Novel vaccine strategies

Mathematical analysis of a Chlamydia epidemic model with pulse vaccination strategy

In this paper, we have considered a dynamical model of Chlamydia disease with varying total population size, bilinear incidence rate and pulse vaccination strategy. We have defined two positive numbers R₀ and (R₁≤ R₀). It is proved that there exists an infection-free periodic solution which is globally attractive if R₀ < 1 and the disease is permanent if R₁> 1 The important mathematical findings for the dynamical behaviour of the Chlamydia disease model are also numerically verified using MATLAB. Finally epidemiological implications of our analytical findings are addressed critically.

Progress towards a needle-free hepatitis B vaccine

Hepatitis B virus (HBV) infection is a worldwide public health problem. Vaccination is the most efficient way to prevent hepatitis B. Despite the success of the currently available vaccine, there is a clear need for the development of new generation of HBV vaccines. Needle-free immunization is an attractive approach for mass immunization campaigns, since avoiding the use of needles reduces the risk of needle-borne diseases and prevents needle-stick injuries and pain, thus augmenting patient compliance and eliminating the need for trained medical personnel. Moreover, this kind of immunization was shown to induce good systemic as well as mucosal immunological responses, which is important for the creation of both a prophylactic and therapeutic vaccine. In order to produce a better, safer, more efficient and more suitable vaccine, adjuvants have been used. In this article, several adjuvants tested over the years for their potential to help create a needle-free vaccine against HBV are reviewed.

Development of genetic markers in the non-structural protein 2 region of a US type 1 porcine reproductive and respiratory syndrome virus: implications for future recombinant marker vaccine development

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be a major problem in the pork industry worldwide. The limitations of current PRRSV vaccines require the development of a new generation of vaccines. One of the key steps in future vaccine development is to include markers for diagnostic differentiation of vaccinated animals from those naturally infected with wild-type virus. Using a cDNA infectious clone of type 1 PRRSV, this study constructed a recombinant green fluorescent protein (GFP)-tagged PRRSV containing a deletion of an immunogenic epitope, ES4, in the nsp2 region. In a nursery pig disease model, the recombinant virus was attenuated with a lower level of viraemia in comparison with that of the parental virus. To complement the marker identification, GFP and ES4 epitope-based ELISAs were developed. Pigs immunized with the recombinant virus lacked antibodies directed against the corresponding deleted epitope, but generated a high-level antibody response to GFP by 14 days post-infection. These results demonstrated that this recombinant marker virus, in conjunction with the diagnostic tests, enables serological differentiation between marker virus-infected animals and those infected with the wild-type virus. This rationally designed marker virus will provide a basis for further development of PRRSV marker vaccines to assist with the control of PRRS.

DNA immunization with plasmids encoding fusion and nucleocapsid proteins of bovine respiratory syncytial virus induces a strong cell-mediated immunity and protects calves against challenge

Respiratory syncytial viruses (RSV) are one of the most important respiratory pathogens of humans and cattle, and there is currently no safe and effective vaccine prophylaxis. In this study, we designed two codon-optimized plasmids encoding the bovine RSV fusion (F) and nucleocapsid (N) proteins and assessed their immunogenicity in young calves. Two administrations of both plasmids elicited low antibody levels but primed a strong cell-mediated immunity characterized by lymphoproliferative response and gamma interferon production in vitro and in vivo. Interestingly, this strong cellular response drastically reduced viral replication, clinical signs, and pulmonary lesions after a highly virulent challenge. Moreover, calves that were further vaccinated with a killed-virus vaccine developed high levels of neutralizing antibody and were fully protected following challenge. These results indicate that DNA vaccination could be a promising alternative to the classical vaccines against RSV in cattle and could therefore open perspectives for vaccinating young infants.

Analysis of a delayed epidemic model with pulse vaccination and saturation incidence

Pulse vaccination is an important strategy for the elimination of infectious diseases. An SEIRS epidemic model with time delays and pulse vaccination is formulated in this paper. Using the discrete dynamical system determined by the stroboscopic map, we obtain the exact infection-free periodic solution of the impulsive epidemic system and prove that the infection-free periodic solution is globally attractive if the vaccination rate is larger than theta*. Moreover, we show that the disease is uniformly persistent if the vaccination rate is less than theta*. The permanence of the model is investigated analytically. Our results indicate that a long latent period of the disease is sufficient condition for the extinction of the disease.

Prime-boost strategies combining DNA and inactivated vaccines confer high immunity and protection in cattle against bovine herpesvirus-1

DNA vaccines have frequently been associated with poor efficacy in large animals. In the present study, one administration of an inactivated marker vaccine to cattle considerably boosted both humoral and cellular arms of the immune response primed with Bovine herpesvirus-1 (BoHV-1) DNA vaccines encoding glycoprotein D (gD) or gC+gD. Calves vaccinated according to the DNA prime-inactivated boost also showed significantly enhanced virological protection as compared to controls. The 4-logarithms reduction of virus shedding observed in primed-boosted animals was comparable to the one previously reported in calves immunized twice with marker vaccines. Intradermal immunization of cattle with DNA vaccines promoted a Th2-biased immune response but also primed a cellular component that was further boosted by the inactivated vaccine. Individual IgG2 titers of vaccinated calves were significantly correlated to IFN-gamma production. The immunization protocol described in the present study demonstrates the complementarity between DNA and conventional marker vaccines.

Enhancing cellular immune response to HBV M DNA vaccine in mice by codelivery of interleukin-18 recombinant

OBJECTIVE

To investigate the effect of interleukin-18 (IL-18) on immune response induced by plasmid encoding hepatitis B virus middle protein antigen and to explore new strategies for prophylactic and therapeutic HBV DNA vaccines.

METHODS

BALB/c mice were immunized with pCMV-M alone or co-immunized with pcDNA3-18 and pCMV-M and then their sera were collected for analysing anti-HBsAg antibody by ELISA; splenocytes were isolated for detecting specific CTL response and cytokine assay in vitro.

RESULTS

The anti-HBs antibody level of mice co-immunized with pcDNA3-18 and pCMV-M was slightly higher than that of mice immunized with pCMV-M alone, but there was not significantly different (P>0.05). Compared with mice injected with pCMV-M, the specific CTL cytotoxity activity of mice immunized with pcDNA3-18 and pCMV-M was significantly enhanced (P<0.05) and the level of IFN-Gamma in supernatant of splenocytes cul-tured with HBsAg in vitro was significantly elevated (P<0.05) while the level of IL-4 had no significant difference (P>0.05).

CONCLUSION

The plasmid encoding IL-18 together with HBV M gene DNA vaccines may enhance specific TH1 cells and CTL cellular immune response induced in mice, so that IL-18 is a promising immune adjuvant.

Generation of a candidate live marker vaccine for equine arteritis virus by deletion of the major virus neutralization domain

Equine arteritis virus (EAV) is an enveloped plus-strand RNA virus of the family Arteriviridae (order Nidovirales) that causes respiratory and reproductive disease in equids. Protective, virus-neutralizing antibodies (VNAb) elicited by infection are directed predominantly against an immunodominant region in the membrane-proximal domain of the viral envelope glycoprotein G(L), allowing recently the establishment of a sensitive peptide enzyme-linked immunosorbent assay (ELISA) based on this particular domain (J. Nugent et al., J. Virol. Methods 90:167-183, 2000). By using an infectious cDNA we have now generated, in the controlled background of a nonvirulent virus, a mutant EAV from which this immunodominant domain was deleted. This virus, EAV-G(L)Delta, replicated to normal titers in culture cells, although at a slower rate than wild-type EAV, and caused an asymptomatic infection in ponies. The antibodies induced neutralized the mutant virus efficiently in vitro but reacted poorly to wild-type EAV strains. Nevertheless, when inoculated subsequently with virulent EAV, the immunized animals, in contrast to nonvaccinated controls, were fully protected against disease; replication of the challenge virus occurred briefly at low though detectable levels. The levels of protection achieved suggest that an immune effector mechanism other than VNAb plays an important role in protection against infection. As expected, infection with EAV-G(L)Delta did not induce a measurable response in our G(L)-peptide ELISA while the challenge infection of the animals clearly did. EAV-G(L)Delta or similar mutants are therefore attractive marker vaccine candidates, enabling serological discrimination between vaccinated and wild-type virus-infected animals.