Intranasal immunization with human papillomavirus type 16 capsomeres in the presence of non-toxic cholera toxin-based adjuvants elicits increased vaginal immunoglobulin levels

A rationally designed flagellin-L2 fusion protein induced serum and mucosal neutralizing antibodies against multiple HPV types

The amino terminus of human papillomavirus (HPV) minor capsid protein L2 harbors several conserved neutralizing epitopes, including aa.17-36 (RG-1 epitope) and aa.65-85 consensus epitope (cL2 epitope), which are considered to be promising for the construction of cost-effective pan-HPV vaccine candidates. However, the immunogenicity of L2 epitope/peptide is rather weak, and the neutralizing spectrum induced by single type of L2 antigen is suboptimal. In this study, we constructed L2 concatemer with HPV18/33/58/59 RG-1 epitopes and 16L2 aa.11-88 peptide, and fused it with flagellin, a strong systemic and mucosal adjuvant, by hypervariable region replacement. A copy of cL2 epitope was also introduced to the C-terminus of the recombinant protein. The resultant Fla-5PcL2 protein can be produced in E. coli expression system with high yield and good stability. We assessed the immunogenicity of Fla-5PcL2 in mouse model via systemic and mucosal route, and found that subcutaneous immunization with Fla-5PcL2 induced robust serum neutralizing antibodies against divergent HPV types, while intranasal immunization with Fla-5PcL2 induced remarkable L2-specific IgA and cross-neutralizing antibodies in mucosal secretions, and medium titers of cross-neutralizing antibodies in sera. Moreover, Fla-5PcL2 induced full protection against vaginal HPV challenges. As mucosal antibodies provide the first-line defense at infection sites, and needle-free immunizations may increase vaccine compliance and require less public health resources, our results demonstrate that Fla-5PcL2 is a promising vaccine candidate which possibly meet the need in low-resource regions.

Integrated molecular and bioprocess engineering for bacterially produced immunogenic modular virus-like particle vaccine displaying 18 kDa rotavirus antigen

A high global burden of rotavirus disease and the unresolved challenges with the marketed rotavirus vaccines, particularly in the developing world, have ignited efforts to develop virus-like particle (VLP) vaccines for rotavirus. While rotavirus-like particles comprising multiple viral proteins can be difficult to process, modular VLPs presenting rotavirus antigenic modules are promising alternatives in reducing process complexity and cost. In this study, integrated molecular and bioprocess engineering approaches were used to simplify the production of modular murine polyomavirus capsomeres and VLPs presenting a rotavirus 18 kDa VP8* antigen. A single construct was generated for dual expression of non-tagged murine polyomavirus capsid protein VP1 and modular VP1 inserted with VP8*, for co-expression in Escherichia coli. Co-expressed proteins assembled into pentameric capsomeres in E. coli. A selective salting-out precipitation and a polishing size exclusion chromatography step allowed the recovery of stable modular capsomeres from cell lysates at high purity, and modular capsomeres were successfully translated into modular VLPs when assembled in vitro. Immunogenicity study in mice showed that modular capsomeres and VLPs induced high levels of VP8*-specific antibodies. Our results demonstrate that a multipronged synthetic biology approach combining molecular and bioprocess engineering enabled simple and low-cost production of highly immunogenic modular capsomeres and VLPs presenting conformational VP8* antigenic modules. This strategy potentially provides a cost-effective production route for modular capsomere and VLP vaccines against rotavirus, highly suitable to manufacturing economics for the developing world. Biotechnol. Bioeng. 2017;114: 397-406. © 2016 Wiley Periodicals, Inc.

Design strategies to address the effect of hydrophobic epitope on stability and in vitro assembly of modular virus-like particle

Virus-like particles (VLPs) and capsomere subunits have shown promising potential as safe and effective vaccine candidates. They can serve as platforms for the display of foreign epitopes on their surfaces in a modular architecture. Depending on the physicochemical properties of the antigenic modules, modularization may affect the expression, solubility and stability of capsomeres, and VLP assembly. In this study, three module designs of a rotavirus hydrophobic peptide (RV10) were synthesized using synthetic biology. Among the three synthetic modules, modularization of the murine polyomavirus VP1 with a single copy of RV10 flanked by long linkers and charged residues resulted in the expression of stable modular capsomeres. Further employing the approach of module titration of RV10 modules on each capsomere via Escherichia coli co-expression of unmodified VP1 and modular VP1-RV10 successfully translated purified modular capomeres into modular VLPs when assembled in vitro. Our results demonstrate that tailoring the physicochemical properties of modules to enhance modular capsomeres stability is achievable through synthetic biology designs. Combined with module titration strategy to avoid steric hindrance to intercapsomere interactions, this allows bioprocessing of bacterially produced in vitro assembled modular VLPs.

Expression of HPV-16 L1 capsomeres with glutathione-S-transferase as a fusion protein in tobacco plastids: an approach for a capsomere-based HPV vaccine

Human Papillomavirus (HPV) is the main cause of cervical cancer, which is the second most severe cancer of women worldwide, particularly in developing countries. Although vaccines against HPV infection are commercially available, they are neither affordable nor accessible to women in low income countries e.g. Africa. Thus, alternative cost-effective vaccine production approaches need to be developed. This study uses tobacco plants to express pentameric capsomeres of HPV that have been reported to generate elevated immune responses against HPV. A modified HPV-16 L1 (L1_2xCysM) protein has been expressed as a fusion protein with glutathione-S-transferase (GST) in tobacco chloroplasts following biolistic transformation. In total 7 transplastomic lines with healthy phenotypes were generated. Site specific integration of the GST-L1_2xCysM and aadA genes was confirmed by PCR. Southern blot analysis verified homogenous transformation of all transplastomic lines. Antigen capture ELISA with the conformation-specific antibody Ritti01, showed protein expression as well as the retention of immunogenic epitopes of L1 protein. In their morphology, GST-L1 expressing tobacco plants were identical to wild type plants and yielded fertile flowers. Taken together, these data enrich knowledge for future development of cost-effective plant-made vaccines against HPV.

Bioengineering virus-like particles as vaccines

Virus-like particle (VLP) technology seeks to harness the optimally tuned immunostimulatory properties of natural viruses while omitting the infectious trait. VLPs that assemble from a single protein have been shown to be safe and highly efficacious in humans, and highly profitable. VLPs emerging from basic research possess varying levels of complexity and comprise single or multiple proteins, with or without a lipid membrane. Complex VLP assembly is traditionally orchestrated within cells using black-box approaches, which are appropriate when knowledge and control over assembly are limited. Recovery challenges including those of adherent and intracellular contaminants must then be addressed. Recent commercial VLPs variously incorporate steps that include VLP in vitro assembly to address these problems robustly, but at the expense of process complexity. Increasing research activity and translation opportunity necessitate bioengineering advances and new bioprocessing modalities for efficient and cost-effective production of VLPs. Emerging approaches are necessarily multi-scale and multi-disciplinary, encompassing diverse fields from computational design of molecules to new macro-scale purification materials. In this review, we highlight historical and emerging VLP vaccine approaches. We overview approaches that seek to specifically engineer a desirable immune response through modular VLP design, and those that seek to improve bioprocess efficiency through inhibition of intracellular assembly to allow optimal use of existing purification technologies prior to cell-free VLP assembly. Greater understanding of VLP assembly and increased interdisciplinary activity will see enormous progress in VLP technology over the coming decade, driven by clear translational opportunity.

Association of skin with the pathogenesis and treatment of neurodegenerative amyloidosis

Amyloidosis are a large group of conformational diseases characterized by abnormal protein folding and assembly which results in the accumulation of insoluble protein aggregates that may accumulate systemically or locally in certain organs or tissue. In local amyloidosis, amyloid deposits are restricted to a particular organ or tissue. Alzheimer’s, Parkinson’s disease, and amyotrophic lateral sclerosis are some examples of neurodegenerative amyloidosis. Local manifestation of protein aggregation in the skin has also been reported. Brain and skin are highly connected at a physiological and pathological level. Recently several studies demonstrated a strong connection between brain and skin in different amyloid diseases. In the present review, we discuss the relevance of the “brain–skin connection” in different neurodegenerative amyloidosis, not only at the pathological level, but also as a strategy for the treatment of these diseases.

Vaccine adjuvants - Current status and prospects on controlled release adjuvancity

The strategy of World Health Organization is to develop efficient and inexpensive vaccine against various infectious diseases amongst children's population. Vaccination is considered as the most cost effective health intervention known to public. Since 90 years various substances have been added in vaccine formulation but still alum is considered as the safest adjuvant for human use licensed by United States Food and Drug Administration. MF 59 and ASO4 are the adjuvants were developed recently and approved for human use. Due to poor adjuvancity, conventional vaccines require multiple recall injection at approximately time intervals to attain optimal immune response. For past approximately two decades the vaccine research has been focused towards the alternation of alum type of adjuvant in order to increase the immunogenicity. The development of new vaccines, is more efficacious or easier to deliver, or both have become an area of research that can certainly benefit from controlled release technology. Especially, the conversion of multiple administration vaccine into single administration vaccine may represent an improved advancement towards the betterment of human health care and welfare. Biodegradable polymer microparticles have been evaluated for delivering antigens in native form, sustained release keeping in mind the safety aspects. In this article we review the overall concept of adjuvants in vaccine technology with special focus towards the prospects of controlled release antigens.

Mucosa-associated epithelial chemokine/CCL28 expression in the uterus attracts CCR10+ IgA plasma cells following mucosal vaccination via estrogen control

Previous studies demonstrated cross talk between mucosal and reproductive organs during secretory IgA Ab induction. In this study, we aimed to clarify the underlying mechanisms of this cross talk. We found significantly higher titers of Ag-specific secretory IgA Ab in the vaginal wash after mucosal vaccination by both the intranasal (i.n.) and the intravaginal routes but not by the s.c. route. Interestingly, Ag-specific IgA Ab-secreting cells (ASCs) were found mainly in the uterus but not in the cervix and vaginal canal after i.n. vaccination. The fact that most Ag-specific IgA ASCs isolated from the uteri of vaccinated mice migrated toward mucosa-associated epithelial chemokine (MEC)/CCL28 suggests dominant expression of CCR10 on the IgA ASCs. Further, IgA ASCs in the uteri of vaccinated mice were reduced drastically in mice treated with neutralizing anti-MEC/CCL28 Ab. Most intriguingly, the female sex hormone estrogen directly regulated MEC/CCL28 expression and was augmented by i.n. vaccination with cholera toxin or stimulators for innate immunity. Further, blockage of estrogen function in the uterus by oral administration of the estrogen antagonist raloxifene significantly inhibited migration of Ag-specific IgA ASCs after i.n. vaccination with OVA plus cholera toxin. Taken together, these data strongly suggest that CCR10(+) IgA ASCs induced by mucosal vaccination via the i.n. route migrate into the uterus in a MEC/CCL28-dependent manner and that estrogen might have a crucial role in the protection against genital infection by regulating MEC/CCL28 expression in the uterus.

Plastid expression of a double-pentameric vaccine candidate containing human papillomavirus-16 L1 antigen fused with LTB as adjuvant: transplastomic plants show pleiotropic phenotypes

Human papillomavirus (HPV) causes cervical cancer in women worldwide, which is currently prevented by vaccines based on virus-like particles (VLPs). However, these vaccines have certain limitations in their availability to developing countries, largely due to elevated costs. Concerning the highest burden of disease in resource-poor countries, development of an improved mucosal and cost-effective vaccine is a necessity. As an alternative to VLPs, capsomeres have been shown to be highly immunogenic and can be used as vaccine candidate. Furthermore, coupling of an adjuvant like Escherichia coli heat-labile enterotoxin subunit B (LTB) to an antigen can increase its immunogenicity and reduce the costs related to separate co-administration of adjuvants. Our study demonstrates the expression of two pentameric proteins: the modified HPV-16 L1 (L1_2xCysM) and LTB as a fusion protein in tobacco chloroplasts. Homoplasmy of the transplastomic plants was confirmed by Southern blotting. Western blot analysis showed that the LTB-L1 fusion protein was properly expressed in the plastids and the recombinant protein was estimated to accumulate up to 2% of total soluble protein. Proper folding and display of conformational epitopes for both LTB and L1 in the fusion protein was confirmed by GM1-ganglioside binding assay and antigen capture ELISA, respectively. However, all transplastomic lines showed chlorosis, male sterility and growth retardation, which persisted in the ensuing four generations studied. Nevertheless, plants reached maturity and produced seeds by pollination with wild-type plants. Taken together, these results pave the way for the possible development of a low-cost adjuvant-coupled vaccine with potentially improved immunogenicity against cervical cancer.

Transplastomic expression of a modified human papillomavirus L1 protein leading to the assembly of capsomeres in tobacco: a step towards cost-effective second-generation vaccines

Certain types of human papillomaviruses (HPV) are causatively associated with cervical carcinoma, the second most common cancer in women worldwide. Due to limitations in the availability of currently used virus-like particle (VLP)-based vaccines against HPV to women of developing countries, where most cases of cervical cancer occur, the development of a cost-effective second-generation vaccine is a necessity. Capsomeres have recently been demonstrated to be highly immunogenic and to have a number of advantages as a potential cost-effective alternative to VLP-based HPV vaccines. We have expressed a mutated HPV-16 L1 (L1_2xCysM) gene that retained the ability to assemble L1 protein to capsomeres in tobacco chloroplasts. The recombinant protein yielded up to 1.5% of total soluble protein. The assembly of capsomeres was examined and verified by cesium chloride density gradient centrifugation and sucrose sedimentation analysis. An antigen capture enzyme-linked immunosorbent assay confirmed the formation of capsomeres by using a conformation-specific monoclonal antibody which recognized the conformational epitopes. Transplastomic tobacco plants exhibited normal growth and morphology, but all such lines showed male sterility in the T₀, T₁ and T₂ generations. Taken together, these results indicate the possibility of producing a low-cost capsomere-based vaccine by plastids.

Virus-like particle vaccines and adjuvants: the HPV paradigm

Complex antigen structures currently represent the most-studied approach for prophylactic as well as therapeutic vaccines. Different types of complex vaccines, including virus-like particles and virosomes, have been developed depending on the nature of the viral pathogen they are trying to replicate (enveloped vs naked) or the modality to express antigenic epitopes (i.e., the binding of envelope protein on liposomic structures). The complex structure of these vaccines provides them with some adjuvanted properties, not uniformly present for all virus-like particle types. The further inclusion of specific adjuvants in vaccine preparations can modify the presentation modality of such particles to the immune system with a specific Th1 versus Th2 polarization efficacy. A paradigm of the relevance of these new adjuvants are the immunological results obtained with the inclusion of monophosphoryl lipid A adjuvant in the formulation of L1-based human papillomavirus-naked virus-like particles to reduce a Th1 cellular immunity impairment, peculiar for alum-derived adjuvants, along with the induction of highly enhanced humoral and memory B-cellular immunity.

Virus-like particles and capsomeres are potent vaccines against cutaneous alpha HPVs

The potential as prophylactic vaccines of L1-based particles from cutaneous genus alpha human papillomavirus (HPV) types has not been assessed so far. However, there is a high medical need for such vaccines since HPV-induced skin warts represent a major burden for children and for immunocompromised adults, such as organ transplant recipients. In this study, we have examined the immunogenicity of capsomeres and virus-like particles (VLPs) from HPV types 2, 27, and 57, the most frequent causative agents of skin warts. Immunization of mice induced immune responses resembling those observed upon vaccination with HPV 16 L1-based antigens. The antibody responses were cross-reactive but type-restricted in their neutralizing capacities. Application of adjuvant led to an enhanced potential to neutralize the respective immunogen type but did not improve cross-neutralization. Vaccination with capsomeres and VLPs from all four analyzed HPV types induced robust IFNgamma-associated T-cell activation. Immunization with mixed VLPs from HPV types 2, 27, and 57 triggered an antibody response similar to that after single-type immunization and capable of efficiently neutralizing all three types. Our results imply that vaccination with combinations of VLPs from cutaneous HPV types constitutes a promising strategy to prevent HPV-induced skin lesions.

Analysis of modified human papillomavirus type 16 L1 capsomeres: the ability to assemble into larger particles correlates with higher immunogenicity

L1 capsomeres purified from Escherichia coli represent an economic alternative to the recently launched virus-like particle (VLP)-based prophylactic vaccines against infection with human papillomavirus types 16 and 18 (HPV-16 and HPV-18), which are causative agents of cervical cancer. It was recently reported that capsomeres are much less immunogenic than VLPs. Numerous modifications of the L1 protein leading to the formation of capsomeres but preventing capsid assembly have been described, such as the replacement of the cysteine residues that form capsid-stabilizing disulfide bonds or the deletion of helix 4. So far, the influence of these modifications on immunogenicity has not been thoroughly investigated. Here, we describe the purification of eight different HPV-16 L1 proteins as capsomeres from Escherichia coli. We compared them for yield, structure, and immunogenicity in mice. All L1 proteins formed almost identical pentameric structures yet differed strongly in their immunogenicity, especially regarding the humoral immune responses. Immunization of TLR4(-/-) mice and DNA immunization by the same constructs confirmed that immunogenicity was independent of different degrees of contamination with copurifying immune-stimulatory molecules from E. coli. We hypothesize that immunogenicity correlates with the intrinsic ability of the capsomeres to assemble into larger particles, as only assembly-competent L1 proteins induced high antibody responses. One of the proteins (L1DeltaN10) proved to be the most immunogenic, inducing antibody titers equivalent to those generated in response to VLPs. However, preassembly prior to injection did not increase immunogenicity. Our data suggest that certain L1 constructs can be used to produce highly immunogenic capsomeres in bacteria as economic alternatives to VLP-based formulations.

Refining HPV 16 L1 purification from E. coli: reducing endotoxin contaminations and their impact on immunogenicity

HPV 16 L1 capsomeres purified from Escherichia coli represent a promising and potentially cost-effective alternative to the recently licensed VLP-based vaccines for the prevention of cervical cancer. However, recombinant protein preparations from bacteria always bear the risk of contaminating endotoxins which are highly toxic in humans and therefore have to be eliminated from vaccine preparations. In this study, we measured the LPS concentration at various stages of the purification of HPV 16 L1 from E. coli and determined that it enhances the immunogenicity of HPV 16 VLPs and capsomeres. We confirmed the immunogenicity of the L1 capsomeres in TLR4(-/-) mice without the enhancing effect of the LPS and then elaborated a suitable protocol using Triton X-114 phase separation for the removal of LPS without any significant protein loss or influence on the structural integrity of the particles. The LPS-free capsomeres purified from E. coli induced neutralizing L1-specific antibodies. Our results demonstrate the excellent potential of capsomeres as an economically interesting alternative vaccine to prevent cervical cancer that could be made available in developing countries.

Immunobiology of human papillomavirus infection and vaccination - implications for second generation vaccines

Prophylactic human papillomavirus (HPV) L1 virus like particle (VLP) vaccines have been shown, in large clinical trials, to be very immunogenic, well-tolerated and highly efficacious against genital disease caused by the vaccine HPV types. However these vaccines, at the present, protect against only two of the 15 oncogenic genital HPV types, they are expensive, delivered by intramuscular injection and require a cold chain. The challenges are to develop cheap, thermo-stable vaccines that can be delivered by non-injectable methods that provide long term (decades) protection at mucosal surfaces to most, if not all, oncogenic HPV types that is as good as the current VLP vaccines. Current approaches include L1 capsomers, L2 protein and peptides, delivery via recombinant L1 bacterial and viral vectors and large-scale VLP production in plants. Rational design and successful development of such vaccines will be based on an understanding of the immune response, and particularly the 'cross talk' between the innate and adaptive responses. This will be central in the development of adjuvants and vaccine formulations that induce the response to provide effective protection.

Translational fusion of chloroplast-expressed human papillomavirus type 16 L1 capsid protein enhances antigen accumulation in transplastomic tobacco

Human Papillomavirus (HPV) is the causal agent of cervical cancer, one of the most common causes of death for women. The major capsid L1 protein self-assembles in Virus Like Particles (VLPs), which are highly immunogenic and suitable for vaccine production. In this study, a plastid transformation approach was assessed in order to produce a plant-based HPV-16 L1 vaccine. Transplastomic plants were obtained after transformation with vectors carrying a chimeric gene encoding the L1 protein either as the native viral (L1(v) gene) or a synthetic sequence optimized for expression in plant plastids (L1(pt) gene) under control of plastid expression signals. The L1 mRNA was detected in plastids and the L1 antigen accumulated up to 1.5% total leaf proteins only when vectors included the 5'-UTR and a short N-terminal coding segment (Downstream Box) of a plastid gene. The half-life of the engineered L1 protein, determined by pulse-chase experiments, is at least 8 h. Formation of immunogenic VLPs in chloroplasts was confirmed by capture ELISA assay using antibodies recognizing conformational epitopes and by electron microscopy.

Prospects and prejudices of human papillomavirus vaccines in India

Cervical cancer is the most common cancer and a leading cause of cancer deaths among women in developing countries. The disease is caused due to persistent infection of one or more of about 15 high-risk human papillomaviruses (HR-HPVs), most commonly by HPV types 16/18. In India, over 98% of cervical cancer cases harbor HPV infection and HPV 16 is the type exclusively (80-90%) prevalent. Unlike the West, HPV infection is most common in women in their third decade (26-35 years) of sexual activity and invasive cancer also arises much later with a peak at about 45-55 years of age. Recently, two successful prophylactic HPV vaccines, a quadrivalent (HPV16/18/6/11) 'Gardasil' by Merck and a bivalent (HPV16/18) 'Cervarix' by GSK have been developed. Several other approaches including plant-based edible, pentameric capsomere-based intranasal and DNA-based vaccines have also been employed to develop prophylactic vaccines. Also, several therapeutic vaccines either protein/peptide based or DNA based are in clinical trials but are yet to establish their efficacy. Though there are several issues regarding implementation of the already developed vaccines in resource limited countries, efforts are being made to develop cost-effective second-generation vaccines. If cost minimized, HPV related new technologies involved in screening tests and vaccines are expected to reduce incidence of cervical cancer and deaths it causes in women from developing countries.

A direct comparison of human papillomavirus type 16 L1 particles reveals a lower immunogenicity of capsomeres than viruslike particles with respect to the induced antibody response

Capsomeres are considered to be an alternative to viruslike particle (VLP)-based vaccines as they can be produced in prokaryotic expression systems. So far, no detailed side-by-side comparison of VLPs and capsomeres has been performed. In the present study, we immunized mice with insect cell-derived human papillomavirus type 16 VLPs and capsomeres. VLPs induced consistently higher antibody titers than capsomeres but the two forms induced similar CD8 T-cell responses after subcutaneous, intranasal, and oral immunization, and at least 20 to 40 times more L1 in the form of capsomeres than in the form of VLPs was needed to achieve comparable antibody responses. These results were confirmed by DNA immunization. The lower immunogenicity of capsomeres was independent of the isotype switch, as it was also observed for the early immunoglobulin M responses. Although there were differences in the display of surface epitopes between the L1 particles, these did not contribute significantly to the differences in the immune responses. capsomeres were less immunogenic than VLPs in Toll-like receptor 4 (TLR4)-deficient mice, suggesting that the lower immunogenicity is not due to a failure of capsomeres to trigger TLR4. We observed better correlation between antibody results from enzyme-linked immunosorbent assays and neutralization assays for sera from VLP-immunized mice than for sera from capsomere-immunized mice, suggesting qualitative differences between VLPs and capsomeres. We also showed that the lower immunogenicity of capsomeres could be compensated by the use of an adjuvant system containing MPL. Taken together, these results suggest that, presumably because of the lower degree of complexity of the antigen organization, capsomeres are significantly less immunogenic than VLPs with respect to the humoral immune response and that this characteristic should be considered in the design of putative capsomere-based prophylactic vaccines.

Oral immunization with different assembly forms of the HPV 16 major capsid protein L1 induces neutralizing antibodies and cytotoxic T-lymphocytes

Human papillomaviruses have been recognized as the causative agent of anogenital cancer. In 2006, a commercial vaccine based on virus-like particles composed of the L1 major capsid protein of the papillomaviruses has been available. This vaccine induces virus-neutralizing antibody responses upon parenteral injection. Here we investigated the oral immunogenicity of different assembly forms of HPV 16 L1, that is: T7-VLPs, T1 particles and capsomeres. Our results show that all three assembly forms induce humoral and cellular immune responses after oral vaccination of mice. The anti-L1 antibodies were conformation-specific and showed neutralizing activity in a pseudovirion-based assay. We also investigated if adjuvants have an influence on the oral immunogenicity of the different L1 forms. For saponins we observed a significant toxicity if applied orally. Co-administration of either CpG DNA or Escherichia coli heat-labile enterotoxin LT(R192G) had no apparent enhancing effect on the production of anti-L1 antibodies. More pronounced was the effect of CpG administration on the long-term immunity as we observed a significantly stronger recall response 244 days after the first vaccination. Compared to capsomeres, VLPs induced stronger humoral immune responses while the CTL responses were induced at comparable levels. Finally, we were also able to induce neutralizing antibodies and L1-specific cytotoxic T-lymphocytes after oral administration of crude extracts of L1-expressing insect cells. In conclusion, all three assembly forms of the L1 protein are immunogenic when administered orally.

Mucosal immunization of piglets with purified F18 fimbriae does not protect against F18+ Escherichia coli infection

Post-weaning diarrhoea and oedema disease in weaned piglets are caused by infection with F4+ or F18+ Escherichia coli strains. There is no commercial vaccine available, but it is shown that oral immunization of weaned piglets with purified F4 fimbriae induces a protective mucosal immune response. In the present study, piglets were orally and nasally immunized with purified F18 fimbriae in the presence of the mucosal adjuvant LT(R192G) or CTA1-DD, respectively. This immunization could not lead to protection against F18+ E. coli infection. The induced F18-specific immune response was directed towards the major subunit FedA and weakly towards the adhesive subunit FedF. The results of these experiments demonstrate that it is difficult to induce protective immunity against F18+ E. coli using the whole fimbriae due to the low response against the adhesin.

Vaccine adjuvants revisited

The development of new adjuvants for human vaccines has become an expanding field of research in the last thirty years, for generating stronger vaccines capable of inducing protective and long-lasting immunity in humans. Instead of such efforts, with several adjuvant strategies approaching to requirements for their clinical application, limitations like adjuvant toxicity remain to be fully surpassed. Here we summarize the current status of adjuvant development, including regulatory recommendations, adjuvant requirements, and adjuvant categories like mineral salts, tensoactive compounds, microorganism-derived adjuvants, emulsions, cytokines, polysaccharides, nucleic acid-based adjuvants, and a section dedicated to particulate antigen delivery systems. The mechanisms of adjuvanticity are also discussed in the light of recent findings on Toll-like receptors' biology and their involvement on immune activation.

[Immunity and antiviral vaccinations. Example: the respiratory mucosa]

OBJECTIVE

As the mucosal surfaces of the respiratory tract represent a major portal of entry for most human viruses and many bacteria, they seem to be a critical component of the mammalian immunologic repertoire. Thus, vaccines stimulating this local immunity could represent an interesting approach to prevent these infections. After detailing the different mechanisms implied in this mucosal immunity, the aim of this study is to analyze the basis of such a vaccination and the different vaccines available to mucosal respiratory tract use.

MUCOSAL IMMUNITY

The major antibody isotype in external secretions is secretory immunoglobin A (S-IgA); the role of IgM (S-IgM) and IgG (S-IgG) are actually questionned. It is, however, interesting that the major effector cells in the mucosal surfaces are not IgA B cells, but T lymphocytes that may represent up to 80% of the entire mucosal lymphoid cell population.

IMMUNOPROPHYLAXIS BY THE MUCOSAL ROUTE

Passive antibodies were shown to protect against mucosal viral infections, such as those caused by RSV, but very high quantities of passive antibodies are needed to restrict virus replication on mucosal surface.In general, factors which favor development of mucosal antibody and cell mediated immune responses include the oral or respiratory immunization and the replicating nature of the vaccine agents. However, to date only a few vaccines have become available to mucosal respiratory tract use, and cold-adapted influenza virus vaccines is the only one available using nasal route. Other parenteral licensed vaccines have not been recommended for mucosal administration. Some of them have been experimentally used with nasal administration of replicating agents (varicella and measles vaccines) or non replicating agents (influenza inactivated vaccine), but have been found to induce a very low mucosal response.

CONCLUSION

Based on the experience with existing vaccines, the development of mucosal immunity or administration of vaccines via the mucosal route is clearly not a prerequisite today for control or prevention of most viral infectious respiratory diseases or diseases with respiratory tract as a route of contamination. But the example of live attenuated intranasal influenza vaccine inducing both systemic and local immune response without immunopathology, is promising for the future of the mucosal immunization against respiratory viral infections.

Transcutaneous beta-amyloid immunization reduces cerebral beta-amyloid deposits without T cell infiltration and microhemorrhage

Alzheimer's disease (AD) immunotherapy accomplished by vaccination with beta-amyloid (Abeta) peptide has proved efficacious in AD mouse models. However, "active" Abeta vaccination strategies for the treatment of cerebral amyloidosis without concurrent induction of detrimental side effects are lacking. We have developed a transcutaneous (t.c.) Abeta vaccination approach and evaluated efficacy and monitored for deleterious side effects, including meningoencephalitis and microhemorrhage, in WT mice and a transgenic mouse model of AD. We demonstrate that t.c. immunization of WT mice with aggregated Abeta(1-42) plus the adjuvant cholera toxin (CT) results in high-titer Abeta antibodies (mainly of the Ig G1 class) and Abeta(1-42)-specific splenocyte immune responses. Confocal microscopy of the t.c. immunization site revealed Langerhans cells in areas of the skin containing the Abeta(1-42) immunogen, suggesting that these unique innate immune cells participate in Abeta(1-42) antigen processing. To evaluate the efficacy of t.c. immunization in reducing cerebral amyloidosis, transgenic PSAPP (APPsw, PSEN1dE9) mice were immunized with aggregated Abeta(1-42) peptide plus CT. Similar to WT mice, PSAPP mice showed high Abeta antibody titers. Most importantly, t.c. immunization with Abeta(1-42) plus CT resulted in significant decreases in cerebral Abeta(1-40,42) levels coincident with increased circulating levels of Abeta(1-40,42), suggesting brain-to-blood efflux of Abeta. Reduction in cerebral amyloidosis was not associated with deleterious side effects, including brain T cell infiltration or cerebral microhemorrhage. Together, these data suggest that t.c. immunization constitutes an effective and potentially safe treatment strategy for AD.

Preparation of recombinant vaccines

Vaccination is one of the most efficient ways to eradicate some infectious diseases in humans and animals. The material traditionally used as vaccines is attenuated or inactivated pathogens. This approach is sometimes limited by the fact that the material for vaccination is not efficient, not available, or generating deleterious side effects. A possible theoretical alternative is the use of recombinant proteins from the pathogens. This implies that the proteins having the capacity to vaccinate have been identified and that they can be produced in sufficient quantity at a low cost. Genetically modified organisms harboring pathogen genes can fulfil these conditions. Microorganisms, animal cells as well as transgenic plants and animals can be the source of recombinant vaccines. Each of these systems that are all getting improved has advantages and limits. Adjuvants must generally be added to the recombinant proteins to enhance their vaccinating capacity. This implies that the proteins used to vaccinate have been purified to avoid any immunization against the contaminants. The efficiency of a recombinant vaccine is poorly predictable. Multiple proteins and various modes of administration must therefore be empirically evaluated on a case-by-case basis. The structure of the recombinant proteins, the composition of the adjuvants and the mode of administration of the vaccines have a strong and not fully predictable impact on the immune response as well as the protection level against pathogens. Recombinant proteins can theoretically also be used as carriers for epitopes from other pathogens. The increasing knowledge of pathogen genomes and the availability of efficient systems to prepare large amounts of recombinant proteins greatly facilitate the potential use of recombinant proteins as vaccines. The present review is a critical analysis of the state of the art in this field.