The yellow fever 17D vaccine virus: molecular basis of viral attenuation and its use as an expression vector

The yellow fever (YF) virus is the prototype flavivirus. The use of molecular techniques has unraveled the basic mechanisms of viral genome structure and expression. Recent trends in flavivirus research include the use of infectious clone technology with which it is possible to recover virus from cloned cDNA. Using this technique, mutations can be introduced at any point of the viral genome and their resulting effect on virus phenotype can be assessed. This approach has opened new possibilities to study several biological viral features with special emphasis on the issue of virulence/attenuation of the YF virus. The feasibility of using YF virus 17D vaccine strain, for which infectious cDNA is available, as a vector for the expression of heterologous antigens is reviewed

Rabies infection and specific effect of vaccination in mice selected for high and low immunobiological parameters

Innate and acquired resistance to rabies infection was investigated in mice genetically selected for high (H) or low (L) antibody responsiveness from selections I, III and IV and in mice selected for maximal (AIRmax) or minimal (AIRmin) acute inflammatory reaction. These mouse lines were infected intramuscularly with different virus dilutions and the LD50 was determined. The HIII and HIV mouse lines were more susceptible than the LIII and LIV lines and the HI line showed a discrete but higher resistance than the LI line. Analysis of the interline (H x L) F1 hybrids from selections III and IV indicated different dominance effects on the "resistant" and" susceptible" phenotypes when the route of vaccination was changed. No differences were observed between the AIRmax and AIRmin mice, suggesting that inflammation plays a minor role in the resistance to rabies virus. The comparison of LD50 in mice vaccinated by distinct routes showed that the highest interline difference occurred after intramuscular vaccination (250-fold between H and L and 800-fold between F1 and L). These results indicate that different mechanisms may participate in acquired antirabies resistance

Malaria vaccine: roadblocks and possible solutions

Malaria remains the most prevalent and devastating parasitic disease worldwide. Vaccination is considered to be an approach that will complement other strategies for prevention and control of the disease in the future. In the last 10 years, intense studies aimed at the development of a malaria vaccine have provided important knowledge of the nature of the host immunological mechanisms of protection and their respective target antigens. It became well established that protective immune responses can be generated against the distinct stages of Plasmodium. However, in general, protective immune responses are directed at stage-specific antigens. The elucidation of the primary structure of these antigens made possible the generation of synthetic and recombinant proteins that are being extensively used in experimental immunizations against the infection. Today, several epitopes of limited polymorphism have been described and protective immunity can be generated by immunization with them. These epitopes are being tested as primary candidates for a subunit vaccine against malaria. Here we critically review the major roadblocks for the development of a malaria vaccine and provide some insight on how these problems are being solved

New vaccine strategies against enterotoxigenic Escherichia coli: II: Enhanced systemic and secreted antibody responses against the CFA/I fimbriae by priming with DNA and boosting with a live recombinant Salmonella vaccine

The induction of systemic (IgG) and mucosal (IgA) antibody responses against the colonization factor I antigen (CFA/I) of enterotoxigenic Escherichia coli (ETEC) was evaluated in mice primed with an intramuscularly delivered CFA/I-encoding DNA vaccine followed by two oral immunizations with a live recombinant Salmonella typhimurium vaccine strain expressing the ETEC antigen. The booster effect induced by the oral immunization was detected two weeks and one year after the administration of the DNA vaccine. The DNA-primed/Salmonella-boosted vaccination regime showed a synergistic effect on the induced CFA/I-specific systemic and secreted antibody levels which could not be attained by either immunization strategy alone. These results suggest that the combined use of DNA vaccines and recombinant Salmonella vaccine strains can be a useful immunization strategy against enteric pathogens.

Comparative sequence analysis of the P-, M- and L-coding region of the measles virus CAM-70 live attenuated vaccine strain

Measles virus is a highly contagious agent which causes a major health problem in developing countries. The viral genomic RNA is single-stranded, nonsegmented and of negative polarity. Many live attenuated vaccines for measles virus have been developed using either the prototype Edmonston strain or other locally isolated measles strains. Despite the diverse geographic origins of the vaccine viruses and the different attenuation methods used, there was remarkable sequence similarity of H, F and N genes among all vaccine strains. CAM-70 is a Japanese measles attenuated vaccine strain widely used in Brazilian children and produced by Bio-Manguinhos since 1982. Previous studies have characterized this vaccine biologically and genomically. Nevertheless, only the F, H and N genes have been sequenced. In the present study we have sequenced the remaining P, M and L genes (approximately 1.6, 1.4 and 6.5 kb, respectively) to complete the genomic characterization of CAM-70 and to assess the extent of genetic relationship between CAM-70 and other current vaccines. These genes were amplified using long-range or standard RT-PCR techniques, and the cDNA was cloned and automatically sequenced using the dideoxy chain-termination method. The sequence analysis comparing previously sequenced genotype A strains with the CAM-70 Bio-Manguinhos strain showed a low divergence among them. However, the CAM-70 strains (CAM-70 Bio-Manguinhos and a recently sequenced CAM-70 submaster seed strain) were assigned to a specific group by phylogenetic analysis using the neighbor-joining method. Information about our product at the genomic level is important for monitoring vaccination campaigns and for future studies of measles virus attenuation.

Human prophylactic vaccine adjuvants and their determinant role in new vaccine formulations

Adjuvants have been considered for a long time to be an accessory and empirical component of vaccine formulations. However, accumulating evidence of their crucial role in initiating and directing the immune response has increased our awareness of the importance of adjuvant research in the past decade. Nevertheless, the importance of adjuvants still is not fully realized by many researchers working in the vaccine field, who are involved mostly in the search for better target antigens. The choice of a proper adjuvant can be determinant for obtaining the best results for a given vaccine candidate, but it is restricted due to intellectual property and know-how issues. Consequently, in most cases the selected adjuvant continues to be the aluminum salt, which has a record of safety, but predominantly constitutes a delivery system (DS). Ideally, new strategies should combine immune potentiators (IP) and DS by mixing both compounds or by obtaining structures that contain both IP and DS. In addition, the term immune polarizer has been introduced as an essential concept in the vaccine design strategies. Here, we review the theme, with emphasis on the discussion of the few licensed new adjuvants, the need for safe mucosal adjuvants and the adjuvant/immunopotentiating activity of conjugation. A summary of toxicology and regulatory issues will also be discussed, and the Finlay Adjuvant Platform is briefly summarized.

Recombinant vaccines and the development of new vaccine strategies

Vaccines were initially developed on an empirical basis, relying mostly on attenuation or inactivation of pathogens. Advances in immunology, molecular biology, biochemistry, genomics, and proteomics have added new perspectives to the vaccinology field. The use of recombinant proteins allows the targeting of immune responses focused against few protective antigens. There are a variety of expression systems with different advantages, allowing the production of large quantities of proteins depending on the required characteristics. Live recombinant bacteria or viral vectors effectively stimulate the immune system as in natural infections and have intrinsic adjuvant properties. DNA vaccines, which consist of non-replicating plasmids, can induce strong long-term cellular immune responses. Prime-boost strategies combine different antigen delivery systems to broaden the immune response. In general, all of these strategies have shown advantages and disadvantages, and their use will depend on the knowledge of the mechanisms of infection of the target pathogen and of the immune response required for protection. In this review, we discuss some of the major breakthroughs that have been achieved using recombinant vaccine technologies, as well as new approaches and strategies for vaccine development, including potential shortcomings and risks.

Experimental models in vaccine research: malaria and leishmaniasis

Animal models have a long history of being useful tools, not only to test and select vaccines, but also to help understand the elaborate details of the immune response that follows infection. Different models have been extensively used to investigate putative immunological correlates of protection against parasitic diseases that are important to reach a successful vaccine. The greatest challenge has been the improvement and adaptation of these models to reflect the reality of human disease and the screening of vaccine candidates capable of overcoming the challenge of natural transmission. This review will discuss the advantages and challenges of using experimental animal models for vaccine development and how the knowledge achieved can be extrapolated to human disease by looking into two important parasitic diseases: malaria and leishmaniasis.

FosteraTM PRRS modified live vaccine efficacy against a Canadian heterologous virulent field strain of porcine reproductive and respiratory syndrome virus (PRRSV).

Vaccination is a useful option to control infection with porcine reproductive and respiratory syndrome virus (PRRSV), and several modified live-PRRSV vaccines have been developed. These vaccines have shown some efficacy in reducing the incidence and severity of clinical disease as well as the duration of viremia and virus shedding but have failed to provide sterilizing immunity. The efficacy of modified live-virus (MLV) vaccines is greater against a homologous strain compared with heterologous PRRSV strains. The objective of this study was to evaluate the efficacy of Fostera PRRS MLV vaccine in protecting against challenge with a heterologous field strain widely circulating in the swine herds of eastern Canada. Forty-six piglets were divided into 4 groups: nonvaccinated-nonchallenged; nonvaccinated-challenged; vaccinated-challenged; and vaccinated-nonchallenged. The animals were vaccinated at 23 d of age with Fostera PRRS and challenged 23 d later with a heterologous field strain of PRRSV (FMV12-1425619). Overall, the vaccine showed some beneficial effects in the challenged animals by reducing the severity of clinical signs and the viral load. A significant difference between nonvaccinated and vaccinated animals was detected for some parameters starting 11 to 13 d after challenge, which suggested that the cell-mediated immune response or other delayed responses could be more important than pre-existing PRRSV antibodies in vaccinated animals within the context of protection against heterologous strains.

Deoxynivalenol (DON) naturally contaminated feed impairs the immune response induced by porcine reproductive and respiratory syndrome virus (PRRSV) live attenuated vaccine

Cereal commodities are frequently contaminated with mycotoxins produced by the secondary metabolism of fungal infection. Among these contaminants, deoxynivalenol (DON), also known as vomitoxin, is the most prevalent type B trichothecene mycotoxin worldwide. Pigs are very sensitive to the toxic effects of DON and are frequently exposed to naturally contaminated feed. Recently, DON naturally contaminated feed has been shown to decrease porcine reproductive and respiratory syndrome virus (PRRSV) specific antibody responses following experimental infection. The objective of this study was to determine the impact of DON naturally contaminated feed on the immune response generated following vaccination with PRRSV live attenuated vaccine. Eighteen pigs were randomly divided into three experimental groups of 6 animals based on DON content of the diets (0, 2.5 and 3.5 mg DON/kg). They were fed these rations one week prior to the vaccination and for all the duration of the immune response evaluation. All pigs were vaccinated intra-muscularly with one dose of Ingelvac® PRRSV modified live vaccine (MLV). Blood samples were collected at day −1, 6, 13, 20, 27 and 35 post vaccination (pv) and tested for PRRSV RNA by RT-qPCR and for virus specific antibodies by ELISA. Results showed that ingestion of DON-contaminated diets significantly decreased PRRSV viremia. All pigs fed control diet were viremic while only 1 (17%) and 3 (50%) out of 6 pigs were viremic in the groups receiving 3.5 and 2.5 mg of DON/kg, respectively. Subsequently, all pigs fed control diet developed PRRSV specific antibodies while only viremic pigs that were fed contaminated diets have developed PRRSV specific antibodies. These results suggest that feeding pigs with DON-contaminated diet could inhibit vaccination efficiency of PRRSV MLV by severely impairing viral replication.

White Spot Syndrone Virus in Penaeids: Histopathology, Development of Polyclonal Antisera and a Cocktail Vaccine

The present study is the first comprehensive approach towards histopathology of White Spot Syndrome Virus (WSSV) in Penaeus indicus. WSSV could be demonstrated in the nuclei of all tissues, except those of midgut, subjected of electron microscopic observation. They were the nuclei of gill, foregut, heart, hepatopancreatic connective tissue, hindgut, nerve and dorsal aorta. A comparison was made between the electron microscopic and histopathological observations and a greater degree of correlation between the two in depicting the severity of the infection of the infection was unraveled. The study also illustrated variations in response and susceptibility of various tissues to WSSV infection. Accordingly, out of the tissues investigated, gill, foregut, hindgut and dorsal aorta exhibited advanced viral multiplication than the other tissues such as heart, midgut, nerve and hepatopancreas. Even though hepatocytes were not infected the connective tissue nuclei were packed with virions.

Truncated VP28 as oral vaccine candidate against WSSV infection in shrimp: An uptake and processing study in the midgut of Penaeus monodon

Several oral vaccination studies have been undertaken to evoke a better protection against white spot syndrome virus (WSSV), amajor shrimp pathogen. Formalin-inactivated virus andWSSV envelope protein VP28 were suggested as candidate vaccine components, but their uptake mechanism upon oral delivery was not elucidated. In this study the fate of these components and of live WSSV, orally intubated to black tiger shrimp (Penaeus monodon) was investigated by immunohistochemistry, employing antibodies specific for VP28 and haemocytes. The midgut has been identified as the most prominent site of WSSV uptake and processing. The truncated recombinant VP28 (rec-VP28), formalin-inactivated virus (IVP) and live WSSV follow an identical uptake route suggested as receptor-mediated endocytosis that starts with adherence of luminal antigens at the apical layers of gut epithelium. Processing of internalized antigens is performed in endo-lysosomal compartments leading to formation of supra-nuclear vacuoles. However, the majority of WSSV-antigens escape these compartments and are transported to the inter-cellular space via transcytosis. Accumulation of the transcytosed antigens in the connective tissue initiates aggregation and degranulation of haemocytes. Finally the antigens exiting the midgut seem to reach the haemolymph. The nearly identical uptake pattern of the different WSSV-antigens suggests that receptors on the apical membrane of shrimp enterocytes recognize rec-VP28 efficiently. Hence the truncated VP28 can be considered suitable for oral vaccination, when the digestion in the foregut can be bypassed

Effect of the human papillomavirus (HPV) quadrivalent vaccine in a subgroup of women with cervical and vulvar disease: Retrospective pooled analysis of trial data

Objectives To determine the effect of human papillomavirus (HPV) quadrivalent vaccine on the risk of developing subsequent disease after an excisional procedure for cervical intraepithelial neoplasia or diagnosis of genital warts, vulvar intraepithelial neoplasia, or vaginal intraepithelial neoplasia. Design Retrospective analysis of data from two international, double blind, placebo controlled, randomised efficacy trials of quadrivalent HPV vaccine (protocol 013 (FUTURE I) and protocol 015 (FUTURE II)). Setting Primary care centres and university or hospital associated health centres in 24 countries and territories around the world. Participants Among 17 622 women aged 15–26 years who underwent 1:1 randomisation to vaccine or placebo, 2054 received cervical surgery or were diagnosed with genital warts, vulvar intraepithelial neoplasia, or vaginal intraepithelial neoplasia. Intervention Three doses of quadrivalent HPV vaccine or placebo at day 1, month 2, and month 6. Main outcome measures Incidence of HPV related disease from 60 days after treatment or diagnosis, expressed as the number of women with an end point per 100 person years at risk. Results A total of 587 vaccine and 763 placebo recipients underwent cervical surgery. The incidence of any subsequent HPV related disease was 6.6 and 12.2 in vaccine and placebo recipients respectively (46.2% reduction (95% confidence interval 22.5% to 63.2%) with vaccination). Vaccination was associated with a significant reduction in risk of any subsequent high grade disease of the cervix by 64.9% (20.1% to 86.3%). A total of 229 vaccine recipients and 475 placebo recipients were diagnosed with genital warts, vulvar intraepithelial neoplasia, or vaginal intraepithelial neoplasia, and the incidence of any subsequent HPV related disease was 20.1 and 31.0 in vaccine and placebo recipients respectively (35.2% reduction (13.8% to 51.8%)). Conclusions Previous vaccination with quadrivalent HPV vaccine among women who had surgical treatment for HPV related disease significantly reduced the incidence of subsequent HPV related disease, including high grade disease.

Four year efficacy of prophylactic human papillomavirus quadrivalent vaccine against low grade cervical, vulvar, and vaginal intraepithelial neoplasia and anogenital warts: randomised controlled trial

Objectives: To evaluate the prophylactic efficacy of the human papillomavirus (HPV) quadrivalent vaccine in preventing low grade cervical, vulvar, and vaginal intraepithelial neoplasias and anogenital warts (condyloma acuminata). Design: Data from two international, double blind, placebo controlled, randomised efficacy trials of quadrivalent HPV vaccine (protocol 013 (FUTURE I) and protocol 015 (FUTURE II)). The trials were to be 4 years in length, and the results reported are from final study data of 42 months' follow-up. Setting: Primary care centres and university or hospital associated health centres in 24 countries and territories around the world. Participants: 17 622 women aged 16-26 years enrolled between December 2001 and May 2003. Major exclusion criteria were lifetime number of sexual partners (>4), history of abnormal cervical smear test results, and pregnancy. Intervention: Three doses of quadrivalent HPV vaccine (for serotypes 6, 11, 16, and 18) or placebo at day 1, month 2, and month 6. Main outcome measures: Vaccine efficacy against cervical, vulvar, and vaginal intraepithelial neoplasia grade I and condyloma in a per protocol susceptible population that included subjects who received all three vaccine doses, tested negative for the relevant vaccine HPV types at day 1 and remained negative through month 7, and had no major protocol violations. Intention to treat, generally HPV naive, and unrestricted susceptible populations were also studied. Results: In the per protocol susceptible population, vaccine efficacy against lesions related to the HPV types in the vaccine was 96% for cervical intraepithelial neoplasia grade I (95% confidence interval 91% to 98%), 100% for both vulvar and vaginal intraepithelial neoplasia grade I (95% CIs 74% to 100%, 64% to 100% respectively), and 99% for condyloma (96% to 100%). Vaccine efficacy against any lesion (regardless of HPV type) in the generally naive population was 30% (17% to 41%), 75% (22% to 94%), and 48% (10% to 71%) for cervical, vulvar, and vaginal intraepithelial neoplasia grade I, respectively, and 83% (74% to 89%) for condyloma. Conclusions: Quadrivalent HPV vaccine provided sustained protection against low grade lesions attributable to vaccine HPV types (6, 11, 16, and 18) and a substantial reduction in the burden of these diseases through 42 months of follow-up. Trial registrations: NCT00092521 and NCT00092534.