When Can One Vaccinate with a Live Vaccine after Wild-Type Dengue Infection?

Recommendations have been issued for vaccinating with the Sanofi Pasteur tetravalent dengue vaccine (CYD-TDV, Dengvaxia^®) individuals aged from 9 to 45/60 years old with a prior dengue virus (DENV) infection and living in endemic countries/areas. One question linked to these recommendations is to determine when it is possible to start vaccination after laboratory confirmed wild-type DENV infection, and this question can be relevant to any live vaccine to be used in endemic areas. To address it, we reviewed and discussed the immunological and practical considerations of live vaccination in this context. Firstly, the nature and kinetics of immune responses triggered by primary or secondary DENV infection may positively or negatively impact subsequent live vaccine take and associated clinical benefit, depending on when vaccination is performed after infection. Secondly, regarding practical aspects, the “easiest” situation would correspond to a confirmed acute dengue fever, only requiring knowing when the patient should come back for vaccination. However, in most cases, it will not be possible to firmly establish the actual date of infection and vaccination may have to take place during well-defined periods, regardless of when prior infection occurred. Evidence that informs health authorities and medical practitioners in formulating vaccine policies and implementing vaccine programs is thus needed. The present work reviewed the different elements of the guidance and proposes some key conclusions and recommendations.

Evaluation of rapid diagnostic tests and conventional enzyme-linked immunosorbent assays to determine prior dengue infection

BACKGROUND

In September 2018, the World Health Organization recommended that prevaccination screening be used with the tetravalent dengue vaccine (CYD-TDV), to ensure that only individuals with evidence of prior dengue infection (PDI) are vaccinated. Dengue rapid diagnostic tests (RDTs) would offer a potential solution for prevaccination screening at the point-of-care, but data on performance of available RDTs for identifying PDI are limited. We determined the suitability of four dengue RDTs and two conventional enzyme-linked immunosorbent assays (ELISAs) to identify PDI and evaluated cross-reactivity with co-circulating flaviviruses.

Methods: Specificity was assessed using 534 dengue-negative [determined by 50% plaque reduction neutralization test (PRNT50)] serum samples from USA (n = 229) and dengue-endemic regions (n = 305). Sensitivity was assessed using 270 samples from recent (n = 90) or remote (n = 90) virologically confirmed prior dengue cases, and dengue PRNT50-positive samples (n = 90). Cross-reactivity was assessed in dengue-seronegative samples that were seropositive for yellow fever (n = 57), Japanese encephalitis (n = 37), West Nile (n = 59) or Zika (n = 41).

Results: Dengue IgG RDTs and the Panbio ELISA exhibited favourable specificities (99-100%), higher than the Focus ELISA (95%). The RDTs had variable sensitivities (40-70%) that were lower than those of the ELISAs (≥90%). Cross-reactivity to other flaviviruses was low with RDTs (≤7%), but more significant with ELISAs (up to 51% for West Nile and 34% for Zika). No cross-reactivity to any of the four closely related flaviviruses was observed with the CTK Biotech RDT. For each SeroTest, sensitivity appeared similar in samples from individuals with recent (<13 months) vs remote (3-4 years) virologically confirmed PDI.

Conclusions: In general, dengue IgG RDTs were found to be more specific and less cross-reactive than the ELISAs, but the latter were more sensitive for identifying PDI cases. Currently available RDTs could be temporizing tools for rapid and safe prevaccination screening until improved RDTs with increased sensitivity become available.

Dengue seroprevalence: data from the clinical development of a tetravalent dengue vaccine in 14 countries (2005-2014)

Dengue seroprevalence data in the literature is limited and the available information is difficult to compare between studies because of the varying survey designs and methods used. We assessed dengue seropositivity across 14 countries using data from 15 trials conducted during the development of a tetravalent dengue vaccine between October 2005 and February 2014. Participants’ dengue seropositivity (n=8592) was determined from baseline (before vaccination) serum samples at two centralized laboratories with the plaque reduction neutralization test (PRNT₅₀). Seropositivity rates generally increased with age in endemic settings. Although seropositivity rates varied across geographical areas, between countries, and within countries by region, no major differences were observed for given age groups between the two endemic regions, Latin America and Asia-Pacific. Seropositivity rates were generally stable over time. The proportion of participants who had only experienced primary infection tended to be higher in younger children than adolescents/adults. These results will help inform and guide dengue control strategies in the participating countries.

Which Dengue Vaccine Approach Is the Most Promising, and Should We Be Concerned about Enhanced Disease after Vaccination? Questions Raised by the Development and Implementation of Dengue Vaccines: Example of the Sanofi Pasteur Tetravalent Dengue Vaccine

Dengue is a still-growing public health concern in many tropical and subtropical regions of the world. The development and implementation of an effective dengue vaccine in these regions is a high priority. This insight focuses on the expected characteristics of a safe and efficacious vaccine, referring to the clinical experience obtained during the development of the first tetravalent dengue vaccine from Sanofi Pasteur, now licensed in several endemic countries. Safety and efficacy data from both short- and long-term follow-up of large-scale efficacy studies will be discussed, as well as the next steps following vaccine introduction.

Characterization of recombinant yellow fever-dengue vaccine viruses with human monoclonal antibodies targeting key conformational epitopes

The recombinant yellow fever-17D-dengue virus, live, attenuated, tetravalent dengue vaccine (CYD-TDV) is licensed in several dengue-endemic countries. Although the vaccine provides protection against dengue, the level of protection differs by serotype and warrants further investigation. We characterized the antigenic properties of each vaccine virus serotype using highly neutralizing human monoclonal antibodies (hmAbs) that bind quaternary structure-dependent epitopes. Specifically, we monitored the binding of dengue virus-1 (DENV-1; 1F4), DENV-2 (2D22) or DENV-3 (5J7) serotype-specific or DENV-1-4 cross-reactive (1C19) hmAbs to the four chimeric yellow fever-dengue vaccine viruses (CYD-1-4) included in phase III vaccine formulations using a range of biochemical and functional assays (dot blot, ELISA, surface plasmon resonance and plaque reduction neutralization assays). In addition, we used the "classic" live, attenuated DENV-2 vaccine serotype, immature CYD-2 viruses and DENV-2 virus-like particles as control antigens for anti-serotype-2 reactivity. The CYD vaccine serotypes were recognized by each hmAbs with the expected specificity, moreover, surface plasmon resonance indicated a high functional affinity interaction with the CYD serotypes. In addition, the hmAbs provided similar protection against CYD and wild-type dengue viruses in the in vitro neutralization assay. Overall, these findings demonstrate that the four CYD viruses used in clinical trials display key conformational and functional epitopes targeted by serotype-specific and/or cross-reactive neutralizing human antibodies. More specifically, we showed that CYD-2 displays serotype- specific epitopes present only on the mature virus. This indicates that the CYD-TDV has the ability to elicit antibody specificities which are similar to those induced by the wild type DENV. Future investigations will be needed to address the nature of CYD-TDV-induced responses after vaccine administration, and how these laboratory markers relate to vaccine efficacy and safety.

Biodistribution and safety of a live attenuated tetravalent dengue vaccine in the cynomolgus monkey

BACKGROUND

The first licensed dengue vaccine is a recombinant, live, attenuated, tetravalent dengue virus vaccine (CYD-TDV; Sanofi Pasteur). This study assessed the biodistribution, shedding, and toxicity of CYD-TDV in a non-human primate model as part of the nonclinical safety assessment program for the vaccine.

METHODS

Cynomolgus monkeys were given one subcutaneous injection of either one human dose (5log₁₀ CCID₅₀/serotype) of CYD-TDV or saline control. Study endpoints included clinical observations, body temperature, body weight, food consumption, clinical pathology, immunogenicity, and post-mortem examinations including histopathology. Viral load, distribution, persistence, and shedding in tissues and body fluids were evaluated by quantitative reverse transcriptase polymerase chain reaction.

RESULTS

The subcutaneous administration of CYD-TDV was well tolerated. There were no toxicological findings other than expected minor local reactions at the injection site. A transient low level of CYD-TDV viral RNA was detected in blood and the viral genome was identified primarily at the injection site and in the draining lymph nodes following immunization.

CONCLUSIONS

These results, together with other data from repeat-dose toxicity and neurovirulence studies, confirm the absence of toxicological concern with CYD-TDV and corroborate clinical study observations.

Integrated immunogenicity analysis of a tetravalent dengue vaccine up to 4 y after vaccination

Two large pivotal phase III studies demonstrated the efficacy of the tetravalent dengue vaccine (CYD-TDV; Dengvaxia®, Sanofi Pasteur) against all dengue serotypes. Here we present an unprecedented integrated summary of the immunogenicity of CYD-TDV to identify the parameters driving the neutralizing humoral immune response and evolution over time. We summarized the immunogenicity profiles of a 3-dose schedule of CYD-TDV administered 6 months apart across 10 phase II and 6 phase III trials undertaken in dengue endemic and non-endemic countries. Dengue neutralizing antibody titers in sera were determined at centralized laboratories using the 50% plaque reduction neutralization test (PRNT50) at baseline, 28 d after the third dose, and annually thereafter for up to 4 y after the third dose in some studies. CYD-TDV elicits neutralizing antibody responses against all 4 dengue serotypes; geometric mean titers (GMTs) increased from baseline to post-dose 3. GMTs were influenced by several parameters including age, baseline dengue seropositivity and region. In the 2 pivotal studies, GMTs decreased initially during the first 2 y post-dose 3 but appear to stabilize or slightly increase again in the third year. GMTs persisted 1.2-3.2-fold higher than baseline levels for up to 4 y post-dose 3 in other studies undertaken in dengue endemic countries. Our integrated analysis captures the fullness of the CYD-TDV immunogenicity profile across studies, age groups and regions; by presenting the available data in this way general trends and substantial outliers within each grouping can be easily identified. CYD-TDV elicits neutralizing antibody responses against all dengue serotypes, with differences by age and endemicity, which persist above baseline levels in endemic countries.

Dissecting Antibodies Induced by a Chimeric Yellow Fever-Dengue, Live-Attenuated, Tetravalent Dengue Vaccine (CYD-TDV) in Naive and Dengue-Exposed Individuals

Sanofi Pasteur has developed a chimeric yellow fever-dengue, live-attenuated, tetravalent dengue vaccine (CYD-TDV) that is currently approved for use in several countries. In clinical trials, CYD-TDV was efficacious at reducing laboratory-confirmed cases of dengue disease. Efficacy varied by dengue virus (DENV) serotype and prevaccination dengue immune status. We compared the properties of antibodies in naive and DENV-exposed individuals who received CYD-TDV. We depleted specific populations of DENV-reactive antibodies from immune serum samples to estimate the contribution of serotype-cross-reactive and type-specific antibodies to neutralization. Subjects with no preexisting immunity to DENV developed neutralizing antibodies to all 4 serotypes of DENV. Further analysis demonstrated that DENV4 was mainly neutralized by type-specific antibodies whereas DENV1, DENV2, and DENV3 were mainly neutralized by serotype cross-reactive antibodies. When subjects with preexisting immunity to DENV were vaccinated, they developed higher levels of neutralizing antibodies than naive subjects who were vaccinated. In preimmune subjects, CYD-TDV boosted cross-reactive neutralizing antibodies while maintaining type-specific neutralizing antibodies acquired before vaccination. Our results demonstrate that the quality of neutralizing antibodies induced by CYD-TDV varies depending on DENV serotype and previous immune status. We discuss the implications of these results for understanding vaccine efficacy.

Potential impact of dengue vaccination: Insights from two large-scale phase III trials with a tetravalent dengue vaccine

BACKGROUND

A tetravalent dengue vaccine demonstrated its protective efficacy in two phase III efficacy studies. Results from these studies were used to derive vaccination impact in the five Asian (Indonesia, Malaysia, Philippines, Thailand, Vietnam) and the five Latin American countries (Brazil, Colombia, Honduras, Mexico and Puerto Rico) participating in these trials.

METHODS

Vaccination impact was investigated with an age-structured, host-vector, serotype-specific compartmental model. Parameters related to vaccine efficacy and levels of dengue transmission were estimated using data collected during the phase III efficacy studies. Several vaccination programs, including routine vaccination at different ages with and without large catch-up campaigns, were investigated.

RESULTS

All vaccination programs explored translated into significant reductions in dengue cases at the population level over the first 10years following vaccine introduction and beyond. The most efficient age for vaccination varied according to transmission intensity and 9years was close to the most efficient age across all settings. The combination of routine vaccination and large catch-up campaigns was found to enable a rapid reduction of dengue burden after vaccine introduction.

CONCLUSION

Our analysis suggests that dengue vaccination can significantly reduce the public health impact of dengue in countries where the disease is endemic.

[Multiple pulmonary opacities revealing toxocariasis]

INTRODUCTION

Toxocariasis is a parasitosis which complicates the accidental infestation of the humans by larvae of a roundworms belonging of the genus Toxocara. In adults, the discovery is often incidental during a hypereosinophilia check-up. Clinical signs are not specific and depend on affected organs.

CASE REPORT

We report the case of a 53-year-old-woman who has consulted for a recent cough, after spontaneous resolution of abdominal pain. The laboratory examination isolated an hypereosinophilia and the liver sonography showed two hypoechogenic nodules. The CT-scan found bilateral lung nodules with ground glass halo. Broncho-alveolar lavage identified an eosinophilic alveolitis. Positive serologic results for toxocariasis and western blot results allowed to conclude to the diagnosis of pulmonary and hepatic toxocariasis.

CONCLUSION

Although rare, pulmonary toxocariasis should be suspect in any lung eosinophilia, especially if the patient has never traveled.

Tetravalent Dengue Vaccine Reduces Symptomatic and Asymptomatic Dengue Virus Infections in Healthy Children and Adolescents Aged 2-16 Years in Asia and Latin America

BACKGROUND

Asymptomatic dengue virus-infected individuals are thought to play a major role in dengue virus transmission. The efficacy of the recently approved quadrivalent CYD-TDV dengue vaccine against asymptomatic dengue virus infection has not been previously assessed.

METHODS

We pooled data for 3 736 individuals who received either CYD-TDV or placebo at 0, 6, and 12 months in the immunogenicity subsets of 2 phase 3 trials (clinical trials registration NCT01373281 and NCT01374516). We defined a seroconversion algorithm (ie, a ≥4-fold increase in the neutralizing antibody titer and a titer of ≥40 from month 13 to month 25) as a surrogate marker of asymptomatic infection in the vaccine and placebo groups.

RESULTS

The algorithm detected seroconversion in 94% of individuals with a diagnosis of virologically confirmed dengue between months 13 and 25, validating its discriminatory power. Among those without virologically confirmed dengue (n = 3 669), 219 of 2 485 in the vaccine group and 157 of 1 184 in the placebo group seroconverted between months 13 and 25, giving a vaccine efficacy of 33.5% (95% confidence interval [CI], 17.9%-46.1%) against asymptomatic infection. Vaccine efficacy was marginally higher in subjects aged 9-16 years (38.6%; 95% CI, 22.1%-51.5%). The annual incidence of asymptomatic dengue virus infection in this age group was 14.8%, which was 4.4 times higher than the incidence for symptomatic dengue (3.4%).

CONCLUSIONS

The observed vaccine efficacy against asymptomatic dengue virus infections is expected to translate into reduced dengue virus transmission if sufficient individuals are vaccinated in dengue-endemic areas.

Dengue vaccine: hypotheses to understand CYD-TDV-induced protection

Dengue virus (DENV) is a human pathogen with a large impact on public health. Although no vaccine against DENV is currently licensed, a recombinant vaccine - chimeric yellow fever virus-DENV tetravalent dengue vaccine (CYD-TDV) - has shown efficacy against symptomatic dengue disease in two recent Phase III clinical trials. Safety observations were also recently reported for these trials. In this Opinion article, we review the data from recent vaccine clinical trials and discuss the putative mechanisms behind the observed efficacy of the vaccine against different forms of the disease, focusing on the interactions between the infecting virus, pre-existing host immunity and vaccine-induced immune responses.

Influence of FcγRIIa-Expressing Cells on the Assessment of Neutralizing and Enhancing Serum Antibodies Elicited by a Live-Attenuated Tetravalent Dengue Vaccine

Background.  Recent trials of recombinant, live-attenuated chimeric yellow fever-dengue tetravalent dengue vaccine (CYD-TDV) demonstrated efficacy against symptomatic, virologically confirmed dengue disease with higher point estimates of efficacy toward dengue virus (DENV)3 and DENV4 and moderate levels toward DENV1 and DENV2. It is interesting to note that serotype-specific efficacy did not correlate with absolute neutralizing antibody (nAb) geometric mean titer (GMT) values measured in a Vero-based plaque reduction neutralization test assay. The absence of Fcγ receptors on Vero cells may explain this observation. Methods.  We performed parallel seroneutralization assays in Vero cells and CV-1 cells that express FcγRIIa (CV-1-Fc) to determine the neutralizing and enhancing capacity of serotype-specific DENV Abs present in CYD-TDV clinical trial sera. Results.  Enhancement of DENV infection was observed in CV-1-Fc cells in naturally exposed nonvaccine sera, mostly for DENV3 and DENV4, at high dilutions. The CYD-TDV-vaccinated sera showed similar enhancement patterns. The CV-1-Fc nAb GMT values were 2- to 9-fold lower than Vero for all serotypes in both naturally infected individuals and CYD-TDV-vaccinated subjects with and without previous dengue immunity. The relative (CV-1-Fc/Vero) GMT decrease for anti-DENV1 and anti-DENV2 responses was not greater than for the other serotypes. Conclusions.  In vitro neutralization assays utilizing FcγRIIa-expressing cells provide evidence that serotype-specific Ab enhancement may not be a primary factor in the serotype-specific efficacy differences exhibited in the CYD-TDV trials.

Assessment of bivalent and tetravalent dengue vaccine formulations in flavivirus-naïve adults in Mexico

Several ChimeriVax-Dengue (CYD)-based vaccination strategies were investigated as potential alternatives to vaccination with tetravalent CYD vaccine (CYD-TDV) in this phase IIa trial conducted in 2008–9 in 150 healthy adults. Participants were randomized and vaccinated on D0 and D105 (± 15 days). One group received bivalent CYD vaccine against serotypes 1 and 3 (CYD-1;3) on day 0 and CYD-2;4 on day 105 (±15 days). Two groups received an injection at each timepoint of a tetravalent blend of CYD-1;3;4 and a VERO cell derived, live attenuated vaccine against serotype 2 (VDV-2), or the reference CYD-TDV. A fourth group received Japanese encephalitis (JE) vaccine on days -14, -7 and 0, followed by CYD-TDV on day 105. Viraemia was infrequent in all groups. CYD-4 viraemia was most frequent after tetravalent vaccination, while CYD-3 viraemia was most frequent after the first bivalent vaccination. Immunogenicity as assessed by 50% plaque reduction neutralisation test on D28 was comparable after the first injection of either tetravalent vaccine, and increased after the second injection, particularly with the blended CYD-1;3;4/ VDV-2 vaccine. In the bivalent vaccine group, immune response against serotype 3 was highest and the second injection elicited a low immune response against CYD 2 and 4. Immune responses after the first injection of CYD-TDV in the JE-primed group were in general higher than after the first injection in the other groups. All tested regimens were well tolerated without marked differences between groups. Bivalent vaccination showed no advantage in terms of immunogenicity.

Clinical trial registration number: NCT00740155

Site-specific characterization of envelope protein N-glycosylation on Sanofi Pasteur's tetravalent CYD dengue vaccine

Recently, several virus studies have shown that protein glycosylation play a fundamental role in the virus-host cell interaction. Glycosylation characterization of the envelope proteins in both insect and mammalian cell-derived dengue virus (DENV) has established that two potential glycosylation residues, the asparagine 67 and 153 can potentially be glycosylated. Moreover, it appears that the glycosylation of these two residues can influence dramatically the virus production and the infection spreading in either mosquito or mammalian cells. The Sanofi Pasteur tetravalent dengue vaccine (CYD) consists of four chimeric viruses produced in mammalian vero cells. As DENV, the CYDs are able to infect human monocyte-derived dendritic cells in vitro via C-type lectins cell-surface molecules. Despite the importance of this interaction, the specific glycosylation pattern of the DENV has not been clearly documented so far. In this paper, we investigated the structure of the N-linked glycans in the four CYD serotypes. Using MALDI-TOF analysis, the N-linked glycans of CYDs were found to be a mix of high-mannose, hybrid and complex glycans. Site-specific N-glycosylation analysis of CYDs using nanoLC-ESI-MS/MS demonstrates that both asparagine residues 67 and 153 are glycosylated. Predominant glycoforms at asparagine 67 are high mannose-type structures while mainly complex- and hybrid-type structures are detected at asparagine 153. In vitro studies have shown that the immunological consequences of infection by the CYD dengue viruses 1-4 versus the wild type parents are comparable in human monocyte-derived dendritic cells. Our E-protein glycan characterizations of CYD are consistent with those observations from the wild type parents and thus support in vitro studies. In addition, these data provide new insights for the role of glycans in the dengue virus-host cell interactions.

Live virus vaccines based on a yellow fever vaccine backbone: standardized template with key considerations for a risk/benefit assessment

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety of live, recombinant viral vaccines incorporating genes from heterologous viruses inserted into the backbone of another virus (so-called "chimeric virus vaccines"). Many viral vector vaccines are in advanced clinical trials. The first such vaccine to be approved for marketing (to date in Australia, Thailand, Malaysia, and the Philippines) is a vaccine against the flavivirus, Japanese encephalitis (JE), which employs a licensed vaccine (yellow fever 17D) as a vector. In this vaccine, two envelope proteins (prM-E) of YF 17D virus were exchanged for the corresponding genes of JE virus, with additional attenuating mutations incorporated into the JE gene inserts. Similar vaccines have been constructed by inserting prM-E genes of dengue and West Nile into YF 17D virus and are in late stage clinical studies. The dengue vaccine is, however, more complex in that it requires a mixture of four live vectors each expressing one of the four dengue serotypes. This vaccine has been evaluated in multiple clinical trials. No significant safety concerns have been found. The Phase 3 trials met their endpoints in terms of overall reduction of confirmed dengue fever, and, most importantly a significant reduction in severe dengue and hospitalization due to dengue. However, based on results that have been published so far, efficacy in preventing serotype 2 infection is less than that for the other three serotypes. In the development of these chimeric vaccines, an important series of comparative studies of safety and efficacy were made using the parental YF 17D vaccine virus as a benchmark. In this paper, we use a standardized template describing the key characteristics of the novel flavivirus vaccine vectors, in comparison to the parental YF 17D vaccine. The template facilitates scientific discourse among key stakeholders by increasing the transparency and comparability of information. The Brighton Collaboration V3SWG template may also be useful as a guide to the evaluation of other recombinant viral vector vaccines.

Cross-serotype immunity induced by immunization with a conserved rhinovirus capsid protein

Human rhinovirus (RV) infections are the principle cause of common colds and precipitate asthma and COPD exacerbations. There is currently no RV vaccine, largely due to the existence of ∼150 strains. We aimed to define highly conserved areas of the RV proteome and test their usefulness as candidate antigens for a broadly cross-reactive vaccine, using a mouse infection model. Regions of the VP0 (VP4+VP2) capsid protein were identified as having high homology across RVs. Immunization with a recombinant VP0 combined with a Th1 promoting adjuvant induced systemic, antigen specific, cross-serotype, cellular and humoral immune responses. Similar cross-reactive responses were observed in the lungs of immunized mice after infection with heterologous RV strains. Immunization enhanced the generation of heterosubtypic neutralizing antibodies and lung memory T cells, and caused more rapid virus clearance. Conserved domains of the RV capsid therefore induce cross-reactive immune responses and represent candidates for a subunit RV vaccine.

Persistence of Th1/Tc1 responses one year after tetravalent dengue vaccination in adults and adolescents in Singapore

To characterize the cell mediated immunity (CMI) induced by the investigational CYD tetravalent dengue vaccine (TDV), we developed a whole-blood, intracellular cytokine staining (ICS) assay and a multiplex assay, each requiring 3 mL of blood. We assessed CMI before and 28 d after a first and third injection of CYD-TDV and one year after the third injection in a subset of 80 adolescents and adults enrolled in a phase II trial in Singapore (ClinicalTrial.gov NCT NCT00880893). CD4/IFNγ/TNFα responses specific to dengue NS3 were detected before vaccination. Vaccination induced YF-17D-NS3-specific CD8/IFNγ responses, without significant TNFα, and a CYD-specific Th1/Tc1 cellular response in all participants, which was characterized by predominant IFNγ secretion compared with TNFα, associated with low level IL-13 secretion in multiplex analysis of peripheral blood mononuclear cells (PBMC) supernatants after restimulation with each the CYD vaccine viruses. Responses were directed mainly against CYD-4 after the first vaccination, and were more balanced against all four serotypes after the third vaccination. The same qualitative profile was observed one year after the third vaccination, with approximately 2-fold lower NS3-specific responses, and 3-fold lower serotype-specific cellular responses. These findings confirm previous observations regarding both the nature and specificity of cellular responses induced by CYD-TDV, and for the first time demonstrate the persistence of cellular responses after one year. We also established the feasibility of analyzing CMI with small blood samples, allowing such analysis to be considered for pediatric trials.

Evaluation of chimeric yellow fever 17D/dengue viral replication in ticks

Chimeric yellow fever 17D/DENV-1-4 viruses (CYD-1-4) have been developed as a tetravalent dengue vaccine candidate which is currently being evaluated in efficacy trials in Asia and America. While YF 17D and DENV are mosquito-borne flaviviruses, it has been shown that CYD-1-4 do not replicate after oral infection in mosquitoes and are not transmitted to new hosts. To further document the risk of environmental dissemination of these viruses, we evaluated the replication of CYD-1-4 in ticks, the vector of tick-borne encephalitis virus (TBEV), another member of the flavivirus family. Females of two hard tick species, Ixodes ricinus and Rhipicephalus appendiculatus, were inoculated intracoelomically with CYD-1-4 viruses and parent viruses (DENV-1-4 and YF 17D). Virus persistence and replication was assessed 2, 16, and 44 days post-inoculation by plaque titration and qRT-PCR. CYD-1-4 viruses were detected in I. ricinus ticks at early time points post-inoculation, but with infectious titers at least 100-fold lower than those observed in TBEV-infected ticks. Unlike TBEV, complete viral clearance occurred by day 44 in most ticks except for CYD-2, which had a tendency to decline. In addition, while about 70% of TBEV-infected I. ricinus nymphs acquired infection by co-feeding with infected tick females on non-viremic hosts, no co-feeding transmission of CYD-2 virus was detected. Based on these results, we conclude that the risk of dissemination of the candidate vaccine viruses by tick bite is highly unlikely.

Stability of yellow fever virus under recombinatory pressure as compared with chikungunya virus

Recombination is a mechanism whereby positive sense single stranded RNA viruses exchange segments of genetic information. Recent phylogenetic analyses of naturally occurring recombinant flaviviruses have raised concerns regarding the potential for the emergence of virulent recombinants either post-vaccination or following co-infection with two distinct wild-type viruses. To characterize the conditions and sequences that favor RNA arthropod-borne virus recombination we constructed yellow fever virus (YFV) 17D recombinant crosses containing complementary deletions in the envelope protein coding sequence. These constructs were designed to strongly favor recombination, and the detection conditions were optimized to achieve high sensitivity recovery of putative recombinants. Full length recombinant YFV 17D virus was never detected under any of the experimental conditions examined, despite achieving estimated YFV replicon co-infection levels of ∼2.4×10⁶ in BHK-21 (vertebrate) cells and ∼1.05×10⁵ in C₇10 (arthropod) cells. Additionally YFV 17D superinfection resistance was observed in vertebrate and arthropod cells harboring a primary infection with wild-type YFV Asibi strain. Furthermore recombination potential was also evaluated using similarly designed chikungunya virus (CHIKV) replicons towards validation of this strategy for recombination detection. Non-homologus recombination was observed for CHIKV within the structural gene coding sequence resulting in an in-frame duplication of capsid and E3 gene. Based on these data, it is concluded that even in the unlikely event of a high level acute co-infection of two distinct YFV genomes in an arthropod or vertebrate host, the generation of viable flavivirus recombinants is extremely unlikely.

Different innate signatures induced in human monocyte-derived dendritic cells by wild-type dengue 3 virus, attenuated but reactogenic dengue 3 vaccine virus, or attenuated nonreactogenic dengue 1-4 vaccine virus strains

DNA microarrays were used to assess the innate gene signature in human myeloid dendritic cells infected with chimeric dengue 1-4 vaccines, a wild-type dengue 3 virus, or a classically attenuated serotype 3 vaccine shown to be reactogenic in humans. We observed a very reproducible signature for each of the 4 chimeric dengue vaccines, involving stimulation of type I interferon and associated genes, together with genes encoding chemokines and other mediators involved in the initiation of adaptive responses. In contrast, wild-typeDEN3 virus induced a predominantly inflammatory profile, while the reactogenic attenuated serotype 3 vaccine appeared to induce a blunted response.

[Tetravalent dengue vaccine development]

The Sanofi Pasteur tetravalent dengue vaccine candidate (TV) is composed of four recombinant live attenuated vaccines based on a yellow fever virus vaccine 17D (YFV 17D) backbone, each expressing the prM and envelope genes of one of the four dengue virus serotypes. Pre-clinical studies have demonstrated that the TV dengue vaccine is genetically and phenotypi- cally stable, non-hepatotropic, less neurovirulent than YFV 17D and does not infect mosquitoes by the oral route. In clinics, TV dengue vaccine reactogeni- city, viraemia induction and antibody responses were investigated in three Phase II trials in endemic and non-endemic countries, which demonstrated its good safety and immunogenicity. An extensive clinical development program for dengue TV is underway including an efficacy trial in Thailand, in an area of high dengue incidence. Assuming continued successful outcomes, initial submissions to regulatory authorities are envisaged within a 5-year period.

Development of Sanofi Pasteur tetravalent dengue vaccine

The Sanofi Pasteur tetravalent dengue vaccine candidate is composed of 4 recombinant live attenuated vaccines based on a yellow fever vaccine 17D (YFV 17D) backbone, each expressing the prM and envelope genes of one of the four dengue virus serotypes. Pre-clinical studies have demonstrated that the TV dengue vaccine is genetically and phenotypically stable, non-hepatotropic, less neurovirulent than YFV 17D and does not infect mosquitoes by the oral route. In vitro and in vivo preclinical studies also showed that the TV dengue vaccine induced controlled stimulation in human dendritic cells and significant immune responses in monkeys. TV dengue vaccine reactogenicity, viraemia induction and antibody responses were investigated in three Phase I trials in the USA, the Philippines and Mexico, in a two or three-dose regimen over a 12 month period. Results showed that the majority of adverse events were mild to moderate and transient in nature. Viraemia was transient and low, and was not increased after initial dengue TV administration, even in the case of incomplete responses. ϕSeropositivity [≥10 in a PRNT 50 assay] was 100% for all four serotypes in flavivirus-naive adults injected with 3 doses of TV dengue vaccine in the USA. Similarly, seropositivity was 88-100% following three administrations in flavivirus-naive Mexican children aged 2-5 years. Furthermore, the proportion of seropositive subjects increased with each dengue TV injection in the Philippines where baseline flavivirus immunity was high. Responses were also monitored at the cellular level in humans, and their level and nature were in good agreement with the observed safety and the immunogenicity of the vaccine. Finally, the challenges inherent to the development of such TV dengue vaccines will also be discussed in the last part of this review. In conclusion, preclinical and clinical results support the favorable immunogenicity and short-term safety of the dengue TV vaccine. An extensive clinical development program for dengue TV is underway including completion of the enrollment of 4,000 4-11 years old children in an efficacy trial in Thailand, in an area of high dengue incidence. Assuming continued successful outcomes, initial submissions to regulatory authorities are envisaged within a 5-year period.

[Long term renal outcome of children born preterm: a regular follow-up is needed]

Most of the published studies evaluating renal prognosis of children born very preterm found asymptomatic abnormalities (blood pressure, glomerular filtration rate GFR, hypercalciuria, decreased renal size, microalbuminuria...) during childhood or early adulthood. The objective of this study was to assess renal function (inulin clearance) in a prospective single-center cohort of children born preterm between 1998 and 2001 (< 30 GW,<1000 g) and to identify neonatal risk factors for renal abnormalities during childhood. Fifty children were included in the final part of the study. At a mean age of 7.6 years, no patient had arterial hypertension or chronic kidney disease, but mean centile for diastolic blood pressure was higher than expected and ultrasounds revealed small-sized kidneys compared to controls. The average GFR was 112 ml/min per 1.73 m(2) (91-158). Two children had microalbuminuria, two had hypercalciuria and one had nephrocalcinosis. Children with intra- or extra-uterine growth retardation had an impaired GFR compared to children with appropriate pre- and post-natal growth (107 vs. 110 vs. 125 ml/min per 1.73 m(2), p<0.05). Children with bronchopulmonary dysplasia had a significant higher microalbuminuria. In conclusion, findings of borderline blood pressure and reduced kidney size in children born preterm can be regarded as markers of reduced nephron number. Long term renal follow-up (blood pressure, serum creatinine, urine albumin / creatinine ratio) should be performed in all children born very preterm, with an early referring when abnormalities are highlighted.

Strategies to improve the effect of vaccination in the elderly: the vaccine producer's perspective

The weakened immune system of elderly people presents particular challenges in the development of vaccines and vaccination strategies for this population. There are well recognized changes in the function of antigen presenting cells (APCs), T cells and B cells in older people. Several strategies to improve vaccination in the elderly have been explored. The use of adjuvants (e.g. emulsions and Toll-like receptor [TLR] agonists) could trigger more potent activation of APCs. The addition of T helper epitopes to the vaccine antigens could enhance T-cell responses by acting as 'intrinsic' adjuvants. The use of interleukin (IL)-7 could improve the expansion of naïve T cells in the elderly, accompanied by a broadened T-cell repertoire. A further means of enhancing antigen presentation and subsequent T-cell activation would be to increase the vaccine dose and/or antigenic content. Vaccination schedules could also be adapted. In particular, vaccination at an earlier age may trigger naïve T cells and subsequent generation of memory cells more efficiently and these cells may be recalled more easily in later life. Vaccination against cytomegalovirus (CMV) early in life has also been proposed to avoid the 'CMV bias' of the immune response that is seen in the elderly population. Immunization routes other than by intramuscular or subcutaneous injection may be more efficient, by delivering antigen to sites enriched in APCs such as the epidermis and/or dermis. Finally, the use of polysaccharide-protein conjugates might enhance the level and functionality of antibodies directed against polysaccharides. These different possibilities, alone or in combination, could improve vaccine efficacy in elderly human populations.

Preclinical and clinical development of YFV 17D-based chimeric vaccines against dengue, West Nile and Japanese encephalitis viruses

Dengue viruses (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV) are major global health and growing medical problems. While a live-attenuated vaccine exists since decades against the prototype flavivirus, yellow fever virus (YFV), there is an urgent need for vaccines against dengue or West Nile diseases, and for improved vaccines against Japanese encephalitis. Live-attenuated chimeric viruses were constructed by replacing the genes coding for Premembrane (prM) and Envelope (E) proteins from YFV 17D vaccine strain with those of heterologous flaviviruses (ChimeriVax technology). This technology has been used to produce vaccine candidates for humans, for construction of a horse vaccine for West Nile fever, and as diagnostic reagents for dengue, Japanese encephalitis, West Nile and St. Louis encephalitis infections. This review focuses on human vaccines and their characterization from the early stages of research through to clinical development. Phenotypic and genetic properties and stability were examined, preclinical evaluation through in vitro or animal models, and clinical testing were carried out. Theoretical environmental concerns linked to the live and genetically modified nature of these vaccines have been carefully addressed. Results of the extensive characterizations are in accordance with the immunogenicity and excellent safety profile of the ChimeriVax-based vaccine candidates, and support their development towards large-scale efficacy trials and registration.

Evaluation of interferences between dengue vaccine serotypes in a monkey model

Interferences between different antigens in the same vaccine formulation have been reported for some vaccines (e.g., polio vaccines, live attenuated dengue vaccine candidates). We examined interferences between the four serotypes of ChimeriVax dengue vaccines (CYDs) in a monkey model when present within a tetravalent formulation in equal concentrations (TV-5555). Immunoassays of vaccinated non-human primates showed that serotype 4 (DEN-4), and to a lesser extent, DEN-1 were dominant in terms of neutralizing antibody levels. Parameters that affected the interferences were identified, including 1) the simultaneous administration of two complementary bivalent vaccines at separate anatomical sites drained by different lymph nodes; 2) the sequential administration of two complementary bivalent vaccines; 3) the establishment of heterologous flavivirus pre-immunity before subsequent tetravalent immunization; 4) the adaptation of formulations by decreasing the dose of the immunodominant serotype; and 5) the administration of a 1-year booster. The applicability of these data to human responses is discussed.

Intradermal, epidermal and transcutaneous vaccination: from immunology to clinical practice

The dermis and epidermis are alternative sites for prophylactic vaccination that have received renewed interest in recent years, not only because of the ease of access to the skin, but also its unique immunological properties. This review discusses the characteristics of the skin, current knowledge on skin immunity and clinical experience with cutaneous immunization against infectious diseases, with a special focus on intradermal immunization. The most widely accepted paradigm explaining the efficacy of cutaneous immunization is reviewed and recent research suggesting where this paradigm may need some refinement is highlighted. Clinical investigations that have concentrated on the intradermal route to vaccinate against influenza, rabies or hepatitis B support the current knowledge on skin immunity and, when combined with recent progress made in the development of user-friendly injection systems, have stimulated the ongoing clinical development of novel vaccines.

Substitution of wild-type yellow fever Asibi sequences for 17D vaccine sequences in ChimeriVax-dengue 4 does not enhance infection of Aedes aegypti mosquitoes

To address concerns that a flavivirus vaccine/wild-type recombinant virus might have a high mosquito infectivity phenotype, the yellow fever virus (YFV) 17D backbone of the ChimeriVax-dengue 4 virus was replaced with the corresponding gene sequences of the virulent YFV Asibi strain. Field-collected and laboratory-colonized Aedes aegypti mosquitoes were fed on blood containing each of the viruses under investigation and held for 14 days after infection. Infection and dissemination rates were based on antigen detection in titrated body or head triturates. Our data indicate that, even in the highly unlikely event of recombination or substantial backbone reversion, virulent sequences do not enhance the transmissibility of ChimeriVax viruses. In light of the low-level viremias that have been observed after vaccination in human volunteers coupled with low mosquito infectivity, it is predicted that the risk of mosquito infection and transmission of ChimeriVax vaccine recombinant/revertant viruses in nature is minimal.

Recombinant chimeric virus with wild-type dengue 4 virus premembrane and envelope and virulent yellow fever virus Asibi backbone sequences is dramatically attenuated in nonhuman primates

Candidate vaccine ChimeriVax viruses are attenuated, efficacious, safe, and highly unlikely to be transmitted by arthropod vectors. Nevertheless, concerns have been raised about the use of these vaccines because of the potential for recombination between vaccine and wild-type (WT) strains. To evaluate the vertebrate pathogenicity of such a worst-case recombinant, ChimeriVax-dengue (DEN) 4 virus was chimerized with the WT Asibi yellow fever virus. In this worst-case scenario, chimeric viruses remained fully attenuated in nonhuman primates. We therefore conclude that, even in the highly unlikely event of "virulent" backbone reversion, the safety of ChimeriVax-DEN vaccines would not be compromised.

Towards a dengue vaccine: Progress to date and remaining challenges

The increased incidence and extended geographical reach of Dengue virus over the past two decades have made the development of an effective vaccine an international urgency. Various strategies are being pursued, including live, vectored and killed/recombinant preparations. For all approaches, the challenge is to induce a broad durable immune response against all four serotypes of Dengue virus simultaneously whilst avoiding the possible exacerbation of risk of developing the severe forms of disease through incomplete or modified responses. This review presents the current state of knowledge and discusses the challenges of further clinical development.

Mouse models of rhinovirus-induced disease and exacerbation of allergic airway inflammation

Rhinoviruses cause serious morbidity and mortality as the major etiological agents of asthma exacerbations and the common cold. A major obstacle to understanding disease pathogenesis and to the development of effective therapies has been the lack of a small-animal model for rhinovirus infection. Of the 100 known rhinovirus serotypes, 90% (the major group) use human intercellular adhesion molecule-1 (ICAM-1) as their cellular receptor and do not bind mouse ICAM-1; the remaining 10% (the minor group) use a member of the low-density lipoprotein receptor family and can bind the mouse counterpart. Here we describe three novel mouse models of rhinovirus infection: minor-group rhinovirus infection of BALB/c mice, major-group rhinovirus infection of transgenic BALB/c mice expressing a mouse-human ICAM-1 chimera and rhinovirus-induced exacerbation of allergic airway inflammation. These models have features similar to those observed in rhinovirus infection in humans, including augmentation of allergic airway inflammation, and will be useful in the development of future therapies for colds and asthma exacerbations.

The perfect mix: recent progress in adjuvant research

Developing efficient and safe adjuvants for use in human vaccines remains both a challenge and a necessity. Past approaches have been largely empirical and generally used a single type of adjuvant, such as aluminium salts or emulsions. However, new vaccine targets often require the induction of well-defined cell-mediated responses in addition to antibodies, and thus new immunostimulants are required. Recent advances in basic immunology have elucidated how early innate immune signals can shape subsequent adaptive responses and this, coupled with improvements in biochemical techniques, has led to the design and development of more specific and focused adjuvants. In this Review, I discuss the research that has made it possible for vaccinologists to now be able to choose between a large panel of adjuvants, which potentially can act synergistically, and combine them in formulations that are specifically adapted to each target and to the relevant correlate(s) of protection.

Innate immune responses in human dendritic cells upon infection by chimeric yellow-fever dengue vaccine serotypes 1-4

Dengue infection is an important public health issue worldwide. The ChimeriVax-Dengue (CYD) vaccine uses yellow fever (YF) 17D vaccine as a live vector. Dendritic cells (DCs) play a key role in initiating immune responses and could be an important primary target of dengue infection. We investigated in vitro the consequences of CYD infection of DCs on their activation/maturation and cytokine production. In CYD-infected DCs, we observed an up-regulation of HLA-DR, CD80, CD86, and CD83. Cells exposed to CYD secreted type I interferons, monocyte chemoattractant protein 1 (MCP-1)/CC chemokine ligand 2 (CCL-2), interleukin-6 (IL-6), and low amounts of tumor necrosis factor-alpha (TNF-alpha), but no IL-10, IL-12, or IL-1alpha. Parental dengue viruses induced a similar array of cytokines, but more TNF-alpha, less IL-6, and less MCP-1/CCL-2 than induced by CYD. Chimeras thus induced DCs maturation and a controlled response accompanied by limited inflammatory cytokine production and consistent expression of anti-viral interferons, in agreement with clinical observations of safety and immunogenicity.

Pneumococcal surface protein A (PspA) is effective at eliciting T cell-mediated responses during invasive pneumococcal disease in adults

Humoral immune response is essential for protection against invasive pneumococcal disease and this property is the basis of the polysaccharide-based anti-pneumococcal vaccines. Pneumococcal surface protein A (PspA), a cell-wall-associated surface protein, is a promising component for the next generation of pneumococcal vaccines. This PspA antigen has been shown to stimulate an antibody-based immunity. In the present study, we evaluated the capacity of PspA to stimulate CD4+ T cells which are needed for the correct development of a B cell based immune response in humans. Cellular immunity to PspA was evaluated by whole-blood culture with different pneumococcal antigens, followed by flow cytometric detection of activated CD4+CD25+ T cells. T cell-mediated immune responses to recombinant PspA proteins were assessed in acute-phase and convalescent blood from adults with invasive pneumococcal disease and in blood from healthy subjects. All cases had detectable antibodies against PspA on admission. We found that invasive pneumococcal disease induced transient T cell depletion but adaptive immune responses strengthened markedly during convalescence. The increased production of both interleukin (IL)-10 and interferon (IFN)-gamma during convalescence suggests that these cytokines may be involved in modulating antibody-based immunity to pneumococcal disease. We demonstrated that PspA is efficient at eliciting T cell immune responses and antibodies to PspA. This study broadens the applicability of recombinant PspA as potent pneumococcal antigen for vaccination against S. pneumoniae.

Comparison by flow cytometry of immune changes induced in human monocyte-derived dendritic cells upon infection with dengue 2 live-attenuated vaccine or 16681 parental strain

Dengue is an important threat for world-wide public health. Different vaccines are under development, which are currently assessed using a battery of in vitro and in vivo assays before moving on to humans. It is also important to assess vaccine characteristics on human primary cells; among them, dendritic cells, the most efficient antigen-presenting cells, are the first targets of dengue virus infection. In this study, we used flow cytometry to compare the consequences of such an infection by dengue serotype 2 live-attenuated vaccine (LAV2) or its parental strain DEN2 16681 (DEN2). Optimal conditions of infection have first been defined by a mathematical approach, and flow cytometry allowed studying modifications induced in both infected and noninfected dendritic cell populations after surface and intracellular labeling. Both DEN2 and LAV2 increased the expression of the phenotypic markers CD80, CD86, CD40, CD1a, HLA ABC and CD83, demonstrating cellular activation. Stimulated dendritic cells produced tumor necrosis factor-alpha in particular, and, to a lower extent, interleukin 6. Of importance, whereas DEN2 induced cytokine production both in the infected and noninfected populations, LAV2-induced cytokine production was restricted to the infected population. This limited activation triggered by LAV2 would be in agreement with its attenuation. In conclusion, these in vitro experiments using primary human dendritic cells may participate, in combination with other assays, to the evaluation of the immunogenicity and safety of dengue vaccine candidates.

Innate and adaptive cellular immunity in flavivirus-naïve human recipients of a live-attenuated dengue serotype 3 vaccine produced in Vero cells (VDV3)

VDV3, a clonal derivative of the Mahidol live-attenuated dengue 3 vaccine was prepared in Vero cells. Despite satisfactory preclinical evaluation, VDV3 was reactogenic in humans. We explored whether immunological mechanisms contributed to this outcome by monitoring innate and adaptive cellular immune responses for 28 days after vaccination. While no variations were seen in serum IL12 or TNFalpha levels, a high IFNgamma secretion was detected from Day 8, concomitant to IFNalpha, followed by IL10. Specific Th1 and CD8 responses were detected on Day 28, with high IFNgamma/TNFalpha ratios. Vaccinees exhibited very homogeneous class I HLA profiles, and a new HLA B60-restricted CD8 epitope was identified in NS3. We propose that, among other factors, adaptive immunity may have contributed to reactogenicity, even after this primary vaccination. In addition, the unexpected discordance observed between preclinical results and clinical outcome in humans led us to reconsider some of our preclinical acceptance criteria. Lessons learned from these results will help us to pursue the development of safe and immunogenic vaccines.

Soil characteristics, heavy metal availability and vegetation recovery at a former metallurgical landfill: Implications in risk assessment and site restoration

Pedological and botanical characteristics of a former metallurgical landfill were examined to assess the risks of heavy metals mobility and to evaluate remediation feasibility. In addition to very high heavy metals levels (Cu, Cr, Mn, Ni, Pb, Zn), the soil was characterized by a lack of clear horizonation, a relatively high pH, a high mineral and organic carbon contents, a low nitrogen level and a high C/N ratio. A two step sequential extraction showed that heavy metals were poorly labile (i.e. not soluble in diluted CaCl2), indicating that their leaching under natural conditions was probably very low. However, extraction with DTPA generated significant amounts of metals (mainly Pb and Cu), suggesting they were potentially mobilizable. A botanical survey of the area showed a biodiverse plant community (28 species and 11 families), with no obvious toxicity symptoms. Measurements of metal contents in dominant species confirmed that they were closely similar to those reported for species growing in unpolluted environments. Consequently, for an effective site restoration, indigenous species could be well suited to cope with local conditions in a phytostabilization strategy.

Do Th1 or Th2 sequence motifs exist in proteins? Identification of amphipatic immunomodulatory domains in Helicobacter pylori catalase

The reasons why some proteins induce a particular type of T helper (Th) response are of fundamental importance but only partially understood. In the present study, amphipatic sequence motifs were identified in N- and C-terminal domains of Helicobacter pylori (Hp) catalase, which are linked to the induction of Th1 or Th2 immune responses, respectively. Alignment of these motifs with other proteins known to induce either Th1 or Th2 responses has lead to the identification of Th1 and Th2 consensus motifs, termed modulotopes. Their immunomodulatory potential was demonstrated by immunisation experiments using recombinant proteins comprising the C-terminal domain of catalase fused with one or several modulotopes and by co-immunisations of C- or N-terminal catalase domains with peptides containing these motifs. In addition to these in vivo data, in vitro assays using Limulus extracts suggested that modulotopes might interfere with responses triggered by danger signals such as LPS. Th1 and Th2 modulotopes are characterised by a specific hydrophobic/hydrophilic pattern, which might be the structural determinant for their activity. Our data suggest that Th1 and/or Th2 motifs may generally exist on proteins, thus offering the possibility of a rational modulation of the immune response.

Identification of two new Helicobacter pylori surface proteins involved in attachment to epithelial cell lines

Helicobacter pylori causes the development of gastritis, gastric ulcers and adenocarcinomas in humans. The establishment of infection is influenced by adherence to the gastric epithelium, and several bacterial adhesins and host cell receptors have been identified. H. pylori recognize the Lewis(b) receptor through the BabA adhesin but also readily adhere to epithelia in the absence of the Lewis(b) epitope, demonstrating the relevance of additional adhesive interactions. This study presents a novel method of identifying bacterial adhesins. Nickel beads were coated with H. pylori-derived, recombinantly expressed ORF proteins, and epithelial cells from the human stomach, intestine or urinary tract were allowed to adhere to those beads. The binding of epithelial cells to the protein-coated nickel beads was confirmed by electron microscopy or flow cytometry using antibodies directed towards the His-tags. Among the five ORFs tested, two new adhesive proteins (HP1188 and HP1430) were identified. Both were expressed on the surface of virulent H. pylori, with the HP1188 protein being most abundant. The purified HP1188 and HP1430 proteins bound more strongly to gastric than to other epithelial cell lines, suggesting that they may be involved in the colonization of the human gastric mucosa. In conclusion, this method facilitates the identification of ORFs of microbial origin involved in cellular interactions such as adherence.

New Adjuvants for Parenteral and Mucosal Vaccines

Developing efficient adjuvants for human vaccines, in order to elicit broad and sustained immune responses at systemic or mucosal levels, remains a challenge for the vaccine industry. Conventional approaches in the past have been largely empirical and partially successful. Selection was based on the balance between toxicity and adjuvanticity, first in an animal model, and then in clinical trials. The advent of improved biochemical techniques has allowed for the purification or construction of new and well characterised adjuvants. In addition, recent advances in our understanding of the immune system, most particularly with respect to early proinflammatory signals, have led to the identification of new biological targets for vaccine adjuvants. In particular, one can now choose adjuvants able to selectively induce T helper (Th)-1 and/or Th2 responses, according to the vaccine target and the desired immune response. As our knowledge of the cell types and cytokines interacting in the immune responses increases, so does our understanding of the mode of action of adjuvants, as well as the way in which they produce adverse effects.

Evaluation by flow cytometry of antibody-dependent enhancement (ADE) of dengue infection by sera from Thai children immunized with a live-attenuated tetravalent dengue vaccine

Sera from Thai children immunized with a live-attenuated tetravalent dengue virus vaccine or from naturally infected age-matched site-control subjects were examined for immune enhancement capacity by a highly reproducible flow cytometric assay in Fc receptor-bearing K562 human cells. None of the sera under study corresponded to cases of severe dengue disease. In parallel assays employing each dengue virus serotype, we found no or only minimal antibody-dependent enhancement (ADE) when sera from vaccinated or control subjects were used at a low serum dilution [1/12] that approximated the in vivo condition. Among sera that exhibited homotypic neutralizing antibody activity against DV1-3, the level correlated with absence of ADE or infection with the respective serotype. Similarly, a broad heterotypic neutralizing antibody response that included all four serotypes was linked to complete absence of K562 cell infection. In contrast, at higher serum dilutions a correlation between breadth of antibody response and heightened immune enhancement emerged, a pattern identical to that observed among control subjects. These findings support the use of live dengue vaccines and protocols that induce broad serotype-specific neutralizing antibody responses, but they also suggest that clinically relevant immune enhancement may not be likely if this is not uniformly achieved after the first immunization.