Simian Virus 40 Virus-like Particles Research Articles

Induction of adaptive immune responses against antigens incorporated within the capsid of simian virus 40.

Simian virus 40 (SV40) is a monkey polyomavirus. The capsid structure is icosahedral and comprises VP1 units that measure 45 nm in diameter. Five SV40 VP1 molecules form one pentamer subunit, and a single icosahedral subunit comprises 72 pentamers; a single SV40 VP1 capsid comprises 360 SV40 VP1 molecules. In a previous study, we showed that an influenza A virus matrix protein 1 (M1) CTL epitope inserted within SV40 virus-like particles (VLPs) induced cytotoxic T lymphocytes (CTLs) without the need for an adjuvant. Here, to address whether SV40 VLPs induce adaptive immune responses against VLP-incorporated antigens, we prepared SV40 VLPs containing M1 or chicken ovalbumin (OVA). This was done by fusing M1 or OVA with the carboxyl terminus of SV40 VP2 and co-expressing them with SV40 VP1 in insect cells using a baculovirus vector. Intraperitoneal (i.p.) or intranasal administration of SV40 VLPs incorporating M1 induced the production of CTLs specific for the M1 epitope without the requirement for adjuvant. The production of antibodies against SV40 VLPs was also induced by i.p. administration of SV40 VLPs in the absence of adjuvant. Finally, the administration of SV40 VLPs incorporating OVA induced anti-OVA antibodies in the absence of adjuvant; in addition, the level of antibody production was comparable with that after i.p. administration of OVA plus alum adjuvant. These results suggest that the SV40 capsid incorporating foreign antigens can be used as a vaccine platform to induce adaptive immune responses without the need for adjuvant.

Revealing in real-time a multistep assembly mechanism for SV40 virus-like particles

Many viruses use their genome as template for self-assembly into an infectious particle. However, this reaction remains elusive because of the transient nature of intermediate structures. To elucidate this process, optical tweezers and acoustic force spectroscopy are used to follow viral assembly in real time. Using Simian virus 40 (SV40) virus-like particles as model system, we reveal a multistep assembly mechanism. Initially, binding of VP1 pentamers to DNA leads to a significantly decreased persistence length. Moreover, the pentamers seem able to stabilize DNA loops. Next, formation of interpentamer interactions results in intermediate structures with reduced contour length. These structures stabilize into objects that permanently decrease the contour length to a degree consistent with DNA compaction in wild-type SV40. These data indicate that a multistep mechanism leads to fully assembled cross-linked SV40 particles. SV40 is studied as drug delivery system. Our insights can help optimize packaging of therapeutic agents in these particles.

In Vivo Targeting and Imaging of Atherosclerosis Using Multifunctional Virus-Like Particles of Simian Virus 40.

Atherosclerosis is a leading cause of death globally. Targeted imaging and therapeutics are desirable for the detection and treatment of the disease. In this study, we developed trifunctional Simian virus 40 (SV40)-based nanoparticles for in vivo targeting and imaging of atherosclerotic plaques. These novel trifunctional SV40-based nanoparticles encapsulate near-infrared quantum dots and bear a targeting element and a drug component. Using trifunctional SV40-based nanoparticles, we were able to noninvasively fluorescently image atherosclerotic plaques in live intact ApoE(-/-) mice. Near-infrared quantum dots encapsulated in the SV40 virus-like particles showed prominent optical properties for in vivo imaging. When different targeting peptides for vascular cell adhesion molecule-1, macrophages, and fibrin were used, early, developmental, and late stages of atherosclerosis could be targeted and imaged in live intact ApoE(-/-) mice, respectively. Targeted SV40 virus-like particles also delivered an increased concentration of the anticoagulant drug Hirulog to atherosclerosis plaques. Our study provides novel SV40-based nanoparticles with multivalency and multifunctionality suitable for in vivo imaging, molecular targeting, and drug delivery in atherosclerosis.

Chimeric SV40 virus-like particles induce specific cytotoxicity and protective immunity against influenza A virus without the need of adjuvants

Virus-like particles (VLPs) are a promising vaccine platform due to the safety and efficiency. However, it is still unclear whether polyomavirus-based VLPs are useful for this purpose. Here, we attempted to evaluate the potential of polyomavirus VLPs for the antiviral vaccine using simian virus 40 (SV40). We constructed chimeric SV40-VLPs carrying an HLA-A⁎02:01-restricted, cytotoxic T lymphocyte (CTL) epitope derived from influenza A virus. HLA-A⁎02:01-transgenic mice were then immunized with the chimeric SV40-VLPs. The chimeric SV40-VLPs effectively induced influenza-specific CTLs and heterosubtypic protection against influenza A viruses without the need of adjuvants. Because DNase I treatment of the chimeric SV40-VLPs did not disrupt CTL induction, the intrinsic adjuvant property may not result from DNA contaminants in the VLP preparation. In addition, immunization with the chimeric SV40-VLPs generated long-lasting memory CTLs. We here propose that the chimeric SV40-VLPs harboring an epitope may be a promising CTL-based vaccine platform with self-adjuvant properties.

SV40 virus-like particles as an effective delivery system and its application to a vaccine carrier

The authors have purified a major capsid protein, VP1 of Simian virus 40 (SV40), using recombinant baculovirus and have established the method of in vitro reassembly of SV40 virus-like particles (SV40-VLPs) from VP1-pentamers. In this reassembly, SV40-VLPs can encapsulate approximately 5 kb exogenous DNA shielded by histone or foreign proteins fused to minor capsid proteins VP2/3 and effectively deliver them into mammalian cells. Insertion of a particular foreign peptide into the surface loops of VP1 provides SV40-VLPs with the ability of cell targeting. Furthermore, SV40-VLPs appear to stimulate innate immunity as a natural adjuvant. Given these characteristics, SV40-VLPs may be a promising vaccine carrier to deliver heterologous antigens for the induction of cytotoxic T lymphocytes without artificial adjuvants. In this review, the authors describe how SV40-VLPs have been developed and engineered, and discuss their potential benefits and challenges as a cytotoxic T lymphocyte-based vaccine platform.

Presentation of functional foreign peptides on the surface of SV40 virus-like particles

Viral capsids of simian virus 40 (SV40) are highly efficient gene delivery vehicles that infect a broad range of cells and tissues. To develop a controlled, cell type-specific delivery system, we sought to display foreign peptides on the capsid surface by genetically manipulating the major capsid protein Vp1. Here we report the identification of two sites within the surface loops of Vp1 that can accommodate foreign peptides in such a way that the foreign peptides are displayed on the surface of the virus-like particles (VLPs) without interfering with VLP assembly or the packaging of viral DNA. Insertion of Flag-tags but not RGD integrin-binding motifs at these sites strongly inhibited cell attachment of VLPs, which normally associate with host cells through cell surface molecules such as major histocompatibility complex (MHC) class I and ganglioside GM1. Instead, VLPs carrying the RGD motifs bound to integrin in vitro and to the cell surface in an RGD-dependent manner. Thus, insertion of foreign sequences into the surface loops of Vp1 can reduce natural virus–cell interactions and even confer an ability to bind to a new target receptor. This study demonstrates the potential usefulness of this strategy for the development of novel delivery vehicles with different cell tropisms.

Viruses from Nonhuman Primates

To the Editor: I read with interest the article by Jones-Engel et al. (1), which described the frequency of viruses infecting temple rhesus macaques. The investigation included the polyomavirus simian virus 40 (SV40), a pathogen recognized to have infected millions of humans who were vaccinated with polio vaccines produced in cultures of rhesus monkey kidney cells (2,3). The authors indicated that technologic advances have improved the specificity of detecting SV40 antibodies and used an enzyme immunoassay based on viruslike particles (VLPs) to perform the analysis (1). However, the specificity of the SV40 enzyme immunoassay is problematic because studies with serum samples from macaques have found that antibodies are cross-reactive with polyomaviruses JCV and BKV (4). In addition, in monkey sera SV40 VLPs correlated with BKV antibodies. Similar conflicting results have been found in human studies that used polyomavirus VLPs assays (3). These limitations are the result of polyomavirus VLPs assays using expression of the VP1 capsid protein (4), a highly homologous gene among JCV, BKV, and SV40 (3). In contrast, modern molecular biology assays are the preferred method for the analysis of SV40 infections (2,3). In addition, these sensitive and specific techniques can provide insights into the distribution of SV40 strains and variants (2,3). This is important because recent data suggest that the biological properties of SV40 strains vary in vivo (5). Because current evidence shows that SV40 infections are identified in some humans and that the virus is associated with selected human malignancies (2,3), prospective longitudinal studies that use molecular techniques are needed to examine the prevalence and ecology of SV40. The Institute of Medicine recognizes that the biologic evidence indicates that infections with this DNA virus could lead to cancer in humans and recommends targeted biologic research of SV40 in human populations (2).

Prevalence and stability of human serum antibodies to simian virus 40 VP1 virus-like particles

Possible human infection with simian virus 40 (SV40) has been of great concern ever since SV40 was discovered in polio vaccines. Human populations are SV40-seropositive, but because of serological cross-reactivity between SV40 and the human polyomaviruses BK virus (BKV) and JC virus (JCV), it is debatable whether these antibodies are specific. An SV40-specific serological assay was established, based on purified virus-like particles (VLPs), where the SV40 VLPs were blocked with hyperimmune sera to BKV and JCV. Competition with SV40 hyperimmune sera was used as a confirmatory test. Among 288 Swedish children of between 1 and 13 years of age, 7.6 % had SV40-specific antibodies. SV40 seroprevalence reached a peak of 14 % at 7-9 years of age. Among 100 control patients with benign tumours, 9 % were SV40-seropositive. However, SV40 DNA was not detectable in corresponding buffy-coat samples. In serial samples taken up to 5 years apart from 141 Finnish women participating in the population-based serological screening for congenital infections, only two of 141 women were SV40-seropositive in both samples. Six women seroconverted and eight women had a loss of antibodies over time. None of the SV40-seropositive samples contained detectable SV40 DNA. In conclusion, there is a low prevalence of SV40-specific antibodies in the Nordic population. The SV40 antibodies appear to have a low stability over time and their origin is not clear.

Lack of serologic evidence for prevalent simian virus 40 infection in humans.

Propagation of poliovirus in monkey kidney cells led to the inadvertent contamination of poliovirus vaccines with simian virus 40 (SV40) between 1955 and 1963. Recent studies using polymerase chain reaction-based strategies have detected SV40 DNA in a large number of tumor types. The finding of SV40 DNA in tumors from individuals who are too young to have been exposed to SV40-contaminated vaccines has led to the suggestion that SV40 has become a prevalent transmissible human pathogen. To test this hypothesis, we screened human sera for antibodies to SV40 using direct and competitive enzyme-linked immunosorbent assays (ELISAs). An ELISA was developed using recombinant SV40 virus-like particles (VLPs) and was validated using sera from naturally infected macaques. VLPs of SV40 and the related ubiquitous human polyomaviruses, JCV and BKV, were used to screen human sera to determine the prevalence of SV40, JCV, and BKV antibodies among a normal population of control subjects (n = 487) and among case patients with either osteosarcoma (n = 122) or prostate cancer (n = 90). A competitive ELISA in which sera were pre-adsorbed with each type of VLP was used to identify cross-reactive antibodies. Correlations of reactivity among the three polyomavirus types were calculated using the Spearman correlation coefficient. All statistical tests were two-sided. BKV and JCV antibodies were prevalent in all case patients and control subjects examined. In contrast, only 6.6% (46/699) of serum samples were positive for SV40 antibodies by ELISA; however, none of these samples could be confirmed as having authentic SV40 antibodies following pre-adsorption with JCV or BKV VLPs. These data indicate that some individuals have BKV and/or JCV antibodies that cross-react with SV40, but they do not provide support for SV40 being a prevalent human pathogen.