that vaccines composed of plasmid DNA can induce both humoral and cell-mediated antimicrobial immunity when administered within hours of birth. In most of these studies, immune responses were measured weeks or months after the initial vaccination, and it is therefore questionable whether the observed responses were actually the result of priming of splenocytes within the neonatal period. Here we show that DNA vaccination at birth results in the rapid induction of antigen-specific CD8(+) T cells within neonatal life. Analyses of T-cell effector functions critical for the resolution of many viral infections revealed that neonatal and adult CD8(+) T cells produce similar arrays of cytokines. Furthermore, the avidities of neonatal and adult CD8(+) T cells for peptide and the rapidity with which they upregulate cytokine production after recall encounters with antigen are similar. Protective immunity against the arenavirus lymphocytic choriomeningitis virus, which is mediated by CD8(+) cytotoxic T cells, is also rapidly acquired within the neonatal period. Collectively these data imply that, at least in the case of CD8(+) T cells, neonates are not as immunodeficient as previously supposed and that DNA vaccines may be an effective and safe means of providing critical cell-mediated antiviral immunity extremely early in life.

Murine neonatal CD4+ lymph node cells are highly deficient in the development of antigen-specific Th1 function in adoptive adult hosts

It is well established that murine neonates are biased toward Th2 responses. Th2-dominant responses are observed following immunization with a variety of Ags, using different carrier/adjuvant systems, and are seen in both BALB/c and C57BL/6 mice. Therefore, Th2 skewing appears to be a universal phenomenon unique to the neonatal period. One important question about this phenomenon is whether these responses are due to T cell intrinsic properties or are regulated by the neonatal environment. Here we have addressed this issue by transferring neonatal or adult CD4(+) lymph node cells to adoptive adult recombinase-activating gene 2(-/-) hosts and studied the development of Th responses. Neonatal CD4(+) cells were highly deficient in the development of both primary and secondary Ag-specific Th1 responses. This did not appear to be due to anergy of a developed population, since exogenous IL-2 only marginally increased production of the Th1 cytokine IFN-gamma. This profound Th1 deficiency was observed despite similar proliferation by neonatal and adult cells within the recombinase-activating gene 2(-/-) hosts. Moreover, neonatal CD4(+) cells up-regulated activation markers in a manner similar to adult CD4(+) cells. Therefore, although their proliferation and phenotypic maturation proceeded normally, neonatal CD4(+) cells appeared to be intrinsically deficient in the functional maturation of Th1 lineage cells. These results offer a candidate explanation for the reduced graft-vs-host responses observed following transplantation of cord blood cells or murine neonatal lymphoid cells to allogeneic adult hosts.

DNA vaccination in the avian

Inoculation of naked DNA represents a novel approach to vaccine and immune therapeutic development. DNA vaccines or genetic immunization offers several advantages over the conventional vaccines for specific immune activation. Although a large number of vaccines have been made and are being used in the poultry industry, there have been no major advances in vaccine technology for this animal industry sector for decades. The potential advantages of DNA vaccines, such as over coming maternal immunity, in ovo delivery and absence of requirement for a cold-chain, combined with immunological efficacy make this new vaccine technology very attractive for the poultry industry. This review lists all of the published reports of experimental DNA vaccines developed for use in poultry and focuses on the trends, potentials and remaining barriers in the development of this new revolution in poultry vaccinology.

Current concepts on active immunization against respiratory syncytial virus for infants and young children

Respiratory syncytial virus (RSV) is the most important causative agent of viral respiratory tract infections in infants and young children. Passive immunization against RSV became available recently, but this does not apply to an effective vaccine as a result of dramatic adverse results of immunization with a RSV candidate vaccine in the 1960s and the lack of full knowledge of the immune response induced by RSV. Nonetheless intensive research during the past two decades has resulted in several interesting candidate vaccines, of which some have gone through testing in humans. These include the subunit vaccines PFP-1, PFP-2, BBG2Na and cold-passaged/temperature-sensitive mutants. The development of candidate vaccines against RSV is discussed. Because of questions, uncertainties and difficulties with the development of effective vaccines against RSV, it will probably be at least another 5 to 10 years before routine immunization against RSV becomes available.

Priming of measles virus-specific humoral- and cellular-immune responses in macaques by DNA vaccination

Although the currently used live attenuated measles vaccines are safe and effective, they are dependent on cold chain maintenance and are often ineffective in young infants due to interference by maternal antibody. Therefore, besides vector-based vaccines, different new generation non-replicating candidate measles vaccines are being considered, including nucleic acid vaccines. We have vaccinated cynomolgus macaques transdermally with DNA plasmids encoding measles virus (MV) proteins. Following two vaccinations, low serum antibody responses were detected. Wild-type measles virus challenge 1 year after vaccination showed reduced viraemia in some animals. However, accelerated humoral- and cellular-immune responses were observed in all vaccinated macaques, demonstrating successful priming by the DNA vaccines.

Genetic immunization of neonates

The vaccination of neonates is generally difficult due to immaturity of the immune system, higher susceptibility to tolerance and potential negative interference of maternal antibodies. Studies carried out in rodents and non-human primates showed that plasmid vaccines expressing microbial antigens, rather than inducing tolerance, triggered significant humoral and cellular immunity with a Th1 component. The ability of bacterial CpG motifs to activate immature antigen-presenting cells is critical for the neonatal immunogenicity of DNA vaccines. In addition, the endogenous production of antigen subsequent to transfection of antigen-presenting cells may explain the lack of inhibition by maternal antibodies of cellular responses. Together, these features make the plasmid vaccines an appealing strategy to prime immune responses against foreign pathogens, during early life. In combination with subsequent boosting using conventional vaccines, DNA vaccine-based regimens may provide a qualitatively superior immunity against microbes. Thorough understanding of immunomodulatory properties of plasmid-vectors may extend their use for early prophylaxis of inflammatory disorders.

Alterations in NF-kappaB and RBP-Jkappa by arenavirus infection of macrophages in vitro and in vivo

Pichinde virus is an arenavirus that infects guinea pigs and serves as an animal model for human Lassa fever. An attenuated Pichinde virus variant (P2) and a virulent variant (P18) are being used to delineate pathogenic mechanisms that culminate in shock. In guinea pigs, the infection has been shown to begin in peritoneal macrophages following intraperitoneal inoculation and then spreads to the spleen and other reticuloendothelial organs. We show here that infection of the murine monocytic cell line P388D1 with either Pichinde virus variant resulted in the induction of inflammatory cytokines and effectors, including interleukin-6 and tumor necrosis factor alpha. Since these genes are regulated in part by the cellular transcription factors NF-kappaB and RBP-Jkappa, we compared the activities of NF-kappaB and RBP-Jkappa in P388D1 cells following infection with Pichinde virus. The attenuated P2 virus inhibited NF-kappaB activation and caused a shift in the size of the RBP-Jkappa complex. The virulent P18 virus showed less inhibition of NF-kappaB and failed to alter the size of the RBP-Jkappa complex. Peritoneal cells from P2-infected guinea pigs showed induction of NF-kappaB RelA/p50 heterodimer and p50/p50 homodimer and manifested an increase in the size of RBP-Jkappa. By contrast, P18 induced large amounts of the NF-kappaB p50/p50 dimer but failed to induce RelA/p50 or to cause an increase in the RBP-Jkappa size. Taken together, these changes suggest that the attenuated viral strain induces an "activation" of macrophages, while the virulent form of the virus does not.

DNA vaccines: future strategies and relevance to intracellular pathogens

Increasing awareness of microbial threat has rekindled interest in the great potential of vaccines for controlling infectious diseases. The fact that diseases caused by intracellular pathogens cannot be overcome by chemotherapy alone has increased our interest in the generation of highly efficacious novel vaccines. Vaccines have proven their efficacy, as the immunoprotection they induce appears to be mediated by long-lived humoral immune responses. However, there are no consistently effective vaccines available against diseases such as tuberculosis and HIV, and other infections caused by intracellular pathogens, which are predominantly controlled by T lymphocytes. This review describes the T-cell populations and the type of immunity that should be activated by successful DNA vaccines against intracellular pathogens. It further discusses the parameters that need to be fulfilled by protective T-cell Ag. We then discuss future approaches for DNA vaccination against diseases in which cell-mediated immune responses are essential for providing protection.

Influence of maternal antibodies on neonatal immunization against respiratory viruses

Vaccines that successfully prevent severe infant respiratory virus diseases should induce protection at a very young age because of the low age of patients who are hospitalized owing to these viruses. Candidate respiratory virus vaccines are being tested in infants who are naïve to infection but seropositive to the viral agents because they possess maternal IgG antibodies (Abs). Transplacental maternal Abs may be partially protective against disease caused by respiratory virus infections. Carefully conducted studies have shown that these Abs can also profoundly suppress or enhance infant immune responses to immunization. The mechanisms underlying regulation of immune responses to viruses by maternal Abs are under investigation. This article explores the current knowledge regarding the effect of maternal Abs on respiratory virus and measles virus immunization, and it reviews the current approaches to overcoming Ab-mediated immunosuppression.

Enhancing T cell activation and antiviral protection by introducing the HIV-1 protein transduction domain into a DNA vaccine

Protein transduction domains (PTD), which can transport proteins or peptides across biological membranes, have been identified in several proteins of viral, invertebrate, and vertebrate origin. Here, we evaluate the immunological and biological consequences of including PTD in synthetic peptides and in DNA vaccines that contain CD8(+) T cell epitopes from lymphocytic choriomeningitis virus (LCMV). Synthetic PTD-peptides did not induce detectable CD8(+) T cell responses. However, fusion of an open reading frame encoding a PTD to an epitope minigene caused transfected tissue culture cells to stimulate epitope-specific T cells much more effectively. Kinetic studies indicated that the epitope reached the surface of transfected cells more rapidly and that the number of transfected cells needed to stimulate T cell responses was reduced by 35- to 50-fold when compared to cells transfected with a standard minigene plasmid. The mechanism underlying the effect of PTD linkage is not clear, but transit of the PTD-attached epitope from transfected cells to nontransfected cells (cross presentation) seemed to play, at most, a minimal role. Mice immunized once with the plasmid encoding the PTD-linked epitope showed a markedly accelerated CD8(+) T cell response and, unlike mice immunized with a standard plasmid, were completely protected against a normally lethal LCMV challenge administered only 8 days post-immunization.

T cell immunity in neonates

Typically, neonates exhibit decreased or aberrant cellular immune responses when compared to adults, resulting in increased susceptibility to infection. However, it is clear that newborns are able to generate adult-like protective T cell responses under certain conditions. The focus of our research is to understand the deficiencies within the neonatal immune system that lead to improper cellular responses and how priming conditions can be altered to elicit the appropriate T cell response necessary to protect against development of pathogen-induced disease. With these goals in mind, we are exploring the attributes of neonatal T cells and their development, as well as the conditions during priming that influence the resulting response to immune challenge during the neonatal period.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

Effect of maternal antibodies on influenza virus-specific immune response elicited by inactivated virus and naked DNA

While vaccines are effective in adults, they are less successful in newborns and infants. Neonatal unresponsiveness to vaccines could be owing to immaturity of lymphocytes and/or to inhibition by maternal antibodies. Unresponsiveness of newborn to vaccines can be overcame by genetic immunization. In the present study we investigated the effect of maternal antibodies on the anti-influenza virus protective response in progeny born to dams immunized with plasmid containing the hemagglutinin gene or UV-inactivated virus. The effect of maternal antibodies was studied in plasmid immunized F1 mice born to BALB/c dams, previously immunized with virus or plasmid and crossed with C57BL/6 males, as well as in offspring born to BALB/c dams immunized with plasmid and then immunized with UV-inactivated WSN virus. We have found that the inhibition period of the anti-HA antibody response in offspring born to dams immunized with DNA is shorter than that of offspring born to dams immunized with virus. Furthermore, there is a persistent inhibitory effect on B cells from offspring born to dams immunized with virus or injected with antiviral monoclonal antibodies (MoAb), after the decline of maternal antibody titers. The analysis of the haemagglutinin-specific clonotype reactivity pattern of offspring born to dams immunized with inactivated influenza virus or with a plasmid showed that clonotypes producing antibodies specific for the immunizing virus strain were predominant in offspring born to dams immunized with DNA compared to those born to dams immunized with virus. Maternal antibodies do not affect cell-mediated immunity. These findings might be used to design efficient vaccination schedules for newborns and infants.