Adenovirus-mediated shRNA interference against porcine circovirus type 2 replication both in vitro and in vivo

shRNA transgenic swine display resistance to infection with the foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) is one of the most important animal pathogens in the world. FMDV naturally infects swine, cattle, and other cloven-hoofed animals. FMD is not adequately controlled by vaccination. An alternative strategy is to develop swine that are genetically resistant to infection. Here, we generated FMDV-specific shRNA transgenic cells targeting either nonstructural protein 2B or polymerase 3D of FMDV. The shRNA-positive transgenic cells displayed significantly lower viral production than that of the control cells after infection with FMDV (P < 0.05). Twenty-three transgenic cloned swine (TGCS) and nine non-transgenic cloned swine (Non-TGCS) were produced by somatic cell nuclear transfer (SCNT). In the FMDV challenge study, one TGCS was completely protected, no clinical signs, no viremia and no viral RNA in the tissues, no non-structural antibody response, another one TGCS swine recovered after showing clinical signs for two days, whereas all of the normal control swine (NS) and Non-TGCS developed typical clinical signs, viremia and viral RNA was determined in the tissues, the non-structural antibody was determined, and one Non-TGCS swine died. The viral RNA load in the blood and tissues of the TGCS was reduced in both challenge doses. These results indicated that the TGCS displayed resistance to the FMDV infection. Immune cells, including CD3⁺, CD4⁺, CD8⁺, CD21⁺, and CD172⁺ cells, and the production of IFN-γ were analyzed, there were no significant differences observed between the TGCS and NS or Non-TGCS, suggesting that the FMDV resistance may be mainly derived from the RNAi-based antiviral pathway. Our work provides a foundation for a breeding approach to preventing infectious disease in swine.

PK15 cell line stably overexpressing IL2 enhances PCV2 replication

Porcine circovirus type 2 (PCV2) is the primary agent responsible for porcine circovirus-associated diseases (PCVADs), which is acknowledged as one of the most economically important diseases for the swine industry worldwide. Currently, the development of PCV2 vaccine against PCVADs and for other applications require large amounts of viral particles. The low propagation rate of PCV2 in vitro limits vaccine production. Previous studies showed that a cell line transfected with the porcine interleukin (IL)-2 gene gave higher PCV2 yield in vitro. However, transient transfection may become less effective and unstable after serial generations. In this work, we constructed a PK15 cell line with stable expression of porcine IL2 by lentivirus transfection. The results demonstrated that the transgenic cell line stably expressed IL2 protein significantly enhanced PCV2 replication. Thus, the transgenic PK15 cell line could be a promising cell line for vaccine production.

Nuclear transporter karyopherin subunit alpha 3 levels modulate Porcine circovirus type 2 replication in PK-15 cells

Entering the nucleus is important for Porcine circovirus type 2 (PCV2) replication. Karyopherins (KPNs) mediate the nuclear import of many cytoplasmic proteins. Our previous study showed that KPNA3 is involved in interferon production during PCV2 infection induced by Poly I:C and ISD (Interferon stimulatory DNA). However, it remains unclear whether PCV2 replication is associated with KPNA3. In the present study, knockdown of KPNA3 promoted the replication of PCV2, whereas overexpression of KPNA3 inhibited PCV2 replication in PK-15 cells. Furthermore, KPNA3 knockdown inhibited IRF3 and reduced the expression of antiviral genes including IFN-β, ISG54, Mx1 and ISG56, while the opposite results were obtained after KPNA3 overexpression. KPNA3 knockdown also promoted p65 nuclear translocation and increased the mRNA expression of IL-10 and IL-1β. These results suggested that KPNA3 facilitates IRF3 entry into the nucleus and the production of an antiviral response, resulting in PCV2 replication inhibition and blockage of NF-κB signal activation.

Significant inhibition of Tembusu virus envelope and NS5 gene using an adenovirus-mediated short hairpin RNA delivery system

Tembusu virus (TMUV) is a mosquito-borne flavivirus, which was first isolated in the tropics during the 1970s. Recently, a disease characterized by ovarian haemorrhage and neurological symptoms was observed in ducks in China, which threatens poultry production. However, there is no suitable vaccination strategy or effective antiviral drugs to combat TMUV infections. Consequently, there is an urgent need to develop a new anti-TMUV therapy. In this study, we report an efficient short hairpin RNA (shRNA) delivery strategy for the inhibition of TMUV production using an adenovirus vector system. Using specifically designed shRNAs based on the E and NS5 protein genes of TMUV, the vector-expressed viral genes, TMUV RNA replication and infectious virus production were downregulated at different levels in Vero cells, where the shRNA (NS52) was highly effective in inhibiting TMUV. Using the human adenovirus type 5 shRNA delivery system, the recombinant adenovirus (rAd-NS52) inhibited TMUV multiplication with high efficiency. Furthermore, the significant dose-dependent inhibition of viral RNA copies induced by rAd-NS52 was found in TMUV-infected cells, which could last for at least 96h post infection. Our results indicated that the adenovirus-mediated delivery of shRNAs could play an active role in future TMUV antiviral therapeutics.

Suppressor of cytokine signaling 3 plays an important role in porcine circovirus type 2 subclinical infection by downregulating proinflammatory responses

Porcine circovirus type 2 (PCV2) causes porcine circovirus-associated diseases and usually evokes a subclinical infection, without any obvious symptoms, in pigs. It remains unclear how PCV2 leads to a subclinical infection. In this study, we found that peripheral blood mononuclear cells (PBMCs) from PCV2-challenged piglets with no significant clinical symptoms exhibited increased expression of suppressor of cytokine signaling (SOCS) 3, but no significant changes in the expression of the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α; this differed from piglets that displayed significant clinical symptoms. IL-6- and TNF-α-mediated signalings were inhibited in PBMCs from subclinical piglets. Elevated SOCS3 levels inhibited IL-6- and TNF-α-mediated NF-kappa-B inhibitor alpha degradation in PBMCs and PK-15 cells. SOCS3 production was also increased in PCV2-infected PK-15 porcine kidney cells, and IL-6 and TNF-α production that was induced by PCV2 in PK-15 cells was significantly increased when SOCS3 was silenced by a small interfering RNA. SOCS3 interacted with signal transducer and activator of transcription 3 and TNF-associated receptor-associated factor 2, suggesting mechanisms by which SOCS3 inhibits IL-6 and TNF-α signaling. We conclude that SOCS3 plays an important role in PCV2 subclinical infection by suppressing inflammatory responses in primary immune cells.

Adenovirus-mediated shRNA interference against HSV-1 replication in vitro

The UL29 and UL28 proteins encoded by herpes simplex virus type 1 (HSV-1) are critical for its replication and packaging, respectively. Research has demonstrated that synthesized siRNA molecules targeting the UL29 gene are able to suppress HSV-2 replication and the UL28-null HSV-1 gene cannot form infectious viruses in vitro. Silencing the UL28 and UL29 genes by RNAi might lead to the development of novel antiviral agents for the treatment of HSV-1 infections. Two kinds of short hairpin RNAs (shRNAs) targeting the UL29 and UL28 genes were chemically synthesized and then delivered into cells by a replication-defective human adenovirus type 5 (Adv5) vector. (-) shRNAs targeting none of the genome of HSV-1 were used as the control. Vero cells were inoculated with Ad-UL28shRNA or Ad-UL29shRNA at a multiplicity of infection (MOI) of 100 and challenged 24 h later with HSV-1 at an MOI of 0.01 to inhibit HSV-1 replication, as measured by the level of the corresponding RNA and proteins. In addition, the amount of progeny virus was assessed at daily intervals. The antiviral effects of Ad-shRNAs at ongoing HSV-1 infection were explored at 12 h after inoculation of the HSV-1. The results showed that the shRNAs delivered by Adv5 significantly suppressed HSV-1 replication in vitro, as determined by the levels of viral RNA transcription, viral protein synthesis, and viral production. The Ad-UL28shRNA and Ad-UL29shRNA suppressed the replication of HSV-1, respectively, compared with the control group (P < 0.001). When Ad-UL28shRNA and Ad-UL29shRNA were combined, a synergistic effect was observed. The antiviral effects could sustain for at least 4 days after the HSV-1 infection (P < 0.001). Furthermore, antiviral effects were achieved 12 h prior to inoculation of Adv5-shRNAs (P < 0.001). Our data demonstrated comparable antiviral activities against herpes simplex virus by shRNAs targeting either UL29 or UL28 sites in vitro and the effectiveness of using the Adv5 delivery of shRNAs. Therefore, the Adv5 delivery of shRNAs targeting the UL29 and UL28 sites probably may provide an alternative strategy for controlling HSV-1 infection.

Heat shock protein 90 is essential for replication of porcine circovirus type 2 in PK-15 cells

Porcine circovirus type 2 (PCV2) is recognized as the causative agent of porcine circovirus-associated disease (PCVAD). However, the mechanism of PCV2 replication has not been understood completely. Heat shock protein 90 (Hsp90) plays an important role in viral genome replication, viral genes expression, and viral particle packaging. In this study, we firstly found that inhibition of Hsp90 by pretreatment of host cells with 17-AAG, a specific inhibitor of Hsp90, or blocking Hsp90α/Hsp90β with siRNA, resulted in significantly reduced viral replication in PK-15 cells. But inhibition of Hsp90 by 17-AAG did not affect PCV2 entry into the host cells. Meanwhile, over-expression of Hsp90α/Hsp90β enhanced PCV2 genome replication and virion production. In addition, Hsp90β was enriched in the nuclear zone in the cells infected with PCV2. But it did not interact with the viral Cap/Rep proteins. It suggested that Hsp90 is required for PCV2 production in PK-15 cells culture. It should be helpful for further evaluating the mechanism of replication and pathogenesis of PCV2 and developing novel antiviral therapies.

Baculovirus expression of the N-terminus of porcine heat shock protein Gp96 improves the immunogenicity of recombinant PCV2 capsid protein

Porcine circovirus type 2 (PCV2) causes significant economic losses to the swine industry worldwide. Heat shock proteins (Hsps) can be used as modulators to enhance both innate and adaptive immune responses. In the present study, recombinant baculoviruses expressing the PCV2Cap protein and the N-terminal 22-370 amino acids of porcine Gp96 (Gp96N), Hsp90, and Hsp70 (rBac-cap/Gp96N, rBac-cap/Hsp90 and rBac-cap/Hsp70, respectively) were constructed and the immune responses were examined in mice and piglets. The mouse experiments showed that rBac-cap/Gp96N increased the titers of specific anti-PCV2 neutralizing antibodies, proliferative responses of peripheral blood mononuclear cells (PBMCs) and IFN-γ levels compared to rBac-cap/Hsp90, rBac-cap/Hsp70, or rBac-cap. The pig experiments showed that the levels of anti-PCV2 antibody, proliferative responses of PBMCs, and IFN-γ in the rBac-cap/Gp96N groups were increased compared to those in rBac-cap group. There were no clear clinical signs of infection following PCV2 challenge in pigs inoculated with recombinant rBac-cap/Gp96N and rBac-cap, and the relative daily weight gains were higher than those in the challenge control (CC) group. The pathological lesions, extent of viremia, and viral loads of the vaccinated groups were milder than those in the CC group. Meanwhile, the extent of viremia and viral load present in the rBac-cap/Gp96N group were significantly lower than those in the rBac-cap group. These results indicated that porcine Gp96N effectively increased the humoral and cell-mediated immune responses of PCV2Cap. Gp96N presents an attractive adjuvant or immunotargeting strategy to enhance the protective efficacy of PCV2 subunit vaccines in swine.

siRNA mediated knockdown of tissue factor expression in pigs for xenotransplantation

Acute vascular rejection (AVR), in particular microvascular thrombosis, is an important barrier to successful pig-to-primate xenotransplantation. Here, we report the generation of pigs with decreased tissue factor (TF) levels induced by small interfering (si)RNA-mediated gene silencing. Porcine fibroblasts were transfected with TF-targeting small hairpin (sh)RNA and used for somatic cell nuclear transfer. Offspring were analyzed for siRNA, TF mRNA and TF protein level. Functionality of TF downregulation was investigated by a whole blood clotting test and a flow chamber assay. TF siRNA was expressed in all twelve liveborn piglets. TF mRNA expression was reduced by 94.1 ± 4.7% in TF knockdown (TFkd) fibroblasts compared to wild-type (WT). TF protein expression in PAEC stimulated with 50 ng/mL TNF-α was significantly lower in TFkd pigs (mean fluorescence intensity TFkd: 7136 ± 136 vs. WT: 13 038 ± 1672). TF downregulation significantly increased clotting time (TFkd: 73.3 ± 8.8 min, WT: 45.8 ± 7.7 min, p < 0.0001) and significantly decreased thrombus formation compared to WT (mean thrombus coverage per viewing field in %; WT: 23.5 ± 13.0, TFkd: 2.6 ± 3.7, p < 0.0001). Our data show that a functional knockdown of TF is compatible with normal development and survival of pigs. TF knockdown could be a valuable component in the generation of multi-transgenic pigs for xenotransplantation.

Heat shock protein 27 is involved in PCV2 infection in PK-15 cells

Porcine circovirus type 2 (PCV2) has been identified as the etiologic agent which causing postweaning multisystemic wasting syndrome in swine farms in the world. Some quantitative proteomic studies showed that many proteins significantly changed in PCV2-infected cells. To explore the role of cellular chaperones during PCV2 infection, cytoprotective chaperone Hsp27 was analyzed in PCV2-infected PK-15 cells in this study. The results showed that Hsp27 could up-regulate and accumulate in phosphorylated forms in the nuclear zone during PCV2 replication. Suppression of Hsp27 phosphorylation with specific chemical inhibitors or downregulation of all forms of Hsp27 via RNA interference significantly reduced the virus replication. Meanwhile, over-expression of Hsp27 enhanced PCV2 genome replication and virion production. It indicated that Hsp27 was required for PCV2 production in PK-15 cells culture. It should be helpful for understanding the mechanism of replication and pathogenesis of PCV2 and development of novel antiviral therapies in the future.

RNAi-based inhibition of porcine reproductive and respiratory syndrome virus replication in transgenic pigs

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We generated transgenic pig expressing PRRSV-specific siRNA.

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Stability of siRNA expression was proved in two generations.

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Type I interferon was not elicited by the expression of siRNA in vivo.

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We proved that transgenic pigs showed substantially decreased virus load in serum after PRRSV infection.

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating viral disease causing heavy losses to the swine industry worldwide. Many studies have shown that transient delivery of small interfering RNA (siRNA) or adenovirus-mediated RNA interfere (RNAi) could potentially inhibit porcine reproductive and respiratory syndrome virus (PRRSV) replication in vivo and in vitro. Here, we applied RNAi to produce transgenic (TG) pigs that constitutively expressed PRRSV-specific siRNA derived from small hairpin RNA (shRNA). First, we evaluated siRNA expression in the founding and F1 generation pigs and confirmed stable transmission. Then, we detected the expression of IFN-β and protein kinase R (PKR) and found no difference among TG, non-transgenic (NTG), and wild-type pigs. Lastly, the F1 generation pigs, including TG and NTG piglets, were challenged with 3 × 10^4.5 TCID₅₀ of JXA1, a highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV). Our results showed that the in vivo siRNA expression substantially reduced the serum HP-PRRSV titers and increased survival time by 3 days when TG pigs were compared with the NTG controls. These data suggested that RNAi-based genetic modification might be used to breed viral-resistant livestock with stable siRNA expression with no complications of siRNA toxicity.

Hsp70 positively regulates porcine circovirus type 2 replication in vitro

The Hsp70 chaperone plays a central role in multiple processes within cells. Porcine circovirus type 2 (PCV2) is the essential causal agent of post-weaning multisystemic wasting syndrome (PMWS), which has spread worldwide. But the mechanism of PCV2 replication remains poorly understood. In this study, we firstly found the positive effect of heat stress on the replication of PCV2 in the continuous porcine monocytic cell line 3D4/31. Downregulation of Hsp70 by the specific chaperone inhibitor Quercetin or RNA interference and upregulation of Hsp70 by expression from a recombinant adenovirus showed that Hsp70 enhanced PCV2 genome replication and virion production. A specific interaction between Hsp70 and PCV2 Cap was confirmed by colocalization by confocal microscopy and co-immunoprecipitation. Furthermore, the NF-κB pathway was activated and caspase-3 activity was reduced when Hsp70 was overexpressed in PCV2-infected 3D4/31 cells. These data suggested that Hsp70 positively regulated PCV2 replication, which being helpful for understanding the molecular mechanism of PCV2 infection.

A possible strategy to produce pigs resistant to porcine reproductive and respiratory syndrome virus

The purpose of this study was to enhance the production of transgenic cloned embryos with porcine reproductive and respiratory syndrome virus (PRRSV) shRNA expression cassettes. To construct transgenic vector with expression targeting against PRRSV, PRRSV shRNA expression cassettes were inserted into pEGFP-N1 and the ability of resulting recombinant plasmid pEGFP-G1 inhibiting virus replication was examined in Marc-145 cells. Results showed that PRRSV replication could be significantly inhibited by pEGFP-G1 in Marc-145 cells compared with the control. The pEGFP-G1 plasmid was used to deliver a transgene expressing EGFP and the PRRSV shRNA into porcine fetal fibroblasts (PFF). Fluorescent-positive cells were used as nuclear donors for somatic cell nuclear transfer (SCNT) to produce shRNA-EGFP transgenic cloned embryos. The effects of trichostatin A (TSA) on production of transgenic cloned embryos were investigated. Reconstructed embryos were designed into 4 groups: Donor cells of Group A were treated with 50nM TSA for 24h before SCNT. Reconstructed embryos of Group B were treated with 50nM TSA for 24h after activation. Both donor cells and reconstructed embryos in Group C were treated with TSA and Group D were the control without TSA treatment. The results showed no difference (p>0.05) in cleavage rates among the 4 groups; however, blastocyst developmental rates of Group B and C (30.9% and 42.0%, respectively) were higher than for Group A and D (21.2% and 22.1%, respectively) with Group C highest among groups (p<0.05). Interestingly, EGFP expression intensity of transgenic cloned blastocysts of Group A was the highest. Our results provide promising evidence toward a new approach for production of transgenic cloned pigs with resistance to PRRSV and possibly a wide variety of other porcine diseases.

Attenuation of porcine circovirus type-2b by replacement with the Rep gene of porcine circovirus type-1

Porcine circovirus type-2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases and has 4 main ORFs, ORF1 (Rep gene), ORF2 (Cap gene), ORF3 within ORF1, and ORF4, which is overlapped with ORF3, and 1 origin (Ori) of replication located between ORF1 and ORF2. The chimeric PCV1-2, containing the PCV2 capsid, PCV1 rep, and Ori genes, is attenuated in pigs. In order to verify the role of the Rep gene or Ori in the virulence of PCV2, 3 chimeric viruses [PCV2b-Ori1 (PCV1 Ori gene cloned into the backbone of PCV2b), PCV2b-rep1 (PCV1 Rep gene cloned into the backbone of PCV2b), and PCV2b-rep1-Ori1 (PCV1 Rep and Ori genes cloned into the backbone of PCV2b)] and 2 wild-type recombinant PCV2b and PCV1 were constructed and identified. The experimental results in piglets showed that clinical symptoms, viremia, viral load, lesions in lymphoid and lung tissues, and IL-10 and TNF-α expression levels in PBMCs in the PCV2b-rep1-Ori1 and PCV2b-rep1 groups were significantly decreased, compared to PCV2-infected piglets. Meanwhile, histological lesions of lymphoid and lung tissues, viral loads in lymphoid tissues, viremia, and TNF-α expression in PBMCs were not significantly different between groups PCV2b-Ori1 and PCV2b, suggesting that the Rep gene (ORF1) likely contributes to viral pathogenicity in vivo.

Construction and immunogenicity of recombinant porcine circovirus-like particles displaying somatostatin

In order to obtain a virus-like particles (VLPs) vaccine both for porcine circovirus type 2 (PCV2) prevention and growth-promotion, somatostatin (SS) gene was fused to the 3'-terminal of ORF2 gene of PCV2 with PCR, and a recombinant baculovirus (rAc-Cap-SS) was constructed. The expression of fusion protein Cap-SS (rCap-SS) with molecular weight of approximately 32kDa was identified by Western blot and indirect immunofluorescence assay in Sf9 cells. The self-assembled VLPs were observed under electron microscopy, which being morphologically similar to the recombinant Cap protein (rCap) expressed in the same baculovirus expressing system. Ninety four-week-old mice were immunized with the recombinant proteins twice. The results showed that mice immunized with rCap-SS protein developed antibody against Cap, which levels being similar to those immunized with rCap protein. The body weight gain and anti-SS antibody in rCap-SS group was higher than those of rCap and negative control groups during 28 and 42 days post inoculation (dpi). Furthermore, twenty 28-day-old piglets were vaccinated twice subcutaneously with the recombinant proteins. The results indicated that PCV2-specific antibody could be induced after vaccination with rCap-SS or rCap protein. Anti-SS antibody could be induced after rCap-SS vaccination and was higher than other groups at 14 and 28 dpi. The level of somatostatin concentration in the blood of pigs in rCap-SS group was significantly decreased at 14 dpi than other groups (P<0.05). The relative daily weight gain (RDWG) of pigs in rCap-SS group was obviously higher than that in other groups at 28 dpi. After challenge with PCV2, pigs in the vaccinated groups had no clearly clinical signs, and the RDWG was significantly higher than that in the challenge control group (CC) (P<0.05). The pathological lesions, viremia and viral load presented in the vaccinated groups were milder than those in challenge control group. It suggested that the recombinant porcine circovirus-like particles displaying somatostatin might be a novel subunit vaccine candidate for preventing PMWS and promoting pig growth.

Viral infection resistance conferred on mice by siRNA transgenesis

RNA interference is an attractive strategy to fight against viral diseases by targeting the mRNA of viral genes. Most studies have reported the transient delivery of small interfering RNA or small hairpin (shRNA) expression constructs. Here, we present the production of transgenic mice stably expressing shRNA or miRNA targeting the IE180 mRNA (immediate early gene) of the pseudorabies virus (PRV) which infects mice and farm animals. We firstly designed non-retroviral shRNA or miRNA expression vectors. Secondly, we selected the most efficient shRNA construct that targeted either the 5'part or 3'UTR of the IE mRNA and was able to knockdown the target gene expression in cultured cells, by measuring systematically the shRNA content and comparing this with the interfering effects. We then produced four lines of transgenic mice expressing different amounts of shRNA or miRNA in the brain but without signs of stimulation of innate immunity. Lastly, we tested their resistance to PRV infection. In all transgenic lines, we observed a significant resistance to viral challenge, the best being achieved with the shRNA construct targeting the 3'UTR of the IE gene. Viral DNA levels in the brains of infected mice were always lower in transgenic mice, even in animals that did not survive. Finally, this work reports an effective strategy to generate transgenic animals producing shRNA from non-retroviral expression vectors. Moreover, these mice are the first transgenic animal models producing shRNA with a significant antiviral effect but without any apparent shRNA toxicity.

Efficacy and future prospects of commercially available and experimental vaccines against porcine circovirus type 2 (PCV2)

Porcine circovirus type 2 (PCV2) is the causative agent of an economically significant collection of disease syndromes in pigs, now known as porcine circovirus associated diseases (PCVADs) in the United States or porcine circovirus diseases (PCVDs) in Europe. Inactivated and subunit vaccines based on PCV2a genotype are commercially available and have been shown to be effective at decreasing mortality and increasing growth parameters in commercial swine herds. Since 2003, there has been a drastic global shift in the predominant prevalence of PCV2b genotype in swine populations, concurrently in most but not all cases with increased severity of clinical disease. Although the current commercial vaccines based on PCV2a do confer cross-protection against PCV2b, novel experimental vaccines based on PCV2b genotype such as modified live-attenuated vaccines are being developed and may provide a superior protection and reduce vaccine costs. In this review, we discuss the current understanding of the impact of PCV2 infection on the host immune response, review the efficacy of the currently available commercial PCV2 vaccines in experimental and field conditions, and provide insight into novel experimental approaches that are useful in the development of next generation vaccines against PCV2.

Potential of adenovirus and baculovirus vectors for the delivery of shRNA against morbilliviruses

Morbilliviruses are important pathogens of humans, ruminants, carnivores and marine mammals. Although good vaccines inducing long-term immunity are available, recurrent outbreaks of measles, canine distemper and peste des petits ruminants (PPR) are observed. In control strategies, antivirals thus could be useful to confine virus spread and application of interfering RNAs is a promising approach, provided they can be delivered efficiently into the host cells. We have constructed recombinant adenovirus and baculovirus vectors expressing short hairpin RNAs (shRNAs) against the PPR virus (PPRV) and compared them in vitro. It was found that both recombinant viruses inhibited PPRV replication with the baculovirus vector, which inhibited generation of infectious progeny by more than 2 log10 and the nucleoprotein expression of PPRV by 73%, being the more efficient. The results show that baculoviral shRNA-expressing vectors have the potential for therapeutic use against morbillivirus infections.

Neutralization of infectivity of porcine circovirus type 2 (PCV2) by capsid-binding 2'F-RNA aptamers

Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus-associated diseases (PCVD), which is responsible for economic losses in the swine industry. The capsid protein of PCV2 has important role for virus neutralization that blocks viral infection. To develop the therapeutic agents, two 2'F-RNA aptamers that bound to the PCV2 capsid protein with nanomole affinity were isolated from a 2'F-RNA library by the Systematic Evolution of Ligands by EXponential enrichment (SELEX). The binding affinity of aptamers was analyzed by Electrophoretic Mobility shift assay (EMSA) and surface plasmon resonance (SPR) analysis. The RNA aptamers have been shown to exhibit high affinity and specificity to PCV2 capsid protein and to neutralize PCV2 infectivity in PK-15 cells in dose dependent manner. Neutralizing aptamers such as this could be promising candidates in developing efficacious anti-PCV2 drugs as well as therapeutic delivery reagent.

Interference of porcine circovirus type 2 ORF2 immunogenicity by ORF1 and ORF3 mixed DNA immunizations in mice

Little is known about the influences of other porcine circovirus type 2 (PCV2) proteins on the immunogenicity of Cap protein. Here we constructed plasmids expressing the ORF1 (pORF1) and ORF3 (pORF3) of PCV2, and mixed either of them with the plasmid expressing ORF2 (pORF2) as combined DNA vaccines, to compare their immunogenicity and protective efficacy. Our data revealed that pORF1 reduced the Cap-specific CD8(+)cell frequency, and both pORF1 and pORF3 attenuated the Cap-specific Th1 and post-challenge-recall VN antibody responses induced by the pORF2 plasmid, despite successful induction of Rep and ORF3 antibodies by pORF1 and pORF3, respectively. Subsequently, protocols with pORF1 or pORF3 showed significantly decreased protective efficacy compared to pORF2 alone. Overall, our data suggested that the ORF1- and ORF3-encoded Rep and ORF3 proteins may interfere with the cellular, humoral and protective immunity of the ORF2-encoded Cap protein in vivo.

Inhibition of porcine reproductive and respiratory syndrome virus replication by adenovirus-mediated RNA interference both in porcine alveolar macrophages and swine

Porcine reproductive and respiratory syndrome virus (PRRSV) has been mainly responsible for the heavy economic losses in many swine-producing regions. Current vaccination strategies and antiviral drugs provide only limited protection. Consequently, there is a need to develop a new antiviral strategy. In this study, two recombinant adenoviruses expressing short-hairpin RNAs (shRNAs) directed against ORF1b of PRRSV S1 strain were constructed and the inhibition of PRRSV replication was determined. The results showed that pretreatment with these shRNAs delivered by recombinant adenovirus could induce a significant inhibition of viral RNA and protein level in Marc-145 cells infected with PRRSV S1 strains. One recombinant adenovirus (rAd-P2) was found to be also effective in inhibiting the replication of highly virulent PRRSV SY0608 strain in Marc-145 cells and porcine alveolar macrophages at both the protein and ORF1b mRNA level. The antiviral effect was dose-dependent and sustained for at least 96h. Twenty 6-week old piglets were assigned to four groups each with five piglets. Groups 1 and 2 were inoculated intramuscularly with rAd-P2 and mock construct rAd-mP2 individually. After 24h, groups 1, 2 and 3 were challenged intramuscularly with the SY0608 strain. Group 4 remained unchallenged but with PBS as mock. The results showed that the viral load of PRRSV in serum and lung tissue of swine was suppressed effectively by rAd-P2. The clinical signs and pathological lesions in the pigs inoculated with rAd-P2 were milder than those in rAd-mP2 negative and PRRSV control. These results indicated that shRNAs mediated by the adenovirus could inhibit PRRSV infection sufficiently in vitro as well as in vivo. RNAi mediated by recombinant adenovirus might be a potential new tool for controlling PRRSV infection. Of course, the protective efficiency of rAd-P2 should be made by using a large number of pigs in future.

Effective suppression of replication of porcine reproductive and respiratory syndrome virus by adenovirus-mediated small interfering RNAs targeting ORF1b, 5 and 7 genes

Porcine reproductive and respiratory syndrome virus has caused hundreds of thousands of deaths in pig farms in many swine-producing areas in the world in recent years. However, at present there is no effective method to prevent and control the disease, and there is a need to develop new antiviral strategies. In this study, four recombinant adenoviruses expressing shRNAs targeting ORF1b, ORF5 and ORF7 were constructed, and it was found that they could down-regulate effectively specific gene expression and inhibit viral replication in MARC-145 cells when compared to the controls. They could also inhibit effectively PRRSV replication in porcine alveolar macrophages. The inhibition effect was dose-dependent and could be sustained for at least 96h in macrophages. In addition, PRRSV replication could be suppressed significantly by shRNA in cells infected previously or simultaneously with PRRSV. The results indicated that the shRNA-expressing rAd5 targeting to various gene regions of PRRSV might be a potential anti-PRRSV strategy.