Immunogenicity and Protective Efficacy of Replication-Incompetent Influenza Virus-Like Particles

Despite the success of influenza virus vaccines in reducing severe illness, their efficacy is suboptimal. We describe here the immunogenicity and protective capacity of replication-incompetent influenza virus-like particles (VLPs) which were generated entirely from cDNAs and lacked either the entire NS gene (encoding both the NS1 and NS2 protein) or only the NS2 gene. In mammalian cells infected with NS gene-deficient VLPs, the nucleoprotein, but not other viral proteins including hemagglutinin (HA) and neuraminidase (NA), was detected. In contrast, cells infected with VLPs expressing NS1 but not NS2 (NS2 knockout) expressed multiple viral proteins, including HA and NA. When challenged with lethal doses of an antigenically homologous mouse-adapted influenza virus, 94% of mice vaccinated with the NS2-knockout VLPs survived, compared with less than 10% of those given the NS-deficient VLPs. These results demonstrate the potential of replication-incompetent NS2-knockout VLPs as novel influenza vaccines and perhaps also as vectors to express genes from entirely unrelated pathogens.     

Versatile Virus-Like Particle Carrier for Epitope Based Vaccines

Background

Recombinant proteins and in particular single domains or peptides are often poorly immunogenic unless conjugated to a carrier protein. Virus-like-particles are a very efficient means to confer high immunogenicity to antigens. We report here the development of virus-like-particles (VLPs) derived from the RNA bacteriophage AP205 for epitope-based vaccines.

Methodology/Principal Findings

Peptides of angiotensin II, S.typhi outer membrane protein (D2), CXCR4 receptor, HIV1 Nef, gonadotropin releasing hormone (GnRH), Influenza A M2-protein were fused to either N- or C-terminus of AP205 coat protein. The A205-peptide fusions assembled into VLPs, and peptides displayed on the VLP were highly immunogenic in mice. GnRH fused to the C-terminus of AP205 induced a strong antibody response that inhibited GnRH function in vivo. Exposure of the M2-protein peptide at the N-terminus of AP205 resulted in a strong M2-specific antibody response upon immunization, protecting 100% of mice from a lethal influenza infection.

Conclusions/Significance

AP205 VLPs are therefore a very efficient and new vaccine system, suitable for complex and long epitopes, of up to at least 55 amino acid residues in length. AP205 VLPs confer a high immunogenicity to displayed epitopes, as shown by inhibition of endogenous GnRH and protective immunity against influenza infection.     

Changes in Human Langerhans Cells Following Intradermal Injection of Influenza Virus-Like Particle Vaccines

There is a significant gap in our fundamental understanding of early morphological and migratory changes in human Langerhans cells (LCs) in response to vaccine stimulation. As the vast majority of LCs studies are conducted in small animal models, substantial interspecies variation in skin architecture and immunity must be considered when extrapolating the results to humans. This study aims to determine whether excised human skin, maintained viable in organ culture, provides a useful human model for measuring and understanding early immune response to intradermally delivered vaccine candidates. Excised human breast skin was maintained viable in air-liquid-interface organ culture. This model was used for the first time to show morphological changes in human LCs stimulated with influenza virus-like particle (VLP) vaccines delivered via intradermal injection. Immunohistochemistry of epidermal sheets and skin sections showed that LCs in VLP treated skin lost their typical dendritic morphology. The cells were more dispersed throughout the epidermis, often in close proximity to the basement membrane, and appeared vertically elongated. Our data provides for increased understanding of the complex morphological, spatial and temporal changes that occur to permit LC migration through the densely packed keratinocytes of the epidermis following exposure to vaccine. Significantly, the data not only supports previous animal data but also provides new and essential evidence of host response to this vaccination strategy in the real human skin environment.     

Chimeric L1-L2 Virus-Like Particles as Potential Broad-Spectrum Human Papillomavirus Vaccines

The amino (N) terminus of the human papillomavirus (HPV) minor capsid protein L2 can induce low-titer, cross-neutralizing antibodies. The aim of this study was to improve immunogenicity of L2 peptides by surface display on highly ordered, self-assembled virus-like particles (VLP) of major capsid protein L1, and to more completely characterize neutralization epitopes of L2. Overlapping peptides comprising amino acids (aa) 2 to 22 (hereafter, chimera or peptide 2-22), 13 to 107, 18 to 31, 17 to 36, 35 to 75, 75 to 112, 115 to 154, 149 to 175, and 172 to 200 of HPV type 16 (HPV16) L2 were genetically engineered into the DE surface loop of bovine papillomavirus type 1 L1 VLP. Except for chimeras 35-75 and 13-107, recombinant fusion proteins assembled into VLP. Vaccination of rabbits with Freund''s adjuvanted native VLP induced higher L2-specific antibody titers than vaccination with corresponding sodium dodecyl sulfate-denatured proteins. Immune sera to epitopes within residues 13 to 154 neutralized HPV16 in pseudovirion neutralization assays, whereas chimera 17-36 induced additional cross-neutralization to divergent high-risk HPV18, -31, -45, -52, and -58; low-risk HPV11; and beta-type HPV5 (titers of 50 to 10,000). Aluminum hydroxide-monophosphoryl lipid A (Alum-MPL)-adjuvanted VLP induced similar patterns of neutralization in both rabbits and mice, albeit with 100-fold-lower titers than Freund''s adjuvant. Importantly, Alum-MPL-adjuvanted immunization with chimeric HPV16L1-HPV16L2 (peptide 17-36) VLP induced neutralization or cross-neutralization of HPV16, -18, -31, -45, -52, and -58; HPV6 and -11; and HPV5 (titers of 50 to 100,000). Immunization with HPV16 L1-HPV16 L2 (chimera 17-36) VLP in adjuvant applicable for human use induces broad-spectrum neutralizing antibodies against HPV types evolutionarily divergent to HPV16 and thus may protect against infection with mucosal high-risk, low-risk, and beta HPV types and associated disease.The more than 100 types of human papillomaviruses (HPV) identified to date (14) are the etiological agents of skin and mucosal papillomas or warts. Persistent infection with high-risk mucosal types, most often HPV type 16 (HPV16) and HPV18, causes cervical cancer, which constitutes the second leading fatal cancer in women worldwide, causing 274,000 deaths per year. Substantial morbidity results from other noncervical HPV-related conditions, such as anogenital warts or anal cancer (23).The development of current prophylactic papillomavirus vaccines was launched by observations that recombinantly expressed major capsid protein L1 self-assembles into virus-like particles (VLP). These empty viral capsids are composed of 360 L1 molecules and resemble native virions in both structure and immunogenicity, yet are nononcogenic and noninfectious. Moreover, VLP cannot replicate because the cells in which VLP are made contain only L1 and no other papillomavirus genes. Subunit VLP vaccines induce high-titer and type-restricted antibody responses to conformational L1 epitopes (12, 26, 39, 44). When applied to women prior to infection, available vaccines targeting the most prevalent high-risk types, HPV16 and HPV18, have demonstrated up to 100% efficacy against persistent infection and associated disease caused by the included types and thus are potentially able to prevent ∼70% of cervical high-grade dysplasias and probably cancers (22, 46). Therefore, use of currently licensed L1 vaccines necessitates continuation of cytological cervical screening of women. The prevention of 96% of cervical cancer would require immunity to seven high-risk HPV types (HPV16, -18, -31, -33, -45, -52, and -58) (32) and the development of more highly multivalent (and presumably costly) L1 VLP vaccines.The search for alternative broader-spectrum immunogens drew attention to the minor capsid protein L2, which is immunogenically subdominant in the context of coexpressed L1-L2 capsids (38). Immunization of animals with the amino (N)-terminal peptide of L2 demonstrated its ability to elicit low-titer neutralizing antibodies that protect against challenge with cognate papillomavirus types in vivo (16, 19), cross-neutralize heterologous types in vitro (25, 33, 38), and confer cross-protection in vivo (17).This study addresses two major issues that may further the development of L2-based broader-spectrum vaccines. First, the N terminus of L2 is more closely examined for potential neutralization epitopes, by incorporating peptides into papillomavirus VLP as peptide-presenting platforms (7, 21, 42). Moreover, we take advantage of the immunogenic characteristics of virion surfaces, such as the dense repetitive surface array of VLP, to induce strong and enduring immune responses to displayed L2 epitopes.     

Evaluation of Recombinant Influenza Virus-Simian Immunodeficiency Virus Vaccines in Macaques

There is an urgent need for human immunodeficiency virus (HIV) vaccines that induce robust mucosal immunity. Influenza A viruses (both H1N1 and H3N2) were engineered to express simian immunodeficiency virus (SIV) CD8 T-cell epitopes and evaluated following administration to the respiratory tracts of 11 pigtail macaques. Influenza virus was readily detected from respiratory tract secretions, although the infections were asymptomatic. Animals seroconverted to influenza virus and generated CD8 and CD4 T-cell responses to influenza virus proteins. SIV-specific CD8 T-cell responses bearing the mucosal homing marker β7 integrin were induced by vaccination of naïve animals. Further, SIV-specific CD8 T-cell responses could be boosted by recombinant influenza virus-SIV vaccination of animals with already-established SIV infection. Sequential vaccination with influenza virus-SIV recombinants of different subtypes (H1N1 followed by H3N2 or vice versa) produced only a limited boost in immunity, probably reflecting T-cell immunity to conserved internal proteins of influenza A virus. SIV challenge of macaques vaccinated with an influenza virus expressing a single SIV CD8 T cell resulted in a large anamnestic recall CD8 T-cell response, but immune escape rapidly ensued and there was no impact on chronic SIV viremia. Although our results suggest that influenza virus-HIV vaccines hold promise for the induction of mucosal immunity to HIV, broader antigen cover will be needed to limit cytotoxic T-lymphocyte escape.Developing a safe and effective human immunodeficiency virus (HIV) vaccine is one of the defining scientific challenges of our time. Induction of peripheral CD8 T-cell immunity to HIV did not protect against sexual exposure to HIV type 1 (HIV-1) in humans in a recent efficacy trial (11, 43). In simian immunodeficiency virus (SIV)-macaque studies, peripheral CD8 T-cell immunity can effectively control viremia (40) but is often observed to have a transient or limited role in delaying SIV disease in macaques (32). The gradual accumulation of immune escape at CD8 T-cell epitopes undermines the effectiveness of CD8 T-cell immunity to SIV (6, 22, 46). It is likely that inducing mucosal CD8 T-cell immunity to HIV will be more effective at limiting viral replication during the very early phases of acute infection, prior to massive viral dissemination and destruction of large numbers of CD4 T cells (50). The induction of multifunctional mucosal CD8 T cells by live attenuated SIV vaccination of macaques is thought to play a significant role in the success of this strategy (25, 26); however, it is unfortunately too dangerous for clinical trials at present.A series of mucosal viral and bacterial HIV vaccine vectors have been studied in recent years; however, none have yet proceeded to advanced clinical trials. Live attenuated poliovirus vectors have shown promise in SIV studies, but these viruses can in rare cases revert to virulence (14). Salmonella-based SIV vaccine vectors are able to induce CD8 T-cell responses which express the α4β7 integrin mucosal homing marker when administered orally (20, 24). However, there may be a much stronger link between concomitant genital tract immunity and immunity induced at respiratory mucosal sites compared to that induced at enteric sites (33, 38, 42). Vesicular stomatitis virus vectors that replicate in the nasal mucosa show promise in SIV-macaque trials but are potentially neurotoxic (55). Replication-competent adenovirus vectors have looked promising in some SHIV-macaque studies (49) but failed to provide significant protection in a recent SIV-macaque study (17) and could have similar issues of enhanced infection rates as seen in the recent efficacy trials of replication-incompetent adenovirus type 5 vectors.A mucosal vector system that has several advantages over existing models but that is relatively unexplored is recombinant attenuated influenza viruses. Such viruses (i) have an existing reverse genetics system to readily generate and manipulate recombinant viruses (31, 34), (ii) are effective as anti-influenza vaccines and licensed for human use (e.g., “Flumist” vaccine [9]) with ready production capability, (iii) have robust respiratory mucosal replication that should facilitate genital mucosal immunity, and (iv) can be generated with a variety of hemagglutinin (H) and neuraminidase (N) glycoproteins, potentially enabling these viruses to be administered sequentially in prime-boost combinations to limit the effect of antivector humoral immunity (34). Mouse-adapted recombinant influenza virus-HIV vectors have been studied in mice and demonstrated significant induction of cellular immunity at mucosal sites (8, 27, 28, 44, 48). However, although several native influenza viruses replicate efficiently in the respiratory tracts of Asian macaque species (10, 12, 52), no studies to date have examined the immunogenicity or efficacy of recombinant attenuated influenza virus-SIV vectors in macaques.     

基于血凝素关键序列的流感病毒疫苗

流感病毒的血凝素(HA)位于流感病毒包膜上,在流感病毒吸附和穿入宿主细胞的过程中起着重要作用.血凝素以三聚体的形式镶嵌在病毒包膜上,每个单体糖蛋白是由两个经二硫键连接的蛋白亚单位组成,即HA1和HA2.血凝素属Ⅰ型膜蛋白,其一级结构含有4个结构域:信号肽(前导序列)、胞浆域、跨膜域和胞外域. 血凝素是流感病毒最主要的表面抗原,它能够诱导机体产生相应的中和抗体以中和病毒.血凝素一般含有5 个抗原决定簇,流感病毒的流行与其抗原结构的变化密切相关.主要就血凝素的结构和功能、流感病毒疫苗以及以血凝素基因关键序列为基础的流感病毒疫苗进行阐述.     

Induction of Long-Term Protective Immune Responses by Influenza H5N1 Virus-Like Particles

Background

Recurrent outbreaks of highly pathogenic H5N1 avian influenza virus pose a threat of eventually causing a pandemic. Early vaccination of the population would be the single most effective measure for the control of an emerging influenza pandemic.

Methodology/Principal Findings

Influenza virus-like particles (VLPs) produced in insect cell-culture substrates do not depend on the availability of fertile eggs for vaccine manufacturing. We produced VLPs containing influenza A/Viet Nam1203/04 (H5N1) hemagglutinin, neuraminidase, and matrix proteins, and investigated their preclinical immunogenicity and protective efficacy. Mice immunized intranasally with H5N1 VLPs developed high levels of H5N1 specific antibodies and were 100% protected against a high dose of homologous H5N1 virus infection at 30 weeks after immunization. Protection is likely to be correlated with humoral and cellular immunologic memory at systemic and mucosal sites as evidenced by rapid anamnestic responses to re-stimulation with viral antigen in vivo and in vitro.

Conclusions/Significance

These results provide support for clinical evaluation of H5N1 VLP vaccination as a public health intervention to mitigate a possible pandemic of H5N1 influenza.     

Virus-Like Particles in Cephalosporium acremonium

Cephalosporium acremonium cultures were studied for the presence of virus-like particles. Relatively few particles were found in the preparations, indicating that the number of particles present in these cells may be much lower than in Penicillium species.     

Characterization of Chikungunya Virus-Like Particles

Chikungunya virus (CHIKV) is becoming a global concern due to the increasing number of outbreaks throughout the world and the absence of any CHIKV-specific vaccine or treatment. Virus-like particles (VLPs) are multistructured proteins that mimic the organization and conformation of native viruses but lack the viral genome. They are noninfectious and potentially safer vaccine candidates. Recent studies demonstrated that the yield of CHIKV VLPs varies depending on the strains, despite the 95% amino acid similarity of the strains. This might be due to the codon usage, since protein expression is differently controlled by different organisms. We optimized the region encoding CHIKV structural proteins, C-E3-E2-6k-E1, inserted it into a mammalian expression vector, and used the resulting construct to transfect 293 cells. We detected 50-kDa proteins corresponding to E1 and/or E2 in the cell lysate and the supernatant. Transmission electron microscopy revealed spherical particles with a 50- to 60-nm diameter in the supernatant that resembled the native CHIKV virions. The buoyant density of the VLPs was 1.23 g/mL, and the yield was 20 µg purified VLPs per 10⁸ cells. The VLPs aggregated when mixed with convalescent sera from chikungunya patients, indicating that their antigenicity is similar to that of native CHIKV. Antibodies elicited with the VLPs were capable of detecting native CHIKV, demonstrating that the VLPs retain immunogenicity similar to that of the native virion. These results indicated that CHIKV VLPs are morphologically, antigenically, and immunologically similar to the native CHIKV, suggesting that they have potential for use in chikungunya vaccines.     

Production of Human Papillomavirus Type 16 L1 Virus-Like Particles by Recombinant Lactobacillus casei Cells

Infections with human papillomavirus type 16 (HPV-16) are closely associated with the development of human cervical carcinoma, which is one of the most common causes of cancer death in women worldwide. At present, the most promising vaccine against HPV-16 infection is based on the L1 major capsid protein, which self-assembles in virus-like particles (VLPs). In this work, we used a lactose-inducible system based on the Lactobacillus casei lactose operon promoter (plac) for expression of the HPV-16 L1 protein in L. casei. Expression was confirmed by Western blotting, and an electron microscopy analysis of L. casei expressing L1 showed that the protein was able to self-assemble into VLPs intracellularly. The presence of conformational epitopes on the L. casei-produced VLPs was confirmed by immunofluorescence using the anti-HPV-16 VLP conformational antibody H16.V5. Moreover, sera from mice that were subcutaneously immunized with L. casei expressing L1 reacted with Spodoptera frugiperda-produced HPV-16 L1 VLPs, as determined by an enzyme-linked immunosorbent assay. The production of L1 VLPs by Lactobacillus opens the possibility for development of new live mucosal prophylactic vaccines.     

Intradermal Vaccination with Influenza Virus-Like Particles by Using Microneedles Induces Protection Superior to That with Intramuscular Immunization

Influenza virus-like particles (VLPs) are a promising cell culture-based vaccine, and the skin is considered an attractive immunization site. In this study, we examined the immunogenicity and protective efficacy of influenza VLPs (H1N1 A/PR/8/34) after skin vaccination using vaccine dried on solid microneedle arrays. Coating of microneedles with influenza VLPs using an unstabilized formulation was found to decrease hemagglutinin (HA) activity, whereas inclusion of trehalose disaccharide preserved the HA activity of influenza VLP vaccines after microneedles were coated. Microneedle vaccination of mice in the skin with a single dose of stabilized influenza VLPs induced 100% protection against challenge infection with a high lethal dose. In contrast, unstabilized influenza VLPs, as well as intramuscularly injected vaccines, provided inferior immunity and only partial protection (≤40%). The stabilized microneedle vaccination group showed IgG2a levels that were 1 order of magnitude higher than those of other groups and had the lowest lung viral titers after challenge. Also, levels of recall immune responses, including hemagglutination inhibition titers, neutralizing antibodies, and antibody-secreting plasma cells, were significantly higher after skin vaccination with stabilized formulations. Therefore, our results indicate that HA stabilization, combined with vaccination via the skin using a vaccine formulated as a solid microneedle patch, confers protection superior to that with intramuscular injection and enables potential dose-sparing effects which are reflected by pronounced increases in rapid recall immune responses against influenza virus.Influenza is a major health threat among infectious diseases, posing a significant burden for public health worldwide. Over 200,000 hospitalizations and approximately 36,000 deaths are estimated to occur annually in the United States alone (48, 49). Vaccination is the most cost-effective measure for controlling influenza. However, the influenza vaccine needs to be updated and manufactured every year due to changes in circulating viral strains. Current influenza vaccines rely on egg substrate-based production, a lengthy process with limited capacity that can cause shortages in available vaccine supplies. The recent 2009 outbreak of H1N1 influenza virus is a good example of the urgent need to develop a more effective vaccine platform and vaccination method (38).Influenza virus-like particles (VLPs) have been suggested as a promising alternative candidate to current influenza vaccines. Influenza VLPs are noninfectious particles that mimic the virus in structure and morphology, can be produced using an egg-free cell culture system, and have been shown to be highly immunogenic, inducing protective immunity (9, 15, 19, 27, 35, 41, 42, 44). Most current vaccines are administered intramuscularly to humans in liquid formulations using hypodermic needles or syringes. Another strategy to meet the potential need for mass vaccination would be to develop an effective method for vaccine delivery to the skin (4, 8, 32, 50, 52). The skin is considered an important peripheral immune organ rich in potent immune-inducing cells, including Langerhans cells (LCs), dermal dendritic cells (DCs), and keratinocytes (5, 13, 14, 22). LCs and DCs residing in the epidermal and dermal layers of the skin have been shown to play an important role in antigen processing and presentation following skin immunization (1, 13, 14, 22). Intradermal (ID) vaccination delivering antigens to the dermal layer of the skin has been performed in many clinical studies and have demonstrated dose-sparing effects in some cases (4, 28, 29). Particularly, ID delivery of vaccines might be more effective in the elderly population (50), the highest risk group for influenza epidemics (49). However, ID delivery of vaccines using hypodermic needles is painful and needs highly trained medical personnel. In addition, more frequent local reactions at the injection site were observed after ID delivery. Therefore, a simple and effective approach for vaccination without using hypodermic needles would be highly desirable.To overcome the skin barrier of the outer layer of stratum corneum, solid microneedles were previously coated with inactivated influenza viruses and used to successfully deliver vaccines to the skin, which provided protection comparable to that with conventional intramuscular immunizations (32, 52). Other vaccines have also been delivered using microneedles (17, 17a), but VLPs have never been used this way before. Delivery of a powdered form of inactivated influenza vaccines to the skin has also been demonstrated using a high-speed jet delivery device (10). These previous studies used high doses of vaccines, possibly due to the instability of vaccines in dry formulations.Influenza hemagglutinin (HA) is responsible for attachment of the virus to sialic acid-containing receptors on target cells. However, it is not well understood how functional activity of HA affects the immunogenicity of influenza VLP vaccines. For the first time in this study, we investigated the effect of HA stability, immune responses, and protective efficacies of solid-microneedle VLP vaccines containing H1 HA as a major influenza viral component after delivery to the skin in comparison to results with intramuscular immunization. We found that the functional integrity of HA in influenza VLPs significantly influenced the immunological and protective outcomes for both microneedle and intramuscular vaccination. In addition, we have observed differential outcomes contributing to the protective immunity by the delivery of HA-stabilized VLPs to the skin in terms of the types of immune responses, recall antibody responses, and viral clearance at an early time point after challenge compared to those induced by intramuscular immunization.     

M2e-Displaying Virus-Like Particles with Associated RNA Promote T Helper 1 Type Adaptive Immunity against Influenza A

The ectodomain of influenza A matrix protein 2 (M2e) is a candidate for a universal influenza A vaccine. We used recombinant Hepatitis B core antigen to produce virus-like particles presenting M2e (M2e-VLPs). We produced the VLPs with and without entrapped nucleic acids and compared their immunogenicity and protective efficacy. Immunization of BALB/c mice with M2e-VLPs containing nucleic acids induced a stronger, Th1-biased antibody response compared to particles lacking nucleic acids. The former also induced a stronger M2e-specific CD4⁺ T cell response, as determined by ELISPOT. Mice vaccinated with alum-adjuvanted M2e-VLPs containing the nucleic acid-binding domain were better protected against influenza A virus challenge than mice vaccinated with similar particles lacking this domain, as deduced from the loss in body weight following challenge with X47 (H3N2) or PR/8 virus. Challenge of mice that had been immunized with M2e-VLPs with or without nucleic acids displayed significantly lower mortality, morbidity and lung virus titers than control-immunized groups. We conclude that nucleic acids present in M2e-VLPs correlate with improved immune protection.     

Distributions of Virus-Like Particles and Prokaryotes within Microenvironments

Microbial interactions are important for ecosystem function, but occur at the microscale and so are difficult to observe. Previous studies in marine systems have shown significant shifts in microbial community abundance and composition over scales of micrometres to centimetres. This study investigates the microscale abundance distributions of virus-like particles (VLPs) and prokaryotes in the lower reaches of a river to determine the extent to which microscale microbial patchiness exists in freshwater systems. Here we report local hotspots surrounded by gradients that reach a maximum 80 and 107 fold change in abundance over 0.9 cm for prokaryotic and VLP subpopulations. Changes in prokaryotic and VLP hotspots were tightly coupled. There were no gradients at tens of centimetres across the boundary layers, which is consistent with strong mixing and turbulence-driven aggregation found in river systems. Quantification of the patchiness shows a marked asymmetry with patches 10 times greater than background common, but depletions being rare or absent in most samples. This consistent asymmetry suggests that coldspots depleted by grazing and lysis are rapidly mixed to background concentrations, while the prevalence of hotspots indicates persistence against disruption. The hotspot to coldspot relative abundance may be useful for understanding microbial river dynamics. The patchiness indicates that the mean- field approach of bulk phase sampling misses the microbially relevant community variation and may underestimate the concentrations of these important microbial groups.     

Electron Microscopic Observations on Virus-Like Particles Associated with SH Antigen

The structural aspects of SH antigen-containing particles were investigated. These studies confirmed the existence of a large spherical particle (ca. 43 nm) and smaller (ca. 20 nm) rod- and sphere-shaped particles. The large particle consists of an outer and inner membrane and a core of "nucleic acid" as seen by positive staining techniques. The outer membrane of the large particle appears to be similar to that of the 20-nm diameter spheres and rods known to possess the SH antigen.     

Presence of Two Virus-Like Particles in Penicillium citrinum

Two icosahedral virus-like particles (28 and 19 nm in diameter, respectively) have been detected in sporogenic and asporogenic segregants of a strain of Penicillium citrinum. The distribution of the two particles differed among the two segregants.     

Synthetic Peptide-Based Vaccines Against Influenza

Summary Advances have been made in the development of vaccines based on synthetic peptides representing protective epitopes of the influenza virus. The study reviewed here evaluates the capacity of three epitopes in different delivery systems to induce specific immune response and protect mice against viral challenge infection. Although peptide vaccines are not in use yet, they continue to be explored as is discussed herewith.     

Synthetic Peptide-Based Vaccines Against Influenza

Advances have been made in the development of vaccines based on synthetic peptides representing protective epitopes of the influenza virus. The study reviewed here evaluates the capacity of three epitopes in different delivery systems to induce specific immune response and protect mice against viral challenge infection. Although peptide vaccines are not in use yet, they continue to be explored as is discussed herewith.     

Virus-Like Particles as an Instrument of Vaccine Production

Molecular Biology - The paper discusses the techniques which are currently implemented for vaccine production based on virus-like particles (VLPs). The factors which determine the characteristics...